ASHRAE ST-16-026

Abstract

Scope: A mass and energy balance approach was used to characterize the performance of parallel fan-powered terminal units (FPTUs) with fixed airflow for applications in building simulation programs. The approach included developing relevant massandenergy balance equations for each component—heating coil, fan/motor combination, and mixer—in a parallel fanpowered terminal unit. Two locations of the heating coil were considered. One location, designated as the traditional configuration, was at the discharge of the unit. The second location, designated as the alternative configuration, was at the secondary air inlet. Fixed-airflow parallel fan-powered terminal units use fan motors that include either permanent split capacitor motors controlled by silicon controlled rectifiers or electronically commutated motors. This paper demonstrates how to incorporate fan/motor combination performance models for both permanent split capacitor and electronically commutated motors into the mass and energy balance approach. These fan models were developed from performance data provided by multiple FPTU manufacturers. The fan/motor performance data included an FPTU, a fan airflow range from 250 to 3500 ft3/min (0.118 to 1.65 m3/s), and a motor size range from 0.333 to 1 hp (249 to 746 W). Leakage was included in the models. The system was implemented in Engineering Equation Solver (EES) and results provided to illustrate the effect of leakage in both cooling and heating operations.