HVAC systems energy demand vs. building energy demand

Building energy demand is the amount of heating and cooling energy required to deliver the desired indoor conditions. It is dependent on various building parameters such as building fabrics, glazing percentage, occupancy pattern, level of internal gains, etc. Despite that building demand is often used for energy performance evaluation in the practice, it can be inaccurate and even misleading when the building is serviced by an HVAC system. The amount of energy required by the HVAC system from the primary sources or systems, to deliver the required heating and cooling in the building, does not equate building demand in most circumstances. An HVAC system may show different energy performance in different buildings, due to that the HVAC system’s characteristics and operational conditions are affected by the thermal load and behaviour of the building. It is therefore necessary to analyse the correlation between building’s dynamic load profile and the performance of the HVAC systems. In this paper, we used a typical rectangular UK office building with combined open plan and cellular offices to analyse the correlation between the building’s heating and cooling load profile and the performance of different HVAC systems, i.e. the variable air volume system (VAV), the constant air volume system (CAV), the fan coil with dedicated outside air system (FC) and the chilled ceiling with radiator heating and dedicated outside air system (ChCeil). Building fabrics are selected to comply with the latest UK national standards. By running a series of simulations in EnergyPlus and in-depth analysis of outputs, we aim to provide a set of guidelines on HVAC system selection at early design stages based on total energy performance