Study of Performance Improvement of Air Conditioning using Various Heat Recovery Techniques

Transcription

1 Study of Performance Improvement of Air Conditioning using Various Heat Recovery Techniques Poonpong Swatdepan *, Umphisak Teeboonma and Chawalit Thinvongpituk Department of Mechanical Engineering, Faculty of Engineering, Ubon Ratchathani University, Thailand Abstract: The objective of this paper was to comparatively study the performance of air conditioning unit between the conventional vapor compression (1), the conventional vapour compression with water tank (2), and the conventional vapor compression with liquid intercooler (3) for decreasing the refrigerant temperature, which is used to reject heat before flow in a condenser and decreasing the refrigerant temperature before flow in an evaporator. The criteria for evaluating the performance of air conditioning unit were energy consumption, coefficient of performance, and energy efficiency ratio. From experimental results, it was found that the conventional vapor compression system 2 and 3 improved the coefficient of performance (COP) and energy efficiency ratio (EER). It is worth to mention that coefficient of performance and energy efficiency ratio of system 2are approximately 18% higher than that of system 1. Keywords: Air Conditioning, Energy Saving 1. INTRODUCTION Ambient temperature (average of o C) and humidity (70-80%) of Thailand are rather high, which affect the living and working efficiency. Therefore, air conditioning in office is necessary. From previous researches, it revealed that amount of energy consumption of air conditioning in building is approximately 50-70% of the total energy consumption. Consequently, energy saving technique for air conditioning system should be examined. Liquid-suction heat exchangers are commonly installed in refrigeration systems in order to increasing the performance of system. Domanski et al. [1] investigated the effect of LLSL-HX on system performance by taking liquid refrigerant from condenser to exchange heat with vapor refrigerant from evaporator. The authors reported that coefficient of performance was increased after installed LLSL-HX. Zhaolin et al. [2] used the PCMs (Phase change materials) to receive the sensible and latent heat form air condition system for washing and bathing processes. It was found that the energy consumption of compressor and heat transfer increased with increasing condenser temperature. Hu and Huang [3] evaluated the performance of the system by using water cooling. The system comprised of a rotary compressor, a water-cooled condenser, an evaporator, a capillary tube, an accumulator, and a separator. It was revealed that the coefficient of performance increased from 2.96 to The objective of this work is to comparatively study the performance of air conditioning systems. The criteria for investigating the performance are energy consumption, coefficient of performance, and energy efficiency ratio. 2. METHODOLOGY This research compared the performances of three air conditioning systems as the followings: 1. Conventional system comprised of a compressor, a condenser, an expansion valve, and an evaporator. The cycle is shown in Fig Conventional system with water tank. This system is similar to system one but water tank is installed. Water tank is made of steel with 0.02 m 3 dimension. Inside is fitted with the 0.93 mm. copper tubes in order to increase surface area. The system is shown in Fig Conventional system with liquid intercooler. This system is also similar to system one but the liquid intercooler is added. The equipment is made of cupper steel with 0.35 m diameter. The system is shown in Fig. 3. Evaporator Evaporator Expansion valve Condenser Expansion valve Water tank Condenser Compressor Compressor Fig. 1 Conventional system Fig. 2 Conventional system with water tank Corresponding author: luechai36@hotmail.com 1

2 Fig. 3 Conventional system with intercooler Fig. 4 Schematic diagram of the air conditioning 2.1 The experimental rig The experimental apparatus consists of a one-ton vapor compression air conditioning. It was installed on the movable rail as shown in Fig. 4. The air temperature was controlled before entering a condenser and an evaporator. In the experiment, entering air temperature was controlled at o C. The system was operated continuously. The temperatures were collected by type-k thermocouples, which are connected to a data logger with the accuracy of ±0.1 o C. In addition, air velocity was also measured by using a hot wire anemometer with the accuracy of ±2%. Finally, electrical energy supplied to system was measured by clamp-on meter with the accuracy of ±0.5%. 2.2 The energy analysis The parameters used for investigating the performance of each system can be computed as the following equations. 1. Heat transfer of condenser is computed by equation (1) where, m c h = air flow rate, kg/s = enthalpy, kj/kg Q = m ( h h ) (1) cond. c ci co 2. Heat transfer at evaporator can be calculated as Q = m ( h h ) (2) evap. e ei eo 3. Coefficient of performance (COP) where, COP = Coefficient of performance Q evap. = heat absorbed at evaporator, kw W comp. = input power, kw Q evap. COP = (3) Wcomp. 4. Energy efficiency ratio (EER) Cooling output EER = (4) Power input EER Cooling out Input power = energy efficiency ratio, Btu/hr/W = heat is absorbed, Btu/hr = input power of compressor, W 3. RESULTS AND DISCUSSIONS To comparative study the system performance, each system was operated at the same condition. The experimental results can be presented as the followings. 2

