Mention the advantages of vapor compression refrigeration system over air refrigeration system.

1. Method of compression of the refrigerant: one of the most important parts of any refrigeration cycle is the compression of the refrigerant since all the further operations depend on it. In the vapor compression refrigeration system the compression of the refrigerant is done by compressor which can be of reciprocating, rotating or centrifugal type. In the vapor absorption of the refrigerant by the absorbent. As the refrigerant is absorbed, it gets converted from the vapor state to liquid state so its volume reduces.
2. Power consumption devices: In the vapor compression cycle the compressor is the major power consuming device while in the vapor absorption cycle the pump used for pumping refrigerant absorbent solution is the major power consuming device.
3. The amount of power required: The compressor of the vapor compression cycle requires large quantities of power for its operation and it increases as the size of the refrigeration system increases. In case of the vapor absorption refrigeration system, the pump requires very small amount of power and it remains almost the same even for higher capacities of refrigeration. Thus the power consumed by the vapor absorption refrigeration system is much more than that required by the vapor compression system.
4. Type of energy required: The vapor absorption system runs mainly on the waste or the extra heat in the plant. Thus one can utilize the extra steam from the boiler, or generate extra steam for the purpose and also use the hot available water. Similarly the waste heat from the diesel engine, hot water from the solar water heater, etc. can also utilized. In case of the vapor compression refrigeration system, the compressor can be run by electric power supply only; no other types of energy can be utilized in these systems.
5. Running cost: The vapor compression refrigeration system can run only on electric power, and they require large amount of power. These days the electric power has become very expensive, hence the running cost of the vapor compression refrigeration system is very high. In case of the absorption refrigeration system only small pump requires electric power and it is quite low. In most of the process industries, where the absorption refrigeration is used, there is some extra steam available from the boiler, which can be used for running the system. Thus in absorption refrigeration system no extra power in the pure electric from is required and the energy that would have otherwise gone wasted is utilized in the plant. Thus the running cost of the absorption refrigeration system is much lesser than the vapor compression system.
6. Foundations required and noise: The compressor of the vapor compression system is operated at very high speeds and it makes lots of vibrations and noise. It also requires very strong foundation so that it can remain intact under vibrations and high pressures of the refrigerant. In the absorption refrigeration system there are no major moving parts hence they don t vibrate, don t make noise and also don t require heavy foundations. The absorption refrigeration system operate silently.
7. Maintenance: Compressor is the crucial part of the vapor compression cycle, and it has number of moving parts. It is very important to do the through lubrication of the compressor and also keep checking it regularly for any defects. The compressor also requires changing of the piston, piston rings, cylinder etc, from time to time. Thus the vapor compression system requires lots of maintenance. Failure of compressor can be very expensive at times as the suction and the discharge valve of the compressor are very expensive. The compressor also requires cooling, for which special pump is very heavy and expensive. The compressor also requires cooling, for which special pump is required to pump the water from the cooling tower to the compressor. Since there are number of moving parts of the compressor that move at very fast speed some or the other failure occurs regularly. In the absorption refrigeration system the only moving part is the small pump that fails rarely. Thus the maintenance required by the vapor compression system is much more than that required by the vapor absorption system.
8. Capacity control of the system: In the vapor compression cycle the capacity control of the system is done from the compressor and in most of the cases step wise capacity control is obtained. In case of the absorption refrigeration system it is possible to obtain step less capacity control and zero capacity when there is no load on the system. Through these days compressors with step less capacity control are available, but they will consume lots of power even if there is zero load on the refrigeration system. In absorption system, when there is zero the power consumption is almost zero.
9. Type of refrigerant used and its cost: In ammonia water absorption refrigeration system, ammonia is used as the refrigerant which is easily and cheaply available. IN lithium bromide system, water is used as the refrigerant, which is also available cheaply and easily. In case of the vapor compression refrigeration system hydrocarbons are used as the refrigerants, which are very expensive.
10. Leakage of the refrigerant: In the absorption refrigeration system there are no leakages of the refrigerant and the refrigeration itself is very cheap. Thus there are almost zero refrigeration recharging costs. In case of the vapor compression system there are lots of leakages of the refrigerant thus regular recharge of the refrigerant is required which is very expensive.
11. Greenhouse effect: Most of the hydrocarbon refrigerants used in the compression refrigeration system produces greenhouse effect. As per the Montreal Protocol their use has to stop completely by the year 2020. In the absorption refrigeration system no refrigerant produces the greenhouse effect, so their use won t be stopped in future.