ventilation specifics for small studio

Hi folks I have read many posts about HVAC on the forum but I'm going around in circles... My very small studio internal space (length 2.8 meters x width 1.7 meters x height 2.2 meters) totals approx 10.5 cubic meters I am aiming at installing a daikin uhuru Sahara which deals with heating, cooling and humidity but crucially for me delivers fresh air at a rate of 24 cubic meters per hour. Based on that claim the fresh air in my studio should be replenished approx every 30 mins is this enough air for 1 person in this space?......Man that sounds pretty lonely actually. On top of this I can't work out what size apperture I need to allow for the air exhaust hole I need to make through the studio walls? Due to the daikin pumping in air at the rate of 24 cubic meters per hour do I need a fan on the exhaust vent? If I do need an exhaust fan what size fan would be suitable for my room based on the specified air intake. Im getting there slowly....Thanks as always

OK, this gets to be a bit complex, but basically it starts with how many room changes per hour you need. According to modern guidelines from organizations such as ASHRAE, the absolute minimum is about 4 room changes per hour, but for a studio it's probably more like 8 to 10 room changes per hour. The actual rate is based on complicated formula that involves the floor area, the number of people per square meter, the type of activity they are engaged in, the efficiency of the ventilation system, position of the stars with respect to the phase of the moon, and what you ate for breakfast 17 years ago on Saturday! :) But here's a table that lays out typical requirements for several types of room. http://www.engineeringtoolbox.com/air-c ... d_867.html Or if you want to get a little more technical: http://en.wikipedia.org/wiki/Air_changes_per_hour http://www.cibse.org/pdfs/ASHRAE%20resi ... 20vent.pdf So, for your aprox. 11 cubic meter room, you would need a minimum of 44 cubic meters per hour, and probably more like 80 to 100 cubic meters per hour. That's one reason why I don't recommend the Uhuru for studios. It's fine for a bedroom, where there is plenty of additional air flow into the room from other sources, but not for a studio that is sealed hermetically. It's a good concept, but not enough to meet even the basic criteria for any decent sized room in a typical studio. In your case, it would provide about 25% of the total air you need. So you can use that system if you want, but you'll need additional ducts to get enough fresh air in, and also out. OK, so that leads to the next question: How big do your ducts have to be? Well, that brings in yet another question: How fast can the air flow? If you could have air flowing at any speed you wanted, then you could use a garden hose to bring in that air. The only trouble is, it would be hissing like a large nest of really angry snakes! SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS!!!! I'm more used to doing this in Imperial measurements (! about the only thing I do do in imperial! Everything else I do in metric. Not sure why I started with imperial for HVAC, but anyway...) So lets convert: 100 cubic meters per hour is about 60 cubic feet per minute, or one cubic foot per second. If you force one cubic foot per second of air through a typical garden hose, where the cross sectional area is maybe 0.3 square inches, that air is coming out a speed of 480 inches per second, 40 feet per second, or 2400 feet per minute! That's roughly 44 km/hr, so that might be just a bit too fast for your studio ! :shock: Drive your car down the road at 44 km/h, and open the window: that's how fast the air would be whoosing out, and that's the noise it would be making. EEEEK! No use for a studio... So clearly you need a duct that's a bit bigger than a garden hose. You figure it out like this: You want the air coming out the vent to be moving no faster than 300 feet per minute (fpm), and preferably 100 fpm. Any faster than that, and the air itself is making an audible noise as it passes through the grill. So how big does the duct have to be to move 60 CFM (cubic feet per minute) of air at 120 feet per minute, for example (I chose that number to make the math easier.... :)? So, simple math... we have to get 60 Cubic Feet of air through the room in one minute... So imagine that amount of air as being a box that is one foot high by one foot wide by 60 feet long (which means the box has a cross sectional area of one square foot), and we have to get that box through the room in one minute. So we'd have to move that box at sixty feet per minute to get it through the room in one minute, since it is 60 feet long. Simple, right? And since we know we can go as fast as 120 feet per minute, then we can actually make the box thinner and longer: we can shrink it down to just six inches high by one foot wide, and make it 120 feet long. There's till the same volume of air that we need to move inside the box (since it is half as high but twice as long 120 feet x 1 foot x 0.5 feet = 60 cubic feet), but now we have to move it twice as fast to get it through the room in one minute. So there you have your answer: to get 60 cubic feet of air per minute through the room at a speed of 120 feet per minute, your duct needs to have an internal cross section of 6 inches high by 12 inches wide, which is roughly 15cm high by 30cm wide. Simple! :) In fact, you could halve the cross section again, doubling the speed again, and you'd still be ok. If you make the duct 15cm x 15cm, then you'd be moving the air at 240 fpm, which is still plenty slow enough for a studio. However! Your ducts MUST be lined on the inside with duct liner, so you need to allow for the thickness of that on each wall. Duct liner is usually 1" thick, or 2.5 cm (aprox.), so you need to add 5cm to each dimension: your 15cm by 15cm duct actually need to measure 20cm by 20cm on the inside, so that once the duct liner is in place, the remaining free cross section is still 15 x 15. The above assumes you are using rectangular sheet metal ducts. If you prefer to go with round sheet metal duct, then do the math for that: 6" duct has a cross sectional area of about 28 square inches, but you need 6" x 6" = 36 square inches, so you'd have to use at least 8 inch round duct, which has an area of about 50 square inches. More than enough. However, if you use flexduct, that would be a problem: flex duct only provides the nominal rated performance when fully stretched, dead straight, and no kinks. In real life, that never happens: it is usually relaxed, bends around corners, and kinks over and around studs, so the actual capacity might be only 50% of the rated capacity. So you'd probably need to go up to 10" duct if you use flex duct and want to keep the system very quiet. That said, for your application, you'd be just fine with 8" flex duct, if you install it carefully. Or you could even use 6" duct for the long runs, then widen it out for a few feet just before it gets to the registers, so the air can slow down before it hits the grill. There's a lot more to it that just that simple explanation, but that should get you on the right track. Oh, and don't forget your silencer boxes! The cross-sectional area must be about twice that of the duct, in order to create a worthwhile impedance mismatch. Hope that helps, and that it didn't confuse you too much! - Stuart -

