Insights into parameter estimation for thermal response tests on borehole heat exchangers. (14th September 2019)

• Record Type: Journal Article
• Authors: Beier, Richard A.
• Is Part Of: Science and technology for the built environment. Volume 25:Number 8(2019)
• Page Start: 947
• Page End: 962
• Publication Date: 2019-09-14
• Subjects: Heating -- Periodicals; Ventilation -- Periodicals; Air conditioning -- Periodicals; Refrigeration and refrigerating machinery -- Periodicals; Indoor air quality -- Periodicals; Indoor air quality; Air conditioning; Heating; Refrigeration and refrigerating machinery; Ventilation; Periodicals; 697
• DOI: 10.1080/23744731.2019.1634969
• Languages: English
• ISSNs: 2374-474X

Abstract

Abstract : Thermal response tests (TRTs) are performed on borehole heat exchangers in order to evaluate ground and borehole thermal properties, which are needed in the design of ground-source heat-pump systems. When parameter estimation techniques are applied to evaluate the ground thermal conductivity and borehole thermal resistance, the map of the root mean square error (RMSE) sometimes shows a shallow descent to the global minimum. This study obtains a steeper descent by estimating the component of borehole resistance without heat capacity as a separate parameter. A temperature derivative curve is introduced to identify the boundaries between three distinct periods of a TRT, which are borehole-dominated, transition, and steady heat-flux periods. The effective borehole resistance and ground thermal conductivity can be evaluated independently from each other during the borehole-dominated and steady heat-flux periods, respectively. Meaningful estimates of the ground volumetric heat capacity can be obtained from the TRTs in this study in only limited cases. The best chance is when the grout and ground thermal conductivities are nearly equal and the borehole thermal resistance is small.