VC-21-010 -- Part-Load Airflow and Power Model of Multispeed Fan-Coil Units with Electronically Commutated Motors

Fan airflow and fan motor power data as a function ofexternal static pressure on 85 fan-coil units with electronicallycommutated motors were analyzed to develop a part-loadairflow and power model that could be used to estimate energyuse of fan-coil units in building simulation programs. Themodel was developed by estimating the intersections of the airdistributionsystem curve with the fan airflow versus externalstatic pressure curves provided by the manufacturers. Theseintersections were then used to estimate part-load airflow andpower fractions referenced to the airflow and power values atthe high airflow setting of the fan-coil unit. At least four startingexternal static pressures at the high airflow setting wereused to define multiple system curves. The intersections ofthese system and airflow and power curves at a given airflowsetting (medium and low) were then averaged to determine thepart-load airflow and power fractions for each fan-coil unit ateach setting. The data generated with this method proved to beindependent of manufacturer, motor size, and cabinet orientation(e.g., horizontal or vertical). A regression analysis wasthen conducted on all the part-load data and a third-degreepolynomial was used to fit the data. The regression was thencompared to the ideal fan law curve.