Simulations on Solar-Assisted Heat Pump Heating Systems Jörn Ruschenburg, Sebastian Herkel, Hans-Martin Henning Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany BauSIM 2010 Vienna, 23 September 2010

Agenda Introduction on topic Simulated systems Simulated building (boundary conditions and implementation) General results Results on “Direct evaporation” Conclusions & Outlook

like system III, but PCM buffer Simulated Systems System III System I no direct evaporation System IV: like system III, but PCM buffer System II

Boundary Conditions System: Flat plate collector with 6 m², tilted 40 °, oriented towards south Tank volume: 700 L for combistorage, 300 L for low-temperature buffer Air-source heat pump with 8 kW heating power Building: Single-family house with 140 m² living space, derived from IEA SHC Task 32 Location: Würzburg, Germany, weather data “Test Reference Year 13” Heating demand: 8400 kWh/a, equivalent to 60 kWh/m²a DHW consumption: 2480 kWh/a, equivalent to 17.7 kWh/m²a DHW storage temperature: 55±0.5 °C

Simulation Setup in IDA ICE

First Results System I Reference II Direct Solar III Solar Source IV Solar Source + PCM SPFSystem 2.73 3.15 3.19 3.21 Large benefit in system efficiency between I and II  direct solar Smaller benefits towards III and IV  weekly designed control, under-sized collector (6 m²)

Annual Energy Balances for System III direct solar benefits (DHW + heating) negligible benefits by solar source

Results on “Direct Evaporation” System I Reference II Direct Solar III Solar Source IV Solar Source + PCM SPFSystem 2.73 3.15 3.09 3.12 Results for I and II remain unchanged  direct evaporation applies Decreasing efficiency between II and III  direct evaporation is not applied for III and IV, instead an additional heat exchanger for brine loop is required, benefits by solar source are too low to compensate

Conclusions & Outlook The interaction of solar collector and heat pump requires both competent sizing and sophisticated control algorithms. This applies especially to systems with solar source (and PCM buffer). The top priority of solar contribution lies on DHW heating. Direct evaporation can hardly be applied for solar sources. The extra brine loop causes a small but relevant drop in source temperature and efficiency. Idea: Direct evaporation not only within ambient air unit, but also within low-temperature buffer storage? Outlook: A comparative study showing the potential of the combination will follow next year, including suitable sizing and control strategies.

Thank You Very Much for Your Attention! Fraunhofer Institute for Solar Energy Systems ISE Jörn Ruschenburg www.ise.fraunhofer.de joern.ruschenburg@ise.fraunhofer.de