thermal energy storage systems - tesse2b...

Thermal Energy

Storage Systems for energy efficient building an integrated solution for residential

building energy storage by solar and geothermal resources Grant agreement number: 680555

D8.5 Training Material TESSe2b DEL 8.5-00/2018

Authors:

IPS – Portugal; CRES - Greece Participant responsible: TEISTE - Greece

TEISTE – Greece; UOI – Greece Final Version, January 2018

GEOTEAM – Austria; SGGW - Poland

RUB – Germany; PCM PRODUCTS – U.K.

ECOSERVEIS – Spain; Z&X - Cyprus

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Thermal Energy Storage Systems for energy efficient

building an integrated solution for residential building

energy storage by solar and geothermal resources

TESS e2b – the smart energy storage

PREFACE

The Tesse2b project: Thermal Energy Storage Systems for Energy Efficient Buildings. An integrated solution for residential

building energy storage by solar and geothermal resources, supported by Horizon 2020, has delivered this Training Material. It has

been developed for the participants of workshops and other educational activities and it is intended to provide relevant and

accessible support for their ongoing education in the respective technological areas. The objective is to demonstrate the relevant

activities developed under the project and come to be a useful source of information for professional training related to the

technology developed in the project. Training courses and workshops will be held by partners drawn from universities, research

organizations and commercial organizations across Europe in Austria, Cyprus, Germany, Greece, Poland, Portugal, Spain, and the

UK. The training material is designed as the course text for a formal training programme in the issues related to Tesse2b, including

practical demonstrations and real case studies based on experience of the project partners.

Tesse2b is a low cost thermal storage technology based on solar collectors and efficient heat pumps for heating, cooling and

domestic hot water (DHW) production. It is an integrated package with thermal storage technology. The tanks developed within

TESSe2b project are integrated with different Phase Change Materials (PCMs) such as, (i) enhanced with nanoparticles paraffins

Phase Change Materials (PCMs) and (ii) salt-hydrates PCMs. In both, a highly efficient heat exchanger is included. It is also coupled

with PCM Borehole Heat Exchangers (BHEs).

In this context, the Training material comprises seven chapters covering all the required info for the reader to understand first

the technology regarding each of the modules and elements of Tesse2b and then the integrated Tesse2b solution that combines

all of them. In Chapter 1, an introduction to Tesse2b objectives and technologies is attempted. TESSe2b interdisciplinary approach

is shown combining technological innovations on different levels as Nano-enhancement of paraffin PCM (NEPCM), smart self-

learning control algorithm, and enhancement of BHEs by integration of PCM into the grout. Chapter 2 is an introduction to phase

change materials and their potential applications. PCMs typologies and types are explained as well PCM enhancement with

nanomaterials and how this is achieved. In Chapter 3 solar thermal technology is presented including up to date developments for

solar collectors, solar thermal energy storage and solar thermal applications.Discussion is limited to solar collectors and systems

for low temperature applications (domestic hot water production, space heating, space cooling) due to the requirements of

Tesse2b. It is provided in brief, carefully selected information regarding the technology exploited by Tesse2b. Chapter 4 presents

geothermal technologies both for deep and shallow geothermal energy. It mainly focuses on shallow geothermal energy

applications for heating, cooling and domestic hot water as these are mainly related with Tesse2b. In Chapter 5 hybrid solar and

geothermal systems combined with PCM are discussed. This concept that is adopted by Tesse2b is quite new, and therefore there

are no equivalents or similar systems to TESSe2b on the market. For that purpose, references to some EC research projects is

initially attempted following by a presentation of Tesse2b solution. The Tesse2b hydraulic scheme is shown and its controler that

coordinates all components of the TESSE2b system, in order to efficiently execute the main functions, is presented together with

the operating modes. Chapter 6 provides information for Tesse2b System Designers, Installers, Maintenance Technicians and End

Users. The important design parameters to take into account when designing a system that uses the TESSe2b solution are shown.

For the installation of TESSe2b solution, the system can be divided in four main components (solar, geothermal, DHW, air

cooling/heating) that must be distinguished in the installation process. A short list of the main activities is discussed. For the

maintenance of TESSe2b, the system follows the general maintenance operations of HVAC/Geothermal/Solar system with thermal

accumulation tanks. The maintenance operation of each component of the system should follow the maintenance operation list

indicated by the component manufacturer. However, it is convenient to make dedicated maintenance operations for the TESSe2b

system as a whole. A list of them is discussed. Finally, in Chapter 7 the Tesse2b pilot sites, where the solution is installed to

demonstrate it at real conditions, are presented. Results from energy simulation are also shown providing information about the

performance of Tesse2b when it is applied in the pilot buildings.

As the Tesse2b project is ongoing, the current training material will be updated until the end of the project to reflect all project

developments and accompanied results from its application in the pilot sites.

For ongoing support and information see the Tesse2b website:www.tesse2b.eu

http://www.tesse2b.eu/

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ACKNOWLEDGEMENTS

This Training material was produced as the result of the Tesse2b project. We are particularly grateful to the partners who

contributed to the continuous development of the material throughout the course of the project.

DISCLAIMER

The sole responsibility of this publication lies with the author. The European Union is not responsible for any use that may be

made of the information contained therein.

http://www.tesse2b.eu/tesse2b/partners#cyprus

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TABLE OF CONTENTS

PREFACE 1

ACKNOWLEDGEMENTS ........................................................................................................................................................................ 2

DISCLAIMER 2

TABLE OF CONTENTS ............................................................................................................................................................................ 3

ABBREVIATIONS ................................................................................................................................................................................... 6

TABLE OF FIGURES ............................................................................................................................................................................... 7

1. TESSe2b project .......................................................................................................................................................... 9

1.1 Objectives .......................................................................................................................................................................... 9

1.2 Technological approach and Methodology ..................................................................................................................... 10

1.3 The Tesse2b consortium as a whole ................................................................................................................................ 12

1.4 References ....................................................................................................................................................................... 13

2. Phase Change Materials ........................................................................................................................................... 14

2.1 Introduction ..................................................................................................................................................................... 14

2.2 PCM typologies ................................................................................................................................................................ 15

2.3 PCM Storage types........................................................................................................................................................... 17

2.4 PCM enhancement nanomaterials .................................................................................................................................. 19

2.5 References ....................................................................................................................................................................... 22

3. Solar Thermal Technologies ...................................................................................................................................... 24

3.1 Introduction ..................................................................................................................................................................... 24

3.2 Solar thermal technologies .............................................................................................................................................. 25

3.2.1 Solar Collectors ............................................................................................................................................................ 27

3.2.2 Solar thermal storage .................................................................................................................................................. 29

3.3 Solar thermal applications ............................................................................................................................................... 29

3.3.1 Solar thermal application for DHW ............................................................................................................................. 30

3.3.2 Solar thermal application for DHW and Space heating ............................................................................................... 30

3.3.3 Solar thermal application for DHW, space heating and cooling.................................................................................. 31

3.4 Solar thermal case study ................................................................................................................................................. 31

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3.4.1 Description of the application ..................................................................................................................................... 31

3.4.2 General description of the system .............................................................................................................................. 32

3.4.3 Technical Characteristics ............................................................................................................................................. 33

3.5 Solar thermal applications with PCM .............................................................................................................................. 34

3.6 References ....................................................................................................................................................................... 35

4 Geothermal Technologies ......................................................................................................................................... 36

4.1 Deep Geothermal Energy ................................................................................................................................................ 36

4.2 Shallow Geothermal Energy ............................................................................................................................................ 37

4.3 Shallow Geothermal applications .................................................................................................................................... 40

4.3.1 Shallow Geothermal application for Heating and Domestic Hot water ...................................................................... 41

4.3.2 ShallowGeothermal application for Heating, Cooling and Domestic Hot water ......................................................... 41

4.4 Case Studies ..................................................................................................................................................................... 42

4.4.1 Introduction................................................................................................................................................................. 42

4.4.2 Layout of BHEs ............................................................................................................................................................. 42

4.4.3 Geothermal application for a single family house....................................................................................................... 43

4.4.4 Geothermal application for an office building ............................................................................................................ 43

4.5 References ....................................................................................................................................................................... 44

5 Hybrid Solar and Geothermal systems combined with PCM .................................................................................... 45

5.1 General overview ............................................................................................................................................................. 45

5.2 Configurations of Hybrid Solar and Geothermal system with PCM storage.................................................................... 46

5.3 Configuration of TESSe2b solution .................................................................................................................................. 50

5.3.1 TESSe2b general hydraulic scheme ............................................................................................................................. 50

5.4 Tesse2b Control System .................................................................................................................................................. 51

5.4.1 Functions and Operating Modes ................................................................................................................................. 51

5.4.2 General Energy Management AND Control Approach ................................................................................................ 52

5.5 References ....................................................................................................................................................................... 53

6 Information for System Designers, Installers, Maintenance Technicians and End Users ......................................... 54

6.1 Information for System Designers ................................................................................................................................... 54

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6.2 Information for installers ................................................................................................................................................. 55

6.3 Information for maintenance technicians ....................................................................................................................... 56

6.4 Information for end users ................................................................................................................................................ 58

6.5 References ....................................................................................................................................................................... 60

7 Demo sites of TESSe2b SolutioN ............................................................................................................................... 61

7.1 Demo site in Austria ........................................................................................................................................................ 61

7.1.1 Brief description of the building in pilot site ............................................................................................................... 61

7.1.2 House characteristics .................................................................................................................................................. 61

7.1.3 Outlook ........................................................................................................................................................................ 62

7.1.4 Energy Building Simulation .......................................................................................................................................... 63

7.2 Demo site in Cyprus ......................................................................................................................................................... 64


7.2.2 Description of the retrofit and the new system .......................................................................................................... 66


7.3 Demo site in Spain ........................................................................................................................................................... 69


7.3.2 Description of the retrofit ........................................................................................................................................... 70

7.3.3 Description of the new system – expected benefits ................................................................................................... 70


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ABBREVIATIONS

BHE: Borehole Heat Exchanger

COP: Coefficient of Performance

CST: Concentrating solar thermal

CTES: Cold Thermal Energy Storage

DHW: Domestic Hot water

DHWTES: Domestic Hot Water Thermal Energy Storage Tank

EPBD: Energy Performance of Buildings Directive

ESP: Electrical Submersible Pump

GCHP: Ground Coupled Heat Pump

GSHP: Ground Source Heat Pump

HE: Heat Exchanger

HP: Heat Pump

HTES: Hot Thermal Energy Storage

HTF: Heat Transfer Fluid

HVAC: Heating, Ventilation, and Air Conditioning

LHTES: Latent Heat Thermal Energy Storage

NEPCM: Nano-Enhanced PCM

NP: Nanoparticle

PCM: Phase Change Material

RES: Renewable Energy Sources

STES: Seasonal Thermal Energy Storage

SPF: Seasonal Performance Factor

ST: Solar Thermal

TES: Thermal Energy Storage

TCM: Thermo-Chemical Material

UTES: Underground thermal energy storage

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TABLE OF FIGURES

FIGURE 1.1 INTERDISCIPLINARY WORK FOR THE DEVELOPMENT OF TESSE2B......................................................................................................... 9

FIGURE 1.2 TESSE2B OVERALL APPROACH.. ................................................................................................................................................ 10

FIGURE 2.1 THERMAL ENERGY STORAGE DEFINITION .................................................................................................................................... 14

FIGURE 2.2 FREEZE/MELT CYCLE ............................................................................................................................................................... 14

FIGURE 2.3 COMPARISON OF STORAGE SYSTEMS ......................................................................................................................................... 15

FIGURE 2.4 TEMPERATURE RANGE FOR ALL CATEGORIES OF PCM. ................................................................................................................... 16

FIGURE 2.5 COMPARISON OF CONVENTIONAL AND PCM SYSTEMS .................................................................................................................. 17

FIGURE 2.6 PLASTIC ENCAPSULATION ........................................................................................................................................................ 18

FIGURE 2.7 ALTERNATIVE ENCAPSULATION METHODS .................................................................................................................................. 19

FIGURE 2.8 MEASURED THERMAL CONDUCTIVITY OF PARAFFIN WAX WITH GRAPHITE NANOPLATELETS AS A FUNCTION OF WEIGHT FRACTION ................. 21

FIGURE 2.9 HEAT OF FUSION AS A FUNCTION OF WEIGHT FRACTION ................................................................................................................. 21

FIGURE 2.10 SPECIFIC HEAT CAPACITANCE AS A FUNCTION OF WEIGHT FRACTION OF (A) LIQUID AT 70OC AND (B) SOLID AT 20OC ................................ 22

FIGURE 3.1 ST APPLICATIONS USING THE TECHNOLOGIES OF (A) COLLECTORS WITHOUT TRANSPARENT COVER, (B) FLAT PLATE COLLECTORS, (C) VACUUM

TUBE COLLECTORS AND (D) COMPOUND PARABOLIC CONCENTRATOR COLLECTORS, SOURCE: (A) SOLE, (B) AND (C) SOLAIR, (D) CALPAK .............. 24

FIGURE 3.2 CST TECHNOLOGIES (A) PARABOLIC THROUGH, (B) LINEAR FRESNEL, (C) CENTRAL RECEIVER AND (D) PARABOLIC DISH .............................. 25

FIGURE 3.3 SUBSYSTEMS OF A TYPICAL LOW TEMPERATURE ST SYSTEM ............................................................................................................ 26

FIGURE 3.4 CIRCULATION SYSTEM OF A ST SYSTEM ....................................................................................................................................... 26

FIGURE 3.5 FLAT PLATE COLLECTOR TECHNOLOGY ELEMENTS .......................................................................................................................... 27

FIGURE 3.6 VACUUM TUBE COLLECTOR TECHNOLOGY (A)DIRECT FLOW (B)HEAT PIPE ........................................................................................... 28

FIGURE 3.7 CONNECTION OF COLLECTORS .................................................................................................................................................. 28

FIGURE 3.8 SOLAR THERMAL STORAGE TANK .............................................................................................................................................. 29

FIGURE 3.9 EFFICIENCY CURVES FOR COLLECTORS AND SOLAR SYSTEM APPLICATIONS ......................................................................................... 29

FIGURE 3.10 FORCED-CIRCULATION SOLAR DHW CONFIGURATIONS WITH (A) INTERNAL HEAT EXCHANGER AND (B) EXTERNAL HEAT EXCHANGER AND TWO

STORAGE TANKS ............................................................................................................................................................................. 30

FIGURE 3.11 SOLAR COMBI SYSTEM FOR DHW AND SPACE HEATING ............................................................................................................... 30

FIGURE 3.12 SOLAR COOLING APPLICATION WITH UNDERGROUND THERMAL ENERGY STORAGE (UTES) ................................................................. 31

FIGURE 3.13 VIEW OF THE OFFICE BUILDING ............................................................................................................................................... 32

FIGURE 3.14 VIEW OF THE SOLAR FIELD ...................................................................................................................................................... 32

FIGURE 3.15 INTERNAL VIEW OF THE UNDERGROUND THERMAL ENERGY STORAGE (UTES) ................................................................................. 33

FIGURE 3.16 CONVENTIONAL ST SYSTEM WITH GSHP ................................................................................................................................. 34

FIGURE 3.17 SOLAR THERMAL SYSTEM WITH GSHP WITH PCM..................................................................................................................... 34

FIGURE 4.1 GEOTHERMAL DOUBLET IN A HYDROTHERMAL SYSTEM .................................................................................................................. 36

FIGURE 4.2 CARBONATE PRECIPITATION IN A PIPE ......................................................................................................................................... 37

FIGURE 4.3 MAIN TYPES OF USING SHALLOW GEOTHERMAL ENERGY. ............................................................................................................... 38

FIGURE 4.4 INSTALLATION OF A DOUBLE-U TUBE IN A BOREHOLE USING AN UNWINDING UNIT. .............................................................................. 38

FIGURE 4.5 GROUTING OF A BHE ............................................................................................................................................................. 39

FIGURE 4.6 PROPAGATION OF TEMPERATURE CLOUDS FOR HEATING (=COOLING OF GROUNDWATER) AND COOLING MODE (= WARMING OF

GROUNDWATER) FOR A SHALLOW GEOTHERMAL GROUNDWATER PROJECT BASED ON A FLOW VOLUME OF 55 L/S) ............................................ 39

FIGURE 4.7 PRODUCTION AND INJECTION WELL FOR GEOTHERMAL USE OF SHALLOW GROUNDWATER ..................................................................... 40

