Development and application of test cases for comparing vertical ground heat exchanger models

The main objective of this paper is to establish a set of test cases for analytical verifications and intermodel comparisons of ground heat exchanger (GHX) models used in building simulation programs. Several test cases are suggested. They range from steady-state heat rejection in a single borehole to varying hourly loads with large yearly thermal imbalance in multiple borehole configurations. The usefulness of the proposed test cases is illustrated by running them with different GHX models. This comparison exercise has shown that 1-D models compare favourably well with the more elaborate 3-D models for relatively small simulation periods. The cyclic heat rejection/collection test has revealed some small deficiency in the load aggregation scheme of a particular model. Finally, the use of the asymmetric (cooling-dominated) load profile test case for a bore field composed of 100 boreholes revealed that the borehole wall temperature predicted by two GHX models can differ by as much as 10oC after a 30 year simulation.