# power sizing for some liebert units

• posted on June 2, 2007, 1:32 am
I am retro-fitting a small 1600sqft datacenter with one or two Liebert units (480V 3-PH).
Can anyone tell me the realistic power draw of these units when in full operation mode?
I will either be using a 10-ton or 20-ton unit.
Alot of people have been telling my that rule of thumb is 1KW per 1 ton, so a 10-ton Liebert should draw 10KW of power.
If my math is right, a 10-ton Liebert pulling 10KW while in operation, would be pulling approx 12amp per phase.
480V x A x 1.732 = 10KVA, so A = 12
The reason why I bring this up is because I was talking to the buildings electrical contractor about the power feeds to the space, which is 200amp 480V 3-PH. I mentioned a single 10-ton Liebert, and he said he usually wires those as a 60amp 480V circuit - which seemed overly high? 60amp breaker, when your only pulling 12-15amps per phase?! I know there can be startup surges, but 60amp seems really high.
Any thoughts?
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• posted on June 2, 2007, 3:43 am

Yeah, get the manufactures specifications, follow them and quit guessing.
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• posted on June 2, 2007, 4:54 pm
See page 24 of www.liebert.com/assets/products/english/products/env/ics/60Hz/tech_dat/acrobat/sl_18510.pdf
essenz wrote:

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• posted on June 2, 2007, 5:59 pm

I don't see why would you ask some thing like that just look up manufacture tag and in most cases you will find they recommendation isn't that simple or literature that comes with unit. This units almost always have two compressors and they also have heaters depend on model so little extra power doesn't hurt but less will. Tony
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• posted on June 4, 2007, 9:44 am
One of the good things about Liebert is that their tech support people are willing to help you out - Call them. Yes you do need to think along the lines of a COP of between 2.5 & 3.5 so the refrigeration side will be 30%~40% of the equipment load in kWh (not kW so if you want the unit to cycle off or have some redundancy then make it a bit bigger but not too much) then multiply this by 40% for the fan load and add it (this can be kW because they'll always be running), plus 8kW/unit for the humidifier and whatever the rating of the reheat element.
I can provide a presentation for close control equipment selection for data centre's - remove the nopam from my address and send a request if you think that would be helpful.