Empirical models of airflow and power consumption were developed for series and parallel variable air volume fan powered terminal units (FPTUs). An experimental setup and test procedure were developed to test the terminal units over typical operating ranges. The terminal units in this study used either an 8 in. (20.32 cm) or a 12 in. (30.48 cm) primary air inlet. All terminal units utilized electronically commutated motor (ECM) controllers. Data collected were compared against previous data collected for silicon controlled rectifier (SCR) units. Generalized models were developed for both series and parallel units, and compared against models developed for SCR units. In addition to the performance modeling, power factor and power quality data were also collected for each terminal unit. The power quality analysis included recording and analyzing harmonic distortion for current, voltage, and power up to the 25th harmonic. The total harmonic distortion (THD) was also recorded and presented. For the series terminal units, models were developed for fan airflow, fan power, and primary airflow. The models for fan airflow all had R2 values above 0.987. The models for fan power all had R2 values above 0.968. The models for primary airflow all had R2 values above 0.895. For the parallel terminal units, models were developed for leakage, fan airflow, fan power, and primary airflow. All of the leakage models had R2 values above 0.826. All of the fan airflow models had R2 values above 0.955. All of the fan power models had R2 values above 0.922. All of the primary airflow models had R2 values above 0.872. The real power THD was below 1.5 percent for both series and parallel FPTUs. The current THD ranged from 84 percent to 172 percent for series FPTUs and from 83 percent to 183 percent for parallel FPTUs. The voltage THD was below 1.4 percent for both series and parallel FPTUs. The performance models developed will help improve the accuracy of building energy simulation programs for heating, ventilation, and air conditioning (HVAC) systems utilizing ECM controlled FPTUs. Increasing the accuracy of these simulations will allow HVAC system designers to better optimize their designs for specific building types in a wide variety of climates.

Semi-empirical models for series fan-powered variable air volume terminal units (FPTUs) were developed based on models of the primary, plenum, fan airflow and the fan power consumption. The experimental setups and test procedures were developed respectively for primary, plenum and fan airflow to test each component of the FPTUs at typical design pressures and airflows. Two sizes of the terminal units from three manufacturers were used in this study. All of the FPTUs were equipped with electronically commutated motors (ECM). Data provided by the models were compared against the data from previous experiments to prove the models’ validity. Regression modeling was performed by using SigmaStat. The model of primary airflow had an R2 above 0.948 for all the terminal units evaluated while the plenum airflow model had an R2 above 0.99. For all the terminal units, the R2 of the fan airflow model was ranged from 0.973 to 0.998. Except for one fan, the fan power consumption model was able to characterize the power performance and had an R2 above 0.986. By combining the airflow and power models, the model for series FPTU was developed. Verification was made to prove the FPTU model’s validity by comparing the measured and predicted data of airflow and power consumption. Correction factors were used in the primary airflow model to compensate for the difference caused by large measurement errors and the system effects. The predicted values were consistent with measurements and no offset was needed in the primary airflow model. Generally, the newly established model was able to describe the airflow performance as well as power consumption of series FPTUs without adding complexity.