Problems Specifying Fresh Air Handlers During Wildfire Conditions
Hey everyone, I was watching this video on indoor air quality during wildfires from Ekobuilt Passive Homes on Youtube (filmed in Ottawa, Canada) and at minute 7:45 the host, Paul Kealy says that they can no longer use Zehnder fresh air machines in Ontario because they have the potential to conflict with some building codes. He says that Ontario codes require a defrost cycle to be built into a fresh air machine (he doesn’t say if it’s an HRV or ERV) so they use one from Jablotron (the Futura) and although that model comes with just a standard filter the company does offer a charcoal filter as an upgrade (to be used during “extreme conditions” like wildfire).
Ekobuilt Passive Homes: Minute 7:45
https://www.youtube.com/watch?v=DL03H9U6yEs&t=1487s
Jablotron Futura
https://www.jablotronlt.com/en/futura/
Given the fact that Zehnder is considered by many to be at the top of the list for high performing fresh air handlers, I was surprised to hear that it may not qualify for use in certain jurisdictions (I’m guessing ones that experience very cold weather).
Does anyone know of other/better options for providing fresh air to a tight, near passive level house in areas that may have to endure wildfire smoke and other air quality issues, whether a very cold climate or not?
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Replies
Jablotron has some interesting control and automation options in that system, similar to the system I built, including 0-10V control of fan speeds. The zoning etc. capabilities are also beyond what I've seen so far in NA. That said, it still states that no pre-heating is required until temps drop below -19C (meaning you need it if gets colder), and you need to provide it with a 16amp service at 220V....so I see no signs of a defrost cycle there unless they have another unit with a defrost damper. Renewaire released a white paper suggesting that their ERV units do not require any type of defrost strategy for most use cases..but they do use a significantly larger ERV core than most.
With regard to filtration, you should check out the thread here on external ERV filtration. I've found that a carbon canister along with two MERV 13 filters allow us to run our ventilation system during smoke events while keeping pm2.5 and VOC at low levels inside. The key though is not relying on a simple carbon coated air filter...they don't work for wild fire smoke. The carbon canister I'm using is a Terrabloom 8" unit which has about 15lbs of activiated carbon contained in a spherical canister. It works quite well, although we only have it inline during smoke events.
This unit has been testing by the NRC here in Canadian Arctic conditions, and is the real deal with no defrost strategy required, and very high efficiency https://www.tempeff.com/products/#rgspk This system runs just fine at temps below -30C, with no defrost cycles. It would run though about $5-6K from what I understand, so is not a cheap unit. I've posted more information about this unit, including the NRC reports on the system in various posts here at GBA.
This is the NRC test brief: https://www.canada.ca/content/dam/polar-polaire/documents/publications/aqhaliat/volume-2/energy-recovery-ventilation-system.pdf
Dennis: Thanks for the info. I also had a look at the Terrabloom unit - I must admit I was a bit surprised to see it's being featured by a company supplying grow-ops.
I guess if you want info on HVAC equipment for cold climates go ask the Alaskans, if you want info on masking odors, ask the grow-ops LOL.
I was curious about your comment about only having the filter inline during smoke events. Do you physically install it when wildfire season starts or did you build in some kind of a bypass pipe or damper so your air stream doesn't pass through it when the filter isn't needed? Where in your system is the filter located?
@rockies63 yep, grow ops. The ECM fans I'm controlling with 0-10V automation for kitchen exhaust and supply/return on the HRV are all compliments of companies that cater to indoor growing. Same thing with the carbon canisters. It was a bit of a discovery as I'm not much of a grow op kind of guy..ha.
This summer, I hung a 8" terrabloom directly under the eave, connected to the HRV intake...which worked great. That said, the pre-filter that comes with these units is cloth and pretty restrictive.
This unit (just finishing it up) https://www.greenbuildingadvisor.com/question/plans-for-external-erv-intake-filter-box
has the canister enclosed, with two 8" dampers. Close the bypass damper, and all pre-filtered air flows through the carbon, then into the HRV system. Open the bypass. and pre-filtered air bypasses the carbon filter, then entering the HRV system. I'll be removing both of the HRV internal filters as they are quite restrictive vs the larger 16x25x4 (fresh air, MERV10 prefilter) and 16x25x1 (MERV10) stale air filter. I have a another filter box on the fresh air intake, warm side, that holds a MERV13 14x14x4, again with low static resistance.
Doing this again, I'd just omit the internal 14x14x4 box and do a single 16x25x4 MERV13 or MERV16 on the external fresh air intake box.