Optimal flow rate for maximizing ground source heat pump performance

Ground source heat pumps (GSHP) already have good performance but it could be 10 to 40% higher if the optimum flow rate was used in the ground loop. For GSHP in particular, it is not known what this optimum flow rate is and how it is affected by changing conditions: e.g. borehole depth, number of boreholes and thermal shunt.

To fill this gap, this project proposes to build a borehole-to-heat-pump model from which general analytical expressions may be derived for the optimum flow rate. The model will be validated with a test rig at KTH Live-in Lab and data from real installations. A simple web-based tool will be developed so that designers may find installation-tailored optimum flow rates.

In addition, an extensive statistical parametric study will be performed. The statistical study will help finding heuristic flow rates: not necessarily exactly optimal but robust over a large range of conditions. This will, in turn, lead to an easier and faster implementation in real installations.