ASHRAE Standard 62.1 Ventilation for Acceptable Indoor Air Quality specifies minimum ventilation rates and other measures intended to provide indoor air quality (IAQ) that is acceptable to human occupants and that minimizes adverse health effects. ASHRAE Standard 62.1 includes three different procedures for ventilation design compliance:
Ventilation Rate Procedure (VRP)
Indoor Air Quality Procedure (IAQP)
Natural Ventilation Procedure
The compliance can be achieved by using a combination of the three ventilation design procedures mentioned above for any project. The key difference between commonly used VRP and IAQP is that the VRP is a prescriptive approach whereas IAQP is a performance-based approach for ventilation design.
While following IAQP, for any zone or system, the building outdoor air intake rates and other system design parameters are based on an analysis of contaminant sources, contaminant concentration limits, and level of perceived indoor air acceptability.
While the VRP allows that recirculated air be cleaned, the specified outdoor air ventilation rates may not be reduced. On the other hand, the IAQP allows any method to be used to achieve the contaminant concentration limits, including source control, air cleaning, or dilution of indoor contaminants with outside air.
When to apply IAQP?
The IAQP requires the building and its ventilation system to be designed to achieve both objective and subjective criteria. The IAQP allows ventilation air to be reduced below rates that would have been required by the VRP if it can be reliably demonstrated that the resulting air quality meets the required criteria. This helps reduce the overall energy usage intensity (EUI) of the project while maintaining indoor air quality.
The IAQP may allow for a more cost-effective solution to providing good air quality, as all design strategies may be considered and compared, including the following:
Dilution ventilation and the commensurate added energy costs of conditioning greater volumes of outdoor air
Controlling contaminants at the source by specifying low-emissions carpets, wall coverings, paints, adhesives, and furnishings
Air cleaning strategies
Evaluation of occupant and/or visitor satisfaction based on perceived air quality in similar buildings or through post-occupancy evaluation