FIGURE 4.8 GCHP OPERATION IN HEATING AND COOLING MODES ................................................................................................................... 40

FIGURE 4.9 REFRIGERATION CYCLE FOR HEATING MODE ................................................................................................................................. 41

FIGURE 4.10 REFRIGERATION CYCLE FOR HEATING MODE. .............................................................................................................................. 42

FIGURE 4.11 DRILLING THE BHES ............................................................................................................................................................. 43

FIGURE 4.12 BHE-FIELD IN VIENNA .......................................................................................................................................................... 44

FIGURE 5.1 RENEWABLE ENERGY SOURCES OVERVIEW AND MAIN TECHNOLOGIES ............................................................................................... 45

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FIGURE 5.2 PCM THERMAL STORAGE HEAT PUMP SYSTEM WITH GROUND LOOP ................................................................................................ 48

FIGURE 5.3 DIAGRAM OF EXPERIMENTAL LABORATORY EQUIPMENT INSTALLED IN IMSAS BRATISLAVA ................................................................... 49

FIGURE 5.4 TESSE2B GENERAL HYDRAULIC SCHEME ..................................................................................................................................... 50

FIGURE 7.1 TESSE2B DEMONSTRATION SITE KAPFENBERG, AUSTRIA ................................................................................................................ 61

FIGURE 7.2 LAYOUT OF THE BUILDING. ....................................................................................................................................................... 62

FIGURE 7.3 BHE LAYOUT FOR THE DEMONSTRATION SITE AUSTRIA. ................................................................................................................. 63

FIGURE 7.4 GEOMETRY MODE FROM DESIGN BUILDER, AUSTRIA DEMO SITE. .................................................................................................... 63

FIGURE 7.5 TESSE2B DEMONSTRATION SITE IN CYPRUS. ................................................................................................................................ 65

FIGURE 7.6 VIEW OF THE PILOT BUILDING IN CYPRUS. ................................................................................................................................... 65

FIGURE 7.7 PLANS OF THE PILOT BUILDING IN CYPRUS ................................................................................................................................... 66

FIGURE 7.8 GEOMETRY MODE FROM DESIGN BUILDER, CYPRUS DEMO SITE ...................................................................................................... 68

FIGURE 7.9 VIEW OF THE SPANISH SITE AREA IN THE MAP .............................................................................................................................. 69

FIGURE 7.10 VIEW OF THE HOUSE AND THE AREA CITED ................................................................................................................................ 69

FIGURE 7.11 BEFORE AND AFTER .............................................................................................................................................................. 70

FIGURE 7.12 VIEW OF WORKS FOR THE DEVELOPMENT OF BHES..................................................................................................................... 71

FIGURE 7.13 GEOMETRY MODE FROM DESIGN BUILDER, BARCELONA DEMO SITE ............................................................................................... 71

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1. TESSE2B PROJECT

1.1 OBJECTIVES

The energy use in buildings has been estimated to be approximately 40% of EU total energy consumption. The Energy Performance

of Buildings Directive (EPBD) requires that all new buildings will have nearly zero-energy demand by the end of 2020, indicating

that the majority of the energy that these buildings would require would come from renewable energy sources (RES). Currently

RES in buildings for domestic heating and hot water production is still limited with a proportion under 1%. Due to this fact, there

is a need of encouraging energy efficiency in buildings, enhance green technologies and promote advance thermal energy storage

solutions, with the view to reduce energy consumption and minimize CO2 emissions.

Why Tesse2b? It enables the optimal use of renewable energy and provides corrective measures against the mismatch that

often occurs between the supply and demand of energy in residential buildings.

What is Tesse2b? It is a low cost thermal storage technology based on solar collectors and efficient heat pumps for heating,

cooling and domestic hot water (DHW) production. It is an integrated package with thermal storage technology (Thermal Energy

Storage tanks – TES tanks), using solar collectors, geothermal energy, thermal accumulation and highly efficient heat pumps for

heating, cooling and domestic hot water (DHW) production. The TES tanks developed within TESSe2b project are integrated with

different Phase Change Materials (PCMs) such as, (i) enhanced with nanoparticles paraffins PCMs and (ii) salt-hydrates PCMs. In

both, a highly efficient heat exchanger is included. It is also coupled with PCM borehole heat exchangers (BHEs). These will take

advantage of the underground thermal storage and maximize the efficiency of the ground heat pumps (GCHP), (Figure 1.1).

The success of TESSe2b solution is based on an interdisciplinary approach (Figure 1.1) combining technological innovations on

different levels:

1. nano-enhancement of paraffin PCM (NEPCM);

2. smart self-learning control algorithm;

3. enhancement of BHES by integration of PCM into the grout;

4. development of a protective and economically feasible coating for the HE, in case of the salt hydrates PCM;

5. Stackable modular design of TES tanks (including the immersed HE).

Figure 1.1 Interdisciplinary work for the development of Tesse2b.

Since the lifetime of TESSe2b solution is among the most critical factors determining its acceptability, reliability and success, special

emphasis will be given in the life-expectancy of the involved components. TESSe2b approaches thermal energy storage and the

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transformation of the existing stock towards very low energy buildings by challenging specific scientific and technological

objectives:

1. Selection and characterization of candidate PCM to ensure optimum design and performance for high efficiency PCM TES

tanks and enhanced PCM borehole heat exchangers;

2. Exploit nanotechnology to develop a new nanocomposite enhanced paraffin PCM (NEPCM);

3. Development of a protective thin film coating against the corrosivity of salt-hydrates to the heat exchanger (HE);

4. Design optimization and development of compact modular TES tanks including a high performance HE;

5. Development of a smart model-based control system for efficient TESSe2b operation and integration into a robust working

prototype;

6. Demonstration, on-site monitoring and technology validation of prototypes of a single building in three pilot sites;

7. Cost-effectiveness analysis of TESSe2b solution to evaluate the return-on-investment period;

8. To design an effective exploitation strategy and business plan to demonstrate the overall benefits in the several levels of

the TESSe2b solution adoption.

For more updated information visit www.tesse2b.eu.

1.2 TECHNOLOGICAL APPROACH AND METHODOLOGY

The overall approach and methodology for the design optimization and implementation of TESSe2b is described in detail below

(Figure 1.2).

Figure 1.2 TESSe2b overall approach.

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TESSe2b PCM TES tanks for short-basis thermal storage This is the main thermal store of TESSe2b solution. The TES tanks have been designed in a compact and modular manner and can

be scaled according to the residential energy needs.TESSe2b solution includes the following modular TES tanks:

Paraffin PCM TES storage tanks

Tanks for residential heating (HTES) and DHW production (DHW) with paraffins PCM in a temperature range shown in Table

1.1.

Tanks for residential cooling (CTES) with paraffins PCM in a temperature range shown in Table 1.1.

Table 1.1 TESSe2b PCM Tank Requirements (Source: Tesse2b deliverables).

Application Abbreviation Temperature Range

Cold Thermal Energy Storage Tank CTES ≈10-17 oC

Hot Thermal Energy Storage Tank HTES ≈38-45 oC

Domestic Hot Water Thermal Energy Storage Tank DHWTES ≈50-60 oC

Salt hydrates PCM TES storage tanks

Tank for residential heating and DHW production with salt hydrates in a temperature range shown in Table 1.1.

Tank for residential cooling with salt hydrates PCM in a temperature range shown in Table 1.1.

One of the main objectives of TESSe2b solution is to design and deliver high energy storage tanks that will be easily integrated in

the stock residential buildings. Therefore, the high density PCM tanks will be built out of a design shape that can be stacked. As

far as the volume of this tank is concerned, it will be small enough to be part of a modular storage tank system and to be scaled

accordingly to the application without requiring large single volume of space. The total volume of the storage system will never

exceed the 2.5 m3 limit.

PCM nano-enhancement TESSe2b solution exploits the development of nanotechnology in order to develop a new nanocomposite enhanced PCM (NEPCM)

paraffin wax for the hot and cold thermal energy storage. Several kinds of nanoparticles (NPs), metallic (Cu), metallic oxides (Fe2O3)

and graphite based nanoplatelets were studied. The aspect ratio of the NPs is of importance. There is an overall increase in the

thermal conductivity due to nanoplatelets additions, the effect is not linear and it is different for each particular type of

nanoparticle. The studied NPs showed that they had no influence on heat of fusion or their influence was negligible.

TESSe2b Heat Exchangers A staggered heat exchanger has been adopted to use in the tanks. Experimental and computational work was carried out to study

parameters as: Tubes and Fins Material; Heat transport fluid mass flow rate; Fins Spacing; Tube circuit length and Fins Height. The

tubes/fins materials have a marginal effect on the HEs performance, since, they have high thermal conductivity compared to the

water and the paraffin; the water flow rate has a significant influence on the HEs thermal performance (water heat flux and the

water discharge temperature); the tube spacing (Fins height) has a strong influence in the time required to fully solidify the PCM.

Also, for the case of salt hydrates, their corrosive nature when in direct contact with metal components was considered. To

overcome this drawback, a permanent coating for the HE was developed with the aim to withstand pitting and galvanic corrosion

phenomena while preserving excellent thermal properties.

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TESSe2b Enhanced PCM BHEs To increase the efficiency of TESSe2b solution, enhanced PCM BHEs are integrated as well. The BHEs approach is adopted instead

of shallow horizontal geothermal heat exchangers that are usually considered to be less effective due to faster depletion of the

stored thermal energy as a result of the seasonal energy balance. The weakest link in borehole HEs is the heat transfer in the

ground that is mainly conductive and its thermal diffusivity is low. This leads to a much slower ground thermal response than the

heat pump requirements, resulting in thermal waves being transmitted into the ground through the BHEs causing lower coefficient

of performance (COP) of ground source heat pumps (GSHP).To improve the effectiveness of BHEs, mixing PCMs directly with

backfill material for the grout will be adopted. Employing PCMs will be an effective way to store thermal energy in the BHEs and

smooth the generated thermal wave. Among the available PCMs the organic paraffin will be the one to be selected and integrated

to BHEs because it is environmental friendly. The PCM will be encapsulated and blend with soil/water to form the borehole grout.

Inside the BHEs there will be two types of PCM for the seasonal charge/discharge cycles.

Design and implementation of smart model-based control system

Smart model-based control system has been developed. The analysis for the appropriate sensors and logical units and actuators

and their selection for the TESSE2b system is a part of the work. The basic models for thermal storage, collector systems and heat

pumps supporting the overall optimization and the control design were established. Different control concepts have been studied

and they were defined all operation modes in the control logic. The models are being developed in Mat lab/Simulink.

Finally, a demonstration and on-site monitoring evaluation of small scale TESSe2b solution at a single building in

three pilot sites along Europe (Austria, Spain, and Cyprus) will be conducted. The aim of this activity will be to; (i)

evaluate the system’s integration into building space, (ii) assess the impact of TESSe2b solution in different climates

and (iii) provide evidence about its overall technical and economic feasibility.

1.3 THE TESSE2B CONSORTIUM AS A WHOLE

The TESSe2b consortium was formed to bring together a multidisciplinary team of companies, research institutions and universities

across Europe that complement each other in terms of background knowledge, technical competence, capability of new

knowledge creation, business and market experience.

The consortium consists of 10 partners from eight European countries.

IPS coordinates the project.

CRES is the Greek national center for renewable energy sources, including geothermal and solar thermal, rational use of energy

and energy saving.

TEISTE represents the Mechanical Engineering Department of TECHNOLOGIKO EKPEDEFTIKO IDRIMASTEREAS ELLADAS which is a

higher education institute.

GEOTEAM is a company with project experience in the exploration, development and monitoring of potable and mineral water

resources and geothermal energy.

UOI represents the laboratory of thin solid films (tsf Lab) of the Department of Physics at University of Ioannina.

SGGW is a research and technological institution focusing on the practical application of renewable energy sources and

technologies in buildings and small-scale installations and their modelling and control also remote via internet.

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RUB is a research and technological institution which represents the Power Systems technology and Power Mechatronics (EneSys)

of University of Bohum.

ECOSERVEIS is a non-profit Organization working on promotion and education on energy, energy efficiency and renewable

energies.

PCM PRODUCTS is a company active in the development of Phase Change Materials and related applications.

Z&X is a company with successful activity in the field of mechanical installations in the field of Renewable Energy, meaning,

geothermal, photovoltaic and solar thermal systems.

1.4 REFERENCES

“Buildings,” Energy. [Online]. Available: http://ec.europa.eu/energy/en/topics/energyefficiency/buildings. [Accessed: 01-Feb-

2015].

EU (European Union), “Energy efficiency, amending Directives 2009/125/EC and 2010/30/EU and repealing Directives 2004/8/EC

and 2006/32/ EC,” Directives, Office Journal of the EU, Brussels, Belgium, 2012.

ΙEA, “Technology Roadmap: Energy Storage,” Paris, France, 2014.

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2. PHASE CHANGE MATERIALS

2.1 INTRODUCTION

What is Thermal Energy Storage (TES)?

Thermal energy storage (TES) is the temporary storage of high or low temperature energy for later use. It bridges the time gap

between energy requirement and energy use. Most TES applications involve a 24 hour storage cycle, but they can also be applied

for any cycle where natural forces such as day and night or seasons can be taken advantage of.

Figure 2.1 Thermal Energy Storage Definition.

(Source: PCMPRODUCTS Sales Documents)

Heat can be stored in two ways. Traditionally, thermal energy is stored as sensible heat such as a conventional domestic hot water

tank. Recently, there has been a movement towards storing this heat as latent heat instead. Phase change materials, commonly

referred to as PCMs, are products that store and release thermal energy during the processes of melting and freezing.

Figure 2.2 Freeze/melt Cycle.

(Source: PCM PRODUCTS Sales Documents)

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This cycle of melting and freezing can occur countless times without degradation. This is because there is no chemical reaction

involved, only physical processes. Water is the most common PCM and it unquestionable that it will always freeze and melt, even

over millions of years.

Storing energy within the latent heat of a PCM offers a number of benefits including:

Lower heat loss to the surroundings compared to sensible heat storage;

Releases and stores heat at a constant temperature allowing for a natural control system;

No requirement for mechanical cooling;

High energy density.

Figure 2.3 Comparison of Storage Systems.


2.2 PCM TYPOLOGIES

There are numerous types of PCMs available. The most common PCMs are water/ice with a phase change at 0 oC, salt hydrates,

eutectics and organics. Recently, there has also been development in solid-solid PCM.

Salt Hydrates are compounds of salt and water and have the advantage of high latent heat of fusion due to their high water

content.The introduction of salts into the water can both raise and lower the freezing point of the water. This allows a range of

PCMs to be created that all have different applications. A disadvantage of using these salts is the potential for phase segregation

during the charging and discharging of the PCM. This is where heavier salt settles at the bottom of the solution and consequently,

the TES capacity of the solution changes. This can a have major impact on the lifetime of the PCM storage.

Eutectics are mixtures of two or more substances mixed in such a way as to provide the desired melting/freezing point. The mixture

melts completely at the design temperature and has the overall composition in both liquid and solid phases which has the main

criteria of a PCM.

16





Organics are materials which are blends of paraffins and fatty alcohols. These PCMs have the advantage of being very chemically

stable, however due to their lower density they can store less heat in a given space than salt hydrate PCM. Additionally they have

poor thermal conductivity and are relatively expensive.

Solid-Solid PCMs that undergo a solid/solid phase transition with the associated absorption and release large amounts of heat are

the latest addition to PCM range. These materials change their crystalline structure from one lattice configuration to another at a

fixed and well-defined temperature, and the transformation can involve latent heats comparable to the most effective solid/liquid

PCMs. Such materials are useful because, unlike solid/liquid PCMs, they do not require nucleation to prevent supercooling.

Additionally, because it is a solid/solid phase change, there is no visible change in the appearance of the PCM (other than a slight

expansion/contraction), and there are no problems associated with handling liquids, i.e. containment, potential leakage, etc. There

is a range of different PCMs available and so they must be carefully considered for any given application.

Figure 2.4 Temperature range for all categories of PCM.


The table below (Table2.1) shows the key differences that must be considered when determining which PCM to use.

17





Table 2.1 Characteristics of PCMs, Source: PCM PRODUCTS Sales Documents.

