| Title | System optimisation of ground-coupled heat- and cold supply for office buildings |
|---|---|
| Authors | Sanner, B; Bockelmann, F; Kühl, L; Mands, E |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | geothermal heat pumps, office heating and cooling, energy optimisation |
| Abstract | In modern office buildings geothermal heating and cooling technology is used increasingly, replacing conventional systems with reversible heat pumps (heating and cooling) and/or direct cooling. In past monitoring projects it became evident that for ground-coupled systems there often is a large discrepancy between efficiency as to the design and according to real-life, monitored operational data. The objective of this project “geo:build – system optimisation of ground-coupled heat- and cold supply for office buildings”, was to identify energetically and economically suitable combinations of geothermal technology and building HVAC equipment. Based upon simulation, monitoring and documentation, the behaviour of the systems, and in particular of the interface between geothermal technology and the building installation, was studied. System optimisation and operational strategies for transition from mechanical to direct cooling and back were discussed, in order to best use the underground as a seasonal thermal storage. Basic preconditions were set by guaranteeing the internal comfort requirements in the rooms, and ensuring a long-term equilibrium with the thermal balance in the underground. Several combinations were tested upon data and behaviour of these building using TRNSYS. For the geothermal part, EED was used as a main tool for ground thermal calculations, with 3D-simulations using FEFLOW being done for comparison at two of the buildings. Results of the system simulations show that the energy cost for electric power can be reduced through optimised use of direct cooling. The geothermal simulations prove the adequacy of the temperature predictions by both EED and FEFLOW; however, due to deviations of the actual heat extraction and injection from the design values, the temperature development is different from that intended during the design stage. For one of the buildings, extrapolations of temperature development in the ground under various scenarios are made by simulation, proving the need for a long-term thermal balance and allowing for measures to adjust this balance. The paper presents three of the buildings and geothermal systems investigated, summarises the monitoring results, and explains the ground temperature simulations. |