Ground source. Ground Source heat pumps (gshp) extract
heat stored in the ground. At depths of 2m and more, the ground temperature
does not deviate very much from the average summer/winter surface
temperatures (around 9 -12C in the UK depending on location). The
most practical way of extracting this energy is to bury a large amount
of pipe in the ground. This is usually laid in horizontal trenches
at 1.5 – 2m depth, but vertical bore-holes are an alternative
method giving similar results.
Water source. A river or small stream can be utilised,
and, in the past systems using copper coils in the water have been
used. Pumping river water through a heat pump is another option, and
can give very good results, but heat pump units require water at temperatures
above 5 to 8°C (varying depending on type). Whilst delivering
very high-efficiencies for much of the time, this system will fail
to operate in the middle of winter during lower temperatures- just
when you need the most heat, so a back-up heat source will be needed.
A spring is a much more stable and better heat source. Its an opportunity
not to be overlooked, offering excellent efficiencies. Acidity and
impurities in the water can sometimes make its use prohibitive Permission
should be sought from the relevant authorities as an abstraction licence
may be needed.
Air source is probably the most common type of heat
pump. The air source system however will be less effective for heating
in winter since the air temperature can become very cold. A back-up
heater in the form of a conventional electric heater is usually included
within the heat pump package. This is far more necessary for air source
systems, and usually controlled automatically.
How is the heat delivered to the building?
Heat pumps usually deliver heat in the form of hot water, as do most
conventional central-heating systems. However, to maintain a high
energy-efficiency, the emitter system should be designed so that the
water temperature is as low as possible. Ideally, a well-designed
underfloor heating system should be used. Radiators may be the only
alternative, but should be significantly larger in area than normal.
Several radiators in one room is advantageous.