1. 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

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

3. 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

4. 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

5. Simulation Setup in IDA ICE

6. 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)

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

8. 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

9. 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.

10. Thank You Very Much for Your Attention!
Fraunhofer Institute for Solar Energy Systems ISE
Jörn Ruschenburg