Evaluation of Heat Pump Operation in a Large Scale Solar Thermal System

(*) Corresponding author

Authors' affiliations

DOI's assignment:
the author of the article can submit here a request for assignment of a DOI number to this resource!
Cost of the service: euros 10,00 (for a DOI)


In the north of Graz, Austria, a large scale solar thermal system (gross collector area: 3885 m²) was installed in 2009 primarily to supply solar heat to a district heating (DH) network especially in summer and to cover part of the heat demand of the on-site buildings. In order to reduce the auxiliary heat needed for the on-site buildings and to prolong the operation time of the solar thermal system, a heat pump, which uses the solar collector loop as exclusive heat source, was installed later on. This way solar heat that is available at temperatures too low for direct solar charging of the TES (thermal energy storage) can still be used. After having performed dynamic system simulations of the installation without the heat pump in TRNSYS to validate the simulation model, the heat pump was implemented into the simulation model. Applying different control strategies to the solar heat pump system an increase of the solar fraction for the heating period (October to March) from 20.5 % without the heat pump up to 33.0 % with heat pump could be reached in the simulations. The interaction between solar thermal system and heat pump in this special configuration turned out to be challenging in terms of control optimization; hydraulic decoupling of the two units is recommended. Based on onsite measurements the performance of the system in February 2013 is evaluated
Copyright © 2013 Praise Worthy Prize - All rights reserved.


Compression Heat Pump; District Heating; Large Scale Solar Thermal System; Measurement; Simulation; Solar Heat Pump

Full Text:



S.J. Sterling and M.R. Collins. Feasibility analysis of an indirect heat pump assisted solar domestic hot water system. Applied Energy, 93(0):11 – 17, 2012.

Solar Energy Laboratory. TRNSYS 17. A Transient System Simulation Program. University of Wisconsin-Madison, 2011.

Angela Dröscher and Andreas Heinz. Implementation of a heat pump in a large scale solar thermal system. European International Journal of Science and Technology, 2(2):119 – 129, 2013.

Peter Omojaro and Cornelia Breitkopf. Direct expansion solar assisted heat pumps: A review of applications and recent research. Renewable and Sustainable Energy Reviews, 22(0):33 – 45, 2013.

Elimar Frank, Michel Haller, Sebastian Herkel, and Jörn Ruschenburg. Systematic classification of combined solar thermal and heat pump systems. In EuroSun 2010 International Conference on Solar Heating, Cooling and Buildings, Graz, Austria, 2010.

Helmut Strasser, Norbert Dorfinger, and Boris Mahler. Stadtwerk: Lehen _Solar energy in urban community in City of Salzburg, Austria. Energy Procedia, 30(0):866 – 874, 2012. 1st International Conference on Solar Heating and Cooling for Buildings and Industry (SHC 2012).

Zentralanstalt für Meteorologie und Geodynamik, 2012.

Michel Haller. TRNSYS Type 832 v3.10 „Dynamic Collector Model by Bengt Perers“. Updated Input-Output Reference. Unpublished.

H. Schranzhofer, P. Puschnig, A. Heinz, and W. Streicher. Validation of a TRNSYS simulation model for PCM energy storages and PCM wall construction elements. In Ecostock Conference 2006, 2006.

Andreas Heinz and Michel Haller. Description of TRNSYS Type 877 (v115). Unpublished.

P.D. Lund. Optimization of a community solar heating system with a heat pump and seasonal storage. Solar Energy, 33(3–4):353 – 361, 1984.

Kamil Kaygusuz. Performance of solar-assisted heat-pump systems. Applied Energy, 51(2):93–109, 1995.

S Kugle, S Green, A Haji-Sheikh, and DYS Lou. Performance of solar assisted heat pump systems in residential applications. Solar Energy, 32(2):169–178, 1984.

J.G Cervantes and E Torres-Reyes. Experiments on a solar-assisted heat pump and an exergy analysis of the system. Applied Thermal Engineering, 22(12):1289 – 1297, 2002.

Y.W. Li, R.Z. Wang, J.Y. Wu, and Y.X. Xu. Experimental performance analysis and optimization of a direct expansion solar-assisted heat pump water heater. Energy, 32(8):1361 – 1374, 2007.

Carolina Fraga, Floriane Mermoud, Pierre Hollmuller, Eric Pampaloni, and Bernard Lachal. Direct Coupling Solar and Heat Pump at Large Scale: Experimental Feedback From an Existing Plant. Energy Procedia, 30(0):590 – 600, 2012. 1st International Conference on Solar Heating and Cooling for Buildings and Industry (SHC 2012).

Michel Y. Haller and Elimar Frank. On the potential of using heat from solar thermal collectors for heat pump evaporators. In ISES Solar World Congress, Kassel, Germany, 2011.

E. Torres-Reyes, M. Picon Nunez, and J.G.de-Cervantes. Exergy analysis and optimization of a solar-assisted heat pump. Energy, 23(4):337 – 344, 1998.

Ivan Malenkovic, Sara Eicher, and Jacques Bony. Definition of main system boundaries and performance figures for reporting on SHP systems. Deliverable B1.1 of SHC Task 44. http://task44.iea-shc.org/, accessed: 2013-03-14, 2012.

Grazer Energieagentur Ges.m.b.H. Emissionsreduktion durch die Fernwärme im Großraum Graz. Technical report, 2009.

Angela Dröscher and Andreas Heinz. Prolonging the running time of a large scale solar thermal system by empolying a heat pump. In EuroSun 2012 International Conference on Solar Heating, Cooling and Buildings, Rijeka, Croatia, 2012.


  • There are currently no refbacks.

Please send any question about this web site to info@praiseworthyprize.com
Copyright © 2005-2023 Praise Worthy Prize