Geothermal Heat Pumps

Download GHP Guide: Introductory Guide to Geothermal Heat Pumps in NZ
Download Factsheet: Geothermal heat pumps (PDF)

Key components

  1. Ground Loop

The ground loop is formed by a network of pipes located underground and outside the building footprint. Depending on the energy load and particulars of the site the loops may be installed in either a vertical or horizontal configuration for closed loop systems, or may be installed in an open loop system to access groundwater or surface water directly. The primary function of the ground loops is to collect heat from or dispose heat to the ground, ground water or surface water. This is achieved by circulating a working fluid through buried or submerged pipes (closed loop systems) or taking ground water or surface water directly (open loop systems).

  1. Heat Pump

In heating mode, the heat pump transfer heat collected in the ground loop into the building. In cooling mode, the process is reversed and heat from the building is transferred to the ground loop for disposal.

  1. Distribution System.

The distribution system delivers or removes heat to/from a building. One of the most efficient methods for space heating is to lay pipes in the buildings concrete floor through which warmed water from the heat pump is circulated. Alternative methods include radiators or forced air systems.

How do they work?

Heat pumps function in the same way as a standard household fridge. The following basic principles are used:
  • A liquid absorbs heat as it vaporises (e.g. boiling water turning into steam)
  • Compressing a gas increases its temperature
  • Expanding a gas reduces its temperature
  • As a gas loses heat, it will turn back into a liquid (e.g. steam condensing back to water)

A heat pump uses these principles, circulating a refrigerant through a loop with two heat exchangers – one exchanger to gain heat, one to lose it.

A refrigerant is a liquid with a very low boiling point, meaning that it can evaporate into a gas and condense back into a liquid at low temperature.

When circulated in a loop between two heat exchangers, the refrigerant gains heat from one exchanger so that it turns into a gas, the gas is compressed, and then passes through the second exchanger where it loses heat, before being expanded, returning to a liquid to begin the cycle again.

In a geothermal heat pump, the first heat exchanger is placed in the circuit with the ground loop, the second in the circuit with the building. The refrigerant can gain heat from the ground loop and lose it to the building, or can operate in reverse; heating or cooling the building respectively.