Solar-Powered Cooling Systems

1. Solar-Powered Cooling Systems Manuel Verduzco Me 209

2. Introduction • Demand for air conditioning systems due to the demand of higher comfort conditions • Increase in electric power demand in the summer which sometimes leads to black outs • Cost and ecofriendly system is needed Solar Absorption Cooling System (SACS) compared to most traditional Vapor Compression Systems (VCS)

3. Background Vapor Compression Systems • consume mechanical energy to produce cold air • uses a mechanical compressor to create the pressure differences necessary to circulate the refrigerant • These systems operate on a vapor-compression cycle (VCC) that consists of a compressor, condenser, throttling value, and an evaporator.

4. Background Compressor • Work drives the compressor. The working fluid @sat vapor goes into the compressor at low pressure, and then the compressor compresses it to a hot, high pressure slightly superheated vapor. The process is isentropic. Condenser • Condenses to a saturated liquid at the same pressure. Heat loss of the condensation may be to the surrounding or by the use of a cooling tower which in turn cools the refrigerant. Throttling valve • The throttling valve takes the sat. liquid and expanded adiabatically to a low pressure where it becomes a sat. mixture. It is a restricting device that causes significant pressure drop in the fluid. Enthalpy is the same. Evaporator • The evaporator takes the cool sat. mixture at low pressure and uses the heat from the surrounding to produce heat transfer that evaporates the liquid portion of the saturated mixture, thus providing cooling to the surrounding.

5. background Vapor absorption system (absorption chillers) • use heat source to produce the cooling effect. • Absorption chillers use the heat source to create pressure differences to circulate the refrigerant. Thus, for that reason absorption chillers are very attractive with a given type of heat source like solar heat. • similar in the fact that they both have a throttling valve, condenser, and evaporator. • some key differences are that VAS requires cooling tower, a pump and that the generator and absorber replaces the compressor.

6. Background • Absorber draws in the refrigerant vapor to mix with the absorbent. As the vapor refrigerant is absorbed, it condenses to liquid mixture. • The absorbent solution is then pumped to the generator, where heat is used to vaporize and separate the refrigerant and the absorber solution. • The refrigerant vapor goes to the condenser and the absorbent travels back down to the absorber. • water as refrigerant and lithium bromide salt as absorbent. • Ammonia for refrigerant

7. background Occasions when a Vapor Absorption System is Preferred • Absorption chillers greatest advantage is their ability to use waste heat that would otherwise be lost. • in facilities that have a high electrical supply charges. Can be used as part of a peak and money saving strategy. • In facilities where the electrical supply is not robust,unreliableor unavailable.. • If not provided with solar panels VAS can be combined with fuel oil/gas. So VAS are preferred in occasions where the cost of electricity compared to fuel oil/gas is higher. • VAS use refrigerants which is more ecofriendly than the refrigerants used for VCS.

8. background Vapor absorption system is incorporated with solar collectors to create the most common solar cooling system called the solar absorption cooling systems (SACS).

9. Background Solar Collectors • evacuated tubular • Combined with VAS to produce the cooling effect, but also can be combined with the boiler to produce a heating effect. • Flat Plate collectors • Parabolic Trough Collectors

10. Background Evacuated tube Collectors

11. First Case Hotel in Santa Maria degli Angeli(Italy), currently has VCS for AC and a boiler for heating water. • The VCS has an electric power of about 25kW and a cooling power of 54kW that uses R22 refrigerant and produces cold water at 6 degrees Celsius. The warm water circuit powered by a natural gas boiler rated out of 216kW that produces 90 degrees Celsius. • A hybrid trigenerationplant (HTP) is an ideal plant to integrate with the existing plant. The economic indicator, NPV, at an effective interest rate of 5% the HTP has a payback period of investment evaluated in 12 years and a reduction of 40% in emissions.

12. Second case Five-floor student hospital in Alexandria, Egypt analyze the general cost associated with a single-and double-effect vapor absorption (two generators) and vapor compression air-conditioning system. • Needs air-conditioning system of a 250 TOR cooling load. • The temperature varieties per room or department. • A Life Cycle Cost (LCC) was used to compare the three systems. The LCC includes all cost factors (Initial cost, operating cost, maintenance, replacement, and estimated energy use) and is evaluated over the complete life of the system. • Using the present worth comparison method the total cost of the VCS is 11% lower than the single-effect VAS. The double-effect VAC is 45% less than the single –effect, and the 30% less than the VCS. • Using the equivalent annual comparison method the double effect VAS is 45% and 37% less than the single –effect VAS and VCS respectively.

13. Conclusion • The initial investment costs for the construction of the SC are much higher than those of tradition vapor compression refrigerators. • These systems in the long run are more ecofriendly, money saving, and energy saving. • Sometimes even though SACS are usually more cost efficient compared to the traditional Vapor compression System, however, it is not always the case