Annual hourly (or shorter) energy simulations are an important part of the design and analysis of ground-coupled heat pump systems. In order to evaluate the fluid temperature in the borehole of a geothermal heat pump system, most of the current models express the heat transfer rate as a sum of step changes in heat transfer rate. The borehole temperature is then computed as a superposition of the different contributions of each time step. The main difference between the different models lies in the way the step response is computed, whether a cylindrical heat source method, a line source method, or a tabulated numerical step response approach is used. Since all these methods are based on a convolution scheme, long time simulations are very time consuming since impulse response is recomputed at each time step. Many load aggregation algorithms have been proposed in order to reduce this computational time. In this paper, we present a new algorithm to evaluate the overall response, which is much faster than the classical convolution scheme.

Units: Dual