Heat Pumps
Heat pumps provide one of the most energy-efficient ways of heating buildings by making use of renewable energy stored in the ground or in the ambient air. They are suitable for a wide variety of building types and are particularly appropriate for low environmental impact projects.
The Earth acts as a huge thermal store absorbing 50% of the sun’s energy and maintaining a constant temperature of 11 to 13°C throughout the year. Heat pumps extract solar energy stored in the ground, water courses and in the air. The systems require electricity to drive the pump and so can be integrated with other technologies to make them completely renewable.
Heat Pump technology is ideal for new builds or complete renovation projects. This is because it is far easier to excavate the required trench and install the under floor heating system in new builds or renovation projects.
Air Source Heat Pumps
Air Source Heat Pumps (ASHP) extract thermal energy from the air and upgrade it to a higher, more useful temperature. By extracting heat from the surrounding air, the heat energy released can be up to 4 times the energy required to power the equipment.
How it works
An ASHP system consists of a compressor and a carefully matched evaporator coil and heat exchanger. A refrigerant liquid which circulates within the system has a boiling point as low a minus 40˚C and evaporates when absorbing heat from the outside air. It is possible to extract considerable heat from the air at temperatures as low as minus 15˚C. The resulting refrigerant gas is then passed via the heat exchanger into water and used to provide space heating through radiators as for conventional heating systems, or via underfloor heating systems.
Costs and Benefits
The amount of energy consumed to operate the pump is much less than would be required to heat the building by conventional means. Heat pumps are inherently efficient as they use low temperature heat created from renewable energy sources, and release relatively low carbon emissions.
ASHPs can be used to provide space heating to a wide range of building types. They are used in houses and community buildings across the country. The technology has, in the first instance, been developed with the housing market in mind so smaller systems up to 12kW have so far been developed. Heat pumps are most suited to energy efficient buildings and are most efficient when supplying low temperature distribution systems as underfloor heating. These pumps are particularly cost effective in areas where mains gas is not available.
An ASHP typically costs in the region of £3,500 (6kW) and £6,000 (12kW), excluding the cost of the distribution systems (e.g. radiators).
Ground Source Heat Pumps
Ground source heat pumps extract heat from the ground and pump it into a building, providing space heating and, in some cases, pre-heat domestic water (essentially a refrigerator working in reverse). In the summer months this process can be reversed to meet the cooling requirements of a building.
For every unit of electricity used to pump the heat, 3-4 units of heat are produced.
There are different types of heat pumps:
- Ground source heat pump - horizontal coil
- Ground source heat pump - vertical borehole
- Water source heat pump
There are three parts to a heat pump
- The loop - which collects the heat
- A heat pump - driven by renewable or mains electricity
- Heat distribution system - heaters
Ground coil - horizontal trenches are drilled to a depth of 1 to 2 meters and can cost less than boreholes, but they require a large area of land. Around 200 meters of pipe work is generally required for a single dwelling.
Borehole - drilled to a depth of between 50 to 100 meters and will benefit from higher ground temperatures than the horizontal trench, although installation costs will be greater. The length of the borehole will depend on the sixe of the heating load and the strata of the ground.
Water source - If you live close to a lake or a watercourse, even if the water is under ice during the winter, the heat in it can still be extracted. The collector hose is laid on the lake bed and held in place by weights. The only work needed on your property is to dig a trench from the water to the house.
Is your site suitable?
Is the ground suitable for digging a trench or borehole?- Check the soil type - different soils have different heat transfer rates
- Use with green electricity for maximum efficiency
Costs and Benefits
A typical 8kW system costs from £9,600.
- Vertical borehole systems would be at a higher end of this scale because they are more difficult to install.
- If sized correctly a heat pump can meet 100% of room heating requirements
- Has a 40 year life span and does not need regular maintenance
- Reduce emissions by 30-35%