Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar Heating of Potable Water in the Student Village Vauban in Freiburg

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 circuit contains a collector field of 142.8 m², which consists of four parallel flow circuits each with three collectors connected in series. The collectors are fixed on the roofing battens of a tiled roof with an inclination angle of 38° and an azimuth of 5° west.

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 four solar buffer storage tanks with a capacity of 1500 liters each.

Two buffer storage tanks are grouped together respectively as one high temperature group (tanks 3+4) and one low temperature group (tanks 1+2).

The discharge of the buffer storage tanks, which is to say the transfer of the stored energy to the potable water, takes place in a second external heat exchanger (WT2). When operating the discharge pump (P3), both storage groups flow in series.

When hot water is extracted, cold water initially flows into a storage tank (1500 liters) where it is preheated by the surplus heat of the boilers (heat recovery). The preheated potable water then flows through the discharge heat exchanger and is heated further when P3 is in operation (continuous flow system). In the fall of 2004, the central heating block was connected to the local heating network of Badenova (wood chip thermal power station). Hence, the heat recovery of the boiler system no longer applies and the potable water is fed directly to the discharge heat exchanger of the solar thermal system.

The heated potable water flows to three reheating tanks, each with a capacity of 1500 liters, where it is heated to the required temperature of 65°C by the heat exchanger of the local heating network.

The operators renovated the system in 2010 and simplified its systems technology. The future measurement system should be smaller and more user-friendly, and it should provide the project members with online data access. This will be implemented under the aegis of the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg.


Simplified diagram of the solar thermal system Freiburg Vauban



This table shows the most important specifications of the solar thermal system in Freiburg Vauban

Project data
Surface143 m²
Collector typeFlat plate collectors
Buffer storage4 x 1500 l
Project costs114 521.- € (801.- €/m²)
Heat exchanger2 Plate heat exchanger
Potable water tank3 x 1500 l
Azimuth / InclinationSouth +5° / 38°
Lowest energy costs0.10 €/kWh
Highest solar yield97 162 kWh/a (679 kWh/m²a)


Click on the pdf-file to receive detailed information on the specifications of the solar thermal system of Freiburg Vauban. The file also includes details of the collectors, the pipes, the carrier medium in the collector’s 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 and monitoring points of the solar thermal system Freiburg Vauban

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.

The student village Vauban 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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