entropy
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posted January 17, 2010 11:23 AM
 Edited By: entropy on 17 Jan 2010 19:26
AC system for garage
Rules in this neck of the woods are living space = space with AC; taxes are on living space.
So I will put an AC system in my new garage after closing.
I am heavily leaning towards the Mitsubishi Split System bc no duct work; simply a compressor outside and 1 air handler inside.
"Mitsubishi Electric helped pioneer the mini-split (or ductless) technology as a means of providing Japan's growing population with a highly efficient way to cool and heat their homes and businesses. They designed the Mr. Slim system to fit into spaces that could not otherwise have been effectively heated or cooled due to the close proximity of Japan's buildings, plus they needed a system that was extremely quiet. See more history below...
The term ductless means simply that no ductwork is involved. The system is comprised of two units: a slim-line outdoor condenser, and an indoor air handler. The condenser supplies coolant to the air handler through refrigerant lines that run through a small opening in the wall or ceiling and into the back of the unit. The air handler takes in supply air from the room through the front grill and dispenses the newly-cooled air back into the room. For certain models special filters are available that promote added humidity control and filtration"
The AC guy is very insistent that an 18000BTU unit will chill/heat the entire 600sq-ft insulated garage, but like my wife always laments, "bigger is better". Or is it?
Mitsubishi has systems up to 34,000BTU.
I can't do much about my wife's griping, but I could just say "bigger" to the AC man.
Any of you folk have experience with split systems???
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Texas12R
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posted January 17, 2010 12:47 PM
I'm not qualified to make a suggestion.
The question I would want to ask would concern
the time needed to bring the garage from 100
to a livable 80 with that humid air you have down there
or perhaps I misunderstood ....
Will the garage return air to the living space
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entropy
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posted January 17, 2010 12:58 PM
quote:
I'm not qualified to make a suggestion.
The question I would want to ask would concern
the time needed to bring the garage from 100
to a livable 80 with that humid air you have down there
or perhaps I misunderstood ....
Will the garage return air to the living space
nope, the garage is a stand-alone system
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whitehendrix
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posted January 17, 2010 04:34 PM
the big thing is how many air changes occur. 18kbtu will suffice in my "professional" opinion. i'm no HVAC guy, but i know a thing or two. part of my engineering degree was air exchanger "rules".
there may be a limit on where to mount it, being it's in a garage you may not be able to have it under 18" from the floor as this can be considerd a Class 1 Div. 2 location under the NEC guidelines.
bigger isn't necessarily better with HVAC systems.. you're still going to have a certain thermal gradient within the room, and have certain losses in area (windows, doors..) that, even with a 750,000but handler, those losses will not change.
ceiling fans go a VERY long way in comfort as they assist in the natural convection that'll occur inside your kingdom.
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TRNorBRN6001
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posted January 17, 2010 05:18 PM
Sorry, can't help you out much, but I am of like mind......Bigger always seems better. LOL
Can't wait to see the new MAN CAVE!
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Texas12R
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posted January 17, 2010 07:01 PM
http://www.mehvac.com/products/btuCalculator.asp
Karl this is a mitsubishi online calculator,
I came up with 21000 btu
you give it a try and see what your result is
could be a over rate factor built in...
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MadMike
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posted January 17, 2010 07:08 PM
does it take a battery? 
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CrotchRocket
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posted January 17, 2010 07:19 PM
Mister Bishi
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aliveagain
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posted January 17, 2010 07:47 PM
Just remember the characteristics of freon is they have a hard time over 95*.It's all about temperature/pressure differentials.I'm not sure, but I would size it for holding steady at your warmest and go just a little bit further in size.If it is too big,it will start cycling a lot and your compressor motor doesn't appreciate the high start up current.If it comes with a soft start that will help.
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entropy
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posted January 18, 2010 02:33 AM
Guys,
thanks for the input!
I think the compressor somehow turns down, doesn't cycle off-on-off-on; the AC guy said something like that.
