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Makeup air for vehicle source capture system

Sifu

Sifu

SAWHORSE
Joined
Sep 3, 2011
Messages
2,809
I have a proposed vehicle source capture system in a repair garage. The IMC doesn't provide any specific guidance on these systems that I can find. Is makeup air for the source capture system required to maintain balance?
 
I believe this should cover it for you...

2021 IMC 501.4 Pressure Equalization​

Mechanical exhaust systems shall be sized to remove the quantity of air required by this chapter to be exhausted. The system shall operate when air is required to be exhausted. Where mechanical exhaust is required in a room or space in other than occupancies in Group R-3 and dwelling units in Group R-2, such space shall be maintained with a neutral or negative pressure. If a greater quantity of air is supplied by a mechanical ventilating supply system than is removed by a mechanical exhaust for a room, adequate means shall be provided for the natural or mechanical exhaust of the excess air supplied. If only a mechanical exhaust system is installed for a room or if a greater quantity of air is removed by a mechanical exhaust system than is supplied by a mechanical ventilating supply system for a room, adequate makeup air shall be provided to satisfy the deficiency.
 
I have the same issue for a nail and pedicure salon, which requires 50 cfm of dedicated exhaust for each work station. Our view is that make-up air is required.

IMC 2021 Definitions:

BALANCED VENTILATION. Any combination of
concurrently operating mechanical exhaust and mechanical
supply whereby the total mechanical exhaust airflow rate is
within 10 percent of the total mechanical supply airflow rate.
Click to expand...

IMC 2021:

403.1 Ventilation system. Mechanical ventilation shall be
provided by a method of supply air and return or exhaust air
except that mechanical ventilation air requirements for
Group R-2, R-3 and R-4 occupancies shall be provided by an
exhaust system, supply system or combination thereof. The
amount of supply air shall be approximately equal to the
amount of return and exhaust air. The system shall not be
prohibited from producing negative or positive pressure. The
system to convey ventilation air shall be designed and
installed in accordance with Chapter 6.
Click to expand...

608.1 Balancing. Air distribution, ventilation and exhaust
systems shall be provided with means to adjust the system to
achieve the design airflow rates and shall be balanced by an
approved method. Ventilation air distribution shall be
balanced by an approved method and such balancing shall
verify that the air distribution system is capable of supplying
and exhausting the airflow rates required by Chapter 4.
Click to expand...
 
I read all the same sections and came to the same conclusions, but there is also this section , which could be read to allow the engineer to design the system as they see fit. In this case, the garage is perfectly balanced, until you extract 1800cfm through the source capture system. On the one hand, one could hang their hat on the initial charging language of 502.14 (underlined), which mandates compliance with 403, and 403 requires a balanced system. The additional source capture system would then be included in that balance. On the other hand, one could say the source capture system is added to the balanced system, not included in it. I don't really see it the second way, but maybe the engineer can convince me. I will have a conversation with them.

More insight is greatly appreciated.




502.14 Motor vehicle operation. In areas where motor vehicles
operate, mechanical ventilation shall be provided in
accordance with Section 403. Additionally, areas in which
stationary motor vehicles are operated shall be provided with
a source capture system that connects directly to the motor
vehicle exhaust systems. Such system shall be engineered by
a registered design professional or shall be factory-built
equipment designed and sized for the purpose.

In the commentary:
No performance criteria are
given for the operation and design of a source capture
system. Therefore, the system must either be designed
by a registered design professional or must be a factory-
built system that is designed and sized for the
intended purpose.
 
The building also has a large shop with a significant dust collection system, and additional room exhaust. No makeup air is provided, and that is spelled out in the IMC. This one is making me question the little I thought I knew.
 
501.4 Is where you need to go for the requirement for makeup air. It applies to any and all exhaust systems, not certain specific ones. How the makeup air is supplied is left up to the designer, but it does need to be supplied. It can come from a dedicated makeup air unit, through economizers in the HVAC system properly controlled, or even a simple motorized or gravity wall damper, but it does need to be provided. Bring a building into too much of a negative and you will have all sorts of problems
 
