# CO2 Monitors to reduce Outside Air



## Mech (Aug 11, 2017)

2015 IMC w/ New Jersey amendments

35,000 sq ft warehouse

The GC asked about monitoring carbon dioxide levels in a warehouse to reduce the operational time of the mechanical ventilation system.  Is this allowed?  I did not see carbon dioxide monitors mentioned.

Thanks,

Mech


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## cda (Aug 11, 2017)

Why is the ventilation required in the first place??

Code section??


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## rgrace (Aug 15, 2017)

I've seen carbon dioxide monitors used in small spaces such as conference rooms to adjust the quantity of outdoor air delivered based on the actual number of occupants in the space. I don't know how this would work in a warehouse if the space had high ceilings. Per 403.3.1.1, the outdoor air has do be delivered to the _breathing zone_ (as defined in Chapter 2). If the occupants are in the _breathing zone_, and the outdoor air is delivered to the _breathing zone_, is it possible to accurately monitor carbon dioxide within the _breathing zone_ and adjust the outdoor air based on that? 403.2, Exception allows for outdoor air reductions when an engineered ventilation system design can prevent the maximum concentration of contaminants from being exceeded. Again, difficult to evaluate, and carbon dioxide is a method for measurement, it doesn't address contaminates of concern. The International Energy Conservation Code. Section C403.2.5.1 requires "demand controlled ventilation" (as defined in Chapter 2) under certain conditions, but does not indicate how this will be accomplished. This probably doesn't help you make a decision, but it is all I have.


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## mark handler (Aug 15, 2017)

All spaces shall be ventilated
See TABLE 6.1 ASHRAE STANDARD 62


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## tmurray (Aug 15, 2017)

What exactly is the GC proposing; that the equipment is shut off, or just exchanging a minor amount of air? I could see using the area only requirements and assuming the rest is unoccupied provided that the monitors are set for no more than 5000 PPM according to Table B-1 in ASHRAE 62, so the monitor trips in additional ventilation. Is there not a mechanical engineer involved?


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## Mech (Aug 15, 2017)

Thanks for the replies.

I am the mechanical engineer, but the projects I typically work on do not use CO2 monitoring, which is why I asked about CO2 monitors.  I was curious what governing body or code allows CO2 monitors to reduce the Outside Air quantity.  The question came up because the job spec called for radiant heat and we told our client, the GC, that ventilation air is required and that it would need to be tempered.  The GC asked about CO2 monitoring to lower the amount of ventilation air or eliminate it because he did not want the ventilation system running if no one is in the building during the week.  I informed him we could probably use occupancy sensors to activate the system instead.


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## cda (Aug 15, 2017)

Mech said:


> Thanks for the replies.
> 
> I am the mechanical engineer, but the projects I typically work on do not use CO2 monitoring, which is why I asked about CO2 monitors.  I was curious what governing body or code allows CO2 monitors to reduce the Outside Air quantity.  The question came up because the job spec called for radiant heat and we told our client, the GC, that ventilation air is required and that it would need to be tempered.  The GC asked about CO2 monitoring to lower the amount of ventilation air or eliminate it because he did not want the ventilation system running if no one is in the building during the week.  I informed him we could probably use occupancy sensors to activate the system instead.




And that is why you are the Engineer!!!


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## tmurray (Aug 16, 2017)

Mech said:


> Thanks for the replies.
> 
> I am the mechanical engineer, but the projects I typically work on do not use CO2 monitoring, which is why I asked about CO2 monitors.  I was curious what governing body or code allows CO2 monitors to reduce the Outside Air quantity.  The question came up because the job spec called for radiant heat and we told our client, the GC, that ventilation air is required and that it would need to be tempered.  The GC asked about CO2 monitoring to lower the amount of ventilation air or eliminate it because he did not want the ventilation system running if no one is in the building during the week.  I informed him we could probably use occupancy sensors to activate the system instead.


I would be more comfortable with occupancy sensors.


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## mark handler (Aug 16, 2017)

There are other contaminates in the air other than 02
Mold, mildew, radon, off gases from products stored, 
Formaldehyde from exposed wood sheathing, and others.


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## Paul Sweet (Aug 16, 2017)

CO2 sensors to reduce ventilation air are most often used in assembly occupancies where the number of occupants can fluctuate.  

The IMC only requires 0.06 CFM/SF for warehouses, and only requires it when the space is occupied.  A timer or interlocking it with the lights might be an easier way to control it.


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## engprosinc (Nov 15, 2017)

Mech said:


> 2015 IMC w/ New Jersey amendments
> 
> 35,000 sq ft warehouse
> 
> ...


