Air Conditioning Standard Refrigeration Systems
Air-standard refrigeration cycles, also known as a reverse Brayton cycle. In these cooling is carried out by non-condensing gas (e.g. air cycle, but not vapour refrigerant cycle. While the cooling load on kg of refrigerant circulates in a vapor-compression cycle is equal to a large part of the enthalpy of vaporization, in the air cycle it is only the product of increase of gas temperature in the low side of the heat exchanger and the specific heat of the gas. Therefore, a large cooling load requires a large mass on velocity. To the equipment of a smaller size, the complete unit can be under pressure, which requires a closed cycle. The throttle valve is used to extend the process into a vapor-compression refrigeration cycle is usually replaced by the expansion of the engine (e.g.. expander) for air cycle refrigeration system. The work required for the refrigerating effect is provided by the refrigerant gas. These systems are of great interest for applications where the weight of cooling unit should be minimized, for example, in the cabin cooling.
Diagram of the locations of major non-standard refrigerating cycle and T-s diagram shown in Fig.
3.64. This system consists of four main elements:
In the compressor, which increases the pressure of the refrigerant from the lowest to the highest value (eg. isentropic compression: 1-2),
An output energy of the heat exchanger, where the high temperature of the refrigerant reduced (e.g. the Isobaric heat dissipation: 2-3),
In the expander, where the pressure and temperature of the refrigerant is reduced (e.g. adiabatic expansion: 3-4), and
An energy input of heat exchanger, which raises the temperature of the refrigerant at constant pressure (e.g. wind, heat: 4-1). This input is known as the cooling load.
The use of air as a coolant becomes more attractive when dual goal to be attained. This is so in the case of the air conditioning when the air can be both in refrigeration and air-conditioning the average. Fig. 3.65 shows the standard cycle air cooling with heat exchanger and T-s diagram. In addition, air-standard refrigeration cycle is commonly used in liquefying air or other gases and also in certain cases, when cooling is needed, for example, air cooling systems.