An improvement to the thermal resistance capacity model (TRCM) used to model borehole heat exchangers is presented. Here, the original model is extended to integrate the thermal capacities of the heat carrier fluid and pipe and to better account for the spacing between the pipes. Model results are compared to results provided by numerical models and show very good agreement. It is shown that the improved model brings a significant improvement for short times over the original model, allowing a rapid computation of the temperature response function at virtually any time and distance from a single borehole. (C) 2012 Elsevier Ltd. All rights reserved.