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Mini Split compressor inside?

max_well

max_well

Member
Hey'all
I'm considering the purchase of a new mini split unit, probably 18k-24k BTU. I'm wondering about the possibility of placing compressor in an adjacent room, which is currently a laundry room. The motivation of this would be to avoid any problems running it during the cold months, as I live in a climate with cold snowy winters and I've read that such units are only rated to work down to certain temps (usually listed with a minimum operating temp of 0 degrees f)..
Also, it seems wasteful to be blow all the heat produced by the unit outside in months that the house is being heated. The laundry has a dryer vent (4") that I would attach a fan to, and is ~7'x8', in a basement.. does anyone have experience with this kind of setup? It seems like the concept is the same as building a box around the back of a window unit and using a fan to remove the generated heat; here the box is the room and I would just use blow the heat into the house in the winter, or a centrifugal fan to pull air from the room outside through the dryer vent in the warmer months.

Any thoughts? ps. those looking for mini split units-- there are several models that are eligible for the 30% federal tax credit on efficient appliances (up to 1500 credit, includes installation costs). Fujitsu and Mitsubishi, for instance, have some very efficient models of varying BTU that fit the guidelines.
 
D

Danks2005

Active member
I think that the room would get very hot very quick, and you would need to ventilate a very large volume of air, and efficiency would degrade to back pressure and poor heat dissipation. I am not an HVAC guy though, this is just a guess.
 
max_well

max_well

Member
Danks2005 said:
I think that the room would get very hot very quick, and you would need to ventilate a very large volume of air, and efficiency would degrade to back pressure and poor heat dissipation. I am not an HVAC guy though, this is just a guess.
Click to expand...

Thanks for you input-- that is the concern in general I think for running an a/c unit with conderser/ compressor confined in an inside space, but the situation seems analogous to those who run a a/c window unit with a box built around the heat exchange at the back-- as long as there is a fan removing enough of the heat then then compressor and condenser are fine. I would use a fan like http://www.northerntool.com/shop/tools/product_200312237_200312237
to move air from the laundry room-- this (8400 cfm) seems like much more air exchange than the centrifugal fans people employ in the a/c box building threads i've researched on icmag. The laundry room that I'm considering is about 500-600 cubic feet max, so a industrial fan like this could exchange the entire air volume in every ~10 seconds or less... seems like it would keep the unit cool enough.

Does anyone know about running these units outside in freezing temps? the whole motivation here is that I've seen specs on mini splits that rate them only down to ~15 f... which is often reached in my climate in the winter. I would think that the efficiency of the condenser would improve with low temps, but maybe only up to a freezing point depending on the coolant used.
thanks for any thoughts.
 
max_well

max_well

Member
dunkybones said:
If it's that cold where you are, why can't you air cool?
Click to expand...

Could definitely air cool in the winter here, but with hot summers and the desire to run sealed room style with co2 supplementation, I prefer to cool with a/c and keep the same parameters in play throughout the year.
 
A

arrg

You could put a fan speed control on the condenser part to slow the fan down as needed to keep the head up so it works right. I have done it on bigger units I might have a controller in the garage I will go look.
 
max_well

max_well

Member
arrg said:
This is the type you need but not this exact one it is not the right voltage for a mini split but you get the idea




http://cgi.ebay.com/NEW-CARRIER-MOT...emQQptZLH_DefaultDomain_0?hash=item3359fe643b
Click to expand...


Hey Bro
Thanks for the info, that's interesting.. so this would prevent the unit from cooling itself to a point that it's inoperable?
ANother thought I had was building an enclosure around the unit in the months of heating season, with a thermostat controlled fan ducting into the house set at ~80 or 90 F that would blow the warm air into my place to assist the furnace... I just hate the wastefulness of all the heat generated by the condenser being blown away into a snowy night... I think this enclosure would keep the condenser from freezing up too.
Does anyone know at what external temperatures mini splits are most efficient, in general. what accounts for them "freezing' up at certain cold temps? Does the pressurized coolant freeze ?

thanks for the thoughts
 
liquidcooled420

liquidcooled420

Member
i have seen a couple grows on this site where people built rooms to put the condensor in and vent the heat outside. One dude had a large one like you see outside for central ac so a mini-split would be possible for sure.

Have you considered a watercooled ac or heat exchanger. I just got a 2 fan water cooled heat exchanger and it is awesome. I have used 'sall sorts of ac and these things are a sealed grower's wet dream. All you need is a water line going in and out, no need to fuck with vent pipes and inline fans. Also they use hardly any electricity 2.5amps per fan
 
A

arrg

max_well said:
Hey Bro
Thanks for the info, that's interesting.. so this would prevent the unit from cooling itself to a point that it's inoperable?
ANother thought I had was building an enclosure around the unit in the months of heating season, with a thermostat controlled fan ducting into the house set at ~80 or 90 F that would blow the warm air into my place to assist the furnace... I just hate the wastefulness of all the heat generated by the condenser being blown away into a snowy night... I think this enclosure would keep the condenser from freezing up too.
Does anyone know at what external temperatures mini splits are most efficient, in general. what accounts for them "freezing' up at certain cold temps? Does the pressurized coolant freeze ?

thanks for the thoughts
Click to expand...


that device slows the fan down so it stays hot enough to work right. I have worked on some units that need to operate like that and another ghetto fix is cardboard over the coils but come summer that better come off or you need a new one. I have never funked around a little mini split but most everything works the same so it should work. The refrigerant does not freeze just the head pressure gets so low being so cold out you need to make sure you have enough head to get it to work right.

