The TESSAS Project in Mol: High Temperature Thermal Energy Storage in Saturated Sand Layers with Vertical Heat Exchangers

Abstract

TESSAS is a European project within the 5th framework program with three partners: Vito - Belgium, IF Technology - the Netherlands and ZAE - Germany. The main goal of this project was to demonstrate and evaluate an underground storage system in a water saturated sand layer for storing high temperature heat. The TESSAS-installation went in operation in May 2002. It concerns a high temperature borehole storage system that stores waste heat at 90?C from a power plant during summer time. During the heating season, the stored heat is discharged and used directly for heating a building of 3.700 m2 floor area. A maximum temperature of 70?C was reached in the underground by September, the temperature dropped to 30?C at the end of the heating season. The borehole field is built up of 144 vertical heat exchangers (single U-tubes) at a depth of 30m in order to create a storage volume of approximately 16.000 m3. This is the thermal equivalent of a water storage of ten million liter. This system creates many opportunities in combination with solar collector systems, cogeneration or waste heat (power plants, industrial heat residues,Ö), not only from a technical and ecological standpoint but also from a economical point of view.