[ieee 2010 ieee control and system graduate research colloquium (icsgrc) - shah alam, malaysia...

Review on Performance of Thermal Energy Storage System at S & T Complex, UiTM Shah Alam,

SelangorM.B.A.Aziz #1 , Z.M.Zain #2, S.R.M.S.Baki#3, and M.N. Muslam*4

# Faculty of Electrical Engineering*Facility Management Office

Universiti Teknologi MARA,

40450 Shah Alam,

Selangor Darul [email protected]

Abstract – This paper presents on the performance of Thermal Energy Storage (TES) system at Complex Science and Technology, University Teknologi MARA Shah Alam Selangor. Various technical aspects and criteria for thermal energy storage systems and applications are discussed and energy saving techniques and environmental impacts of these systems are highlighted with illustrative examples. This study describes the result of the operation of the TES system. The data obtained were observed and analyzed to measure the cooling load demand capacity, electrical load, and building load profile of S & TComplex in certain duration. The results show that, the operation of TES is not fully utilized. The ice charging process does not constantly meet the nominal tank capacity of 10,800 RTh. Energy consumption is higher since the chiller has to top up the remaining cooling capacity during peak period. Also, in this paper the Building Energy Index of S & T is calculated as 201.48kWh/m2/year. In conclusion, data retrieve will be valuable assets as to forecast and predict the amount of energy use for future benefits.

Keywords – Thermal Energy Storage (TES), Building Energy Index (BEI)

I. INTRODUCTION

Thermal energy storage (TES) has gained popularity among building owners in Malaysia. In principle, TES system is a load management technology with great potential to shift load from peak to off-peak utility periods [1-4]. TES system can bea new measure to be considered as a method to promote energy efficiency and the energy usage in building foremost, leading to energy conservation. There are mainly three types of TES systems, i.e. sensible (e.g. water and rock), latent (e.g. water/ice and salt hydrates) and thermo chemical (e.g. inorganic substances). The selection of TES is mainly dependent on the storage period required, i.e. diurnal or seasonal, economic viability, operating conditions, etc. In practice, many research and development activities related to energy have been concentrated on the efficient energy use and energy savings, leading to energy-conservation. In this regard, TES appears to be one of the most attractive thermal applications and exergy as the best tool in analyzing their

performances [5, 6]. However, for many cases, the field performance data have indicated that this technology has substantial problems in real-life application, as might be expected with many new technologies [7-12].

The main aim of the paper is to address the issues related to the field performance of TES system at Complex Science and Technology (S&T), University Teknologi MARA Shah Alam Selangor. A case study will be carried out to investigate howeffective the operation of TES system to provide thermal comfort at this Complex.

A. Thermal Energy Storage (TES) at S & T Complex

S & T Complex was built with a centralised chiller water plant with Thermal Energy Storage (TES) scheme in year 2002. The plant was commissioned in June 2002 with capacity of 3600 RT installed Chiller capacity and 10,800 RTh Thermal Energy Storage capacity. In principle, the design of the TES scheme is meant to shift load from peak to off-peak.Table 1 below, shows the S & T Complex district cooling design.

TABLE IDISTRICT COOLING DESIGN

Chiller Installed 2 x 1800 RT Base Mode2 x 1250 RT Ice Mode

Thermal Storage Capacity 45 x 240 RTh Ice Cell

Building Cooling Load Requirement

Block 1 550 RTBlock 2 580 RTBlock 3 380 RTBlock 4 850 RTBlock 5 660 RTTower 1 290 RTTower 2 290 RT

MaxCooling Demand 3600

The TES plant used Dunhanbush Ice Cell Technology with 45 number of Ice cell stored under car part area. The plant was designed to have one unit chiller 900 RT x 2 compressors to charge the Ice Cell during an off-peak hour between 2200 hrs to 0700 hrs.

