In-situ fan differential pressure rise for a series VAV-fan-powered terminal unit with SCR control
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2015 ASHRAE. Open-source and commercial energy simulation programs require differential pressure rise as an input when simulating variable air volume (VAV) HVAC systems usingfan powered terminal units. Typically, these data are generated by the fan/motor manufacturer under standard testing protocols. The fan/motor set is then installed into the finished series fan powered terminal unit and the ensemble is tested as a unitary piece of equipment by the terminal unit manufacturer. Some blogs recommend values as high as 2.5 or greater in. w.g. (622.7 Pa) of differential pressure rise across the fan. Differential static pressure data were collected for fan airflow rates ranging from 500 to 1, 300 ft3/min (0.236 to 0.613 m3/s) while holding a constant downstream static pressure of 0.25 in. w.g. (62.3 Pa) using an 8 in. (203 mm) VAV series fan-powered terminal unit. The differential static pressure rise for this fan ranged from 0.128 to 0.246 in. w.g. (31.9 to 61.3 Pa). From these data, a linear relationship between total airflow and series fan differential static pressure could be inferred. The results show that the low static pressure rise across the fan can be linearly related to total fan airflow. This work will lead to improved input values for use in energy simulation programs and better estimates for energy performance for VAV systems using fan-powered terminal units.
