HVAC for soundproof/ 100% air tight room

[Bartl007]

This forum is great! Thanks in advance for any help you can provide.


I'm currently in the planning stages for a theater/media room that will be extensively sound isolated and air sealed from the rest of the home.


The space has no windows, is all below grade in a basement and currently (unfinished) is a comfortable 72 degrees even in the hot humid summer months (90+degrees).


For sound isolation purposes the room will have r-13 and r-19 insulation in all wall and ceiling cavities and will be essentially air tight with acoustic caulk along all floor/ceiling/wall junctions as well as a completely air tight/sealed doorway.


According to my cooling load calculations, adults at rest produce ~500 BTU/hr and with a maximum occupancy of 9 seats, total body heat will approach (500btu *9=) 4500 BTU/hr. A video projector will also be located in the space which produces (655 watts * 3.41=) 2233 BTU/hr. Total cooling load of (2233btu+4500btu=) 6733 BTU/hr


Converted to CFM (400cfm=12,000btu/hr) my total cooling load requires 224cfm of cool air


All other equipment and heat sources will be located outside the space and managed/ventilated separately.


My question is about the type and number of minisplit units (low noise) that would be needed to ventilate the space which is 800sf in total area and ceiling height of 9ft, but has some irregularities in shape (open concept) that may prevent cool air from being dispersed evenly (pictured below with wall partitions in red)


My initial thought is to have a celling mounted MLZ model 9k btu Mitsubishi mini split cassette in the front of the main room (pictured in blue), but my concern is: will this circulate enough air to ventilate the adjacent spaces?


Should I size up to the 12k btu unit given the 8000 cubic feet of space to fill, or consider another 9k unit in the game room?

 

[WorthFlorida]

I'm not an expert by any means in load calculations but with a room that tight you will need a fresh air exchange. Closing it off can also allow the humidity to increase to very high levels. The smallest mini split may all that would be needed for long run times to dehumidify the area. Before closing things up, get a humidity meter to start tracking the levels. You really do not want to be above 60%. Others on this forum will probably give the load needs.

 

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[Bartl007]

Thanks so much for the feedback.


That's a great point and it is definitely more humid in the space as it stands unfinished and I would guess 60-70% humidity levels as measured with my tip-of-finger hygrometer.


The mechanical ventilation plans I've been pondering are as follows:


Option1: install a DUCTED mini split with a fresh air intake


Option 2: install a ductLESS MLZ series mini split as depicted in the ceiling joist. Then install a fresh air intake box with a small section of ductwork and an inline fan (picture below) that would draw air in from the adjacent unfinished space to the left, then have a matching exhaust box on the opposite side of the room that would take conditioned air out of the room and into the mechanical room.

The only problem with option 2, is that the "fresh" air coming into the room would be humid/unconditioned and I worry about the ability of the mini split to adequately dehumidify without overcooling.

Any thoughts?

 

[WorthFlorida]

Try it first, no harm. If the humidity remains high for the room, add a dehumidifier in the unconditioned space or another mini split cassette in the unconditioned space.

 

[Bartl007]

Thanks again, I've considered swapping the water heater (needs to be replaced soon anyway) for a hybrid heat pump model that would help dehumidify that space somewhat. I'm not sure if that would be enough dehumidification but may be worth a try.

Back to my original question, after running numbers through the cool calc manual J site, its only suggesting 6700btu load needed for cooling the space which pretty well matches the lowest fan speed (212cfm) of the 9k Mitsubishi mlz-kp09na. Would this unit be enough to spread cool air out into the adjacent open concept rooms (game room and entry space) connected by large (5-9' wide) cased openings?

 

[Fitter30]

One of my concerns is the concentration of condition air just in the main room and the low cfm. Any added dehumidifier will add heat. They make mini air handers and could 4" duct to each area with a 1 ton unit..

 

[Bartl007]

Thanks for the input. That is my concern as well. The other aspect is that any ducted system needs to be QUIET, as in, duct and grill velocity of less that 250 feet per minute. That essentially means oversized (8 or 10 inch+) ducts and linear bar type diffusors for both supply and return (in a DUCTED system).