If a single AHU is supplying outside air to multiple zones through VAV boxes, outside air measurements need to be tested at the AHU level but not a the VAV boxes.

Outside air measurements need to be tested at the system level, and so measurements would need to be taken at each AHU, not just the single supply fan.

If for some reason you needed to make corrections to the ventilation system in order to meet the ventilation prerequisite during the review process, you could do so without having to reset the performance period for all of the performance-based credits. Outside air measurements can and must be redone to confirm that the systems meet the prerequisite after the corrections were made.

You may not have to do the calculations for each of the systems. Under LEED v4, if all or some of the systems have similar parameters, sampling of the systems is allowed. It is likely that the same sampling approach is acceptable under LEEDv4.1. Here’s a list of the parameters that must be similar for the systems to conduct a sample:

There is currently no allowance for this, but a pilot Alternative Compliance Path may be applicable. Teams should contact GBCI to discuss.

If any systems do not meet the required outside airflow during the initial testing the following actions should be taken: If the system (damper) set points for the worst-case condition can be modified to supply sufficient outside air to meet the minimum outdoor air requirements, the team must do so. If the system is incapable of providing enough outside air to meet the minimum requirements, the prerequisite will not be met.

Section 7.6.3.3 of ASHRAE Standard 111-2008 describes the Flow Rate Approximation by Temperature Ratio method for determining outdoor airflow when the outdoor airflow itself cannot be directly measured. The method involves taking temperature measurements of the outside air, the return air, the supply air (mixed air), and the supply air volume. See the standard for more details and note that to maintain an acceptable level of accuracy, a temperature difference of 25°F to 50°F (14°C to 28°C) must be present between the outdoor air and return air temperatures.

In the United States, the list of current non-attainment areas can be viewed on EPA’s Greenbook website here. As of December 2021, some locations within California and Pennsylvania are listed as non-attainment areas for particulate matter 2.5. If your project is located outside the United States, you’ll need to research data on recorded readings for particulate matter at your project location.