One of the college buildings of the Technical Colleges at Butzbach is a low energy building, demon­strating various building construction technologies in order to reduce the thermal loads of the building. However, demand for active cooling and air-conditioning arises from high internal loads, caused through occupation and computer training courses. The building is used throughout the summer. At present, air-conditioning of the 335 m2 seminar area is performed with two supply/return air systems with heat recovery, providing the required hygienic air change rate. The supply air is moderately pre­cooled by means of ground heat exchangers. The additional solar cooling system, which is currently in the planning phase, will consist of 60 m2 vacuum tube collectors, providing driving heat for two ab­sorption chillers of 10 kW chilling capacity each (type: suninverse of the company Sonnenklima, Berlin). In this application, the collector fluid again is pure water, the collectors are supplied by Para- digma. A heat exchanger for pressure decoupling in the hot water circuit is not foreseen. In periods of high demand for air-conditioning and cooling, the concept allows for a separate operation of the chil­lers: while one operates at low chilled water temperatures for supply air cooling and dehumidification, the second chiller operates the chilled ceilings in the seminar rooms at higher chilled water tempera­tures. For this reason, 130 m2 of chilled ceilings will be installed.

The whole system will be operated in a solar autonomous cooling mode, i. e., without additional driving heat for the chiller operation from the condensing boiler of the college building. The monito­ring of the system is done by ZfS Hilden. The installation of the system is foreseen in late summer 2008. Figure 8 presents a view at the low energy building, and figure 9 shows a sketch of the solar air­conditioning system.

Supply air (2 x 1250 m3/h)

Collector Buffer vacuum tube 2 m3 60 m2

Chilled ceilings (130 m3)

Heat rejection (wet, open)

Figure 9 Simplified scheme of the solar air-conditioning system at the low-energy college building at Butzbach.
The configuration allows to operate the generators of the chillers in series: while the first one produces chilled
water for supply air dehumidification at low chilled water temperatures, the second one is thermally driven with
the return heat from the first one and produces chilled water at temperatures > 15°C for the chilled ceilings.
Consequently, the temperature difference between supply/return fluid in the solar circuit is increased.

References

[1] Hans-Martin Henning: Solar cooling and air-conditioning — thermodynamic analysis and overview about technical solutions. Proceedings of the EuroSun2006, June 27-30, 2006, Glasgow, Scotland

[2] Hans-Martin Henning, Edo Wiemken: Solar Cooling. Proceedings of the ISES Solar World Congress, September 18-21, 2007, Bejing, China

[3] Hans-Martin Henning (Editor): Solar-Assisted Air-Conditioning of Buildings — A Handbook for Planners. Published 2004 in the frame of Task 25 of the Heating & Cooling Programmes of the IEA. Revised edition 2007. Springer Wien New York, ISBN 978-3-211-73095-9

[4] Edo Wiemken: Solar cooling and air-conditioning — Programmes and projects for demonstration and technology transfer. Proceedings of the 9th International Symposium Gleisdorf Solar, September 3-5, 2008, Gleisdorf, Austria

[5] Laura Siso Miroo, Tim Selke, Anita Preisler: Market Opportunities for Solar Cooling. Results from the ROCOCO Project. Proceedings of the International Seminar Solar Air-Conditioning — Experiences and Practical Applications. June 11th, 2008, Munich, Germany

[6] Uli Jakob: Overview on Small Capacity Systems. Proceedings of the International Seminar Solar Air­Conditioning — Experiences and Practical Applications. June 11th, 2008, Munich, Germany

[7] SOLARTHERMIE 2000plus. Forderkonzept des Ministeriums fur Umwelt, Naturschutz und Reaktorsicherheit im Rahmen des Energieforschungsprogramms des Bundes. Carried out by the Project Management Organisation Julich (PtJ). www. solarthermie2000plus. de