CO2 in Air – Why is my Air Stale and Stuffy?

by / Wednesday, 05 June 2013 / Published in Healthy Building Inspections & Testing
CO2 in the air

CO2 in the Air – Why is My Air Stale and Stuffy?

Carbon Dioxide and Its Relation to Your Interior Air Quality. CO2 in the Air.

Why is my air “Stale?”

Many of my clients often complain of either specific symptoms, general malaise, or “just not feeling right” when in a building they spend a significant amount of time in; such as their home or office.   As an IAQ professional, it can be quite a challenge to determine the root cause or causes of occupant complaints.

Rarely is an exact cause identified.  It is often the case that a number of contributing factors are acting together, acting in an additive or multiplicative manner.  Small amounts of many contaminants, each on their own at levels that would not cause symptoms or concern, can add up to cause occupant symptoms and complaints.

Tracking down each individual contaminant source and either eliminating, encapsulating, segregating, or filtering them is often highly impractical, if not impossible.  Usually the best and most effective method of eliminating or reducing these contaminants to an acceptable level is by dilution.  This is most easily accomplished by the introduction of fresh, outside air.

We will discuss how measuring and monitoring interior Carbon Dioxide levels can help identify well-sealed or “Stale” conditions, and how to use CO2 in the air to help determine how much ventilation is required and if current ventilation is effective.

Today’s modern, ultra-efficient, tightly sealed buildings often compound the issue.  The remodeling of older homes and buildings can often seal them quite tightly.  Buildings that were designed for a few occupants, such as a warehouse, have been remodeled as an office and now contain many more occupants than the original HVAC system was designed to handle.  Typically, the issue of ventilation and fresh air intake is inadequately addressed or not addressed at all.  This can allow contaminants to continuously build up in a sealed space.

CO2 in Modern Homes Can Be High - "Build Tight, Ventilate Right!"

CO2 in Modern Homes Can Be High – “Build Tight, Ventilate Right!”

The EPA, in “Building Codes and IAQ” states:

How energy is conserved through building practices can have profound importance to the health of occupants because the majority of building energy goes to conditioning the air that occupants breathe.  Buildings in the past had high air change rates that ensured that the pollutants generated indoors were constantly diluted with outdoor air. However, except when outdoor climate conditions are complementary to what is desired indoors, such air changes require energy to condition the air for health and comfort indoors. This energy burden can be significant during outdoor temperature and humidity extremes.

In general, the primary ways of conserving energy in buildings involves:

(1) Improving the energy efficiency of equipment and appliances and reducing their unnecessary use, and

(2) Improving the thermal performance of the building envelope and reducing air change rates to minimize the energy used to condition the indoor air. This latter function– reducing air change rates—puts energy conservation in conflict with providing adequate indoor air quality if it provides insufficient outdoor air to dilute indoor generated contaminants, or insufficiently replace air exhausted by exhaust fans, clothes dryers and combustion equipment. This is of concern in all buildings, but especially in homes where adequate ventilation has traditionally relied on infiltration or occupant use of windows.”

Passive ventilation, i.e. opening windows, is a very effective and often “green” (it does not use fans or other electrical or mechanical means of moving air) way to ventilate a building and thus dilute contaminants.  This method is only energy efficient when the outside air is at a comfortable temperature and humidity.  Thus, in conditions where the outside air is excessively cold or warm, dry or humid, other methods of ventilation may be necessary to achieve desired energy efficiency.

Fortunately, there are engineering solutions such as HRV’s (Heat Recovery Ventilator) and ERV’s (Energy Recovery Ventilator) as well as other ventilation options that are more thermally efficient than just opening windows.

How can I tell if my air is “Stale”? Measuring CO2 in the Air.

CO2 in the air

CO2 Measurement Outdoor

Now, how to determine if your space is extremely well sealed, stale or stuffy?

I like to use Carbon Dioxide measurements and monitoring to help determine the state of interior air, ventilation effectiveness and “stuffiness.”

What is Carbon Dioxide (CO2)?

Carbon Dioxide a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances, as well as a byproduct of hydrocarbon combustion.

From an IAQ standpoint, CO2 in the air is a surrogate for indoor pollutants emitted by humans and correlates with human metabolic activity. Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. Humans are the main indoor source of carbon dioxide. Indoor levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity.  Basically, the more occupants in a given sealed indoor space, the more quickly CO2 levels will increase, and conversely, Oxygen levels will decrease.  So interior CO2 levels are useful way to measure how “Stale” a given interior space may be.

