Air quality sensor / controller?
After much time spent thinking about an air exchange system retrofit for my home, I’m amazed at the installed cost, and am left questioning the necessity of it all. I reputable installer has quoted me $3,500 to $4,000 for a HRV-based air exchange system, so I’m wishing for a cheaper and/or more scientific way to determine my home’s ventilation needs, other than something that just vents continuously regardless of conditions.
This article intrigued me:
https://www.greenbuildingadvisor.com/blogs/dept/green-building-news/monitoring-air-quality-home
If air quality can be cheaply monitored, could ventilation also be controlled and use on an as-needed basis? I’m not looking for a passive house ventilation system, but maybe something that could tell my bath fans to run (hopefully not all that often) based on air quality triggers? We’re living in the home now, with no issues other than the house does smell somewhat stale after leaving for a few days with no doors or windows opening. It’s hard to justify spending $4K plus annual operating costs without any data defining the problem. Or maybe ignorance is bliss.
Does anyone have any experience with air quality monitoring? Is it accurate? What contaminants should I be most concerned with watching? VOCs, carbon dioxide, formaldehyde? Any recommended products? Are there any sensors that can ‘talk’ to a switch or control a fan without spending a fortune?
Thanks for any info or experiences!
Ryan
Minneapolis, MN
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Replies
Here are a couple of items I saw in a REI store recently. You could certainly find ways to control your own ventilation equipment using similar stuff. It's rarely done in homes because people don't want to pay for it or deal with it.
Probably the easiest, cheapest, and low tech way is to do two things:
1. Get a simple CO2 monitor without triggers and use it for several months to monitor the CO2 levels in your home. Check patterns of accumulations of CO2 with different things going on in the home.
2. Using your existing bathroom fan buy a timer to control it based on the patterns you've observed. The timer can be simple or complex depending on your needs.
This would probably work fine if your house isn't extremely air tight. Basically it probably will work nearly as efficiently as a dedicated ventilation fan as you will be trading long periods of low ventilation rates for pulses of high ventilation rates using an existing bath fan. Of course, it won't have the Gee Whiz factor a DC driven Panasonic fan would have. And you'll save 200 bucks or so on the fan (unless you need a new one for other reasons.)
Ryan,
At least one U.S. manufacturer sells a ventilation system that responds to CO2 sensors and VOC sensors. The system is called the Conditioning Energy Recovery Ventilator, or CERV.
GBA has published a detailed review of this system. Here is a link to the article: A Balanced Ventilation System With a Built-In Heat Pump.
I suspect, however, that your desire for "something that runs based on air quality triggers" and your desire for something "cheaper" are at odds. After paying for installation, a CERV system will cost you $7,000 to $9,000.
If you want to ventilate based on indoor conditions, you can always take the traditional route: when you see condensation on your windows during the winter, turn on the bath fan. When the condensation is gone, turn the bath fan off. The human being is the sensor and the controller; that's cheap.
I searched for your previous posts and it looks like you have an older house that has insulation/window upgrades, is now "tighter then most new homes", and you already have radon mitigation. It also looks like you don't want to deal with extensive ducting retrofits. It would be helpful to let people know your actual blower door test results.
I think you're likely overthinking this, most people don't monitor the air quality of their homes, unless they're experiencing some specific problem. What you should do (based on the tighter home and stale air after a few days) is have some kind of consistent ventilation and keep an eye on humidity. Buy a couple/few of the $10-$20 relative humidity meters and place them around your house. My understanding is that the target range for winter relative humidity in your climate is 25-35%, give or take a few.
As long as they're installed correctly and venting to the right place, you can use regular bath fans for ventilation. Get a controller:
http://www.supplyhouse.com/Honeywell-HVC0001-Digital-Bath-Fan-Control-Premier-White
and set it to run 15 minutes out of every hour. Adjust that timing amount based on what you see for indoor humidity and perceived air "freshness".
If your bath fans are old, loud, and not working well....consider replacing them with a Panasonic WhisperGreen.