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The goal of this study was to quantify the efficiency ofblowers driven by electronically commutated motors (ECMs)in horizontal low-profile fan coil units (FCUs) over the typicalrange of operating pressure. The airflow and power of twelveFCUs from three manufactures were measured over an externalstatic pressure (ESP) range from 0 to 125 Pa (0 to 0.5 in.w.g.) in a well-instrumented laboratory environment. The overallefficiency of blower/motor combination was also determinedfrom the experimental measurements. Due to differentECM controls, the effect of increasing ESP on airflow andpower varies among units from different manufactures. Blowerswith constant torque control may suffer from moderate tosignificant airflow decreases while blowers with constantairflow control maintains airflow over the tested ESP range.The overall efficiency increased with increasing ESP althoughdrops in efficiency were measured at the higher end of ESPs atlower speeds. The maximum overall efficiency measured fromthe twelve units was under 25% while 91% of the data pointswere below 20%, which was dramatically lower than thedefault efficiency of 60 to 70% in building energy simulationprograms. Statistical measures of 25% percentile, median, and75% percentile in the overall efficiency over the tested ESPrange were identified through statistical analysis. Theseresults provided important information on the power calculationsof blowers with ECMs in horizontal low-profile fan coilunits with ESPs ranging from 0 to 125 Pa (0 to 0.5 in. w.g.).