Heatpumps have been in use for many years now and the basic principle is displayed in virtually everyone’s home, the fridge in your home basically extracts the heat from the inside the fridge and discharges it into the air on the back of the fridge.
A heatpump is designed to extract heat from the earth or water, it then passes through a plate heat exchanger where the low grade heat is transferred to the refrigerant. It then passes through a compressor and from there to condesor/heatexchanger for your heating system, the gases then pass to an expansion valve and back to the evaporator.
During this process the low grade heat extract (3 to 5°C) is increased to give a flow temperature of 35°c. the amount of heat generated can be between 4 and 5 times the amount of electricity used to power the unit. This means a CoP of between 4 and 5 ( 400 to 500% efficient).
Air Source Heatpumps
Air source heatpumps are the cheapest to install, however they have a lower CoP than ground source. Installation is simpler, however consideration should be given to nuisance noise and planning permission may be required.
Ground source heatpumps
Ground source heatpumps offer higher efficiencies than air source heatpumps, however the installation cost is higher as either ground loops or boreholes are needed and this can double the purchase cost of the installation materials.
Heatpumps are at the most efficient transferring heat from ground water, however permission from the local water authority is required prior to installing and a licence fee may be charged.
With all heatpumps the highest efficiencies are obtained by keeping the flow temperatures to the lowest level possible (normally 35°C), in the case of air source heatpumps the efficiency and output are quoted as standard at 7°C ambient temperature and 35°C flow temperature. If either the ambient temperature or the flow temperature differ from this then both the output and efficiency will be affected. It is important that the output is rated at no more than 0°C otherwise the unit may not be capable of meeting the heat demand in winter weather.
It is important for all heat pump installations that the units are correctly sized and that the installing company specifies the output of the unit and the design criteria. They should also specify whether the heat pump is the sole means of heating and hot water, or the system would be bivalent with top up from another source of energy.