Free Cooling

Air conditioning can also be provided by a process called free cooling which uses pumps to circulate a coolant such as air, water, or a water-glycol mixture from a cold source, which in turn acts as a heat sink for the energy that is removed from the cooled space. Common storage media are cool outside air, deep aquifers, or a natural underground rock mass accessed via a cluster of small-diameter boreholes. Some systems with small storage capacity are hybrid systems, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added because the temperature of the storage gradually increases during the cooling season, thereby declining its effectiveness.