Hello all,
Great forum here! I have a question on ventilation.
I have two rooms that I would like to have fresh air coming into.
One room is a 300 Sq. Ft. Live Room/Rehearsal Room, the other is a 250 Sq. Ft. "Control Room". From reading posts on this forum, it looks like I should be able suck the air out of the rooms while having fresh air come in naturally (no fan).
To accomplish this, I think this fan will work: http://www.pureairproducts.com/hepafilt ... vs275a.htm
My plan is to suck the air out of the rooms with that fan using 5 inch duct...the fresh air supply will be provided through a separate 5" duct (however with no fan).
My air conditioning will be a mini-split system.
1. Will this work? (245 CFM split between two rooms?)
2. Should I use a fan for the supply?
3. If I use flex duct, would sound be minimized between rooms, or should I build some silencers?
4. Would I be better off using a dedicated fan for each room such as this one?: http://www.pureairproducts.com/inlineho ... thp190.htm
5. Could I use the fan in question #4 for both room if I built silencers?
Additionally, when looking at whole house ventilation units like this one: http://www.pureairproducts.com/heatreco ... tvh704.htm
The CFM's seem low compared to other cheaper units...are these designed to hook up to a existing air handler and not work in their own?
I think that's all for now...thanks for the help!
Ventilation Question
Originally posted at johnlsayers.com, topic 11560.
Hi guitarman. Welcome!
How can air get in "naturally", when you have two hermetically sealed air-tight barriers between you and the outside world? (assuming you built the room right). There are no "natural" paths for air to get into your control room, if you built it right. You need to have some kind of duct work, with in-line silencers and all the other usual acoustic precautions (over-size ducts, several 90-degree bends, acoustic duct liner, mechanical decoupling, etc.). Or maybe I just didn't understand what you were saying... - Stuart -I should be able suck the air out of the rooms while having fresh air come in naturally (no fan).
As I said above, my plan is to suck the air out of the rooms with that fan using 5 inch duct...the fresh air supply will be provided through a separate 5" duct (however with no fan).
I think my post may have been too long and confusing :)
I just want to make sure I'm going to buy the right stuff...
Ok, after doing some more reading, it looks like I need to shoot for about 10-12 air changes per hour.
So for the 250 Sq. Ft. room, the calculation is as follows:
250*8 (Ceiling Height)=2000 Ft3
2000/60min=33.33
33.33 x 10 air changes/hour = 333 CFM
33.33 x 12 air changes/hour = 399 CFM
For the 300 Sq. Ft. room I would need this:
10 air changes per hour = 400 CFM
12 air changes per hour = 480 CFM
If I have this wrong, please let me know!
Now here is what I'm not clear on, when a fan says 400 CFM and it has two ports such as this one: http://www.pureairproducts.com/hepafilt ... vs275a.htm, is the CFM split between the ports or is the CFM calculation for the whole system?
In other words, do I need to get two 400 CFM fans (one for each room) or can both rooms share one 400 CFM fan?
And how does duct lenght figure into this? If I use the whole length of a 25' flex duct, is the CFM figure reduced by the time it gets to the end of the duct?
so much to learn!!
Thanks for the help!
Am I on the right track?
Ok,
I'm about to buy two of these: http://www.iaqsource.com/product.php?p= ... egory=1252
One for each room to suck out the old air.
Am I doing the right thing?
Does anyone think that these silencers would work ok? http://www.iaqsource.com/product.php?p= ... uct=111138
Or should I just build my own?
Thanks for any help!
Is there something I missed?
Aloha,
Check your PM. :wink:
Aloha 8)
Thanks! PM sent back.
I've read hundreds of pages trying to figure what I'm doing :)
Per my last post, I'm doing to purchase 2 of the 400 CFM fans for each room to suck the old air out.
There is a section of the duct that will be exposed outside of the rooms and not contained within the walls. I'm using the insulated flex duct; should I be concerned about noise from the duct itself? (i.e., music radiating from the duct, or will the duct contain the noise?). The rooms are not going to share any ducting, so I'm not concerned about noise between rooms.
Both the fresh air intake and old air blowing out will from the roof of the structure (about 20ft in the air), should I be concerned about bothering my neighbors with noise? (using the insulated flex duct?)
I’ll draw a picture soon and post it….
Ok, so now I'm confused...
I was reading a book last night by Rod Gervais, it's called Home Recording Studio: Build it Like the Pros...you guys should check it out! :mrgreen:
Anyway, he says he uses a figure of 15 CFM per person. In my 300 Sq. Ft. room, that is 2400 CF, if I have a max of 6 people in the room at one time, that is 90 CFM. If use a 90 CFM fan, by my calculation, that is roughly 2.3 air changes per hour (if my calculation is correct).
I've read on here and other sites that I should be shooting for 10-12 air changes per hour.
Is 10-12 changes overkill?
Is 2.3 changes not enough?
Am I overthinking this?
