Performance test methods and the ecological assessment of combined solar thermal and heat pump systems

Brief description

At the Institute for Thermodynamics and Thermal Engineering (ITW), University of Stuttgart (Germany) a new project called WPSol had been started. The project was related to the development of performance test methods and the ecological assessment of combined solar thermal and heat pump systems used for domestic hot water preparation and space heating.

In order to be able to describe the energetic efficiency and the environmental impact of combined systems using solar thermal and heat pumps in an objective manner, it was necessary to have available corresponding test and assessment procedures, among others for the characterisation of the thermal performance of heat pumps under dynamic conditions. Such performance assessment procedures were not yet common standard, similar to standardised planning and simulation tools for the complete solar and heat pump installations, which were still lacking, also.

Therefore, the main aims of the project WPSol were the development of techniques for the assessment of the efficiency of combined solar heat pump systems for domestic hot water preparation and space heating, and the development and validation of a simulation program for such systems, respectively.

Test bench for heat pumps
Test bench for heat pumps

With regard to the development of dynamic performance assessment procedures and corresponding mathematical models, detailed measurements of different heat pumps under dynamic conditions were planned. During this process specific characteristic parameters for the heat pumps were determined, which in combination with the corresponding numeric models allowed for a detailed description of the heat pump’s thermal behaviour.

A subsequent validation of this assessment procedure on the basis of in-situ measurements of several solar and heat pump systems of different types installed in single-family houses was carried out, as well. All system simulations were carried out mainly by means of the software TRNSYS. Furthermore, the development of a procedure which allows an integral primary energetic and ecological description of the solar and heat pump systems by means of life cycle assessments (LCA) was also undertaken during the course of the WPSol project.



Project duration

09/2010 - 08/2015


Project partners

  • General Solar Systems GmbH (Sonnenkraft)
  • Prometall-Fertigungstechnik
  • Schüco International KG
  • Viessmann Wärmepumpen GmbH



 Das Projekt "WPSol" wurde durch das Bundesministerium für Wirtschaft und Energie (BMWi), aufgrund eines Beschlusses des Deutschen Bundestages durch den Projektträger Jülich unter dem Förderkennzeichen 0325967A gefördert. Die Autorinnen und Autoren danken für die Unterstützung und übernehmen die Verantwortung für den Inhalt dieser Veröffentlichung.


This image shows Dr.-Ing. Harald Drück

Dr.-Ing. Harald Drück


Research Coordinator and Team Lead

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