Investigation of the operating characteristic of a demand-controlled 368 m deep CO2 thermosyphon geothermal borehole heat exchanger for building heating

Abstract

This paper examines a 368 m deep geothermal probe for heating an existing building. The geothermal probe based on the thermosyphon principle works with CO2. The working fluid evaporates and condenses in the probe so that no pump is required for transportation. The geothermal probe has an output of up to 22 kW at an underground temperature of up to 18°C. The demand-controlled use of the geothermal probe was investigated and the installed heat pump was optimized for its use. The average COP of the last heating season was between 2,3 and 4,6. For the second heating season the temperature of the soil around the probe is also measured via a distributed temperature sensing system, that covers the whole depth of the probe. It has been shown that the ground temperature only cools down to a certain point and does not fall below this point after a short regeneration period. It was shown that the heat pump with geothermal probe operates at constant temperatures at the evaporator compared to air heat pumps, even at cold outside temperatures.