High BTU theater - AC return vent mod - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 09-12-2019, 04:49 AM - Thread Starter
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High BTU theater - AC return vent mod

My theater is about 24’ x 24’ x and a multi angular ceiling height of about 15’ near the front screen wall. Near the peak at 15’ there is a very large supply and return which are about 16” x 16” plus. They are about 5’ or 6’ apart (which is less than ideal). I have all my theater equipment in the theater (many McIntosh amps, an MX160 etc...). The bulk of the equipment is under the main supply and return, which is a good thing. The rack puts out moderate heat, but not near as much as the 5000es. I can’t relocate any of the equipment outside the theater, nor is a hush box feasible for the projector.

The issue is, the 5000es is in the back of the room and far away from the supply/return. The ceiling height near the projector slopes down to about 8’. The 5000es puts out a fair amount of heat even in low mode and quite a bit more in high (over 80 on the laser). On warm to hot days the 5000 strains the AC system a bit due to its high BTUs and location. The theater has its own AC zone with motorized dampers. The total house system is 5 tons with 4 motorized zones. 2 speed condenser with variable speed air handler.

My options are to put in a Mitsubishi mini split to assist in cooling at some point in the future. However, even if I did a mini split, part of the issue in the theater is the heat from the 5000 has nowhere to go as it is not near any returns. My thoughts are... to put a Y at the main return, and a reduction collar at the main return so internally it’s half the size that it used to be (reduced to approx 10”). Then branch off the same main return at the Y creating a second 10” return as close to the projector as we can reach (about 18’ away). I’m sure you would recommend the return ceiling vent be located as close to the front of the projector as possible. Perhaps a foot or two in front of the 5000, as the ceiling slopes up in front of the projector and heat rises. Vent can’t be in back of it, as it is not reachable... ceiling starts to pinch there. The main and only supply stays put in its original location.

Is this a logical path? Without the giant return at the ceiling peak (now reduced in size by 50%, and a second return down low, will that make things worse in the room, especially when the projector is not On? Heat rises, which favors the high up (peak return), but capturing the heat as it leaves the projector may help excessive heat dispersion into the room. In theory I would think this mod is the better way to go. Correct?


My HVAC guy is top notch, but a bit torn as to how effective this HVAC mod it will be. He has minimal experience with high BTU theaters, especially with a fairly large BTU projector in the rear of a room.

Thanks!

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post #2 of 9 Old 09-12-2019, 05:50 AM
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I think you are battling the close proximity of the supply and return located high in the peak of the room. I think trying to force more of the air out the back maybe even 65- 75% will help mix things up, leaving a smaller return up in the peak will help pull air that gathers there. Once the return system is divided you could even experiment with totally blocking the return in the peak or changing the % mix if you install dampers in the lines.
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post #3 of 9 Old 09-12-2019, 12:51 PM - Thread Starter
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I think you are battling the close proximity of the supply and return located high in the peak of the room. I think trying to force more of the air out the back maybe even 65- 75% will help mix things up, leaving a smaller return up in the peak will help pull air that gathers there. Once the return system is divided you could even experiment with totally blocking the return in the peak or changing the % mix if you install dampers in the lines.
Hello Jeff. Yes, I never liked the close proximity of the supply/return. When the AC system first went in, there was poor access above the theater, which contributed to the sub optimal placement of the supply/return. Since then, I have built an access door plus a plywood raceway around the space above the theater, so access is greatly improved. This was partly done for Atmos install access as well. So now things can be modified/improved.

1) So you are recommending that the second return near the projector get 65- 75% of the air intake, which reduces the peak return to 25-35% of the air intake, correct?

Access is a bit tricky to adjust the dampers often. Perhaps I could have remote controlled dampers put in?

2) Do you think splitting up the main supply with a Y and extending a second supply to another area in the theater is worth the effort? If anything it moves some supply air away from the return that is in close proximity. The existing main supply/return is towards the right front off the theater. So perhaps put a second supply towards the left front of the theater.

As always... thank you for your input.
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post #4 of 9 Old 09-12-2019, 01:04 PM
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I'm just guessing at the percentages, if this was a flat ceiling you would just move 100% of the return to the rear and force all of the supply in the front and the room would have good mixing. But with a peak, hot air will gather and you need to pull some out. If you can distribute the supply Left and right that will help with mixing.
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post #5 of 9 Old 09-12-2019, 01:53 PM - Thread Starter
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I fully agree. Over a year ago, I presented the idea of adding Y splitters at the supply and return ducts to my hvac company, but they thought the BTU load in the theater is so high it will help, but only marginally. I do see his point, but I also agree with what you have said in your responses. I am reassured that we are on the same page. I think adding both a second return and a second supply is the way to go. I will have another talk with my HVAC company. When completed I will post the results.

Thanks again Jeff...
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post #6 of 9 Old 09-12-2019, 07:03 PM
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Just a thought, but with the sloped ceiling consider splitting the supply side instead of the return, sending ~50% of cool air to the rear, and the return at the peak up front gathering it all.

I'm not an HVAC guy... would the size of such a split supply or split return duct to the rear be roughly the same? If so, perhaps you can try it one way, measure, then try the other.

Generally better to have supply in front and return in the rear but with the slope up to the front that may not be the case.
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post #7 of 9 Old 09-13-2019, 05:48 AM
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sending the cool air to the rear is a logical alternative for solving the close proximity problem of the supply and return. You are however fighting the human physiology issues of preferring cool air hitting you in the face rather than the back of your neck. Need to look at the seating positions relative to where a rear supply would be located, could work.
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post #8 of 9 Old 09-13-2019, 06:42 AM - Thread Starter
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Sending cool air to the back of the theater is certainly an option, but I would think capturing the 5000’s heat by putting a return just in front of the projector would prevent the heat from dispersing in the room. The heat emitted from the 5000 due to the ceiling angle should rise right up into the return. Then add a second return to the left of the screen aimed at the single row of 4 chairs, while the right supply also assists cooling the area aimed at the front of the seating.
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post #9 of 9 Old 09-16-2019, 05:31 AM
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Quote:
Originally Posted by G-Rex View Post
Sending cool air to the back of the theater is certainly an option, but I would think capturing the 5000’s heat by putting a return just in front of the projector would prevent the heat from dispersing in the room. The heat emitted from the 5000 due to the ceiling angle should rise right up into the return. Then add a second return to the left of the screen aimed at the single row of 4 chairs, while the right supply also assists cooling the area aimed at the front of the seating.

This is my thought too. Take out the heat right at the source, I may also put a return on the AV rack . The cool air incoming would flow in from the opposite and lower corner of the room. By creating this natural convection the cool air will flow across the room keeping the occupants and other components more comfortable as well . Now to find an all in one air exchanger with AC and HEPA filter, does this even exist ? We shall see soon enough.

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