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post #1 of 11 Old 06-30-2020, 06:52 AM - Thread Starter
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HVAC Deadvent Supply/Return

The finished room will be approximately 1912 cubic feet and in the basement. The majority of the time it will just be 2 people in the room. (and 2 dogs). The finished ceiling height will only be 7'2" so I do not have the space to build a soffit to run HVAC lines.

I currently have 1-6" round supply line coming in to the room off the main HVAC trunk. I plan to extend this run to the far side of the room and then run it down a joist cavity. There is no return for that room. I also cannot access the main trunk supply or return lines from the theater room side. The rest of the basement is finished besides the storage room.

I plan to install a deadvent return connected to the top of the AV rack using an AC Infinity Cloudline T6. This should be no issue as the storage room is unfinished.

Should I also install a deadvent supply behind the screen wall or will the single HVAC supply line be sufficient?

If I need to install a deadvent supply, I do not want to take any space from the adjacent finished rooms, so this deadvent and fan would need to be inside the theater. One option would to build it vertically in the corner or I could run it horizontally along the ceiling to save some space on the stage as the ceiling height behind the screen isn't a concern. The other issue is where to pull the air from as there is a closet on the wall where the deadvent would be installed.
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post #2 of 11 Old 06-30-2020, 08:29 AM
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Are you soundproofing the room? If you are I suggest you have a supply as well for when the HVAC is not running. Soundproof spaces are sealed and can get stuffy if you do not have a way to exchange the air when the HVAC is not on.
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post #3 of 11 Old 06-30-2020, 09:47 AM - Thread Starter
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Are you soundproofing the room? If you are I suggest you have a supply as well for when the HVAC is not running. Soundproof spaces are sealed and can get stuffy if you do not have a way to exchange the air when the HVAC is not on.
Yeah the room will be soundproofed.



It looks like the I could get the Cloudline S6 for the supply side and connect it to the same controller as the T6. I would just need to figure out if the control line can be extended.
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post #4 of 11 Old 06-30-2020, 11:04 AM
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Yeah the room will be soundproofed.



It looks like the I could get the Cloudline S6 for the supply side and connect it to the same controller as the T6. I would just need to figure out if the control line can be extended.
I use the T8's in my system and run them on separate controllers. I made an extension cord for mine it was about 25/30' and works fine. I did that so that I didn't have to cut the ACinfinity wires. If your interested let me know I can provide the info on ends I used, I think they were from Amazon but it took me a couple tries to get the right ones.

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post #5 of 11 Old 06-30-2020, 11:50 AM - Thread Starter
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Quote:
Originally Posted by pkinneb View Post
I use the T8's in my system and run them on separate controllers. I made an extension cord for mine it was about 25/30' and works fine. I did that so that I didn't have to cut the ACinfinity wires. If your interested let me know I can provide the info on ends I used, I think they were from Amazon but it took me a couple tries to get the right ones.
Yeah that would be really helpful, thanks pkinneb! Did you use a dead vent setup?



ACPH = (60*CFM)/VOL
ACPH = Air CHanges per Hour
CFM = cubic feet minute
VOL = volume of room


If I wanted to do at least 6 ACPH that would require at least 191 CFM.


Vel_air = CFM/Area



Then if I wanted a maximum of 250 fpm at the register that would require 0.76 square feet. That would be at least an 11x10 opening!


At 10 ACPH that is 318 CFM and an area of 1.27 square feet! That is quite a large opening for the dead vents.



I am not even sure how big to make the HVAC supply opening.
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post #6 of 11 Old 06-30-2020, 12:00 PM - Thread Starter
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@pkinneb Just started looking through your build thread. Very impressive!


With your T8's, I see you have a circular cutout for the registers, is that an 8 inch diameter hole? Do you notice much air noise when running the T8s?


edit: looking closer at your thread it looks like the round openings were outside your theater and you built some boxes for inside the theater.

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post #7 of 11 Old 06-30-2020, 01:06 PM
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Quote:
Originally Posted by tmn107 View Post
Yeah that would be really helpful, thanks pkinneb! Did you use a dead vent setup?



ACPH = (60*CFM)/VOL
ACPH = Air CHanges per Hour
CFM = cubic feet minute
VOL = volume of room


If I wanted to do at least 6 ACPH that would require at least 191 CFM.


Vel_air = CFM/Area



Then if I wanted a maximum of 250 fpm at the register that would require 0.76 square feet. That would be at least an 11x10 opening!


