Hourly energy simulations are an important part of the design and analysis of ground-source 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. Since all these methods are based on a convolution scheme, long time simulations are very time consuming. Many load aggregation algorithms have been proposed in order to reduce this computational time. In a previous paper we proposed a new algorithm to evaluate the overall response which was much faster than the classical aggregation schemes. However this new algorithm was based on the cylindrical source step response for a single borehole. In this paper, we present a generalization of this scheme for any kind of step response making it a very powerful tool for hourly simulations. (C) 2009 Elsevier Ltd. All rights reserved.