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Investigation on solar hybrid cooling system with high latent cooling load.

ABSTRACT

The air conditioning (A/C) system operates to make comfortable circumstances. In Iraq, the air conditioners are the principal cause of high electrical demand. In summer, the outer temperature sometimes exceeds 50 [degrees]C. This significantly effects on the A/C system performance and power consumed. In the present work, the improvement in mechanical and electrical performance of split A/C system is investigated experimentally and analytically. The ambient air temperatures are taken from 35 [degrees]C to 45 [degrees]C in the experimental study. The performance of the conventional and the proposal A/C system split type were compared. The results show that, the using of the solar A/C system had not better performance and energy saving than the conventional one. With the using of the solar system, the cooling capacity, condenser capacity, COP, and COPU at 45 [degrees]C and 57 [degrees]C are decreased respectively. While with the conventional system they have an elevated values if compared with the proposed system.

KEYWORDS: hybrid cooling system, air conditioning, cooling and condenser capacity.

INTRODUCTION

Air Conditioning is the process of varying the properties of air to be more comfortable conditions, typically with the aim of distributing the conditioned air to an occupied space such as a building, house or vehicle to improve thermal comfort and indoor air quality. In common use, an air A/C is a device that decrease or increase the temperature of the conditioned space. The cooling is typically achieved through a refrigeration cycle, but sometimes evaporation or free cooling is used [1]. The split A/C system is usually used for small and medium scale of residential buildings. These systems have the conventional components of the cooling system: compressor, evaporator, condenser, and expansion valve [2]. The refrigeration is defined as any process of heat removal. More specifically, refrigeration is defined as the branch of science that deals with the process of reducing and maintaining the temperature of a space or material below the temperature of the surroundings. In any practical refrigeration system, maintaining low temperature requires the removal of heat from the product at low temperature and discharging it to a higher temperature reservoir [3].

The integrate of solar energy with the air conditioning system in elevated ambient temperature areas provide a new way for increasing the performance and energy consumed for the air conditioning systems. The main advantage of using the solar assisted air conditioning that is simultaneously occur with the summer months. The use of solar assisted air conditioning is significantly reducing the electricity consumption. The operation of the solar assisted air conditioning generate from a fact that the running of these systems are always need to the conventional source of energy. In addition, these systems are economized for power consumed if compared with the conventional air conditioning system, due to the highest energy for driving these systems come from the solar thermal collector. The main operation of the A/C systems is cooling and dehumidification of conditioned space for thermal comfort [4].

Due to the importance of A/C systems, there are many researches done for improving the performance and energy saving of these systems based on solar energy. Zhai et al. 2005 [5] investigate an experimental studies regarding with a solar air collector (SAC) with length of channel 1500 mm and width 500 mm. The experimental results indicate that the optimum inclination angle for the SAC was 45o and 1 m channel length. In addition the theoretical analysis for heat balance equations is agree well with the experimental results. Balghouthi et al. 2005 [6] mentioned that the use of solar power for driving the cooling cycles was very important for minimizing the power consumed and performance enhancement especially with availability of solar energy. In order to achieve the cooling with solar assist energy, the solar energy was used with an absorption chillier that use a lithium bromide solution and water. The system used was simulated with the TRNSYS program in order to select and size the different components of the solar system as; heat exchangers, storage tank, and collectors. Ali et al. 2007 [7] provided a proposed design for A/C system prototype using solar energy for producing a cold or heat feeling. In addition, for studying the performance of the A/C system, the numerical model was implemented. The real meteorological data was used for predicting the performance of the system with, this model. The theoretical model was used to predict the system behavior of various environment conditions.

Desideri et al. 2009 [8] described a different solar cooling technique, and its operation, advantages and limits of these systems. The system studied included an absorption chiller integrated with solar flat plate collectors as first case, while the second submission was the hybrid regeneration plant (thermo solar regeneration). The experimental results were obtained based on existing users and achieve the advantages and disadvantages for suggesting the better solution for the two studied cases. The A/C systems are generally work based vapor compression cycle, so the increasing of electric energy consumes in summer months will be high. The hybrid regeneration and solar cooling plants A/C systems and can minimize the power consumption by take advantage of the maximum solar radiation and cooling demand simultaneity in summer months. Fong et al. 2010 [9] made a comparative study for five solar cooling systems types included; solar absorption refrigeration, solar mechanical compression refrigeration, solar electric compression refrigeration, and solar solid desiccant cooling. The performance criteria includes; coefficient of performance (COP), solar thermal gain, power consumption, and solar fraction. From this study, it found that solar absorption refrigeration and solar electric compression refrigeration had a high energy saving also have a beast performance. La et al. 2011 [10] investigated an experimental and theoretical analysis for solar hybrid air conditioning system using flat plate solar collector array for 90 [m.sup.2]. The performance of the system was testified using TRNSYS simulation studio. The experimental results showed that the cooling capacity, the electric COP, thermal COP improvement was 35.7%, 11.48 and 1.0 respectively. The electric power consumption reduced by 31%.