3 system 1 system 2 system Fig. 5 Refrigerant temperatures at inlet compressors Figure 5 indicates the refrigerant temperature at inlet compressors. It was obviously seen from Fig. 5 that compressor inlet temperature of system 3 is the highest (13 o C). This is due to working fluid absorbs heat load from two heat sources such as evaporator and intercooler. As a result of intercooler, heat load of system is higher than that of other systems system 1 system 2 system Fig. 6 Refrigerant temperatures at outlet compressors Figure 6 indicates the refrigerant temperature at outlet compressors. It was also found that outlet temperature of compressor for system 3 is the highest. This is due to the effect of heat load as discussed earlier in Fig.5. Furthermore, it was seen that outlet temperature of compressor for system 2 is the lowest (56 o C). It can be explained by the fact that heat load rejected at condenser is high due to the effect of water tank. It should be emphasized here that system 2 has heat exchangers such as a condenser and water tank. 3

4 70 W ater tem p.in w ater tank Refri.tem p.in w ater tank Refri.temp.out water tank Fig. 7 Water temperature in the water accumulator Figure 7 shows the temperature of water in the water tank. This system the working fluid rejected heat at a water tank and a condenser. At the first stage, energy of refrigerant is absorbed by water filled in a tank. Consequently, water temperature is increased from o C to 40 o C within 120 min. In the experiment, water in a tank was removed when water temperature was 40 o C. Subsequently, fresh water was filled for replacing hot water and then the water was heated up again as shown in Fig Fig. 8 Refrigerant temperature at intercooler Figure 8 shows inlet and outlet temperature of refrigerants at intercooler equipment, especially for inlet evaporator part. It can be seen from Fig.8 that outlet temperature of refrigerant is 0.5 o C lower than inlet refrigerant temperature. This is due to the fact that refrigerant of this part rejects heat at intercooler. The heat rejected at this equipment is absorbed by another part of refrigerant which results in high inlet temperature of compressor for system 3 as discussed in Fig.5. 4

5 Power,kW Power sys1 Power sys2 Power sys Fig. 9 The power input compressor Figure.9 indicates the amount of compressor input power. It was found that input power of compressor for system 1, 2, and 3 are 0.98 kw, 0.97 kw, and 0.96 kw, respectively. 3 COP System 1 COP System 2 COP System 3 COP Fig. 10 COP of the air-conditioning system Figure 10 presents the coefficient of performance of each air-conditioning system. It is clearly seen that the COP of system 2 is the highest (2.9) whereas that of system 1 is the lowest (2.4). 5

6 EER System 1 EER System 2 EER System 3 EER,Btu/hr/W Fig. 11 EER of the air-conditioning system Figure 11 illustrates the energy efficiency ratio of each air-conditioning system. The EER of system 1, 2, and 3 are 7.8, 9.8, and 8.9, respectively. 4. CONCLUSION From the experimental results, it can be concluded that system 2 provides the best energy efficiency. It yields COP and EER of 2.9 and 9.8, respectively. Additionally, it should be noted that COP and EER of system 2 are approximately 18% higher than that of system REFERENCES [1] Domanski, PA, Didion DA, and Doyle JP. (1994) Evaluation of suction-line/liquid-line heat exchange in the refrigeration cycle, Rev Int Froid, 7, (7), pp [2] Zhaolin Gu, Hongjuan Liu, and Yun Li. (2004) Thermal energy recovery of air conditioning system heat recovery system calculation and phase change materials development, Applied Thermal Engineering, 24, pp [3] Hu,S.S. and Huang,B.J.(2005) Study of a high efficiency residential split water-cooled air conditioner, Applied Thermal Engineering, 25, pp