In densely populated areas where many ground source heat pump (GSHP) systems are present, it becomes important to consider the thermal influence ofneighbouring GSHP installations while designing these systems. This question has started to become frequent in cities like Stockholm in Sweden. For thedesign and performance analyses of the GSHP systems, simulations at different detail levels regarding time step are used. Borehole heat loads of realinstallations can be estimated with different time resolution from case to case. This article presents a first step towards the development of a model to calculatethe mutual influence of neighbouring GSHP installations: a first elementary model is developed to quantify such influence, then the error introduced whenperforming simulations with different heat load steps, i.e. annual and hourly, is analyzed from a perspective of multiple neighbouring GSHP installations.It is found that a negligible error is derived when considering low temporal resolution data.