Bergero and Chiari 2011 [11] showed that the A/C systems can achieve significant energy savings via using of a hybrid system, which a vapor compression inverse cycle has been integrated with the air dehumidification system working with Lithium Chloride LiCl solution. The advantage is that the A/C work at a higher evaporation temperature with the proposed system than the conventional system. The performance of the enhanced system was compared with the conventional system. The results showed that the energy saving was exceed 60% if compared with the base line system. Wrobel et al. 2013 [12] introduced a pilot installation of a geothermal solar and thermal assisted A/C system located in Hamburg, Germany. The combination of a radiant heat exchanger with a desiccant assisted A/C system provides a high efficiency HVAC system. So, this study presented an economic and energy evaluation for a highly efficient HVAC system at different geographical positions. In addition, analyzed the performance of a hybrid A/C system containing of a desiccant wheel and an electrical chiller. The mathematical model calibrated at the open cycle desiccant A/C system in Hamburg. By comparing the total energy demand and the peak demand and of A/C system for the improved conventional system, a significant advantage of the maximum cooling energy is between (28-32) % and the peak heat energy between (30-51) percent of that of the base line system.

Al Ugla et al. 2016 [13] confirmed that 65% of the power consumed in Saudi Arabia caused by Air-conditioning in the building sector and the use of solar energy provide large amount of energy saving. This work compared three types of A/C systems; solar photovoltaic PV vapor compression solar, Lithium bromide LiBr H2O absorption, and conventional vapor compression. The results appear that the solar absorption system was more economically than a solar PV vapor compression system. The possibility of both solar-powered systems improves as the size of the commercial building and the electricity rate increase. The results show that the COP was improve via increasing the evaporator operating temperature and decreasing the condenser operating temperature. The results appear that the COP becomes 0.7644 instead of 0.7 after improving the performance using solar power.

The present work aims to enhance the performance of split A/C system unit and improving the energy saving at elevated ambient temperature. Experimental and mathematical investigations had been done to achieve this aim. The A/C system has been integrated with the evacuated tube solar collector for executing a maximum performance improvement and energy saving. The performance criteria of cooling capacity, condenser capacity, compressor power consumption, COP, and COPU have been enhanced. Finally, a comparative study has been done between the performance of the conventional and proposal split A/C system.

Experimental Work:

The experimental setup, shown in Fig.1, consist of: 1-split type air-condition system model [SK -1.5 W]. It's built with supply and return pipes between the indoor and outdoor units. The physical data of A/C component is given in Table 1. The split unit is provided with a rotary compressor which is manufactured by Mitsubishi company with a rated input power of (600-860 W), cooling capacity (1200 BTU/W h).

[FIGURE 1 OMITTED]

The condenser coil is designed from a flat aluminum fins bounded to two rows round copper tubes with staggered arrangement. The expansion device of the A/C system used is a capillary tube installed in the outdoor unit. Also, the DX evaporator is made from copper tubes with aluminum fins. The entire wall around the evaporator is insulated with arm flex material. 2- the test room, it's diminutions is (3x4.5x3) m .The test room contain the indoor unit of test rig and measuring devise such as power meter, turbine flow meter, anemometer, humidity meter, pressure gages temperature sensors which connected with data logger and laptop as shown in Fig.2.

[FIGURE 2 OMITTED]

The high pressure gauge has a double continuous scale. It is usually connected to the high pressure side of the refrigeration cycle. The location of pressure gages which used are: two high pressure gages before and after the air cooled condenser, two low pressure gages before and after the evaporator, two high pressure gages before and after the storage tank, one after the compressor and one after the capillary tube. The low pressure gauge was connected to the low pressure side of the cycle. The pressure gages used in the experimental test are shown in Fig. 3.

[FIGURE 3 OMITTED]

Storage tank, connection pipe, valves and collector were added to the conventional refrigeration cycle to minimize the compressor power consumption and in order to enhance the coefficient of performance of refrigeration cycle. Three valves were used to run the refrigeration cycle with or without the solar energy effect. The specification of these parts is listed in table 1.

