| Abstract |
The heating and cooling demands of a University building at the National Technical University of Athens (NTUA) Campus in Zografou Athens, amounting respectively at 1000 kWth and 700 kWC, are partially covered by a geothermal heat pump system (Interklima), which combines heat pumps fed by both groundwater and a field of vertical earth heat exchangers (VEHEs). These systems, respectively, utilize the thermal energy content of the ground water and of the rocks present in the shallow earth adjacent to the building. The project was supported by the THERMIE programme (Project BU.468.94. HE) with CRES being the project coordinator. Combining both groundwater and earth heat exchangers, required a special design configuration, which was accomplished through two plate heat exchangers. The groundwater provides 234 kWth of thermal energy to Heat Pump Unit 2 through the first heat exchanger, plus an additional 62,5 kWth to the water circulating within the VEHEs and the evaporator of Heat Pump Unit 1, through the second heat exchanger. The 13 VEHEs provide 76.5 kWth to the Heat Pump Unit 1. The Geothermal Heat Pump system provides a total of 526 kWth of heating at the condensers of the heat pumps and 461 kWC of cooling at the evaporators. Of these 373 kWth of heating is provided through heat exchanging, from the earth during the heating period in the winter, whereas the earth is furnished with 598 kWth during the cooling period of the summer. Integration of the geothermal heat pumps into the building heating system did not encounter any problems, as the building was already equipped with fan-coils. After the water leaves the plate heat exchangers, it is either returned into the ground through a reinjection borehole, or it is used for irrigation purposes. The total energy production and saving achieved by the unit operation is 60 Tonnes Oil Equivalent (TOE)/year produced/substituted for heating and 46,2 TOE/year saved from cooling. The estimated simple payback period of the innovation compared to the conventional systems is 9,11 years. |