Ground Heat Pump

A fluid, known as a refrigerant, is circulated through an underground loop of polyethylene pipe. The refrigerant absorbs heat from the earth during the winter and dissipates heat from the building during the summer. The heat or cold from the fluid is converted to hot or cool air by circulating it through water-to-refrigerant and refrigerant-to-air heat exchangers (similar to a car radiator). Ground heat pumps are very efficient, utilising the relatively constant temperature of the ground to obtain heat during the winter and provide cooling during the summer. The loop of polyethylene pipe buried in the ground can be installed vertically or horizontally.

Vertical Closed Loop Vertically bored systems reduce the amount of ground area required for a Ground Heat Pump design for a given heating or cooling load. These systems are ideal for residential or commercial refurbishment applications where major site disruption is not possible during system implementation.

As year round ground temperatures in the United Kingdom stabilize at approximately 10 degrees centigrade at a depth of eight metres, vertical bore systems allow access to stable ground temperatures. Therefore vertical closed loop Ground Heat Pump designs are suitable for year round space and direct water heating applications.

It is worth remembering that site geology will significantly affect vertical bore costs and therefore impact upon the return on investment one can expect from the Ground Heat Pump design. Also, other issues such as site hydrogeology and far field temperature will affect system performance.

 

Horizontal Closed Loop Horizontal matrix system designs are ideal in new developments where major site disruption is acceptable. Horizontal designs are ideally placed underneath new car parks or in areas where long term land development is guaranteed not to occur. They are ideally suited to retail building development.

Horizontal designs are very cost effective to implement but seasonal temperature variations in the United Kingdom will affect system performance. The fluctuations in ground temperature that can be expected at depths less than three metres will therefore be a major design consideration.

Where circumstances allow, a horizontal ground heat pump can also be designed to utilise bodies of water such as lakes, rivers or the sea as heat sources or heat sinks.

 

Open loop versions of Ground Heat Pumps work in the same way as closed loop systems but continually draw upon a reliable "warm" water source such as aquifers or the sea. Cooled water is returned to the source water body at a distance that does not affect the temperature of the source. The advantage of open loop Ground Heat Pump systems is that they take advantage of a constant temperature heat source. Where aquifers are available in the United Kingdom water temperatures can range upwards from ten degrees centigrade. Warm brine sources are rare in the UK.

Open loop systems present source contamination risks both during implementation and operations and therefore this type of Ground Heat Pump must be carefully designed to meet local planning and environmental agency regulations.