It's been recommended to me that I build my plenum 2 times the size of the duct wide and 4 times as long. Does anyone know if this should be the dimensions of the inside of the box after adding rigid insulation? (so adding 4" to each dimension to account for 2" 703 on each side?
Ventilation plenum questions
Originally posted at johnlsayers.com, topic 9990.
Tom,
close........
What you want is 2 times the volume in size - and you want this to be long enough so that you can install at least 2 baffles before existing the silencer - wioth the runs through those baffles equal to the duct.
So - for a 12" square duct (and I would use the same for a round duct) it would be clear inside dimensions of 2'x2' at the end - yes measured from the inside face of insulation.
you would then have a baffle 2' high by 1' long running parallel to the duct inlet which would be 1' clear inside measured from the inside of the insulation in the box.
Then you would install (on the opposite wall) another baffle with a 12" clear opening measured from the inside face of the 1st baffle - and then 12" clear to the endof the box.
So the box would be 2'x2' clear inside - and then would measure a total of 3'-4" clear to the outlet if you were using 2" thick baffles.
BUT - I don't reccomend the baffles be made out of just rigid duct board - but rather a MDF board or plywood which can be rabbetted into the box and thus give structural strength to it - these are then wrapped with the ridig fiberglass to quiet then noise down.
Done in this manner you decrease the velocity by 1/2.
I hope you can follow that.
Rod
- and then
Thanks Rod!
I've read it several times and I can now visualize what you're saying!
Does anything change if the inlet and outlet aren't facing each other? (If I don't have enough space in-between leaves). So if the inlet comes in on the side of the plenum at the bottom, and then the outlet leaves the top out of the top of the plenum (if it's placed so that the longest side is vertical).
Here's a picture to help explain what I mean (I didn't draw the baffles, not sure if they would be the same?)
Yes that would be fine- one comment though - the reason for the baffle is 2 fold - 1. stop the transmission of any sound that might be being carried through the duct itself. 2. slow down the velocity with the intent of quieting the ruch of air into the room. If you size the outlet the same as the inlet you will not acheive the 2nd goal - the velocity will step up to exactly the same as it was before - If you are working with inexpensive grilles and louvers this will result in a lot of extra noise....... The louvers (for example) that I specify come from a company called Nailor - have a NC (noise criterion) rating of 0 at 450 cfm - and around 15 at 650 cfm - (15 is below the level of hearing (on average) - but they also run as much as 850 dollars apiece - If you want to work with inexpensive louvers then you probably want your outlets the same size (in arera) as your box- resulting in the lower velocity....... sor for a inlet of 12 x 12 - you would want your outlet to be a full 1x2 (or adjust the box accordingly and make it 1.5 square. OK? RodDoes anything change if the inlet and outlet aren't facing each other? (If I don't have enough space in-between leaves). So if the inlet comes in on the side of the plenum at the bottom, and then the outlet leaves the top out of the top of the plenum (if it's placed so that the longest side is vertical). Here's a picture to help explain what I mean (I didn't draw the baffles, not sure if they would be the same?)
