Experimental Investigation of Solar Hybrid Desiccant Cooling System in Hot and Humid Weather of Malaysia MM SALEHI DEZFOULI, Z HASHIM, MH RUSLAN, B BAKHTYAR, K SOPIAN, A ZAHARIM, S MAT, A RACHMAN, Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia 43600 UKM Bangi, Selangor, MALAYSIA. salehi.solar@yahoo.com; k_sopian@yahoo.com Abstract: - In this study, experimental investigation of solar hybrid solid desiccant by using conventional vapor compression (VAC) as on part of cooling unit was carried out under the humid and hot weather conditions of Malaysia. In this system latent load is removed by the silica-gel solid desiccant wheel, and sensible heat load is removed by heat recovery wheel and cooling coil of VAC. Thermal unit was consisting of 12 m 2 evacuated tube (solar collector) and axillary heater. Supply air mass flow rate and regeneration air mass flow rate for this system were 0.028(kg/s) and 0.120 (kg/s) respectively. The COP, effectiveness of desiccant wheel, and rotary heat recovery wheel of this system are 0.6, 0.50, and 0.80 respectively. Therefore, output qualified supply air with 20.9 o C temperature, and 7.7 (gr/kg) was achieved by using solar hybrid desiccant cooling in hot and humid weather of Malaysia.. Keywords:- desiccant cooling, solar thermal energy, hot and humid, 1 Introduction High electricity consumption costs due to the use of conventional vapor compression systems is one of the concerns of people around the world particularly in hot and humid areas where people need to favorable weather in throughout the year. In the Malaysia, rapid increase of energy consumption due to using conventional aircondition (AC) was considerable in past few years[1]. Therefore, reduce of electricity consumption of is very important in hot and humid weather of Malaysia [2]. Desiccant is one of the solutions to reduce the electricity consumption of conventional air condition. A potential alternative is solar-desiccant because of its ability in the utilization of free solar energy and application of natural sorption dehumidification process[3]. Desiccant cooling system is consisting of three main components such as desiccant unit, heat source unit, and cooling unit[4]. Depending on weather conditions of each region, components of each unit become selected or designed and then hybrid desiccant cooling system can be achieved by combination these unites. The role of desiccant unit is removing latent load thus it attracts moisture of entering air stream by forcing it through a desiccant material (solid or liquid) and then drying the air to cooling unit. Moisture absorption in desiccant material can be driving out by thermal energy from heat source unit. Heat source unit can be solar energy, geothermal, biomass thermal, and natural gas heating. Cooling unit has been playing a critical role in the improvement of desiccant cooling system as handling of sensible load. There are some options to design cooling unit such as evaporative cooling, radiation cooling, the evaporator of a conventional vapor compression, cooling coil, heat recovery, and heat pipe. Pennington in 1955 patented the first desiccant which is commonly known as the ventilation cycle[5]. Scientifics and researchers had many studies on the different methods to develop hybrid desiccant by using renewable energy in hot and humid climates. Niu et al[6] investigated an air-conditioning system combining chilled-ceiling with desiccant cooling to find energy saving potential in hot and humid weathers. They concluded that chilled-ceiling combined with desiccant cooling could save up to 44% of primary energy, in comparison with constant volume all-air system. Lafuenti et al[7] proposed new configuration for solar cooling ISBN: 978-1-61804-139-5 172
system by using solid desiccant wheel as dehumidifier and single stage LiBr-water absorption cycle as chiller for cooling unit. Stabat et al[8] simulated indirect evaporative system and desiccant for one office building in Trappes (close to Paris) to find limits of feasibility and energy consumption of the desiccant cooling system. They found that indirect evaporative cooling can be used in temperate climates that their climate is not too humid. Tsay et al [9] investigated applicability of combining desiccant cooling system with heat pump for an experimental building located in Ciba city, Japan where was hot and humid. They found that the relatively low regeneration temperature provided by exhaust heat of condenser of a heat pump can improve the energy efficiency. Fong et al.[10] carried out the simulation and empirical studies of solar hybrid desiccant used for commercial premised with high latent cooling load in subtropical Hong Kong. It was found that the solar hybrid desiccant had more superior cooling and energy performance than the conventional centrized air-conditioning (AC) system in the mentioned location. Also, Fong et al.[11] developed a simulation model (TRNSYS) of an integrated radiant cooling by absorption refrigeration and desiccant dehumidification for high- tech offices in subtropical climate. Beccali et al.