Advantages Disadvantages

Organic Simple to use

Non-corrosive

No supercooling

No nucleating agents

Generally more expensive

Low latent heat/density

Often have a broader melting range

Can be combustible

Salt-Based Generally cheaper

High latent heat/density

Well defined phase change temperature

Non-flammable

Needs careful preparation

Needs additives to stabilise for long term use

Prone to supercooling

Can be corrosive to some metals

2.3 PCM STORAGE TYPES

HVAC Applications

Designers and engineers throughout the world have developed different techniques, however, the main design criteria remains

the same, "Full" and "Partial" storage. Figure 2.5 illustrates how a PCM TES tank could be implemented into a system, storing any

excess heat or cold.

Figure 2.5 Comparison of Conventional and PCM Systems.


Full storage

Systems shift the total cooling/heating load to the off-peak period and the cooling/heating source is never used during the peak

period in order to achieve the maximum economy, this type of system results in a smaller cooling/heating source but a larger

required storage volume.

Partial storage Systems utilises the cooling/heating source during the peak periods in order to reduce the initial storage capacity. This type of

system is widely used to limit the demand during the peak period. This technique is called "demand limiting", where excess

capacity is supplemented by a TES source in order to stay below the maximum electrical demand limit.

Conventional

PCM Energy Storage Concept

18





In principle, full storage provides the most economical running costs with the penalty of a larger initial investment cost and space

requirement. Partial storage is relatively cheaper in comparison, however the associated running costs are higher. Both techniques

can be applied to both new and existing systems, and if done with the proper consultation, the costs can be recovered in a short

time span.

Mobile Application PCMs are widely used for temperature controlled transport. It is able to provide the needed heating or cooling whilst a shipment

is in transit. Mechanical cooling often requires large, high energy consuming, heavy machinery which would be very unpractical

for most logistical operations. By charging a PCM and then placing into an insulated container a product can be kept at a target

temperature for a given length of time. Due to the nature of PCM, there is a wide variety of temperatures which can be selected

depending on the needs of the item being transported. These have been successfully implemented for the transit of biological

materials and other temperature sensitive products such as chemical test samples.

PCM Encapsulation Because of the nature of PCMs, they must be contained appropriately. The encapsulation of the PCM is very important because if

it is done poorly, the system can become contaminated and the overall heat transfer from the TES into the system will suffer. The

principle type of encapsulation of PCM is macro-encapsulation in plastic containers, they are cheap, readily available and can take

many forms as seen in Figure 2.6.

Figure 2.6 Plastic Encapsulation.


These plastic containers can be engineered to ensure that they are stackable and give a large surface area to promote a high rate

of heat transfer for both the charging and discharging of the TES. Alternatively metal can be used which further improve the heat

transfer rate, however this comes at a cost.

Alternative encapsulation methods also exist; Figure 2.7 illustrates some of the different ways that PCM can be applied. Pouches

are often most useful in mobile applications with the benefits of flexibility and modularity, however they have the drawback of

not being robust. One method of encapsulation attempts to avoid the issue of handling liquids entirely by absorbing PCM directly

onto a powder, at which point the powders can be applied in numerous ways.

19





Figure 2.7 Alternative Encapsulation Methods.


2.4 PCM ENHANCEMENT NANOMATERIALS

Heat stored in the solid-liquid phase transition in phase-change materials is one of the most preferred forms for energy storage,

due to the large latent heat and negligible temperature and volumetric changes associated with the phase transition. Paraffin wax

in particular has attracted attention because of its low cost, stability and chemical inertness. However, paraffin wax, in common

with many phase change materials, has low thermal conductivity, which inhibits quick heat transfer and thus limits its use as an

energy storage material.

In order to overcome the thermal conductivity problem, common in many phase change materials, a number of different

nanoparticle suspensions have been explored such as carbon-based nanostructures (nanofibers, Nano platelets, graphite

nanoparticles, graphene flakes and carbon nanotubes), metallic (Ag, Al, Cu, Fe) and metal oxides (Al2O3, CuO, Fe3O4, TiO2)

nanoparticles. It was found that in general, carbon based nanostructures and carbon nanotubes exhibit by far greater

enhancement of thermal conductivity in comparison to metallic/metal oxide nanoparticles.

In the last decade or so extensive research has been focused on the study of the thermal properties of Nano fluids, defined as

fluids with nanoparticle suspensions. Nano-fluids with suspensions of metallic or nonmetallic solid nanoparticles with sizes

between 1 and 100 nm from materials with higher conductivity than the base fluid exhibited higher thermal conductivity in

comparison with the equivalent macro-particle suspensions. These enhancement effects can be large in relatively low particle

volume or mass fractions making nanofluids attractive from a cost effect point of view as well. Typically, the thermal conductivity

of the composite material was found to depend on the thermal conductivities of the constituent materials, the concentration of

the diluted phase, as well as size and shape of the dispersed particles. In particular, a non-linear dependence on concentration

was observed in the limit of low concentration. Thermal conduction was found to improve with decreasing particle size, although

non-linearly and non-consistently, presumably because the smaller particles would have a larger surface to volume area, thus

enabling better heat conduction. A number of theoretical studies have suggested that the reduced particle size induces

mechanisms in the suspension that could account for the increased thermal conductivity such as, the Brownian motion of the

nanoparticles, liquid layering at the liquid/particle interface and the effect of nanoparticle clustering. In particular, the effect of

clustering was found to be important. Effective medium theories that take into account the clustering effects give better

20





agreement with experimental values of thermal conductivity. The effective volume of a cluster is considered much larger than the

volume of the particles due to the lower packing fraction (ratio of the volume of the solid particles in the cluster to the total volume

of the cluster) of the cluster. Heat transfer is assumed to be faster within such clusters and thus the volume fraction of the highly

conductive phase, now taken to be the cluster rather than the solid particles, is also larger. Experiments have shown that indeed

nanoparticles may not stay dispersed for long, forming as well as clusters, linear chain configurations, and fractal shaped

aggregates. In addition, longer aspect ratio particles such as nanofibers, carbon nanotubes, or nanowires were found to enhance

thermal conductivity even further. A number of studies show that when spherical and cylindrical particle shapes are compared,

the cylinders show an increased thermal conductivity over the spheres for the same volume fraction and particle volume. It was

hypothesized that the longer aspect ratio particles can form a mesh that spans throughout the fluid and thus conducts heat

throughout the fluid.

With respect to phase change materials, quite a few studies have been reported in the literature involving a number of different

higher conductive additives and those pertaining to paraffin wax are summarized below. Graphite nanofibers with diameters of 2-

1000 nm and lengths up to 100 μm with a thermal conductivity of around 880 W/mK, mixed with paraffin (melting temperature

of 56 oC and thermal conductivity of 0.25 W/mK) were reported to increase the thermal conductivity up to 180% at an 8% wt

fraction. A simultaneous decrease in the latent heat of fusion from 271.6 J/g from pure paraffin to 242.7 J/g for the 8%wt NP

enhanced paraffin was also observed.

In Tesse2b we have chosen to work with exfoliated expanded graphite Nano platelets of differing sizes, aspect ratios and surface

area. The nanoplatelets have an in-plane and out-of-plane thermal conductivity of 3000 and 6 W/mK respectively. They were

chosen because of their superior thermal conductivity, comparable to that of carbon nanotubes, at a much less cost and thus

feasible for applications. They also come with high dimensional aspect ratios and that can be tailored to different sizes. We report

here on the measured thermal conductivities of the composites materials, as well as the specific heats and heats of fusion as a

function of mass fraction up to 6%. Composites of paraffin and graphite nanoplatelets with diameters in the 1-15 μm range and

thicknesses in the 6-15 nm range were prepared. For 6% weight fraction with the 15 μm diameter nanoplatelets the thermal

conductivity of the composite is found to be 0.78 W/mK representing ~250% increase on the pure paraffin thermal conductivity

measured at 0.22 W/mK. We have found that the thermal conductivity is enhanced at even lower weight fraction though, with

the addition of 1% weight fraction of Nano platelets of 15 μm diameter (k=0.44 W/mK, ~100% increase). In addition, the heat of

fusion has been found to reduce up to 10% when increasing weight fraction, but to remain very close to the pure value, within 2%,

for low weight fractions. Some preliminary efforts were undertaken to compare our findings in thermal conductivity with

theoretical predictions within the effective medium approach.

The measured thermal conductivities of paraffin wax as a function of weight fraction of graphite nanoplatelets with different sizes,

aspect ratios and surface area can be seen in Figure 2.8: (squares, M15) d=15 μm and t=6-8 nm, Surface Area=120-150 m2/g;

(rombus, Μ5) d=5 μm and t=6-8 nm, Surface Area=120-150 m2/g; (crosses, H5) d=5 μm t= 15nm, Surface Area= 50-80 m2/g);

(triangle C750) d<2 μm, thickness a few nm and surface area=750 m2/g.

There is an overall increase in the thermal conductivity upon the nanoplatelets additions, although the effect is not linear and it is

different for each particular type of nanoparticle. The largest increase can be seen to occur for the M15 sample in the low weight

fraction regime up to 1% and at 6% weight fraction. The thermal conductivity is increased 100% to the value of 0.44 W/mK from

the 0.22 W/mK for pure paraffin for 1% weight fraction (~0.4 % volume fraction) and almost 250% at 6% weight fraction (~2.6%

volume fraction). The thermal conductivity does not increase linearly. The increase observed though is similar to that found in the

literature for a similar sized graphite nanoplatelet of 15 μm diameter. Samples M5 and M15 differ only in the diameter, sample

H5 has the same diameter as M5 but smaller overall surface area. Samples with M5 also show significant increase in the thermal

conductivity of the order of 60% to 100% for weight fractions between 2 and 6% (~0.8% and 2.5% volume fraction). The composite

with C750, the nanoplatelets with the smaller size, more spherical shape and the larger surface area has less effect on the thermal

conductivity than the rest, a small increase of ~13%, rather constant for the whole range studied. At the higher end studied, 6%

weight fraction (~2.5% volume fraction) for samples M5 and H5, the enhancement is leveling off or reduced in contrast to M15 in

which the thermal conductivity is greatly enhanced.

21





Figure 2.8 Measured thermal conductivity of paraffin wax with graphite nanoplatelets as a function of weight fraction.

(Source: UOI)

In Figure 2.9, the heat of fusion is shown as a function of the weight fraction for the different nanoplatelets: (squares, M15)

diameter=15μm thickness=6-8nm, Surface Area=120-150m2/g; (rombus, Μ5) diameter=5 μm thickness=6-8nm, Surface Area=120-

150 m2/g; (triangles C750) d< 2 μm, thickness a few nm and surface area=750 m2/g. It can be seen that for the small weight fraction

of 1% that the thermal conductivity, in the case of samples M15, has increased 100%, the heat of fusion has only been reduced

slightly (~2%).

Figure 2.9 Heat of fusion as a function of weight fraction.

(Source: UOI)

The heat of fusion is gradually reduced with the increase of weight fraction to about 10% for a 6% weight fraction. Similar trend is

seen for the samples with C750 nanoplatelets. Interestingly, the M5 nanoplatelets seem to leave the heat of fusion largely

unaffected up to 6% weight fraction.

Similarly, the specific heat capacitance Cp (Figure 2.10) shows negligible change as a function of weight fraction for the liquid phase

for the M15 at the 1% weight fraction.

k so

lid (

W/m

K)

weight fraction

A53 + M15

A53 + M5

A53+C750

A53 + H5

ΔΗ

(J/

g)

weight fraction

ΔΗ (J/g)

A53 + M15

A53 + M5

A53+C750

22





(a) (b)

Figure 2.10 Specific heat capacitance as a function of weight fraction of (a) liquid at 70oC and (b) solid at 20oC.

(Squares: M15, Rhombus: Μ5, Triangles: C750; Source: UOI)

In the solid phase the respective change is of the order of 2% at the 1% weight concentration, increasing to 14% at the maximum

weight fraction studied. The important issue that has to be addressed refers to aggregation and sedimentation problems. Besides

the obvious solution of stirring, functionalization of the nanoparticles has to be applied.

In conclusion, nanoplatelets of expanded graphite mixed in paraffin were found to increase the thermal conductivity at relative

low weight concentration; 1% and 6% weight fraction of the M15 type, 15 µm in diameter and 6-8 nm thick graphite nanoparticles,

increased the thermal conductivity by 100% to 250% respectively. At the same time the heat of fusion was only slightly reduced

from 2-10% for the 1 and 6% weight fraction respectively. The results provide an efficient and easy way for improving the thermal

properties of PCMs, suitable for thermal storage applications.

2.5 REFERENCES

Beggs C., UreZ . “Environmental Benefits of Ice TES in Retailing Application”, CIBSE/ASHRAE Joint National Conference, Part II,

Harrogate, Sep. 1996, UK

Oliver D, Andrews S., “ Energy Storage Systems Past Present and Future Applications, A Maclean Hunter Business Studies, October

1989

ASHRAE Handbook, “HVAC Systems and Applications“, Issue: 2008, Section 50

Burton G, UreZ . “Eutectic Thermal Energy Storage Systems”, CIBSE National Conference, Volume II, Alexandra Palace, Oct. 1997,

UK

PCM Products Ltd. Sales Literature, www.pcmproducts.net

Thermal Storage of passive, energy saving technology. CIBSE North West Presentation, http://www .cibsenorthwest.co.uk/TES-

2008.pdf

Ure Z., “Low Energy Cooling Technologies for Buildings”, I.Mech. Seminar Publications, 1998-7, Page 85, S5556/007/98

Ure Z., “ World-wide TES Applications ”CIBSE/ASHRAE CONFERENCE 1999, Harrogate / UK

Ure Z., “ Positive Temperature Eutectic (PCM) Thermal Energy Storage Systems”, ASHRAE 2004, Anaheim Meeting

http://www.slideshare.net/PCMProducts/pcm-thermal-energy-storagesystems-ashrae-2004-conference-paper

CIBSE Design Guide B, “Heating, ventilation, and Air Conditioning”, Page 2-94 - 2.997

Cp

liq

uid

(J/

gC)

weight fraction

Cp liquid T=75oC

Cp

so

lid (

J/gC

)

weigt fraction

Cp solid T=20oC

23





ICAX™ provides Renewable Heat and Renewable Cooling to buildings, http://www.icax.co.uk

Szokolay S.V, “Solar Energy and Building”, The Architectural Press Ltd., London, 1976

Ukrainczyk S., Kurajica S., Sipusie J. "Thermophysical Comparison of Five Commercial Paraffin Waxes as Latent Heat Storage

Materials", Chemical Biochemical Engineering Quarterly Q.24, 2010

Sharma D., Kitano H., Sagara K. "Phase Change Materials for Low Temperature Solar Thermal Applications", Res. Rep. Fac. Eng.

Mie Univ., Vol. 29, Page 31-64, 2004

Mavrigiannaki A., Ampatzi E. "Latent Heat Storage in Building Elements: A Systematic Review on Properties and Contextual

Performance Factors", Renewable and Sustainable Energy Reviews 60, 2016

24





3. SOLAR THERMAL TECHNOLOGIES

3.1 INTRODUCTION

Solar energy is a renewable energy source which can be converted into useful thermal energy by a Solar Thermal (ST) system. This

thermal energy may be used directly or be converted to other kinds of energy, such as mechanical, electrical, chemical. ST systems

include equipment and devices, producing fluid of low (T < 100 οC), medium (100ο< T < 400 οC) or high (T > 400 οC) temperatures,

depending on the system application.

The most common ST application is the production of Domestic Hot Water (DHW) in the residential sector through thermosiphon

systems. Other known and commercially available ST applications are:

Heat air production, mainly for applications such as drying of products and materials and spaces heating;

DHW production and space heating, using forced-circulation ST systems;

DHW production, space heating and space cooling using forced circulation ST systems and thermal chillers;

Hot water steam and/or hot air production for industrial applications;

Electricity production using concentrating solar collectors.

The main component of a ST system is the solar collector. ST technologies for low temperature applications include flat plate solar

collectors, with different design features and without solar radiation concentration, where all the parts of the collector system

are stationary.

The available collector technologies are (Figure 3.1):

Collector without transparent cover, mainly used for swimming pools heating;

Flat plate collectors;

Vacuum tube collectors;

Compound parabolic concentrator collectors.

(a) (b)

(c) (d)

Figure 3.1 ST applications using the technologies of (a) Collectors without transparent cover, (b) Flat plate collectors, (c) Vacuum tube collectors and (d)

Compound parabolic concentrator collectors.

