Why can I just set the outside air intake flow rates manually?
Damper blades and operators deteriorate over time and their positions can vary as a result of linkage hysteresis. Intake flow rates are difficult to measure with hand-held instruments in the field. To complicate matters, pressure changes on the intake system result from changes in wind speed and direction as well as seasonal changes in stack effect. These pressure changes can significantly increase or decrease outside airflow rates into the building. Changes in the mixed air plenum pressure will compound the problem in VAV systems. In addition, many systems will require that the outside airflow rate be continuously reset to meet changing conditions within the building. Instruments and controls must be used that can react to these changes, in real time, so that the proper dilution airflow rate can be continuously maintained, as is required in the latest proposed addenda (U) to ASHRAE 62-1999.
