A very efficient source of energy for water source heat pump systems
is the Earth itself. Ground Source Heat Pumps use the Earth’s natural
solar collection and heat storage capabilities as an infinite heat
source/heat sink.

At between 1.7m and 3m below the ground, the temperature changes from
17C in the summer to 10C in the winter. Deeper down however, the
temperature of the ground is a constant 10C all year round. It is
these relatively constant, dependable temperatures that can be
harnessed using Ground Source Heat Pumps.

The constant ground temperature allows the heat pump to operate at
optimum efficiency in both heating and cooling, as the high summer or
low winter temperatures do not influence performance. Heat is
extracted or rejected into the ground using water, which is pumped
through a network of plastic pipes.

There are two standard ground source methods available.
Open Loop and Closed Loop (Bore Hole or Slinky):

• Open Loop – Large bodies of water can be utilised as a stable source
  of water at a relatively constant temperature. This can be either
  surface water or ground water. Surface water would include lakes,
  reservoirs, rivers and the sea.
• Closed Loop Slinky – A trench is dug to a depth of between 1.7m to
  3m and a plastic spiral pipe is laid into the bottom. The pipe is
  covered with sand to provide good ground-to-pipe contact and the
  trench is backfilled with the excavated soil.
• Closed Loop Bore Hole – A series of holes are drilled doun into the
  ground at a depth of 50 to 130m, depending on geothermal conditions.
  Two water pipes connected via a ‘u bend’ are fed directly into these
  holes and then surrounded by a conductive grout.