A great introduction to ground and water source heat pumps

Ground and water source heat pumps (GSHP) are easy to run once installed and provide low-carbon heating or cooling. Average reduction in CO2 emissions are reported to be from 25 % to 70%. These reductions depend on the use of GSHP - either for cooling, heating, or both. These systems offer the benefits of reduced running and maintenance costs, and overall energy bills, which offsets the up-front capital investment that is often higher than for conventional systems.

GSHP exploit the stable temperature of the ground and use it as a source of heating or cooling. GSHPs are most efficient with low-temperature heating systems such as underfloor and wall heating, or low-temperature cooling systems such as chilled beams.

There are different variations of GSHPs:

• Open-loop system: Groundwater is extracted from and returned to a suitable aquifer below the site; output depends on the amount of water extracted. This system is more efficient than closed-loop systems, less boreholes are needed. They are also the most cost-efficient GSHP system and the cooling effect of groundwater can also be used.
• Closed-loop vertical system: A heat exchange fluid is circulated through pipes laid vertically in one or several boreholes in the ground. Output is fairly predictable.
• Closed-loop horizontal system: A heat exchange fluid is circulated through pipes laid horizontally in trenches in the ground at a non-frost depth. A large area of ground is required, which becomes unusable for any further construction.

Result

Open-loop systems tend to involve greater up-front cost and testing. Nonetheless, they appear to be more cost effective, i.e. the cost per kW of heat output for an open-loop system is between € 1 130 and € 2 270, while for a closed-loop system it is between € 1 810 and € 3 630.

Keep in mind that conditions and solutions vary from site to site, which affects the cost of GSHP installations. Assessing site feasibility and researching technology options are important steps. As a backup system for peak heating demand, an electrical cartridge is installed in the GSHP. Alternatively, the GSHP can be paired with gas boilers to handle peak heating demands and to provide a back-up system.