Results:

The effect of combination between the direct expansion air conditioner and a vacuum solar collector that is installed after the compressor were considered experimentally in the present work. The effect of ambient temperature and condenser row reduction on the system performance also considered. An A/C unit is installed after a lot of preparations to become suitable for the experimental work. In order to compute the Refrigeration capacity, the CoolPack package was used.

a. Effect of ambient temperature on refrigeration system with vacuum solar collector:

The outdoor ambient temperature is very important dominant parameter that affects the refrigeration systems. Fig.4 show the relation between compressor power consumption, work and losses with ambient air temperature, the losses be find is higher which is approach halve the work require. Fig.5 show the condenser capacity reduce with the ambient temperature rise and there is a different between the refrigerant condenser capacity and air condenser capacity due to the effectiveness of coil. Fig.6 show the evaporator capacity reduce with the ambient temperature rise and also there is a different between the refrigerant evaporator capacity and air evaporator capacity due to the effectiveness of coil. The reduction in the capacity of the refrigerant and the air is slightly little while the reduction in the capacity for the condenser be sharply, the resin in the condenser is working in touch with the outside. Fig.7 show the coefficient of performance of Carnot and actual cycle reduce as the ambient air temperature rise. The coefficient of performance of Carnot is higher than the coefficient of performance of actual due to the losses. Fig.8 show as ambient air temperature rise, the energy efficiency ratio and seasonal energy efficiency ratio reduce, seasonal energy efficiency ratio working between (8.6-10.7) which the number used by Europe and United States at (1990-2000), the energy efficiency ratio lower ten which is bad. Fig.9 and Fig.10 show the relation between the overall heat transfer coefficient by L.M.T.D and NTU method with ambient air temperature. The value of overall heat transfer coefficient by L.M.T.D method is higher, the rezone of different between two methods is there assumption, where L.M.T.D keep constant young. Fig.11 show the effectiveness of condenser and evaporator with ambient temperature. The effectiveness of condenser is higher than effectiveness of evaporator can related to the type of manufacture. Fig.12 show the performance of refrigeration system with vacuum solar collector.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

[FIGURE 11 OMITTED]

[FIGURE 12 OMITTED]

b. Comparison between the refrigeration system without vacuum solar collector and with vacuum solar collector:

Figures from (13-19) show the performance of refrigeration system with and without vacuum solar collector at different ambient temperature (35 oC, 40 oC and 45 oC). The experimental results as shown in figures (13) and (14) show that the evaporator capacity and condenser capacity with vacuum solar collector is lower than the evaporator capacity and condenser capacity without solar collector. Figure (15) show that the power consumption without using vacuum solar collector is lower than power consumption when using vacuum solar collector this cause the lower coefficient of performance for refrigeration system with using vacuum solar collector as shown in figure (16). Figure (17) show the relation between the power losses of refrigeration system with and without using vacuum solar collector. Figure (18) and figure (19) show that lower energy efficiency ratio and lower seasonal energy efficiency ratio for refrigeration system with using vacuum solar collector. The rezone for above results may related to the bad design of manufacture for matching between vacuum solar collector and original system or this type of system not compatible with Iraqi climate. May be this type of system is working best at winter season on heating mode because an intensity of solar radiation in winter season is more than in summer season. Figure 20 show the performance of refrigeration system without vacuum solar collector.

[FIGURE 13 OMITTED]

[FIGURE 14 OMITTED]

[FIGURE 15 OMITTED]

[FIGURE 16 OMITTED]

[FIGURE 17 OMITTED]

[FIGURE 18 OMITTED]

[FIGURE 19 OMITTED]

[FIGURE 20 OMITTED]

c. Effect of condenser row reduction on refrigeration system with vacuum solar collector:

The reduction of condenser row cusses lower heat transfer area between refrigeration side and air side which causes lower condenser capacity and lower evaporator capacity and lower work as shown in Table (2), but the coefficient of performance and energy efficiency ratio increase by (6.95% and 22.22%) respectively. The result show, there was un-matching in design between the parts of refrigeration system from manufacture. Fig. 21 show the performance of refrigeration system without vacuum solar collector.

[FIGURE 21 OMITTED]

Conclusions:

The present work investigates comparative study between conventional A/C system and the solar A/C system. From the results obtained the concluding remark can be summarized as shown below:

1. At elevated ambient air temperatures, the conventional system gives more performance improvement than solar system.

2. The condenser capacity with the conventional system is higher than the solar system.

3. The cooling capacity, condenser capacity for the conventional system is high than the solar system.

4. Fault detection with the proposed SCS provides additional reliability, stability, safe operation, protection and long life for the A/C system parts.

5. This proposed solar system is not compatible, economic, and efficient with the weather condition of IRAQ.

REFERENCES

[1] Althouse, D., C.H. Turnquist and Alfred F. Bracciano, 2004. Modern Refrigeration and Air Conditioning, [18.sup.th] Edition, the Goodheart-Willcox Company, Inc., Tinley Park, Illinois.