[12] have studied about analysis of the energy and economic performance of desiccant cooling systems equipped with hybrid photovoltaic/thermal (PV/T) collectors for applications in hot and humid climates. They concluded that in most of the considered cases, the configurations with integrated heat pumps demonstrate the best results in terms of primary energy saving. This paper presents a study on experimental investigation of solar hybrid desiccant cooling system combining with conventional vapor compression in hot humid weather of Malaysia. Figure 1: experimental setup of solar desiccant Table 1 shows specification components of solar hybrid desiccant. The desiccant wheel is designed to operate with both a 50% area for reactivation and 50% for process (50/50). The diameter of the wheel is 250 mm and its width is 533 mm. The heat recovery wheel is an aluminum honeycomb structure with 77.8% efficiency. It rotates at 12 rev min-1. Table 1: Specification of solar cooling components 2. Material and Methods 2.1 Experimental setup The solar hybrid desiccant was established near the test room located in Solar Technology Park, UKM Malaysia. Figure 1 shows the experimental setup of system that conducted to the test room by ducts. The test room has a length 3 m, width of 2 m, and height of 3 m. The desiccant consist of three main units: a) solid desiccant wheel which is used silica gel as absorber, b) heat sources which is used evacuated tube collector and auxiliary heater c) and cooling unit which is used a heat recovery wheel, and vapor compression air conditioning system as cooling coil. ISBN: 978-1-61804-139-5 173 The diameter of the regenerator is 700 mm and its width is 700 mm. The electrical consumptions of the motor blower motor and electrical heater are about 150 W, and 1500W respectively. Hot water with 80-120 o C temperature is produced by using 12m 2 solar evacuated tube while electrical heater is installed as auxiliary heater in cloudy time. The installed cooling coil of vapor compression system is 10,000 btu/hr. 2.2 Experimental procedure Figure 2 shows schematic of air process in solar hybrid desiccant. This system has 8
stages to produce air with suitable temperature and humidity (comfort thermal) for test room that operates by following process: (1) entering ambient air to desiccant wheel and moisture absorption by dehumidifier, (2) cooling air by heat recovery wheel, (3) cooling air by cooling coil of vapor compression system, (4) driving favorable air to test room by blower, (5) returning air from test room to heat recovery wheel, (6) heating air by heat exchanger (solar thermal) or heater, (7) removing the air humidity in dehumidifier by using hot air, and then (8) dropping output air to ambient. Q COP Q COOL Re generation m r m ( h [( h h ) + ( h h )] 7 s 6 1 h Where m s (g/s) is mass flow rate of supply air, m r (g/s) is mass flow rate of return air, and h(j/g) is enthalpy of air. The effectiveness of desiccant wheel and rotary heat recovery wheel can be expressed by relations (2), (3) respectively [4]: T T 2 1 ε DW (2) T7 T1 T T 2 3 ε RHW (3) T2 T5 4 ) 3 4 Fig. 2. The schematic of solar hybrid desiccant Experimental test of solar desiccant cooling system was done during three hours (at 12,40 pm to 15,40 pm) in 4th September 2012. ADAM data acquisition has been used to do monitoring and recording temperature, humidity, air flow rate in each stage of air process and also radiation intensity. The ADAM system was consist of three part such as 4018 to monitoring temperature and humidity, 4018-12 to monitor air flow rate and radiation intensity, and 4510 to recording in computer. 2.3 determinations of performance, and effectiveness The Coefficient of Performance (COP) of the solar desiccant can be calculated by rate of heat extracted share on rate of heat regeneration[9]. Rate of heat extracted is cooling capacity of this system that supplied cooling air to room m s ( h 1 h4 ). Rate of heat regeneration is consisting of two parts such as: (a) regeneration heat input by heater and solar thermal m r ( h 7 h6 ) and, (b) cooling energy input by cooling coil m r ( h 3 h4 ).Therefore, the COP of the system is obtained by following relation (1): 3 Discussions and Analysis Results of experimental test as flow chart and psychometric chart are shown in figure 3, and 4 respectively. In the first point ambient air with 33.8 o C temperature and 27.1(gr/kg) specific humidity enters to desiccant wheel, after absorbing humidity by dehumidifier in second point, temperature increases to 41.2 o C, and specific humidity reduces to 7.7 (gr/kg). Fig.3. Flow chart of solar hybrid desiccant cooling system In the next step air enters in heat recovery wheel (first part of cooling unit) so that in the third point temperature reduces to 28.9oC but specific humidity remains unchanged. When air passes through the cooling coil (second part of cooling unit) temperature reduces to 20.9 o C, but as the specific humidity remains constant, so this air as supply air inters to room. In return air process, air with 26 o C and 9.8 (gr/kg) (fifth point) exhausts from room and enters in other side of heat recovery wheel. Temperature of exhaust air from recovery wheel (sixth point) increases to 32 o C, In the next step, air by getting heat from solar thermal (evacuated tube collector) and auxiliary heater (seventh point) has ability to releasing humidity in return side of desiccant ISBN: 978-1-61804-139-5 174
