Portable A/C unit for studio? HVAC question...

I just got a quote for $3800 to have a mini-split installed with separate fans for the room to circulate fresh air in...no thanks! Gonna have to try something different. I'm thinking about getting one of these or someting similar to handle my fresh air AND cooling needs: http://www.sylvane.com/delonghi-pac-t100p-ac.html It has an intake and exhaust port...I want to run the exhaust up the wall and to the garage attic. And take air in from the crawl space. So 15-20 feet more duct with silencers... Checking these out: http://www.hvacquick.com/scfnconfig.php ... hqupoo5jp6 Is this idea even worth pursuing? Any suggestions? Room will be 9 x 19 x 9. Let's round up and say 1600 cubic feet. I'll just turn the dang thing off while recording....

Study this thread thoroughly. I had at one time considered the use of a unit such as that, but I decided to do a mini split instead. I just got my mini split operating three days ago and it's niiiiiiiiiiiiice! :twisted: You can order a mini split system online, have it shipped to your place, and then do the lion's share of the installation work on the mini split installation yourself (as I did) and hire a pro to do the final hookup. You'll save hundreds, perhaps thousands of dollars. Note that you still need a fresh air mechanical system to comply with code, unless you have operable windows. Neither mini splits nor portable air conditioners are rated for this. --Keith :mrgreen:

I knew it was too good to be true...

Keith, Can you outline the steps it took to install your mini-split? I'm completely intimidated, but if you made it sound easier to do, I'd give it a shot...

Well, I'll be honest -- as a novice, I made some mistakes along the way. They weren't horrible, but if I were to do it again, I'd make fewer of them. ;-) First thing's first: spec the right system. Make sure it's properly sized. Rod's book covers this in good detail. In my case it was pretty easy because my room's really small and I got the smallest system available (3/4-ton, i.e., 9,000 BTU). Ordinarily you don't want to oversize a system because that's just as bad as undersizing a system. However, in studio contexts, it's generally better to size larger than typical because of the heat-generating gear, number of bodies, physical activity (we drummers sweat! ;-)), etc. Take the time to study HVAC and learn the basics. Once you find the system you want (let's suppose it's Sanyo, just since that's what I became most familiar with, although there are other worthy brands I'm sure), go to that manufacturer's Web site, locate the installation instructions document, download it, and study it carefully. Recognize that there are things you'll be comfortable doing and things you won't/can't. Determine what you can/will do yourself and plan to have a pro do the other things, like charging the system and firing it up for the first time. As far as the actual installation steps that I followed, as convoluted as it gets, I'd recommend studying the last several pages of my thread in which I detail what I did, including the mistakes. Hopefully you'll learn from them and not repeat them. I'll close by saying that I was really intimidated at first too... But I remember the Saturday I spent studying the installation instructions for the mini split system that I bought, how I was totally "geeked out" reading and re-reading the steps in the manual and carefully studying the illustrations, and how my confidence level kept increasing the more that I read. Prior to starting my build, I had no framing experience, no jackhammering experience, no demolition hammer experience, no plywood ripping experience, no framing experience, no drywall experience, some electrical experience, and certainly no HVAC experience... Yet countless hours of studying threads here and a plethora of other resources on the Internet, the more inspired and confident I became. I'm sure if I had some of these experiences going into the project, I'd have been done over a year ago! :lol: Such is the pace of an inexperienced-yet-meticulous person that I am. DIY studio building is not for everyone... And there are certainly many phases of the project where one meets intimidation, as I can surely attest. Hell -- just getting my entire body into my attic given my ten foot ceilings and fear of heights was an event to celebrate! :lol: But if you're committed to the end result and willing to go carefully beyond your comfort zone to save a lot of money and develop some skills that will come in handy later in life, then I'm convinced you can do it, and you'll have lots of cheerleaders here to root you on. :) --Keith :mrgreen:

sharward wrote:

Ordinarily you don't want to oversize a system because that's just as bad as undersizing a system. However, in studio contexts, it's generally better to size larger than typical because of the heat-generating gear, number of bodies, physical activity (we drummers sweat! ;-)), etc.

