Office building of Ott Ingenieure in Langenau, Germany

Description of the application

The office building of Ott Ingenieure in Langenau is air-conditioned during summer with a solar thermally assisted chilled water system. The chilled water is provided at a temperature of approx. 13 C. It is mainly used for the chilled ceilings at the offices, but additionally for supply air cooling of the central air handling unit. Since the business of Ott Ingenieure covers also heating systems and solar thermal systems, the application is a demonstration of solar applications as well.

General description of the system

The system technology is a closed cycle chilled water system with a medium-sized absorption chiller. Three heat sources are available, providing heat for chiller operation and for space heating: a solar thermal vacuum tube collector system, a CHP unit and a gas boiler. The CHP unit runs on heat demand. The chilled water serves for supply air cooling of a central air handling unit and is used to operate the chilled ceilings in the offices. Heat rejection is done using an open wet cooling tower. Additional back-up systems on the cold side (e.g., electrically driven compression chiller) are not applied.

Central air-conditioning unit


closed cycle

Nominal capacity

35 kWcold

Type of closed system


Brand of chiller unit

Yazaki WFC 10

Chilled water application

Chilled ceilings, supply air cooling



Heat rejection system

open wet cooling tower

Solar thermal

Collector type

vacuum tubes

Brand of collector

Seido 26

Collector area

30 m2 absorber

Tilt angle, orientation

25, 45 south-west

Collector fluid


Typical operation temperature

85 C driving temperature for chiller operation


Heat storage

2 m3 water

Cold storage

1 m3 water

Auxiliary heating support

CHP with 19.5 kW heating capacity, gas boiler with 50 kW heating capacity

Use of auxiliary heating system

auxiliary driving source for chiller, auxiliary driving source for space heating in winter

Auxiliary chiller


System performance

From a monitoring period in 1999, an annual coefficient of performance (COP) of 0.50 was obtained. The solar thermal coverage of the total heat input for heating and cooling was 12 %; the contribution of the gas boiler and of the CHP to the heat input was 44 % each. From the energy balance, a specific annual collector yield of 286 kWh/ma was determined.

System reliability and overall success of the installation

The system showed less solar coverage than expected, of which one reason is connected with the limitation in size of the collector array. A revision of the collector system is planned. The sufficient cooperation of three heat generation units requires some effort in the design of the system control.  Some reliability problems are connected with the CHP unit, but the overall reliability of the solar thermally driven cold production is good; the overall concept is correct and promising.

General information

Type of building  office building
Location  Langenau, Germany (4830 North, 1007 East)
In operation since  1997
System operated by  Ott Ingenieure
Air-conditioned area  415 m2



Collector area
Building view
Collector area

Clicking an image opens the gallery view.

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