IEA HPP Annex 32: Economical heating and cooling systems for low energy houses

In the last decades, the heating energy demand for new buildings in residential areas had been reduced continuously through technical innovation and improved standards of insulation, while the risk of overheating during the summer months was rising simultaneously due to an increasing share of glass usage in architecture and increasing internal heat loads.

Therefore efficient cooling technologies for buildings improved in importance. Innovative heat pump systems offer the opportunity to combine functions for heating, cooling and domestic hot water production in one device. In the course of the IEA HPP ANNEX 32 project, these heat pump systems were tested under real condition in order to evaluate their efficiency.

The participation of AIT at IEA HPP Annex 32 was limited to task 3 - “Field monitoring of integrated heat pump systems”. The main content of this work package was: configuration of an adequate monitoring concept, operation test of the chosen systems and measuring equipment, summary and comparison of the results. Therefore nine conventional heat pump systems and two compact units, which were situated in Upper-, Lower Austria and Styria, had been analyzed. The logged monitoring data of these units had been evaluated and the seasonal performance factor (SPF) was set as the main rating criteria. This offered the opportunity for a general efficiency rating of the different heat pump systems. The analysis of the conventional systems has shown that the SPF of the ground coupled units is above 4, whereas the SPF of the air-systems is above 3.

These results are, considering the different system boundaries, similar to those shown in the Swiss FAWA study (Bundesamt für Energie: Feldanalyse vom Wärmepumpenanlagen FAWA 1996-2003, Schlussbericht April 2004) and the German “efficiency” heat pump study (Renewable energy world: Heat pumps in action, page 74-78, September - October 2009) undertaken by ISE Fraunhofer.

The main difference to the German and Swiss units observed is the system configuration. These countries favour the usage of heating puffer tanks, while in Austria ground coupled systems are directly integrated into the heat sink. Consequently, the screed of the floor heating can be used as thermal mass of the whole heating system. This configuration is only viable, if the storage mass of the building is huge enough, in order to meet the specified manufacturer’s minimum period of performance. Hence, for the calculation of the SPF the buffer tank pump and the storage losses can be neglected.

However, the Austrian air-to-water units are all designed with heating buffer tanks. The analysis of indoor and outdoor temperature of these conventional systems has shown that the cooling demand was non existent. This was caused by the fact, that these buildings had no south- or west- orientated glass areas. The concept of the compact units with the collector laid in the working space of the building, pre-heating of ambient air by the heat pump and additional regeneration of heat source by passive cooling causes a SPF between 4.1 and 4.3.

These results are similar to those of the conventional ground coupled systems. Furthermore the SPF for domestic hot water production reaches values up to 3.7, caused by a higher heat source temperature generated by passive cooling. The energy demand of future buildings will lessen more and more and the passive house standard will spread.

This development will be reinforced by EU (Richtlinie zur Gesamteffizienz von Gebäuden, 2009) legislation aiming at zero-energy buildings by 2018 and 2020 respectively. Especially for these kinds of buildings the demand for compact units will rise. The optimal operating of these compact units needs a better cooperation between the various lots, because the facilities themselves influence the system configuration and the system efficiency significantly.

Project management

Ao.Univ.-Prof. René Rieberer
Technische Universität Graz, Institut für Wärmetechnik
Inffeldgasse 25/B
8010 Graz

DI (FH) Andreas Zottl
Energy Department
Sustainable Thermal Energy Systems
AIT Austrian Institute of Technology
Österreichisches Forschungs- und Prüfzentrum Arsenal Ges.m.b.H
Giefinggasse 2
1210 Wien

Project collaborators

Technische Universität Graz, Institut für Wärmetechnik:

• Dr. Andreas Heinz
• Stefan Bernhard (Sept. 2007 - Jan. 2008)
• Julien Lequenne (Mar. 2008 - Aug. 2008)
• Patrick Hauser (Sept. 2008 - Sept. 2009)
• Dr. Klaus Martin (Nov. 2008 - Feb. 2009)

AIT Austrian Institute of Technology:

• Ing. Heinrich Huber, MSc
• DI (FH) Johannes Schnitzer
• Ing. Wolfgang Leitzinger