Modeling of ECM Controlled Series Fan-powered VAV Terminal Units



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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.