Originally Posted by
bob_scheel
Most cities adopt a code which specifies how much fresh air a specific type of occupancy requires. This can be either an absolute number or it can be a CO2 target. 1000 ppm CO2 is a typical target when adjusting ventilation by occupancy demand. If the building doesn't measure IAQ but just introduces a fixed amount then you need to know if there is a dedicated fresh air handling unit AHU, or if fresh air is obtained via a minimum position fresh air damper.
In your situation I would ask how is the amount of fresh air controlled in this bldg.? If they have CO2 sensors then they should be able to tell you the setpoint. If not then ask how they do preventative maintenance and assure that there is adequate fresh air. What is minimum fresh air damper position?
Have they measured CO2 levels?
If a dedicated fresh air handler then the amount is not going to vary.
Probably more important is what kind of filters are used? What is their efficiency? 80% filters won't do much for allergens etc. HEPA 99% are best but very rare in residential occupancies.
Note that CO2 is not normally considered a contaminant but it is a good indicator of how much fresh air is being introduced.
In residential ventilation, using CO2 levels should be used to indicate the amount of fresh air getting into the space. Some suggest that you get an air change in 4-5 hours when the space is occupied. A 2,500 sqft. space with 9' ceilings needs about 80 cfm of fresh air at a minimum when occupied to purge indoor pollutants. The 1,000 ppm CO2 indicates roughly 15 cfm of fresh air per person. This is great for meeting rooms with significant number of occupants. In a home, I would suggest that you use a CO2 as a indicator of the amount of fresh air to change the air in 4-5 hours. With 450 ppm of CO2 outside, one person would be roughly 650 ppm, 850 ppm for 2 occupants, 1,250 for 4 occupants etc. At these low occupancy levels, you are ventilating to purge indoor building pollutants not occupants pollutants or renewing oxygen. I like the idea of using CO2 levels to activate ventilation. During cold windy weather most homes more than enough fresh to purge indoor pollutants. Thus, the CO2 levels are so low that a home with 2 occupants is <800 ppm CO2 and no ventilation is needed. During calm warm weather, ventilation is needed whenever the home is occupied. This would save much in ventilating cost.
Regards TB
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"