Congrats on building your place! It sounds like you have done quite a bit already. Like you say, there are things you could have done different, but that's water under the bridge now...
The vast majority of mini-split systems do not include ventilation. A very few of them do have a small fresh air intake pipe, but even then it isn't sufficient for studio needs. Most mini-split systems simply recirculate air inside the room, and either heat it, cool it, dehumidify it, or do nothing to it except move it.The part that I am confused on is 2 different "professionals" have told me that the mini-split should be sufficient to bring in new air from the outside and remove old air.
Those are the typical non-ducted units that you see on the walls of rooms.
But I'm wondering if the professionals that you spoke to were talking about DUCTED mini-split systems, that are meant to be part of a complete system. Non-ducted ones just hang on a wall, suck in room air at the top, then blow it back out the front. Ducted systems (also called "AHU" for Air Handler Unit) are not mounted inside the room at all: they are external to the room, and mounted inside a duct. OR rather, there's one duct leading into the unit, which is the "return" duct coming back from the room(s), and one duct leaving the unit, which is the "supply" duct that takes the conditioned air to the room(s). The "return" duct usually has another duct branching off from it, to dump stale air overboard, and an additional duct feeding into it, which is fresh air from outside. In that case, the "mini-split" really is supplying fresh air to the room, and removing stale air, but not by itself! There's the entire ducting system associate with it, and there is usually also some type of fan that is either forcing the fresh air into the return duct, right before it goes into the AHU, or sucking stale air out of that duct, further upstream.
So ask those guys if they were talking about ducted mini-splits, or not.
Here's what the two different types look like: The one on the left is the typical non-ducted "wall" unit type of mini-split condenser, and the one on the right is the ducted "AHU" type of mini-split condenser.
Here's a typical AHU mounted in the ceiling space, above a room, showing the ducts: As you can see, there are small plenums on either side of the actual AHU. The ducts connect to the plenums.
That sounds about right, but do take into account that you need more capacity in a studio than you do in a typical house, for several reasons: 1) occupancy: you will have more people in your room than you would in the same sized room in a normal house, 2) biology: they people that are there will be "working" in the sense that they are not just sitting still, doing nothing - they are playing instruments, jamming! 3) gear: the musicians will be using instruments that produce heat: amplifiers, computers, foot-pedals, effects boxes, etc. So the sensible heat load is higher than normal, and the latent heat load is higher than normal. While 9000 BTU might be fine for a typical room of that size in your house, you probably need more in your case, because it is a studio. There's also the issue of how much fresh air you will be bringing in: that has to be treated by the system before getting into the room. If the incoming air is very humid, or very hot, then you need a larger capacity in BTU to deal with that.So far the most concrete recommendation I have received is for a 9000 btu Fujistsu mini-split system.
There's a lot more to HVAC than meets the eye at first glance.
Right. Although the ducts are not really there to move humidity in and out: They sort of do that, yes, but only because the air that they are designed to move has humidity in it. The AHU itself deals with the humidity: it removes the humidity form the air by condensing it out as liquid water, which needs to be drained away somewhere. That's referred to as the "latent heat load" of the air. The interesting thing is that the AHU CANNOT cool the air until it has first removed enough humidity! So if your AHU is too small, it will use all of its BTU capacity just in removing humidity, and there will be none left over for cooling: so the room will never cool down, even though the humidity will be fine. This is why you need to make sure that you account for the latent heat load in your calculations. That latent heat loads comes from several places: 1) moist air coming in from the outside world through the fresh air intake duct, 2) every breath that each musician exhales has 100% humidity. The harder they breathe, the more humidity the put into the air, 3) Sweat: if they are jamming hard, they are sweating. That sweat evaporates from their skin into the air, which increases the humidity, 4) beverages: every cup of coffee, glass of soda, beer, water, or whatever, is also evaporating, putting more humidity unto the air. 5) food. Things like pizza, hamburgers, even salads, have wet surfaces, from which water evaporates. Etc. So if you and a half dozen buddies are jamming away intensely in there, breathing hard and sweating, while eating pizza and drinking beer, on a hot humid day, there's a very high latent heat load in the air inside your room, and the AHU has to remove that BEFORE it can start cooling the air.This doesn't seem to jive with everything I have read here regarding the need for additional ventilation and ducts to move air/humidity into and out of the structure.
Therefore, it is very important to do the math, and figure out your latent heat load, as well as your sensible heat load. The sensible heat load is things like computers, lights, amps and other gear that the musicians might be using. Aything that uses electricity will be putting out plain old heat, which is referred to as the "sensible heat load" in HVAC jargon.
So: you need to figure your total heat load, which is the sum of latent and sensible, for the very worst case: hot humid day, room full of hot sweat musicians playing hard, eating and drinking, with stacks of powerful gear running full-bore. You dimension your mini-split to be able to handle that load when it is running on its highest setting. It can then run on lower settings under less extreme circumstances.
Find out if they have extensive experience in designing HVAC for recording studios, or if they are just typical, ordinary HVAC guys that deal with houses and offices. Studios are VERY different from houses and offices. If they have little or no experience in doing HVAC for recording studios, then you are probably talking to the wrong people.I know extremely little about the subject, so am torn on trusting these experts.
Designing HVAC for a studio is a big deal: When I design studios for my customers, I often spend as much time on getting the HVAC right, as I do on the entire rest of the studio! I'm not sure if you have seen the corner control room thread ( http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368 ), but that's a typical example. There's not much in that thread about the HVAC, as the thread is all related to the final acoustics treatment of his control room, but you can see some of the HVAC in a few of the photos. But basically when I designed the corner control room studio, I spent a LOT of time on getting the HVAC right (pages of calculations!), and the owner spent a LOT of time building and installing the various parts of that system.
The reason you can't see much of it in the photos in his thread, is precisely because I took a lot of care to hide it! The registers are flush with the visible ceiling surface, and most of the ducting is inside the ceiling cavity, above the inner-leaf ceiling of the actual rooms, but below the middle-leaf isolation ceiling.
In the corner control room case, there is an AHU (ducted mini-split) that is completely outside of the isolated area of the studio, in the ceiling space above the bathroom. It connects to the studio through a pair of silencer boxes above the hallway, outside the bathroom. And from there it is distributed to the individual rooms, also through a pair of silencers for each room. Here's an overview of the HVAC system design in the corner control room studio: Thu AHU is marked, in the lower left corner of the image. Represented as a simple metallic box. The fresh air intake is through the front wall of the building, just to the right of the AHU: it looks like a rectangle on the exterior wall. The stale air exhaust is up through the vertical duct above the bathroom, out through the roof. In that image, the ducts are color coded: all the metallic silvery color ducting is "supply" air, going into the rooms, and all the ducting colored light brownish-pink color, is "return" ducting, taking air out of the rooms and back to the AHU, or exhaust.
OK, that's more complex than what you need in your case, because that's a professional purpose-built studio with control room, live room, bathroom and lobby, but it gives you an idea of what is involved.
Hope that helps get you on the right track!
- Stuart -