First in situ determination of the thermal performance of a U-tube borehole heat exchanger, in Cyprus
Date Issued
August 2006
Author(s)
Abstract
A borehole heat exchanger can be used for the injection or extraction of thermal energy into/from
the ground. One of the methods that can be used to determine the characteristics of a borehole Utube
heat exchanger is the line source method which is simple and does not need expensive
equipment. This method is explained and a test is performed in order to determine a borehole’s
characteristics in layers consisting of clay, silt and sand at various analogies. For the borehole under
test the ground thermal conductivity (λ) was found to be 2.7 W/(m K) and the effective borehole
thermal resistance (Rb) to be 0.10 K/(W/m). The results of the test are very sensitive to the amount
of initial data that are discarded. The test is also sensitive to the daily flux penetration through the
ground which gradually increases the temperature of the top layers in summer and to the variation
of the heating coil injection rate which affect the temperature of the fluid of the heat exchanger at
some later time.
the ground. One of the methods that can be used to determine the characteristics of a borehole Utube
heat exchanger is the line source method which is simple and does not need expensive
equipment. This method is explained and a test is performed in order to determine a borehole’s
characteristics in layers consisting of clay, silt and sand at various analogies. For the borehole under
test the ground thermal conductivity (λ) was found to be 2.7 W/(m K) and the effective borehole
thermal resistance (Rb) to be 0.10 K/(W/m). The results of the test are very sensitive to the amount
of initial data that are discarded. The test is also sensitive to the daily flux penetration through the
ground which gradually increases the temperature of the top layers in summer and to the variation
of the heating coil injection rate which affect the temperature of the fluid of the heat exchanger at
some later time.
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