| Title | Cascade Heating and Cooling of a Hotel Resort - 6 Years Operational Experience with a 400 m Deep BHE Alignment in an Alpine Dolomite Karst Aquifer |
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| Authors | Ingo SASS; Clemens LEHR, Rafael SCHÄFFER, Friedl KAINZNER, Josef STOCK |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Cascade heating, Middle deep System, Karst Aquifer, Cooling, Operating Data |
| Abstract | A luxury resort in the Tyrolean Alps was extended in 2013 and 2014 for the fifth time. This opportunity was used to install borehole heat exchangers (BHE) in a dolomitic karstified aquifer. The marble karst aquifer of the Hochstegen formation was explored and developed as an intermediate-depth geothermal energy storage system. Karst aquifers on the one hand may improve the efficiency of geothermal systems due to increased permeabilities but on the other hand high groundwater velocities can reduce the efficiency of the underground heat storage capacity. The explored aquifer sharply declines from a thrust fold contact to the Tauern Window into the deeper underground. Enhanced geothermal response tests have been carried out before and after completion of the geothermal array. Optical frequency domain reflectometry methods have been applied to assess the hydrogeological and geothermal properties of the subsurface and integrity of the BHE itself. The first eGRT thermal conductivity profile shows sections of conductive dominated heat transfer in the upper section and convective in the lower karstified well bore section. The second one shows reduced influence of groundwater flow which is interpreted as a clogging effect by cementation of the neighboring BHEs. The linear borehole heat exchanger systems have been percussion drilled. In total 3.600 m BHE were completed in nine wellbores. The BHE have been drilled in an alignment. The underground installation was connected to three heat pumps and three thermal storage tanks with different temperature ranges. Two years were used to optimize the cascade operation and another four years of operational routine were monitored and evaluated. The presentation will compare the designing approach (1 GWh/a heat extraction and 0.4 GWh/a cooling load) with the obtained performance after five years of full operation in heating and cooling this particular hotel complex. The systems was dedicated to supply the 25 x 12.5 m outdoor swimming pool e.g.. It will be demonstrated how the systems performance and COP developed and how optimization measure could be implemented. The mean temperature level (heating) that is needed for building equipment and appliances are 55 °C. |