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Question On Converting Garage To Studio/Rehearsal Space
Old 1 hour ago
Gear Head

Originally Posted by RyanC View Post
A couple quick points-

ACH is the wrong metric to use for 100% fresh active ventilation. Frankly air changes is pretty useless because you could be talking about a ducted system with no fresh air at all (which won't work for a scenario where there is little to no infiltration), one with an economizer or OA intake (where it works, but you only get fresh air when there is a call to heat/cool) and neither of those the same as 100% fresh, continuous active ventilation.

For HRV's ERV's the calculation is much more simple. It's just the number of people in the room and the type of activity they are doing.

Check ASHRAE 62.1, pages 13 and 14-

Not the newest version but you get the jist. Generally 10-15 cfm per person is acceptable.

You DO NOT need ~180cfm for a space this size unless you plan on have >18 people in there.

I'm using these ERV's (3 of them) each covering a zone in the studio that accommodates a max of about 10 people, and A LOT of static pressure (this is the next thing you need to know).

With the ERV running, and 10 people in the big room, we were unable to change the reading on a CO2 meter (borrowed a fancy one from a grower) all doing jumping jacks and running in place. That's probably only about 10cfm per person or maybe less based on my static pressure estimate. Point being the ASHRAE standard is likely calling for overventilation considering there was nothing we could do to even move the CO2 meter, let alone see levels that are considered unsafe.

Regarding static pressure, this is the amount of resistance to airflow that your duct system and baffle boxes have. Smaller ducts, longer ducts, and 90, 180 etc turns increase static pressure. The fans in the ERV unit themselves will also vary how much CFM they can deliver into how much Static pressure. So google 'duct static pressure calculator', and then do your best to estimate the duct runs you have. I would assume your static pressure is maybe 30% higher than the estimator, and then look for an ERV that can deliver the required CFM per person into that amount of static pressure (measured usually in "In/H2O").

It's better to over ventilate than under, you can always use dampers to increase the systems static pressure and reduce ventilation.

One other thing, the baffle boxes should have double or more the cross sectional area as the ducts that are connected to them, and this should have no duct transition (IE no tapering of the duct from the small size to the large- generally for ERV go straight from square to round). The impedance change there increases iso, and the larger cross sectional area of the baffle box reduces static pressure in it.

Not sure where you are at in all of this, but one thing to consider for venting your roof (if you don't go "hot roof") is to do it actively with a fan. This way you could build a small baffle box for the fan under the eve outside if you end up needing it.

Hope that helps
Hey Ryan,

Thanks for chiming in.

A lot has happened since i last updated this thread/asked questions, specifically about the HVAC. I have been primarily reading/posting over at the John Sayers studio design website. Basically all of the stuff you just wrote, I learned/figured out over the last several weeks. But I'm glad everything you said just confirms all of it, so thank you.

I did end up having the "hot roof" installed. It was a bit more expensive than I wanted it to be, but I did the demolition of the old roof myself, which saved me quite a bit of money. Plus with them installing the hot roof, it saved me a ton of time cutting up drywall and OSB to put in the stud bays under the roof deck. I just put another layer on TOP of the roof deck, which was much easier and faster.

At some point in the near future I'll update the progress from this build with pictures and descriptions. A lot has happened in the last few months.
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