Development of an efficiency model for electronically commutated motor fan systems in air handling units

Abstract

Motor-driven fan systems in air handling units (AHUs) account for 15.9% of the electricity consumption in commercial buildings. Currently electronically commutated motors (ECMs) have seen increasing applications to replace induction motors for energy savings. While efficiency models for motor-driven fan systems are essential for building energy management, there is no valid efficiency model for ECM fan systems. Therefore, this paper is to develop and validate an efficiency model for ECM fan systems, which can be applied to evaluate the motor input power at given fan airflow rate and head. First, an efficiency model is developed and calibrated using the manufacturer data of a 5.2 kW ECM fan. Innovatively a fan efficiency correction coefficient is introduced to consider the bias of affinity laws and the correlation between motor efficiency and motor shaft power is verified. Then the calibrated efficiency model is validated in an AHU with an array of four calibrated ECM fans. It was found that the proposed fan efficiency correction coefficient can improve the fan efficiency model accuracy by 20% at 20% rated motor speed. Moreover, the validation results show that the developed efficiency model can accurately evaluate the motor input power with an error of 0.096 kW or 1.8%.

Nomenclature
H	=	fan head (Pa)
N	=	motor and fan speed (rpm)
n	=	total number of samples
Q	=	fan airflow rate (m3/s or m3/h)
u	=	uncertainty
W	=	power (kW or W)
η	=	efficiency
${\alpha }_c$	=	efficiency correction coefficient

Subscripts
i	=	ideal
j	=	jth sample
m	=	motor
r	=	rated
s	=	shaft

Acknowledgments

The authors thank ebm-papst Inc. for their support to provide the ECM fan operating data and specially thank Mr. Armin Hauer for the explanation of the manufacturer experimental setup.