small studio HVAC- fresh air questions.

Hi, Here is a question for Rod (great book) or other HVAC brains. I have a small garage studio that needs cooling/fresh air. Approx. 380 sq. ft. with a low 7.5 ft ceiling. I also have a 90 sq. ft. booth that is used very occasionally for overdubs. It has registers and 8” ducts already installed for supply and return. The studio already has 2 - 12”x16” ceiling “holes” (formerly, NS10 speaker soffits) to use for registers. They are not optimally placed, but may suffice. My plan is to install a Mitsubishi 1.5 or -2 ton mini split in the studio for the hottest days… Also I need to get some cooling into the booth. ….but…….. 2/3 of the year the outside air is cool enough and electricity is expensive enough that I want to avoid using the A/C if possible. Usually 10-15 degrees “F” cooler. Fresh air is important too. Attached is a crude sketch of the room. There is a beam in the attic that precludes installing any ducts to the right of the center of the room such as where the piano is. I work alone 90% of the time at moderate levels and my gear has a bit of heat load. The room is double wall construction and well insulated. I have a water heater closet that is an air lock between the studio and outside. It already has 2 vents to allow fresh air for water heater gas combustion. Also, a 14” attic space above the studio. I want to cut another vent in the closet wall to the outside to pull fresh, cool air into my studio. I already have those 2 - 12”x16” ceiling “holes” to use for registers. My idea is to install flex duct and an inline fan to push fresh air into one hole, and create a loop by connecting the other hole to vent into my 90 sq. ft. booth and use the return from the booth to vent back to the outside (maybe with another switched inline fan to pull air from the booth). I’m thinking of using the Panasonic Whisperline 200cfm or 400cfm fans with 8” flex, and building baffle boxes for the ceiling holes. Routing: Fresh Vent - inline fan (optional*) - Studio ceiling supply…. then: Studio ceiling return - booth supply; booth return – inline fan - outside vent. *When it is hot, I will just need to decide if I need to dampen the fresh intake and turn off the 1st inline fan. That will still let the 2nd inline fan pull warm air from the booth and draw cooled air from the Studio into the Booth. Another idea is to install a small central air handler unit in the upper part of the water heater closet to cool both rooms with ducts and just use the fan part of it most of the time to circulate air and save energy. It seems like that would require using more energy to run the larger fan and then I still need to get fresh air into the space. If I just circulate the studio air, it wont be as cool as outside air. SO, my main concern is not to be depending on running the A/C all the time. My sound leakage is not a big problem, in fact, I currently keep the side closet door open and have a pedestal fan forcing in fresh air, but that is pretty loud, and I work at night a lot, so I will need to keep the door closed.....even though it is much cooler at night. That is the air I want in the studio, quietly and efficiently. My budget is $5-6K. What do you think of my ideas? How is my airflow/comfort level considering the duct size and fan cfm? Should I cut a fresh air supply register just above and behind my head to push air in at low velocity? Can anyone provide an easy baffle design for 8” duct? Roughly: 48”x16”x12”. For the baffle, I’m concerned about fiberglass particles and the formaldehyde they use to hold it together. I see most people use 703 rigid board. Is there a safer board to use in the baffles. I used a lot of Ultra-touch Recycled Cotton bats for absorbsion in the rooms. Maybe I should use the cotton and cover it with cloth? Thanks for any replies, NGK

pic of ceiling, looking into sound lock and booth:

anyone??

i think a proper air handler will last longer in terms of continuously running even if the cooling function isn't - basically setting the fan on - and using proper ducting to both rooms.

thanks for your reply, My previous studio had a very quiet central system and worked well when it was on cooling.........but here, the air handler would be circulating warm studio air. not very cool unless I used the compressor. Also, I believe the fan draws a lot more amps than the inline fans. NGK

depends, either way, a recirculation system will be moving studio + fresh air... you'll need some cooling either way. my preference if you have the space and budget is for a air handler w/ cooling system. if you look around there are also a lot of high efficiency units out there nowadays so the fan consumption shouldn't be too big a deal compared to have solid air flow in your space.

bumping...... fresh/cool air is free, and in the interest of conservation, I need the lowest (amps) drawing fan system to bring this 100% fresh air right behind me in the mix position. Still looking for help with amount of airflow, etc. Any other comments? thanks, ngk :)

maybe look into an aerotec unit to exchange the air with the outside. its designed for good air exchange rates and preserving isolation. for lining a plenum - consider 1" duct liner - John Manville or equiv. instead of 703 or other fiberglass. this should provide the quieting you're looking for and not potentially release particles that will irritate you. the cotton batts might be workable but i'd be concerned about dampness. also - back on the air handler topic - there are a number of devices out there that perform energy efficient air exchange on a proper hvac system. you might check with a local hvac company to see what options they have. this may be more effective also from the standpoint of sensible and latent loads.