OK... yeah that's way too expensive for me. Does this apply to the exhaust ducts as well?If you want to work with inexpensive louvers then you probably want your outlets the same size (in arera) as your box- resulting in the lower velocity....... sor for a inlet of 12 x 12 - you would want your outlet to be a full 1x2 (or adjust the box accordingly and make it 1.5 square. OK? Rod
Sure nuff......... Do you have any idea of what your HVAC volume and Velocity will be? RodOK... yeah that's way too expensive for me. Does this apply to the exhaust ducts as well?If you want to work with inexpensive louvers then you probably want your outlets the same size (in arera) as your box- resulting in the lower velocity....... sor for a inlet of 12 x 12 - you would want your outlet to be a full 1x2 (or adjust the box accordingly and make it 1.5 square. OK? Rod
:oops: No, i'm not sure how I would do that?? My room is roughly 190 square feet. I'm only planning on using baseboard heating and a ventilation system. So this duct work will only be used for ventilation. I'm starting to wonder if I should tie into the HVAC system of my house (and have a professional handle that part). I've framed around the main return and supply ducts. It seems like it wouldn't be too difficult to tie into that with only one plenum for the supply and only one for the return (since the ducts run in-between leaves). But I guess this won't solve the ventilation need. I was looking at a product from Suncourt, the DB208 fan. These are the specs. 8" diameter fan Max Boosted CFM 500 (it's considered a duct booster fan) Free Air CFM 210 Amps .75 Housing Length 8" dBA/Sones 54/2.8 Maybe I would be better off adding fresh air to the house's main HVAC system and just bring that into the studio room? That would save me from having to put holes in the side of the house (by the studio) and I could run larger and shorter duct work that way (so long as it didn't effect the quality of air getting to the rest of the house.... which is why I keep leaving this idea alone). What are your thoughts on that?Do you have any idea of what your HVAC volume and Velocity will be? Rod
My first thoughts are that this is one NOISY fan - you would do a whole lot better to spend a few extra buck and get something quieter........... Next - what do you mean when you say ventilation air - do you mean outside fresh air? Because unless you have either a window or door that opens from your room directly to the outside - that is what is required - fresh air ducted directly form the outside. The holes in the side of the house answer the question - but the thought afterwards is heading wrong - However - in the winter time you are going to be pulling (sometimes) sub-freezing temps into the house - and this air is going to have to be treated somehow. And - In the summer - when it's 90% outside with RH levels areound 85% it is going to be unbearable in your room - depending on how much outboard gear you have - that could also be the case when it's 70 or 75......... In Power Station (for example) - in Ct - the AC runs year round when the gear is running - the heat is going for the iso booths and main rooms - but in the control room - it's AC year round........ You have lots to think about....... Rod:oops: No, i'm not sure how I would do that?? My room is roughly 190 square feet. I'm only planning on using baseboard heating and a ventilation system. So this duct work will only be used for ventilation. I'm starting to wonder if I should tie into the HVAC system of my house (and have a professional handle that part). I've framed around the main return and supply ducts. It seems like it wouldn't be too difficult to tie into that with only one plenum for the supply and only one for the return (since the ducts run in-between leaves). But I guess this won't solve the ventilation need. I was looking at a product from Suncourt, the DB208 fan. These are the specs. 8" diameter fan Max Boosted CFM 500 (it's considered a duct booster fan) Free Air CFM 210 Amps .75 Housing Length 8" dBA/Sones 54/2.8 Maybe I would be better off adding fresh air to the house's main HVAC system and just bring that into the studio room? That would save me from having to put holes in the side of the house (by the studio) and I could run larger and shorter duct work that way (so long as it didn't effect the quality of air getting to the rest of the house.... which is why I keep leaving this idea alone). What are your thoughts on that?Do you have any idea of what your HVAC volume and Velocity will be? Rod
What do you think about this fan then? http://www.homecenter.com/ProductDetails.asp?SID=130495 1.7 Sones vs. 2.8 in the suncourt model. It's a 6" diameter duct with 340/322/302 CFM ??My first thoughts are that this is one NOISY fan - you would do a whole lot better to spend a few extra buck and get something quieter...........
I meant connected directly with the outside - unless I connect with my house's HVAC system. I guess that's where I'm heading wrong (for ventilation considerations at least?)Next - what do you mean when you say ventilation air - do you mean outside fresh air? Because unless you have either a window or door that opens from your room directly to the outside - that is what is required - fresh air ducted directly form the outside. The holes in the side of the house answer the question - but the thought afterwards is heading wrong -
What do you mean by "treated" - are you just saying that I will definitely need to provide heat? I know I will need a barometric damper, but are you suggesting that there is something else I should use? Suncourt told me not to use their heat recovery ventilation systems because they would circulate way too much air for my room because of it's size and it would be very inefficient.However - in the winter time you are going to be pulling (sometimes) sub-freezing temps into the house - and this air is going to have to be treated somehow.