Buddy, you blew that one - actually it's just the opposite - slightly undersized - never oversized. you must have either missed this in chapter 7 - or for some reason it just didn't click:

UNDERSTANDING THE SYSTEM AS A WHOLE How does this actually work? This is where things get “sticky.” When it comes to HVAC design (as mentioned earlier), you have sensible cooling loads and latent cooling loads. Sensible cooling relates directly to the ability of the unit to cool the air, while latent cooling relates to the ability of the unit to dehumidify the air. Gear and lighting loads do not add humidity to the air in a space, but people do, as can fresh outside air. It’s important for you to understand the sensible versus latent loads in your rooms and to purchase equipment that meets those needs, which is no small challenge. It might surprise you to know this, but the vast majority of mechanical contractors get this wrong—even on something as “simple” as a home. They tend to use calculation methods that are questionable at best, and then add “fudge factors” to cover themselves. If their calculations come to 3 1/2 tons of cooling for your home, they’ll tell you to get 4, explaining to you that this will make sure that on even the hottest days of summer you’ll always have plenty of cooling. Although this is partly true, it’s also very wrong. It’s partly true because you will never have to worry about having enough cooling. It’s very wrong because it isn’t the right kind of cooling. What happens is that the unit is so oversized that it super-cools your home, utilizing very short run-times, which means that you don’t get enough air moved across the coils to properly dehumidify your home. This also could cause additional wear and tear on your compressor motor and higher electrical bills for you. Air conditioners are generally ineffi cient in the fi rst stages of operation, while their effi ciency increases the longer they run. If the on-time of an air conditioner is only fi ve minutes, the effi ciency (EER) is somewhere around 6.2. On the other hand, with a properly sized air conditioner, the same amount of cooling would take place in a little less than 10 minutes, and the efficiency would rise to 6.9. This additional run-time would save the customer about 10% of their energy costs. The ability of an air conditioner to remove moisture (i.e., its latent capacity) is lowest at the beginning of an air conditioner cycle. In order to remove moisture from the air, the coil has to cool to the point of creating dew point, and then it has to have time to cycle the room through complete air changes. As the warm moist air passes over the coils, the moisture wets the coil and (when the unit runs long enough) fl ows off the coil into the drip pan. It is then removed, either through the use of gravity drains or with condensate pumps. When the compressor short cycles, the moisture on the coil does not complete condensing, and, when the unit stops, the moisture on the coil evaporates back into the indoor air.

What part of that suggests that oversizing is acceptable? It is possible to design systems with multiple speed fans (which is what I generally do) so that you have reserve when yu need itin the future - but in the low speed you should be there or else you will have humidity problems - (unless you're in Nevada).

Thanks Keith, you're truly an inspiration to us all and I will do my best to follow your example. Thanks for the encouragement! Thanks for chiming in Rod. I've bought your book twice now. I'm waiting for the second copy to arrive- lol

studio_drums wrote:

Thanks for chiming in Rod. I've bought your book twice now. I'm waiting for the second copy to arrive- lol

SD, WOW- even I wouldn't buy my book twice......... what's the story behind wht happened to the first copy? Rod

Thanks for setting me straight, Rod! :oops:

Rod, Lost it during the move I guess...it might turn up, but I can't wait for that. I've got a studio to build! I was really interested in your opinion on the portable A/C units, I thought that I could extend the hoses and use supplemental fans to make up for any loss in airflow due to the increase in static pressure. My idea is to use air from an adjacent family room to supply fresh air, and to exhaust up into the garage attic. I was going to do this for the mini-split as well. I could take in fresh air from the outside, but the air will be harder to cool and dehumidify. By the way, if you're ever in my area, I'd gladly pay for your time for a consult... :) Just off I-95 at the DE- MD border

studio_drums wrote:

. . . I thought that I could extend the hoses and use supplemental fans to make up for any loss in airflow due to the increase in static pressure.

