As of October 2014, a new calculator
is available for the Minimum Indoor Air Quality Performance prerequisite. This correction includes the new calculator in the guidance for multiple-zone systems.
1. In Step-by-Step Guidance, Mechanically Ventilated Spaces (and Mixed-Mode Spaces When a Mechanical Ventilation is Active), [BD+C page 611, Step 2; ID+C page 311, Step 2; BO+M page 399, Step 4]
Replace the first sentence in last the bullet with the following: "For multiple-zone systems, use the calculator provided by USGBC or ASHRAE’s 62MZCalc Spreadsheet."
2. In Further Explanation, Calculations for Multiple-Zone Recirculating Systems [BD+C page 617; ID+C page 316; BO+M page 402]
Replace the first paragraph with the following: "Because of the complexity of the calculations for multiple-zone recirculating systems, project teams must use the calculator provided by USGBC, ASHRAE's 62MZCalc spreadsheet, or energy modeling software to perform the ventilation rate procedure calculations and determine the amount of outdoor air required at the system level."
3. In Further Explanation, Calculations for Multiple-Zone Recirculating Systems, System Ventilation Efficiency [BD+C page 617; ID+C page 317; BO+M page 402]
Replace the second and third paragraphs with the following: "The critical zone is the zone with the highest proportion of required outdoor air to provided supply air. Critical zones are often densely occupied spaces, such as conference rooms. If using the calculator provided by USGBC or ASHRAE’s 62MZCalc spreadsheet, when all zones are entered, the critical zone for the system is determined automatically.
For large projects, it may not be feasible to enter each individual zone. In these cases, the mechanical engineer can determine the outdoor air required for the system simply by identifying the potentially critical zone(s). For a detailed discussion of identifying critical zones, see ASHRAE Standard 62.1–2010, Appendix A–A3.1, Selecting Zones for Calculation, and ASHRAE 62.1–2010 User’s Manual, Example 6-L."