2010 IEEE Control and System Graduate Research Colloquium

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Ton

sT

ons

This will give a low production cost benefits to UiTM where the night tariff is much cheaper compared to the peak period [13].

Fig. 1 Operation schematic diagram of the plant

As shown in Figure 1, the whole system consists of 3 closed circuit namely primary, secondary, and tertiary loop. The liquid flowing in the primary loop is ethylene glycol and chilled water flows in the secondary and tertiary loops. This design of multiple loops allowed the system to operate in all 5 operating modes; ice build, ice build with cooling, cooling with ice, cooling with chiller, and cooling with ice and chiller.

The plant utilizes partial storage operating strategy in which during discharge mode, the ice storage and the chiller running day mode work together to cover the building load. This strategy is quite critical, where controlling the contribution of chiller and ice storage are critical to the system economy and comfort. Modulating valves are used to manage the relative contribution of storage and chiller.

Since cooling load reflected by numbers of occupant and chiller production, aiming to achieve and maintaining 44oF is important as to achieve thermal comfort. As the load and chiller contribution varies, the modulating valves will automatically allow sufficiently flow though the storage system to maintain 42oF of ethylene glycol to be supplied to the primary HX. In between ethylene glycol and chiller water, the process of heat transfer is occurred, to gain the desired temperature of 44oF, chilled water will be supplied to the Air Handling Units (AHU) and Fan Coil Unit (FCU) for the entire building.

The plant is using water cooled chillers regarding of its beneficial contribution in S & T Complex. This system usually embedded inside the building and heat from chiller is carried by reculating water to outdoor cooling tower. Its potential advantages appear in term of energy efficiency referring to operational time of chiller in S & T Complex building.

B. Operational Strategies for TES system

In S & T Complex, TES is by using latter mode. Both chiller and ice storage, actually running side by side to handle the peak load requirement of the building. Charging schedule

is from 9.00 p.m. until the 7.00 a.m. for the next day while the rest is for discharging time. This might seem to be complex and quite critical as to controlling both components of TES system which also lead to economical option and comfort.

Several strategies are available for charging and discharging storage to meet cooling demand during peak hours. These are:

24 hour Period

Fig. 2 Full Storage or Load Shifting

Full Storage strategy or Load Shifting strategy as shown in Figure 2, it also coined, operated by shifting the entire on-peak cooling load to off-peak hours. This system would require a large storage facility or a small cooling load. It is designed to operate at full capacity during all off-peak hours to charge storage on the hottest anticipated days. Anotherpoint to note is that this strategy is most attractive where on-peak demand charges are high or the on-peak period is short [14].

24 hour Period

Fig. 3 Partial Storage; Load-Levelling

As shown in Figure 3, for the partial storage system, while chiller runs to meet part of the peak period cooling demand. Here, the chiller has relatively smaller capacity when compared to that of the design load. Partial storage system

Chiller Charging StorageChiller Meets Load DirectlyStorage Meets Load

LoadChiller On


LoadChiller On


50

Ton

smay be run as load-levelling or demand-limiting operations. In a load-levelling system the chiller is sized to run at its full capacity for 24 hours on the hottest days. This strategy is most effective where the peak-cooling load is much higher than the average load [14].

24 hour Period

Fig. 4 Partial-Storage; Demand-Limiting

In a demand-limiting system, as shown in Figure 4, the chiller runs at reduced capacity during on-peak hours and is often controlled to limit the facility’s peak demand charge. Demand savings and equipment costs are higher that they would be for a load-levelling system, and lower than for a full-storage system [14].

C. Building Energy Indices

The index selected would depend on the intended application of the index and the normalizing factor. Among Architects the normalizing factor for comparing buildings is the gross floor area. The most commonly used index for comparing energy use in buildings is therefore the Building Energy Use Index (BEI). This is usually expressed as kWh/m2/year which measure the total energy used in a building for one year in kilowatts hours divided by the gross floor area of the building in square meters [15].

