30 May 2005

PERFORMANCE AUDITS OF HEAT PUMPS— PROCEDURES AND UNCERTAINTIES


Heat pumps are used for climate control of buildings and processes. Experience indicates that their
real-world efficiency often is considerably below the theoretical potential. This has been noted by the
European Union and hence the Directive on Energy Performance of Buildings includes the status of airconditioning
and heating systems.
Performance audits can detect deviations and indicate ways of upgrading the performance. A survey
indicates a shortage of proven, cost-effective methods but a Nordic work has resulted in two in situ test
methods. One is based on traditional external measurements of energy inputs and outputs. The other relies
on internal measurements of temperatures and pressures inside the refrigerant system. Both methods
include requirements on accuracy and stability and methods to compare stated performance with
measured data.
The internal measuring principle has been validated by means of laboratory measurements and
sensitivity analysis. Deviations between the internal and external methods were typically less than 5 %.
One particular advantage of the internal principle is the possibility to disclose a deviation from expected
performance and simultaneously provide information regarding the cause.