Small server room air conditioning

ochadd

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We're installing a small server room at a remote office 12'x13'. I'm estimating six 2u servers (700-1100 watts max each) and three 48 port POE switches. Small stuff like UPS, WAN equipment, etc. In the past I've used mini-split systems from Mitsubishi and Fujitsu. Great in the summer but they don't work when temps drop to 0 F or lower. We can see -20 F at times. They'v'e all had problems even after low pressure or something additions that I was told solves the AC-in-the-winter problem. Two different HVAC companies locally are pitching the same style mini-split systems. Another is telling me a heat exchanger/heat pump. I want something that is just going to work no matter if it's 110 or -20 f. Any suggestions?
Thanks
 

BinarySynapse

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Why not just use the already cold air from outside instead of trying cool off the hot air inside?
 

ochadd

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I believe that's what a heat pump and the mini split do.
 

bds1904

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An air source heat pump will still have trouble with cold temps. Dumping heat into cold air will still create moisture buildup on the condenser and in turn ice.

All A/C units are heat pumps. The ones sold as heat pumps generally are more efficient and use rotary compressors. They are also normally reversable to provide heat also. The lowest temp ones I've seen work are -5f after being retrofitted with a low temp kit.

That being said a true geothermal ground source heat pump (one with a well) will work all year no matter what. More expensive up front but they are super efficient and just plain work.
 

Dead Parrot

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A simple package unit for normal AC temps say down to 40*F.

For when it is colder outside, a modified heat exchanger that sucks outside air through the exchanger and vents same air back outside. Something like those gas fired heaters you often see in auto repair shops except instead of where the gas fire would go, modify to use the outside cold air. Would think a HVAC contractor should be able to make something like that up. That way, your cooling cost in the cold times is the electricity needed to run two small fans.
 

J-Will

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A simple package unit for normal AC temps say down to 40*F.

For when it is colder outside, a modified heat exchanger that sucks outside air through the exchanger and vents same air back outside. Something like those gas fired heaters you often see in auto repair shops except instead of where the gas fire would go, modify to use the outside cold air. Would think a HVAC contractor should be able to make something like that up. That way, your cooling cost in the cold times is the electricity needed to run two small fans.

you're suggesting he pay someone to "make something like that up" for a what appears to be mission critical components?
 

ChRoNo16

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Why would the outside temp be affecting interior so much? is this not a building with heat? also those systems should generate a good ammount of heat themselves, so with a small enough room, if its a super cold winter you would think you could essentially just turn off the AC, or am I crazy?
 

ochadd

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With the AC off the room will still get too warm even when outdoor temperature is freezing. Another similar server room we have I've seen get to 90 before we caught it in the morning and that had an outside wall. This new server room will be centrally located in the facility with no outside walls.
 

ChRoNo16

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I think a small AC unit as you first described using in the past would be fine, but if having parts mounted outside (Im guessing is a part of the problem) would a smaller portable unit for like a home work? I mean they run like 500 bucks but how many BTU's is needed?
 

Dead Parrot

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you're suggesting he pay someone to "make something like that up" for a what appears to be mission critical components?

Sure. OP already said that traditional systems were failing when it got cold outside and was asking for ideas that won't freeze up. If a HVAC contractor thinks they can design a heat exchanger that uses outside air as the cold source, why not? Nothing to freeze up. Moving parts are two fans, one for the outside air, the 2nd for the inside air.
 

bman212121

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It took a bit of tuning for us when a company installed one, but whatever was the issue got sorted out. I don't have a model off hand but I believe it was a 3 Ton split unit made by Carrier. We had to wait for this new model to come in to get it, and that was maybe 2 - 3 years ago. It is designed to handle the cold temperatures without freezing up like the Mitsu does. I know for a fact it stayed working under more than a foot of snow at -20F.

What a lot of people don't realize is that there is a lot of BTU being generated inside of that room. It doesn't matter what time of year it is that AC unit is going to be working 24/7. The problem with AC units is that they work off of a temperature differential. One side might be 70F and the other 40F. The cooling side can have too much cooling applied even under load, causing the compressor to work harder and having the lines freeze up which usually trips the overload circuit. As soon as that happens the massive amount of heat that is being generated inside of the room is no longer being pulled out of the room, and builds up in a hurry. After the 2nd of 3rd time and losing a server we finally got someone to get a backup unit installed. You certainly don't want the outside air to come inside because you'll either end up with too much humidity, or believe it or not, too low of humidity. Most people know that condensation is bad, but if the air is too dry, that's what causes static buildup.

If I can find someone who's still at that place I might be able to get a model number off the unit for you. But it's definitely worth looking into because I do know that it works. I believe the units are a bit more underpowered than the equivalent mitsu, but I think part of what helps make it function is that it uses a lower temperature differential between the high and low sides, so it can go to a lower temp before it freezes.

I think this looks about right:
Performance Commercial Ductless AC System - 38HDF/40QNC | Carrier - Home Comfort

You'd definitely need the 3 ton from what it sounds, but IMO if it's setup for cold temps it's more like a 2 - 2.5 T mitsu. It has up a a 200' line length so even if the server room is in the middle of the building you should hopefully be able to get to the outside for the condenser.
 

