2002 Volume 24 Issue 4 Pages 329-338
In this paper, the effects of natural convection at the annulus of heat exchange wells in Ground-Coupled Heat Pump (GCHP) systems were investigated using analytical solutions and evaluated by field test results. For the analysis of natural convection effect, Rayleigh numbers were evaluated using experimental correlations for the determination of Nusselt numbers in the closed layer between the heat exchange pipe and the well wall. A computer program to predict temperature performances of heat exchange wells was developed using the above Nusselt number and cylindrical source functions. The interpretation method was verified using thermal response test results conducted at a test well drilled in Akita City, Japan. Sensitivity studies using the above procedure showed (i) effect of natural convection at the annulus is more pronounced in operating GCHP systems for cooling purposes than in operating them for heating purposes, (ii) larger well diameter is more advantageous in terms of heat transfer.