Air source heat pumps

Level 3 Diploma in Electrical Installations (Buildings and Structures)

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Air source heat pump

Unit 301: Understand the fundamental principles and requirements of environmental technology systems



Air source heat pumpsAir source heat pumps absorb heat from the outside air. This heat can used to heat radiators, under floor heating systems, or warm air convectors and hot water in your home.



Air source heat pumpsAn air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. It can get heat from the air even when the temperature is as low as -15ºC.



Air source heat pumpsHeat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the air is constantly being renewed naturally.



Heat from the air is absorbed at low temperature via an evaporator into a fluid that becomes a gas at low temperature.

How do air source heat pumps work?



This fluid then passes through a compressor where its temperature is increased so it becomes a hot gas.




The heat in the gas is transferred via the condenser to heat the heating and hot water circuits of the house.




The gas cools and becomes a liquid and is then passed through the expansion device that cools it even more. It then returns to the evaporator for the cycle to start again.




There are two main types of air source heat pump system:

• An air-to-water system distributes heat via the wet central heating system. Heat pumps work much more efficiently at a lower temperature than a standard boiler system would so they are more suitable for underfloor heating systems or larger radiators, which give out heat at lower temperatures over longer periods of time.

• An air-to-air system produces warm air which is circulated by fans to heat the home. They are unlikely to provide you with hot water as well.



• The efficiency of a heat pump is usually called its ‘Coefficient of Performance’ (COP), which is simply a ratio of heat output to energy input, both being expressed in kW. Thus a heat pump absorbing 1kW of electricity, collecting 4kW of energy from the air and delivering 5kW of heat to heating water is said to have a COP of 5:1.

• Naturally this ratio will vary according to the temperature of the water and the ambient air.

Coefficient of Performance



The heat pump is generally installed outside.

• Select a location where any potential noise disturbance is minimised.

• Provide a firm level base capable of supporting the weight of the machine. Fixing holes are generally provided for bolting the machine down to the base.

Installation location



• If wall mounting, ensure that the wall and framework are capable of supporting the machine and use anti-vibration mounts to prevent noise transmission.

• If installing in a location exposed to strong wind, do not face the air outlet of the unit against the direction of the wind as wind entering the unit may impede the normal airflow and result in a malfunction.




• Allow for the minimum clearances around the machine, as detailed in manufacturer's instructions, required for unobstructed airflow and access to service panels.

• Consider protection from extreme weather conditions with a cover or enclosure if the machine is installed externally.




• Consider fitting a protective guard where the machine could be exposed to vandalism or other damage.

• If installed in a plant room or other building, ensure that the air outlet is positioned directly adjacent to the outside wall with inlet and discharge grilles or apertures of minimum free areas as detailed in the manufacturer's instructions.

• Ensure all pipe work is adequately lagged.




• From 1 December 2011 the installation of an air source heat pump on domestic premises is considered to be permitted development, not needing an application for planning permission, provided ALL the limits and conditions listed below are met.

• These permitted development rights apply to the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within the curtilage (garden or grounds) of a house or block of flats, including on a building within that curtilage. A block of flats must consist wholly of flats (eg should not also contain commercial premises).

Planning requirements



• Typically uses between 25 and 33% of the electricity required for normal electric heating.

• Few moving parts, the fan and compressor – the mechanical maintenance required is minimal. Although the outdoor heat exchanger and fan need to be kept free of leaves and snow etc to ensure that air is freely circulated over the heat exchanger.

• All that is required is an electricity supply, there's no need for LPG or other fuel deliveries.

• It can heat either water or air for the property.

Advantages of air source heat pumps



• An air-to-air ASHP can be switched so that it will cool the property in summer.

• When correctly specified, an air-to-water ASHP can provide full central heating and domestic hot water up to 75ºC. In theory, they can operate with an external air temperature down to below -10ºC, although the efficiency does reduce as air temperatures drop.

Advantages of air source heat pumps



• Air source heat pumps require electricity for operation so they are not carbon neutral unless some form of renewable electricity generation is used.

• External space is needed to locate the outside unit. These can be noisy and possibly consideredunsightly.

• The cost of installation is high, especially, if retro fitted.

• Generally, ASHP doesn’t work very well withconventional radiator space heating systems, the lower temperature produced by most ASHP are better suited to underfloor heating, so retro fitting may require considerable work.

Disadvantages of air source heat pumps



• The outdoor unit on some systems may 'frost up’ when outdoor temperatures drop towards freezing and there is moisture in the air – this would restrict the flow of air through the unit. Some units incorporate a 'defrosting system' which reverses the ASHP to occasionally heat the coil – while this prevents it from freezing up, it does reduce the systems efficiency.

• As the efficiency of air source heat pumps falls as the air temperature falls, it may be necessary to have another source of heatingto supplement the ASHP in extremely coldtemperatures.

Disadvantages of air source heat pumps



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Date post:	11-Apr-2017
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Air source heat pumps

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