We are modelling an office building in Switzerland with LEED v4 Core and Shell and have a question regarding the required ventilation rate for parking garages. According to ASHRAE 62.1 Table 6.4, a minimum exhaust rate of 3.7 l/sm² is required. This would more than double the rate as required by our national standard SWKI VA 103-01. We would like to keep the rate prescribed by our national code, but maintain the credit for EQ Minimum Indoor Air Quality Performance and EA Minimum Energy Performance.

We would like to apply LI 10371 and LI 10247 and model garage demand controlled ventilation. This gives us the next points to consider:

- we should prove that our approach suffices with an Exceptional Calculation Measure (ECM)

- the proposed building is modeled as designed, taking into account requirements for sensors as in LI 10371

- Focus can be limited to contaminant CO

- a minimum of 0.05 cfm/sq ft (= 0.258 l/sm²) must be guaranteed

- LI 10371: CO must be limited according to values in ASHRAE 62.1 addendum d, but LI 10247 states: "all concentration limits must be based on local code or some other cognizant authority. If the contaminant is CO, a concentration limit of 35 ppm time-weighted average (8 hours) and levels not the exceed 50 ppm at any time is recommended."

We have some questions about the correct procedure, to assure compliance with LEED, and realize a sufficient air quality in the parking garage with energy-efficient systems.

Our national code maintains a limit for CO of 100 ppm, which is proven through a stationary CFD simulation. The number of cars, usage of the building, driving distance, start/stops etc are taken into account when determining the minimal ventilation rate. The exposure time is not mentioned and can also not be considered in our stationary simulation. As it is a parking garage, people will not linger here. In ASHRAE 62.1 Table B-2 gives the maximum exposure (WHO/Europe) of 90 ppm for 15 minutes. As mentioned before, in LI 10247, a much lower threshold is recommended (but not required?).

Would it suffice for EAp2, as ECM, if we can prove with a CFD simulation that our parking garage ventilation concept maintains a maximum CO level of 90 ppm? A narrative can explain how the sensors are placed, on which thresholds they will act, and what is taken into account in our national standard to determine flow rates?

For IEQp1, would it suffice that we can theoretically realize the 3.7 l/sm² with the smoke extraction fans? However, they are only activated in case of an emergency.

Thank you for your feedback!