I know... :oops: It seems like it gets more frustrating every day. I do have a pretty nice dehumidifier that keeps the basement very dry currently. I guess that will help with the heat in the summer, but i'm not sure it will be enough once I start bringing in fresh air. I don't know about connecting to my home's main HVAC duct work and adding ventilation ducts -- That's a lot of plenum's and I'm not sure i'll have enough space. :roll: Plus it won't have it's own thermostat and I guess it could decrease the amount of air I get to the second floor.You have lots to think about....... Rod
depending on how you mount the fan, if its inline it could be placed outside the room. Panasonic makes some very quiet exhaust and inline fans.
http://www.ventingdirect.com/
It looks much better - should do fine.What do you think about this fan then? http://www.homecenter.com/ProductDetails.asp?SID=130495 1.7 Sones vs. 2.8 in the suncourt model. It's a 6" diameter duct with 340/322/302 CFM ??My first thoughts are that this is one NOISY fan - you would do a whole lot better to spend a few extra buck and get something quieter...........
I meant connected directly with the outside - unless I connect with my house's HVAC system. I guess that's where I'm heading wrong (for ventilation considerations at least?) [/quote] It can always connect to your home's HVAC system in some manner - but it also has to provide fresh air directly from the outside to the rooms.Next - what do you mean when you say ventilation air - do you mean outside fresh air? Because unless you have either a window or door that opens from your room directly to the outside - that is what is required - fresh air ducted directly form the outside. The holes in the side of the house answer the question - but the thought afterwards is heading wrong -
What do you mean by "treated" - are you just saying that I will definitely need to provide heat? I know I will need a barometric damper, but are you suggesting that there is something else I should use? Suncourt told me not to use their heat recovery ventilation systems because they would circulate way too much air for my room because of it's size and it would be very inefficient. [/quote] I am saying exactly what you are reading - in the winter - when it's 20 degrees below freezing (F) and you start pumping the air into you room - it will be hitting you the same temerature as it is outside - and will make it a bear to maintain temeratures in your space. It needs to be tempered in some manner (electric copil connected to a T-Stat or to a sensor and controller mounted directly in the duct itself - but one way or another you have to heat that winter air up somehow before pumping it into your room.However - in the winter time you are going to be pulling (sometimes) sub-freezing temps into the house - and this air is going to have to be treated somehow.
I know... :oops: It seems like it gets more frustrating every day. I do have a pretty nice dehumidifier that keeps the basement very dry currently. I guess that will help with the heat in the summer, but i'm not sure it will be enough once I start bringing in fresh air. I don't know about connecting to my home's main HVAC duct work and adding ventilation ducts -- That's a lot of plenum's and I'm not sure i'll have enough space. :roll: Plus it won't have it's own thermostat and I guess it could decrease the amount of air I get to the second floor.[/quote] Dry will not help with the heat - 95 degrees dry heat is still heat - and will still dehydrate you. Did you ever actually take all of your gear - the lighting - people - , etc., etc. and do the heat analysis I talked about in the book? If not you should - you are going to be in deep trouble in the summer (possibly even the winter) because even though these rooms have little or no solar gain to raise the heat inside of them - they also do not allow much to escape for the very same reasons........ the are so super insulated the heat builds up faster than it can ever escape....... You need to think hard about this - Sincerely, RodYou have lots to think about....... Rod
Hey Rod,
I'm a little stuck now with my options, can you answer a few questions to help me rule out some ideas? Sorry if this jumps around a bit, there's just a lot of questions going through my head. First I'll add that i'm hoping that the ventilation system can be set up with a switch so that I can use it when I need it - so if it's too loud, at least I can turn it off temporarily when recording.
I'm going to get in touch with a professional HVAC person to discuss options with them and get an idea of the impact of connecting to my home's HVAC set up, and let them know that I want fresh air ventilation. We'll see how that goes.
1. Because of how my room is set up - the easiest/best place for me to put the passive intake was a place that would be completely covered up by drywall and inaccessible. I'm realizing now that may be a problem. Since i'll need something that can treat the cold fresh air... can you confirm that I will need access to the passive duct work? Is there any way around that?
Connecting to my home's HVAC will at least solve the heating/cooling part of things - so long as I can control it with it's own thermostat so that it doesn't get too hot down there (without adding a new unit).
