Unlike traditional chillers that use mechanical refrigeration, Free Cooling uses naturally cool air or water instead to lower the air temperature in a building.
With this approach, a modulating valve allows all or part of the chilled water to bypass existing chillers and run through the free cooling system when the ambient air temperature drops to a set temperature. This requires less power since it harnesses the lower ambient air temperature to cool the water in the system, making it a greener and more cost-effective option.
Free cooling does have its limitations, however. For example, it can be difficult to avoid freezing once the cooling tower water temperature gets below 39 °F. Another shortcoming is the temperature difference across the heat exchanger. A heat exchanger that has a very low temperature difference can become economically unviable. The economics of the heat exchanger allow for a minimum free cooling water temperature of about 41°F.