Evaluation of a field test with retrofit heat pumps

The efficiency of electrically driven compression heat pumps for existing dwellings has been evaluated with the help of data from a field test of E.ON Energie AG, conducted through the Fraunhofer Institute for Solar Energy Systems in Freiburg. The data has been verified and grouped to allow for a detailed analysis. This analysis of the heat pump field test shows that evaluable data exist for 43 out of 77 field test objects. Of these 43 objects, 21 are air-to-water heat pumps, 17 are brine-to-water heat pumps with horizontal ground source heat exchangers, and 5 are brine-to-water heat pumps with vertical ground source heat exchangers. A mean seasonal performance factor of 2.3 for air-coupled devices and 2.9 for ground-coupled devices shows that applying heat pumps (installed 2007) of various manufacturers in existing buildings is questionable with respect to primary energy savings and CO2 emissions. Therefore, the performance data of heat pumps is compared to condensing boilers with a fuel utilization efficiency of 0.96. Different fuel utilization efficiencies are calculated, as well as different primary energy and emission conversion factors. The best systems achieved seasonal performance factors of 3.0 (air) and 4.0 (ground-coupled). The great difference to the mean values illustrates the high potential of this technology on the one hand and the necessity to optimize the total system on the other.