The heating system, called inter-seasonal heat transfer, uses a network of fluid-filled pipes laid under the pavement to collect heat during the summer months, when runways may reach 122 degrees during the day. These pipes transfer the energy to subterranean "thermal banks" where the ground insulates stored heat. During the long winter, the summer’s solar energy can be tapped by using heat pumps to bring warm fluids back to the surface. Even the heat produced by an airport’s air conditioning system, rather than venting to the atmosphere, can be piped into underground storage adding still more heat to the system.
Source: fastcoexist.comAdded: 21 May 2012