Frequently Asked Questions About Heat Pumps
Can they be installed as a retro-fit solution?
Yes, although this may be more complex if there is a need to change the original heating distribution system. It is essential to insulate the home well before installation.
Are heat pumps safe?
Yes. Unlike conventional gas and oil heating systems, there is no combustion process involved and no risks of gas or oil leaks. The refrigerant commonly used is R407C/R404A, and the HFCs used in these are acceptable for use in today’s environment.
Are heat pumps costly to buy and operate?
A heat pump is more costly to purchase than a conventional boiler, although grants are available for accredited products. An important consideration is that the operating costs are very low. Unlike the requirement for gas boilers, there are no maintenance and servicing costs associated with heat pumps.
How do heat pumps differ from boilers?
There are no gas or oil connections as they use renewable energy sources. They provide lower flow temperature water (up to 55oC generally) compared to a boiler (generally 70-82oC) and their capacity for supplying useful energy is dependent on input temperature from ground/air/water. Heat pumps are much more efficient (boiler can achieve no more than 100% efficiency) and have no compulsory annual servicing requirement.
Can heat pumps be used for cooling purposes?
Some heat pumps are available that can be used in reverse mode to provide summer cooling. The waste heat (i.e. the heat extracted in the cooling process) can be used to pre-heat domestic hot water.
How is domestic hot water delivered and what type of hot water cylinder do I need?
Domestic hot water is normally stored at 60-65oC and as the heat pumps can generally only lift temperatures to around 45-50 oC, an additional water heating element will be required. This is usually an electric heating element in the water cylinder for boost. It is normal to try to use an offpeak tariff for hot water provision by the heat pump and this can reduced the costs for boost with appropriate control. Larger coil cylinders are required for heat transfer but both direct and indirect cylinder types are suitable.
Some manufacturers supply high temperature heat pumps to satisfy total hot water demand but there will be a reduction in CoP.
As a rule of thumb, ensure 200W/person is added to the design load if the heat pump is to be used for domestic hot water production.
Should I buy an air source or a ground source heat pump?
There are advantages and disadvantages to each type of system. See the table in ‘Different Technologies’.
What size heat pump will I need? How much space is needed for the ground collector if I choose a ground source heat pump?
To calculate the approximate amount of ground collector area required, consult your installer. However, the size of heat pump and amount of space required for a horizontal ground collector (the most popular type for domestic applications) will vary depending on:
- The heat load of the building (kW).
- The amount of energy the ground conditions are able to give up.
If a borehole is being considered, then less ground space will be required – although good access is needed for the machinery.
Why do I need to insulate first?
Insulation is the most cost-effective energy efficiency measure, and should always be undertaken as a priority over any renewable technology. Undoubtedly, the fabric of a building should be optimized before installing a heat pump, by insulating walls, loft space or roof, draught proofing and installing double glazing. You cannot access the grants without improving energy efficiency, and the heat pump will probably be over-sized if improvements are made later on.