Analysis of borehole thermal resistance is important for the standard sizing of ground heat exchanger (GHE). In this paper, a p-linear dimensionless average fluid temperature is proposed to estimate borehole thermal resistance. A p-linear dimensionless fluid temperature and p-linear dimensionless average fluid temperature are introduced, and the p-linear dimensionless fluid temperature is compared with theoretical dimensionless fluid temperature calculated by quasi-three-dimensional model for both single and double U-tubes. Results show that the p-linear dimensionless temperatures with parameters p -> 0 and p= -1/2 are respectively in good agreement with the theoretical dimensionless fluid temperatures of single and double U-tubes. Therefore, the dimensionless logarithmic mean temperature for p -> 0 and the dimensionless geometric mean temperature for p = -1/2 should respectively be adopted to reasonably estimate the thermal resistance of single and double U-tube boreholes. (C) 2010 Elsevier Ltd. All rights reserved.