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why is the Data-Center energy so high in DOE energyplus large office prototype models?

asked 2014-10-15 11:37:28 -0600

EmirPekdemir gravatar image

updated 2015-11-11 13:04:44 -0600

Are UPS rooms included in the Data-Center plug-loads? (whereas they should only be giving out heat, without drawing much electricity)

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@Emir Pekdemir: Welcome to UH! Could you add a little bit more info in your question please? Try adding a link to the large office prototype you're mentioning (I don't see a datacenter plug load in refbldglargeofficenew2004v1-47-2) as well as the DC plug-load value in question too.

Right now it would take me some research before I can even gauge whether or not I could help. Thanks!

Julien Marrec gravatar image Julien Marrec  ( 2014-10-16 03:55:53 -0600 )edit

@Emir. (nice name!) You may also want to add the 'energyplus' tag so that members of the EnergyPlus team that subscribe to that tag will get the question.

__AmirRoth__ gravatar image __AmirRoth__  ( 2014-10-16 09:05:18 -0600 )edit

Haha Thanks @Amir. @Julien They were added after 2004!

EmirPekdemir gravatar image EmirPekdemir  ( 2014-10-16 13:52:36 -0600 )edit

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answered 2014-10-16 12:59:34 -0600

The changes to the Prototype Building Models (including the data center addition) are described here: Enhancements to ASHRAE Standard 90.1 Prototype Building Models. Here is the relevant excerpt: IT Equipment Loads

Equipment in data centers typically includes servers, storage devices, network equipment, and uninterruptable power supplies ( UPS ). Literature review indicates the IT load density for core data centers usually lies between 30 and 60 W/ft2 for large office buildings (LBNL 2001 - 2004; Richman et al. 2008 ; NREL 2009 ). The IT closets are composed primarily of network equipment such as high power switches, routers, and UPS. In some cases, the IT closets can be small computer server rooms . Because there is no specific power density found in the literature for IT closets, we assume that the IT closets have power density at 20 W/ ft2, which is the minimum threshold value defined for computer rooms in Standard 90.1. Thus, the equipment load densities used are as follows:

  • Core data center : 45 W/ft2 of IT load
  • IT closets : 20 W/ft2

Additionally, based on looking at the IDF file, these loads are running ALWAYS_ON (24/7/365), and 100% of the heat gain is going into the zone, with 50% of the heat being sensible and the other 50% being radiant. The HVAC equipment must remove this heat to meet the heating setpoints. Here is the excerpt from the IDF file that shows the Core data center electric load:

    DataCenter_Basement_MiscPlug_Equip,  !- Name
    DataCenter_basement_ZN_6,!- Zone or ZoneList Name
    ALWAYS_ON,               !- Schedule Name
    Watts/Area,              !- Design Level Calculation Method
    0,                       !- Design Level {W}
    484.423246742185,        !- Watts per Zone Floor Area {W/m2}
    ,                        !- Watts per Person {W/person}
    0.0000,                  !- Fraction Latent
    0.5000,                  !- Fraction Radiant
    0.0000,                  !- Fraction Lost
    DataCenter_PlugLoads;    !- End-Use Subcategory
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Thanks Andrew. Really useful documentation. The second part of the question is more on the UPS power. As this graph shows, although UPS equipment is ON all the time, their electricity usage drops significantly after they are charged. (yet still they give out heat). Do you know if UPS equipment is modeled as a plug-load or just a heat source?

EmirPekdemir gravatar image EmirPekdemir  ( 2014-10-16 14:09:19 -0600 )edit

UPS is apparently lumped in here. And assumes it's always charged. It only models the losses of the UPS. See @DancingDavidE 's answer below

Julien Marrec gravatar image Julien Marrec  ( 2014-10-17 02:23:08 -0600 )edit

answered 2014-10-16 19:07:07 -0600

I'm "thinking out loud here" - so if someone can jump in that knows the specific answer, please post.

I don't expect that the prototype buildings necessarily had separate thermal zones for the UPS equipment in an office building's data center. I guess the common practice might vary somewhat throughout the time periods of the prototype buildings (only modeled explicitly after 2004 apparently!) as to which energy storage technology is used in office building data centers, and whether this room would have a separate ventilation system or would have the equipment located in the same room as the server racks.

The assumption for 45 W/ft2 of heat gain likely includes losses related to the UPS system to be picked up as heat, and I wouldn't expect the model to include any dedicated time for charging the UPS showing a spike in kW.

@Emir Pekdemir, if you are working on a specific building that had UPS batteries requiring separate ventilation, then I think you should modify the prototype model to include a separate zone if you are also itemizing the server floor power, cooling, and ventilation energy.

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Thanks @DancingDavidE, I guess the point I am trying to make is although 45W/ft2 could be the right value for the cooling load, it may not necessarily reflect the electricity usage of a Data Center. I am also thinking and typing out loud here :)

EmirPekdemir gravatar image EmirPekdemir  ( 2014-10-17 15:10:26 -0600 )edit

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Asked: 2014-10-15 11:37:28 -0600

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Last updated: Oct 16 '14