An experimental investigation of the effects of some design and operational parameters on heat transfer rate per unit borehole length

Borehole cost is an important part of the total cost of a ground source heat pump system. Optimization studies to increase the heat transfer rate per unit borehole length (unit HTR value) can decrease the cost and make the system more feasible. Therefore, in this study, the effects of borehole depth, flow velocity, pipe diameter as well as the space between the pipes on unit HTR value are experimentally investigated. Unit HTR values of 50m and 100m boreholes are compared. Similarly three different flow velocities are used during the experiments to show the effect of flow velocity on unit HTR values. Pipes of 32mm and 40mm diameter are used in boreholes to investigate the effect of pipe diameter on unit HTR values. Two different spaces (97 mm and 120 mm) between the axes of the pipes (shank space) are considered and unit HTR values are measured. Moreover, last two cases are also modelled by COMSOL Multi-physics software environment to make some further analyses. Experimental results are discussed to obtain higher unit HTR values.