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Title : The study paper on solar absorption air-conditioning systems
Authors :Mallinath G Desai [1] ;Phaniraja patel G B[2];
University: Government engineering college Raichur
ISSN :
Volume: 01 Issue: 01
Publication Year: June 2026
ABSTRACT
An environmental control system utilizing solar energy would generally be more cost-effective if it were used to provide both heating and cooling requirements in the building it serves. Various solar powered heating systems have been tested extensively, but solar powered air-conditioners have received little more than short-term demonstration attention. Solar powered absorption cooling systems can serve both heating and cooling requirements in the building it serves. Many researchers have studied the solar absorption air conditioning system in order to make it economically and technically viable. A number of attempts have been made by researchers to improve the performance of the solar applied air-conditioning subsystems. . This study paper will help many researchers working in this area and provide them with fundamental knowledge on absorption systems, and a detailed review on the past efforts in the field of solar absorption cooling systems with the absorption pair of lithium-bromide and water.
Keywords: Absorption chiller; Air-conditioning; Lithium bromide and water; Solar energy etc
Introduction
Air-conditioning is a particularly attractive application for solar energy because of the near coincidence of peak cooling loads with the available solar power. Many arrangements or cycles are possible. solar collectors can be used to provide energy for absorption cooling, desiccant cooling, Although a large potential market exists for this technology, existing solar cooling systems are not competitive with electricity-driven or gas-fired air- conditioning systems because of their high first costs. Lowering the cost of components and improving their performance could reduce the cost of solar cooling systems. Improvements such as reduced collector area, because of improved system performance, and reduced collector cost will lower the cost of solar components. The performance coefficient of an absorption air-conditioner, defined as the ratio of the heat transfer rate into the evaporator to the heat transfer rate into the generator, can be calculated as a function of the temperatures identified previously. Solar energy is one of the most available forms of energy on the Earth’s surface, besides; it is very promising and generous. The earth’s surface receives a daily solar dose of 10E+8 KW-hr, which is equivalent to 500 000 billion oil barrels that is one thousand times any oil reserve known to man. The solar energy is collector area dependent, and is a diluted form of energy and is available for only a fraction of the day. Also, its availability depends on several factors such as latitude and sky clearness. At the same time, its system requires high initial cost. But on the other hand, it has some attractive features such as its system requiring minimum maintenance and operation cost, and it does not have negative effects on the environment. Another important feature of solar energy is its ability to satisfy rural areas where conventional energy systems might be not suitable or uneconomical.
Literature survey
Charters and Chen [1] had made a comparison study on air-cooled and water-cooled systems. In January 1998, a solar powered two-stage absorption air-conditioning system was installed in China [2].The system has a cooling power of 100 kW, with collector areas of 500 m2. The nominal generating temperature of the chiller is about 65-750C, and the COP of the chiller is greater than 0.4. This kind of machine was originally suggested by Tanaka, it was first installed at a new building of the Energy Engineering Department of Oita University, Kyushu [3]. After successful operation for a two-year test period, the solar air-conditioning system was operated with steam as the auxiliary fuel. The identical single-double effect absorption chiller was also operated at the Kabe Office Building of the Chugoku Electric Company in Hiroshima.
This is where solar air conditioning comes in: The summer sun, which heats up offices, also delivers the energy to cool them. The thermal use of solar energy offers itself: Days that have the greatest need for cooling are also the very same days that offer the maximum possible solar energy gain.
The demand for air conditioning in offices, hotels, laboratories or public buildings such as museums is considerable. This is true not only in southern Europe, but also in Germany and middle Europe. Under adequate conditions, solar and solar-assisted air conditioning systems can be reasonable alternatives to conventional air conditioning systems. This Solar-Report will briefly inform you over the possibilities and technology of solar air conditioning and will also cover economic aspects.
Methods
1) Single effect solar absorption air-conditioning system.
2) Double-effect solar absorption air-conditioning system
Single effect solar absorption airconditioning system.
To begin with, the solar energy is gained through the collector and is accumulated in the storage tank. Then, the hot water in the storage tank is supplied to the generator to boil of water vapor from a solution of lithium bromide and water. The water vapor is cooled down in the condenser and then passed to the evaporator where it again is evaporated at low pressure, thereby providing cooling to the required space. Meanwhile, the strong solution leaving the generator to the absorber passes through a heat exchanger in order to preheat the weak solution entering the generator. In the absorber, the strong solution absorbs the water vapor leaving the evaporator. Cooling water from the cooling tower removes the heat by mixing and condensation. Since the temperature of the absorber has a higher influence on the efficiency of the system than the condensing temperature, the heat-rejection (cooling water) fluid, is allowed to flow through the absorber first and then to the condenser [5]. An auxiliary energy source is provided, so that the hot water is supplied to the generator when solar energy is not sufficient to heat the water to the required temperature level needed by the generator.
Graph1.1single effect absorption air conditioning system
The main process taking place in the chiller is as follows (as shown in Figure 1.2).
• Line 1-7: The weak solution from the absorber at point 1 is pumped through the heat exchanger to the generator; point 7 indicates the properties of the solution at the outlet of the heat exchanger. During the process 1-7, the concentration of the weak solution is held constant.