The refrigerant acts like butane in a lighter like in winter the flame is small due to low pressure but slowing the fan down is like putting the lighter in your pocket warming it up boosting pressure so it works well.

I would do the water cool in the winter maybe run a controller to pump glycol form a coil outside to an inside coil as needed or just to those icebox light coolers.

I was thinking of going water cooled if I grew around here and just dump tap down the drain using that to cool. Tap is free here so I don't care how much it takes even full blast 24/7
 
Holdin'

Holdin'

Moon-grass farmer
Veteran
I install various mini splits a few times a month through the company I work for (mostly residential), they're just getting popular in my area in a residence.

Commercially, I've installed hundreds at the company I used to work for.

The condenser must be outside. Unless you vent the room that it is in to the extreme like someone mentioned. Which wouldn't be worth it in my opinion.

15 seer qualifies for the tax credit for regular splits, for mini splits I'm sure it's the same but I'd have to check.

And also like someone mention, you'd be better off just not using the mini split in the winter months, and air cooling with the cold air from outside. Not only will you save your mini split, you'll save $$$.

The only problem with my advice in this aspect is that I live in a very mild climate. We never get below zero and rarely get above 100. So I never really have these concerns about extreme temps when dealing with customers.

If you absolutely need the outdoor unit indoors, I could probably retrieve some information from various factory reps and my mentors on how to achieve this, although I know it's not recommended either way.
 
max_well

max_well

Member
Holdin' said:
I install various mini splits a few times a month through the company I work for (mostly residential), they're just getting popular in my area in a residence.

Commercially, I've installed hundreds at the company I used to work for.

The condenser must be outside. Unless you vent the room that it is in to the extreme like someone mentioned. Which wouldn't be worth it in my opinion.

15 seer qualifies for the tax credit for regular splits, for mini splits I'm sure it's the same but I'd have to check.

And also like someone mention, you'd be better off just not using the mini split in the winter months, and air cooling with the cold air from outside. Not only will you save your mini split, you'll save $$$.

The only problem with my advice in this aspect is that I live in a very mild climate. We never get below zero and rarely get above 100. So I never really have these concerns about extreme temps when dealing with customers.

If you absolutely need the outdoor unit indoors, I could probably retrieve some information from various factory reps and my mentors on how to achieve this, although I know it's not recommended either way.
Click to expand...

Thanks for all the helpful input.. I've been researching the topic pretty thoroughly. This thread gave me lots of insight:
http://www.icmag.com/ic/showthread.php?t=126484
Guy is using a 12" fan to vent out a condenser room that houses a big a/c (3.5 ton)... seems like his motivation in to keep everything the extra level of stealthy...

I checked out the Excel Air models , in particular this one:
http://www.bghydro.com/BGH/ItemMatr...d&selelement4=undefined&selelement5=undefined
The concept here is to house the compressor separate from the condenser unit. Compressor goes in a sound proof box (presumably inside), and the condenser and fan sit outside, which makes the outside kept portion quieter. They have special lines and connections allowing someone to DIY install, and connect /disconnect without losing line charge, making things more portable. In the literature it states: "Do not place condensing unit in a covered area without consulting Excel Air Systems... you must have fresh air no warmer than 85 f cooling refrigerant ... Caution: the fan on the outdoor condensing unit is not designed to move air through any ductwork. Additional blower must be installed for this. Required amount of air is 550 cfm per ton."
check here for links to install guide:
http://www.excelair.ca/2tonpackage.html

The $5200+ price tag on this seems a little steep, considering you could get this kind of DIY model:
http://www.clearanceac.com/index.php?l=product_detail&p=96
which is 1 ton model, and has efficiency (20 SEER), that qualifies it for 30% federal tax credit (from Mitsubishi website, the requirements are:
CEE Level: Tier 2
SEER: 15 or higher
EER: 12.5 or higher
HSPF: 8.5 or higher)

So one could theoretically purchase 2 of these for ~$3700 shipped and get the fed gov to pay you back for $1100 in tax credit form, so 2 Ton cooling for about half the price of the Excel.
Fujitsu and Mitsubishi have some models that also qualify for the tax credit. Nothing like having the government help fund your grow! Note that this credit also applies to 30% of installation costs.

The more I read about it the more feasible it seems to run the whole unit inside... As long as the space housing the conderser is big enough to prevent static pressure from slowing the condensor fan, and enough air exchange cfm is provided to keep the local environment around the unit cool, it won't know if it's inside or out. Does anyone know at what temperature the compressor on such a split unit will function most efficiently?
 
R

RedRain

checkout www.heatexchanger.ca they sell water cooled ACs that use water to cool the refrigerant, instead of an outside unit. you will still draw moisture from the air like a normal ac system as well.

H&M also sells silent A/C systems and are MUCH cheaper than excel, plus they have been around for a decade at least...talk to Des he will hook you up
 
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