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tcchin
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posted January 18, 2010 11:19 AM
I don't see an 18k BTU offering on the Mitsubishi website. I only see 16.2k and 22.2k. The chart below (room size in left column and BTU in the right) is from the GE site:
100–150 5,050–5,250
150–250 6,000–6,300
300–400 8,000–8,900
400–450 9,900–10,500
450–550 11,600–12,000
550–700 13,700–14,300
700–1,050 17,600–18,450
1,200–1,600 22,900–25,200
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Y2KZX12R
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posted January 18, 2010 11:37 AM
Karl, about 4 years ago I put a mini split system in my house. I researched the crap out of them and came to the conclusion that......
I didn't need it as a heat pump. That's an option you may want to think about thou as it may get cool out there from time to time. Its an option on all the mini split systems.
I needed about 30-34,000 btu's of total cooling based on the worksheets you can download.
I could and did install the whole thing myself.
And that the mitsubishis were way over priced. I bought a Fujitsu Halcyon on the recommendations of 3 people I know in the HVAC business. They are a middle of the road unit as far as price.
You will need to buy a line kit and do some simple wiring also.
You will need to pour a small pad for it to sit on.
The units all come precharged (for up to 100ft of line), so all you need to do is have someone with an evacuate come and evacuate the line for a few hours and then open the valves and throw the switch.
When mounting the indoor unit you want to mount it high so it draws in the hot air from up high.
You only need one inside unit because you are cooling/heating one room.
One thing to remember that you CAN over size an A/C unit and it wont work properly. If the unit cools the room too fast then it wont remove the humidity and its cold an clammy in the room. It must be sized properly so as it also removes the humidity.
Like I said Karl I did the install 100% my-self and it was so easy a cave man can do it.
Any questions give me a shout.
Shop around on the Internet once you know the size BTU unit you need, the prices vary on these units by about 75%. The Fujitsu unit came highly recommended by all 3 HVAC guys I know.
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posted January 18, 2010 11:39 AM
Oh and yes, all the new seer 13 and higher units use inverters and DC motors so they are variable speed and draw much much less power than the old ones that used to turn on and off and on and off....
Mines a seer 15 which was the highest at that time. There even higher now.
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rtbain
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posted January 18, 2010 03:36 PM
Stay as far away from heat pumps as you can. If you are all electric go with heat strips. The heat pump is basically an a/c run in reverse. If it gets too cold a heat pump uses heat strips for back up. You will never feel warm with a heat pump. You lose efficiency, gain complexity and ‘feel’ cold. Your compressor runs year round so it wears out faster. Go natural gas if possible.
Be very careful about comparing results. Someone from a dry climate may love a certain system. Our winters are cold and wet.
Don't go too big on the a/c size because it will have a hard time drawing the humidity down. x1.5 the recommended is the most I would use.
Since you are working in a dirty environment double the size of your return air and use high efficiency filters. It’s just like a race motor. No air in, no air out. If you increase return air size and use high efficiency filters you can dramatically reduce dirt and dust in the air.
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whitehendrix
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posted January 18, 2010 05:15 PM
interesting they're rectifying and running DC now.. running actual inverters on the compressors??
kinda odd, but unique. the refrigerant must be at a certain pressure to work correctly, dropping off compressor rpms will just keep it (refrigerant) in a gaseous state.
def a big +1 on heat pumps. they have come a long way, but not far enough imho. and they don't really offer any heat below a certain temp anyway, since the system reverses and is removing heat from the outside and treating the evaporator as the condenser and vice versa in heat pump mode.
no outside "heat" = no inside heat..
you need someone to come wire that bad boy, let me know!!!
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ill never own a busa unless
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entropy
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posted January 19, 2010 03:56 AM
A lot of great info, thanks guys!!!
Despite Jim's "even a cave man could do it", i will have it installed, already got the guy lined up. The install guy was talking about the seer operation.
But if it is seer, wouldn't a bigger BTU unit just run slower than a smaller one once the room got to temp?
Stay away from heat pump? Yep i can do that.
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Y2KZX12R
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posted January 19, 2010 04:22 AM
Edited By: Y2KZX12R on 19 Jan 2010 12:23
SEER = Seasonal Efficiency Energy Rating. The higher the number the higher the efficiency of the unit. So the annual operating cost is less.
