A Comparison of the Annual Energy Use of Fixed- and Variable-Airflow Parallel Fan-Powered Terminal Units in a Small Office Building

摘要

A mass and energy balance (MEB) approach was implemented using Engineering Equation Solver (EES) (Klein and Alvarado 2015) to estimate the annual energy performance of a single-ductvariable-air-volume (VAV) system withfixed-and variable-airflow parallel fan-powered terminal units (FPTUs). Fans with both permanent-split capacitor motors controlled by silicon control rectifiers and electronically commutated motors (ECMs) were evaluated, along with the energy impact of leakage. A comparison was also provided to variable- and fixed-airflow series FPTUs. Hourly zone loads in a five-zone building were generated using Energy-Plus. The hourly zone loads and weather data were used as input to a single-duct VA V system model using EES to estimate the energy use for a five-zone building in five cities: Houston, TX; Phoenix, AZ; Chicago, IL; New York, NY; and San Francisco, CA. The results showed less than 0.4% difference in energy use between the fixed-airflow ECM and PSC parallel FPTUs. Variable-airflow parallel units provided a maximum of 0.8% savings compared to the baseline fixed-airflow parallel FPTU. Leakages of 5% and 10% in cooling mode were simulated for parallel FPTUs. Parallel units with 5% leakage performed comparably to variable-airflow series units. Increasing leakage to 10% negated any benefit that a parallel unit had over the variable-airflow series units in all five cities.