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Direct expansion is also possible wherein the refrigerant is used to chill theincoming air directly without the chilled water circuit.Ammonia， which is anexcellent refrigerant， is used in this sort of application. Special alarm systems would have to be utili.ed to detect the loss of the refrigerant into the combustion air and to shut down and evacuate the refrigeration system.
Absorption Cooling Systems. Absorption systems typically employlithium-bromide (Li-Br) andwater， with the Li-Br being the absorber and the water acting as the refrigerant. Such systems can cool the inlet air to 50 oF (10 oC). Figure 2-37 is a schematic of an absorption refrigerated inlet system for the gas turbine. The cooling shown on the psychometric chart is identical to the one for the mechanical system. The heat for the absorptionchiller can be provided bygas，steam， or gas turbine exhaust. Absorption systems can be designed to be either single or double effect. A single effectsystem will have a coefficient of performance (COP) of0.7-0.9， and a doubleeffectunit， a COP of 1.15. Part load performance of absorption systems isrelatively good， and efficiency does not drop off at part load like it does with mechanical refrigeration systems. The costs of these systems are much higher than theevaporative cooling system， however refrigerated inlet cooling systems in hot humid climates are more effective due to the very high humidity.
Combination of Evaporative and Refrigerated Inlet Systems
Depending on the specifics of theproject，location， climatic conditions，enginetype， and economic factors， a hybrid system utili.ing a combination of the above technologies may be the best. The possibility of using fogging
Exhaust
Steam Generator
Absorption Chiller
1
Air

Figure 2-.7. Absorption refrigerated inlet cooling system.
systems ahead of the mechanical inlet refrigeration system should be con-sidered as seen in Figure 2-38. This may notalways be intuitive， since evaporative cooling is an adiabatic process that occurs at constant enthalpy.When water is evaporated into an airstream， any reduction in sensible heat is accompanied by an increase in the latent heat of the air stream (the heat in the air stream being used to effect a phase change in the water from liquid tothe vapor phase). lf fog is applied in front of a chillingcoil， the temperaturewill be decreased when the fog evaporates， but since the chiller coil will haveto work harder to remove the evaporated water from the airsteam， the result would yield no thermodynamic advantage.
To maximi.e theeffect， the chiller must be designed in such a manner that in combination with evaporative cooling the maximum reduction in tem-perature is achieved. This can be done by designing a slightly undersi.edchiller， which is not capable of bringing the air temperature down to the ambient dew point temperature; but in conjunction with evaporative coolingthe same effect can be achieved， thus taking the advantage of evaporative cooling to reduce the load of refrigeration.

Generator

Water
Steam

Thermal Energy Storage Systems
These systems are usually designed to operate the refrigeration system at off-peak hours and then use the refrigerated media at peak hours. The refrigerated media in most cases is ice and the gas turbine air is then passedthrough themedia， which lowers it inlet temperature as seen in Figure 2-39. The si.e of the refrigeration system is greatly reduced as it can operate for8-10 hours at off-peak conditions to make theice， which is thenstored， and air passed through it at peak operating hours that may only be for about 4-6 hours.
The cost for such a system runs about .90-.110jkW. And have been successfully employed for gas turbines producing 100-200 MW.
Injection of CompressedAir，Steam， or Water for Increasing .o.er
Mid-Compressor Flashing of Water.ln this system， the water is injected into the mid-stages of the compressor to cool the air and approach an
　
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