4369 (RP-980) -- Experimental Analysis of Measurement and Control Techniques of Outside Air Intake Rates in VAV Systems PDF

This paper presents the results of an experimental evaluation of four airflow measurement techniques and six control techniques used for maintaining minimum outside air intake rates in variable air volume (VAV) systems. The experimental testing was conducted in a controllable environment using a laboratory equipped with a full-size HVAC system. The experimental study indicated that control strategies using the direct measurement of the outside airflow from an averaging pitot-tube array or an electronic thermal anemometer provided the best ventilation control. System control using the outside airflow rate calculated from a CO₂ concentration balance also provided adequate control of ventilation rates expect when occupancy was low or when the outside air represented a small fraction of the supply air delivered. In addition, results showed that the use of a temperature balance to calculate outside air intake rates is not valid under common building operating conditions. When measurement of the outside airflow rate was not possible, plenum pressure control was capable of providing adequate control of outside air intake rates. Finally, a fixed minimum outside air damper position and volumetric fan tracking control strategies both proved to be inadequate control techniques for maintaining minimum ventilation rates in VAV systems.

Units: I-P