klarenbeek said:
501.4 Is where you need to go for the requirement for makeup air. It applies to any and all exhaust systems, not certain specific ones. How the makeup air is supplied is left up to the designer, but it does need to be supplied. It can come from a dedicated makeup air unit, through economizers in the HVAC system properly controlled, or even a simple motorized or gravity wall damper, but it does need to be provided. Bring a building into too much of a negative and you will have all sorts of problems
Click to expand...
These spaces are in the thousands of cfm's negative. There is no MAU, no transfer grills or dampers, natural ventilation is not allowed to be used, at least in the repair garage, and if used elsewhere it should at least be noted, however I can't imagine relying on the opening of doors (not sure you could open them with that pressure imbalance) in our climate, and the supply air is not enough. For example, in one room the supply is 5,000cfm, the room exhaust is 1,700cfm, the dust collection exhaust is 15,000cfm. I understand a slight negative balance but that is so off I figure I must be missing something. I don't see any makeup air from any source from the designer. I am sure they will set me straight when I talk with them.
 
Sifu said:
I read all the same sections and came to the same conclusions, but there is also this section , which could be read to allow the engineer to design the system as they see fit. In this case, the garage is perfectly balanced, until you extract 1800cfm through the source capture system. On the one hand, one could hang their hat on the initial charging language of 502.14 (underlined), which mandates compliance with 403, and 403 requires a balanced system. The additional source capture system would then be included in that balance. On the other hand, one could say the source capture system is added to the balanced system, not included in it. I don't really see it the second way, but maybe the engineer can convince me. I will have a conversation with them.

More insight is greatly appreciated.




502.14 Motor vehicle operation. In areas where motor vehicles
operate, mechanical ventilation shall be provided in
accordance with Section 403. Additionally, areas in which
stationary motor vehicles are operated shall be provided with
a source capture system that connects directly to the motor
vehicle exhaust systems. Such system shall be engineered by
a registered design professional or shall be factory-built
equipment designed and sized for the purpose.

In the commentary:
No performance criteria are
given for the operation and design of a source capture
system. Therefore, the system must either be designed
by a registered design professional or must be a factory-
built system that is designed and sized for the
intended purpose.
Click to expand...

I think both the language and the intent of the code are clear. The system is balanced when the 1,800 cfm source capture system is not operating. Perfect. But the system also has to be balanced when the 1,800 cfm source capture system is operating, so there needs to be an 1,800 cfm make-up air system that's interlocked so it starts up when the source capture system is turned on.
 
Sifu said:
The building also has a large shop with a significant dust collection system, and additional room exhaust. No makeup air is provided, and that is spelled out in the IMC. This one is making me question the little I thought I knew.
Click to expand...

The fact that no make-up air is provided doesn't mean that the code doesn't require make-up air -- it just means that whoever designed and built it didn't follow the code.
 
Fire station us a lot of point of source exhaust capture, the garage door is most offend open at the time of operating the system. Let not make this to complicated.
 
TheCommish said:
Fire station us a lot of point of source exhaust capture, the garage door is most offend open at the time of operating the system. Let not make this to complicated.
Click to expand...

What's complicated? The code is clear.

Motor vehicle repair shops have used source capture systems for many years. When I was a kid they used to have a round hole cut in the overhead doors and they'd just run a flex hose from the exhaust outlet through that hole when they needed to run an engine in the shop, but those days are long gone. There's no way just opening an overhead door when a source capture system is operating meets to code -- especially in a climate like Massachusetts, when outdoor daytime temperatures may not rise higher than 20 degrees.
 
TheCommish said:
Fire station us a lot of point of source exhaust capture, the garage door is most offend open at the time of operating the system. Let not make this to complicated
Click to expand...
Betting the doors won't be opened when its -10.

Its NOT complicated. 501.4 requires pressure equalization for ALL exhaust systems. If it is approximately equal when the exhaust system is off but not when the exhaust system is on, the requirement of section 501.4 is not being met. The designer needs to provide a source of makeup air for the exhaust system. Ventilation air required in chapter 4 can also serve the dual purpose of makeup air, but if it isn't enough, additional makeup air will be required when the exhaust system is on.
 
Inspector Gadget said:
Question from the Canuck: Do your codes empower ASHRAE 62.1?

ASHRAE requires 1.5cfm of *outside air* per square foot of repair garage space.
Click to expand...
For a repair garage, section 403 of the IMC requires 0.75 CFM of general exhaust per square foot, as the base ventilation rate for all repair garages. 502.14 requires the source capture wherever stationary vehicles run. The source capture is in addition to, not in place of, the 0.75 CFM. Makeup air is needed for both systems...
 
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