CPD Programme
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Design of air source heat pump
systems for heating and hot water
The UK has a challenging and legally binding target of generating 15 per
cent of its energy from renewables by 2020. The government’s Renewable
Energy Strategy has recognised the potential of commercial buildings
to contribute to this shift, and the potential for air source heat pumps is
starting to be recognised. In December 2008, the European parliament
adopted an EU directive on the Promotion of Renewable Energy Sources,
which expanded its definition of renewable energy sources to include air
and water source heat pumps, in addition to ground source heat pumps.
Now all three technologies are being promoted as part of EU policy to get
member states to increase their use of renewable energies and this ruling
will make its way into UK legislation in 2010.
Coefficient of performance (incl. power input to pump)
T
his CPD article examines some air source heat pumps producing hot water.
6
practical issues in selecting and The efficiency is principally a function of the
35C
5
applying air to water heat pumps. heat pump’s operating temperatures, the
50C
4
For an introduction it would be useful evaporating and condensing temperatures
3
to refer back to the May 2009 CPD article, and these will be a function of the air intake
2
where the basic operating principles of a temperature and the hot water temperature
1
heat pump are described, with its related required. As far as wanting to improve
0
performance characteristics. Note that efficiency is concerned, if the evaporating
-20 -10 0 10 20 30 40
Ambient air temperature(deg C)
efficiency of a heat pump is defined using the temperature could be raised by 1K and the
Coefficient of Performance(COPh) (heating) condensing temperature reduced by 1K,
Figure 1 Performance of Air-Water heat pump for hot
water temperatures of 35C and 50C
or Energy Efficiency Ratio(EER) (cooling). performance of the system will increase
COP
h
= Useful Heating Capacity (kW)/ quite considerably, by between 4 and 8 per capacity range 3 to 15kW. Once the air and
Power Input to drive the system (kW) cent. Figure 1 shows the variation in COP
h
water temperatures are fixed, improvement
Values between 2 and 5 are attainable for for a typical air-to-water heat pump in the in efficiency is achieved by heat exchanger >
www.cibsejournal.com February 2010 CIBSE Journal 63
CIBSEfeb10 pp63-66 cpd.indd 63 1/29/10 2:36:55 PM
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