Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar Heating of Potable Water at Baden-Baden City Hospital

The circuit diagram below shows a simplified version of the solar thermal system with the corresponding components. The whole system is subdivided into three different circuits: the collector circuit, the buffer storage circuit and the potable water circuit.

The collector field of 276 m² consists of 35 collector modules; five collectors (max) are connected in series. The collectors are fixed on the flat roof of the hospital with an inclination angle of 45° and an azimuth of +/- 0° South. 

The water glycol mixture in the collector circuit is heated by solar irradiation. It is then transferred to the heat exchanger by a recirculation pump. The loading pump in the consecutive (secondary) circuit feeds the energy to the three solar buffer storage tanks with a capacity of 4000 liters each.

One buffer storage tank serves as high temperature tank, the other two as low temperature tanks. The high temperature tanks are always loaded first. Originally, this should have been possible either way with a changeover valve. Yet, this changeover did not work properly and was eventually disengaged. Because of the high reflow temperature, the efficiency of the collector circuit, and hence the solar yield, was reduced.

The discharge of the buffer storage, which is to say the transfer of solar energy to the potable water, takes place in a second external heat exchanger (WT2). When operating the discharge pump, water is taken from the high temperature tank and then released to the preheating tank. The reflow of the heat exchanger is fed to the other buffer storage tanks.

If warm water is taken,  cold water flows to the preheating tank with a capacity of 1 500 liters. Once the temperature difference between preheating tank and buffer storage tank reaches a sufficient level, the discharge pump and the potable water pump switch on and heat the preheating tank via the heat exchanger.

The potable water goes out of the preheating tank to the two consecutive reheating tanks with capacity of 3 000 liters each. There the gas boilers heat it up to 45°C, if necessary.

Simplified diagram of the solar thermal system Baden-Baden City Hospital


This table shows the most important specifications of the solar thermal system of Baden-Baden City Hospital.


Project Data
Surface276 m²
Collector typeflat plate collectors with anti-reflective glass
Buffer storage3 x 4 000 ltrs
Project costs195 777,- € (709,- €/m²)
Heat exchanger2 plate heat exchanger
Preheating tank1.500 ltrs
Azimuth/ InclinationSouth / 45°
Lowest energy cost0.14 €/kWh
Highest solar yield 124.125 kWh/a (450 kWh/m²a)

Click on the pdf-file to receive detailed information on the specifications of the solar thermal system of Baden-Baden City Hospital. The file also includes details of the collectors, the pipes, the carrier medium in the collector circuit and the heat exchanger between the different circuits.

Measurement Technique

The following diagram shows the system’s measurement and monitoring sensors. The monitoring sensors are essential for the functioning of the whole system; the measurement sensors are used for the extended functionality control of the solar thermal system.

Diagram of the measurement points of the solar thermal system Baden-Baden City Hospital

DATAPOOL provides access to our data server

Via DATAPOOL you can access selected data of this solar thermal system. You can choose from various illustrations like line charts, carpet plots, or scatter plots.

Baden-Baden City Hospital can be found on the Datapool pages under Solar Thermal Systems.

The individual measurement points of the data pool can be found in the diagram above or here.

For a list of the measurement points, click here.

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