Deconvolution and convolution methods for thermal response tests on borehole heat exchangers

Abstract

A thermal response test (TRT) on a borehole evaluates ground and borehole properties, which are needed in the design of borehole fields for ground source heat pump systems. Variation in the heat input rate during a TRT complicates the data analysis, when the electrical power to the test equipment is unintentionally interrupted, or other unwanted changes in the power supply occur. Then, the measured transient temperature curve is a convolution of the varying rate and the constant-unit-rate response function. A deconvolution method has been developed to determine the borehole temperature response that would have occurred if the heat input rate would have remained fixed. The deconvolution technique and the conventional temporal superposition method are validated with TRT data sets with interruptions carried out in a laboratory sandbox. The methods are also applied to field TRT data sets. The deconvolution method has the advantage of generating a smoothed temperature derivative curve, which is used to identify three distinct time periods during a TRT to enhance the analysis.