I don't want it to get stuffy in there, and at the same time, I don't want to over spend.
At this point, I'm probably talking to myself...but if anyone has any input, I would appreciate it.
Aloha,
No input to offer at the moment, but I'm listening/reading/watching :wink: Did you try PM'ing the others I mentioned? Hang in there. :D Aloha 8)At this point, I'm probably talking to myself...but if anyone has any input, I would appreciate it.
I just sent them a PM...hopefully one of them will jump in. I'm working on a drawing right now, so I will probably post it up tonight...Aloha,No input to offer at the moment, but I'm listening/reading/watching :wink: Did you try PM'ing the others I mentioned? Hang in there. :D Aloha 8)At this point, I'm probably talking to myself...but if anyone has any input, I would appreciate it.
Question about silencers and decreased air speed:
I plan on building some silencers that will at the same time decrease the air speed. Rod suggests doubling the size of the duct to decrease the air speed by half.
Is he talking about the duct diameter measurement or area of the duct?
The area of a 6" duct is 28.26 sq.in., if I double the duct size the area of that 12" duct if now 113.04 sq.in....or am I wanted to double the area? If took the area of the 6" duct: 28.26 x 2 = 56.52..so I could use a (theoretically) 8.5 inch duct for the inlet into the silencer?
OK, more than a couple of things to deal with here........
To begin, The American Society of Heating, Refrigeration and Air-Conditioning Engineering (ASHRAE) recommends (in its Standard 62-1999, "Ventilation for Acceptable Indoor Air Quality") that homes receive .35 air changes per hour, but not less than 15 cubic feet per minute (cfm) per person.
Therefor I set the MINIMUM at 15 cfm per person...... 10 to 12 exchanges per hour is getting a wee bit on the wild side of conservative. If you want to push that a bit feel free - but double that would still only be slightly less than 1 complete change per hour.
Remember - you are exhausting tempered air - and whether it's winter or summr - that is a lot of energy you're throwing away when you get into things like 10 to 12 full exchanges. Every cubic foot of air you bring into the building has to be either heated or cooled - depending on the season.
Now - the trick is to maximize volume while minimizing velocity...... so to begin with you are much better off with the largest duct (within reason of course) for your initial runs - if you could go immediately from the 6" connection at the fan and increase to 8 or even 10" - you are ahead of the curve.... the final run into the room is always nice if you can use an iso-box - at which time you want a minimum of double the area of the supply - which will decrease the veolcity by 1/2 - while maintaining the volume.
Your choice of duct is wide open - although I do not especially love the flex ducts - this because it's hard to install them without having areas sag - which causes back pressure and increases velocity - thus working the fan harder with more potential for noise..... BUT - if you do a real nice job and don't have that problem - they work fine....... again I point out that the larger duct you use the better off you are.
Generally you don't have an excess of pressure loss (static pressue) when running 25 or 30' runs - over that you really should run some calcs to make sure you aren't overloading the fans...... every foot of duct adds SOME back pressure to the fan unit- which in turn means it delivers less air flow than the design with 0.00 psig static pressure (measured in water pressure) Look at the flow rate chart for the fan you plan to use....... steady for the first .05 inches of static pressure at 400 cfm..... but it drops like a rock from that point on - the supply is down to 200 cfm by the time you hit .9" of static pressure - and only 5 cfm at 1.4" static.
http://www.suncourt.com/CentraxAirflowGraphs.html
So short runs or oversized ducts are required to maxamize delivery.
I hope this helped,
Rod
As always, useful info, Rod.
A quick question (I'm trying not to hijack the thread!). Ducts I see here are usually metal or flex, but is there any reason why they could not be something else? EG, could you make ducts from materials like thin plywood / sheetrock / polycarbonate sheeting / large diameter PVC pipe / etc? Also, an you line then with plain mineral wool / fibreglass, or does it have to be ductliner?
- Stuart -
Thanks for the post; that did help a lot. I believe I have a better understanding now of what I need to do.
Wow, I didn’t even think to look at the fans spec to see how they perform when the pressure changes. It looks like the Fantech fans perform much better. Even though my runs will be short (less than 20’), I’m going to stick with the Fantech.
I knew the .35 recommendation from doing research before, but I thought with 4 or 5 or 6 people rocking out it may get a bit stuffy with so few air changes.
So I guess now my questions are:
Is 2 to 3 air changes enough for a rehearsal room?
Is it better to suck air out or to blow air in or both?
Either way, I think I’ll go with one (or two) of these:
http://www.iaqsource.com/product.php?p= ... egory=1252
If I share that fan between rooms (sucking or blowing), I can get over 4 air changes per hour for the 250 Sq. Ft. room and just under 4 air changes per hour for the 300 Sq. Ft room (in theory)…
Hey guitarman,
Any update on your install? Did you stick with the flexduct? Did you end up using any silencers? I'm currently trying to wrap my head around how to make things work for my build;
http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=11485&p=86589#p86589