Simulation of CSHPSS Systems with a Duct Ground Store

Pahud, Daniel and Hellström, Göran (1997) Simulation of CSHPSS Systems with a Duct Ground Store. In: Megastock'97 7th International Conference on Thermal Energy Storage, 18-21 June 1997, Sapporo, Japan.

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The design of a solar heating system using a duct store in the ground requires design procedures that account for the different thermal processes involved. In order to obtain an accurate evaluation of the system heat balance, system performances have to be calculated with high resolution over several years, if not the lifetime of the system. Reliable and accurate simulation tools which use the TRNSYS programme have been developed for the simulation of Central Solar Heating Plants with Seasonal Storage (CSHPSS) using a ground duct store. The simulated systems involve a collector array, a short-term water buffer store, a ground duct store, an auxiliary heat supply and a heat distribution network to the consumer. The version of the duct heat storage model (DST) for TRNSYS has been improved based on the results of analyses performed with more detailed programmes. The flexibility of the TRNSYS programme makes the tools easily adaptable to a particular problem. The simulation tools are applied to a system defined for typical Swiss conditions. Optimal ratios between the main system parameters are sought for sizing purposes. The influence of the load size, load type (size of the proportion of domestic hot water) and load temperature levels are investigated. Several thousand simulations have been performed; these have helped to characterize and highlight important points in the design of such systems. Comparisons are made with systems having only a water store. They show that a duct store becomes economically more attractive for solar fraction larger than typically 50%, i.e. for seasonal heat storage. Corst reduction should be concentrated on cheaper collectors, as two thirds to three quarters of the solar cost is due to the collector array.

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