ERV / General Ventilation Options

[sansbury]

We're finalizing HVAC choices for the 28x44 shop/garage I started almost a year ago and I'm trying to figure out the ventilation side of things. Would appreciate feedback from those who've gone before around what they would and wouldn't do again!

The building itself is close to airtight and insulated to residential standards (code requirement) and will be heated with a Mitsubishi cold-climate mini-split system. My work is a mix of machine shop and woodworking with a little bit of welding (GTAW) thrown into the mix. I don't currently do any large scale spray painting or that kind of thing.

I will be getting a good dust extractor and a hefty dust collector for the woodworking side of things, and probably an overhead HEPA filter for that area as well. Also planning some type of fume extractor/filter like the Fume Dog for the welding area.

My installer said this is the ERV unit he typically put in a space this size. It runs up to 225 CFM which would give a full turn of the volume (interior 26x42x11' => 12K CF) in 54 minutes.

https://renewaire.com/erv/ev-premium-m/

I am wondering if that is adequately sized or if I'd want to go bigger or different. Also interested in best practices for filtering, intake/output placements, etc. One thing I was considering, but know nothing about what is possible/smart, is locating the ouputs at one end of the garage over from the woodwork area and placing the intakes at the other end, so that I'm sucking in the least fine particulate.

 

[dcg9381]

Where are you? That makes a difference. Here we don't HRV/ERV anything (it's unnecessary as we run HVAC all the time) if your home is not in the "tightly sealed" class.

Personally, I don't worry about "air quality" on a shop when considering an ERV. Even foam insulated, by crappy roll up doors leak like crazy. And on the wood shop side, I'm shoving enough **** into the air that air handling is really a giant dust collector and a separate filtration system. I'd bet the ERV calculation is "residential" and doesn't consider what you're doing, but YMMV.

 

[sansbury]

Western Massachusetts, and yeah, the building is close to airtight with pretty serious insulated garage doors. Up here code basically requires any insulated structure to meet residential requirements even if it's not a living space.

Right now the installer is quoting me 3-4K for the ERV install which is basically pocket change in the context of this whole project, so I'm not against doing it if it's going to improve the air quality.

 

[dcg9381]

Up north it seems to be about humidity control. Are you planning on using this with the doors open (that's what I'd be doing in MA all summer)? I've done 2 residential structures in foam down south and basically disconnected the fresh air vents, they were not meeting "tightly sealed" enough and HVAC took care of humidity. My shop, I'm 100% sure is not "tightly sealed" - so it's a non-issue, the wood shop is enclosed outside the HVAC envelope.

I have no reason to suggest that your contractor is off... We do pretty crazy HRV/ERV installs up north designed to book spec, but they are residential. I've never done a tightly sealed wood shop up north. We do have a wood shop in MI with no controls at all, we just open the door. Either way, you've got to meet code on this deal. Wood shops produce a lot of air waste.

 

[sansbury]

Are you planning on using this with the doors open (that's what I'd be doing in MA all summer)?

Yeah, I think so. There's generally only 2-4 weeks a year when it gets really uncomfortably hot out of the sun, and that usually only part of the day. We only have A/C in our bedroom in the house.

Either way, you've got to meet code on this deal.

Since this qualifies as a personal-use accessory structure code doesn't require anything specific on the ventilation side. The big thing was that I had to meet residential standards for the insulation and building envelope, so quite a bit went into that, but the HVAC side was pretty much whatever I wanted to do.

 

[nadogail]

I have a sort of Air Cleaner in my workshop. I got the idea from watching a Ted Talk Video.
It’s made from a Box Fan that a former tenant left behind, and 5 Furnace Filters that are the same size as the fan. The filters and formed into a cube. The fan draws air through the filters and exhausts filtered air into the shop.
it is all held together with metal foil backed Duct Tape and sits on a platform suspended on Jack Chain from the ceiling joists. It is plugged into the wall and controlled by a switch that I can reach from the floor under the “Air Cleaner “ I mounted a 4 square box on the platform and the switch and fan receptacle are in the box.
I ordered a case of filters and the box and cover plate from Amazon, the plywood, switch and electrical parts were already in the truck stock in my Service Van.

 

[Denwood]

I'd look at the Renewaire Premium L instead as it is more efficient with a larger core. If you're doing a cold climate mini-split, you'll find the Premium L efficiency 88%@60 CFM quite compelling at the price. It's not the "smartest" ERV out there but easy enough to balance etc. with two ECM motors...and boost mode if needed to clear out fumes etc. as required. You'll want to order that switch with the unit. They also offer an occupancy sensor as an additional control if desired.

I would do the stale air intake on the "cleanest" end of your shop and do the fresh air at the other...that's all you need. If you locate the ERV at the clean end, then you only have one duct run interior. You'll want miniumum 10 feet separation on the external air intake/exhaust.

100% you should be looking at ditching the filters that come with the unit and build yourself filter boxes external. I've found it actually makes more sense to put the fresh air filter box outside the building (hanging on the exterior wall) as then you don't have to worry about insulating it. You'll just need to insulate the supply/return (cold side only) ducting inside the building. A 5x16x20 works very well at MERV10 and should run about $25 each. You should also have an inline filter on the stale air side of things as shop dust will be an issue...again I'd use a 5x16x20..MERV 8 is fine.

This is my external setup with MERV16 and a 15lb charcoal canister (can be enabled/disabled) for wild fire smoke. MDO ply works great for this application so you can 100% DIY. The filter box and frame are held in magnetically and take about 10 seconds to remove



More on page 2 of this thread that may give you some ideas for the filter boxes.

Super Efficient HRV retrofit with smoke filter for $300?

@PoorUB , yes, I've retrofitted an older HRV by removing the single inefficient internal fan (about 350 watts) and replacing with two external ED fans (about 30 watts typical) which can be automated for speed control etc. Typically the outside air is pretty good, but in Spring heavy with...

www.garagejournal.com

 

[fitter30]

4 air changes per hour for a welding shop. Most welding at a bench flex tube at a exhaust would be nice.