Filtered Outdoor Air for ERV
andyfrog
| Posted in Mechanicals on
Additional filtration case upstream or downstream of ERV intake?
I’ve been wondering about this but haven’t seen too many real world examples. I know ERVs have their own built in filters but during wildfire smoke season it seems like those would get overwhelmed pretty quickly with their surface area.
To me it seems like filtering the outdoor air before it gets to the ERV is the better option, but I’m not sure.
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Replies
You do want to filter before the unit, the problem is there are not a lot of options of in-line filters. I use a Fantech FB6 wrapped it in rigid to avoid condensation. This takes a 10x20 filter which works much better than the washable foam filter in the ERV and cheaper than most specialty filters.
If you want to filter smoke, you need a two stage filter. First stage carbon filter for the smell and a 2nd stage HEPA filter for the small particles.
Not too many options for this, you can try hydroponics sites for grow-op filters. Fantech and Lifebreath make one with a built in fan, you could connect either before the ERV and not use the fan or connect it after the ERV with as shown on P10 here:
https://www.lifebreath.com/wp-content/uploads/2020/12/69-TFP_EN_1220.pdf
You can also talk to your local HVAC sheet metal shop an they can fab up a filter frame with ducting that can take say a 1" carbon filter and a 4" merv 16 filter.
Charcoal filters do work on ERV prefilters to reduce/eliminate smoke (tested myself using an external smoke hood/filter combination) and I suspect given the frequency of this question, is a viable product at this point. I'd agree with AKOs that is hard to find what you need on the market. That said, this is a simple fab shop project and may be cheaper for you.
Using a charcoal impregnated furnace filter also helps both with random house odours and smoke that does make it into the home. They do work.
These are a low cost option : https://www.hvacquick.com/products.php/residential/Air-Filters/Inline-Filter-Boxes/HVACQuick-CFB-Series-MERV-13-Inline-Filter-Boxes
but you may need to insulate it if used a prefilter.
Is there any reason why the filter box can't be outside the envelope? (Screened and sheltered of course.)
I would put the filter box in the conditioned space if at all possible so that you wouldn't have to worry about weather. Most paper air filters do not like to get wet.
There is more info that might be helpful to you in this other recent thread:
https://www.greenbuildingadvisor.com/question/filter-box-for-regular-charcoal-filters?_gl=1*wd2sbz*_up*MQ..*_ga*MTU1MzY1NzcyOS4xNjY1NTE4NTYy*_ga_SBNZMMC0G6*MTY2NTUxODU2Mi4xLjAuMTY2NTUxODU5NC4wLjAuMA..
Bill
The filter box should be somewhere where it is easy to replace the filter, this means somewhere inside the utility room in the house, thus needs to be insulated. Don't skimp on this.
I put my ERV filter into the back of a kitchen cabinet where I had to cut one of the shelfs around the filter box. To replace the filter I have empty out the cabinet and take out the shelf to be able to finally take off the front cover. This very quickly become annoying to the point that I will re-plumb it so I can access the filter directly.