The Once and Future Theater - Page 5

I'm not sure that a booster fan in your HVAC lines will get you the flow you are looking for. I.e. adding a 300 cfm fan in your 6" HVAC line will probably not give 300 cfm total flow, and if I had to guess it would cause problems with cooling in other parts of the basement.

If it were my theater, I would supplement the HVAC line with another supply and return that pull from and exhaust to another part of the basement (i.e. dead vents), each with an inline fan. It's probably overkill, but if you are planning sound isolation, that room is going to be sealed up and you won't have any other air exchange. This does two things, it will supplement your cooling from the AC by pulling cool air from other rooms and exhausting hot air, and it will also keep fresh air moving in.

The issue that Big and Morph1c had is a result of high air velocity. As an example, if you use a 6" flex line connected to a 300 cfm fan then the air in that line is moving at

Cross section area (A) = pi*(r)^2 = pi*(0.25')^2 = 0.196 s.f.
Flow velocity = cfm/A = 300/0.196 = 1,530 fpm

That's way too fast and will be very noisy. If that 6" line connected to your HVAC is only moving 75 cfm, then the velocity drops to

Flow Velocity = 75/.196 = 382 fpm

Still too fast, but then again you can usually hear the air coming out of the registers in your house, so it's a reasonable number I think. Also, if you look at this post, someone actually measured the flow coming from their 5" supply, and it roughly agrees with the numbers we're playing with, and the chart with regard to flow.

So, the solution to all that is to slow down the air before it gets to and/or enters your theater. For the HVAC supply, you're probably OK with a large register as this will allow the air to slow down. For the dead vents, since they will probably be moving more air, you can do what Big and Morph1c did by either adding a few feet of 8" just before your register, or if you have the room, just run a larger duct for the entire length. You can combine this with a lot of area that those ducts have to transition from the duct to the room to help things as well. The higher the cfm, the more cross sectional area is needed. A box is not ideal because turbulent air is noisy, too, but if it's big enough you shouldn't have a problem. Ideally, you would have a smooth transition from your duct to your register (like the shroud on a ducted fan).

Whew! I think I'm getting a repetitive stress injury from all this typing Of course, all this advice is worth exactly what you've paid for it, so I'd seek a second opinion if you can! My line of work has a lot more to do with electrons than this mechanical stuff

You should be able to do that as well. You're talking about a zoned system, and considering that you have a variable speed AHU, it's probably capable of being zoned. Assuming assuming that's the case, and assuming that it's not already, to make it automated you will probably need a new controller (to operate the dampers) as well as at least one new thermostat for the theater zone and possibly two depending on what you already have. I agree with RT that zoning a basement would probably be best left to the pro's, and in this case you would be able to tell them that you need cooling for X number of people, and you need a minimum of 6 air exchanges per hour, with a maximum velocity of 250 fpm. I would ask to see the manual J as well, and double check to make sure they are not just telling you they've met all those requirements.

The cost of adding a zone to an already zoned system is minimal, I think it was around $600 for me. However, once I reached the limit on the number of zones for my controller, it was more like $1,000 - $1,500 to upgrade controllers and add the zone. I'm sure costs will vary from area to area, but that gives you an idea.

Hmmmmm..... Well, there is another option.

First, you say you don't have an existing thermostat, but what controls the unit now ?

Assuming there is a thermostat for the basement, you could run two 7" or 8" lines from your HVAC to your theater. This would give you the necessary cfm (again, assuming all of my previous posts are even close to correct). You can then move your existing thermostat into the theater, and set it to run the blower whenever you are in there. Then you'll get your air exchanges and the AC will kick on whenever the temp gets too high. You can also get thermostats with a remote (handheld) thermostat that you can take from room to room, but that again requires you to buy another thermostat.

The downside is you'll be cooling the entire basement when the theater calls for AC. Although, I don't suppose that's much different than your current setup. This will be mitigated somewhat by running the blower continuously while you're in the theater.

