3.6.5 Zone Level Air Flow

For systems 5 through 8, set the minimum airflow to be the greater of 30% of zone peak airflow, or the outside air ventilation rate.

Defines the type of fan-powered induction box. This is either:

• Series; or
• Parallel

The source of ventilation for an HVAC system. The choices are:

• Natural (by operable openings)
• Mechanical (by fan)

Same as the proposed design except in the following cases:

• Where the proposed design has a zone air distribution effectiveness greater than 1.0, the baseline ventilation shall be calculated using the proposed design ventilation rate procedure calculation with the zone air distribution effectiveness changed to 1.0.
• If the proposed design ventilation rate exceeds that required by the rating authority or building official, then the baseline design ventilation rate shall be only what is required by the rating authority or building official, whichever is greater.
• If a kitchen zone design exhaust rate is greater than 5,000 cfm, use system type 5 or 7 with a demand ventilation system on 75% of the exhaust air. The system shall reduce exhaust and replacement air system airflow rates by 50% for one half of the kitchen occupied hours in the baseline design.

The method used to determine outside air ventilation needed for each hour in the simulation. This information is reported to the system serving the zone. The method of controlling outside air at the system level in response to this information is discussed under secondary systems. Options at the zone level are:

• Occupant sensors: When the space is occupied, the outside air requirement is equal to the design ventilation rate, otherwise, the outside air requirement is the minimum ventilation rate.
• CO₂ sensors in the space: The outside air is determined to maintain a maximum CO₂ concentration in the space. This may be approximated by multiplying the ventilation rate per occupant times the number of occupants for that hour.
• Turnstiles to determine the number of occupants in the space (appropriate for theatres, etc.): The outside air requirement is modulated based on the number of occupants in the space, based on the turnstile counts.
• Fixed ventilation rate. Outside air is delivered to the zone at a constant rate and is equal to the design ventilation rate (see above).

For green building incentive programs, set to CO₂ sensors in the space if the design occupancy is greater than 40 people per 1,000 ft² and the system design outdoor air flow rate is greater than 1,200 cfm, otherwise set to fixed ventilation rate.

For green building incentive programs, set to CO2 sensors in the space if the design occupancy is greater than 40 people per 1,000 ft² and the system design outdoor air flow rate is greater than 1,200 cfm, otherwise set to fixed ventilation rate.

Also for green building incentive programs, enclosed parking garages greater than 30,000 ft² must automatically detect contaminant levels (typically CO) and stage or modulate fan airflow rates to 50% or less provided acceptable contaminant levels are maintained.  This requirement does not apply to garages where the ventilation system motor nameplate horsepower ratio exceeds 1500 ft²/hp, or if there is no mechanical heating or cooling.  In addition, this requirement does not apply if it is not permitted by the authority having jurisdiction.