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Solar heat pump systems for heating applications: Analysis of system performance and possible solutions for improving system performance.

Author(s) : POPPI S.

Type of monograph: Doctoral thesis

Summary

Solar heat pump systems (SHPs) are systems that combine solar energy and heat pumps. Solar thermal systems can be used for delivering thermal heat directly to the system loads and/or as source for the heat pump, while solar photovoltaic systems provide electricity to the system.
In this thesis, solar thermal and photovoltaic systems combined with heat pumps for heating applications are treated. Moreover, a specific focus is given to solar thermal systems in “parallel” configuration with heat pumps, so called when solar thermal is used directly for covering heat loads of the system.
The overall aims of the thesis are to: a) investigate techno-economics of solar systems, both thermal and photovoltaic, in combination with heat pump systems; and b) investigate possible solutions for improving system performance of a reference solar thermal and heat pump system for residential heating applications. In this thesis, a systematic approach is presented and used for analyzing system improvements in the reference system. The effect of the system improvements on system performance of the reference system was evaluated by means of system simulations.
Techno-economics of SHPs are investigated in the first part of the thesis. An economic comparison, based on the available literature of systems for residential heating applications, showed that there are clear trends for decreasing payback times of SHPs with increasing solar resource and with decreasing heating degree-days; however results for photovoltaic heat pumps may vary significantly according to metering policies in place. Simulation results of the reference solar thermal and heat pump system in two central European climates confirmed the general trend of variation in payback with increasing solar resource. Furthermore, it was shown that payback time of the reference solar thermal system becomes significantly longer by increasing the collector area.
Cost-effective solutions for improving system performance of the reference solar thermal and heat pump system are investigated in the second part of the thesis. As cost-effectiveness depends significantly on boundary conditions (climates and building heat loads) as well as on assumptions concerning costs, general conclusions were difficult to derive.
For the chosen boundary conditions (Carcassonne and Zurich climates as well as two house standards with specific heat demand that varies from 23 to 123 kWh/m2·year in the two climates), the configuration with the “four pipe” connection showed potential for being more cost-effective for the system that works with relatively low temperature (35/30 °C) in the heating distribution system (floor heating) than the system with radiators (55/45 °C). Heat pump with vapor injection cycle was shown to be interesting, especially for delivering heat at high temperatures for hot water preparation and in the heat distribution system. The use of variable speed compressor was shown not to be always economically justifiable. Despite that, this technology is very common and represents state of the art for systems with air source heat pumps.
Finally, the thesis ends with a cost-effectiveness analysis of a novel solar thermal and heat pump system. The system was designed for the house building with higher demand for space heating (123 kWh/m2·year) and with a heating distribution system with radiators, and in the Zurich climate. For the given boundary conditions, the novel system had 14% (relative change) higher seasonal performance compared to the reference system, and used much less electricity (>1230 kWh/year less).
Results of the cost-effectiveness analysis showed small cost benefits (expressed in terms of “additional investment limit”) for the novel system compared to the reference system. As the novel system is much more complex than the reference system, it is very difficult for the novel system to be more cost-effective than the reference system for the given economic boundary conditions.

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Pages: 111

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Details

  • Original title: Solar heat pump systems for heating applications: Analysis of system performance and possible solutions for improving system performance.
  • Record ID : 30022666
  • Languages: English
  • Publication: KTH (Royal Institute of Technology), Department of Energy Technology - Sweden/Sweden
  • Publication date: 2017/10/09

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