VC-20-007 -- Using Normalized Airflows and Powers to Model the Performance of Multispeed Fan-Coil Units with Permanent Split Capacitor Fan Motors (RP-1741)

Four manufacturers provided laboratory airflow andpower data as a function of external static pressure for37 multispeed fan-coil units with permanent split capacitormotors. These data were used to develop an airflow performancemodel of fan-coil units that could be implemented in abuilding simulation program. The fan-coil units had fanmotors ranging from 0.033 hp to 0.75 hp (25 W to 560 W) andmaximum airflows that ranged from 242 ft3/min to 2646 ft3/min(0.11 m3/s to 1.25 m3/s). The model included normalized fanmotor power and fan airflow at each speed setting. Thenormalized power versus normalized airflow data for therange of external static pressures typically plotted in a groupingof data at each speed setting. These average normalizedpowers and airflows were evaluated for each unit. The normalizedvalues were combined with a linear fit to the high airflowand power curves to develop a straightforward process forgenerating airflow and power curves as a function of externalstatic pressure. A procedure was developed to determine theintersection of the air system curve with the fan-coil airflowand power curves. The resulting model could be used todescribe the airflow and power performance of a specificmanufacturer’s permanent split capacitor fan-coil unit overmultiple speeds and external static pressures.