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Post by Mountainbiking Fool on Jun 22, 2017 10:32:58 GMT -5
My theater room is 19' X 16' X 8' and only has one A/C register in it. I would like to add at least one more, maybe two. My question is, is it better to add 2 smaller ones or one large one?
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Post by Boomzilla on Jun 22, 2017 10:45:10 GMT -5
Hmmm...
Are you trying to get more air through the room? Are all the doors open between the HT room and the air-return register? You can't just blow air into a room - it has to also have a way to get out.
As to your question big vs. little - There's a higher probability of wind noise through smaller registers due to the higher velocity. The bigger you make the registers, the lower the air velocity and the more likely they are to be silent. Now if you have duct or fan noise, there's nothing that the outlet registers can do to change that.
Best of luck!
Boom
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Post by ngmitter on Jun 22, 2017 11:00:07 GMT -5
HVAC Engineer here. It's highly depends on the system and room arrangement. You need to balance several factors, as boomzilla outlined.
1) Assuming you are keeping the same volume of air (CFM), you need to coordinate the velocity of air out of the two smaller diffusers. It's possible that the new diffusers have a combined total free area more than that of a single diffuser, so air velocities could be less. Velocity is related to noise, and as we all know, less room noise is better in a home theater. The noise is a function of materials, grille shape, and velocity. There's no hard or fast rule which one is going to be quieter. Commercial companies, such as Titus, publish this information based on empirical measurements. We use this when designing HVAC systems.
2) Another concern is what they call "throw". This is the distance the air will travel from the diffuser. If the throw is too low, the room may not get proper mixing. Some people will get warm or cold vs. others. If the throw is too high, the room mixing might be uncomfortable due to a draft. Air velocity across the skin has a huge impact on human comfort.
Can you post a few pictures and maybe a sketch of the layout? I should be get back to doing real work this afternoon...but I'll take a look later if I have time.
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Post by Mountainbiking Fool on Jun 22, 2017 12:10:51 GMT -5
HVAC Engineer here. It highly depends on the system and room arrangement. You need to balance several factors, as boomzilla outlined. 1) Assuming you are keeping the same volume of air (CFM), you need to coordinate the velocity of air out of the two smaller diffusers. It's possible that the new diffusers have a combined total free area more than that of a single diffuser, so air velocities could be less. Velocity is related to noise, and as we all know, less room noise is better in a home theater. The noise is a function of materials, grille shape, and velocity. There's no hard or fast rule which one is going to be quieter. Commercial companies, such as Titus, publish this information based on empirical measurements. We use this when designing HVAC systems. 2) Another concern is what they call "throw". This is the distance the air will travel from the diffuser. If the throw is too low, the room may not get proper mixing. Some people will get warm or cold vs. others. If the throw is too high, the room mixing might be uncomfortable due to a draft. Air velocity across the skin has a huge impact on human comfort. Can you post a few pictures and maybe a sketch of the layout? I should be get back to doing real work this afternoon...but I'll take a look later if I have time. Here is a rough drawing of the room. When I get home I can take better pics. I would like to put the vent(s) in the ceiling between the first and second row.  |
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Post by Mountainbiking Fool on Jun 22, 2017 12:17:47 GMT -5
Hmmm... Are you trying to get more air through the room? Are all the doors open between the HT room and the air-return register? You can't just blow air into a room - it has to also have a way to get out. As to your question big vs. little - There's a higher probability of wind noise through smaller registers due to the higher velocity. The bigger you make the registers, the lower the air velocity and the more likely they are to be silent. Now if you have duct or fan noise, there's nothing that the outlet registers can do to change that. Best of luck! Boom The room gets hot. Air can get out of the room when the door is closed due to the shutters that are on the left wall, the opening is 8'W X 2'H. Thanks Boom! |
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Post by ÈlTwo on Jun 22, 2017 13:40:59 GMT -5
If the room is getting that hot, have you considered adding a return to the room?
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Post by Mountainbiking Fool on Jun 23, 2017 8:50:50 GMT -5
If the room is getting that hot, have you considered adding a return to the room? There is one already there. There is an A/C register right across the hall from the entry into the theater. The theater room was open and the wall was not there before, so the vent blew directly into the room but know since I bulit a wall and closed it off, the vent no longer blows directly into the room and there is just one vent in the room. |
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Post by ÈlTwo on Jun 23, 2017 10:47:52 GMT -5
So you have one vent and one return in a 16 x 19 room.
You show a vent 12" from the ceiling, all the way near a corner of the room, but where is the return?
I think pictures might help. Personally, I'm having a little difficulty seeing how that vent in that placement can efficiently cool the room (unless it's some ginormous directed vent).
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Post by Mountainbiking Fool on Jun 23, 2017 11:36:51 GMT -5
So you have one vent and one return in a 16 x 19 room. You show a vent 12" from the ceiling, all the way near a corner of the room, but where is the return? I think pictures might help. Personally, I'm having a little difficulty seeing how that vent in that placement can efficiently cool the room (unless it's some ginormous directed vent). There is an A/C register right across the hall from the entry into the theater. The theater room was open and the wall was not there before, so the vent blew directly into the room but know since I bulit a wall and closed it off, the vent no longer blows directly into the room and there is just one vent in the room.  This is the entry now after I added the wall  Entry before I added the wall  |
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Post by ÈlTwo on Jun 23, 2017 12:33:15 GMT -5
Let the pro take a look at that info, but the only way that room gets cool during the day is if it's less than 60 degrees outside.
You show only one vent and no return (an air intake for the system) in that room.
I'm definitely no expert but you'll need at least another diffuser in that room, and then need to rebalance the system using the dampers that should be in the line and/or trunks.
I would also make sure my system is large enough for my house.
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Post by cleestedwood on Jun 23, 2017 17:19:24 GMT -5
Is the ceiling finished where the main duct trunklines are located? Are the floor joists 2X10 or 2X12 ? Adding more openings to a system usually decreases cfm per opening if blower speeds remain unchanged. It is fairly easy to add extra openings depending on access to the supply trunkline and open joist space.
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Post by Mountainbiking Fool on Jun 26, 2017 8:04:52 GMT -5
Is the ceiling finished where the main duct trunklines are located? Are the floor joists 2X10 or 2X12 ? Adding more openings to a system usually decreases cfm per opening if blower speeds remain unchanged. It is fairly easy to add extra openings depending on access to the supply trunkline and open joist space. I have a slab foundation but the vent ducts are very close to this room in the attic. The central HVAC unit is also located about 5 ft from this room. |
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Post by hilodb1 on Jul 18, 2017 0:17:38 GMT -5
Former HVAC mechanical designer/engineer, currently a HVAC mechanical contractor.
Sounds like your system is undersized for the occupancy of the space. If the space is getting hot no amount of extra air is going to cool the space of your system doesn't have the capacity. What's your current A/C system capacity?
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Post by Mountainbiking Fool on Jul 21, 2017 11:05:14 GMT -5
Former HVAC mechanical designer/engineer, currently a HVAC mechanical contractor. Sounds like your system is undersized for the occupancy of the space. If the space is getting hot no amount of extra air is going to cool the space of your system doesn't have the capacity. What's your current A/C system capacity? I will look what the capacity is when I get home. I was able to add another 8" duct 2 weeks ago and now the room is a lot cooler and it's comfortable to sit in with the door closed. |
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