The Use of the Underground as a Geothermal Storage for Different Heating and Cooling Needs

The heating and cooling needs of a building show usually a strong daily and seasonal variation. The shallow underground is a cost-efficient store for compensating the daily and seasonal delay between need and supply of heat and cold. Mostly borehole heat exchangers (BHE) are used to develop and operate the geothermal store. The leading parameters for the design of optimized installations are demonstrated by a project with complex energy demand. 1. CRITERIA FOR BHE-SYSTEMS Today, the borehole heat exchanger technology is technically matured. Compared to conventional installations borehole heat exchanger systems are competitive and even attractive for energy production and storage especially for objects with very large heating and cooling demands. Due to the comparatively high cost fraction for drilling, the proper design of BHE systems is crucial for large-scale projects to optimise costs and sustainable functionality. The most important constraints come from the energy concept of the building. BHE-systems are very efficient, if they are not only used for heat production, but also used to store waste heat from cooling systems into the ground. This seasonal use of the ground improves the coefficient of performance of the heat pumps and also reduces the cooling down effect of the ground during the heating season. The efficiency of the socalled seasonal storage is much higher, if the heating and cooling energy demand is equilibrated over a specific period.