Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar Heating of Potable Water HBK Singen

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 264 m² consists of 20 collector modules subdivided into four parallel flow circuits each with five collectors connected in series. The collectors are fixed as a ‚Solar Roof’ on the roof of the facility management building with an inclination angle of 30° and an azimuth of -52° southeast. 

The water glycol mixture in the collector circuit is heated by solar irradiation. It is then transferred to the heat exchanger (WT1) by a recirculation pump (P1). The loading pump (P2) in the consecutive (secondary) circuit feeds the energy to the three solar buffer storage tanks with a capacity of 5000 liters each.

The buffer storages are charged one after the other. Buffer storage 1 is the primary storage. If the temperature difference is too low and this buffer storage cannot be charged anymore, the valves switch over to storage 2. Buffer storage 3 is the last to be charged. The extraction of heat to the heat exchanger WT1 always takes place at storage 3 (coldest storage). This way, the temperature layers constitute quickly and the heat is quickly at one’s disposal at high temperatures.

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). If the temperature difference between the buffer storage tanks and the potable water tanks is sufficient, discharge pump three switches on. Heated potable water is extracted from storage 1 at the top where temperature is highest. The reflow of WT2 is transferred to storage 3. At the same time, recirculation pump P4 switches on. It extracts the potable water from the preheating tanks (storage 3 and 4 with 1000 liters each) via the discharge heat exchanger WT2. There, the potable water is heated by solar energy and then transferred to the storage tanks.

If warm water is extracted, the heated potable water flows from the preheating tanks to the two consecutive reheating tanks (each with 1.000 L). If required, the warm water can be heated up to the set temperature by conventional appliances. The conventional heating consists of a serial connection of the independent thermal power station and gas boilers. If there is not enough solar energy available, the independent cogeneration switches on. If it is still not sufficient, the gas boilers are also used. 

The legionella control unit is operated around 11 pm every day. A changeover valve opens the pipe to the preheating tanks so that all four potable water tanks are fed with reheated potable water until all tanks reach a temperature of 70°C. Afterwards, the valve switches over to the reheating tanks, to prevent the preheating tanks from being flooded with reheated water.

Simplified diagram of the solar thermal system HBK Singen


This table shows the most important specifications of the solar thermal system HBK Singen.

Project Data
Surface264 m²
Collector typeSolar-Roof flat plate collectors
Buffer storage

3 x 5 000 ltrs

Project costs183 759,- € (696,- €/m²)
Heat exchanger2 plate heat exchanger
Preheating tank2 x 1 000 ltrs
Azimuth / InclinationSoutheast (-52°)/ 30
Lowest energy costs0.15 €/kWh
Highest solar yield109 922 kWh/a (416 kWh/m²a)


Click on the pdf-file to receive detailed information on the specifications of the solar thermal system of HBK Singen. 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 HBK Singen

Access our Data Sever via DATAPOOL

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.

HBK Singen can also 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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