II. METHODOLOGY

Building Automatic Systems (BAS) is a computerized system which is meant for controlling and monitoring mechanical and electrical component within the building.From there, it acts as a massive data logger which records the entire cooling component data and activities for TES systems.All of these can be seen by monitoring and assessing chiller plant control module of S & T Complex located at ground level. The panel was able to access information on each component of TES system; ice cell, cooling tower, heat exchange, chiller plant, pump and other components. Data was recorded in hourly time within the system. In analyzing the available data, a month of complete data were taken along with electrical load incorporating with TES system. Also to accompany the overall information was the chiller plant daily log sheet, for example, include the percentage of opening

valve as to maintain temperature in range of 45°F and below,the supply and return temperature of building chilled water, flow rate of ice cell, chill water along with ice cell mixed together with chilled water and operating activities in daily for chiller.

Equation (1) below is the temperature conversion formula from Fahrenheit to Celsius [16]:

9

532 FahrenheitCelsius (1)

The amount of energy used in buildings depends firstly on what it is used for. Thus, the initial and most important step in isolating the factors affecting energy use is to determine its end-use. The energy audits carried out by Pusat Tenaga Malaysia, PTM, of Office buildings in Malaysia revealed that the majority of Malaysian Office building had BEI in the range of 200 to 250kWh/m2/year [17].

TABLE IIELECTRICITY BIL. FOR S & T COMPLEX IN 5 MONTH

Month Other (kWh) S & T (kWh) Total (kWh)OCT (2009) 1074075 982110 2056185NOV (2009) 939448 1078594 2018042DEC (2009) 775015 1029860 1804875JAN (2010) 980602 1127661 2108263FEB (2010) 848205 1037261 1885466MAC (2010) 1019212 1196882 2216094

Average 2014820.83

Calculation of Building Energy Index:

Average of Energy, kWh in 6 month = 2,014,820.83

Estimated total Energy, kWh for 1 year,= 2,014820.83 x 12= 24,177,849.96

Total Energy (kWh) ÷ Gross Floor Area in S & T,= 24,177,849.96 ÷ 120,000 m²= 201.48kWh/ m2/year

Hence, the Building Energy Index; = 201.48kWh/m²/year

III. RESULTS & DISCUSSION

As the cycle of occupancy in building varies with time, so does the cooling requirement which the cool storage systems used the refrigerant to create a reservoir of cold material. Based on the cooling profiles, the outputs were manipulated based on numbers of person’s vacant. From 2100 until 0700 hours, the system began elevated the storage with ice slurry. During the rate of occupant is at minimal level, the demands for cooling were almost not required. The patterns of parameters are normally not consistent as it depends on the occupancy schedules.


