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Task 26

Publications / Outcomes

Outcomes of Task 26

Task 26 is completed

By Operating Agent Werner Weiss, AEE INTEC, Arbeitsgemeinschaft ERNEUERBARE ENERGIE, Institute for Sustainable Technologies, Feldgasse 19, 8200 Gleisdorf, Austria.

Since the beginning of the eighties, the rate of growth in the use of solar collectors for domestic hot water preparation has shown that solar heating systems are both mature and technically reliable. But for several years solar thermal systems have seemed to be essentially restricted to this application.

From 1990 and further, the industry offered more and more solar combisystems, but basic scientific knowledge was missing in certain areas and methods. The designs resulted mainly from field experiences and they had not been carefully optimised. A first international survey in 1997 revealed more than 20 different designs that did not necessarily reflect local climate and local practice only. Collaborative work in analysing and optimising combisystems was seen as a proactive action that could favour good systems on a more global market than the national one.

Common definitions of terms were also missing and standardised test procedures were not available for this type of system. This means that it was difficult to determine a meaningful performance rating and even more difficult to compare the systems. For domestic hot water systems, a great effort has been made in IEA SH&C Task 14 to assess and compare performances of different designs. For solar combisystems, the question of finding a "best" solution in a given situation had no answer in 1997. Therefore, international co-operation was needed to analyse and review more designs and ideas than one sole country could cover. It was felt that an IEA activity was the best way to deal with solar combisystems in a scientific and co-ordinated way. Considering that, the Solar Heating and Cooling Programme of the International Energy Agency (IEA) launched in 1998 Task 26 called “Solar Combisystems”.

From autumn 1998 to December 2002, 35 experts from nine European countries and the USA and 16 solar industries have been working together to further develop and optimise solar combisystems for detached single-family houses, groups of single-family houses and multi-family houses. Furthermore, standardised classification and evaluation processes and design tools were developed for these systems. Proposals for the international standardisation of combisystem test procedures were another major outcome of Task 26.

To achieve the objectives of the Task, the participants carried out the research and devel­opment in the framework of the following three Subtasks:

  • Subtask A: Solar Combisystems Survey and Dissemination of Task Results. Lead Country : Switzerland, represented by Jean-Marc Suter, Suter Consulting, Berne
  • Subtask B: Development of Performance Test Methods and Numerical Models for Combisystems and their Components. Lead Country: The Nether­lands, represented by Huib Visser, TNO, Delft
  • Subtask C: Optimisation of Combisystems for the Market. Lead Country: Austria, represented by Wolfgang Streicher, Graz University of Technology, Graz

The further development and optimisation of systems and their designs by the Task 26’s participants resulted in innovative systems with better performance-cost ratings. Besides, architectural integration of the collector arrays together with durability and reliability of solar combisystems were investigated. This should lead to greater confidence of the end user in this technology. Solar industry and builders were involved in all activities in order to accelerate dissemination of results as broad as possible.

In summary, Task 26 produced the following:

  • The coloured booklet “Solar Combisystems in Austria, Denmark, Finland, France, Germany, Sweden, Switzerland, the Netherlands and the USA – Overview 2000”
  • The book “Solar Heating Systems for Houses – A Design Handbook for Solar Combisystems”
  • 19 technical reports
  • Proceedings of six industry workshops
  • Three Industry Newsletters
  • Test facilities in five European countries

With the exception of the test facilities and the book “Solar Heating Systems for Houses – A Design Handbook for Solar Combisystems” which will be published by James & James in July or August 2003 all documents can be downloaded from the web site of the IEA Solar Heating and Cooling Programme under Publication section.


The coloured booklet “Solar Combisystems in Austria, Denmark, Finland, France, Germany, Sweden, Switzerland, the Netherlands and the USA – Overview 2000”

The coloured brochure gives an overview of relevant existing and new solar combisystem designs in Austria, Denmark, Finland, France, Germany, Sweden, Switzerland and The Netherlands. The brochure is targeted at architects, engineers, HVAC companies and buyers of solar installations.

The brochure only presents those generic systems, which have already proved their worth several times in the practice in various realisations. The different system concepts can partly be put down to the different conditions prevailing in the individual countries.

> View the brochure


Solar Heating Systems for Houses – A Design Handbook for Solar Combisystems

The book summarises all results of Task 26. In 13 chapters, it focuses on heat demand of buildings, different system designs and built examples, building-related aspects like space requirements of the systems and architectural integration of collector arrays, performance as well as durability and reliability of solar combisystems, and last but not least, dimensioning and testing of solar combisystems.

This book can be ordered from:
James and James (Science Publishers) Ltd.
8-12 Camden High Street
London NW1 0JH, UK


Technical Reports

Technical reports document some specific results and findings of Task 26 and provide details and background information on the topic presented.

