Utilising Ground Source Heat Pumps For Energy

Ground source heat pumps offer a relatively inexpensive and environmentally friendly way to use waste heat from the earth for heating and cooling both residential and commercial buildings. Initial set-up costs can be quite a bit higher than conventional air-source systems, but geothermal heat pumps offer substantially lower ownership costs over the long term.

Ground source heat pumps (GSHPs) are systems that use the earth’s temperature to provide heating, cooling and hot water for commercial establishments and residential buildings. The systems are designed to take advantage of the fact that temperatures remain at a near constant level of between 7° C and 21° C just a few feet below the ground, regardless of geographic location or surface air temperatures. During winter, the systems essentially extract heat from the ground and transfer it to a commercial building or home, while in summer the systems extract heat from building interiors and transfer it to the ground. Ground source heat pumps are electrically powered and are sometimes referred to as geothermal heat pumps, or geo-exchange pumps, or simply as earth-coupled heat pumps.

A full-fledged GSHP system consists of a heat pump, a ground loop system for absorbing heat from the ground or rejecting it back to the ground, and air ducts or radiant floor systems for delivering the hot or cold air. The ground loop system typically consists of numerous loops of plastic tubing filled with antifreeze liquid or water, buried underground in horizontal or vertical fashion. During winter, the liquid in the loops collects heat from the ground and pushes it to the heat pump where a compressor raises the temperature even more before circulating it through the building. The flow of the liquid inside the loops is reversed during summer. This results in the warmer air being drawn out from the building and transferred to the earth while cooler liquid is circulated back to the heat pump and then through the building. An open loop system works in more or less the same fashion, but in this case the liquid in the loops is usually ejected into the ground.

Typically, horizontal closed looped systems are easier and less expensive to implement because they require relatively less digging and burying. However, since ground temperatures tend to vary quit a bit close to the surface of the earth, the loops have to be deployed over a relatively wide area to be truly effective. In contrast, a vertical loop system is more effective at collecting and transferring heat, but they are more expensive to implement and involve considerable digging work.

Ground source heat pumps have been in use since the 1940s and are considered a more environmentally-friendly and cost-effective alternative to conventional air-transfer based heating and cooling systems. Studies have show that GSHP systems have heating efficiencies up to 70% higher than conventional systems and cooling efficiencies of nearly 40% more than air-conditioners. The initial cost of setting up a geothermal heat pump can be quite steep compared to conventional heating and cooling systems. However, over the long term the pumps are cheaper to own and to maintain. They also can deliver up to 50% savings on energy consumption. In some cases, a geothermal heat pump is installed along with an air-source heat pump in order to reduce initial installation costs.