NIOSH considers indoor air concentrations of carbon dioxide that exceed 1,000 ppm (parts per million in air) are a marker suggesting inadequate ventilation.

ASHRAE (American Society of Heating, Refrigerating and Air-conditioning Engineers) recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.   (Normal range for outdoor levels are typically in the 350-450 ppm range)

OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes.

I tend to use the NIOSH recommendations in my inspections and surveys.  If I measure CO2 levels above 1,000 ppm, I will take a closer look at the ventilation situation.  A one-time sampling can be deceptive.  Perhaps the building was empty when sampled, and normally there are 40 workers in the space.  Perhaps the windows are open on a nice day, when normally they are closed all winter.   I prefer data logging CO2, with measurements every 15 minutes, for at least 48 hours, a week preferable, to make sure multiple conditions are sampled.  If the average level of CO2 is around or above 1,000 ppm, remedial action may be recommended.

Monitoring Interior CO2 in the Air 

co2 in the air

CO2 Measurement Interior

There are several decent and not overly expensive (under $500) CO2 monitors available.  Some have features that will log readings over time or turn on a ventilation fan or system if CO2 levels climb above a user set concentration.

It is important to note that bringing in fresh air from the exterior is only beneficial if the outside air is clean.  Air pollution can be quite severe in some areas.  Outdoor air being brought into a building for occupant ventilation should at a minimum meet EPA NAAQS (National Ambient Air Quality Standards).  Many local Air Quality Management Districts, such as the Bay Area Air Quality Management District in my area around San Francisco, California, sample, measure and publish data about local exterior air quality and compare their results to the EPA’s NAAQS.

ASHRAE Standard 62.1 states that “Outdoor air not meeting EPA standards to be treated to prescribed levels for PM10, PM2.5, and ozone.”

If exterior air does meet EPA NAAQS, how much fresh air needs to be introduced into a “Stale”, interior environment?

How Much Fresh Air Do I Need?

The International Mechanical Code, IMC-2009, recommends 0.35 ACH (air changes per hour) and not less than 15 cfm (cubic feet per minute) of fresh air ventilation per occupant for a residential environment.  This can be accomplished through infiltration, passive or active ventilation:

CO2 in the air

Old World Style, Natural Ventilation

– Natural ventilation shall be through windows, doors, louvers or other approved openings to the outdoor air with ready access to and controllable by the building occupants.

– Openable area shall be at least 4% of the floor area, or mechanically ventilated with system capable of producing 0.35 ACH in the room, or whole-house mechanical ventilation capable of supplying 15 cfm per occupant.

– In HVAC systems, mixing outdoor air with return air is allowed.

– Return air must not be from identified contaminated spaces (e.g. bathroom).

– Supply and return air flow must be approximately equal.

ASHRAE Standard 62.1-2010 recommends in an office environment a minimum of 5 cfm per occupant. Outside Air must be delivered to occupants’ breathing zone at prescribed rates for all occupied spaces, during all hours of occupancy, and at full or part load conditions.

Conclusion

With today’s modern, well sealed buildings, it is becoming more and more important to be aware of how “Stale” our interior air is and to also be aware how important fresh air ventilation is to the health of occupants and to the importance of reducing via dilution the accumulation of interior air contaminants that that affect occupant health.  Monitoring CO2 levels is a fairly easy and inexpensive way to indirectly determine interior “Stuffiness” and ventilation effectiveness.

 

 

 

13 Responses to “CO2 in Air – Why is my Air Stale and Stuffy?”

  1. Alex Stadtner says :

    CO2 meters are very finicky and sensitive. So just breathing too close to the sensor can cause a false alarm. But it’s highly probably your HVAC system doesn’t have an outside air supply and that whenever the home is occupied and the doors/windows are closed that your CO2 will increase significantly. Look at the numbers in your bedroom in the morning. If you have insufficient outside air ventilation it should be pretty clear. CO2 is not usually an indicator gas for AC systems. Possible, but unlikely. More likely your CO2 levels are high because of your own respiration and insufficient outside air ventilation.

  2. Susie says :

    Can a faulty home AC unit blow CO2 into the home? I bought a CO2 meter, turned on the AC, and all the sudden the CO2 shot up to almost 1800PPM.