wheel.so, temperature of seventh point increases to 48.8 o C and then exhaust air with 41.7 o C temperature from desiccant wheel driven to environment (eighth point). Specific humidity of fifth, sixth and seventh points remain constant. In this system latent load is removed by the silica-gel solid desiccant wheel, and sensible heat load is removed by heat recovery wheel and cooling coil of VAC. Therefore, output qualified supply air can be achieved by using traditional VAC as one part of cooling unit in solar hybrid desiccant cooling in hot and humid area. Fig. 4. Psychometric chart of solar hybrid desiccant Table 2 shows enthalpy, relative humidity, and dry bulb temperature values of the points of solar hybrid desiccant. Supply air mass flow rate and regeneration air mass flow rate for this system were 0.028(kg/s) and 0.120 (kg/s) respectively. The COP of this system based on these result and equation (1) is about 0.6. The effectiveness of desiccant wheel and rotary heat recovery wheel of this system based on equation (2), and (3) are 0.50, and 0.80 respectively. Figure 5 shows comparison of outdoor temperature and indoor temperature versus time (h) by using solar desiccant. Indoor temperature changes are in the range of 17.6-22.2 o C and Outdoor temperature changes are in the range of 32-36 o C during the three hours experimental test. Therefore, indoor temperature changes have arisen due to of outdoor temperature changes. Fig. 5. Indoor and outdoor Temperature Figure 6 shows comparison of outdoor relative humidity and indoor relative humidity versus time (h) by using solar desiccant. Table 2: Numerical values of the points Fig.6. indoor and outdoor relative humidity During the three hours experimental test indoor relative humidity changes in the range of ISBN: 978-1-61804-139-5 175
46%-56% and outdoor relative humidity changes in the range of 73%- 82%. Therefore, outdoor relative humidity changes are reason of indoor relative humidity changes. 4 Conclusions This paper presents experimental investigation of solar hybrid desiccant by using traditional VAC, without using evaporative cooling in hot and humid weather of Malaysia. Indoor conditions: 20.9 o C, 7.7 gr/kg, by using this system with COP: 0.6 was reached while outdoor conditions was 33.8 o C, 27.1gr/kg. In this system heat recovery wheel, and cooling coil of VAC were used as cooling unit to remove sensible load. Latent heat was removed by the desiccant wheel. The results of this system shows that output qualified supply air can be achieved even without using evaporative cooling by using traditional VAC as one part of cooling unit in solar hybrid solid desiccant cooling in hot and humid area. It was found that solar hybrid solid desiccant cooling system provided considerable energy savings in comparison with conventional vapor compression in hot and humid area. Acknowledgements The authors would like to thank the Solar Energy Research Institute (SERI), University Kebangsaan Malaysia for providing the laboratory facilities and technical support. References [1] B Bakhtyar, K Sopian, A Zaharim, O saadatian, "The effects of Feed in Tariff on Foreign Direct Investment in Malaysia," in Thermal Engineering and Environment, Zlin, 2012 (WSEAS). [2] Rachman, A., et al. Solar air conditioning system using desiccant wheel technology. 2010: World Scientific and Engineering Academy and Society (WSEAS). [3] Enteria, N., et al., Performance of solardesiccant with Silica-Gel (SiO2) and Titanium Dioxide (TiO2) desiccant wheel applied in East Asian climates. Solar energy, 2012. 86(5): p. 1261-1279. [4] Daou, K., R. Wang, and Z. Xia, Desiccant cooling air conditioning: a review. Renewable and Sustainable Energy Reviews, 2006. 10(2): p. 55-77. [5] Davanagere, B., S. Sherif, and D. Goswami, A feasibility study of a solar desiccant air conditioning system Part I: psychrometrics and analysis of the conditioned zone. International journal of energy research, 1999. 23(1): p. 7-21. [6] Niu, J., L. Zhang, and H. Zuo, Energy savings potential of chilled-ceiling combined with desiccant cooling in hot and humid climates. Energy and Buildings, 2002. 34(5): p. 487-495. [7] Lafuenti, I., et al., New Solutions for the Use of Solar Cooling in Hot and Humid Weather Conditions. [8] Stabat, P., S. Ginestet, and D. Marchio. Limits of feasibility & energy consumption of desiccant evaporative cooling in temperate climates. 2003. [9] Tsay, Y.S., et al., Study on the applicability of combining a desiccant with a heat pump in a hot and humid climate. ASHRAE transactions, 2006: p. 189-194. [10] Fong, K., et al., Investigation on solar hybrid desiccant for commercial premises with high latent cooling load in subtropical Hong Kong. Applied Thermal Engineering, 2011. [11] Fong, K., et al., Solar hybrid for high-tech offices in subtropical climate- Radiant cooling by absorption refrigeration and desiccant dehumidification. Energy Conversion and Management, 2011. 52(8-9): p. 2883-2894. [12] Beccali, M., P. Finocchiaro, and B. Nocke, Energy and economic assessment of desiccant s coupled with single glazed air and hybrid PV/thermal solar collectors for applications in hot and humid climate. Solar energy, 2009. 83(10): p. 1828-1846. ISBN: 978-1-61804-139-5 176