This paper investigates the interaction between supermarket heating, ventilation and air conditioning and refrigeration systems through simulation in EnergyPlus. This interaction has been studied by modelling a generic UK supermarket. The impact on the sum of HVAC and refrigeration energy consumption due to changes in a range of operating conditions was studied. These include the effect of altering HVAC temperature set-points, supply air temperatures and refrigeration case operating temperatures on their overall energy use. Optimum values of the supply air temperature, to minimise CO2 emissions, delivered by the HVAC system were found to vary with UK location, with typical values around 14o C to 16o C.