Error analysis of measurement and control techniques of outside air intake rates in VAV systems.

This paper provides a theoretical error analysis of common airflow measurement and control techniques to maintain minimum outside air intake rates in variable air volume (VA V) systems. The results of the error analysis indicate that control strategies using direct airflow measurement from either an averaging Pitot-tube array or an electronic thermal anemometry provided the best ventilation control. Calculation of the outside airflow rate using a C02 concentration balance can a lso allow for adequate system control, except when occupancy is low or when the outside air represents a small fraction of the supply air delivered. In addition, the results show that the use of the temperature balance technique to calculate the outside air intake rate is not adequate under common building operating conditions. In the case when measurement of the outside airflow rates is not possible, plenum pressure control can provide adequate control of outside air intake rates. Finally, the use of a fixed minimum outside air damper position or a volumetric fan tracking control strategy both proved to be inadequate control techniques for maintaining minimum ventilation rates in VA V systems.