HVAC Retrofit. How can I incorperate HEPA filtration to a fresh air system?
I am designing a retrofit HVAC system for a 1950’s 1400 sqft single family home in San Diego built on a raised foundation with no existing ductwork. The crawl space has been brought into the building envelope via encapsulation including an intermitten fresh air supply and dehumidifier. It’s still tight down there, with only 24″ of clear height in most spaces
The next stages of the project involve conditioning the air of the home. Primary goal is to reduce the risk of ultrafine particulates due to adjacency to major highway while minimizing electrical costs. I plan to condition the space with a 3 head minisplit system due to extremely high utility costs in the area ($0.60 per kWh and climbing).
Does anyone have any recommendations for a fully ducted ERV/HRV system that can be combined with a HEPA filter?
I am in search of a whole house system connecting a fresh air system (HRV/ERV) to a HEPA system that can recirculate. I plan to install 4 supplies (3 bedroom, 1 living room) and 2 exhausts ( 1 kitchen, 1 bathroom). Ideally, I use one set of ductwork to supply fresh air and all filtration needs, all run through the crawl space.
Essentially, what I am looking to do is use the HRV/ERVs an air handler that has recirculate mode(does this exist) with the HEPA system incorporated on the supply side (like the FANTECH CM3000). Is it possible to get these systems to work together, or should I commit to installing full size ductwork for a conventional forced air system with a two stage heat pump, air handler, HRV/ERV, and HEPA filtration system all in line? My concern with switching to a forced air system is that it’s too large to fit into our crawl space so it would have to be relocated into to the vented attic that is outside the building envelope. Alternatively, all ducting could run through the attic, with equipment located in the garage for easier maintenance.
Thank you in advance, really appreciate any and all information on this
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Replies
Some ERVs can be had with a HEPA filter but these tend to be pretty pricy to replace.
One option is to use an external HEPA filter box in-line like a Fantech HS300 Lifebreath TFP3000HEPA. You can look at the diagram on P10 on how to connect it up to an ERV:
https://www.lifebreath.com/wp-content/uploads/2022/04/69-TFP3000-RTO_EN.pdf
The only change I would make to that diagram is to add a butterfly damper to the open breather T port so that if not needed for extra filtering, you can turn off the fan in the unit and use only the blower in the ERV.
Since you have a crawlspace and you are already running ducts, I would install a small ducted air handler in there. Even the smallest wall mount in a bedroom in your mild climate is silly oversized, chances are you'll have efficiency and comfort issues with it.
A single ducted air handler can easily carry the whole place plus you can now have a proper air filter instead of the washable mesh on the wall mount. The fresh air feed from the ERV/Filter can be connected to the return on the air handler and use that to distribute the fresh air through the house.
Thanks a lot for your reply, it has allowed me to rethink this entirely and I will most certainly be following your advice on a single ducted air handler with a heat pump, ERV, and HEPA filtration.
Don't make my mistake, and make sure you confirm any ducted unit you get will qualify for relevant tax incentives! In the US, not all ducted heat pumps -- even many of the variable inverter systems -- qualify for the Federal IRA heat pump tax incentive.
You may want to consider a high-MERV filter following by an activated carbon filter (or use one of the combo units) in place of the HEPA filter. This might save you some money and open up some more options for you, for only slightly less effective filtration.
Bill
Chiming in to say I appreciate the help! My separately ducted ERV + HEPA system is online and absolutely stellar. Living the good life now!
What did you end up doing? Please post pics.