Studies on IAQ of balanced ventilation vs no ventilation?
Michael Maines
| Posted in General Questions on
Someone in the industry recently challenged my assertion that having a properly designed and installed ERV was obviously better for indoor air quality than simply opening a window, and asked me to provide studies that prove my point. I imagine that most fans and practitioners of building science would agree with me, but does anyone have sources to share that prove (or disprove) my point?
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Replies
Michael,
Forgive me - I'm sort of thinking out loud here, and have no useful links.
It seems like there are several parts to this:
In terms of the quality of the fresh air, given that both come from the same source, isn't the only difference any filtration that occurs in the mechanically introduced system?
In terms of the air exchange, the mechanical system provides predictable levels of outside air, where relying on natural ventilation varies wildly.
Some mechanical systems allow you to control interior levels of humidity.
Malcolm, I agree that filtration is the main difference. There's also the fact that people are unlikely to open windows when it's cold out, but they will still use mechanical ventilation.
Michael,
"There's also the fact that people are unlikely to open windows when it's cold out, but they will still use mechanical ventilation."
We have an interesting variant on the problem here. Our code mandates full time mechanical ventilation, but many owners turn it off as soon as they move in - and as you say do not substitute natural ventilation instead. The problem was bad enough the code now mandates that the switch controlling the system be located in an inconvenient place to discourage the practice.
I generally don't like the trend of more complex and technologically dependent houses, but I'd love to see a prominently located humidity meter and CO2 level indicator in each new house. I think that would make the case you are trying to pretty successfully.
I've read in many places that owners often turn off their ventilation systems. Why is this? From my point of view, I am paying good money to have a system installed, for all the reasons I don't have to explain to you. Why do people shut them off?
kewiso3,
From their perspective the system is there because they were required to have it. Many builders think the same way, and put in whatever will pass, as opposed to thinking though a good ventilation system. I don't think many people see the link between it and good IAQ. All they experience is what they see as unnecessary noise and uncomfortable air movement.
They also often think it is there to compensate for having a tight house - which many people are still not convinced is a good idea.
Why? Noise. A well sealed house can be pretty quiet, so fan noise can seem louder than if there was already some background noise.
Do we include temperature within IAQ?
Ie: an HRV or ERV helps temper the ventilated air in higher differential seasons (winter and summer) vs opening a window. In the latter of the example, I'll go so far to say the experience of my indoor air isn't very good if I open the window in the winter.
Jamie
Yes, temperature is a component of IAQ.
The window is better for ventilation if operated properly. Higher CFM and gives ventilation at the spot needed.
If windows aren't operated properly, then a central ventilation system (ERV or otherwise) has the advantage of automatically ventilating the entire building without any intervention.
The fundamental point of an ERV is to save on energy costs compared to opening a window.
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What about when it's too hot or cold outside, it's raining, it's pollen season, if there are security concerns?...
I agree. ERV has the advantage if windows can't be operated including if the air needs filtration.
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This is mostly for exhaust/supply/no ventilation but a lot of info there:
https://www.energy.ca.gov/sites/default/files/2021-05/CEC-500-2020-023.pdf
Excellent, thank you!
Filtration and energy efficiency are certainly the benefits to a centralized ventilation system. Ultimately providing homeowners with information and understanding of how these systems work and the advantages they offer is key. HRV’s have been a standard for new construction in my market since the late 90’s still I hear from homeowners regularly that they were told by their HVAC contractor to leave the unit off because it is ineffective on only there to keep the code official happy. Best scenario in my opinion is a well designed ventilation system paired with well planned operable windows and education, that way homeowners get the best of both systems.
One huge component of IAQ is what the outside conditions (pollution, allergens, wildfire smoke, brake dust, etc.) are. A home next to I-15 in Salt Lake City compared to a home in Kauai, Hawaii are going to be totally different if you have the windows open. I’d also wager that the outdoor CO2 levels are quite a bit different in New York City vs Whistler, BC. So leaning on a study to show mechanical ventilation is superior may have a lot of caveats depending on location.