A. Schenke, D. Mangold
Solar — und Warmetechnik Stuttgart (SWT)

— ein Forschungsinstitut der Steinbeis-Stiftung
Pfaffenwaldring 10, D-70550 Stuttgart; Email: schenke@swt-stuttgart. de
Tel: +49-(0)711-685-3896, Fax: +49-(0)711-685-3242

R. Croy, F. A. Peuser
ZFS — Rationelle Energietechnik GmbH
Verbindungsstr. 19 40723 Hilden

J. Scheuren, W. Eisenmann

Institut fur Solarenergieforschung GmbH Hameln/Emmerthal (ISFH)

Am Ohrberg 1 31860 Emmerthal

T. Siems, M. Rommel

Fraunhofer Institut fur Solare Energiesysteme (ISE)

Heidenhofstr. 2 79110 Freiburg

In the past German R+D-programme “Solarthermie-2000” large thermal solar systems for tap water heating have been investigated and basic principles for planning and dimensioning developed. In the following programme “Solarthermie2000plus” the same will be done for large thermal solar systems for both tap water and room heating (so called combi-systems) with at least 100 m2 collector area. Similar investigations have been done for combi-systems in one — family houses. However, large combi-systems differ from these small systems in respect of construction of the solar collector field, the heat stores, the heat exchangers and the connection to the conventional heating technique. The few existing large thermal solar combi-systems in Germany differ very much from each other which shows a great uncertainty of how to design such systems. Therefore it is necessary to develop guidelines for planning and dimensioning of this system technology as well as to further establish this technology on the market. The project is split up in three tasks shared between four partners. In this paper the partners and their tasks are presented.

1. Aims of the Project

In the past, large thermal solar systems were mainly used for tap water heating. In recent years there is a tendency to use this technique for both tap water and room heating. With these systems higher solar fractions of the total annual heat demand of buildings can be achieved. In the range of small thermal solar systems with collector areas of up to 20 m2 combi-systems add up to 20 % of the total thermal solar market. There already is a large range of complete products which can easily be installed and which provide reliable results. However, in small systems the variation of system configurations does not strongly affect the solar fraction and specific solar heat costs [1].

This is different in the range of large thermal solar systems with at least 100 m2 of solar collectors. In the German R+D-programme Solarthermie-2000 large thermal solar systems (collector area > 100 m2) for tap water heating were investigated [2]. Finally the technical standard was implemented in technical rules [3]. For solar systems for tap water and room heating no such rules exist. As these systems are mainly built in public buildings (such as hospitals or schools,…) or in housing areas of public building promoters, their profitability is a very important factor. Variation of system configuration leads to very different results. Thus the large solar combi-systems must be designed at optimal cost in respect of investment and operation. The necessary service should be as low as possible.

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Existing large thermal solar combi-systems (about 20 in Germany) are very diverse in design, regarding the solar collector field, the heat stores, the heat exchangers and the connection to the conventional heating technique. There are no sufficiently documented operating results of these systems. That is why no reliable propositions can be given for designing new systems. This research project aims at the implementation of recommendations and technical rules for the design of large thermal solar combi-systems. Therefore six existing solar combi-systems will be investigated over a period of two years. With the help of simulations in TRNSYS [4] based on the measured data the advantages and disadvantages of the different systems will be identified. Economically advantageous improvements will be carried out. Special studies on the stagnation effects of single collectors and collector fields in the existing systems and on test stands will be done to give recommendations on how to reduce stagnation in solar collectors. The joint research project began in October 2003 and will be running for 2 ЛА years.