At 10 ACPH that is 318 CFM and an area of 1.27 square feet! That is quite a large opening for the dead vents.



I am not even sure how big to make the HVAC supply opening.
Here is the cable I bought and then extended to suit my needs. Using this meant I didn't have to cut into the ACinfinity cords at all.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I have my supply coming from the rec room into the theater on the screen wall and the return pulls out of the back into the hallway. I split the return into a 6" insulated flex duct going to the rear of the room and 4" flex duct going to the top of the rack. You cannot hear the supply ever unless above 6 (1-8 speed settings) The return you can hear above 3 primarily becuase of the 4" duct if I had to do over I would have used 6" there as well. Having said that I rarely run them above 2 and the room is comfortable.

I used insulated flex duct for everything and as you noted I made over sized Linacoustic lined boxes for in the theater.

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post #8 of 11 Old 06-30-2020, 06:36 PM
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You can checkout my build in my signature. I used air exchange in and out plus my one HVAC register. Like pkinneb said it can get stuffy in there without adding fresh air besides the HVAC. My intake is at the bottom of my av rack and goes thru my stage. Then return is in the back of the room that returns to the top of the av rack.

In your design you can do the same with your stage and exit with your av rack in the back of the room.
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post #9 of 11 Old 06-30-2020, 06:53 PM
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I assume the supply duct is in the ceiling? Can you get back to the main trunk. 6" isn't enough. The return your talking about is going to where? The storage room? Where does the air go from there? How does it get back to your furnace/AHU? How important is temperature control in your HT room? Do you have cooling currently? Im a commercial HVAC contractor going on 30+ years so Im still learning but I know a bit about temperature control and airflow.

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post #10 of 11 Old 07-01-2020, 04:36 AM - Thread Starter
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Quote:
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I assume the supply duct is in the ceiling? Can you get back to the main trunk. 6" isn't enough.
Yes the 6 inch duct is in the ceiling. I cannot access the main trunk.

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Originally Posted by Deaf-Forever View Post
The return your talking about is going to where? The storage room? Where does the air go from there? How does it get back to your furnace/AHU?
The return is a dead vent that will pull air from the theater room into the storage room from above the AV rack. The air can then be pulled back into HVAC return that is in the basement.

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Originally Posted by Deaf-Forever View Post
How important is temperature control in your HT room? Do you have cooling currently? Im a commercial HVAC contractor going on 30+ years so Im still learning but I know a bit about temperature control and airflow.
The room has never been closed in, but since it has 2 walls that are underground the temperature is usually fairly consistent throughout the year. The only HVAC that was in the room before finishing the rest of the basement was that single supply line.
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post #11 of 11 Old 07-05-2020, 12:18 AM
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Quote:
Originally Posted by tmn107 View Post
Yeah that would be really helpful, thanks pkinneb! Did you use a dead vent setup?



ACPH = (60*CFM)/VOL
ACPH = Air CHanges per Hour
CFM = cubic feet minute
VOL = volume of room


If I wanted to do at least 6 ACPH that would require at least 191 CFM.


Vel_air = CFM/Area



Then if I wanted a maximum of 250 fpm at the register that would require 0.76 square feet. That would be at least an 11x10 opening!
Don't forget that the register itself causes some level of obstruction to airflow and does not represent a 100% open path to the air. The typical register can have an open area somewhere between 60-80% of the listed size. So to compensate for the blockage and still maintain your target velocity you would need a register closer to 1 square foot or 12" x 12".

At 10 ACPH that is 318 CFM and an area of 1.27 square feet! That is quite a large opening for the dead vents.



I am not even sure how big to make the HVAC supply opening.
From above, I would go with 12" x 12" at a minimum. 10 ACPH is probably more than what you need.

One other thing to consider is that you need both a supply and a return air path for the room. Currently, you are venting all of the supply air through your equipment, then through the dead vent, through the adjacent room and then back to the air handler. The problems I see with this arrangement are:
  1. All the air goes through your equipment, which is probably much more than necessary to keep your gear cool. This will increase the amount of dust that builds up on the equipment and decrease equipment cooling over time. The dust problem can be solved with an air filter before the air goes through your equipment, however, this just makes problem #2 even worse
  2. The return path has more airflow resistance than is desired and will probably require greater static pressure to achieve the desired airflow. The end result will be less airflow than expected, especially if the door to the other room is ever closed. You really need a separate return vent that provides a low resistance path for the return airflow.
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