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In this study, the test method EN 14825 for testing heat pumps is validated by verifying the sensitivity of the seasonal space heating energy efficiency ηs, (declared on the energy efficiency label) in relation to the nominal heating capacity Pdesign. Therefore, the two major parts of the test method, the measurement part and the calculation part, were investigated. The calculation part was subjected to a sensitivity analysis in order to identify the properties of a heat pump which have a strong influence on ηs. The analysis revealed that the energy consumption in special operating states, the duration in activemode and seasonal performance values in active-mode (SCOPon) significantly affect the sensitivity of ηs. Especially short operating times, in which the heat pump is in active-mode, lead to large changes in ηs with varying Pdesign. In addition, the range of power of Pdesign turned out to have an increasing Impact on ηs with decreasing Pdesign. For Pdesign values ≤10 kW, the sensitivity of ηs increases tremendously.
Especially the determination of the ηs for devices with short operating times in active-mode (1400 h) and low values for Pdesign (≤10 kW) cannot be reproduced anymore.
The Federal Institute for Materials Research and Testing (BAM) has developed a load-based test method (compensation method) to determine the energy efficency of heat pumps and air conditioners. The method allows for testing with unfixed compressor speed and active control of the unit. Thus, at low part loads the unit under test is allowed to cycle on-off, when the frequency of the compressor drops below its minimum threshold. Therefore, the associated efficiency losses are directly measured and correction calculations as for the current steady state tests become obsolete. In addition, the testing can be performed without the support of the manufacturer by market surveillance authorities, for instance, since no frequency and expansion valve settings are required. To prove that the compensation method is repeatable and reproducible three round robin tests have been organised by BAM.