This prerequisite establishes a baseline for providing a minimum amount of outdoor air to buildings in order to maintain good indoor air quality and keep occupants comfortable and healthy. This prerequisite references ASHRAE 62.1-2007 (with errata but without addenda) and is often more stringent than local building codes, although it is not likely to entail any added costs.

Two cases, both may be needed

The compliance paths for mechanically ventilated and naturally ventilated spaces, Case 1 and Case 2, are somewhat different and you may need to follow both paths for the same building on a space-by-space basis. Spaces served only by natural ventilation must follow the distinct requirements set out in Case 2, even if other spaces in the same building are mechanically ventilated and are following Case 1. Mixed-mode spaces which alternate between natural or mechanical ventilation must follow the compliance path for mechanical ventilation, Case 1.

For additions and major renovations, confirm that all ventilation systems serving the project meet the ventilation rates required by ASHRAE 62.1 2007, even if the ventilation system design itself is outside the scope of the project. If base building systems do not meet the standard’s requirements, you will need to either increase ventilation rates to comply or provide detailed analysis documenting the constraints and explaining why the base building systems cannot be upgraded.

There’s some confusion in this language on whether mixed-mode refers to a ventilation design with both natural and mechanical ventilation all the time, which needs to be divided up to show compliance, or to a system where either is optional, in which case the worst-case design conditions are for when only the mechanical systems are used and window are shut.

Any ventilation systems serving the project are covered

Commercial interior projects will need to confirm that any ventilation systems serving the project meet the ventilation rates required by ASHRAE 62.1-2007, even if the ventilation system design itself is outside the scope of the project. If base building systems cannot be modified to meet the standard’s requirements, you will need to provide detailed analysis documenting the constraints and explaining why the base building systems cannot be upgraded. Systems must be able to provide at least 10 cfm per person to meet this prerequisite.

ASHRAE 62.1: 2007 vs. 2004

The 2007 edition of ASHRAE 62.1 combines  62.1-2004 and the eight approved and published addenda to the 2004 edition. The new edition does the following:

• Clarifies dehumidification analysis requirements and offers exceptions to the 65% relative humidity limit requirement and to the net-positive intake-airflow requirement.
• Corrects occupant category inconsistencies and provides additional information for several occupancy categories.
• Updates references and clarifies the text particularly as related to subjective evaluation of air quality.
• Updates information to be consistent with the U.S. EPA National Ambient Air Quality Standards.
• Includes a new  appendix that summarizes the documentation requirements in the body of the standard, thus providing a single point of reference for users.
• Requires proper design for buildings that contain both ETS and ETS-free areas, by requiring classification of areas based on expected presence of ETS, pressurization of ETS-free areas, separation of ETS and ETS-free areas, and cautionary signage for ETS-areas.