(Source: (a) SOLE, (b) and (c) Solair, (d) Calpak)

25





For medium and high temperature applications, solar collectors utilize concentrating technology. Concentrating solar thermal

(CST) systems use mirrors or lenses with tracking systems to focus a large area of sunlight onto a smaller area. The concentrated

irradiation can then provide industrial process heating or cooling or can be used to drive a conventional power plant.

There are four commercial types of CST technologies (Figure 3.2):

Parabolic through;

Linear Fresnel;

Central receiver, also called Solar Tower;

Parabolic dish.

This document will discuss only the ST technologies that apply to the TESSe2b project, that is the solar collectors and systems for

low temperature applications (domestic hot water production, space heating and space cooling).

3.2 SOLAR THERMAL TECHNOLOGIES

ST systems consist of devices that use solar radiation to produce and distribute heat, at the point and at the temperature needed

by the user of the system.

The heat is transferred through Heat Transfer Fluid (HTF). The most common HTF is water, or water-glycol mixture of air. There

are two types of ST systems, the thermosiphon and the forced-circulation. The main difference of the two types is the way the HTF

is circulated between the collector and the storage tank.

Thermosiphon- also called natural flow – systems, use the “thermosiphonic phenomenon “and they are typically used for Domestic

Hot Water (DHW) production. A typical thermosiphon ST system consists of one or two collectors connected to a storage tank,

through a circulation system. Thermosiphon systems use gravity to circulate the HTF (usually water) between collector and tank.

The HTF is heated in the collector, rises to the top of storage tank and cools down, then flows back to the bottom of the collector.

(a) (b)

(c) (d)

Figure 3.2 CST technologies (a) Parabolic through, (b) Linear Fresnel, (c) Central receiver and (d) Parabolic dish.

(Source: EU-SOLARIS)

26





The main benefit of a thermosiphon system there is no need for a pumping of control system. This ST system type is most common

in the frost-free climates of Southern Europe.

A typical forced-circulation ST system for low temperatures applications consists of one or more collectors connected to a

circulation system that distributes heat at the point of use. The main components of a ST system as illustrated in Figure 3.3 are:

Solar collectors;

Storage system;

Circulation - hydraulic system;

Control system;

Back-up system.

Figure 3.3 Subsystems of a typical low temperature ST system.

(Source: Solarpraxis, 2005)

Due to the importance of solar collectors and storage system, they will be analysed separately at the next subchapters.

The circulation-hydraulic system refers to the piping, pumping elements and thermal insulation, designed to transfer the thermal

energy to storage and to the point of use. In the forced-circulation systems, the circulation system is made up of the primary

circuit, the secondary circuit and the consumption circuit, as shown in Figure 3.4.

Figure 3.4 Circulation system of a ST system.


Specifically for large scale ST systems, an important component is the control system. This system ensures the proper and efficient

operation of the ST systems. It includes components such as temperature sensors, flow meters, flow controllers and various

automations, which adjust inputs and outputs and optimize system functions.

A back-up system is necessary for periods of low solar radiation levels.

27





3.2.1 SOLAR COLLECTORS

The most common solar collector technologies for low temperature applications are the flat plate collectors and the vacuum

tube collectors. The flat plate collectors are the simplest and most widely used collector type. This solar collector includes an

isolated casing, on one side of which there is a transparent cover made of glass or plastic. Solar rays hit the transparent cover

and reach the flat surface. A spectral selective coating may be used on the surface to enhance the absorption of the solar

irradiation. Underneath and in contact with the surface there are copper tubes containing the HTF. The HTF that flows inside the

tubes carries the energy out of the solar collector. Thick insulation is positioned below the tubes to prevent further thermal

losses. The basic elements of flat plate collector are shown in Figure 3.5.

Figure 3.5 Flat plate collector technology elements.


The vacuum tube collectors consist of a series of vacuum glass tubes, each of which includes an absorber fin attached to a copper

pipe. The fin is covered with a selective coating that transfers heat to the HTF that circulates through the copper pipe. These

copper pipes are all connected to a common manifold which is then connected to a storage tank. Due to the presence of vacuum,

these collectors have less thermal losses than the flat plate, resulting in temperatures higher than 100 oC. This feature enables

them for temperature demanding applications, such as industrial process heat and solar cooling or for areas with cold cloudy

weather. The main elements of a vacuum tube collector are illustrated in Figure 3.6. Two types of vacuum tube collectors are

mostly used.

Direct Flow

Direct flow evacuated tube collectors, or U-pipe collectors, have two copper pipes inside the vacuum glass tube. One pipe is the

flow while the other is the return. Both pipes are connected at the bottom of the tube with a U-bend. The absorber fin separates

the flow and the return pipes. Direct flow collectors are not flexible as the heat pipe types, since in the event of a tube cracking,

the whole system requires draining.

Heat Pipe

In this configuration, the vacuum glass tube contains the absorber fin and one copper pipe in which the HTF flows. Due to the

presence of the vacuum, the HTF is quickly heated, becomes lighter and rises up to the top portion of the pipe. The main advantage

of the heat pipe collectors is that there is a “dry” connection between the absorber plate and the manifold making installation

much easier. In the event of a tube cracking, each individual tube can be exchanged without emptying the entire system or

dismantling the collector.

In Figure 3.6 the main elements of the two types of vacuum tube collector are illustrated.

28





Figure 3.6 Vacuum tube collector technology (a) direct flow (b) heat pipe.

(Source: (a) Calpak (b) Solarpraxis)

The solar collectors may be connected in different configurations (Figure 3.7):

In series: with this connection, higher temperatures are reached (lower energy efficiency), but there are higher pressure

losses.

Parallel: lower pressure losses and lower temperature differential (higher energy efficiency).

Series-Parallel Combination: this connection is a mixture of the two previously mentioned connections, which is used in

medium or large sized installation.

Figure 3.7 Connection of collectors.


The typical flow in the collector system is about 50lt/m2/h. However, large-scale solar plants (i.e. plants with collector areas greater

than 200 m2) implemented the so called “low flow” strategy, where the typical values for the flow rate in the primary (collector)

circuit is about 12-15 lt/m2/h (Solarpraxis, 2005; Procesol, 2002). The main advantages of a low-flow system (compared to the

typical high flow systems with about lt/m2/h) are as follows:

Simpler hydraulic configurations are possible (many collectors in series);

Smaller (and shorter) tubes are required;

Smaller pumps are needed.

In series solar connection, the flow is the same for all the collectors, while in parallel connection, the flows are added up. When

the installation uses the series-parallel combination connection, proper calculations should be made to ensure that the internal

distribution of the fluid becomes as uniform as possible.

29





3.2.2 SOLAR THERMAL STORAGE

The storage tank is an essential element of a ST system. In this tank, the thermal energy from the HTF, previously obtained in the

solar collector system and transferred by the circulation system, is stored. These tanks are isolated, filled in usually with water or

water-based antifreeze mixtures. The storage tanks may be classified according to the three following criteria:

Horizontal or vertical position

Inclusive or exclusive of heat exchanger. If the heat exchanger is included, its configuration could be of serpentine or of shell

or of tube type.

Type of material used in its construction

In Figure 3.8, different types of storage tanks are illustrated. The TESSe2b project and this training material also study alternative

thermal storage technologies, including the PCM products in the storage tanks.

Figure 3.8 Solar Thermal Storage tank.


3.3 SOLAR THERMAL APPLICATIONS

ST technologies can be implemented for a variety of applications. It is important to choose the suitable technology of solar collector

for the required application in order to achieve high efficiency in the examined temperature differential between collector and

ambient medium. In Figure 3.9, the correlation of the ST application with the appropriate ST collector type is shown.

Figure 3.9 Efficiency Curves for Collectors and Solar System Applications.

(Source: Solar praxis, 2005)

30





3.3.1 SOLAR THERMAL APPLICATION FOR DHW

The most common ST application in Europe is the production of Domestic Hot water (DHW). Solar DHW systems are usually

designed to cover 100% of the hot water requirements in summer and 40-80% of the total annual hot water needs. In these ST

systems, a supplementary heater is also included.

For medium and large-scale applications, central ST systems for DHW production are used. These are forced-circulation ST systems,

the basic features of which are included in the subchapter “Solar thermal technologies”. The simplest configuration of this

application is the one with an integrated electric heater in the storage tank. In Figure 3.10, the configurations of ST applications

for DHW production with internal and external heat exchanger are shown.

(a) (b) Figure 3.10 Forced-Circulation Solar DHW configurations with (a) internal heat exchanger and (b) external heat exchanger and two storage tanks.

(Source: Valentin)

3.3.2 SOLAR THERMAL APPLICATION FOR DHW AND SPACE HEATING

ST systems which, besides DHW production, contribute to the space heating are called Solar Combi systems. Solar Combi systems

are more commonly installed in Central and Northern Europe, where there is a long heating period. Of all the heating systems

using solar energy, heated floors are the most accessible and offer the greatest advantages, mainly because they work at low

temperatures and as a result, the overall efficiency is considerable. A Solar Combi systems configuration with “tank in tank” storage

type is given in Figure 3.11.

Figure 3.11 Solar Combi system for DHW and space heating.

(Source: Valentin)

31





3.3.3 SOLAR THERMAL APPLICATION FOR DHW, SPACE HEATING AND COOLING

The addition of thermal chiller in a Solar Combi system enables the system to address all building’s thermal and cooling demands.

These systems exploit the solar energy the whole year, by space heating in winter, solar cooling in summer and DHW throughout

the year. Moreover, space cooling loads coincide with the high solar radiation and since the solar cooling system is heat driven,

the building’s electrical loads are reduced, as well as the problems associated with peak power demand during summer.

The main feature of a solar cooling system, besides the solar collector field, is the thermal chiller. On the thermal supply side, the

ST system is rather conventional, consisting of high quality solar collectors, a storage circulation-hydraulic, control and back-up

systems. The two main solar cooling processes are:

Closed cycles, where absorption chillers produce chilled water for use in space conditioning equipment.

Open cycles, where desiccant evaporative cooling systems (DEC) produce chilled air for use in air conditioning equipment

ST cooling may also operate in the evening by using thermal storage. In Figure 3.12, the configuration a solar heating and cooling

system with underground thermal energy storage (UTES) is shown. This plant configuration refers to the Greek demo plant of

“High-Combi” project, described in the “case study” subunit of this chapter.

Figure 3.12 Solar Cooling application with underground thermal energy storage (UTES).

(Source: High-Combi)

3.4 SOLAR THERMAL CASE STUDY

3.4.1 DESCRIPTION OF THE APPLICATION

In this section a solar thermal plant case study is shown. The plant is installed in an existing office building, at the site of the Centre

for Renewable Energy Sources and Saving - CRES in Athens (latitude 38° 00’ N & longitude 23° 55’ E), Greece. The building covers

a total of 427 m2 with a volume of 1296 m3, which is typical of medium sized offices and multifamily buildings. The building was

constructed in 2000 and was initially designated as laboratory. In 2008, the building was renovated and it is currently used as

office. Table 3.1 presents general information of the case study.

32





Table 3.1 Solar Thermal Case Study General Information.

Application: Solar Heating and Cooling

Owner: CRES

Location: Pikermi, Attica

Type of Building: Office building

In operation since: 2011 (December)

Air conditioned area: 427 m2

3.4.2 GENERAL DESCRIPTION OF THE SYSTEM

The Greek plant operates since December 2011. The plant design includes ST collectors, a seasonal underground thermal energy

storage, a heat driven cooling machine, heat rejection units and a heat pump. In heating operation, hot water is provided to the

building at 40 oC. During low demand periods, such as autumn, a large amount of thermal energy is stored with the view of

recovering it at the following energy demanding heating period. The heat pump, which serves as auxiliary system, is driven by solar

energy. In cooling operation, the absorption machine provides chilled water to the building at 7 oC. Thermal energy, by means of

hot water over 65 oC, drives the cooling process. The estimated solar fraction is around 85% of total thermal energy requirements

of the building.

Figure 3.13 View of the office building.

(Source: High Combi)

Figure 3.14 View of the solar field.

(Source: High Combi)

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Figure 3.15 Internal view of the Underground Thermal Energy Storage (UTES).

(Source: High-Combi)

3.4.3 TECHNICAL CHARACTERISTICS

The technical characteristics of the system developed are shown in Table 3.2. Further information is available at the ST System

Department of CRES.

Table 3.2 Technical characteristics of the solar thermal plant.

Solar Thermal

Collector Type: Selective Flat Plate

Collector Area: 149.5 m2 (Gross area)

Heating Load: 12.3 ΜWh/y

Solar Cooling

Technology: Closed cycle

Nominal

capacity:

35 kW

System’s type: Absorption (LiBr)

Cooling Load: 19.4 MWh/y

Configuration

Heat storage 58 m3 (water underground thermal energy storage)N/A

Cold storage: Heat Hump (water to water driven by solar heat)18 kW

Nominal

capacity:

Auxiliary heating

system:

7

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3.5 SOLAR THERMAL APPLICATIONS WITH PCM

The objective of the TESSe2b project is to examine and optimize the ST and Geothermal systems by using PCM products in the

thermal storages of the systems. In the following figures (Figures 3.16 and 3.17) the conventional STS with Heat Pump (HP) and

the STS with PCM in the storage tank for heating and cooling are presented. The HP could optionally be a Ground Source Heat

Pump (GSHP). More details about these configurations are given in Chapter 5.

Figure 3.16 Conventional ST System with (GS)HP.

(Source:TESSe2b)

Figure 3.17 Solar Thermal System with GSHP with PCM.

(Source: TESSe2b)

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3.6 REFERENCES

Calpak, Calpak-Cicero Hellas S.A. Industrial Market Applications, available at http://www.calpak.gr/. Last accessed 09/01/2018

ESTIF - European Solar Thermal Industry Federation. http://www.estif.org/st_energy/technology/, Last accessed: 15/11/17.

EU-SOLARIS-The European Research Infrastructure for Concentrated Solar Power project. EU – Solaris brochure, available at:

http://www.eusolaris.eu/Portals/0/documents/EUS Brochure final%20version.pdf/

http:www.cres.gr/cres/files/xrisima/ekdoseis/ekdoseis EN10.pdf. Last accesed: 09/01/2018

High Combi - High Solar Fraction Heating and Cooling Systems with Combination of Innovative Components & Methods project.

High Combi brochure and final report, available at http://www.cres.gr/files/crisima/ekdoseis/ekdoseis EN9.pdf Last accessed:

11/01/2018

Procesol, Procesol II- Solar thermal plants in industrial processes. Design and maintenance guidelines brochure, available at

http://www.cres.gr/cres/files/xrisima/ekdoseis/ekdoseis_EN9.pdf Last accessed: 11/01/2018.

Solair, Solair – Increasing the market implementation of Solar Air conditioning systems for small and medium applications in the

residential and commercial buildings project. Solar air-conditioning brochure, available at http://www.solair-

project.eu/fileadmin/SOLAIR_uploads/DOCS/Guidelines/SOLAIR_Brochure_EN.pdf /

http://www.cres.gr/cres/files/xrisima/ekdoseis/ekdoseis_EN12.pdf, Last accessed: 09/01/2018.

Solarpraxis, Solarpraxis AG and the Center of the New Energy Studies (CENTER). (2005). Low–Temperature Solar Thermal

Systems - Course for Installers training material (CD ROM). Solarpraxis AG in association with European Copper Institute (2005).

SOLE, Sole S.A. – Solar Appliances Manufacturer, Solar Pool Heating, available at https://www.eurostar-solar.com/solar-pool-

heaters.html, Last accessed: 09/01/2018.

TESSe2b, TEESe2b -Thermal Energy Storage Systems for Energy Efficient Buildings. An integrated solution for residential building

energy storage by solar and geothermal resources project. Solar Thermal System Department, CRES (2016)

Valentin, Valentin Software GmbH. TSOL Solar Thermal System Configurations, available at https://www.valentin-

software.com/en/products/solar-thermal/pvsol-pro/system-configurations.Last accessed: 09/01/2018.

http://www.calpak.gr/

http://www.estif.org/st_energy/technology/

http://www.eusolaris.eu/Portals/0/documents/EUS

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4 GEOTHERMAL TECHNOLOGIES

4.1 DEEP GEOTHERMAL ENERGY

Direct heat use is the most common form of utilization of geothermal energy. Space and district heating, industrial and

horticultural uses and balneology (curing, recreation) are the best-known forms of utilization. For the economic use of

hydrothermal resources aquifers of high transmissivities with high temperatures have to be tapped. Fractured and karstified rocks

exhibit the best prerequisites whereas porous aquifer in sedimentary basins generally show decreasing porosities with depth

because of the weight of the overburden and the increasing age of the formations. In areas with moderate heat flow drilling depths

of at least 2000 m are necessary to reach a temperature level of 80 oC, which is regarded as the lower limit for district heating in

Mid Europe. Deep wells in the South German Molasse have recently reached a borehole length of up to 6000 m to tap thermal

waters with temperature of more than 140 oC.

