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CO2 Monitors to reduce Outside Air

Discussion in 'Commercial Mechanical Codes' started by Mech, Aug 11, 2017.

  1. Mech

    Mech Sawhorse

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    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
     
  2. cda

    cda Sawhorse

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    Why is the ventilation required in the first place??

    Code section??
     
    Msradell likes this.
  3. rgrace

    rgrace Sawhorse

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    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.
     
  4. mark handler

    mark handler Sawhorse

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    All spaces shall be ventilated
    See TABLE 6.1 ASHRAE STANDARD 62
     
  5. tmurray

    tmurray Sawhorse

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    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?
     
  6. Mech

    Mech Sawhorse

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    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.
     
    cda likes this.
  7. cda

    cda Sawhorse

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    And that is why you are the Engineer!!!
     
  8. tmurray

    tmurray Sawhorse

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    I would be more comfortable with occupancy sensors.
     
  9. mark handler

    mark handler Sawhorse

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    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.
     
    #9 mark handler, Aug 16, 2017 at 7:11 AM
    Last edited: Aug 16, 2017 at 7:20 AM
  10. Paul Sweet

    Paul Sweet Sawhorse

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    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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