Heat Pump Technology

Heat pumps are available as either air source (ASHP) or ground source (GSHP).

Heat pumps use basic thermodynamic principles to convert latent heat (contained within either the ambient air or stored heat source in the ground) into heat energy that can be used to provide heating and hot water. Heat pumps can therefore be classified as a renewable energy source because the heat in the ambient air or ground is replenished by the sun.

There are two types of heat pump: ‘air to air’ and ‘air to water’.

1. Air to air heat pumps release the captured energy through an air heat exchanger, which is then forced (by fan) around the dwelling through ducting, or directly into the room; most commercial buildings use this type of heating medium. 

2. Air to water heat pumps release the energy into a water circuit which is then used to distribute the heat via radiators or a piped underfloor heating circuit.

Heat pumps and radiator heating

Standard wall mounted radiators generally need much higher temperatures to operate efficiently, around 70 - 75°C, requiring a much higher output (usually a boiler) of hot water to supply the radiator heating system.

Heat pumps can work with radiators but they will need to be much larger to distribute the lower heat output efficiently into the room. The question is, why install a heat pump to supply warm water to an inefficient radiator heating system that relies on convection currents to heat the room? An alternative option - and more efficient use of heat pump technology - exists to heat the room using the benefits of lower water temperatures produced by a heat pump to supply warm water to a piped underfloor heating system. 

Heat pumps and underfloor heating

Heat pumps are designed to operate between 30°C and 60°C, however, the ideal temperature for heat pumps working at their optimum efficiency is around 35°C -achieving maximum Coefficient of Performance (CoP).

Heat pumps are therefore more efficient when demand is low, making heat pumps well suited to supply low level warm water to piped underfloor heating systems. The typical flow temperature of warm water circulating around a piped heating circuit is around 35°C, making heat pumps the ideal partner for water underfloor heating applications.

Domestic boilers on the other hand operate at much higher temperatures, around 70°C. This hot water is then blended down to a typical 35°C working temperature when pumped around the underfloor heating pipework circuit via a mixing valve located at the manifold - for more information on mixing and blending hot water using a boiler hot water source click water temperature control valve

In the majority of cases - typically new build - converting room floors to low-level radiators allows the complete removal of unsightly radiators, freeing up the walls for greater living space.  Underfloor heating can deliver heat into the room more efficiently by taking advantage of the lower water temperatures produced by a heat pump to distribute the radiant heat directly into the room through the flooring.

Water underfloor heating, when combined with a heat pump, can bring the benefits of a more sustainable heat source into the living space that takes direct advantage of this form of low carbon heating technology.

About ‘Coefficient of Performance’ (CoP)

CoP is a ratio indicating the amount of energy required to run the heat pump, compared with the amount of energy being produced by the heat pump to heat the water.

A heat pump providing flow temperatures of 35°C to a well designed underfloor heating system should acheive a CoP of around 4. This means for every kilowatt (kW) of energy used to run a heat pump, 4 kW of energy is being given to the heating system in return.

It is important to note that seasonal changes to the ambient temperature will affect the CoP of an air source heat pump, reducing the CoP proportionately; ground source heat pumps are not affected by these season variations to the same degree, due to the mean temperatures below ground (subject to depth) remaining constant throughout the year.

An increasingly popular method of home heating

Upward spiraling energy costs and advances in heating technology, have positioned air source heat pumps as a very realistic alternative to the conventional fossil-fueled heating system.

How An Air Source Heat Pump Works

Air to water technology 

Air to water heat pumps employ the dynamics of the vapour/compression cycle used for many years in the basic refrigeration process found within a domestic fridge. A low pressure, low boiling point liquid (refrigerant) is exposed to a higher temperature in the coil of the evaporator. The liquid boils off to a gas and in doing so, absorbs energy. The refrigerant gas is then compressed to a higher pressure and temperature before passing through a heat exchanger where it gives its heat energy to water. The heated water is then delivered to a cylinder or heating System. After passing through the heat exchanger the refrigerant condenses back into a liquid before starting the process again.

Sizing A Heat Pump

Selecting the correct size of heat pump for your installation can be a difficult choice given all the various factors involved (insulation, heat loss calculations, double glazing, U Values, volume of air changes, general aspect of the building etc, etc.). Therefore, advice should be taken before ordering your Aerona heat pump to establish the correct output size of unit to match your energy requirement.

The Microgeneration Certification Scheme (MCS)

Grants are available for domestic microgeneration systems through the Government’s Low Carbon Buildings Programme. Air source heat pumps qualify for a maximum grant of £850 and must be installed by Microgeneration Certification Scheme (MCS) certified installer to qualify.

For more information on grants available for your home energy improvement click on Energy Saving Trust

Technology for the future

Renewable energy has a key role to play in reducing CO2 emissions and, in particular, the installation of a heat pump is an effective way of reducing a building’s carbon footprint, therefore helping the environment.

Renewable Heat Incentive and further information

In February the Government published detailed consultation proposals for the world’s first Renewable Heat Incentive (RHI) program which will pay people for the heat they generate themselves. The scheme, which is due to start in April 2011, is expected to lead to a rapid increase in the number of homes and offices heated by woodfuel, biogas, solar thermal, heat pumps and waste-to energy technologies.

For more information on the new government renewable energy incentive policy - click: Renewable Heat Incentive Scheme

Latest announcement issued by the government with details of the RHI scheme - click: Press Notice

Useful information on the RHI scheme by the online Which? consumer guides magazine gives clear questions and answers and qualification criteria - click: Which? RHI Explained 

Further information on the RHI scheme and qualification criteria is also available from this website covering Eligibility For Grants