Related EU Projects

In this project, the extension of the existing cooling capacity was realised with an Aquifer Thermal Energy Storage (ATES) instead of a conventional chiller. Compared with a chiller, the use of ATES reduced the electricity consumption for cooling by 50%. Moreover, the heat that was extracted from the ventilation supply air in summer was stored in the aquifer to be utilised in winter for (pre)heating ventilation air. The integration of the ATES system in the installation with 2 chillers enabled also short-term cold storage in summer. Therefore, the risk of cold shortage due to climatic influences (warm summer and/or mild winter), was compensated for without costly investments in extra chiller capacity. Furthermore, the combined use of the aquifer system for seasonal cold and heat storage, as well as short-term cold storage made the system more profitable. Consequently ATES can also be attractive for smaller projects with existing cooling systems that have to be extended. Therefore, this will enlarge the market potential for ATES. For instance, in the first half of summer 1994 (April, May, June and July) the storage delivered 256 MWhth (megawatt hours of heat) cold and 82,000 kWhe (kilowatt hours of electricity) were saved. No additional cooling was applied thanks to the lower temperature in the cold storage.

The project demonstrated:

- That the required extension of the cooling capacity in the hospital can be realised by storage or "winter cold" in a sand-layer (aquifer) in the soil, and that such a storage system can be integrated in the existing cooling system.

- The technical and economical feasibility of combined seasonal cold and heat storage in an aquifer for cooling and (pre)heating ventilation supply air.

- And the advantages of using the aquifer for short time storage of cold that is loaded at night with the available chillers, thus creating extra facilities for energy management and compensating for risks of cold shortage due to climatic influences.

This project was an innovative system for the storage of residual heat in an aquifer at the University of Utrecht. By using heat storage, the number of operating hours of the heat and power installations during the summer period was increased as the heat produced was usefully employed. The stored heat was used during winter for space heating. As a consequence, less gas had to be used for space heating during the winter months and during summer less electricity had to be purchased. The degree of utilisation of the heat and power installations was increased, while the primary energy consumption was reduced.

The aim of the project was to demonstrate a practical applicability of heat storage in aquifers, in combination with combined heat and power installations in order to augment the useful exploitation of these installations. These installations were regulated on the basis of the heat requirements of the buildings of the university complex, which meant that at a reduced heat demand during summer, the installations were run at part load to avoid unprofitable production of excess heat. This led to a lower total yield of the heat and power installations and additional electricity also had to be purchased. As a result, residual heat in the form of water at a temperature of 90°C was stored in an aquifer and then used to produce electricity, which was used by the university complex. The stored residual heat was used in winter for the heating of a few buildings of the complex. In the feasibility study it was estimated that a thermal result (the heat stored which was then retrieved) of about 65% to 75% in the third year was achieved. At the realisation of the heat storage, additional data of the soil structure was obtained, thus soil structure could be represented better diagrammatically.