| Abstract |
This paper covers a study on eight office buildings using shallow geothermal technology (ground source heat pumps, with some aspects of underground thermal energy storage - UTES) for space heating and cooling via heat pumps, chillers or passive cooling. The types of ground coupling include both borehole heat exchangers (BHE) and groundwater wells; however, the main emphasis on the results in this paper is on the BHE plants. Most of the buildings are located in the West of Germany (Nordrhein-Westfalen and Hessen), with relatively mild climate. The main goal of the monitoring was to assess the performance of the geothermal systems, their adaptation to the building systems, reliability, etc. Results show the feasibility of the general shallow geothermal concepts, with medium to high energy efficiencies. However, loss of performance and temporary breakdown of some systems as well as inconsistent concept implementation were observed. While one plant reached exceptional performance with a total (annual) SPF around 7-8, there was also a plant with total SPF below 4, which is disappointing in today standards. Some optimizations of energy efficiency and controller performance have been achieved during the process. A recurring theme is a big difference in the building demand data given during system design and the heating and cooling actually consumed once the projects were in operation – most required considerably less, rendering the systems somewhat oversized. The monitored data were also used to validate design software. The applicability of easy-to-use programs like EED could be confirmed for large systems with a high number of BHE. For groundwater wells (incl. ATES) operation modelling, some simple methods can be used for pre-design, but numerical models are still required, in particular when groundwater flow is high enough to have a measurable influence. Thermal impact on the ground and groundwater was investigated in some cases, and all projects can be said to have either no impact at all, or at least no negative impact. |