The same air cooling process occurs when a refrigerant is used in the cooling coils. The direct refrigerant cooling system consists of either a vapor compression or an absorption system. For direct refrigerant cooling (DRC), the liquid refrigerant is used directly in the cooling coils (evaporator coil(s)). The refrigeration system evaporator coils can be of many configurations. The refrigerant is usually pumped to the coils, using some type of overfeed system (ASHRAE 1996), and a pressure over feed system has been used in at least one ammonia refrigerant installation (e.g., Dow 1996). Typically, a refrigerant pump is used in an overfeed system. Pressurized overfeed and refrigerant pump systems experience approximately the same parasitic load, as pressurized overfeed systems tend to reduce compressor capacity compared to pumped systems.

The evaporator can be either single stage or multiple stages operating at different pressures and temperatures (see, e.g., Kohlenberger 1995). Multiple-stage systems typically operate at higher efficiencies, but at higher equipment costs, and require more space, though They may reduce parasitic loads (Kohlenberger 1997).

The DRC system eliminates the secondary fluid (or water) pumps required in the SFC system, which may simplify operation and maintenance. A direct refrigerant cooling system can result in a wide range of parasitic power, from as little as 4% to 5% to 30% of the turbine generator capacity. The DRC system can also provide cooling during all of the 24-hour day, as can a partial thermal storage system.

The DRC cooling system requires a much...