Minimum outside air control methods for VAV systems

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:211828

Elovitz, D M ^[1]

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1. Energy Economics, Inc., Natick, MA (United States)

Since 1973, various editions of ASHRAE Standard 62 have established criteria for determining the amount of outside air ventilation necessary to achieve acceptable indoor air quantity. That amount is the minimum outside air quantity. In a constant-volume system, once that quantity has been properly determined and the system has been set up to take in that minimum outside air quantity, they could be confident that they would always have enough outside air ventilation to dilute contaminants generated within the building--unless some sort of mechanical failure occurred or someone changed the controls. But the growing popularity of variable-air-volume (VAV) systems has introduced new factors into the equation and new challenges for designers. This discussion considers only the minimum outside air quantity for ventilation and does not address system operation during the outside air economizer cycle. When the system is on an outside air economizer, the outside air quantity is based on the need for cooling and is generally greater than the minimum required for ventilation. If, during very cold weather, satisfying the temperature requirement would mean less outside air than the minimum ventilation quantity, then whatever minimum outside air control strategy is selected would come into play. For simplicity and clarity, the discussion completely ignores the economizer cycle since the concern is with maintaining minimum ventilation. Similarly, the discussion is in terms of systems with return fans. A relief fan that provides power exhaust to outdoors may be used in stead of a return fan, or there may be a single supply fan with neither a return fan nor a relief fan. Generally, the issues of stable measurement and control are the same as those discussed with a return fan.

• OSTI ID: 211828
• Report Number(s): CONF-950624--
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
AIR QUALITY
BUILDINGS
INDOOR AIR POLLUTION
VARIATIONS
VENTILATION