Free Cooling - Plate and Frame

One method for reducing water chiller energy consumption is to add free cooling. The method shown here uses a plate and-frame waterside economizer that pre-cools the chilled water before it enters the chiller's evaporator. When the ambient wet bulb temperature is low enough, the heat exchanger allows the transfer of heat from the return chilled water to the water returning from the cooling tower. Lowering the temperature of the water entering the evaporator reduces both chiller loading and energy consumption.

The plate-and-frame method of free cooling requires an additional heat exchanger. This adds to the initial cost of the system and increases pumping costs due to the added pressure loss. Free cooling is only of significant value when the ambient wet bulb temperature is lower than the design return chilled water by about 10°F. The cooling tower must be designed for winter operation, and the water entering the chiller condenser must be maintained within the manufacturer's specified temperature limits while the chiller is operating.

Note that plate-and-frame free cooling can be accomplished with a variety of piping arrangements, depending on the operational characteristics desired. The schematic illustrated here shows just one method of piping that can be used to permit simultaneous free cooling and mechanical cooling.