units utilize the heat in the outside air and can operate in temperatures
below –10°C. Their efficiency is much lower than that
of the Water to water as more power is consumed moving the air and
raising the temperature through a greater temperature difference.
Also a factor which is not considered in the efficiency calculation
is the energy required for defrost. In Ireland we have a damp, humid
climate. Therefore the air contains alot of moisture giving rise
to alot of ice forming on the evaporator. Unbelieveably, this is
not a problem in much colder countries where the air temperature
is sub-zero as no moisture is contained in the air. Even though
their ambient temperature is lower their heat pumps often operate
Another aspect is that
as the ambient temperature falls so too does the performance of
the unit. Therefore when you most need heat the unit produces less.
For this reason the industry considers this type of heating as by-valent
(requires back-up/assist). Many units incorporate immersions as
this back-up, this in return reduces efficiency from 350% to 100%.
Air to water units are rated to operate at 2°C and 35°C
at this temperature an efficiency of up to 350% can be expected.
The benefit is that no earth works or well boring is required for
the Air to water units, resulting in reduced capital expenditure.
An Air to water heat pump can be used for central heating, domestic
hot water or a combination of both.
We recommend using a small
air to water heat pump to suppy domestic hot water outside the winter
months and using a water to water or other ground coupled heat pump
for winter time heating.
The use of an electric
immersion can be avoided completely with energy savings of up to
75% when an air to water heat pump is utilized.