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Calculation method for the seasonal performance of heat pump compact units and validation

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For the heating of low energy houses according to the MINERGIE® or MINERGIE-P® Standard with significantly reduced heat energy needs heat pump compact units have been developed in the recent years, which combined the functions space heating, domestic hot water and ventilation in one unit. To assess the overall performance, the seasonal performance factor (SPF) has to be calculated by a standardised method. The SPF is one basic number for the buildings energy certificate, as it is introduced in EU member countries based on the EU Building Energy Performance Directive (EPBD). In this project charged by the Swiss Federal Office of Energy (SFOE) a test procedure has been elaborated at the University of Technics and Architecture HTA Luzern in order to deliver the required component characteristic for the calculation of the SPF by test rig measurements. The test procedure is based on European standards and test methods of the German Passive House Institute and the German Institute of Building Technologies DIBt. The Institut of Energy in Building of the University of Applied Sciences Northwestern Switzerland (up to 31.12.2005: FHBB, Institute of Energy) developed a calculation method based on temperature classes („bin method“) for the calculation of the SPF of combined heat pump systems for space heating and domestic hot water (DHW). In the frame of the EPBD the method has been implemented in the European draft standard prEN 15316-4.2, which will soon be sent out to formal vote. In this project the method has been extended to compact units. In order to gather experience with the real behaviour of pilot plants detailed field monitoring of two compact units has been performed. One pilot plant is installed in a single family house according to the MINERGIE® standard in Gelterkinden (canton Baselland, CH), using a compact unit designed for heat loads of MINERGIE® houses with hydronic distribution by a floor heating system. The other pilot plant is a single family house in Zeiningen (canton Aargau, CH) according to MINERGIE-P® with a compact unit designed for ultra-low energy houses. The compact unit is originally designed for air heating distribution, but has been modified to a prototype application with hydronic heat emission by thermally-activated building structures for this project. The pilot plant in Gelterkinden delivered the results that in wintertime, 78% of the electrical energy is used by the heat pump, 5% by the electrical back-up heating and 17% for auxiliaries including the ventilation fans and circulation pump of the heating system. The resulting overall SPF-HP of the heat pump is 3.8, while the SPF-S of the system related to the energy need of the space heating and DHW distribution varied between 2.4 in summertime and 3.1 in wintertime at a measurement uncertainty of 4 - 7%. Calculated values correspond to the field monitoring in the range of ±6% and thereby are in the range of the exactness of the field monitoring on the one hand and the component characteristics on the other hand. Most important impact on the SPF is the source and sink temperature level, since the heat pump is the core component of the system. The field monitoring of the pilot plant in Zeiningen yielded, that in wintertime 36% of the electrical energy was used by the heat pump, 47% by the electrical back-up heater and 17% by auxiliary components. The SPF-HP of the heat pump was 2.8 while the SPF-S of the overall system is 1.8 due to the higher fraction of electrical back-up energy. Reasons for the higher back-up energy use was the low heating capacity of the heat pump of 1.5 kW related to a building design heat load of 2.5 kW.