From page 20 of my project thread:

sharward wrote:

I just spoke with a kind and helpful customer service representative at Soleus International, Inc. We talked about my situation (she even looked at the last couple of pages of this thread to see my illustrations). Here's what I learned:

They're serious when they say you can't extend the hoses. They're serious when they say you have to keep the lines as straight as possible. "Arcing" the lines is OK but "bending," especially at 90 degrees, is very bad for the system. She said the air bounces off the wall of the 90 degree turn and comes back towards the unit (in the case of exhaust). Extending the lines and using booster fans at the end to push air in (intake) and pull air out (exhaust) may work, but they can't guarantee it (obviously). She knows of a case where someone used a booster fan on a unit with an exhaust line and it seemed to work fine. However, she recalls that unit was not the same as the MAC-10K which has two hoses (one intake, one exhaust). There is an intake vent behind the unit, near where the hoses connect, which means enclosing the unit in a niche without a generous clearance around it will not work. :cry:

She suggested I place the unit along the long wall closest to the outside to accommodate an "as short as possible" run. I'm concerned about what that would do to my isolation though. :? The rep was very helpful in trying to advise me to do such things as making sure I know what the return policies are of whatever retailer I purchase from, so that I could return it if it doesn't work out. I had to explain that if it doesn't work out, my entire project doesn't work out, so the prospect of a restocking fee is the least of my concerns. :cry: :cry: :cry: :cry: :cry: This is not fun. :cry: :cry: :cry: :cry: :cry:

studio_drums wrote:

My idea is to use air from an adjacent family room to supply fresh air, and to exhaust up into the garage attic.

I'm 99% sure exhausting directly into an attic is a no-go as far as code compliance is concerned. I know it's not kosher for exhaust fans in bathrooms, laundry rooms, etc.

studio_drums wrote:

I was going to do this for the mini-split as well. I could take in fresh air from the outside, but the air will be harder to cool and dehumidify.

What "this" are you talking about? Mini split systems are (typically) ductless... :roll: :?: --Keith :mrgreen:

I meant using the same ventilation plan for minisplit or portable A/C. The garage is vented to the outside, I thought that would make it okay... I just got off the phone with another HVAC guy... He was talking about slightly oversizing the unit. I asked: "Isn't it better to undersize slightly if anything since the unit needs to run for a while to remove the humidity from the air? I read about that somewhere..." He said confidently: "No." He generaly "puts in bigger coils" as well, he says, saying this is better for dehumidifying. I also asked about code requirements for air recirculation and he said they're mostly for commercial installs- not residential...it shouldn't be a problem. Of course, I believe Rod and NOT him...and I can't wait to get Rod's book again and REALLY pay attention to the HVAC part this time...

studio_drums wrote:

I also asked about code requirements for air recirculation and he said they're mostly for commercial installs- not residential...it shouldn't be a problem.

I disagree when there are no operable windows in a habitable residential room, whether it is a sleeping room or not. --Keith :mrgreen:

sharward wrote:

studio_drums wrote:

I also asked about code requirements for air recirculation and he said they're mostly for commercial installs- not residential...it shouldn't be a problem.

I disagree when there are no operable windows in a habitable residential room, whether it is a sleeping room or not. --Keith :mrgreen:

Keith is right on the money with this - even the residential codes have requirements for windows (or doors) directly connected to the outdoors for habitable spaces (for fresh air purposes) and require mechanically providing air if this cannot be accomplished - and that mchanically provided air must come from directly outside the building - not within the structure. He is also correct that exhausting air to the attic is a no-no. Rod

Well it's about friggin' time I got something right! :lol: :P :twisted: :D

studio_drums wrote:

He was talking about slightly oversizing the unit. I asked: "Isn't it better to undersize slightly if anything since the unit needs to run for a while to remove the humidity from the air? I read about that somewhere..." He said confidently: "No." He generaly "puts in bigger coils" as well, he says, saying this is better for dehumidifying.

Well he is wrong - not that a larger coil will handle dehumidification if a unit is oversized - but in general that this is a bad way to go. As I point out in the book - not only is short run cycles bad for helping to maintain humidity levels - but it is also an added expense from an operations point of view - you never run long enough to make the best cooling cost for the dollar......... Tell him that i said it would be nice if in addition to the larger coil - if he would pay all of the extra money in energy costs this this will run you in the life of the equipment. Well he doesn't see things the way that I do (or that ASHRAE - the American Society of Heating, Refrigerating and Air-Conditioning Engineers - do) but what the heck - you can't have it all I guess. Rod

This guy is specing a 12,000 BTU Fujitsu 13.5 SEER 9Wx 18.5L X 8.5H room. 95 % of the time I'll be by myself. Is he close?

studio_drums wrote:

This guy is specing a 12,000 BTU Fujitsu 13.5 SEER 9Wx 18.5L X 8.5H room. 95 % of the time I'll be by myself. Is he close?

