Air source heat pumps

Level 3 Diploma in Electrical Installations (Buildings and Structures)
© 2015 City and Guilds of London Institute. All rights reserved. 1 of 20
PowerPointpresentation
Air source heat pump
Unit 301: Understand the fundamental principles
and requirements of environmental technology
systems

Air source heat pumps
Air 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.

An 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.

Heat 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 considered
unsightly.
• The cost of installation is high, especially,
if retro fitted.
• Generally, ASHP doesn’t work very well with
conventional 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 heating
to supplement the ASHP in extremely cold
temperatures.
Disadvantages of air source heat pumps

Any questions?

Air source heat pumps

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Air source heat pumps