  3. […] CO2 in the Air – Why is My Air Stale and Stuffy? Carbon Dioxide and Its Relation to Your Interior Air Quality. CO2 in the Air. Why is my air “Stale?” Many of my clients often complain of either specific symptoms, general malaise, or “just not feeling right” when in a building they spend a significant amount of time in; such as their home or office. As an IAQ professional, it can be quite a challenge to determine the root cause or causes of occupant complaints. Rarely is an exact cause identified. Tracking down each individual contaminant source and either eliminating, encapsulating, segregating, or filtering them is often highly impractical, if not impossible. We will discuss how measuring and monitoring interior Carbon Dioxide levels can help identify well-sealed or “Stale” conditions, and how to use CO2 in the air to help determine how much ventilation is required and if current ventilation is effective. […]

  4. mitch in Manila says :

    Hey David,

    where can i buy one of those neat CO2 monitors?

    the air here in Manila stinks.

    your old pal,

    mitch b.

  5. David Sasse says :

    Austin,
    Yes, exterior air pollution can be a problem. We need fresh oxygen in our buildings, and we need to exhaust CO2, but if the outside air os polluted then we might be bringing in fine respirable particulates if we open windows. The best option would be an HRV (Heat Recovery Ventilator) or ERV (Energy Recovery Ventilator) with an integrated HEPA filter. This will allow air from outside to be introduced into the building, but after going through an effective particulate filter. The HRV and ERV also provide heat exchange to save energy vs. opening windows when the interior and exterior temperatures are significantly different.

  6. David Sasse says :

    Ionizers do not help with “Stale” air. Only fresh air ventilation, i.e. bringing in fresh oxygen and air from outside. Commercial buildings in the US with no operable windows should be subject to ASHRAE 62.2 which states the HVAC system should supply at least 15 CFM of fresh, outside air per occupant or provide at least 0.35 ACH (air changes per hour).

  7. Ann says :

    do ionizers help stale air? I’m in an office with no windows. I have a sealed sky light.

  8. Austin says :

    Thanks for the insightful article. I live and work in China and often get in arguments with my colleagues about whether or not to open the windows in our office. I’m adverse to the idea (a) because it feels wrong to run A/C or heating with the windows wide open and (b) in Shanghai, pm2.5 levels are above 35 µg/m^3 almost all the time, and *well* above that a majority of days. We have a couple of powerful fans with HEPA filters strapped to them which can fairly quickly clean the air if the windows are closed, but I doubt they have enough throughput to keep the air clean with the windows open (not to mention we’d need to switch filters once a week). My argument is that if we just leave the windows open at night, we can probably keep them closed during the day without excessive CO2 buildup. I’ve purchased a CO2 sensor to test this hypothesis, but I’m wondering, if it turns out that the CO2 levels do go above 1000ppm during the day, is there any way to manage this without introducing outside air? Maybe plants, algae, some sort of cheap consumer CO2 scrubber? Thanks!

  9. Alex Stadtner says :

    Someone older and wiser than myself once said, “if it aint one thing, it’s another!”
    Hang in there. You might check your local ordinances. Many cities and states have rules about how close you can smoke next to an operable window or door.
    Clean fresh air and water should be a human right, but all around the world it’s a right we have to fight for and buy right now.
    Good luck!

  10. DAB says :

    I enjoyed this article, despite it not being an area of science I’m all that familiar with. I know dozens of scientists working in a sick building, where windows have been sealed shut – this decided along with having air conditioning units in each room 20 years ago, which are badly aged, and probably don’t improve the air. Management not sufficiently incentivised to change it. Just moved to a new build flat – very warm, opened a window for some fresh air, and someone smoking outside.

  11. Alex Stadtner says :

    Natural ventilation can be “calculated” (or “predicted”) through computational fluid dynamic (CFD) modeling. It takes software, some of which is available for free, and some knowhow to set up a model. Even the best model is a best-guess, but a CFD model can help predict ventilation rates, ventilation effectiveness for various areas, and direction and speed of airflow, etc. Check out this recent blog about Natural Ventilation, where our building science expert discusses cross- and stack-ventilation.

    There is no general rule of thumb without modeling, because of the many variables involved in CFD computations. You mentioned if there was no wind outside, and other influencing factors would include size and height of windows, indoor/outdoor temperatures, if there are any fans indoors, interior layout, size of overhangs, etc.

  12. john says :

    Without mechanical ventilation, how can the ventilation through open windows be calculated? Is the ventilation through open windows equivalent to some mechanical cfm value? per square foot? And assuming no wind? And how does mosquito nets on the windows affect ventilation?

  13. […] Air Quality is almost always associated with SBS (and BRI). Whether from insufficient ventilation, excessive accumulation of indoor air pollutants, or a combination thereof, IAQ is almost always […]

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