I have no idea - how exaclty is your room constructed - all details (floors/walls/celings/ doors and door gasketing - any windows? - and a complete list of all of your gear along with wattage use for each piece. I designed an hvac system for a studio in NC where the control room had a 3 ton unit - so a ton doesn't sound like a lot to me for that - but again it is dependant on exactly what you have (or will have tommororw if you knw something for sure). Rod

Mine's a 16 SEER. 8) 13 is the minimum.

Rod, I got my 2nd copy on Friday- LOL I'll probably have a PC with monitor and a couple of racks of outboard mic preamps: API 3124 (can't find wattage on API's site), maybe a small summing mixer, a couple of small near field monitor speakers... I'm pretty sure I'm doing 4 layers of 5/8" drywall on a standard 2x4 wood stud frame- no windows- 1 door. I see you touched briefly on the topic of portable A/C's in your book...don't you think adding a couple inline fans to the longer ducts could work?

Hi All, I know I'm a little late in jumping in, so I hope that you'll forgive me. There have been some great points made here. However, I think there are a few things did not get covered quite well. It may make more problems for the discussion and may not, but I feel they need to be noted at least. I did a bit of A/C work in my past and my father has been in the A/C business for about 30 years. (just a background note) First, to my knowledge, :? there are no easily available ways to compute exact cooling needs. Most A/C contractors go by very general guidelines which have flaws. They also go by experience, some less reliable than others. So, most contractors tend to err on the fat side. I'm here in N. Central Texas, so our weather can range anywhere from near 0 degrees F to near 120 degrees with humidity all over the map. The last thing a contractor is going to do is undersize a unit unless he just wants to cut costs. Since most all new units will be more efficient than older ones, energy savings is hardly considered. The customer will likely be grateful for the lower electric bill in any case. What is considered is whether the customer is going to call you out on one of the extreme days and you have to explain to the customer that the unit is running fine and up to capacity, it's just simply too small. I have personally had to deal with working in a space that has high humidity due to an oversized unit. (it was installed in a building I purchased) For me, it was a matter of lowering the thermostat a few degrees (3-4) until the humidity problem was eliminated. A portable dehumidifier was also an option. Again, my personal choice (having lived where it gets hot and humid at the same time) is to have a unit slightly (note I said slightly) :) oversized to deal with high loads of high ambient (outdoors) heat or the occasion when "whoops, I never thought I'd ever have that many people in here or playing on tube gear." :oops: Or, later deciding that you need three or four more computers that put off a lot of heat, but now you can't cool the space because you installed just enough unit for the needs at the time. I think the key is to know the difference between slightly larger and ridiculously larger. Here in Texas, with an average home with average windows, insulation, etc., I'll take a 4-ton unit in a 3.5-ton house as opposed to a 3-ton unit any day. Most particularly a 110 degree day. Also, my experience with slowing the fan on an evaporator/air-handler too much can cause a unit to freeze (as in forming a block of ice encasing the evaporator). This happens because there isn't enough air flow over the coil to keep the coil temperature above freezing, so the condensation, rather than running off the coil, freezes onto the coil. When that happens it not only stops cooling (no airflow through ice), but it also is very bad for a compressor. As far as the portable with fans. My thinking is this. It might work and it might not. Since no one has seemed to have tried it, no one has a definitive answer. Are you willing to live with the prospect that it might not? Just my two cents. Hope I didn't speak out of line. :) Scott

I was inside my attic today and took note of the label on my coil box (or whatevr that thing is called). It says 49,000 BTU, which I believe is 4.083 ton. The house is 1973 square feet, single story, with 10 foot ceilings throughout. Temperatures here usually peak at around 115°F a few days per year, typically with low humidity. Too bad that thing is only 10 SEER. :-( --Keith :mrgreen: