The main findings of the studies on open adsorption storage designed for seasonal storage of solar heat, as reported by ITW in Germany, are the following:

• An effective sorption storage integrated in a conventional mechanical ventilation system has been developed in the Institute of Thermodynamics and Thermal Engineering (ITW), University of Stuttgart and was theoretical and experimental investigated

• For the first time, highly filled zeolite honeycomb structures made by extrusion of zeolite powder using thermoplastic polymers as plasticising aid and binder are used as adsorbent. Honeycomb structures have decisive advantages compared with fixed beds of spheres or other shaped bodies. They show excellent adsorption kinetics and generate low pressure losses along the process length. In open cycle processes low pressure drop is important to minimise the electric power consumption of the fans.

• Theoretical analysis has been carried out. Special attention has been given to precisely incorporate the appropriate physical and chemical processes that occur during adsorption and desorption, into the theoretical model; this will then reflect the proper performance of the proposed sorption system under real practical conditions.

• Simulation of the space heating for a residential building based on sorption storage was carried out using TRNSYS. The sorption process was evaluated using a 1-D two-phase model with heat — and mass-balance in a separate numerical routine.

• A prototype sorption storage tank integrated into a commercially available residential heating system has been built at ITW. The system has been scaled to achieve short cycles on a weekly basis, so that the system could be tested under varying conditions.

• Theoretical analysis shows that, compared to the adsorption period, the desorption process is more sensitive to several input parameters.

• Experiments have been carried out that demonstrate the technical feasibility of the proposed system under real operating condition. The experimental results concerning the thermal behaviour of the adsorption/desorption process and the achieved heat storage capacity are in good agreement with the theoretical analyses. Furthermore it has been shown that the solar thermal desorption

conditions using high performance CPC collectors performs well. Special attention was given to achieve the necessary high desorption temperature of 180°C inside the sorption store.