[2] Ibrahim Dincer, 2000. Refrigeration Systems and Application, John Wiley & Sons Ltd.

[3] Dossat, J.R. and J.T. Horan, 2005. "Principles of refrigeration" fifth edition, Wideband Communication Systems, NJ: Prentice Hall PTR.

[4] Solar Thermal Collectors in Polymeric Materials, 2013. "A Novel Approach Towards Higher Operating Temperatures", Springer, Retrieved.

[5] Zhai, X.Q., Y.J. Dai, R.Z. Wang, 2005. "Experimental investigation on air heating and natural ventilation of a solar air collector", Energy and Buildings, 37: 373-381.

[6] Moncef Balghouthi, Mohamed Hachemi Chahbani, Amenallah Guizani, 2005. " Solar Powered air conditioning as a solution to reduce environmental pollution in Tunisia", Desalination Journal, 185: 105-110.

[7] Chaouki Ali, Habib Ben Bacha, Mounir Baccar, Aref Y. Maalej, 2007. "Dynamic modelling and simulation of a new air conditioning prototype by solar energy", Renewable Energy, 32: 200-215.

[8] Umberto Desideri, Stefania Proietti, Paolo Sdringola, 2009." Solar-powered cooling systems: Technical and economic analysis on industrial refrigeration and air-conditioning applications," Applied Energy, 86: 1376-1386.

[9] Fong, K.F., T.T. Chow, C.K. Lee, Z. Lin, L.S. Chan, 2010. "Comparative study of different solar cooling systems for buildings in subtropical city," Solar Energy, 84: 227-244.

[10] Dong La, Yanjun Dai, Yong Li, Tianshu Ge, Ruzhu Wang, 2011. "Case study and theoretical analysis of a solar driven two-stage rotary desiccant cooling system assisted by vapor compression air-conditioning", Solar Energy, 85: 2997-3009.

[11] Stefano Bergero, Anna Chiari, 2011. "On the performances of a hybrid air-conditioning system in different climatic Conditions", Energy, 36: 5261-5273.

[12] Jan Wrobel, Pablo Sanabria Walter, Gerhard Schmitz, 2013. " Performance of a solar assisted air conditioning system at different locations",Solar Energy, 92: 69-83.

[13] Al-Ugla, A.A., M.A.I El-Shaarawi, S.A.M. Said, A.M. Al-Qutub, 2016. "Techno-economic analysis of solar-assisted air-conditioning systems for commercial buildings in Saudi Arabia", Renewable and Sustainable Energy Reviews, 54: 1301-1310.

(1) Hasanen Mohammad Hussain, (2) Laith Jaafer Habeeb, (3) Orhan Jalal Abbas

(1,2) University of Technology, Mechanical Engineering Department

(3) Minister of Construction and Housing and Public Municipalities

Address For Correspondence:

Hasanen Mohammad Hussain, University of Technology, Mechanical Engineering Department

Received 8 November 2016; Accepted 28 March 2017; Available online 15 April 2017
Table 1: Specification of storage tank, coil, collector, connection
pipes and valves.

Storage tank
Outside diameter                   (cm)  20
Outside length                     (cm)  80
The coil inside the tank
Shape                                    Spiral
Length                             (cm)  50
cycle diameter                     (cm)  10
Number of cycle                          30 cycle
Collector
Number of tubes                          40
Inside diameter                    (cm)   3.7
Outside diameter                   (cm)   4.7
Clearance between tubes            (mm)   5
Length of tube                     (cm)  50
Length of tube exhibit to the sun  (cm)  43

   Connection pipes
   Location                            Length (cm)  Diameter (in)

   Pipe from compressor to tank        80           3/8
   Pipe from tank to condenser         80           3/8
   Pipe from capillary to evaporator    3.4         1/4
   Pipe from evaporator to compressor   3.4         1/2
   Valves
   Number of valves                                 3

Table 2: Effect of condenser row reduction on refrigeration system with
vacuum solar collector at ambient temperature 40 [degrees]C.

[T.sub.amb]    parameters  Solar system  Solar system with one
                                         row

               Qe (kW)     3.43          2.35
               Qc (kW)     4.23          2.86
40 [degrees]C  Power (kW)  1.3           1.15
               COP         4.28          4.6
               EER         7             9

[T.sub.amb]    Present of variation
               %

               -45.95
               -47.90
40 [degrees]C  -13.04
                +6.95
               +22.22
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Author:Hussain, Hasanen Mohammad; Habeeb, Laith Jaafer; Abbas, Orhan Jalal
Publication:Advances in Environmental Biology
Article Type:Report
Date:Apr 1, 2017
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