Generally, utilization is based on a geothermal doublet, where one well is used as producer and one as injector (see Figure 4.1).

Reinjection of the fluids after utilization is essential for preserving the natural pressure conditions in the aquifer. Geothermal

projects without reinjection have seen tremendous pressure drawdown which can reduce the productivity of neighboring wells

and can lead to subsidence in the meter range.

Figure 4.1 Geothermal Doublet in a hydrothermal system.

(Source: Leibniz-Institute for Applied Geophysics).

The geothermal fluid is pumped to the surface with the help of an electrical submersible pump (ESP). Lineshaft pumps which have

their motor at surface are less common in Mid Europe. Temperatures higher than 120 oC are still an issue for the ESP's, causing

long downtimes for repairs or replacing the device. Precipitation of carbonate and sulphide minerals has turned out to be a threat

to projects in the temperature range over 100 oC. To prevent degassing and change in the partial pressure of carbon dioxide which

can lead to heavy carbonate precipitation, well head pressures in the order of >15 bar are recommended. These pressures have

to be generated by the pump; therefore, the pump design is a critical path in geothermal installation.

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Figure 4.2 Carbonate precipitation in a pipe.

(Source: STOBER & BUCHER, 2014)

For the heat transfer at the surface heat exchangers are used. In the heat exchanger the geothermal fluid and the working fluid of

the grid are separated in order to prevent mixing of the fluids. In district heating systems the working fluid is circulated in the

geothermal grid by transmission pumps.

The biggest advantage of geothermal energy lies in their basic load capacity. This results in a large number of annual full load

hours. To cover peak demands peaking stations, run with oil or gas, are installed. This additional heating also serves for

redundancy.

4.2 SHALLOW GEOTHERMAL ENERGY

Shallow hydrothermal systems, with temperatures below 25 oC, work from a geological point of view similar to the deep systems.

For generating the appropriate heat level heat pumps (GRSHP) are used.

Figure 4.3 shows the major types of utilization of shallow geothermal energy. Collectors, which are installed a depth not deeper

than 2 m are a special form of thermal utilization as they mainly use solar radiation. The effectiveness of the system greatly

depends on the moisture content of the soil, the coverage of the soil and the shading of the area. The heat exchanger pipes can

be installed in a trench or are installed as horizontal loops. As a rule of thumb the installation area of the loops should be in the

order of 2 times the surface to be heated. Specific heat extraction values vary from 10 W/m² for dry non-cohesive soils and 40

W/m² for water saturated sand or gravel. Both figures refer to 1800 annual full load hours. Due to requirement of earthmoving

work, surface collectors are usually used for heating and cooling of new installations of private houses.

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Figure 4.3 Main types of using shallow geothermal energy.

(Source: EU-project GROUNDHIT)

Borehole heat exchangers (BHEs) are an effective way of utilizing shallow geothermal energy. The critical path in the completion

of a borehole heat exchanger is the installation of the pipes (Figure 4.4) and the grouting (Figure 4.5). The grouting has to ensure

the heat transfer to the circulating fluid and has to seal the annulus thus preventing uncontrolled flow of fluids or gases. Ascending

or descending fluids can be an issue in sedimentary sequences with successions of permeable and less permeable strata of

different pressure regimes. In areas where drinking water supply relies on ground water from deeper confined strata, a

concentration of BHEs with defective annulus seals can lead to a significant pressure drop in the deep systems when groundwater

can ascend to unconfined aquifers at or near the surface. This issue effected the prohibition of BHEs or depth -restriction in some

sensitive areas in Austria.

Figure 4.4 Installation of a double-U tube in a borehole using an unwinding unit.

(Source: GEOTEAM)

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Figure 4.5 Grouting of a BHE.

(Source: Tholen & Walker-Hertkorn, 2008)

The use of groundwater for heat pump applications is the most effective form of using shallow geothermal energy. Given an aquifer

with sufficient permeability two wells serving as production and reinjection well respectively are sited. Water well use for

geothermal use requires basic knowledge of the underground hydrogeological properties, preferentially permeability, porosity

and distant velocity of the groundwater, to assess the essential distance between the production and reinjection and the

propagation of the thermal cloud in the groundwater body. In a legal sense the area of influence of a site is defined by the 1 K-line

of alteration in respect to the natural groundwater temperatures. For big installations this requires hydraulic-thermal computer

modelling (Figure 4.6).

Figure 4.6 Propagation of temperature clouds for heating (=cooling of groundwater) and cooling mode (= warming of groundwater) for a shallow geothermal

groundwater project based on a flow volume of 55 l/s).

(Source: GEOTEAM)

For private houses flow-volume requirements are low as a flow of 0.25 m³/h relates to an evaporator load of 1 kW. The wells have

to be designed and built according to the standards of well construction in order to ensure water production without solid particles

and prevent the input of atmospheric oxygen into the system to avoid the precipitation of iron and/or manganese compounds.

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Figure 4.7 Production and injection well for geothermal use of shallow groundwater.

(Source: VDI 4640)

4.3 SHALLOW GEOTHERMAL APPLICATIONS

Shallow geothermal energy is exploited by Ground Coupled Heat Pumps, a very mature and reliable technology for heating, cooling

and domestic hot water production in the built environment.

Ground Coupled Heat Pump systems consist of the ground source system, the Ground Coupled Heat Pump (GCHP) and the low-

temperature heating system inside the building. In the heating mode, the ground source system exchanges heat with GCHP

through its evaporator. Inside the GCHP the refrigeration cycle is performed and by the use of condenser, heat is released with

the building. The reversible operation is performed in the cooling mode. In other words, these systems work like a reversible

refrigerator by removing heat from the underground and rejecting it into the building in the heating mode and vice versa in the

cooling mode. It has to be mentioned that these systems have significantly higher efficiency in relation to the air-to-air heat pump

systems due to the almost invariant temperature of the underground throughout the year.

Figure 4.8 GCHP operation in heating and cooling modes

(Source: Benou A., 2008)

Since GCHP systems are high efficiency systems that are installed in low-energy consumption buildings, the target is always

optimising system parameters as well as the overall system design and operation in order to maximize COP (Coefficient of

Performance) and SPF (Seasonal Performance Factor). The main parameter in order to get the optimum system operation is the

heat pump which is the core of the system. This can be achieved by the use of a heat pump either with an inverter in compressor

41





or with compressors in series (large systems with capacities higher than 60 kWth) in order to adjust the heat pump (compressor)

operation according to the user’s energy profile. On the other hand, the overall system operation can be adjusted by the use of

inverter circulators in order to minimize the electricity consumption. The overall energy consumption can be minimized as in all

heating/cooling systems by the use of a compensation system.

4.3.1 SHALLOW GEOTHERMAL APPLICATION FOR HEATING AND DOMESTIC HOT WATER

Ground Source Heat Pumps for heating and domestic hot water production are widely spread in Northern and Central Europe

since needs for heating are dominant and practically cooling is not used. In these cases, geothermal heat pumps are designed only

for heating and DHW. On the following schematic diagram, refrigeration cycle only for heating mode is depicted.

Figure 4.9 Refrigeration cycle for heating mode.

(Source: https://www.caplor.co.uk/renewable-heat/heat-pumps/how-do-air-source-heat-pumps-work/)

4.3.2 SHALLOWGEOTHERMAL APPLICATION FOR HEATING, COOLING AND DOMESTIC HOT WATER

Ground Coupled Heat Pumps for heating, cooling and domestic hot water production are used in moderate climates, especially in

Mediterranean countries, where heating is necessary during the winter but also cooling during the summer due to quite high

temperatures. In these cases, the refrigeration cycle must be reversible from the heating to cooling mode and vice versa so a 4-

way valve is necessary. This valve can be added externally the refrigeration cycle when the heat pump is designed only for heating.

However, the heat pump is more efficient when it is designed for heating and cooling as well and the 4-way valve is included in

the refrigeration cycle as it is shown in the following schematic diagram.

Moreover, in order to produce cooling and DHW simultaneously there are three alternatives:

Reverse instantaneously from cooling to heating mode for DHW production. In case of significant DHW needs a separate

heat pump for DHW is used.

Heat pump with desuperheater in the refrigeration cycle with relatively reduced heat pump efficiency (see below).

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Figure 4.10 Refrigeration cycle for heating mode.

(Source: Botzios Valaskakis A., 2006)

Moreover, in order to generate cooling and DHW simultaneously there are three alternatives:

Reverse instantaneously from cooling to heating mode for DHW production. In case of significant DHW needs a separate

heat pump for DHW is used;

Heat pump with desuperheater in the refrigeration cycle with relatively reduced heat pump efficiency;

Rejection heat of the condenser to the DHW tank using a heating element to increase temperature since the outlet

condensing temperature is about 30 oC.

4.4 CASE STUDIES

4.4.1 INTRODUCTION

The most crucial point in planning a GSHP-System is to determine the length and the configuration of the BHEs. The designer has

to find a balance between the requirements of the heating system and economic considerations: too short BHEs will cause severe

restrictions in the performance of the heat pump, as it will be forced to work at lower outflow temperatures of the BHEs thus

decreasing the COP. On the other side the construction of the BHEs is one of the most cost-intensive parts of the system, so a

larger number of BHE-meters can make the whole project uneconomic.

4.4.2 LAYOUT OF BHES

The basic parameters for the final layout of a BHE-system are:

The requirements of the building, such as heating and/or cooling power, the annual energy used for heating/cooling (and the

distribution during the year), domestic hot water etc;

The geological setting of the site, defining the underground temperature and the specific heat extraction;

Available space.

For small systems such as single family houses in most of the cases the layout will be done by using simplified methods and

estimations. So it is a common method to calculate the required BHE-length using the power of the heat pump and a specific heat

extraction rate which is defined by the expected geology. Usually the used values range between 35 W/m and 60 W/m. In case of

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single utilization (heating or cooling) it is essential that the BHEs are installed with enough distance between so that the thermal

influence between them during the operation season can be reduced to a minimum. Usually a distance of 8 meters is

recommended.

For larger systems it is highly recommend to perform a thermal response test (TRT) in at least one pilot-BHE to acquire the essential

underground parameters. The final design of the BHE-field should be based on hydraulic-thermal modelling using dedicated

software tools. When applying these tools, the designer can vary the design parameters such as the numbers of BHEs, the borehole

depth, the distance between the BHEs etc. to achieve the optimal BHE-field for the project. In combined heating and cooling

applications reducing the distance between the individual BHEs has a positive effect as the heat of the cooling period can be stored

in the underground to support the system during winter.

4.4.3 GEOTHERMAL APPLICATION FOR A SINGLE FAMILY HOUSE

In this section, typical data for a geothermal application for a single family house are presented. The house is located near Graz.

The power of the heat pump was 13.3 kW with COP 4.8. The needed energy load from underground was 10.5 kW while the

estimated extraction rate was 40 W/m. The required total BHE-length was 262.5 meters. Three BHEs, 90 meters each were drilled

(270 meters in total, see also Figure 4.11).

Figure 4.11 Drilling the BHEs.

(Source: GEOTEAM)

4.4.4 GEOTHERMAL APPLICATION FOR AN OFFICE BUILDING

In this section, typical data for a geothermal application for an office building are presented. The office building is located in Vienna.

Total heating power is 375 kW and total cooling power is 300 kW. Preliminary investigations were conducted with the thermal

response test. The design tool used was Earth Energy Designer. The BHE-field consists of 57 BHEs, three rows with 19 BHEs each

and is completely situated underneath the building. The length of BHEs is 125 meters (total length 7125 meters) and the distance

between the BHEs is 4 meters.

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Figure 4.12 BHE-field in Vienna.

(Source: GEOTEAM)

4.5 REFERENCES

STOBER, I. & BUCHER, K. (2014): Geothermie.- 2. Auflage, Springer Verlag Berlin, Heidelberg, 280 p., ISBN 978-3-642-41762-7, 2014

THOLEN, M. & WALKER-HERTKORN, S. (2008): Arbeitshilfen Geothermie. Grundlagen für oberflächennahe

Erdwärmesondenbohrungen.- Wirtschafts- u. Verlagsges. Gas u. Wasser, ISBN 978-3-895-54167-4, 2008, Bonn.

VDI 4640 Blatt 2. Thermische Nutzung des Untergrundes. Erdgekoppelte Wärmepumpenanlagen.- Verein Deutscher Ingenieure,

Beuth Verlag, 43 S., 01.09.2001, Berlin.

Benou A. (2008), “Ground Source Heat Pumps”, Seminar in the framework of the Best-Result – Building and Energy Systems and

Technologies in Renewable Energy Sources Update and Linked Training, IEE project.

https://www.caplor.co.uk/renewable-heat/heat-pumps/how-do-air-source-heat-pumps-work/

Botzios-Valaskakis A. (2006), “Installers’ specialization in Ground Source Heat Pumps”, Seminar in the framework of the EARTH –

Extend Accredited Renewables Training for Heating,IEE project.

https://www.caplor.co.uk/renewable-heat/heat-pumps/how-do-air-source-heat-pumps-work/

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5 HYBRID SOLAR AND GEOTHERMAL SYSTEMS COMBINED WITH PCM

5.1 GENERAL OVERVIEW

Renewable thermal technologies harness renewable energy sources to provide ambient heating and ambient cooling for inside

space air and for DHW. Renewable thermal technologies can utilize a broad range of local renewable energy sources to reduce

energy costs and increase energy efficiency.

Different Renewable thermal technologies can deliver heating and/or cooling at different temperature levels which define the

suitability of different technologies for meeting specific heat requirements in the various sectors, from small domestic applications

to large scale applications used in industrial processes and district heating and cooling networks. Figure 5.1 shows an overview of

the main energy sources and technologies.

Figure 5.1 Renewable energy sources overview and main technologies.

(Source: Yale, 2017)

In the case of residential domestic systems, the efficiency of the thermal infrastructure can be improved through the usage of

small scale heat driven heating/cooling technologies like heat pumps for residential buildings, combined with thermal energy

storage (TES).Thermal energy storage stocks thermal energy by heating or cooling a storage medium so that the energy can be

used at a later time. TES can help balance energy demand and supply on a daily, weekly and even seasonal basis (Yale, 2017).

46





To increase the efficiency of systems with heat pumps costs, to increase performance, to improve reliability and increase the

applicability, some measures have been identified (York 2016, IEA 2011, RHC 2013 and RHC 2014a):

Develop and introduce heat pumps with higher output temperature for application in existing buildings equipped with high

temperature distribution systems;

Improve COP through more efficient components and systems for heat pumps;

Improve the efficiency of boreholes through improved pipe materials and better thermal transfer materials;

Develop efficient low‐temperature space heating systems and high‐temperature space cooling systems integrated with heat

pumps (particularly for use in near zero energy buildings);

Develop integrated and hybrid systems that combine multiple functions (e.g. space‐conditioning and water heating) and

hybrid heat pump systems that are paired with other energy technologies (e.g. storage, solar thermal and solar PV) to achieve

high levels of performance;

Develop standardized kits and plug‐and‐play systems for ease of installation and use;

Develop integrated control strategies and automation for ease of use.

These strategies have been considered in the development of the TEESe2b solution combined with the usage of a Hybrid

Solar/Geothermal system combined with Phase Change Materials (PCM’s).

Hybrid systems are defined as those systems which provide heating, cooling and / or domestic hot water through the combination

of two or more energy sources into a single system, and therefore overcoming the limitations of individual technologies (RHC,

2014).

5.2 CONFIGURATIONS OF HYBRID SOLAR AND GEOTHERMAL SYSTEM WITH PCM STORAGE

The concept of using a Hybrid Solar and Geothermal system combined with PCM is quite new, and therefore there are no

equivalent or similar systems to TESSe2b on the market. However, there are some systems under study and development, but

most of them are still in a research development status.

