Air Source Heat Pumps (ASHP) extract 'low quality heat'
from the outside air and transfer it into a building as useful
heat - often likened to a refrigerator working in reverse.
Air Source Heat Pumps use electricity to operate but have
a relatively high efficiency. - typically they use between 25
to 33% the electricity used by a normal electric heater to
produce the same amount of heat (see below regarding
performance).
There are two types of Air Source Heat Pumps:
1.
Air to Water - where the heat extracted is used to heat
water for use within the building.
2.
Air to Air - where the heat extracted is used to heat air
for space heating within the building.
3.
An Air Source Heat Pump consists of an outdoor unit
incorporating:
•
A fan,
•
A heat exchanger, over which outside air is blown,
•
A compressor, which circulates a refrigerant to extract
the low quality heat,
•
A means of transferring the heat into the building.
The indoor unit consists of a heat exchanger where the
heat extracted by the outside unit is transferred to either
the domestic hot water system or air for circulating around
the property.
Air Source Heat Pumps
How air source heat pumps work
Essentially, air-to-water
heat pumps operate in a
similar way to fridges –
but in reverse. A fan-
powered unit is used to
extract warmth from the
outside air to provide
space heating and hot
water for the home.
“The fan blows air over a coil, which contains a working fluid
that absorbs the warmth. This is condensed using an electric
compressor to increase its temperature, before being
passed through a heat exchanger to warm water for the
central heating system,” says Brian Horne, domestic energy
expert at the Energy Saving Trust.
An appliance’s efficiency level is measured according to its
coefficient of performance (COP), which indicates the
amount of usable energy extracted from the air compared to
how much electricity is used to power the pump. For
example, a COP of five means that for every one kilowatt
(1kW) of electricity used, 5kW of heat is produced.
In addition to their excellent efficiency, ASHPs offer a raft of
other benefits. “Modern versions are very quiet and come
with energy-monitoring systems and internet-based smart
controls,” says Max Halliwell, product marketing manager for
heating at Mitsubishi Electric. “Many of the best models are
inverter-driven, which means they modulate power
consumption to suit the needs of the house at that moment.”
If installed correctly by an MCS (Microgeneration
Certification Scheme) accredited engineer, homeowners can
expect their device to deliver effective performance for
approximately 15-20 years – which compares well to boilers
and other renewable heat source options.
Advantages
•
Air Source Heating 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 (mounting the
external unit on a wall, as the illustration above,
reduces likely blockages).
•
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.
•
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 75°C. In theory, they can operate with an external
air temperature down to below -10°C, although the
efficiency. does reduce as air temperatures drop.