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WP4 - Heat pumps (Deliverable 4.1)

The full report is confidential and will not be distributed to the public. However, a brief summary of the contents are given here.

An overview on available literature material about potential breakthroughs in the field of heat pumps for combined solar and heat pump systems for residential buildings has been given and the selection of breakthroughs to be further investigated in phase 2 of the MacSheep project has been carried out.

A total number of 14 different topics have been addressed, concerning changes and improvements of single components and alternative refrigerant cycle layouts and control strategies.

Breakthroughs on the component level within the refrigerant cycle that are addressed in the report are the use of a variable speed compressor for adapting the heating capacity, optimized (microchannel and microplate) heat exchangers, optimized fans and motors for air source evaporators and electronic expansion valves.

Moving one level higher to the whole refrigerant cycle, several topics are discussed, involving alternative layouts of the cycle, alternative refrigerants and alternative control approaches. Investigated topics concerning the cycle layout are the use of vapor-injection cycles to improve the heat pump performance at high pressure ratios, the use of a desuperheater for domestic hot water (DHW) preparation, and a subcooler for DHW preheating and heat pumps with CO2 as refrigerant. Regarding the control of the cycle compressor discharge temperature control are addressed.

One important topic which has to be seen in close connection to WP5 (storage) and WP6 (Control) is the system integration of the heat pump. The performance of a combined solar and heat pump system is significantly influenced by the way how the heat pump and the other components are connected hydraulically and how they are controlled. This involves also the possibility of using two (or more) heat sources for the heat pump in such systems.

In phase 2 of the MacSheep project the breakthroughs that are considered as most promising by the project consortium will be evaluated concerning their energy savings potential and their costs.

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