Annual Energy Performance Evaluation of Series and Parallel Fixed-Airflow Fan-Powered Terminal Units

摘要

Given the limited capacity of modeling fan-powered terminal units (FPTUs) in EnergyPlus, an alternative model following the mass and energy balance approach was developed and implemented in Engineering Equation Solver (EES) to capture the terminal unit performance over a range of design options and operating characteristics. To evaluate the ability of the alternative model for energy calculation and investigate the energy impact of FPTU design options, the annual energy consumption of a single-story, five-zone office building with a single-duct variable-air-volume (VAV) system was determined in EnergyPlus and EES. Parametric runs were performed in both EnergyPlus and EES with the combination of two terminal unit fan motor types, three sizing factors for electronically commutated motors (ECMs), and five climate conditions. Although different modeling assumptions existed between the EnergyPlus and EES models, the comparative analysis revealed that both models could be used to quantify the energy savings from different motor types and equipment oversizing for fixed-airflow FPTUs. Compared to the energy use of series FPTUs with permanent split capacitor (PSC) motors, results showed 3.5%-6.7% annual energy savings by increasing ECM sizing factors in series units. The energy benefit of increasing ECM sizingfactors in parallel units was significantly smaller than the savings in series units because the electricity savings from parallel terminal unit fans tended to be offset by the increased energy use of supplemental heating. Without considering the energy impact of air leakage from parallel units, results showed that parallel units always used less annual energy than series units regardless of motor type. However, strategically sized series ECM FPTUs could narrow the gap in energy use between series and parallel FPTUs.