There are some related European projects that study the possibility of using Hybrid Solar and Geothermal systems combined with

PCM Storages.

The EU 7th Frame financed project EINSTEIN - Effective INtegration of Seasonal Thermal Energy storage systems IN existing

buildings. The overall objective of the project is the development, evaluation and demonstration of a low energy heating system

based on Seasonal Thermal Energy Storage (STES) systems in combination with Heat Pumps for space heating and DHW

requirements for existing buildings to drastically reduce energy consumption in buildings. This project doesn’t use PCM materials.

The EU 7th Frame financed project COMTES - Combined development of COMpact Thermal Energy Storage technologies. The

overall goal of the COMTES project is the technological development and demonstration of three compact thermal energy storage

technologies, in three parallel development lines (Line A, Line B and Line C). Line A is related with Solid sorption heat storage:

Thermal energy storage by adsorption of water vapour in a solid sorption material. As solid sorption material zeolite is used. Line

B is related with Liquid sorption heat storage: heat storage by absorption of water vapour in a liquid. Sodium hydroxide (NaOH) is

used as the liquid sorption material. Line C is related with supercooling PCM heat storage: Storage of heat in a supercooling phase

change material. The material used with the required supercooling characteristic is sodium acetate trihydrate – NaCH3COO *

3H2O. This project doesn’t use geothermal energy.

The EU 7th Frame financed project MERITS - More Effective use of Renewables Including compact seasonal Thermal energy

Storage. The aim is to build a prototype of a fully functioning compact rechargeable heat battery that would fit in for example a

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cellar or underground a garden. In addition, business models and market strategies are developed to foster market take-up before

2020. The key development issues are 1) the delivery of heat on different dedicated temperature levels for heating, cooling and

domestic hot water, 2) the tailoring to the requirements of individual dwellings, 3) the design and development of a dedicated

solar collector, and 4) the integrated design for the different components and enhanced thermo-chemical materials, including the

control system. Furthermore, the project includes the development of business models and market strategies to foster market

take-up before 2020.

The EU H2020 financed project CREATE – Compact Retrofit Advanced Thermal Energy Storage. The main aim of CREATE is to

develop and demonstrate the storage of seasonal solar energy as heat battery, i.e. an advanced thermal storage system based on

Thermo-Chemical Materials (TCMs), that enables economically affordable, compact and loss-free storage of heat in existing

buildings. This project uses geothermal energy to help the process.

The EU H2020 financed project E2VENT - Energy Efficient Ventilated Façades for Optimal Adaptability and Heat Exchange

enabling low energy architectural concepts for the refurbishment of existing buildings. E2VENT main goal is the development of

an Energy Efficient Ventilated Facades for Optimal Adaptability and Heat Exchange enabling low energy architectural concepts for

the refurbishment of existing buildings. A Latent Heat Thermal Energy Storage based on phase change materials properties may

be implemented providing a heat storage system for the reduction of peak of electricity consumption and/or for cooling in

summer. This project doesn’t use geothermal energy and the solar energy is captured in the building façade.

The EU H2020 financed project SCORES - Self Consumption of Renewable Energy by hybrid Storage systems. The project aims is

to develop and demonstrate in the field a building energy system including new compact hybrid storage technologies, that

optimizes supply, storage and demand of electricity and heat in residential buildings, increasing self-consumption of local

renewable energy in residential buildings at the lowest cost. The SCORES concept is to develop several key-technologies in parallel,

second-life Li-ion batteries, compact thermal storage by Phase-Change Materials, high performance hot-water heat pump supplied

by hybrid photovoltaic and solar collectors (PVT), Chemical Looping Combustion heat storage (seasonal storage), integrated

through a smart Building Energy Management System (BEMS), and to demonstrate them together in a hybrid energy system. This

project doesn’t use geothermal energy.

The EU H2020 financed project HYBUILD - Innovative compact HYbrid electrical/thermal storage systems for low energy

Buildings. The project aim is to develop two innovative compact hybrid electrical/thermal storage systems for stand-alone and

district connected buildings. The hybrid storage concepts are based on: a compact sorption storage, based on a patented way to

integrate an innovative adsorbent material within an efficient high surface heat exchanger, a high density latent storage, based on

a high performance aluminium micro-channel heat exchanger with additional PCM layers, and an efficient electric storage. The

balancing of thermal and electrical energy flows are realized by seamless integration of electric building components in a DC

coupled system and by efficient conversion and upgrading of electric surplus and renewable thermal energy sources by

compression and adsorption heat pumps. This project doesn’t use geothermal energy.

There are not many scientific articles related with Hybrid Solar and Geothermal system with PCM storages usages. Some of them

use two of these components, namely solar energy, geothermal energy or PCM´s.

In order to investigate the performance of the combined solar-heat pump system with energy storage in encapsulated phase

change material (PCM) packings for residential heating in Trabzon, Turkey, an experimental set-up was constructed (Kaigusuz,

1999). The experimental results were obtained from November to May during the heating season for two heating systems. These

systems are an in-series heat pump system and a parallel heat pump system. The experimentally obtained results are used to

calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load meet by

“free” energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. In this

study, the experimental set-up was developed to determine the performance of the series and parallel heat pump system, solar

collectors and energy storage tank filled by PCM used for residential heating. The effects of various system parameters on the

response of indoor air temperature of the building, the temperature variation of the PCM in the energy storage tank and the

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temperatures of the heat transfer fluid (water) in the solar collectors and energy storage tank for series and parallel heat pump

system were investigated. Also, the collector and storage efficiencies, heat pump COP, seasonal performance factor (SPF), the

building heating load, heat-supplied fraction of the heating load by the systems and energy consumption of the combined solar-

heat pump system during the cold season were calculated.

Some applications of copper heat exchangers embedded in PCM including air and ground source heat pump space heating and

cooling in which the use of a compact TES unit offers higher COP due to condenser and evaporator temperature optimization were

described by Shabtay (Shabtay,et Black, 2014). This paper covers the design, performance and economics for using a TES unit to

replacing a conventional hot water storage tank in a heat pump water heater and a solar thermal water heater. TES unit

optimization for a HPWH allowed for lower return temperature to the compressor, constant exit water temperature, faster

charging time and reduced unit size by as much as 60% compared to a conventional water tank. TES unit optimization for a solar

thermal application permits replacement of large water tanks with lighter weight TES units that can be placed on interior or

exterior walls. Overall, this paper describes how optimized designs of thermal energy storage systems for domestic hot water

delivery (now in development) are compact, have flexible form factor for applications in buildings where space is at a premium,

deliver hot water at a constant output temperature, operate for a longer time for the same volume, or have increased efficiency

over conventional systems.

Shabtay (Shabtay,et Black, 2014) stresses that ground source systems can be designed with a hot side and a cold side where each

unit contains a copper heat exchanger in PCM, (which eliminates the need for an expensive stainless steel plate heat exchanger);

the condenser and evaporator are embedded in their respective PCMs. The refrigerant cycle is exposed to fixed temperatures,

therefore, improving system COP. Cold water is sent to the air handlers instead of refrigerant. Excess cold or heat is absorbed by

the ground loop. The hot side produces hot water in PCM storage and has a dual purpose in winter for hot water and space heating

by sending hot water through the air handlers (Figure 5.2).

Figure 5.2 PCM thermal storage heat pump system with ground loop.

(Source: Shabtay and Black, 2014)

The main conclusions of this paper for the studied system are:

Immersing a heat exchanger in PCM as means of water thermal storage by can significantly reduce the volume of water

storage systems;

The unit performs like a 150 litre water tank size unit within the required parameters. It delivers water over 40 oC for 15

minutes. The phase-change process delivers the required amount of energy in a stable and uniform manner;

The water pressure drop is at an acceptable level of 0.2 bars (3 psi);

The PCM unit can store 5 times more energy than water in the useful range of 40 oC to 52 oC;

The sensible energy needed to raise the PCM temperature to 48 oC is half that needed for water;

The use of extended surfaces in the form of aluminium fins and the fin pitch selected provided an equivalent thermal

conductivity of 23 W/moC;

This PCM thermal storage technology is applicable to air conditioning systems, and heat pumps with ground loops.

Cold water PCM

thermal storage

unit (5°C)

Hot water PCM

thermal storage

Undergroun

d trench

49





Benli (Benli, 2011) studied the thermal energy performance of ground heat pump with latent heat thermal energy storage (calcium

chloride hexahydrate as the PCM) in Turkey. Experimental and theoretical studies have been done for the ground heat pump with

phase change material actively by using the heat pump and passively by using the latent heat storage with the phase change

material. Results obtained showed that the heating overall coefficient of performance of the system (COPsys) and the ground heat

pump performance (COPHP) were around the range of 2–3.5 and 2.3–3.8, respectively.

In order to test the various methods for production, transfer and consumption of energy obtained from various renewable sources

a laboratory device (Figure5.3) equipped with photovoltaic collectors, concentrated thermo-solar collectors, heat pumps for

conversion of geothermal energy from boreholes, heat storage vessels and advanced control units. An experimental unit was

installed IMSAS in Bratislava (Jerz et al, 2015).

Figure 5.3, Diagram of experimental laboratory equipment installed in IMSAS Bratislava.

(Source: Jerz et al, 2015)

A heat exchanger consisting of 6 pieces of tubular Al profile has been filled by PCMRT28HC (Rubitherm, 2014).Heated water flowed

through the central opening of Al profiles and the side openings have been filled by PCM. The total weight of Al profiles connected

in series was 6.8 kg, the weight of PCM was 1.7 kg and the volume of the water tested was 56 litres. The water has been heated

by constant power of 1600 W until the temperature reached 62 oC. It has been compared the speed of free water cooling to a

temperature of 24 oC in the case of heat exchanger with and without PCM filling.

An innovative structural design of heat exchanger filled by PCM-based composite material was also tested. The granules of

aluminium scrap are mixed to PCM in order to facilitate improved heat transfer from the whole volume of PCM to the surroundings

during storing as well as during dissipating of heat due to thermal conductivity enhancement of material for heat storage.

Results show that the aluminium foam panels provide an excellent alternative for built-in ceiling radiators for efficient heating or

cooling of rooms using low potential energy resources. The porous structure of aluminium foam absorbs or dissipates

homogenously latent heat at almost constant temperature if PCMs with phase change at the temperature range between 23 oC

and 28 oC are used for storage of the heat obtained from renewable energy sources. Authors conclude that these features of

aluminium foam panels in combination with smart temperature control systems, significantly reduce the energy consumption of

heating/air conditioning systems of future ZEBs. The energy storage systems based on thermal storage seem to be unavoidable in

order to have return-on-investment period below ten years in the case of energy efficient small family houses.

50





5.3 CONFIGURATION OF TESSE2B SOLUTION

5.3.1 TESSE2B GENERAL HYDRAULIC SCHEME

The general hydraulic scheme of TESSe2b solution is shown in Figure 5.4. The main components of the system are the Solar Thermal

Collectors, the Geothermal Heat Pumps with vertical Borehole Heat Exchangers (BHE) and three energy storage systems in the

form of PCM tanks with immersed heat exchangers. Each type of tank is filled with adequate PCMs of different working

temperatures in order to efficiently provide domestic hot water, space heating and space cooling. Additional components include

the heat dissipator, circulating pumps, control valves and the necessary sensors for control and monitoring.

Figure 5.4 TESSe2b general hydraulic scheme.

(Source: Tesse2b)

The Tesse2b solution will be initially demonstrated on residential houses with low‐temperature space heating systems and high‐

temperature space cooling systems which are energy efficient. But the system configuration is flexible and it can be easily adapted

to provide other types of end devices, mainly by using PCMs with suitable phase change temperature for the storage tanks. The

TESSe2b solution can be installed not only in new buildings but also in buildings with pre-existing heating and cooling system,

without replacing the heating and cooling terminal units. The PCM tanks have a modular design that allows flexible sizing and

scaling of the system to meet thermal energy needs of residential buildings with various sizes and for different climates.

Additionally, the TESSe2b system has an integrated monitoring system to collect and store measured data that can be used by the

user and by system installers for real-time and off-line evaluation of the system performance. The system can be monitored

remotely by installers and any problems such as faulty components or suboptimum system operation can be identified without

the need to visit the building site.

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5.4 TESSE2B CONTROL SYSTEM

5.4.1 FUNCTIONS AND OPERATING MODES

The control system coordinates all components of the TESSE2b system, in order to efficiently execute the main functions of the

system which are the following:

• Provision of space heating and cooling using solar and geothermal energy;

• Provision of dehumidification during cooling, when allowed by the cooling end device;

• Provision of domestic hot water (DHW);

• Storing of solar and geothermal energy for heating and cooling;

• Safe operation and protection of system components.

These functions are executed by the TESSe2b central controller. The central controller ensures that all times the appropriate flow

and inlet temperature are provided to the heating and cooling terminal units of the building to efficiently heat or cool the building

and to provide while maintaining sufficient thermal comfort for the occupants. The air temperature inside a room or zone of the

building will be controlled by a separate decentralized control device and thermostat, which is not part of the TESSe2b system. In

this TESSe2b controller is independent of the building installation and it will be able to operate with a range of heating and cooling

devices such as fan coils, underfloor pipes, in wall pipes, radiators etc. The TESSe2b controller has also the task to sustain the

operating temperatures of hot and cold PCM tanks within the safety limits of the PCM material with the aim extend their lifetime

as well as to perform other safety functions e.g. Legionella prevention (if necessary), safety operation in case of a component

failure or during extreme weather conditions. The different operating modes possible with the TESSe2b control system are listed

in Table 5.1. Table 5.1: TESSe2b operating modes

Description Mode From To

Charging DHW PCM by Solar Collectors DHW Solar Collectors PCM Storage for Domestic Hot Water

Charging DHW PCM by Heat Pump DHW Heat Pump PCM Storage for Domestic Hot Water

Charging DHW PCM by Backup Heater* DHW Backup Heater PCM Storage for Domestic Hot Water

Legionella Protection* DHW Backup Heater PCM Storage for Domestic Hot Water

Charging Hot PCM by Solar Collectors Heating Solar Collectors Hot PCM Storage

Charging Hot PCM by Heat Pump Heating Heat Pump Hot PCM Storage

Space Heating by Hot PCM Heating Hot PCM Storage Building Terminal Units

Space Heating by HPCM & Heat Pump Heating Hot PCM Storage & HP Building Terminal Units

Space Heating by Heat Pump Heating Heat Pump Building Terminal Units

Overheating prevention Heating Solar Collectors Heat Dissipater

Charging Cold PCM by Heat Pump Cooling Heat Pump Cold PCM Storage

Space Cooling by CPCM Cooling Cold PCM Storage Building Terminal Units

Space Cooling by CPCM and Heat Pump Cooling Cold PCM Storage & HP Building Terminal Units

Space Cooling by Heat Pump Cooling Heat Pump Building Terminal Units

Space Cooling by Heat Pump &

Dehumidification

Cooling Heat Pump Building Terminal Units

Holiday Mode - - -

Service Mode - - -

*optional mode

52





5.4.2 GENERAL ENERGY MANAGEMENT AND CONTROL APPROACH

The coordination of the main system components is done automatically by the TESSe2b controller. The controller measures or

estimates various system parameters in order to detect the thermal energy needs of the building, solar availability as well as the

state of PCM storage tanks and BHEs. Based on the state of the system, the most appropriate operating mode is activated to

optimally coordinate the thermal energy transfer between the solar and geothermal sources, storage tanks and the building. The

heating or cooling demand is detected by monitoring the inlet and outlet temperature of the heating and cooling devices of the

building. Then the controller automatically adapts the flow and the temperature of the transfer fluid in order to ensure that the

house will be properly heated, cooled or dehumidified. The controller will also ensure that there is always enough heat in the PCM

tank that is used to provide Domestic Hot Water for the users. The operation of the solar collectors is continuously monitored in

order prevent overheating by actively dissipating excess solar energy to the environment.

