Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar Heating of Potable Water Mindelheim County 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 total surface covered by the flat collectors amounts to 120m². Its azimuth is -40° Southeast at an inclination angle of 29°. The collector field is subdivided into three equal sections operating parallel. Again, every section is subdivided into two sections that run parallel, each with nine collectors connected in series. The collectors are fixed with aluminum profiles on the metal roof of the hospital, which is inclined at an angle of 7°.

The water glycol mixture in the collector circuit is heated by solar irradiation. If the temperature difference between the collector circuit mixture and the water in the buffer storage is sufficient, the liquid of the collector circuit 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 solar buffer storage tank, which has a capacity of 6000 liters.

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).

Once the heat in the buffer storage has reached a sufficient level, the discharge pumps of the buffer storage circuit (P3) and the potable water circuit (P4) are switched on and the heat is transferred from the buffer storage to the potable water of the preheating tank. This process continues until the preheating tank for potable water is fully charged or until there is no heat left in the buffer storage. The tank holds 3000 liters.

When hot water is extracted, the potable water heated by solar power flows from the preheating tank to two reheating reservoirs with a capacity of 3000 liters each that are connected in series. There it is heated by two gas-heated tanks to the required warm water temperature of 65°C.

For health and safety reasons, i.e. the prevention of legionella infections, both the preheating tank and the storage tank are heated up to a minimum temperature of 60°C at least once a day. 

Simplified diagram of the solar thermal system of Mindelheim County Hospital


This table shows the most important specifications of the solar thermal system of Mindelheim County Hospital.

Surface120 m²
Collector typeFlat plate collectors
Buffer storage6000 ltrs
Project costs108 486 € (907 €/m²)
Heat exchanger2 Plate heat exchanger
Potable water tank3000 ltrs
Orientation / InclinationSoutheast -40° / 29°
Lowest energy costs0.125 €/kWh
Highest solar yield

75 570 kWh/a (630 kWh/m²a)


Click on the pdf-file to receive detailed information on the specifications of the solar thermal system of Mindelheim County 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 and monitoring points of Mindelheim County Hospital.

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.

Mindelheim County Council 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.