I don't know specific answers to your questions, but I think you should be able to either wire the fans to be triggered by your equipment (some amps/AVRs/etc have 12 V triggers I believe) or to turn on with the HVAC blower. It may require an intermediate relay, but I can't imagine it would be too complicated.

The next part of that question is something I asked my HVAC contractor a hundred different ways, but he was pretty adamant that you can't have two thermostats controlling one unit/zone. I wanted a thermostat in my theater and a thermostat in my game room that would both control the basement zone where one could be set to override the other. He said it didn't' work that way. He did, however, recommend a thermostat with a remote control. That way I could either take the remote into the theater or into the game room with me. The remote has a temp sensor, so it tries to keep the temp adjusted for whatever room it's in. I haven't decided which route I'm going to go yet.

This seems like it could work if it had a computer interface. It is not something I would be able to do, but maybe a Control4 or HTPC system would be able to make this work.

Could you put a built in bench there? Maybe something with cabinets or drawers under it? I think the standard chair height is around 16", so that window doesn't need to be too high above the floor for a bench to fit under it if it needs to.

Maybe media storage? You could make it look like a library nook with floor-to-ceiling shelves for the media and a window seat under the window. You could store blankets and pillows under the window seat.

I like the big riser extension outside the theater entrance. That big platform setting a couple of steps up from the main floor could help create a pretty dramatic theater entrance.

You could use the space for a dead vent system pulling cool air into the theater. The hot air exit would need to go higher up on the wall inside the theater.

That's what my HVAC guys recommended. Either tstat can call for air, and the other "side" just gets heated or cooled more than necessary. At the time I thought it was nice they were trying to save me money. In retrospect, I think they may have just wanted to keep things simple (due to lack of competency).

If you used a dead vent to exchange air between the two "sides" it help mix the air, but I'm still not convinced dead vents are a good thing. I could see it as a passive air return, or possibly with a remote mounted blower, but the idea of putting an inline fan in the wall of the theater seems counter productive.

Dead vents will help with pressure differentials, but not temperature. And unless "powered" via a connected forced air duct line (either return or supply), the amount of flow felt between the spaces will only be the pressure differential between the two zones and will have negligible pressure impact on temperature.

Most of the talk with dead vents here on this forum is meant to eliminate the direct path of the air (and sound in both directions from leaving the room. I have never personally seen one used for anything other than sound dampening or pressure balancing.

The only method of air exchange that I have in my room are two dead vents to exchange air with the rest of the basement. I did not run any supplies or returns from the house's main HVAC sysyem.

The one drawing air out in the back of the room is powered with an inline fan and the one in the front is unpowered. Since the room is sealed up so tight from the soundproofing, the decrease in pressure from the return causes close to the same amount of airflow through the supply.

Since the room isn't finished yet, I haven't had a chance to actually sit through a two hour movie and test how comfortable it is, but so far with me working in there I haven't had a problem. I've seen dead vents used successfully quite a few times. Ted White's home theater stands out as one I can remember. He did the same thing as me and has had it running successfully for over 10 years.

The other nice thing about having dead vents is that it effectively seperates the theater from the rest of the house. For those periods in the spring and fall when heating or cooling aren't necessary and the windows are left open in the rest of the house, you don't have to turn on the home's HVAC just to make the theater comfortable.

I'm not saying that running actual HVAC supplies and returns to the theater is a bad thing; it's certainly a very good thing to do. But dead vents can be successful if employed correctly as well.

Ummmmm............Time for plan B maybe? Not enough power Scotty! I need more power!

Regards,

RTROSE

Haircut and a Shave?

Time for some Captain Morgan??

Hi Fred, I am mostly a lurker here but reading this reminded me of when I won my Grafik Eye off of Ebay. I totally know how you feel, you will love it, what model did you get? I was lucky enough to find a great deal on Ebay for the RS232 control module so now I can even control each of the individual zones intensities not just scenes its awesome! Good luck on your drywall stack!

-Brent

+1 to that!! I was going to say that before I even saw your post. I guess great minds think alike....