The solar energy is actively stored in ‘hot’ PCM tanks with immersed heat exchangers that operate at two temperature levels, one

for DHW provision and the other for space heating provision. No water is stored in the PCM tank for DHW, eliminating the danger

of Legionella development. The PCM tank for DHW can also be heated by the Geothermal Heat Pump when needed. Energy for

space heating is provided first by the hot PCM tank and when the heating demand cannot be met by the HPCM then the Heat

Pump provides the additional thermal power. Space cooling is provided directly to the building by the Geothermal Heat Pump. If

different electrical tariffs are available that vary during the day, the Heat Pump can also be used to charge a portion of the hot

PCM tank as well as the whole of the cold PCM tank during the period which the electricity is cheap and use this energy later,

especially if significant thermal demand is needed during the daily peaks of electrical demand during which the cost per kWh is

the highest. In this way, by shifting the electricity demand of the heat pump during the day, savings in operating costs can be

achieved. This feature becomes more significant with the development of ‘smart grids’ in which energy prices vary dynamically

depending not only on the energy demand but also on the availability of intermittent renewables such as solar and wind and

demand-site management can be very beneficial for the end users as well as for energy utility operators. Additionally, forecasting

methods can be combined with the TESSe2b system to predict peaks in heating or cooling demand and to proactively charge the

available storage systems to later use them simultaneously with the Heat Pump during the high demand period. This improves

comfort levels during very cold or hot periods and it can allow for a smaller kW sizing of the Geothermal Heat Pump since it does

not have to cover the peaks in demand.

53





5.5 REFERENCES

Benli, H., (2011). “Energetic performance analysis of a ground-source heat pump system with latent heat storage for a greenhouse

heating”. Energy Conversion and Management 2011;52:581–9.

European Technology Platform for Renewable Heating and Cooling (RHC)(2013):“Cross-CuttingTechnology Roadmap”.

European Technology Platform for Renewable Heating and Cooling (RHC)(2014a):“Common implementation road map for

renewable heating and cooling technologies”.

European Technology Platform for Renewable Heating and Cooling (RHC)(2014b): “Solar Heating and Cooling Technology

Roadmap”.

Jerz, J., Tobolka P, Michenka V., Dvorák T.(2015), “Heat Storage in Future Zero-Energy Buildings”. International Journal of

Innovative Research in Science, Engineering and Technology. DOI:10.15680/IJIRSET.2015.0408003.

Kaigusuz, (1999), “Investigation of a combined solar-heat pump system for residential heating”, .Int. J. Energy Res. 23: 1213}1223.

Rubitherm Technologies GmbH, (2014), “Rubitherm PCM RT28HT – Data sheet of company Rubitherm Technologies GmbH”,

Berlin, Germany

Sanner, B, (2008): Guidelines, standards, certification and legal permits for Ground Source Heat Pumps in the European Union.

Proc. IEA Heat Pump Conference 2008, paper 4.02, 9 p., Zürich.

Shabtay,Y., L., Black, J.R.H (2014), “Compact hot water storage systems combining copper tube with high conductivity graphite

and phase change materials”. Energy Procedia 48 ( 2014 ) 423 – 430.

Yale, Center for Business and the Environment (2017), “An Overview of Renewable Thermal Technologies”.

54





6 INFORMATION FOR SYSTEM DESIGNERS, INSTALLERS, MAINTENANCE TECHNICIANS AN D END USERS

6.1 INFORMATION FOR SYSTEM DESIGNERS

When studying, designing and developing a system that will use the TESSe2b solution, there are some important design parameters

that the project designer should know and take under consideration. Table 6.1 resumes them.

Table 6.1 TESSe2b summary of important design parameters.

Unit/Equipment Actions needed Parameters to consider

Borehole Heat Exchangers Perform ground thermal response test Number of boreholes (#)

Know Borehole Thermal Resistance Boreholes depth (m)

Know specific heat extraction rate Soil temperature (ºC)

Know PCM properties (for ground) PCM quantity (#)

Heat Pump (HP) Know Heating needs Heating capacity (kW)

Know Cooling needs Cooling capacity (kW)

Select Heat Pump COP

EER Inverter or on-off

Pump (HP to boreholes) Calculate piping circuit (HP to BH) Water flow rate (m3/s)

Select pump Pressure drop (Pa)

Solar Collectors Calculate the solar collector surface Location

Select solar inclination and orientation Local Solar Radiation(MJ/m2)

Select solar collector Solar Collector efficiency

Solar Heat Dissipater Calculate the heat transfer rate necessary to dissipate in case of no solar consumption

Heat dissipation rate on solar dissipater (J/s)

Pump (Solar collector circuit) Calculate piping circuit (Solar circuit) Water flow rate (m3/s)


Domestic Hot Water Tank Calculate volume of tank Tank volume (m3)

Calculate heat dissipation rate on tank DHW PCM properties

Heat dissipation rate on tank (J/s)

PCM Hot Storage Tank Calculate volume of tank Tank volume (m3)

Calculate heat dissipation rate on tank Hot PCM properties


PCM Cold Storage Tank Calculate volume of tank Tank volume (m3)

Calculate heat dissipation rate on tank Cold PCM Properties


Pump (House Load) Calculate piping circuit (house circuit) Water flow rate (m3/s)


House Calculate cool loads Envelope characteristics walls, windows)

Calculate heat load Occupation, equipment, …

Calculate DWH needs Outside and inside temp, Solar radiation

Implement thermal simulation Occupants, DHW Equipment

55





The general approach for a system that uses TESSe2b is similar for a Domestic HVAC + DWH system with some complementary

considerations. As in any HVAC + DWH system there are some key points to consider:

1. Perform detail thermal simulation that takes under consideration the heating, cooling and DHW demands in an hourly and

annual basis (cooling, heating and DWH thermal loads);

2. Dimensioning/selecting the Heat Pump, based in thermal necessities and on the overall performance of the Heat Pump,

namely the COP, SPF, and water circulation temperatures;

3. Dimensioning the number and depth of ground boreholes, based on soil properties and thermal response test;

4. Dimensioning/selecting the DHW Tank volume based on DHW needs;

5. Dimensioning/selecting the PCM Hot Storage Tank volume based on heating needs, heat dissipation rate on the tank and

available solar radiation;

6. Dimensioning/selecting the PCM cold Storage Tank volume based on cooling needs, heat dissipation rate on the tank and

electricity tariff schemes;

7. Dimensioning/selecting the solar collectors based on local solar radiation, orientation, inclination and efficiency of solar

collector;

8. Dimensioning/selecting the solar heat dissipator based on the heat transfer rate necessary to dissipate in case of no solar

consumption;

9. Dimensioning the three water piping circuits (HP to boreholes, solar circuit and house Load) considering the piping (type of

tubes) and all the accessories needed;

10. Selecting the three water pumps for the system (HP to boreholes, solar circuit and house Load) based on the circuits piping

characteristics, namely pressure drop, water flow rate, accessories and pump efficiency;

11. Selecting all the instrumentation and accessories necessary to support information and feed the smart control system.

6.2 INFORMATION FOR INSTALLERS

For the installation of TESSe2b solution, the system can be divided in four main components (solar, geothermal, DHW, air

cooling/heating) that must be distinguished in the installation process. A short list of the main activities, necessary when installing

the system are presented below:

1. Installation on the geothermal side (drilling, pipe laying, well construction, etc);

2. Installation of solar panels circuit (solar panel, solar dissipator, solar circuit water pump, etc);

3. Installation of heat pump (refrigerating/thermodynamic systems, systems under pressure, electrical safety, etc);

4. Installation of DHW thermal accumulation tank;

5. Installation of PCM’s thermal accumulation tanks (Cold water and hot water);

6. Installation of traditional heating and air conditioning equipment (plumbing, fan-coils, radiators, etc);

7. Implementation of the three-different system piping’s (solar, DHW, ambient cooling and ambient heating);

8. Implementation of the control system and field instrumentation;

9. Power supply to the system.

One important aspect when considering the installation of TESSe2b system is the European standardisation or normalisation on

the design or installation of ground source heat pump systems. Table 6.2 list the most important European standards and

guidelines related (Sanner, 2008).

56





Table 6.2 Resume of most important European standards and guidelines (Source: Sanner, 2008 adapted).

StandardEquipment

EN378-1:2008 Refrigerating systems and heat pumps – Safety and environmental requirements–Part1: Basic requirements, definitions, classification and selection criteria

EN255-3 Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors –Heating mode-Testing and requirements for marking for domestic hot water units

EN14511-1:2004 Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling–Parts1-4

ISO13256-1:1998 Water-source heat pumps—Testing and rating for performance-Part1:Water-to-air and brine-to-air heat pumps

ISO13256-2:1998 Water-source heat pumps—Testing and rating for performance-Part2: Water-to-water and brine-to-water heat pumps

EN12828:2003 Heating systems in buildings–Design for water based heating systems

EN12831:2003 Heatingsystemsinbuildings-Methodforcalculationofthedesignheatload

EN15316/4/2:2008 Heating systems in buildings-Method for calculation of system energy requirements and system efficiencies-Part4-2: Space heating generation systems, heat pump systems

EN15450:2007 Heating systems in buildings. Design of heat pump heating systems

6.3 INFORMATION FOR MAINTENANCE TECHNICIANS

For the maintenance of TESSe2b, the system follows the general maintenance operations of HVAC/Geothermal/Solar system with

thermal accumulation tanks. The maintenance operation of each component of the system (heat pump, solar collector, solar

dissipator, pumps, etc.) should follow the maintenance operation list indicated by the component manufacturer. Nevertheless, in

addition to these specific maintenance operations indicated by the respective component manufacturer, it is convenient to make

dedicated maintenance operations for the TESSe2b system as a whole. One to two maintenance visits per year is the

recommended for the system.Table6.3 presents a brief resume list of this TESSe2b maintenance operations.

57





Table 6.3 TESSe2b equipment maintenance list (resume).

Equipment Maintenance operations

Borehole Heat Exchangers Verify general state

Verify the inlet/outlet water temperature

Verify the heat of extraction/rejection

Verify water flow rate

Heat Pump (HP) Verify general state

Verify power supply (V)

Verify electric consumption (V)

Measure noise level (dB)

Check refrigeration charge

Check low and high pressure (cycle)

Verify/clean heat exchangers and check for damage

Verify water flow rate (low side and high side)

Pump (HP to boreholes) Verify water flow rate

Verify inlet/outlet water pressure

Verify general state




Solar Collectors Verify surface cleaning and status


Solar Heat Dissipater Verify running mode of air ventilator

Verify motor ventilator consumption (V and Amp)

Inspect state of coil

Pump (Solar collector circuit) Verify water flow rate






Domestic Hot Water Tank Verify general state


PCM Hot Storage Tank Verify general state



PCM Cold Storage Tank Verify general state



Pump (House Load) Verify water flow rate






Smart control system Check all functionalities (heating, cooling, DHW, etc)

58





6.4 INFORMATION FOR END USERS

End users of TESSe2b are informed that this solution is an integrated package with thermal storage technology, using solar

collectors, geothermal energy, thermal accumulation and highly efficient heat pumps for heating, cooling and production of DHW.

As a general description of the components of the system, it is important to know that TESSe2b uses advanced compact integrated

PCM TES tanks exploiting renewable energy sources, like the solar energy and geothermal energy, coupled with enhanced PCM

borehole heat exchangers (BHEs). TESSe2b includes two TES tanks specially developed that integrates PCM materials, and two

highly efficient heat exchangers.

The TESSe2b control system ensures the correct and most efficient operation. The operations that the TESSe2b system assures are

the heating, cooling and dehumidification of the residential house, (using solar and geothermal energy), the provision of DHW,

the storing of solar and geothermal energy for heating and cooling in PCM tanks and the safe operation and protection of the

system components.

As general benefits of TESSe2b solution we can point:

One single appliance provides heating and cooling of ambient residential air and DHW;

The maintenance costs and time are reduced compared to the conventional separate equipment, based on fossil fuel sources

(boilers and HVAC equipment);

Initial implementation costs can be reduced (based on the correct choice of the equipment) when compared to the

conventional separate equipment based on fossil fuel sources (boilers and HVAC equipment);

Reduction in implementation space (only one equipment for both HVAC and DHW);

Reduction of noise (no exterior condensing units);

Higher equipment performance due to favourable ground temperatures and solar utilization;

Reduction of CO2footprintwhen compared to traditional boilers and AVAC equipment, due to the utilization of renewable

energy sources (solar and geothermal) and the utilization of thermal accumulation;

Reduction on the monthly operation cost due to the possible operation of unit during reduced tariff rates of energy and

energy accumulation.

Table 6.4 presents a brief resume of the main components of TESSe2b system and the purpose of each component in the system.

Water piping Verify water piping and accessories state

Verify water piping and accessories for water leaks

Verify insolation (if applied)

House terminal units - fan-coils (not

included in the system))



Verify water flow rate

Verify/clean air filter

Inspect state of coil

Verify running mode of air ventilator

Verify motor ventilator consumption (V and Amp)

Verify thermostats

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Table 6.4 TESSe2b main components and equipment purposes.

Unit equipment Purpose

Borehole Heat Exchangers Capture energy from the ground to be used by the system to provide cooling and heating

for the ambient air in the house and for providing domestic hot water

Heat Pump (HP) Produce cooled and/or hot water to be used for ambient air cooling and heating.

Produce hot water to be used for domestic hot water in the house appliances

Pump (HP to boreholes) Circulate water between the heat pump and the ground boreholes

Solar Collectors Capture solar energy to be used by the system to provide hot water that will be used by

the heat pump or to heating for the ambient air in the house and for providing domestic

hot water

Solar Heat Dissipater Dissipate the excess of solar energy in case that is necessary

Pump (Solar collector

circuit)

Circulate water in the solar collector circuit

Domestic Hot Water Tank To accumulate hot water to be used to the domestic hot water appliances

PCM Hot Storage Tank To accumulate hot water to be used to ambient air heating

To transfer energy from PCM´s to hot water

PCM Cold Storage Tank To accumulate cold water to be used to ambient air cooling

To transfer energy from PCM´s to cold water

Pump (House Load) Circulate water in the domestic house circuit

House terminal units - fan-

cols (not included in the

system)

Heating the ambient air using the hot water that circulates inside de house

Cooling the ambient air using the cold water that circulates inside de house

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6.5 REFERENCES

Benli, H., (2011). “Energetic performance analysis of a ground-source heat pump system with latent heat storage for a greenhouse

heating”. Energy Conversion and Management 2011;52:581–9.

European Technology Platform for Renewable Heating and Cooling(RHC)(2013):“Cross-CuttingTechnology Roadmap”.

European Technology Platform for Renewable Heating and Cooling (RHC)(2014a):“Common implementation roadmap for

renewable heating and cooling technologies”.

European Technology Platform for Renewable Heating and Cooling (RHC)(2014b):“Solar Heating and CoolingTechnology

Roadmap”.

Jerz, J., Tobolka P, Michenka V., Dvorák T.(2015), “Heat Storage in Future Zero-Energy Buildings”. International Journal of

Innovative Research in Science, Engineering and Technology. DOI:10.15680/IJIRSET.2015.0408003.

Kaigusuz, (1999), “Investigation of a combined solar-heat pump system for residential heating”, Int. J. Energy Res. 23: 1213}1223.

Rubitherm Technologies GmbH, (2014), “Rubitherm PCM RT28HT – Data sheet of company Rubitherm Technologies GmbH”,

Berlin, Germany

Sanner, B, (2008): Guidelines, standards, certification and legal permits for Ground Source Heat Pumps in the European Union.

Proc. IEA Heat Pump Conference 2008, paper 4.02, 9 p., Zürich.

Shabtay, Y., L., Black, J.R.H (2014), “Compact hot water storage systems combining copper tube with high conductivity graphite

and phase change materials”. Energy Procedia 48 ( 2014 ) 423 – 430.

Yale, Center for Business and the Environment (2017?), “An Overview of Renewable Thermal Technologies”.

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7 DEMO SITES OF TESSE2B SOLUTION

In this Chapter, the Tesse2b demo sites where the developed solution will be demonstrated are presented. One of the objectives

of Tesse2b is demonstration, on-site monitoring and technology validation of prototypes of a single building in three pilot sites.

TESSe2b project will demonstrate how the integration of this technological solution of solar and geothermal energy can result in

improving energy efficiency and decrease costs. The TESSe2b demonstration sites are located in Austria, Spain and Cyprus with

the purpose to test Tesse2b in different climates throughout Europe. Works in the buildings have not yet finalized, however, it is

worth mentioning the required modifications that are required. Also, results from energy simulations that are provided for the

three selected buildings help to understand the expected performance of the system.

7.1 DEMO SITE IN AUSTRIA

7.1.1 BRIEF DESCRIPTION OF THE BUILDING IN PILOT SITE

The house selected for the demonstration site Austria is situated in Kapfenberg, a town some 40 kilometres north of Graz, within

the grounds of a technical school (Figure 7.1).