Thanks Stuart you just saved me a lot of money and heartache! I'm not going to go With the daikin uhuru as its clearly does not bring in enough fresh air for the studio on its own. Im going to look into my other choice a quality portable a/c the olimpia issimo. Its quiet compared to most portable a/c and about 60% cheaper than the uhuru. http://static.uk.olimpiasplendid.com/up ... odotto.pdf Your info is exactly what I'll need at the moment. I can now start to put together a detailed plan for a/c, ventilation fan, ducting and silencers. Can't thank you enough fella Tim

Its quiet compared to most...

Hey Tim, at over 60 dB(A) I'd hardly call that "quiet"!!! :shock: It would have to be about one thousand times quieter than that to be usable in a studio: 30 db(A) would still not be silent, would would be usable. I would suggest that you still go for a mini-split system, which can be even quieter than that. Some of them are rated at 25 dB(A) for the internal unit, which is about where it needs to be. Under 30, certainly.

Your info is exactly what I'll need at the moment. ... Can't thank you enough fella

That's what we're here for! :) But do take care to research this in more detail before you start buying stuff and cutting wood/metal. There's a lot more too it than just CFM and fpm. For instance, you need to start looking at static pressure, and fan ratings, and dampers, and air filters, and all that fun stuff. The entire ventilation system obviously offers some resistance to the passage of air, and this is measured as "static pressure". The fan(s) you need for moving the air through the ventilation system are rated to provide X amount of CFM at Y amount of static pressure, so you do need to be careful with that! Unscrupulous manufacturers only publish a single CFM rating, but don't tell you what static pressure that is for. That means that they just measured it with NO load on it at all! That's how much air the fan can move in a free space, a totally open environment, with no ducts on it. As soon as you put it in a duct, the actual volume that it can move drops considerably, and "how much" it drops depends on the static pressure of the duct system. So you need to figure that out for your room, and take it into account when sizing your fan. For example, look at this series of fans : http://fantech.net/download/450483-rvf-brochure I recently specified the RVF6 for a studio in LA. Look at the table on the last page: the fan itself is rated at 242 CFM, which is great, but that's for no static pressure. If your system presents 1" of static pressure, then that fan can only move 68 CFM, and if your system has higher static pressure then that fan is no use at all: beyond the rating. You'd have to move up to the next model to handle that. Fortunately, in this studio the static pressure was only about 0.3" inches, and we only needed 150 CFM, so this fan worked fine. In fact, we put a speed controller on it, since it would have moved too much air too fast when running full speed into 0.3" static pressure load. So the studio owner can now adjust the speed to get the correct flow: if there are more people in the room, he can turn it up a bit for more fresh air, or if it is just him in there, then he can turn it down. We could have put an automatic controller on it with a CO2 sensor to adjust the speed all by itself depending on how many people are in the room (more people exhale more CO2...), but the extra cost did not justify that, for him. Note that we could also have used the RVF4XL model, as it can move enough air with the 0.3" load, but that's for a 4" duct and we needed 6" ducts for this studio, to keep the air moving slow enough, and quietly enough... Not trying to confuse you or scare you! Just pointing out that there are more things to take into account with HVAC. I think I already mentioned that it seems to be the most forgotten, ignored and neglected part of home studio design, but it is one of the most important! After all, if the room sounds fantastic and looks superb but you can't work in it for more than a couple of hours without passing out from lack of oxygen, then it ain't much of a studio! :) (OK, so passing out and dying are unlikely, but having everyone develop head-aches and nausea from the hot, stuffy, unpleasant air isn't a whole lot better!) - Stuart -

Hi Stuart thanks the extra Info really is helpful

But do take care to research this in more detail before you start buying stuff and cutting wood/metal

aye will do, I'll put up a drawing for approval before I do anything else. All the best Tim