Energy modelling and analysis of variable speed series fan-powered terminal units (FPTUs) using energy management system (EMS) in EnergyPlus

The energy impact of constant and variable speed fan operations in series fan-powered terminal units (FPTUs) was investigated by simulating a small office building with four climates in EnergyPlus. While the existing module in EnergyPlus was used to model the performance of constant speed FPTUs, the performance model of variable speed FPTUs was implemented by using energy management system and user-defined modules. Compared with constant speed FPTUs, the variable speed FPTUs could save up to 90% of terminal unit fan energy, 4% of central supply fan energy, and 6% of central cooling coil energy although the heating energy increased due to reduction of fan motor heat gains. The overall savings in the HVAC system was in a range of 15-35% depending on local climates. The demonstration of modelling variable speed series FPTUs in EnergyPlus could increase the awareness of energy efficiency design and promote its incorporation into standard EnergyPlus modules.