Development of System Simulation Tools of Central Solar Heating Plants with a Seasonal Duct Store in The Ground

Pahud, Daniel (1995) Development of System Simulation Tools of Central Solar Heating Plants with a Seasonal Duct Store in The Ground. Project Report. UNSPECIFIED.

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Abstract

Large use of solar energy for heating purposes requires large heat storage facilities to overcome the seasonal discrepancy between the summer heat supply and the winter heat demand. Different types of heat stores in the ground have been extensively studied both from the practical and theoretical point of view. Included are water-based heat stores, e.g. pits and rock caverns, and duct ground heat stores, e.g. vertical coils in clay and boreholes in rock. Practical experience is more extensive for water stores than for ground stores. However, duct ground stores are a very interesting alternative. Large stores can be achieved at a low cost, without requiring exclusive use of large ground surface area. Such stores have to be studied and optimised in a complete energy system. Duct ground heat stores fed by solar collectors are characterised by intensive heat transfer rates that last only part of a day. This phenomenon results in large temperature differences between the heat carrier fluid and the average temperature level of the store, and produces unnecessary quality losses. The use of a water buffer tank between the solar collectors and the store will improve the system's performance. In consequence, different possibilities of system operation are possible. Research work is required to characterise such systems, in order to establish an optimal ratio between the different subsystems' size as well as to develop a strategy for an optimal system operation. Detailed and accurate system simulation programmes are required to perform such analysis. This study has been carried out in the Department of Mathematical Physics at Lund University (Sweden), financed by a grant from the National Swiss Funds for Scientific Research, which was awarded by the Research Commission of the University of Geneva (Switzerland).

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