Address: Viktor-Kaplan Straße 3, 8605 Kapfenberg/Austria

Coordinates: 47°26'30.26"N/15°18'2.19"E

Figure 7.1 Tesse2b demonstration site Kapfenberg, Austria.

The house is owned by the Bundesimmobiliengesellschaft (BIG). The BIG is owned for 100% by the republic of Austria and is the

company that is managing all the real estates which are property of the republic of Austria.

7.1.2 HOUSE CHARACTERISTICS

The House has one level with a total dwelling area of 202 m² and a cellar under some parts. It was built in 2003, a thermal insulation

has been done in 2010. The current thermal insulation characteristics are:

• Base: 16 cm EPS;

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• Walls: 18 cm EPS;

• Roof: 14 cm Mineral Rock Wool.

The object serves as accommodation for the school's janitor and it is parted into two dwelling units of approx. 90 m² each (see

Figure 7.2). Unit 1 is currently inhabited by three people; Unit 2 cannot be used because of floor damages due to groundheaving.

Figure 7.2 Layout of the building.

The house is currently heated by oil with an annual consumption of approx. 4000 liters oil (for heating and domestic hot water),

the house is heated with radiators. The power of the heating system (33 kW) is clearly oversized due to the thermal renovation

of 2010.

7.1.3 OUTLOOK

The floor in Unit 2 has to be renovated due to the damages caused by ground heaving. These works are currently scheduled to be

done 2018 and therefore match perfectly the schedule of the TESSe2b – project. Within this works a retrofit of the heating system

for both units will be done, so heating and cooling will be possible using the TESSe2b-system.

The heating power of the heat pump will be 12 kW. Four BHEs with a total length of 420 meters will be installed east of the building

(see Figure 7.3), 2 BHEs with and 2 BHEs without PCM.

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Figure 7.3 BHE – layout for the demonstration site Austria.

7.1.4 ENERGY BUILDING SIMULATION

To characterize the energy needs of the house, for heating and cooling, it was be done dynamic energy simulations of the building.

The energy simulation made by Design Builder software ((http://www.designbuilder.co.uk/). This software was validated by

ANSI/ASHRAE standard 140.

It was used the climate date for Graz, from the data base of the Design Builder.

The design indoor air temperature considered for design it was 20 oC for heating season and 25 oC for cooling season.

The geometry of the building and the characteristics of the thermal envelope it was provided by the architect.

Figure 7.4 shows the model of the geometry used in the Design Builder.

Figure 7.4 Geometry mode from Design Builder, Austria demo site.

http://www.designbuilder.co.uk/

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The estimate of DHW heating needs it was done considering a daily consumption of 160 liters of DHW at 45 oC and the typical

monthly profile of fresh water temperature in Austria.

The number of solar collectors, hot PCM tanks and cold PCM tanks were optimised by parametric analysis.

The solar radiation collected by solar panels was calculated considering the climate data and the characteristics of the solar

collector (Vacuum collectors) and the collector open surface (10 collectors, 2.15 m2 each).

It was considered 4 hot PCM tanks (heat transfer rate, 2.16 kW, energy storage, 12.1 kWh, each). The PCM used was the A44.

For cold PCM tanks it was considered 2 tanks (heat transfer rate, 2.16 kW, energy storage, 8.63 kWh, each). The PCM used was

A9.

To evaluate the performance of the thermal envelope of the building it was repeated the simulations but replace the actual

thermal envelope by the reference thermal envelope, based in the EPC methodology, for Austria.

Table 7.1 shows the main results of both simulations.

Table 7.1 Results from energy building simulations (real building, reference thermal envelope) in Austria pilot site.

Conditions

Heating

Capacity

(kW]

Cooling

Capacity

(kW)

Heating

Annual

needs

(kWh/m2)

Cooling

Annual

needs

(kWh/m2)

Solar

Collector

(vacuum)

Hot

PCM

Tanks

Cold

PCM

Tanks

Solar

Fraction

Heating

Solar

Fraction

Heating +

DHW

Heating

needs shifted

day to night

(total – solar)

Cooling

needs

shifted day

to night

Real 14.39 4.67 55.08 8.67 10.00 4.00 2.00 11.8% 20.9% 43.7% 57.8%

Ref 14.00 4.74 49.35 10.12 10.00 4.00 2.00 12.1% 22.2% 46.6% 56.4%

The predicted heating capacity is 14.39 kW and the cooling capacity is 4.67 kW. The specific energy needs is 55.08 kWh/(m2y) for

heating and 8.67 kWh/(m2y) for cooling.

Comparing with the results from the reference thermal envelope it is possible to verify that the real building has similar energy

needs, slightly higher than the reference (more 12%) for heating and slightly lower for cooling (less 14%).

The use of Hot PCM tanks allows to reach a solar fraction for heating of 11.8% and allows to shift 43.7% of heating needs from day

to night.

Considering the use of cold PCM tanks is it possible to shift 57.8% of the cooling needs from day to night.

7.2 DEMO SITE IN CYPRUS


The house is located at Meliou village, a small traditional village, 35 kilometers from Pafos town airport and 14 meters from the

Latchi beach area. It is built in a plot of 3500 m², which is at a high of 420 meters from the sea level. Its area is 180 m2 (100 m2 of

ground floor and 80 m2 of first floor).

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Figure 7.5 Tesse2b demonstration site in Cyprus.

The house is 28 years old and it’s in good condition (Figure 7.6). It is made of brick plastered walls and roof tiling. The underground

area is rich in geothermal energy due to the number of water springs and underground waters.

The coverage of heating needs is made through oil fired boiler and burner and the use radiators. Cooling needs are covered with

split units. Regarding DHW production, the existing domestic hot water system is a solar system with two solar panels and hot

water cylinder on the roof with emergency 3 KW electronic element. The hot water cylinder is also connected to the oil boiler.

Figure 7.6 View of the pilot building in Cyprus.

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Figure 7.7 Plans of the pilot building in Cyprus.

7.2.2 DESCRIPTION OF THE RETROFIT AND THE NEW SYSTEM

The works for the retrofit and the installation of the new system include:

WORKS INSIDE THE HOUSE

PPR Piping for all the fan coil units (two circuits, one of each floor), including cleaning, flushing, filling up the system

insulation etc;

Removal of existing radiators, existing radiators, existing piping and insulation;

Supply and installation of fan coil units;

Installation of all conduits, wiring and electrical boxes for all controls sensors and power supply to fan coil units;

Supply and installation of all sensors, controls, isolators etc;

All building work, carpenter work, painter etc, necessary for all above;

Removal of all existing timers, thermostats and controls;

Pressure test of the system.

WORKS ON THE TILE ROOF

Supply and installation of the weather station;

Removal of existing Photovoltaic panels and reinstall to new position on the roof to make space for the solar panels;

Removal of existing solar system and piping;

Supply and installation of new solar panels;

PPR piping form the plantroom to the solar panels and connection to the solar panels, including insulation, water proofing

etc;

New PPR piping for domestic how water, from the new positions of the hot Water cylinder, in plant room to the existing

piping on the roof, including insulation, water proofing etc;

Installation of ducts, wiring, electrical boxes etc;

Supply and installation of all sensors, control etc;

All building and painter work, necessary for all the above work;

Pressure test of the system;

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WORKS OUTSIDE THE HOUSE

Cleaning and levelling the area and prepare for the geothermal boreholes;

Drilling of bore holes, backfilling with special grouting and removal away all mad;

Supply and installation of the geothermal heat exchangers;

All piping from the geothermal heat exchangers to the manifold;

Supply and installation of the underground geothermal manifold complete with cover, supports, air vent, main valves,

balancing valves etc;

Supply and installation of the piping from the geothermal manifold to the plant room;

All electrical conduits and wiring, in and from the geothermal boreholes to the manifold and plant room;

Supply and installation of all sensors in the boreholes and the manifold;

All building work necessary for the above work, including channels in ground and concrete drive way and patio, backfilling

and new concrete;

Pressure test of system.

WORKS IN THE PLANT ROOM

Supply and installation of Heat pump;

Supply and installation of geothermal pumps;

Supply and installation of solar pump;

Supply and installation of secondary pumps;

All electrical conduits, cables, supports, for all sensors, electrical valves and controls;

Supply and installation of all controls, sensors and electric valves;

Supply and installation of the power supply panel complete with isolators, overloads, relays etc;

Supply and installation of all ducts, metal trays and supports. Cables, Local wood isolators etc;

Supply and installation of all pipe work, insulation, supports and metal trays, valves fittings etc;

Pressure test of the system;

General marking and labelling as fitted drawings, operation manuals of machinery installed etc;

Testing and commissioning the system.


To characterize the energy needs of the house, for heating and cooling, it was be done dynamic energy simulations of the building.

The energy simulation made by Design Builder software ((http://www.designbuilder.co.uk/). This software was validated by

ANSI/ASHRAE standard 140.

It was used the climate date for Larnaka, from the data base of the Design Builder. The design indoor air temperature considered

for design it was 20 oC for heating season and 25 oC for cooling season. The geometry of the building and the characteristics of the

thermal envelope it was provided by the architect. Figure 7.8 shows the model of the geometry used in the Design Builder.


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Figure 7.8 Geometry mode from Design Builder, Cyprus demo site.


monthly profile of fresh water temperature in Austria.

The number of solar collectors, hot PCM tanks and cold PCM tanks were optimised by parametric analysis.

The solar radiation collected by solar panels was calculated considering the climate data and the characteristics of the solar

collector (Flat plate collectors) and the collector open surface (10 collectors, 2.37 m2 each).

It was considered 3 hot PCM tanks (heat transfer rate, 2.16 kW, energy storage, 12.1 kWh, each). The PCM used was the A44.

For cold PCM tanks it was considered 3 tanks (heat transfer rate, 2.16 kW, energy storage, 8.63 kWh, each). The PCM used was

A9.


thermal envelope by the reference thermal envelope, based in the EPC methodology, for Cyprus.


Table 7.2 Results from energy building simulations (real building, reference thermal envelope) in Cyprus pilot site.

Conditions

Heating

Capacity

(kW]

Cooling

Capacity

(kW)

Heating

Annual

needs

(kWh/m2)

Cooling

Annual

needs

(kWh/m2)

Solar

Collector

(Flat)

Hot

PCM

Tanks

Cold

PCM

Tanks

Solar

Fraction

Heating

Solar

Fraction

Heating +

DHW

Heating

needs shifted

day to night

(total – solar)

Cooling

needs

shifted day

to night

Real 17.03 18.56 45.34 69.92 10.00 3.00 3.00 30.5 % 42.3 % 44.8 % 30.3 %

Ref 14.45 9.79 21.92 49.77 10.00 3.00 3.00 49.4 % 65.2% 36.4 % 40.7 %


heating and 69.92 kWh/(m2y) for cooling. Comparing with the results from the reference thermal envelope it is possible to verify

that the real building has higher needs of heating (more 106%) and cooling (more 40%).

Based on the capacity shown in Table 7.2 and taking into account the ground capacity it is predicted that ten BHEs with a total

length of 100 meters each will be required.

The use of Hot PCM tanks allows to reach a solar fraction for heating of 30.5% and allows to shift 44.8% of heating needs from day

to night. Considering the use of cold PCM tanks is it possible to shift 30.3% of the cooling needs from day to night.

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7.3 DEMO SITE IN SPAIN


The Spanish TESSe2b demosite is located in a small town 100 kilometers far from Barcelona called Calonge de Segarra. With 202

citizens, 37 km2 of surface and 643 meters of altitude, Calonge de Segarra has a Continental - Mediterranean climate due to its

relative altitude of 600 to 780 meters. It is characterized by quite cold winters, with an average of 3 oC in February, minimums

between 2 and 10 oC, with a lot of fog, temperatures often below 0 oC, frost and some snowfall. The summers are warm, with an

average of 21 oC in July, with maximums up to 35 oC.

The precipitations are irregular, mainly occurring in autumn and spring, the summer being the driest season. The average annual

precipitation is about 500 mm. In winter, precipitation is usually in form of snow.

Figure 7.9 View of the Spanish site area in the map.

The selected house has the following characteristics:

Surface: 150 m2 distributed in two floors;

Year of construction: 18th century (last refurbishment 2017);

Ownership: Municipality;

Use: Social Housing;

Tenants: Family of 4.

Figure 7.10 View of the house and the area cited.

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7.3.2 DESCRIPTION OF THE RETROFIT

Originally the house was a summer camp-house with a big living room, kitchen, several rooms and three bathrooms. The

refurbishment made in 2017 change the disposition of the rooms leaving the ground floor as it was and changing the 1st floor with

only one bathroom and 4 big bedrooms.

Concerning energy efficiency, all windows have been replaced by double glazed windows to improve the insulation of the house.

Figure 7.11 Before and after.

7.3.3 DESCRIPTION OF THE NEW SYSTEM – EXPECTED BENEFITS

The new system includes the installation of the following components:

2 BHE 90m depth using a single 40 mm polyethylene pipe;

2 BHE 90m depth using a double 40 mm polyethylene pipe;

One circuit filled with PCM;

12 kW Ground Source Heat Pump;

10 solar flat collectors;

10 low temperature radiators;

4 Hot PCM Tanks;

2 Cold PCM Tanks;

1 PCM Domestic Hot Water Tank;

1 weather station with solar radiation sensor;

1 control box with energy demand management;

The scheme shown in Figure 5.4 explains the integration of the different elements.

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The TESSe2b system will be able to provide solar panels, the PCM tanks, hot water and the capacity to cool and heat the house

using the GSHP. The algorithm will determine when it is the best moment to use these different sources. The decision will be based

on weather variables/forecast, energy demand and electricity price in order to optimize the contribution of renewable energy,

energy efficiency and total cost.

Figure 7.12 View of works for the development of BHEs.


To characterize the energy needs of the house, for heating and cooling, dynamic energy simulations of the building were

attempted. The energy simulation made by Design Builder software ((http://www.designbuilder.co.uk/). This software was

validated by ANSI/ASHRAE standard 140.

The climate data for Barcelona, from the data base of the Design Builder were used. The design indoor air temperature considered

for design it was 20 oC for heating season and 25 oC for cooling season. The geometry of the building and the characteristics of the

thermal envelope it was provided by the architect. Figure 7.13 shows the model of the geometry used in the Design Builder.

Figure 7.13 Geometry mode from Design Builder, Barcelona demo site.


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monthly profile of fresh water temperature in Barcelona. The number of solar collectors, hot PCM tanks and cold PCM tanks were

optimised by parametric analysis. The solar radiation collected by solar panels was calculated considering the climate data and the

characteristics of the solar collector (flat panel collectors) and the collector open surface (9 collectors, 2.37 m2 each). It was

considered 4 hot PCM tanks (heat transfer rate, 2.16 kW, energy storage capacity 12.1 kWh, each). The PCM used was the A44.

For cold PCM tanks it was considered 2 tanks (heat transfer rate, 2.16 kW, energy storage capacity 8.63 kWh, each). The PCM used

was A9.


thermal envelope by the reference thermal envelope, based in the EPC methodology, for Barcelona.


Table 7.3 Results from energy building simulations (real building, reference thermal envelope) in Spanish pilot site.

Conditions

Heating

Capacity

(kW]

Cooling

Capacity

(kW)

Heating

Annual

needs

(kWh/m2)

Cooling

Annual

needs

(kWh/m2)

Solar

Collector

(Flat)

Hot

PCM

Tanks

Cold

PCM

Tanks

Solar

Fraction

Heating

Solar

Fraction

Heating +

DHW

Heating

needs shifted

day to night

(total – solar)

Cooling

needs

shifted day

to night

Real 11.30 5.04 46.38 8.93 9.00 4.00 2.00 40.1% 54.9% 0.0% 92.7%

Ref 10.41 4.35 41.11 6.05 9.00 4.00 2.00 43.4% 58.7% 8.9% 95.5%


heating and 8.93 kWh/(m2y) for cooling.

Comparing with the results from the reference thermal envelope it is possible to verify that the real building has similar energy

needs, slightly higher than the reference.

The use of Hot PCM tanks allows to reach a solar fraction for heating of 40.1%. However, there is no possibility of changing the

heating needs from day to night, using lower electric tariffs.

Considering the use of cold PCM tanks it is possible to shift most of the cooling needs, 92.7% from day to night.