2. For heat, since the room will be highly insulated, if I would use baseboard (my original plan), can I use less than the guideline of 10 watts per square foot? I figure if I use basboard, I will keep the temp quite low since the room will either heat up quickly as you pointed out, or not be occupied. I was thinking of using 1, 1000 watt (4') hydronic baseboard heater if I go this route. Do you think that would be sufficient?
3. Is there anything I need to point out to the HVAC person that would effect their input based on the requirements of the plenum and the fact that this is an air-tight room? Anything a residential HVAC person with no experience in studio construction is likely to screw up?
4. I just realized that the CFM for the noisier fan I talked about earlier is 210 ("Free Air CFM"). This was suggested after saying the HRV would exchange the air too many times and would be a bad idea for such a small room. However the CFM in the specs for the smaller model is only 70 CFM on the low setting (doesn't specify "Free Air CFM"). How do you read what CFM means in real world situations?
Thanks!
Tom
I'm planning (very imminently!) to purchase a big HRV for my room, big to accommodate the static pressure I must overcome due to my long duct runs. I too am concerned about there being [i]too much[i] ventilation to be practical at times, so I'll be relying on the ability to slow the fan down via the speed settings the fan is capable of (3 speeds).
I figure it will probably run on the lowest speed most of the time, and that I can crank it up to a higher speed if there are multiple people and/or I want to flush out the room of the air in it. There may be times that it's especially nice outside temperaturewise (70s F) and I'd like to bring that air in, like a whole house fan would do.
Nevertheless, I'm watching this thread closely!
--Keith :mrgreen:
Hey Keith -- Will you easily be able to turn the HRV off? It would be nice to turn it off when you're not using the room! Considering the room will probably be unoccupied much more often than it is occupied, that would be a great help.
Tom, Tie it right into the red light system - there isn't anything wrong with that....I'm a little stuck now with my options, can you answer a few questions to help me rule out some ideas? Sorry if this jumps around a bit, there's just a lot of questions going through my head. First I'll add that i'm hoping that the ventilation system can be set up with a switch so that I can use it when I need it - so if it's too loud, at least I can turn it off temporarily when recording.
Sounds like a great idea (by the way - it isn't that you want - perhaps you do - but even more it is a rather strict code requirementI'm going to get in touch with a professional HVAC person to discuss options with them and get an idea of the impact of connecting to my home's HVAC set up, and let them know that I want fresh air ventilation. We'll see how that goes.
If the air is truly passive - and you are hooking it into your system similar to what I show in my book - then I can see no reason that you would require access to it.1. Because of how my room is set up - the easiest/best place for me to put the passive intake was a place that would be completely covered up by drywall and inaccessible. I'm realizing now that may be a problem. Since i'll need something that can treat the cold fresh air... can you confirm that I will need access to the passive duct work? Is there any way around that?
Connecting to my home's HVAC will at least solve the heating/cooling part of things - so long as I can control it with it's own thermostat so that it doesn't get too hot down there (without adding a new unit).
If I were you I wouldn't do that....... you might well find yourself in a situation where you only wanted to quietly play an acoustic guitar for hours on end while you wrote some music - at that point in time tou won't have any gain from gear to speak of.2. For heat, since the room will be highly insulated, if I would use baseboard (my original plan), can I use less than the guideline of 10 watts per square foot? I figure if I use basboard, I will keep the temp quite low since the room will either heat up quickly as you pointed out, or not be occupied. I was thinking of using 1, 1000 watt (4') hydronic baseboard heater if I go this route. Do you think that would be sufficient?
Heck yeah - they might very well say that your home system can handle the load when it can't - home systems are generally over designed - BUT - on the cooling side a 1/2 ton or so of excess doesn't go a long way towards supplying a control room that needs 3 tons of cooling due to equipment and humidity gain from fresh air. I would point out the actual heating load that will exist in the building - STRESS the fact that it is a super insulated air tight space - perhaps they'll get it......... I wold also give them exact numbers for the fresh air contribution to latent heat loads........3. Is there anything I need to point out to the HVAC person that would effect their input based on the requirements of the plenum and the fact that this is an air-tight room? Anything a residential HVAC person with no experience in studio construction is likely to screw up?
