DC-83-08-2 -- Vertical Concentric Tube Ground-Coupled Heat Exchangers PDF

An experimental and analytical project to study the design of vertical, concentric-tube ground-coupled heat exchangers for use in heat pump applications is described. The experimental apparatus consists of a concentric configuration of two 155-ft (47.2-m) polyvinylchloride (PVC) pipes (sealed at both ends with connections so that hot or cold water could be pumped through the system) with instrumentation to measure heat transfer. This heat exchanger was placed in a well with an 8-in (0.20-m) inside diameter (ID), which was backfilled with sand to establish good thermal contact. Heat transfer was measured for heat exchanger operation under several sets of operating conditions. A mathematical model was developed and converted into a computer program to simulate the operation of the ground-coupled heat exchanger. Data collected using the experimental apparatus was used to validate the computer program, and the computer model was then used to study the effects of variations in heat exchanger length, diameter, flow rate, and thermal conductivity and the thermal conductivity of the ground on the heat exchanger performance. Results are presented.