Development, Verification, and Implementation Of a Horizontal Buried Pipe Ground Heat Transfer Model in Energyplus

Abstract

A buried pipe heat transfer model was developed and implemented within the EnergyPlus simulation program. Three models: a modified earth tube model, a fully radial finite difference model, and a mixed-coordinate implicit finite difference model were tested against a robust verification model developed in Fluent. The earth tube model's extreme simplicity led to poor tests upon verification. The radial model encountered stability problems. The mixed-coordinate model proved the most stable and accurate of the finite difference models. The mixed-coordinate system model was selected for implementation in EnergyPlus. This model utilizes a radial coordinate system in the near pipe region, with a Cartesian system throughout the rest of the domain. The far-field boundary is a function of time and depth.. The initial implementation agreed to the verification model with an annual RMS error of 1.72�C on the exiting fluid temperature. The EnergyPlus implementation agreed to the initial implementation to within 0.12�C.