We are attempting to use special circumstances to satisfy the minimum air quality performance, as our project does not fall under a category.

We have a repair garage where work on vehicles is powered by compressed natural gas. We are planning to go with the option (a) ASHRAE trying to achieve this credit. Table 6-1 in ASHRAE 62.1 does not have ventilation requirements for an auto repair shop, so filling out their minimum air performance calculator is probably not going to be helpful. Table 6-4 details exhaust requirements (1.5CF/sf), but this is double what is required by the IMC, and would have greatly increased the size and price of all the equipment provided for the space. I would put the following into the special circumstances section and we will see if we get a response.

This is the recommendation (below) from our ME....has anyone else had a similar situation? 

"The CNG repair shop will be provided with 0.75CFM/sf of exhaust air during all occupied times. While this does not meet the requirement listed in table 6-4 of ASHRAE 62.1 – 2010, the exhaust system will operate in conjunction with gas detection sensors. When potentially harmful gases are detected within the space, a separate exhaust fan capable of exhausting 2.18 CFM/sf will turn on and will continue to exhaust air from the space at this rate until the sensors detect that there are no longer any potentially harmful gases present within the space. This design was chosen as it meets and exceeds the requirements listed in the International Mechanical code regarding auto repair shops where work is conducted on vehicles that operate off of compressed natural gas, and the project budget would not have been able to accommodate each piece of mechanical equipment having to double in size.”

We are not technically meeting the 1.5CFM/sf requirement at all times, but our rationale is clear (above).....Again, anyone have any experience with this one?

Carla Galvanoni

Institute for the Built Environment, Fort Collins, CO