Heat Pumps are available in three formats; ground source, water-to-water and air source. All of these use the natural environment as the energy source. Ground source heat pumps take heat from the ground through either shallow horizontal pipe systems or looped pipes in sealed boreholes. Water-to-water heat pumps use two open boreholes,  one housing a submersible pump which delivers warm ground or mine water to the heat, the second is then used to return the cooled water back to the ground. Air source heat pumps extract heat directly from the air.