ChRoNo16

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If I remember right for the Main datacenter portion of the building we had 4 huge liebert units, basically 2 running at a time, and 2 as backups, and if any of them lost heartbeat it paged staff immediately and switched on a backup unit.
 

bds1904

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When you get the bids to install different units don't forget to ask if the unit has a variable speed compressor. That will allow you to get a larger unit than you need (right now) without wasting all kinds of electricity. A larger unit will also buy you some insurance on super-hot days. Be sure to ask about the companies experiance installing units being used to cool server rooms and get references of jobs completed. Most experienced companies will also know, understand and recommend a solution to monitor the temp and alert you also.

I think you'll find -20f a hard number to achieve for a reasonable price, but we all know you get what you pay for.
 

ochadd

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Thanks for the suggestions. I'm eagerly monitoring the thread yet.

Just to clarify my original post... Both the Misubishi and Fujitsu units have low ambient kits installed. Not low pressure as I originally said. They look identical to the Carrier unit bmas212121 linked but I'm not sure how many ton they are. I know there is a Carrier dealer here but he's not one I originally had bid it. I'll have to check into it.

What I use at one location that does falter below 0 f.
Fujitsu Halcyon ASU24CL1 indoor unit
Fujitsu Halcyon AOU24CL1 outdoor unit

The Fujitsu replaced a Mitsubishi Mr. Slim
 
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Red Squirrel

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A lot of our COs just have air intake/exhaust vents. The humidity is not that big of an issue, it's not like you're just dumping outside air into the building in one shot, the air mixes at a rather slow rate. Winter air is also very dry. If anything you have to worry about dryness than wetness. In our manned office where I work we actually have a 3 phase humidifier in the office space so the air does not feel as dry for us.
 
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rma

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I would use the following rules:
Low End Temperature 18°C (64.4 °F)
High End Temperature 27°C (80.6 °F)
Low End Moisture 30% RH
High End Moisture 55% RH

As Red Squirrel says, the problems is when you get as low as 30% RH you will see ESD problems arise in the dry air (bearings in hard drives and fans tend to dry out and die before time, electronics die because of ESD discharges.), when getting to high moist electrolytic problems arise between equipment, this tend to start a corrosion in electronics.

I work in electronics manufacturing, and we use large scale humidifiers in the productions areas to prevent the humidity to get below 30%, this is normal practice.

I used normal outside air for cooling in the winter alongside AC's from panasonic.
these 2 things combined makes a economic solution.
 

whizbang

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Another option for the mini-splits is to put the compressor in an interior room like a garage or maintenance closet. We have a mini-split for our MDF in a school that the compressor is housed in a custodial closet with an exhuast fan to the outside. That way we don't have to worry about the outside temp and the heat from the compressor is vented to outside.
 

Red Squirrel

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Yep I've seen compressors being placed indoors actually. At my main office the server room AC unit compressors are actually right in the garage where all the bucket trucks park. You kinda want to heat that space anyway so it's more efficient than dumping all that heat outside when you're paying to heat another part of the building. On sorta similar subject been thinking about how clothes dryers waste so much heat, if it was not for lint and excess humidity could dump it inside the house. I need to work on some kind of heat exchanger one day to do this. It is tempting to just dump that air into the furnace return.... but that is a terrible idea. :p

One challenge with winter and humidity is that you want to increase the humidity, but not so much that you start getting frost inside. At my house I find I can't really bring humidity any higher than 20% before I get ice on all the windows. I guess in a commercial building with no windows such as a CO/data centre this is probably less of an issue.
 

cantalup

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I would use the following rules:
Low End Temperature 18°C (64.4 °F)
High End Temperature 27°C (80.6 °F)
Low End Moisture 30% RH
High End Moisture 55%
As Red Squirrel says, the problems is when you get as low as 30% RH you will see ESD problems arise in the dry air (bearings in hard drives and fans tend to dry out and die before time, electronics die because of ESD discharges.), when getting to high moist electrolytic problems arise between equipment, this tend to start a corrosion in electronics.

I work in electronics manufacturing, and we use large scale humidifiers in the productions areas to prevent the humidity to get below 30%, this is normal practice.

I used normal outside air for cooling in the winter alongside AC's from panasonic.
these 2 things combined makes a economic solution.

would like to share on my current configuration that has been running for > 4 years.
on my running server rack with my own temperature and humidity control/sensor,
I follow with my minor changes -> Best Practices for data center & server room monitoring


Moisture range 40%-60%, 35%-40% is "alert"(to tell humidity is below normal, and doable), and will trigger something (humidifier) when <34%, 61-65% is "alert", >66 is critical
Intake temperature from front rack: 16-29C (ideally as you said, 18-27C, I extend a bit..)
outtake temperature from back rack: <= 20°C than intake temperature.
 

Red Squirrel

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Red Squirrel dont you have quite the network setup in your basement?

Yeah was talking about the company I work for though. I still did not built any hvac into my home server room yet. I want to though. Basically it will be some kind of air splitter using damper/servos that can take/exhaust air from/to different locations based on conditions. Ex: in winter I want to keep the heat inside the house, in summer I may want to exhaust it etc. Also need to mitigate battery hydrogen, so even when I want to keep the heat I probably will have to go through a HRV so the actual air goes outside but the heat is retained as new air comes in.

Right now my basement is not insulated yet and server room is not walled in, so it's mostly just passive cooling. Downside is zero temp regulation so get lot of temp swings. It gets down to like 12C in there at night and the sensor is on the ceiling so it's probably colder in reality. I need to change all of that some time. Money is mostly the limiter though, I put so much money into that I kinda decided to slow down. :p
 

ChRoNo16

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I hear you on the money thing, I got a new baby coming in the fall so I have had to stop working on my server projects completely, worth it in the end tho ;)
 
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