LoadChiller On


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TABLE IIISAMPLE OUTPUT OF TEMPERATURE FOR ICE CELL OPERATION

Supply Return Supply Return V1 V2

TM 14 TM 11 TM14 TM11 % %

21:00 44.96 40.79 0 100

22:00 33.69 30.20 0 100

23:00 32.12 14.00 0 100

0:00 22.37 17.16 0 100

1:00 22.33 18.40 0 100

2:00 22.35 18.30 0 100

3:00 22.15 17.80 0 100

4:00 21.90 17.62 0 100

5:00 21.70 17.55 0 100

6:00 21.85 17.48 0 100

7:00 45.66 52.17 35 65

8:00 41.32 47.93 35 65

9:00 40.93 47.83 30 70

10:00 41.02 47.77 30 70

11:00 41.40 47.69 30 70

12:00 41.64 47.98 25 75

13:00 41.24 47.33 25 75

14:00 41.34 47.11 25 75

15:00 44.00 49.04 20 80

16:00 42.28 48.84 15 85

17:00 42.60 48.97 15 85

18:00 51.92 56.99 0 100

19:00 52.05 57.41 0 100

20:00 53.10 57.80 0 100

Time

Ice cell charging overall temp

Ice cell discharge overall temp

Modulating

Valve

Mechanical parts such as valves were into played by regulating the opening of inlet toward important section foremost the ice modular tank as to allow completely developing of ice in it. As stated in the table 3, V1 valve which is to bypass the flow of chilled water is closed completely as to allow the chilled water to make ice in ice cellduring charging mode, allowing V2 to be fully open 100%thus toward into ice making. Both of control valves were utilized to control ice-melting rates by controlling the chilled water flow rates and the chilled water temperature. At 0700, temperature was monitored as to maintain it under range of 42 to 45F. As hours passing by and number of occupant increasing, both valve is regulate based on this factors. The temperature capacity of chilled water is starting to deteriorate as increase in absorbing heats within the buildings.

Data were taken during normal semester and mid-termbreak time starting from 2nd February until 8th February and 16th to 22nd 2010 in same month at 0700 until 2100. Theminimum of chilled water supply is 42.30 °F (5.722 °C) during Saturday as shown in Figure 5, as occupant is not very dense compared on weekdays.

Fig. 5 Building Chilled Water Supply for 1st week of February 2010

Fig. 6 Building Chilled Water Return for 1st week of the February 2010

Fig. 7 Building Chilled Water Supply for Mid-Term Break

Fig. 8 Building Chilled Water Return for Mid-Term Break

The baseline temperature of chilled water supply is 11oC, while the baseline temperature of chilled water return is 15oC. The temperature of chilled water supply and chilled water


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return of the Complex are going above the baseline at 3.00 pm, as shown in Figure 5 and 6. For Mid-term break, the temperature of building chilled water supply is above 11oC at uncertain time compare to normal semester (as shown in Figure 5) and the temperature of chilled water return is above 15oC also at uncertain time as shown in Figure 7 and 8.

Fig. 9 Ice Cell RT & Building RT for 1st week of the February 2010

Fig. 10 Ice Cell RT & Building RT for Mid-term

In Figure 9, the maximum building load analysed in that particular week was 2124 RT at 7:36:22 a.m. on Thursday, 4th

February 2010. During time of discharging, the building RT dramatically increased. This is because of the increased of occupancy in the building. Instead of that, as shown in Figure 9 and 10, the demand cooling profiles were insufficient but during the weekend on Mid-term break (as shown in Figure 10), ice cell RT capacities were extra enough to support the building RT since buildings were less occupied.

Fig. 11 Pattern of Electrical Load for 1st week of the February 2010

Fig. 12 Pattern of Electrical Load for Mid-term Break

Since most electrical rates include demand charges during peak time or higher day versus night kWh charges. The use of electricity at night versus peak daytime hours can lead to large savings on energy bills. From the study, the maximum value of electrical load on February is 1968.6 kW. In Figure 11, shows that, the pattern of electrical loads are same all over the week except for the loads on weekend where only 1112.6 kW was required but the pattern of electrical loads on mid-term break quite differ all over the week, as shown in Figure 12. This case happen because of the operations of chiller depends on the number of user in the building.

Currently, from calculation the Building Energy Index (BEI) of S & T Complex is 201.48kWh/m2/year. The best BEI practice and recommended by Malaysian Standard is 125kWh/m²/year [15]. Therefore, S & T Complex BEI is 62.43% above the recommended value. Meanwhile, the recommended achievable target is 160Kwh/m²/year which is 28% saving.

Nevertheless, this reference new suggestion for the value especially the concept of the green building has been forwarded now, where the Building Energy Index as high as 202kWh/m2/year still acceptable.

IV CONCLUSION

From the study, the TES system built in S&T Complex doesnot provide an adequate cooling throughout the entirecomplex. The historical data obtained are very crucial to determine the overall systems performance. The profiles do varies every time when cooling is supplied throughout the buildings. There are several factors need to be considered to improve the performance of TES system including the numbers of occupancy, weather and the control modes.

