I agree with all contributors the evaporative cooling needs only a blower motor and a small water pump. The working pressure is the ambient pressure which means no high loads are subjected on the motors. In the other side, vapor compression system needs power to operate the compressor and two fans, one for the condenser and the other one for the evaporator. The pressure ratio for the cooling fluid is high which means the need for high power.

Regards  

The evaporative cooling is due to the heat energy gained from the water reducing the energy consumption compared to mechanical cooling .  This cooling process is economical and adopted mostly for temporary storage of fruits and vegetables. 

Evaporative cooling is a physical phenomenon (say using the solar radiation) that does not need an external work to be exerted. To the contrary, the vapor compression systems require energy for the compression process and, hence, it is less efficient compared to evaporative cooling.

Hope this answer your question.

Professor Yehia Khalil

Yale University

USA

Generally, the required energy input depends on the applied pressure that can produce desired cooling effect. So, the required energy input increases as the system pressure increases. In evaporative cooling system, the desired cooling effect can be achieved at (1 bar) which is atmospheric pressure. While in mechanical vapor compression systems, the cooling effect require higher applied pressure to enable successful vapor compression processes and consequently higher energy input is required.

Evaporative cooling is favored by increasing the evaporation surface and contact with air. For example in industrial cooling towers with water cooling by evaporation. Is used mostly reduce the temperature of hot water to near ambient temperature. Vapor compression needs energy input but can be used for refrigeration at lower temperatures, for instance below 0ºC. The choice of refrigeration method depends on the temperature to be obtained.

Evaporative coolers required less energy as only fan and pump are required to produce only cooling by water evaporation while in case of VCR compressor, evaporator and condenser fans are required to produce cooling by evaporation of refrigerant which consumes more energy due to production of very low temperature and condensation of process air to control the air humidity.

Don't forgot about the energy:water nexus. It takes energy to pump and treat the water to the building for use in evaporative cooling. It also takes water to generate electricity in many power plant types. Depending on your climate and utility grid evaporative cooling may be helpful or harmful. 

I agree with all contributors the evaporative cooling needs only a blower motor and a small water pump. The working pressure is the ambient pressure which means no high loads are subjected on the motors. In the other side, vapor compression system needs power to operate the compressor and two fans, one for the condenser and the other one for the evaporator. The pressure ratio for the cooling fluid is high which means the need for high power.

Regards  

Forgot to add a note on the types of evaporative coolers. There's the wetted media type, and the atomizing type (Meefog). There's also direct, indirect, and direct/indirect evaporative cooling options. 

I really appreciate to all dear Professor/Dr for taking a time to consider my question and Thank you so much for complete answers. 

Best regards,

Theoretically, the energy needed to evaporate a liquid is the same in an athmospheric evaporator as in a vacuum (or compressor) one. The apprent difference comes from the fact that the energy to evaporate the water is taken to the ambient air which is therefore cooled and humidified. This enery is free and generally  not accounted. 

Another reson is that a compressor can cool a radiator (heat exchanger) on which the air, passing through it, is not only cooled but can also be dryed. Therefore, its enthalpy (energy content including sensible heat and latend heat resulting from the water content) can be reduced.  The evaporative cooler does not reduce the enthalpy of the air, it cools it but humidifies it at the same time. 

Remember that we cannot do anything without energy. Energy (including mass according to Einstein) cannot be created or destroyed, but only transformed form one of its aspects to another. The big issue now is to transform less non renewable energy as oil, gas, uranium and transform more renewabe elergy such as solar, wind, and geothermal. Evaporative coolers use more solar energy and less electric power from the grid than compressor coolers.