Some Considerations

• The most common refrigerants, CCl2F2, Freon-12 (CFCs). Detrimental to the ozone (O3) layer, thus leading to the penetration of more ultraviolet radiation into the earth atmosphere. Solution: replaced by Refrigerant 134a, CF2FCF3.

• In order to produce reasonable heat transfer, the temperature difference should be as high as possible ( > 10°C). Therefore, in the evaporator the temperature should be as low as possible. It can be achieved by reducing the pressure. Problem: too low of a pressure (below atmospheric pressure) can cause air leakage into the system. Ex: at atmospheric pressure, refrigerant 134 has a saturation temp. of -26.43°C.

• Heat pumps and air conditioners have the same mechanical components. Therefore, a combined system to meet both heating and cooling requirements. Just reverse the cycle such that the evaporator becomes the condenser, and the condenser becomes evaporator. (Perfect in areas where large cooling load is needed during summer and relatively small heating load during winter)

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