IEA Heatpump Programm Annex 28





National project:


Besides the project management the Swiss contribution refers to both the development of a test procedure and a calculation method.

In Switzerland, a research focus in the field of heat pumps is the development of so-called “retrofit heat pumps” for the replacement of boilers in existing buildings. These research activities led to the development of a cascade heat pump using condensate subcooling for the domestic hot water heating (awarded as “Swiss retrofit heat pump” - SRHP). This system is now on the Swiss market by the manufacturer KWT.

As a first step, a test procedure and a calculation method for this combined operating system with cascade heat pump using condensate subcooling was developed. The results were compared to an alternate operating Siemens heat pump with DHW storage in parallel of the manufacturer Novelan.

Test procedure

The test procedure, that was developed at the former national heat pump test centre WPZ Töss is based on the existing standards EN 255-2 and EN 255-3, which cover the operation modes "single heating" and "single DHW production". For the alternate operating system these two standards are sufficient, since the heating and domestic hot water operation is independent and thus the two operation modes can be tested separately.

For the combined operation the heat pump characteristic changes significantly and testing according to these standards is not sufficient. Therefore the test procedure provides another testing sequence performed in parallel, i.e. the testing cycle for the domestic hot water according to EN 255-3 is accomplished during the operation of the heating system.

Following the black-box approach, the electrical input to the system cannot be redistributed to the two services of space heating and domestic hot water production in simultaneous operation. In alternate operating systems the heating operation is not influenced by the domestic hot water. Thus the assumption is made that this is the criterion for the redistribution as well in simultaneous operation, i.e. a deterioration or amelioration of the COP-value is entirely accounted to the domestic hot water operation. This might not be physically true, but the approach has the advantage, that the resulting COP-values are comparable to the ones of alternate operating systems. For the calculation of the seasonal performance only the total electrical energy is needed, as only the overall efficiency in combined operation is of importance. The results of the testing are the three characteristics for the respective operation modes.

Calculation method

The calculation method is based on a bin approach already used in the NTH Project of the SFOE. The bin approach uses the cumulative annual frequency of the heating degree hours vs. the outside dry bulb air temperature. The total operation interval is thereby divided into temperature classes called bins. The ratio of the bin area to the total area reflects an energetic weighting factor for the performance factor at this operation point. This bin performance factor takes into account the energy demand (for heating or DHW), the temperature conditions at the respective operation point, systems losses for cycling operation and eventually installed storages as well as additional auxiliary energies not considered during testing. By this energetic weighting of the bin performance factors the seasonal performance for the whole operation interval can be calculated.

For the different services, e.g. heating and domestic hot water, single seasonal performance factors are weighted with the respective energy amounts for the service.

For simultaneous operation, the calculation performs an energetic weighting with the seasonal performance factor for the three operation modes "single heating", "single domestic hot water", "combined heating and domestic hot water" based on the component characteristic delivered by the test procedure.

The respective energy amounts produced in combined and single operation modes are evaluated based on the running time, which is defined by the actual heat demand and the output capacity at the respective operation point. As the control system has an impact, as well, preliminary simulations to deliver the fraction of combined operation have been performed and expressed in a correction factor.


In the second step this test procedure and calculation method is to be validated and evaluated with regard to the application to other system configurations. In particular, this includes a further development to systems, which contain ventilation, too, for instance compact units for ultra low energy houses. Therefore field measurements of these systems are planned in parallel to the extension of the testing and calculation to handle air distribution system and combined space heating/cooling, DHW and ventilation.


Swiss national team IEA HPP Annex 28

Operating Agent:

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Carsten Wemhöner
Institute of Energy in Building
University of Applied Sciences Basel
St. Jakobs-Strasse 84
CH – 4132 Muttenz
Tel: +41-(0)61-467 - 4573
Fax: +41-(0)61-467 - 4543


National team leader

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Prof. Dr. Thomas Afjei
Institute of Energy in Building
University of Applied Sciences Basel
St. Jakobs-Strasse 84
CH – 4132 Muttenz
Tel: +41 - (0)61-467-4349
Fax: +41 – (0)61-467-4543


National team:

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Up to 2004
André Montani
Dreikönigstr. 18
CH – 8002 Zürich
Tel: +41-(0)1-207-5842


visit page From 2004 on
Dominique Helfenfinger
University of Applied Sciences Lucerne
Technikumstr. 21
CH – 6048 Horw
Tel: +41-(0)41-3493224

Swiss heat pump and building technology links
visit page homepage of the Swiss research programme for ambient heat
Heat pump association Switzerland
Swiss national heat pump test centre
visit page Swiss national test centre for ventilation systems
visit page Manufacturer association for heat pumps
visit page Swiss association of refrigeration
visit page Swiss association of geothermal energy
visit page Swiss association of engineers and architects - responsible for the standardisation in the field of HVAC systems
visit page Building and Renewable energy network
visit page Centre of Energy and sustainability in the building sector at EMPA

last update:22.01.2008

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