Technical Reports of Subtask A

  1. Validation and background information on the FSC procedure
  2. Stagnation behaviour of solar thermal systems
  3. A calculation model for assessment of reliability in Solar Combisystems
  4. Solar Combisystems - Changes on the market since Task beginning
  5. Library of references on Solar Combisystems

Technical Reports of Subtask B

  1. European test facilities for solar combisystems and heat stores
  2. Hot water performance of solar combistores
  3. Direct characterisation test procedure for Solar Combisystems
  4. Combitest – Initial Development of the AC/DC Test Method
  5. Development of the Direct Characterisation test procedure for solar combisystems
  6. The Concise Cycle Test Method - a Twelve Day System Test
  7. Validation of the CTSS Test Procedure by in-situ measurements
  8. Performance Testing of Solar Combisystems - Comparison of the CTSS with the ACDC Procedure
  9. A Solar Collector Model for TRNSYS Simulation and System Testing
  10. Research into average meteorological conditions

Technical Reports of Subtask C

  1. Report on Solar Combisystems modelled in Task 26 (system description, modelling, sensitivity, optimisation)
  2. Analysis of System Reports of Task 26 for Sensitivity of Parameters
  3. Elements and Examples of “Dream Systems” of Solar Combisystems
  4. Material Demand and Accumulated Energy Expense of Solar Combisystems


Proceedings of Industry Workshops

The addressed topics of industry workshops are presented in the following.

Oslo, Norway, April 8, 2002 (5.034 kb)

  • Solar combisystems for a sustainable energy future
  • Solar energy - a political issue?
  • Solar energy in the Norwegian energy policy
  • Combination of solar and natural gas in Dutch products
  • Solar heating with a storage-integrated condensing gas burner
  • Influence of different combistore concepts on the overall system performance
  • Facade- integrated collectors - constructions, building physics and the results of two monitored systems
  • Architectural integration of solar energy
  • The Norwegian solar energy industry

Rapperswil, Switzerland, October 10, 2001 (2.313 kb)

  • European market on thermal solar energy with a special focus on solar combisystems
  • Solar combisystems - a system overview
  • Dimensioning of solar combisystems
  • Architectural integration of solar collectors, visual aspects
  • Roof- integrated collectors, S.E.T. Solar-Roof, a single finished compact unit
  • Integration of solar collectors into facades
  • Facade- integrated collectors - constructions, building physics and results of two monitored systems
  • Stagnation behaviour: the influence of the hydraulics on thermal stress of the components including the heat transfer fluid
  • Long-term stability of heat transfer fluids, experience of the producers
  • Use of glycol-water mixtures in solar systems from the point of view of the manufacturer

Delft, the Netherlands, April 2, 2001 (2.263 kb)

  • European market on thermal solar energy with a special focus on solar combisystems
  • Solar combisystems - a system overview
  • A new generation of solar combisystems ATAGtag S-HR Solargascombi II
  • Daalderop solar systems for domestic appliance: monosolar and multisolar
  • Thermera® heat transfer fluid - a natural solution for heat transfer in building technology
  • Drain back in small systems
  • Recent experiences with large solar thermal systems in the Netherlands
  • Legionella in hot water preparation
  • Legionella and solar domestic hot water systems
  • Roof integration of large collector areas - experiences from Norway
  • Facade integration - a new and promising opportunity for thermal solar collectors

Espoo, Finland, October 9, 2000 (2.532 kb)

  • The solar thermal market in Finland and future plans
  • Solar combisystems - scope and goals of Task 26
  • Durability and reliability of solar combisystems
  • The Ekoviikki-large scale solar project: project overview and general system design
  • Multi-family houses with solar system and district heating connection
  • Multi-family houses with solar and geothermal heating system
  • Monitoring results of a Swiss 30 m² system with 11 m³ storage tank
  • Solar combisystem for a multi-apartment building - the Klosterenga project in Oslo
  • System design and monitoring results of Austrian large scale solar combisystems for multiple family houses and office buildings
  • Wagner office building: first experiences and measurements
  • Performance of an air-based solar thermal system after twenty years of operation
  • Space heating and DHW system with standard tank
  • Modular heat exchange module for solar heating systems
  • Solus II storage tanks

Borlänge, Sweden, April 3, 2000 (685 kb)

  • Tests on the stagnation behaviour of solar combisystems
  • The behaviour of heat transfer media in solar active thermal systems in view of the stagnation conditions
  • Emissions from small biomass boilers
  • Solar combisystem with integrated pellet burner in store
  • Study of combined solar and biomass heating systems in Denmark
  • Solar heating system for a new single-family house

Stuttgart, Germany, October 4, 1999 (375 kb)

  • The Austrian solar thermal market
  • Market development in Denmark since 1990
  • Finnish solar collector market development 1995-1998
  • Solar market in France
  • Current status in Sweden (1999)
  • Solar market in Switzerland 1990-1998
  • Thermal solar energy in the Netherlands in 1999
  • Solar market in the USA - 1998
  • European product standards for solar domestic hot water systems reaching maturity
  • Future solar thermal pump strategy
  • Innovative pump developments in Switzerland
  • Field tests of high efficiency small circulation pump
  • Life cycle analyses of solar heating systems


Design Tool for Combisystems "CombiSun"

Design Tool for Combisystems "CombiSun" is a design tool for architects and engineers to compare solar combisystems and properly size according to specific requirements for use. Data from the Task work has been used to characterize some 10 generic systems. The characteristic functions obtained for each of these systems provided the main background information for CombiSun. The programme can be downloaded from the following web site http://www.elle-kilde.dk/altener-combi/dwload.html


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