V RECOMMENDATION

As a new technology emerging rapidly, so does TES system. The implementation of Building Automation System (BAS) with Energy Management System (EMS) can save energy better and extend the capabilities of existing system.Data retrieved from chiller plant module should be collected more efficient in term of easily medium interface such as USBis not in present currently. To conduct a thorough inspection on each ice cell condition such as specific gravity of the liquid, purity of the water, water level and condition during ice build and ice melt. This is important as to ensure that there


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the sufficient cooling energy can be stored during ice built mode. The TES system control mechanism via V1 and V2 must be readjusted accordingly as to optimize chiller capacity to maximum during the peak load and ice cell act as back up to top up the shortage. The objective is to ensure no short cycling of the chiller during the day and causing shortage of ice for back up on peak load.

The installation of TES system is not only focused in certain area but should be built into new facilities as to promoting energy cost program and utilizing the effectiveness of system itself. A more suitable, establish and long term rate structure should be imposed as to encourage off-peak energy use. The important part is government and non-government agencies collaboration are required to provide financial incentives as to support the initiative in developing TES systems in any buildings.

ACKNOWLEDGMENT

The authors acknowledge the support of Research Management Institute (RMI) and Facility Management Office, University Teknologi MARA, Malaysia for the project.

REFERENCES

[1] Opportunities in thermal storage R&D, EPRI Rep. EM-3159-SR, Electric Power Research Institute, Palo Alto, CA, USA, 1983.

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[3] Commercial cool storage presentation material, EPRI Rep. EM-4405, Electric Power Research Institute, Palo Alto, CA, USA, 1986.

[4] Cool storage marketing guidebook, EPRI Report EM-5841, Electric Power Research Institute, 1988.

[5] M.A. Rosen, Appropriate thermodynamic performance measures for closed system for thermal energy storage, ASME Journal of Solar Energy Engineering 144 (1992) 100-105.

[6] I. Dincer, S. Dost, X. Li, Performance analyses of sensible heat storage system for thermal application, International Journal of Energy Research 21 (10) (1997) 1157-1171.

[7] M.A. Piette, Analysis of a commercial ice-storage system: Design principles and measured performance, Energy Build., 14 (1990) 337-350.

[8] Performance of cool storage system, EPRI Rep. EM-4044, Electric Power Research Institute, Palo Alto, CA, USA, 1985.

[9] Operation and performance of commercial cool storage systems, EPRI Rep. CU-6561, , Electric Power Research Institute, Palo Alto, CA, USA, 1989.

[10] M.A. Piette, E. Wyatt and J. Harris, Technology assessment: thermal cool storage in commercial buildings, Rep. LBL-25521, Lawrence Berkeley Laboratory, Berkeley, CA, 1988.

[11] M.A. Piette and J. Harris, Program experience report: commercial cool storage, Rep. LBL-25782, Lawrence Berkeley Laboratory, Berkeley, CA, 1988.

[12] M.A. Piette, Learning from experiences with thermal storage: managing electrical loads in buildings, CADDET Analysis Series Number 4, Centre for the Analysis and Dissemination of Demonstrated Energy Technology, Sittard, Netherlands, 1990.

[13] R. Zainuddin, Review on Operating Improvement of the Air Conditioning System at Complex Science and Technology, University Teknologi MARA Shah Alam Selangor, 2005.

[14] Takasago Thermal Engineering Co. Ltd, ‘Operating Strategies of Thermal Energy Storage’, http://www.tte-net.co.jp, accessed at 9.00pm March 13, 2010

[15] Code of Practice on Energy Efficiency and Use of Renewable Energy for Non-Residential Buildings, Department of Standards Malaysia, MS 1525: 2007.

[16] Measurement conversion calculator for metric and imperial systems, http://www.asknumbers.com., accessed at 8.30pm March 13, 2010.

[17] “MECM LEO SEMINAR Advances on Energy Efficiency and Sustainability in Building” Palace of Golden Horses Kuala Lumpur 21-22 January 2003.


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