BEAMA

 There are no gas or oil connections as they use renewable energy sources. They provide lower flow temperature water (up to 55oC generally) compared to a boiler (generally 70-82oC) and their capacity for supplying useful energy is dependent on input temperature (from ground/air/water). Heat pumps are much more efficient (boiler can achieve no more than 100% efficiency) and have no compulsory annual servicing equipment.

Heat pumps can be sited indoors or outdoors. Householders should consider advice from an accredited installer regarding ground conditions for ground source heat pumps as performance is linked to heat extraction potential (wet soil better than dry). Also, it is worth noting that trenching for ground loops requires access to land and a bore hole will require access for drilling equipment.

Air source heat pumps achieve good CoPs due to relatively high ambient winter air temperatures.

Heat pumps use a carbon and cost free input energy (from the air or ground) which is converted into useful heat. This means that where a heat pump has a co-efficient of performance of say 4, 75% of the energy is from the environment with 25% from the electrical energy.

The conversion process uses electricity to drive the compressor within the heat pump cycle but so long as the efficiency of the heat pump is greater than 100%, it is energy and carbon efficient. For example, a typical 4kW ground source heat pump is 400% efficient in that it gives 4kW of useful heat for every 1kW of electricity used. This is expressed normally as a spot measurement called Coefficient of Performance (in this case a CoP of 4). Efficiencies of 250-500% are generally available in the UK. Conditions of operation determine the spot measured Co P i.e. Air/ground temperature and Water flow temperature. Those conditions tend to be from laboratory conditions and not real in use testing. If the householder uses a renewable energy tariff then the input energy is also carbon free, creating a truly renewable and zero carbon system.

We know that through the conversion process, environmental energy input is turned into higher kW of heat. Compare that to a gas fired electricity production plant in which an input fuel (at a highly volatile price) is used in a generation process. In general, the cost of electricity power for the heat pump process is less volatile than gas. (recent npower increases have been 5% higher for gas than electric and is consistent with historical price rises)

The most important consideration is the operating costs which are very low. Unlike the requirement for gas boilers, there are no maintenance and servicing costs associated with heat pumps.

Heat pumps are more expensive than gas and oil boiler equivalents but attract only 5% VAT and grants are available to reduce the cost. In England and Wales, the Low Carbon Buildings Programme provides grants of up to £1200 to individual householders for the installation of ground source heat pumps and £900 for air source heat pumps. The air source heat pump grant is expected to be available from around March 2008 once the first air source products and contractors are approved to the Microgeneration Certification Scheme requirements.

In Scotland, grants are available for both ground source and air source heat pumps to a value of up to 30% of the installation cost or a maximum of £4000.

Heat Pumps can use various sources of energy but the common sources are ground (using solar heat from the earth) and air (ambient air). The energy sources are inexhaustible and the solar heat within the ground is replenished continually.

Radiator systems designed for boilers tend not to be optimal for heat pumps. Radiators need higher temperatures (typically 70-80 oc powered by boiler) but heat pumps require flow temperatures around 55 oc. Therefore, underfloor heating is the preferred distribution method. Large surface area radiators are an option and as a rule of thumb, a 20oc reduction in flow temperature requires a 100% oversize of emitter.

Domestic hot water is normally stored at 60-65oc and as the heat pumps can generally only lift temperatures to around 45-50 oc, an additional water heating element will be required. This is usually an electric heating element in the water cylinder for boost. It is normal to try to use an off peak tariff for hot water provision by the heat pump and this can reduced the costs for boost with appropriate control. Larger coil cylinders are required for heat transfer but both direct and indirect cylinder types are suitable. Some manufacturers supply high temperature heat pumps to satisfy total hot water demand but there will be a reduction in CoP.

As a rule of thumb, ensure 200W/person is added to the design load if the heat pump is to be used for domestic hot water production.

Air source heat pumps can provide efficient benefits at temperatures as low as -20oc. Average temperatures in the UK range from 2 oc to 22 oc. The record low was -10 oc.

The efficiency of a heat pump is determined by two critical factors. Efficiency reduces as temperatures falls to very low levels e.g. 0 oc, and hot water system temperature increases.

There is no combustion process involved with the heat pump process (termed as a 'cold' heat medium). There are no risks of gas leaks or oil spills.

The refrigerant commonly used is R407C/R404A and these HFCs are currently acceptable for use in today?s environment. The refrigeration systems tend to be pre-charged.

Heat pumps are available in reverse mode to provide summer cooling. The waste heat (i.e. the heat extracted in the cooling process) can be used to pre-heat domestic hot water.