I would get at least a SEER 15 or higher rated unit. I don't know if there even making SEER 13 or lower anymore now.
These units are more efficient that an A coil in a duct system and have zero heat loss threw the ducts because there's no duct work.
There are filters on the top of the unit that will filter the air.
WH, once the evaporator is cold and the room temp is where you want it to be the expansion valve is only letting a very small amount of liquid to be released into the evaporator so the demand on the compressor is very low. This allows the DC compressor motor to only run at a slow speed, just enough to keep the high side pressure at the desired pressure.
Its interesting because on an automotive system or an older A/C unit the high side and low side pressures are in constant flux. With these systems the computer and the variable compressor/condenser/evaporator motors are all keeping the pressures on the high and low sides steady at optimal pressures with very little change in pressures.
This also makes them VERY quiet.
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entropy
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posted January 19, 2010 05:37 AM
Jim,
so wouldn't a big SEER machine be able to run fine at low demand???
Then put out mojo cold air when needed??
always back to my desire to have a real big machine for quick cool down, and also be able to have lotsa air blowing directly on the work area when the door is open, say doing heat cycles.
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Y2KZX12R
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posted January 19, 2010 07:05 AM
Edited By: Y2KZX12R on 19 Jan 2010 15:05
quote:
Jim,
so wouldn't a big SEER machine be able to run fine at low demand???
Then put out mojo cold air when needed??
Yes once the room is cooled down it will run at a lower speed when its on auto. But you can always run it on high manually.
Like I said, if you cool the room too fast then it doesn't remove as much humidity and its cold and damp in there. You want the unit to have to run for a certain amount of time to remove the humidity. They even have a mode to dry the air.
So size it accordingly for the room size and type of room. Most sizing worksheets ask for window sizes, ceiling height, type of room, if there a stove, the R value of the walls and ceiling etc.
Its not a big deal if you go a little bigger like from a 25,000 btu to a 28,000 btu.
But if you need a 16,000 btu don't get a 33,000 btu etc.
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entropy
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posted January 19, 2010 01:14 PM
Jim,
Thanks for the info!!!
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tcchin
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posted January 19, 2010 03:37 PM
I say you get a 40k BTU chiller that runs at 100% duty cycle and use a boiler to regulate the actual air temp. That's how they do it in the building where I work. Of course, if the chiller or the boiler break, as they often do, then things get a little sketchy.
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whitehendrix
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posted January 19, 2010 06:39 PM
is there anything you don't know, Jim and Tim?
lol
makes good sense to switch to DC. even tho theres slight losses in rectification, they're probably null and void when compared to the inrush over a day's worth of starting up the compressor..
cool stuff.. literally..
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weapon. The black is for formal
occasions. - ZRXDean
ill never own a busa unless
someone gives me one.... and then
ill sell it -KZScott
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Y2KZX12R
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posted January 20, 2010 05:06 AM
quote:
is there anything you don't know, Jim and Tim?
lol
I just happened to buy and install one of these types of units a few years back so like I do with anything else, I studied the crap out of it to educate myself before jumping in head first.
Exactly what Karl is doing right now... 
I just did the same thing with the new TV we just got. Samsung 52" 240hz LCD.
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narider
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posted January 21, 2010 06:26 AM
2500 sq ft with 20 foot ceiling at shop with 5 ton external a/c unit and Propane gas (reznor style) heater.
Can cool or heat everything extremely fast, but I keep it very comfortable between 68 an 72 degrees 24/7 year round.
Not sure if any of it's an underkill or overkill, and my bills are big... but not as big as they would be for not working because we're cold or hot in there or for getting wrong measurements because my tooling or parts are not at the proper temp to measure.
Sounds like a neat system Karl, and great info from everyone. I'll be looking for something for the home garage next year (for now it's the torpedo and radiant heaters in the cold, and the squirell cage and wooden prop fan in the heat), so thanks for this thread.
Todd
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entropy
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posted January 21, 2010 08:26 AM
hey Todd,
I am learning every inch of the way!!!
Karl
BTW: We gonna see you and that greasy/sexy/fast-paced wife of yours at the Texas Mile in March?
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