Why does IAQ go up when ACH goes down? I thought outside air was healthier.
I’ve been trying to educate myself on the topic of building science. This site, the Building Science podcast, the EnergyVanguard blog, there’s a lot there for a layman. I’m a bit confused about something I’ve been hearing though and I feel like it’s being oversimplified and maybe even distorted. Can someone help me sort this out? Let me be clear before I dive into my question, that this is not about efficiency, it is about IAQ.
Here’s what I’ve been hearing and need help working through. Air quality has an impact on our health (no argument or confusion from me there). Outside air is healthier than air inside a home because of all the contaminants, off-gassing from manufactured products, off gassing from cooking/heating/fireplaces, and mold found in many homes (okay, that sounds very plausible). Why then, would just decreasing the number of air changes per hour make the IAQ better if less “fresh” air is being brought in? Isn’t that an oversimplification? If the walls of a home are already being kept dry, wouldn’t it take more than just lowering the ACH to improve the IAQ? Would it be more accurate to say that it’s not really about lowering the ACH, but that it is instead about choosing to use the best MERV rated air filter you can, avoiding or buying fewer manufactured products that are going to off-gas and hence increase the contaminants in your air, by controlling the humidity in your home, and whatever else I’m not thinking of?