# Another Enclosed Parking Garage Question



## tim walocha (May 17, 2016)

2012 Edition

This one has to do with 501.2.  Parking garage exhaust leaves the garage under positive pressure and is combined with toilet exhaust also under positive pressure.  the combined duct then goes through a rated tenant separation wall (garage to corridor and B Group tenant space).  Eventually discharge to exterior.  I have three code violations here correct?
1. No damper permitted in exhaust duct.
2. No combining of systems in same duct.
3. positive pressure duct in occupied space. 

Sounds simple but I can't find a code section for number 3.  I think section 501.2 addresses number 2 but it doesn't say that different types of environmental air shall be independent, just environmental air shall be independent of all other exhaust systems.  (Not the same thing in my book)

Code sections please!


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## @david (May 17, 2016)

Since the exhaust is taken from a garage it has high levels of contaminates...co2 and possible vapors - 502.1.4. Requires the duct exhaust to conform with the requirements of 510 hazardous exhaust. Section 510.6.1.  will prohibit fire and smoke dampers. 506.6.2, 506.3,506.4 and the next section should make some serious changes. The install probably has more than the 3 violations.
Virginia sections but should be same in the IMC 2012


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## cda (May 17, 2016)

welcome mmmmmmm


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## Builder Bob (May 18, 2016)

501.2 deals with enviromental air -- defined as *ENVIRONMENTAL AIR. *Air that is conveyed to or from occupied areas through ducts which are not part of the heating or air-conditioning system, such as ventilation for human usage, domestic kitchen range exhaust, bathroom exhaust, domestic clothes dryer exhaust and parking garage exhaust.


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## Builder Bob (May 18, 2016)

*502.13 Public garages. *
Mechanical exhaust systems for public garages, as required in Chapter 4, shall operate continuously or in accordance with Section 404.

*SECTION 404 ENCLOSED PARKING GARAGES 

404.1 Enclosed parking garages. *
Mechanical ventilation systems for enclosed parking garages shall be permitted to operate intermittently in accordance with Item 1, Item 2 or both. 

1. The system shall be arranged to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.
2. The system shall be arranged to operate automatically by means of carbon monoxide detectors applied in conjunction with nitrogen dioxide detectors. Such detectors shall be installed in accordance with their manufacturers’ recommendations.
*404.2 Minimum ventilation. *
Automatic operation of the system shall not reduce the ventilation airflow rate below 0.05 cfm per square foot (0.00025 m3/s • m2) of the floor area and the system shall be capable of producing a ventilation airflow rate of 0.75 cfm per square foot (0.0038 m3/s • m2) of floor area. *

404.3 Occupied spaces accessory to public garages. *
Connecting offices, waiting rooms, ticket booths and similar uses that are accessory to a public garage shall be maintained at a positive pressure and shall be provided with ventilation in accordance with Section 403.3.


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## rgrace (May 18, 2016)

(1) Parking garage exhaust is not "hazardous" exhaust, it is defined in Chapter 2 as environmental air. There is nothing in the code that prohibits a damper from being installed in this system. (2) Because bathroom exhaust and garage exhaust are both considered environmental air, 501.2 permits these exhaust systems to be combined. (3) Positive pressure ducts refers to plenum spaces only in 601.4, not occupied spaces.


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## tim walocha (May 18, 2016)

Builder Bob,
Your two posts are understood.  here is the dilemma or inconsistency in the code.  Your provided code section definition of environmental air indicates the garage exhaust is considered _environmental air_  and subject to 501.  I don't think it can be both environmental air and exhaust. 404.3 definitely applies and that addresses issue number 3 above.

1 and 2 are still up for discussion.


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## tim walocha (May 18, 2016)

I think Rgrace interpretation makes the most code sense but I still don't like it.


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## Builder Bob (May 19, 2016)

According to 501.2 garage exhaust is considered environmental air...... Also you are correct that 1 & 2 are up for discussion., 

I added the discussion about the definition because I did not agree with the exhaust being hazardous.  

The other section 404.1 was included because that is all the guidance you get from the mechanical code about enclosed parking garages.

Now, as far as # 1 goes, that may be an issue that comes into play with IBC 717 Ducts and Transfer openings. 

As far number # 2 goes, it may be allowed as a combined system as long as 501.4 can be met while maintaining the requirements of 404.2.

I believe an air balancing report may be required for the areas where the restrooms are and ensure that the garage exhaust is running at peak speeds. It may prove problematic with excessive air flow out of the restrooms to get the HVAC system to balance. 

We run into this problem a lot of times when kitchen exhaust hoods and the air balancing report don't take into account the interaction of normal HVAC and exhaust in a kitchen.


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## JBI (May 19, 2016)

"  I don't think it can be both environmental air and exhaust."
While still in the garage it is 'environmental air', once it enters the ducts that take it out of the building it is 'exhaust'.

"Parking garage exhaust is not "hazardous" exhaust" and "I did not agree with the exhaust being hazardous."
If it were not 'hazardous' then why would it need to be exhausted to the exterior and triggered by a combination of occupants and CO/Nitrogen Dioxide sensors?


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## Builder Bob (May 19, 2016)

I believe that the terminology within the definition is causing a lot of confusion here....per the definition of the code, parking garage exhaust is environmental air.

The only saving grace to the original post is that the combining of two environmental air systems into one from outside the thermal envelope of the building and from unconditioned air, may play havoc on the energy code requirements while maintaining the air flow required for both systems.


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## rgrace (May 25, 2016)

tim walocha said:


> I think Rgrace interpretation makes the most code sense but I still don't like it.


 
(big smile) There are a lot of code sections that I do not like, that's why they get changed every three years and I get involved. For now, not liking it is not enough reason to reject it, and will not stand up to a challenge to a review board.


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