The Ventilation Rate Procedure is a prescriptive ASHRAE 62.1 method that calculates required outdoor air based on occupancy and floor area. This straightforward approach uses fixed formulas to determine ventilation rates without requiring ongoing indoor air quality monitoring. It serves as the most commonly used compliance pathway for standard commercial applications.
Calculation Methodology
The procedure combines two components: ventilation per occupant (ranging from 5 to 20 CFM/person depending on space type) and ventilation per unit area (0.06 to 0.12 CFM/square foot). For example, a 5,000-square-foot office with 50 occupants requires: (50 × 15 CFM) + (5,000 × 0.06 CFM) = 1,050 CFM minimum outdoor air. The standard accounts for occupancy diversity through zone-based calculations rather than building-wide averages.
Advantages and Limitations
This procedure offers simplicity, predictability, and lower implementation costs compared to IAQ Procedure alternatives. However, it may over-ventilate lightly-occupied spaces or under-ventilate densely-occupied areas. The method works best for typical building types with consistent occupancy patterns. Systems must include demand-controlled ventilation capabilities in variable-occupancy spaces to optimize efficiency while maintaining compliance.