Low Energy House - Air Source Heat Pumps - ASHP

Air Source Heat Pumps take low grade heat from air, upgrade it, and supply it to home Heating and Domestic Hot Water Systems. Air Source Heat Pumps are compact units that can be located on the outside wall of a house. The use of Air Source Heat Pumps can lead to considerable saving of fossil fuels

Types of Air Source Heat Pumps

The technology used in heat pumps is the same as that used in a domestic refrigerator. A refrigerator extracts heat from its contents and pumps that heat to a radiator on the outside of the cabinet, where it is dispersed. Similarly, an air source heat pump extracts heat from ordinary outside air and pumps it into a building, where it can be used for heating.

There are two types of air source heat pumps:

Air to Air Heat Pumps - Provide warm air which is circulated through a building using a ducted ventilation system with fans.

Air to Water Heat Pumps - Provide heating in a building, usually through an underfloor heating system.

Air Source Heat Pumps - System Efficiency

For every unit of electricity used to power an air source heat pump system, between 3 and 4 units of heat are extracted and distributed. At this high level of efficiency, there are less carbon dioxide emissions than with a gas boiler system.

In many cases, it may also be possible to provide the electricity, required to operate the system, by means of renewable energy, eliminating the need for fossil fuel energy altogether. Alternatively, green electricity can be purchased, or Solar PV, or another form of renewable electricity generating system can be installed to power the compressor and pump.

Air Source Heat Pumps - Suitability

Air source heat pump technology has been developed for the housing market providing systems up to 12 kilowatts. Heat efficient pumps are most suited to energy efficient buildings and are most efficient when supplying low temperature distribution systems such as underfloor heating.

Benefits of Air Source Heat Pumps

Air source heat pumps should provide all the heating requirements of a well insulated property in all but the most extreme conditions. When used in combination with an immersion heater or thermal store the heating and hot water needs should both be met. An outside air source heat pump working efficiently can reduce energy consumption for heating by up to 50 per cent when compared with conventional fuel heating systems.

The amount of energy consumed to operate the pump is much less than would be required to heat a house 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.

Air Source Heat Pumps have three main parts:

Evaporator

• Outside air is pumped to the heat exchanger that is housed inside the Heat Pump Unit. The refrigerant expands in the evaporator then changes from liquid to gas and absorbs the heat from the outside air.

Compressor

• The refrigerant is pumped to the compressor where it is pressurised and super-heated to the temperature required by the heat distribution circuit in the building.

Condenser

• The condenser transfers the heat to air or water. In an air to water system, the heat produced is used to heat water which can be used to pre-heat water in a storage tank or circulate through underfloor heating or radiators.

Controls

An electronic control system is incorporated in the Heat Pump unit to operate the temperature and timing functions.

Air Source Heat Pumps - Heat Distribution System

Air to Air Heat Pump Systems provide warm air which is circulated through a building using a ducted ventilation system with fans.

The heat produced by an Air to Water Heat Pump System is at a low temperature relative to that required for central heating. It can be combined with radiators, although the radiators have to be very large in area and are therefore not very practical. Underfloor heating normally operates at a lower temperature so the efficiency of the heat pump is greatly improved using this system. Alternatively, the heat produced by the Air to Water Heat Pump can be used to pre-heat the domestic hot water supply that is contained in a special storage cylinder or thermal store.

Before considering any system of renewable energy, it is advisable to improve the energy efficiency of the house through improved, insulation, draught proofing, low energy lights and heating controls