Heat pumps 2 Specification
The principles of heat pump technology using ground, air or water sources (provided by ENER-G)
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‘When I’m running through a specification or
set of drawings, this pops up time and time again. We then advise that there needs to be a technical change to the system to allow it to operate effectively. To me, the fundamentals need to be better understood by designers.’ Nonetheless, he says, heat pumps are less scary than
they are often perceived to be: ‘When I work through the design process with designers, the unknowns become very clear in terms of how they should design their heating systems – operating requirements, flow rates, temperature drops, how they should control the heat pumps, and so on – and they start asking what all the fuss was about. ‘The heat pump simply delivers heating or cooling
into the building. If it is a refurbishment, it is likely that the thermal properties of the building will be improved by better glazing and better insulation which brings the heating requirements of the building down. ‘As a result, if there are available soft areas in which
boreholes or horizontal trenches can be incorporated, then ground-source heat pump systems become more viable. If not, there is the air-source option.’
Ground or air? Heat pumps have started to make significant inroads into the heat-generation sector, according to Terry Seward, commercial manager of trade organisation FETA, which includes the Heat Pump Association among its members. ‘The domestic market is growing rapidly and will be predominantly either air-to-water or ground-to-water,’ Seward says. ‘Market research
42 CIBSE Journal August 2010
suggests that air-to-water will be dominant and that is what we are seeing today.’ The choice between a ground-source heat pump (GSHP) and an air-source heat pump (ASHP) will be made on capital cost, running cost and practicability grounds, says Tony Barnes, sales director at Calorex. GSHP installations are more expensive because of the need for the ground heat collector. However, they are more efficient than ASHPs. As provision
The fundamentals of heat pumps
need to be better understood by designers – Lee Marshall
for heat collectors can be made at the initial design and construction stage, it is often easier to install GSHPs in new buildings than it is to retrofit them to existing buildings. ‘With existing buildings, an ASHP will often be
installed in conjunction with an existing fossil fuel boiler and be sized to supply maybe 85% of the total heat demand. Most of the running cost and carbon savings can be realised for a relatively low capital cost, and the existing boiler will help meet the heating demand in exceptionally cold conditions or when a rapid increase in temperature is required.’ Dimplex has witnessed large air-source heat pumps
(particularly 30-40kW plus) becoming popular in the commercial sector. Davis says: ‘Large air-source units are now available that can be just as efficient as
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