• Line 7-2-3: Process 7-2 shows the sensible heating of the weak solution in the generator, and 2-3 indicates the boiling of water vapour from the solution at the constant condensing pressure Pc (although the boiling pressure is a little higher than the condensing pressure, the difference is negligible). During this process, the weak solution becomes a strong solution.
• Line 3-8: Symbolizes the strong solution passing to the absorber through the heat exchanger, in which it preheats the weak solution flowing from the absorber to the generator. During this process, the concentration of the strong solution is constant.
• Line 8-4-1: Indicates the idealized process of absorption of water vapour from the evaporator by the strong solution in the absorber.
• Line 2-5: Denotes the condensation of water vapour in the condenser by the cooling water from the cooling tower, at constant condensing pressure Pc.
• Line 5-6: Shows the flow of condensed water from the condenser to the evaporator.
• Line 6-1: Indicates the evaporation of the water in the evaporator due to the prevailing low pressure Pe. Also, the water absorbs the heat from the space to be cooled. The water vapour from the evaporator is, in turn, absorbed by the strong solution in the absorber, thus completing the cycle of refrigeration.
Double-effect solar absorption air-conditioning system
The high-pressure generator for steam is independently located from the low-pressure generator for solar and hot water vapor from the high-pressure generator before being condensed. A high-pressure generator gives a primary effect and alow-pressure generator a secondary effect, thus being called a double effect. Therefore, a double effect cycle requires lower heat input to produce the same cooling effect, when compared to a single effect system. Therefore, a double effect system results in higher COP
Fig. 1.2 shows the fowchart of the two-stage absorption chiller. The cycle is divided into high-pressure stage and low-pressure stage. Diluted LiBr solution in the high-pressure generator is heated by hot water. Generated water vapor is condensed in the condenser. The condensed water flows into the evaporator (low-pressure stage) to be evaporated, producing the refrigerating effect. A concentrated solution from the high-pressure generator enters into the high-pressure absorber and absorbs water vapor generated from the low-pressure generator, thus changing back to a diluted solution. This solution is then pumped back to the high-pressure generator, completing a high-pressure cycle. The concentrated solution in the low-pressure generator goes down into the low-pressure absorber and absorbs water vapor from the evaporator. The diluted solution from the low-pressure absorber is then pumped back to the low-pressure generator, completing a low-pressure cycle. Thus, refrigerant water is made in the high-pressure stage and the absorbent-concentrated solution is made in the low-pressure stage. So, through the high-pressure absorption process, the generation process in the low-pressure generator occurs under a lower pressure, completing a full refrigeration cycle.
Comparison of single and two stage solar absorption air-conditioning system
Single stage Two stage
1) capital cost of the system is more 1) capital cost is less compare to single stage
2) It have only one common generator 2) It consist of low pressure and high pressure generator
3)It consist of single heat exchanger 3) it consist of primary and secondary heat exchanger
4) Crystallization occurs 4)Crystallization does not occurs
Advantages of solar absorption air-conditioning system
1) Easy installation, making operation time less consuming.
2) Solar Air-Conditioning is environment friendly.
3) Applicable in most climates
4) Much cheaper than photovoltaic solar conventional air conditioners
5) the main component of air-conditioning system assisted by solar energy does not require the use of compressors or refrigerants harmful to the environment
6) Reduce electricity bills by using Solar Energy to run Air Conditioners, refrigerators and Freezers
7) Do not require highly qualified person to maintain the system.
8) Simple Design
9) Low maintenance cost
10) During Non-Sunny days LPG can be used as backup energy source.
Disadvantages of solar absorption air-conditioning system
1) Currently only available for commercial buildings
2) Initial cost is high.
Recommendations for future research work
A solar powered absorption air-conditioning system is a complex, dynamic system and it is difficult to predict with any certainty the annual energy saving, and therefore, the return on investment. This uncertainty in system evaluation is a further obstacle to the wider application of solar cooling. In order to improve the system design of a solar powered absorption air-conditioning system, a parametric study must be carried out to investigate the influence of key parameters on the overall system performance. If experiments were used to perform the parametric study, effects of one key parameter on the overall system performance would normally require several cooling seasons and hence, years to establish a conclusion. Also, it is extremely difficult to keep the performance of the system components to be constant over entire experimental period as the components deteriorate with time. Therefore, in order to avoid extremely difficult and expensive experimentation, researchers can develop and validate a robust dynamic model of the solar powered absorption air- conditioning system and simulation can be done to study the system. This will help to perform the parametric study on the model rather then the physical system itself.
Conclusion
Solar absorption air-conditioning has the advantage of both the supply of the sunshine and the need for refrigeration reach maximum levels in the same season. Although solar powered air-conditioning systems are readily available in commercial sizes, existing solar cooling systems are not competitive with conventional electricity-driven or gas-fired air-conditioning systems because of their high first cost. Several technical problems associated with the design and development of absorption chillers based on continuous cycles have been successively resolved, and new trends gradually developed towards the redesign of the chiller generator for operation at temperatures lower than 1008C. There are many other achievements carried out by researchers, nevertheless, further improvements should be made tothe solar powered air-conditioning systems in order to compete with the conventional air-conditioning systems.
REFERENCES
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