Numerical Simulation of Deep Bore Heat Pumps

English Abstract:

Depletion of fossil fuels in the nature poses a greater threat to our civilization. To meet the energy challenges, environmentally friendly renewable energy sources are being explored. The availability of underground energy is more abundant and comparatively easy to extract. One such technology deals with exploitation of earth’s energy referred to as geothermal energy. Deep Bore Heat Pumps, that extract energy during winter times and discharge temperatures during summer, are gaining prominence and popularity due to its simplicity and reliability. Commissioning of this system requires large investment, which usually relies on reliable, powerful guesstimating tools. Therefore, there is a strong need to develop tools to arrive at optimal sizing of deep borehole exchangers.

This paper presents the results of a three-dimensional numerical simulation model for a U-Tube type of heat exchanger. This may be a gross simplification of the fact that there is grout and earth surrounding the exchanger. But, this approximation of considering a constant temperature reduces much pre-processing and computational effort. The PVC is considered as pipe material and water is as heat exchanger fluid. The heat is transferred from the outer surface to the water because of the conductivity of the solid material of the pipe and flow of the water. A velocity inlet and pressure outlet model is assumed. By solving the energy equation and laminar flow, the velocity and pressure profiles are obtained.

A thorough parametric study is conducted by using different span lengths, diameter of the pipe, velocity of the fluid and conductivity of the material. This study helped us in establishing the empirical equations for the temperature rise, power requirements and variables of the process viz., velocity, pressure drop etc.