Step-wise algorithm for estimating multi-parameter of the ground and geothermal heat exchangers from thermal response tests

This paper proposes an innovative algorithm using the idea of step-wise to estimate of multiple parameters of the shallow ground and U-shaped geothermal heat exchangers. This procedure uses an infinite composite-medium line-source solution. The short-term solution not only enables testing data collected during short times (< 10 h) to be used in parameter estimation but also provides a feasible approach to estimating geometric parameters and thermal properties inside a borehole. The step-wise estimation consists of four stages: 1) determine soil thermal conductivity k(s), 2) estimate the thermal conductivity of grout k(b), 3) estimate the distance between centers of U-tube pipe D, the thermal diffusivities of soil and grout, a(s) and a(b), and 4) an iteration process if necessary. The outstanding feature of this step-wise algorithm is that the TRT data used in each step can be controlled separately, which can increase the accuracy of estimation because it alleviates the linear dependence among the sensitivities of parameters. It is shown that the accuracy of the estimates is ranked in descending order as follows: k(b) (+/- 1.0%), k(s) (+/- 2.0%), D (+/- 16.0%), a(s) (+/- 20.0%) and a(b) (+/- 70.0%). (C) 2020 Elsevier Ltd. All rights reserved.