Chamber of Commerce ‘Südlicher Oberrhein’ (IHK-SO) in Freiburg, Germany

Description of the application

A seminar room and a cafeteria area of the building, often used as seminar room as well, are connected to a deseccant evaporative cooling system for air-conditioning of these areas. Although passive measures like external shading, high quality glazing etc. have been applied to prevent high solar gains, the large glazing fraction of the rooms requires for active cooling. During cooling and dehumidification use in summer, the system is solar thermally autonomous driven. Additional heat from a gas boiler is used in winter for supply air heating only. 

General description of the system

The system technology is an open cycle desiccant evaporative cooling system, using solar thermal heat for regeneration of the desiccant wheel. The desiccant wheel contains silicagel as sorption material. The regeneration is driven solar autonomous by flat-plate air collectors, a heat storage is not applied. The air volume flow rate in the air handling unit varies in a broad range according to the requirements; the air volume flow rate through the air collectors is independent from the air-handling volume flow rate in order to allow an optimised operation of the desiccant wheel.  During winter, the supply air is pre-heated by the collectors and heated according to the set values by a fossil back-up system.

Central air-conditioning unit


open cycle (DEC)

Nominal air volume flow rate

10,200 m3/h

Minimum air volume flow rate

2,500 m3/h

Desiccant cooling system type

solid desiccant

Desiccant type

Silica Gel

Cooling capacity

max. 60 kW

Brand of desiccant unit


Solar thermal

Collector type

air collector, flat-plate

Brand of collector


Collector area

92 m2 aperture

Tilt angle, orientation

0 °,  south

Collector fluid


Typical operation temperature

70 °C regeneration temperature of sorption wheel


Heat storage


Cold storage


Auxiliary heating support

gas boiler

Use of auxiliary heating system

supply air heating in winter

Auxiliary chiller


System performance

In the desiccant cooling mode, an annual coefficient of performance (COP) of 0.43 was obtained. The solar coverage of the overall heat input (supply air heating and regeneration heat) was on an annual average 50%. A specific annual collector yield of 111 kWh/m²a was achieved. The performance of the system is limited due to the limited use of the seminar rooms and subsequently limited activation of the air handling unit (in 2004: 1080 hours).

System reliability and overall success of the installation

After the start of the system, improvements in the system control were necessary to allow a sufficient system operation. From this experience, a carefull initialization period is unavoidable. The system concept of autonomous cooling operation is an appropriate solution in this application. In less than 5 % of operation hours, the room air states exceed the set values. The acceptance of the system by the users is very good. As a consequence of the installed solar air collector system, the collector system contributes to 10 % of the total system cost only.

General information

Type of building  Seminar and cafeteria room of the IHK-SO building
Location  Freiburg, Germany (48° North, 7°50’ East)
In operation since  2001
System operated by  IHK-SO
Air-conditioned area  213 m2



Cooled area: seminar room

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Specific information

Further specific information about the system are included in the filled in technical questionnaire.



For more information on the project please feel free to contact:

Edo Wiemken