One of the most common questions we are asked is what is the difference between geoexchange and geothermal?
The answer is not necessarily that simple and is open to debate depending on the country you are in and what terms are used historically in your area. In many instances, especially in the North American market, the term geothermal is almost inter-changeable between geothermal heat pumps as used for heating and cooling (ie geoexchange) and geothermal energy as used for the generation of electricity.
To confuse the issue further, it is not as simple as choosing between geoexchange and geothermal as other terms or phrases used include ‘ground source’, ‘ground coupled’, ‘direct geothermal’, ‘low temperature geothermal’, ‘true geothermal’ and more.
The term ‘geoexchange’ has been widely adopted in Australia, and increasingly elsewhere, for the following reasons:
- It is a technically more accurate description for a technology that utilises the ground (geo) or water bodies as a heat source in winter and heat sink in summer (exchange);
- The temperature of the ground is a function of its exposure to solar radiation and not unique geothermal anomalies such as volcanic features or hot rocks; and
- The emergence of geothermal as a form of energy generation and the widespread use of this term in the public domain has resulted in some misinterpretations and public confusion, including within both industries.
So what is a geoexchange system?
Over the years we have found it of further use to explain geoexchange as an entire system that consists of the following:
- Ground Heat Exchanger (GHX): The component that provides the heat exchange with the ground. It is constructed of polyethylene (PE) pipe and can be closed vertical (boreholes) or closed horizontal (trenches) within the ground or it can use surface water bodies as a closed loop or an open loop system (mostly aquifers). For more details on the various loop systems, click here.
- Ground Source Heat Pump (GSHP): This is the actual heat pump or air conditioner that is located within the building and provides the thermostat controlled temperature to the building. It is the mechanical component of the system. GSHPs can be used for hydronic heating or chilled water (water to water GSHP) or for the delivery of ducted air conditioning (water to air GSHP).
- Distribution System: The distribution or delivery of heating, cooling and hot water. For example, an underfloor hydronic heating system is the distribution for a water to water GSHP and centralised ducting is the distribution for a water to air GSHP. The supply of domestic hot water, either directly or indirectly, is also part of the distribution system.
This diagram illustrates a geoexchange system:
We have found that this breakdown approach to the components of a geoexchange system provides a better understanding of how it works as well as the benefits it provides. It also highlights the integrative system approach of geoexchange and the importance of a holistic approach to design and installation.
If you have any questions on the above please contact us.