The integration of the heat pumps in a DC microgrid requires suitable converters, which were selected according to technical and economic constraints given by CSEM. In particular, recommendations were made for the AC/DC grid converters, the DC/DC converters for the integration with the electrical storage and the DC/DC converter for PV systems that might be available. In addition, a user interface was realised, to simplify monitoring and supervision during the installation in HYBUILD demonstration sites.
The compression heat pump to be used in the Continental system is equipped with a frequency converter. On the other hand, the Mediterranean heat pump is using a fixed speed compressor, so a separate frequency drive for the compressor has been selected and installed. On the Continental system, the heat pump developed by AIT and OCHS with the integrated RPW-HEX developed by AKG was tested in a controlled laboratory environment at AIT. The tests showed the system can handle DC supply voltages in the design range without any interruption in the operation and that the efficiency decreases with increasing DC supply voltage.
In the case of the Mediterranean heat pump, developed by DAIK and NTUA,
selected results from the preliminary tests of the heat pump before and after interventions regarding the installation of the electrical components for DC operation and of the RPW-HEX are presented. The results allowed the identification of the most suitable AC/DC converter for the compressor and the verification that the changes due to the installation of the electrical components and the RPW-HEX did not affect the operation of the compressor.
Besides, monitoring protocols for the instantaneous and seasonal performance indicators of both the heat pumps, based on real time data available from the installed sensors, were defined. Even though measuring the instantaneous COP and EER values for the Continental and the Mediterranean heat pumps respectively can be achieved through assumptions (and provided that the state of the refrigerant at the outlet of the condenser is not in the two-phase region for the continental design), using a Seasonal Performance Factor based on the measured values on the water side for both the system can directly lead to more reliable results, provided that this Factor refers to a long enough time period.
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This article’s authors and institutions:
CSEM – Nelson Koch, Pierre-Jean Alet
AIT – Klemens Marx, Tilman Barz, Johann Emhofer OCHS – Michael Wiesflecker
NTUA – Sotirios Karellas, Stratis Varvagiannis
DAIK – Nikolaos Barmparitsas
CNR – Andrea Frazzica, Valeria Palomba