[Bldg-sim] Modeling an UPS (UNCLASSIFIED)

[Nick Caton]

Hi Camilo,

John's assessment covers the majority of typical small UPS scenarios I've run into as well.  I caution you to *not* equate the term "efficiency" with losses.  That rabbit hole goes deep!  Nominal UPS efficiencies (such as 97%) typically are referencing a full-load condition.  The number plummets under partial or "no-load" (normal, sometimes) operation.  More food for thought in the resource attached.

For a smallish UPS (serving a few items in a single rack) - John's suggestion to determine a typical constant loss is the way to go.

100kVA is in a threshold that could be something more substantial.  I think you are best advised talking to a rep for the specific equipment you're dealing with to nail down losses/power drawn under *normal* operation (i.e. normal power on). This figure could be all over the place depending on the project/equipment specifics.

Once known, if you understand that consumption/loss to be effectively constant, you could treat it simply as a process load / internal heat gain for the appropriate space, similar to a space plug load.  If the losses are potentially substantial and vary with the downstream draw, as with transformer losses, you might establish a fractional efficiency curve and model the UPS just as a transformer upstream of the appropriate loads, with appropriate scheduling (I'm somewhat familiar with procedure for eQuest, but I expect there must be similar capacity on the energyplus side of things).

I've yet to encounter a modeling scenario where I was asked to include a power outage within the simulation - I expect you should focus on losses under normal operation unless told otherwise.

Best of luck!

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com 

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Eurek, John S NWO
Sent: Wednesday, October 10, 2012 1:14 PM
To: Camilo Velez :::Green Factory:::; bldg-sim at lists.onebuilding.org; EnergyPlus_Support at yahoogroups.com
Subject: Re: [Bldg-sim] Modeling an UPS (UNCLASSIFIED)

Classification: UNCLASSIFIED
Caveats: NONE

Look at the efficiency, this should tell you the amount of energy which turns into heat. The ones I've used in models were somewhere between 95 to 97%.  So a 97% efficient 100KVA would be at a nearly constant load of 3KVA.

I think a UPS is just a giant trickle charger on a battery.

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Camilo Velez :::Green Factory:::
Sent: Sunday, September 30, 2012 10:39 PM
To: bldg-sim at lists.onebuilding.org; EnergyPlus_Support at yahoogroups.com
Subject: [Bldg-sim] Modeling an UPS

Hello all


I'm trying to mdel an UPS (Uninterruptible Power System) but I'm not sure of what would be the power that I should model. The capacity of the UPS is 100KVA, but this capacity will be use only when a "emergency" happens, the rest of the time the UPS will be in some kind of "stand by" mode with the battery full charged, so how much it will consume while it is in this mode?

Thank you.


Classification: UNCLASSIFIED
Caveats: NONE


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