exchange chamber ventilation system

Hi! here are my first posts with all the posting requirements. viewtopic.php?f=1&t=11037 and viewtopic.php?f=2&t=11162 I've finished with the beefing-up part for my external leaf (ceiling) and now it's time for Ventilation. I want to do the exchange chamber concept in Rod's book. I have already a HVR system that brings fresh air to the house. I'll just move some pipes (round duct) to match my studios plans to bring that fresh air into my exchange chamber. Of course, I'll make it balanced by a professionnal. HRV duct moving (pics 1 to 4): in blue, the fresh air from outside and in red the stale air that go outside. Now my plans for the exchange chamber (pic 5): I'll put an inline fan that will suck air out of both control and live room (brown) and throw it in the chamber close to the ceiling. The fresh (and cold hopefully) air will enter natrally by the other duct (green) close to the floor. I want to use the FG 6XL from fantec (http://www.fantech.net/fg.htm). They sait that it is 100% speed controlable, so I'll be able to set it quiet or powerful depending on the situation. It can blow about 300 CFM at 1 inch of static pressure. I Guess it's powerful enough for my needs? I'll be most of the time alone in my control room and there will be 1 to 4 persons in the live room... Max! I want mostly to record drums, so one person most of the time. I have to use round duct of 6 inches because my ceilng is low (7'8") and I want to pass the pipes into the web joist trusses. And more, there is already plenty of 6" round duct for HRV plus the water pipes etc... So I'll have to make some compromise there... I'll put big silencers at the end of the pipes to slow down the air and keep the ventilation quiet. I hope this will work.... Am I in the right way? Any comments are welcome. Yohann

xray view

Oh, one more thing, is the new ducts (green and brown) are to long to make it work? it's about 65 feets of 6" duct.... will my fan be powerful enough? I'm not really good with duct size and lenght. Thanks yohann

Sketchup file for those interested: http://www.yohannboudreault.com/Studio/Studio_6.16.skp you can navigate through the sketchup file if you need more angle, or zooms. It's 800k and the forum only allow less than 500k...

What I do see is that your new ducts (the green and brown ones) are practically dead straight runs in the section between your CR and LR. So you will have a direct simple path for sound to get from CR to LR, right through your duct, bypassing those nice thick acoustic walls, windows, doors... I don't know much about HVAC yet (that's coming up soon on my list of "things to learn about"), but I do know that you should not have straight duct runs that directly connect rooms. You need to put several 90 degree corners in the ductwork, and also line the inside. If not, then it's basically like cutting a whole in your wall. You have a couple of 90 degree bends, but I don't think that's enough, is it? Now, how you do that is a question for the HVAC guru's here. - Stuart -

Hi Soundman2020, there is actually four 90 degrees plus 2 silencer box (not drawn) for the sound to get from one room to another. I tought it was enough... I really would like to line my round ducts, but if they are 6", they'll become 4" to 5" after.... I think it is gonna be to small..... maybe someone knows.... I'd like to have 2 feets over my studio to put all that stuff, but I only have 10"... :cry: Yohann

OK, maybe 4 x 90 is enough. Like I said, I'm not up to speed on HVAC yet. Maybe I should just shut up and wait for the experts to offer their opinions!

Every inputs are appreciated! Thanks for taking the time to help. Yohann

Look at the duct sizing also. The c/r is about 1,000 ft^3. With 12 air changes hour that works out to around 200 ft^3 per minute. Working with 4" (internal diameter) ducts the area is around 12 "^2. That is an air velocity of ~1,500 fpm. The generic standard I use for home studios is 300 cfm. Rod, who pops in here regularly, uses 100 fpm. There is post recently made here with excellent links for HVAC sizing. Andre

Ok. I’ve studied some of the forum posts, Rod’s example in his book and some web pages (by the way, this one is pretty cool: http://www.engineeringtoolbox.com/ductw ... d_883.html) and I understand a bit more the way things works in ventilation. (I still have a lot to learn...) I know that I have to slow down the air velocity. To achieve that, I should use bigger ducts. The main problem for me is the room to put big ducts, so I’ll have to make compromises… One thing came to my mind though :idea: : I could use 6” duct for every part of my new booth ducts (green and brown) except the 4’ branches that go into the CR and LR. If I put bigger ducts there (I can go up to 10” in these areas), an air volume of 200 cfm would give me around 366 fpm in a 10” round duct which is a lot better. Will this work if just a part of the system is 10”? I could even line those 10” duct! Maybe I don’t need 12 air change/hour if I'm alone? That would reduce the fpm too… If I'm following the Rod's example, he uses 100 cfm, so at that rate, I would have about 183 fpm in that 10" portion of the duct. And at the end, there will be silencer too to damp more noise. Will this idea work better?

Another question came to my mind..... Will this exchange chamber unballance my HRV? In theory, it should not, but it's gonna pull a lot of air to the booth (green)... The same amount of air should come back to rebalance through the pipe though (brown)... Anyone?

If you increase the diameter to 10" for the final portions and line them, make them at least 5' long. Do not forget to calculate and size the grilles also. You will have to check what the design pressure is for the HRV unit. Yes extra ducting will increase the pressure. As far number of air exchanges per goes, you have received and read the recommendations of experts. If you decide not to follow the recommendations, that is your choice. Andre