Air Source Heat Pumps

What are they?

An air source heat pump will take the heat from the outside air and use this free source of energy to provide heating within a building.

There are two types of system: air to air systems will provide warm air which is used to heat the building. Air to water systems provide heating through radiators or underfloor heating system.

Air source heat pumps can offer an efficient and economic method of heating homes. Installation can be as simple as locating the air source heat pump outside the property, connecting up to a wet heating circuit using flexible hoses and commissioning using the electronic controls.

Air source heat pumps can offer substantial carbon savings compared to other heating sources such as electric storage heaters and oil boilers. Under typical conditions, air source heat pumps operate at efficiencies between 200% and 400%. This means that for every kW of (electrical) energy put into the unit you get between 2kW and 4kW of (heat) energy out.

The efficiency varies depending on the difference between the outside air temperature and the central heating water temperature. The smaller the difference, the greater the efficiency. For this reason, air source heat pumps are ideally suited to lower temperature central heating systems and so the design of the heating circuit is important.

How Do They Work?

Heat pumps are often referred to as ‘refrigerators in reverse’ and this is a good analogy. A heat pump consists of four main components; evaporator, compressor, condenser and expansion valve. A refrigerant is circulated around these components.

• In an air source heat pump, air is drawn over the evaporator that gives up heat to the cooler liquid refrigerant which then boils. Even though the vapourised refrigerant is still fairly low temperature, significant amounts of heat have been extracted from the air.

• The warmed (but still low temperature) refrigerant then passes through a compressor that increases the pressure of the vapour. One of those easily forgotten laws of physics tells us that if the pressure of a gas increases, the temperature is also increased. This higher temperature is now useful for domestic heating.

• The higher temperature refrigerant then passes through the condenser, condensing as it gives up heat to the cooler return water of a wet heating system. When the pressure was increased, the boiling point was also increased and this is why the refrigerant now condenses at a higher temperature than when it was boiled.

• Those kilowatts of heat extracted from the air are now transferred to the domestic heating system plus the electrical energy used by the compressor that has also been converted into heat energy. The liquid refrigerant then passes through an expansion valve that reduces the pressure of liquid, returning the refrigerant to its original state ready to repeat the cycle.

Main Uses

• Underfloor heating arrays

• Low temperature panel radiators

• Skirting radiators

• Fan convector radiators

• Ideal for use with Solar Domestic Hot Water (DHW)