University of Minho School of Engineering Centre of Biological Engineering

Engenharia para a Qualidade de Vida: MOBILIDADE E ENERGIA – Semana da Escola de Engenharia -11 a 16 de Outubro de 2010

Introduction

Taking into consideration the excessive energy consumption in recent years, it must be realized that the building sector is an extremely important sector to intervene. According to Balaras, the European building stock stands for 33% of the final energy consumption and 50% of electricity use.

There are also some predictions pointing out that if a significant change of practice does not take place, in 2050 the building stock will represent 80% of the total energy consumption. Conscious of this problematic, the European Union launched some Directives to promote the sustainable development of the building sector reducing its excessive energy consumption. The last one, EPBD-Recast, is very restrictive and sets the so called 20-20-20 targets: reduce the greenhouse gases emissions in 20%, reduce the community’s energy consumption in 20% and increase the share of energy from renewable sources to 20% until 2020. This can only be reached if some actions on existing buildings are taken. In this context, a massive rehabilitation of the existent building stock must be started and new refurbishment solutions must be developed. Conscious of these needs, the LFTC – UMinho, funded by FCT (PTDC /ECM/67373/2006), is developing an optimized prefabricated façade retrofit module for Portuguese residential buildings, helping contributing to these targets.

Building Stock Measurement Campaign In order to develop effective and efficient retrofit modules, we need to know what are the major needs and problems of the building stock. To pursuit this objective, a measurement campaign in different buildings was carried out to identify the main energy pathologies, which are: low insulation levels (high U values) of the envelope, high air infiltrations rates and abundant thermal bridges. These problems can be overcome by reinforcing the envelope insulation and applying more airtight windows frames and doors or using mechanical ventilation systems with heat recovery.

Author* PEDRO SILVA

Supervisors: Manuela Almeida, Luís Bragança; Co-Supervisor: Vasco Mesquita

* psilva@civil.uminho.pt

HIGH ENERGY EFFICIENCY PREFABRICATED RETROFIT MODULE DEVELOPMENT

Building Stock Measurement Campaign – Thermal Bridges

Prefabricated Retrofit Module

To reinforce the insulation level of existing buildings, it is being developed a prefabricated module based on traditional discontinuous prefabricated insulating finishing, although with integrated ducts to lodge different kinds of tubes and cables, optimized levels of insulation and with a mounting system that allows a simple application and removal. The module composition is:

The application of the solution to the existing wall is going to uphold two phases: 1st - placement of the metallic supporting structure; 2nd - application of the module to the supporting structure with a system of indentation pins (module) and gaps (supporting structure)

Module performance optimization

Energy performance - a dynamic simulation tool was applied (eQuest®) and the performance of an existing building was estimated considering the original envelope (U=1.9 W/m2.ºC) and the application of the retrofit module on the existing building walls (U=0.2 W/m2.ºC). The results showed that this measure, together with the reinforcement of the others envelope elements, led to a significant reduction of the total energy needs that went from 320 kWh/m2year (of the original building) to 86.8 kWh/m2year;

Conclusions

The development of a new prefabricated retrofit module for residential buildings is relevant – the implementation of this type of solutions can result in a substantial overall reduction of the energy needs that can be higher than 70% if the application of the retrofit module is complemented with a systematic improvement of the building envelope. For the final validation of the retrofit module, several prototypes were built and instrumented with monitoring equipment and their thermal performance certified.

AcknowledgmentThe authors would like to thanks to FCT (Fundação para a Ciência e Tecnologia) for funding the Project PTDC/ECM/ 67373/2006, and also for the scholarship SFRH / BDE / 15599 / 2006 to the author Pedro Silva. Also a special recognition to the DST, S.A. board of directors, namely to Eng. José Teixeira, for the investment provided to the accomplishment of several studies presented in this paper.

Domingos da Silva Teixeira, S.A.

Construction Year Energy Consumption

200

150

100

50

kWh/m2.y Image adapted from Mark Zimmerman

aluminium composite finishing (3mm); agglomerated black cork insulation (60mm); steel U-profiles (3mm); extruded polystyrene insulation (XPS – 120mm) with or without moulded ducts or negative for ducts and cables; smart vapour retardant; aluminium composite finishing (3mm).

25.3

37.9 °C

30

35

Several module prototypes were built and tested on LFTC Test Cells and the theoretical thermal transmittance, U, of 0.23 W/m2.ºC has been confirmed.

Design optimization - a 3D modelling tool was applied – Google SketchUp® - in order to study and optimize the module application to the existing wall and the interaction between modules;

Other issues - it was applied the tool THERM® to optimize the module in terms of thermal bridges and the tool Wufi® to confirm the inexistence of condensation inside the module.

Retrofit Module installation method