Free air is with 0" of static pressure - I would expect the new fan you speced to have a static rating for each of the fan speed setting.4. I just realized that the CFM for the noisier fan I talked about earlier is 210 ("Free Air CFM"). This was suggested after saying the HRV would exchange the air too many times and would be a bad idea for such a small room. However the CFM in the specs for the smaller model is only 70 CFM on the low setting (doesn't specify "Free Air CFM"). How do you read what CFM means in real world situations?
Yes, I'll be able to turn it off, or set it to any of three speeds for various intervals. I just ordered the Fantech VHR 2004 system yesterday and I ordered the ED5 premium controller at the same time.Hey Keith -- Will you easily be able to turn the HRV off? It would be nice to turn it off when you're not using the room! Considering the room will probably be unoccupied much more often than it is occupied, that would be a great help.
I think I may have an idea how to handle ventilation for my situation.
For the passive intake duct, I was thinking I could have one duct coming in from the outside combined with a duct from my home's hvac system (which I can access in-between leaves). This will hopefully treat the air coming from the outside so that it's not too cold in the winter and not too hot in the summer.
I'm hoping to only take a little away from my home's HVAC because I don't want to impact the quality of air to the rest of the house. I'm not yet sure how to do that (decreasing the size of a duct will probably only increase the velocity?).
I will have to be more careful about silencing the noise of the air flow now. I wasn't as concerned before because I could just turn off the ventilation.
My biggest concern though is how will I know that i'm getting enough fresh air ventilation. When I turn my exhaust fan on, if my homes HVAC is on or off, will I get a proper mix... or what can I do to get a proper mix?
Tom, any way you look at it - if you introduce the outside air directly into your house system - it will affect the house system on a large scale. The passive intake has to connect directly to your HVAC return duct (and close to the air handler unit at that) just in order to work. Your least expensive option would be to take the line in seperately - and add it's own inline electric heat element to temper the air. That way you could keep the fresh air flowing even if the remainder of the system was shut off. I hope that helped. RodI think I may have an idea how to handle ventilation for my situation. For the passive intake duct, I was thinking I could have one duct coming in from the outside combined with a duct from my home's hvac system (which I can access in-between leaves). This will hopefully treat the air coming from the outside so that it's not too cold in the winter and not too hot in the summer. I'm hoping to only take a little away from my home's HVAC because I don't want to impact the quality of air to the rest of the house. I'm not yet sure how to do that (decreasing the size of a duct will probably only increase the velocity?). I will have to be more careful about silencing the noise of the air flow now. I wasn't as concerned before because I could just turn off the ventilation. My biggest concern though is how will I know that i'm getting enough fresh air ventilation. When I turn my exhaust fan on, if my homes HVAC is on or off, will I get a proper mix... or what can I do to get a proper mix?
Rod, Do you have any recommendations or examples of a heater that is ideal for this situation? I can't seem to find much on the internet. How will this work so that it only comes on when it's cold outside? Is there a way that I could set this up so that I have access to the heater without having to build an access door to get to it? Can it be located right behind the register before the air enters the studio? Thanks!Tom, any way you look at it - if you introduce the outside air directly into your house system - it will affect the house system on a large scale. The passive intake has to connect directly to your HVAC return duct (and close to the air handler unit at that) just in order to work. Your least expensive option would be to take the line in seperately - and add it's own inline electric heat element to temper the air. That way you could keep the fresh air flowing even if the remainder of the system was shut off. I hope that helped. Rod
Tom,
it installs directly in the duct itself - not in a fan box or body.
Try this:
http://www.farnam-custom.com/air_heaters/duct.html
You can control it with a mini-T stat installed directly in the duct itself - then it can throttle on/off to maintain whatever you set as the minimum air temp being fed into the room.
Rod
Hi Rod,
I want to construct a plenum as you described in this topic for the purpose of attenuation. It is for air extraction. My air velocity is around 260 fpm. Round duct input output of 12".
Could you tell me what the db reduction across the bands would be achieved by a plenum of this design?
I have a more in dept post on my hvac here.. http://www.johnlsayers.com/phpBB2/viewtopic.php?t=10314
Kindest Regards,
Joe