Empirical models of airflow output, power consumption, and primary airflow were developed for parallel fan powered variable air volume terminal units at typical operating pressures. Both 8 in. (203 mm) and 12 in. (304 mm) primary air inlet terminal units from three manufacturers were evaluated. Generalized models were developed from the experimental data with coefficients varying by size and manufacturer.

Fan power and airflow data were collected at downstream static pressures over a range from 0.1 to 0.5 in. w.g. (25 to 125 Pa). Upstream static pressures ranged from 0.1 to 2.0 in. w.g. (25 to 498 Pa). Data were collected at four primary air damper positions and at four terminal unit fan speeds. Model variables included the RMS voltage entering the terminal unit fan, the inlet air differential sensor pressure, and the downstream static pressure. A model was also developed to quantify air leakage when the unit fan was off.

In all but one of the VAV terminal units, the resulting models of airflow and power had R2 values greater than 0.90. For the exception, excessive air leakage from the unit appeared to limit the ability of the airflow and power models to capture the variation in the experimental data. These performance models can be used in HVAC simulation programs to model parallel fan powered VAV systems.

Units: Dual