Ventilation in unoccupied garage - ASHRAE 62.1

[DomDoucet]

I am working on the HVAC design of a new fire hall building. The fire department is 100% volunteer based and the building will be unoccupied most of the time. The truck bay and bunker room is roughly 6000 square feet; there are 5 truck bays. We have exhaust fans and fresh air intake louvers tied in to sensors (CO, NOx, CO2). The office/training area is served by an HRV with heating coil controlled by occupancy sensor. Reading ASHRAE 62.1, I am trying to determine if constant ventilation is required in the truck bay during unoccupied times. Using the Ventilation Rate Procedure, there is very little information on designing for unoccupied space. Table 6-4 indicates exhaust rates of 0.75 CFM/sq foot for Parking Garage; however, I interpret this as a large garage with lots of traffic. I don't feel Parking Garage suits for the fire hall truck bay.
Any thoughts?

 

[jkauwale]

I believe your design approach with the exhaust fans and sensors (CO, NOx, CO2) is an excellent approach. If you are looking for a sizing method for the exhaust fans in the truck bay then I would use the Industrial Ventilation book. I worked on a 4 vehicle truck bay for an Aircraft Fire Fighting Facility and I referred to this book for recommended practices. It had a section on Vehicle Ventilation that was helpful.

I think you are correct and the ASHRAE Parking Garage rate is not the best source.

With all of this being said, you will have to refer to your Authority Having Jurisdiction for the final say.

Justin K, P.E.

http://www.engproguides.com

 

[DomDoucet]

Thank you!

 

[Drazen]

while not knowing your jurisdiction requirements, i could generally tell that all changes per hour for car parks are related to demand periods, and demand periods are most of time determined firstly by CO sensors, than eventually by other sensors.

that often means car park fans are quite large but are idling most of time. you can freely say that car park is unoccupied 24 hours a day - presence of people is negligible - but ventilation controlled by sensors must be on all the time.

this applies to car parks, not to repair garages.

 

[DrRTU]

You are going in the correct direction. 0.75 CFM/ft2 of exhaust when CO or NOx are in alarm. Make sure you have correct sensor quantity and placement. 100% makeup capibility. Diesel exhaust stays high, CO runs low so a high space may need hi / low exhaust. Use 0.05 CFM/ft2 continuous - a HRV/ERV would be nice. If they operate the truck/car other than to move in or out of space, design a tailpipe collection system. Reel or telescope tube on a rail works best. Show tailpipe system as an alternate so it does not come back later as an issue later.

 

[DomDoucet]

On what is 0.05 CFM/ft2 based? HRV is what we are considering for continuous ventilation.
A dedicated tailpipe collection system is not required in this case; we have cleared it with the appropriate authorities.

 

[DrRTU]

IMC-2009 section 404 - plus it keeps the fuel odor down. The AHJ may be good without source capture but make sure the fire department knows it not in the base. Fire departments are very good with codes and they know what has gone into peer stations.

 

[Drazen]

it really depends on jurisdiction, but in general i believe it is better to have short hourly sessions for minimum ventilation than having continuous ventilation.

as you have to design fans for mandatory extraction, they will inevitably be larger and to avoid speed adjustments and permanent cooling of structures, something like 5 minutes fan work per hour, no matter whether sensors will trigger or not, would work if jurisdiction allows it, and, of course, local habits can have influence as well.

 

[DomDoucet]

DrRTU: Thank you for the reference. Yes, the fire department is aware; they specifically requested not to have exhaust capture. This is a volunteer department and they are not interested in paying for equipment that is absolutely required.

Drazen: Thanks for your recommendation. We were considering interval ventilation as opposed to continuous as well. If we go with an HRV, we could allow for continuous ventilation when the truck bay is occupied and doors are closed (in winter for example). We are currently discussing with the AHJ.

 

[DomDoucet]

Correction: They are not interested in paying for equipment that is NOT absolutely required. The absence of the dedicated tailpipe system has been approved by the authority as well as the head fire chief for the area.

 

[Drazen]

tailpipe is needed for repair garages, or places where motor will be on for extended period of time, as mandated by authorities.

as i always use intermittent ventilation, i do not fully comprehend utilization of continuous ventilation with hrv so I became curious . garages are not heated so you would need to avoid too much cooling on very cold days, but at such days hrv would be exposed to freezing as well, therefore you would need to introduce some heating and than things are becoming more and more expensive if i did not miss something.

 

[DomDoucet]

Drazen: The fire truck garage is considered a "storage garage" as there will be no repair done in the garage. The garage is heated as it can be used for training of the volunteer fire fighters and there are exposed water lines; we also need to protect the equipment located in the fire trucks. The HRV we are specifying is equipped with a defrost mode which recirculates return air within the unit for a few minutes if outdoor air temperature is below -5C. In this way, the HRV is protected. We will also have a small electric heating coil in the supply duct of the HRV so as not to introduce very cold air to the space.

We have received approval from AHJ for the following installation: Exhaust fans & fresh air intakes controlled by NOx and CO sensors. Small HRV for intermittent ventilation to provide fresh air to the space and control humidity (we agree that continuous is overkill).