I am working on an eight bay 9,000 sq ft tractor trailer repair shop in NJ. Each of the eight bays will have a dedicated hose reel system to capture the tractor exhaust and vent it outside. Based on NJ IMC, I have to design a ventilation system to provide 0.75CFM/sq ft (as long as there is no fuel dispensed or stored inside the building}. I plan to install six or seven powered  exhaust fans in the walls, one between each overhead door, and the same number of motorized dampers in the walls on the opposite side of the building. This seems like a logical way to address the ventilation requirement. However, it gets cold in NJ, so I will have to temper the ventilation air in the winter. Although there will be six gas fired unit heaters mounted about 10' above the floor throughout the facility, I think they will have a hard time maintaining the temperature in the shop in the winter. Any ideas on the best way to temper the air other than a gas fired air handler? 
Thanks


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## cda (Nov 15, 2017)

engprosinc said:


> I am working on an eight bay 9,000 sq ft tractor trailer repair shop in NJ. Each of the eight bays will have a dedicated hose reel system to capture the tractor exhaust and vent it outside. Based on NJ IMC, I have to design a ventilation system to provide 0.75CFM/sq ft (as long as there is no fuel dispensed or stored inside the building}. I plan to install six or seven powered  exhaust fans in the walls, one between each overhead door, and the same number of motorized dampers in the walls on the opposite side of the building. This seems like a logical way to address the ventilation requirement. However, it gets cold in NJ, so I will have to temper the ventilation air in the winter. Although there will be six gas fired unit heaters mounted about 10' above the floor throughout the facility, I think they will have a hard time maintaining the temperature in the shop in the winter. Any ideas on the best way to temper the air other than a gas fired air handler?
> Thanks




So the exhaust extractor is not a substitute??


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## cda (Nov 15, 2017)

Not an engineer but .75 does not seem like it would take much exhaust ??

Do you have a link to the code requirement


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## Mech (Nov 15, 2017)

Engprosinc - It is probably best to start a new thread rather than change the direction of an existing thread.  In PA, I spec gas fired MUAs, either a 100% OA unit that can recirculate all the interior air during unoccupied hours or a unit that can recirculate part of the interior air during occupied hours and all of the interior air during unoccupied hours.  The reason for the latter is if the MAU supplies more air than is required to be exhausted.  I do not want to exhaust excess air and I do not want to pressurize the space.   I increase the exhaust air about 10% beyond the code exhaust requirement and supply air so that the garage is negative compared to adjoining office areas.

CDA - The following is based on 2009 IMC.  The code dictates 0.75 cfm/sf for a repair garage - think fumes and odors from motor oils, spilled gasoline / diesel fuel, gear oils (real smelly), etc.  Section 502.14 requires a source capture system to connect directly to the vehicle, with a few exceptions.  Exceptions would not apply here as the engines would be running for diagnostic reasons.


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## tmurray (Nov 16, 2017)

We just did this with our works garage and I spec'ed that the fans and dampers are interconnected to the co system. They only come on when there is a build up of co in the building. They don't run at all in the summer time (doors are left open during the day) and just run for a couple minutes a day in the winter months. There is a manual override as well. I'm not sure how often the guys run it though.


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## Builder Bob (Nov 21, 2017)

what about the re-calibration for the the co detectors and replacement of the sensors? just because a sensor is installed, doesn't mean it doesn't have to be maintained. The code is very silent on these applications. With the troubles we are having with maintenance of fire alarm and fire sprinkler systems, i do not see where this will be properly maintained.


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## Builder Bob (Nov 21, 2017)

FYI - Honeywell commercial carbon monoxide detector - excerpt from technical manual

11.1 Operational Life The pellistors used in the Catalytic flammable gas sensor can suffer from a loss of sensitivity when in the presence of poisons or inhibitors, e.g. silicones, sulphides, chlorine, lead or halogenated hydrocarbons. The pellistors are poison resistant to maximize the operational life of the Catalytic flammable sensor. A typical operating life, subject to the presence of poisons/inhibitors is 36 months. The NDIR (infrared) flammable gas sensor is not affected by the above-mentioned poisons and therefore has a longer life span. A typical operating life is 5 years. Typical life of a toxic gas sensor is dependant on the application, frequency and amount of gas exposure. Under normal conditions (3 monthly visual inspection and 6 monthly test/recalibration), the XCD Oxygen and other toxic sensors have an expected life equal to or greater than 24 months. WARNINGS Access to the interior of the transmitter, when carrying out any work, must only be conducted by trained personnel. Care should be taken when removing and refitting the Sensepoint XCD plug-in Sensor Cartridge to the Sensor Socket so that damage to the connection pins can be avoided. Before carrying out any work ensure local regulations and site procedures are followed. Appropriate standards must be followed to maintain the overall certification of the sensor and transmitter. To reduce the risk of ignition of hazardous atmosphere, de-classify the area or disconnect the equipment from the supply circuit before opening the transmitter enclosure. Keep assembly tightly closed during operation. Never attempt to open a junction box/enclosure or replace/refit the sensor in potentially hazardous atmospheres. Take care when handling sensors as they may contain corrosive solutions. Do not tamper with or in any way disassemble the sensor. Do not expose to temperatures outside the recommended ranges. Do not expose sensors under storage conditions to organic solvents or flammable liquids. At the end of their working life, replacement electrochemical sensors for oxygen and toxic gas must be disposed of in an environmentally safe manner. Disposal should be according to local waste management requirements and environmental legislation. Alternatively, old replaceable sensors may be securely packaged and returned to Honeywell Analytics clearly marked for environmental disposal. Electrochemical sensors should NOT be incinerated as this action may cause the cell to emit toxic fumes. Sensepoint XCD Technical Manual


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## cda (Nov 21, 2017)

Builder Bob said:


> what about the re-calibration for the the co detectors and replacement of the sensors? just because a sensor is installed, doesn't mean it doesn't have to be maintained. The code is very silent on these applications. With the troubles we are having with maintenance of fire alarm and fire sprinkler systems, i do not see where this will be properly maintained.




Yep saw a place where they were installed, and removed at a later date


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