The solar assisted district heating system with seasonal thermal energy storage in Eggenstein — Leopoldshafen (Germany) is the first system realized with existing renovated buildings. The project was initiated by a major refurbishment of the school, the gym and the existing district heating system. An additional gym with shed roof carrying 600 m2 of flat plate collectors (FC) was built. Together with a public swimming pool and a fire station the district heating system consists of buildings with a gross building area of 12 000 m2. For seasonal thermal storage of the solar heat produced by 1 600 m2 of flat plate collectors a 4 500 m3 gravel-water thermal energy store (TES) is integrated into the district heating system, see Fig. 1.

renovated school

1000 m2 FC

new gym

gravel-water thermal
energy store

Fig. 1: Solar assisted district heating system with 1600 m2 flat plate collectors and seasonal storage in

Eggenstein-Leopoldshafen (Germany

For backup heating two 600 kW gas boilers and a 30 m3 buffer store are available. Discharging of the seasonal TES down to 10 °C is facilitated by the use of a heat pump with a thermal power of 60 kW. Thus, the thermal capacity of the store is increased by 75% compared to discharging of the heat store to a return temperature of the heating net of 40 °C.

A detailed description of the system concept is given in [1]. Furthermore, optimization of the solar assisted district heating system by means of TRNSYS simulations is presented in [2]. This paper focuses on the design and construction of the gravel-water store and the measurement concept of the system.