Thoughts on this HVAC silencer?
Posted: Fri, 2021-Dec-17, 19:32
I'm working on some design ideas for a single room studio. For background's sake, the general plan is room-in-room construction with 2 layers of mass in each leaf. It's about 300 sq ft overall. I was planning to go the route of placing a minisplit in the room and depositing fresh air a few feet above it. I figure I will need about 100cfm of fresh air.
I have access to a small adjacent room that I can place the outer silencers in. As there is space for it, those will be pretty "standard". I'm looking at Gregwor's design as a guide.
I realize that everything depends on everything else and it's hard to ask a question without going into every aspect of the design. But I'd like to focus on the inner silencers here. Due to a number of space constraints, I'm looking at placing these inside the inner leaf joists. In order to accommodate the inside out ceiling, I plan to use 2x12 joists. This provides a decent amount of room for treatment and maybe just enough space for the silencers, although the height is still limited to about 6" after adding 1" duct liner. Joists are 24" apart.
Here is a cross section of a pair of joists. The outer ceiling is "outside in" meaning the drywall is facing in.
My ceiling modules alternate between 7' and 8' long (to span 15'). Consequently, I would make the two inner silencers 7' long, probably a little longer than they need to be, but perhaps a little more effective. The inlet is going to be smaller than I'd like due to minimal space between the walls. I think I can fit a bit of 8" flex duct in there, between inner and outer silencers. I calculated the air speed with each change in area. While air enters the box at 300fpm, it would leave at 200fpm and go into a plenum which slows it down further. With a pair of 10x10 registers at the end, I figure about 70fpm (assuming I did the math right, thinking 2 registers at 10x10 would be equivalent to a single 200 sq in opening.
Here's a diagram of the supply. Does this seem like a reasonably effective plan? I'm trying to avoid soffits in the room and there isn't any space above the ceiling, so this seems like the only decent option to me. One thought I had was to make the silencer shorter and the plenum longer, in order to give the air time to slow down. For example, I could make the whole thing 8' long and make half of it a plenum.
The distance from inlet to register needs to be about 11'. The return would pretty much be identical within a joist at the other end of the room.
I have access to a small adjacent room that I can place the outer silencers in. As there is space for it, those will be pretty "standard". I'm looking at Gregwor's design as a guide.
I realize that everything depends on everything else and it's hard to ask a question without going into every aspect of the design. But I'd like to focus on the inner silencers here. Due to a number of space constraints, I'm looking at placing these inside the inner leaf joists. In order to accommodate the inside out ceiling, I plan to use 2x12 joists. This provides a decent amount of room for treatment and maybe just enough space for the silencers, although the height is still limited to about 6" after adding 1" duct liner. Joists are 24" apart.
Here is a cross section of a pair of joists. The outer ceiling is "outside in" meaning the drywall is facing in.
My ceiling modules alternate between 7' and 8' long (to span 15'). Consequently, I would make the two inner silencers 7' long, probably a little longer than they need to be, but perhaps a little more effective. The inlet is going to be smaller than I'd like due to minimal space between the walls. I think I can fit a bit of 8" flex duct in there, between inner and outer silencers. I calculated the air speed with each change in area. While air enters the box at 300fpm, it would leave at 200fpm and go into a plenum which slows it down further. With a pair of 10x10 registers at the end, I figure about 70fpm (assuming I did the math right, thinking 2 registers at 10x10 would be equivalent to a single 200 sq in opening.
Here's a diagram of the supply. Does this seem like a reasonably effective plan? I'm trying to avoid soffits in the room and there isn't any space above the ceiling, so this seems like the only decent option to me. One thought I had was to make the silencer shorter and the plenum longer, in order to give the air time to slow down. For example, I could make the whole thing 8' long and make half of it a plenum.
The distance from inlet to register needs to be about 11'. The return would pretty much be identical within a joist at the other end of the room.