[BLDG-SIM] Internal Loads for Office Buildings

I.G. Theaker igt at integral-design-engineering.ca
Wed Dec 5 09:26:06 PST 2001

Hello, fellow Bldg-Sim listers,

In the early 90s, I took two looks at office plug loads for the British
Columbia Buildings Corporation:
o "Measurement of Heat Output of Typical Office Equipment" (1991)
o "Office Equipment Energy Use in the Richard Blanshard Building, 1992 &
1994" (1995)
(These might be the studies Brian Fountain referred to.  While I was here in
BC, and loosely connected with the BC EMTF, I don't recall any EMTF reports
on the subject.)

The first study measured electricity draw of typical computer equipment, a
facsimile and a medium-sized photocopier, using a BMI Mod. 3060 Power
Profiler, which could capture the effects of switching power supplies.  The
computers covered the SOFTA for the time (8086s, 286s, 386s and 486s -
remember them?) but the measurements may shed some light on todays' Pentiums
and Athlons; I believe the chip consumption was only a small part of the
total.  I suspect a bigger issue today is probably penetration of LCD
screens, rather than CRTs.

For a workplace of 10 people, at 150 sq.ft. / workstation, with a (typical
for the time) mix of 1 computer per station, 2 printers, a fax & a
photocopier, I estimated typical office plug loads at 0.65 W/sq.ft.

The second study used data gathered over several weeks from 3 floors of
BCBCs 244,000 sq.ft. Richard Blanshard Building, a government office in
Victoria where the receptacle circuits were broken out from lighting.  The
devices used were ACM Mod 3710s, which again could capture voltage & current
waveform distortions due to switching power supplies.  The measured floors
had ~425 occupants on 68,387 sq.ft., with 256 PCs and 406 computer monitors
(the difference made up by terminals connected to a mini-comp); with a
typical mix of printers, photocopiers, etc.

For all three measured floors:
- peak simultaneous plug load demand was 0.883 W/sq.ft.
- during occupied hours, the mean plug load demand was 0.792 W/sq.ft.
- unoccupied hours mean plug load demand was 0.360 W/sq.ft.

(Isn't it a pity that what we've gained in lighting has largely been lost to
plug loads?)

These studies indicated that using office equipment nameplate ratings would
overestimate actual electricity demand and heat output by 480 & 590%,

However, if you use these measurements, please note that
- the computers measured are not P3s & 4s or Athlons, nor equipped with CDs
or CD-Rs/RWs
- in some "high-tech" installations such as server farms, stockbrokers,
graphics etc., computer density are often much higher than 1 / worker
- LCDs draw much less than the CRTs measured
- If Energy Star equipment features are enabled, unoccupied demands might be
much lower.

Personally, for simulation of typical offices, I still use 0.8 - 0.9
W/sq.ft., and enquire about LCD screen penetration, & numbers of computers /
worker.  For "high-tech" installations like server farms, I'd recommend
measuring the typical equipment to be installed, with 'meters' capable of
capturing switching power supplies' voltage & current waveform distortions -
*not* a standard RMS meter.

If anyone on the list knows of electricity demand & consumption measurements
of current computers and LCD screens, I suspect we'd all appreciate hearing
about them.

Hope this helps,
Ian Theaker, P.Eng.

- - -- --- ----- -------- ------------- --------------------- --------------
Integral Design / Engineering           Helping create beautiful,
Ste. 303 - 2050 Scotia Street           comfortable, ecologically-
Vancouver, BC V5T 4T1 Canada     responsive buildings.
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----- Original Message -----
From: "Jason Glazer" <jglazer at gard.com>
To: <BLDG-SIM at gard.com>
Sent: Wednesday, December 05, 2001 7:14 AM
Subject: [BLDG-SIM] Internal Loads for Office Buildings

You might want to check out some of the publications LBNL
has been doing in the area of office equipment at:


The most recent report shows that less than half of the
computers were turned off at night.


On 5 Dec 2001, at 7:57, Brian Fountain wrote:

> I recall a study by the British Columbia Energy Management
> Task Force that monitored the current draw on outlet
> circuits in a couple of buildings in the mid-1990's.  As
> suggested below, it found plug loads to be in the order of
> 0.75 to 0.85W/ft² during the day.  The interesting part was
> the unoccupied plug loads of around 0.35W/ft².
>   -----Original Message-----
>   From: postman at gard.com [mailto:postman at gard.com]On Behalf
>   Of Tom Anderson Sent: Wednesday, December 05, 2001 5:47 AM
>   To: BLDG-SIM at gard.com Cc: BLDG-SIM at gard.com Subject:
>   [BLDG-SIM] Internal Loads for Office Buildings
>   If by high tech buildings you are referring to a modern
>   office buildings,
> then loads from desktop PC's, monitors, printers, copiers,
> etc. typically will be about .5 watts per square foot, but
> may range from .5 to 1.0 watts per foot.  Note the actual
> power use by such equipment is well below the nameplate
> power data.
>   Refer to published ASHRAE papers, starting in 1994,
>   authored by Chris
> Wilkins, who reported on extensive monitoring of such loads
> in real world office buildings.
>   Lighting loads, refer to 90.1-1999 for maximum power
>   densities permissible
> for office occupancies.  But lighting designers who apply
> efficient fixtures for interior lighting design can easily
> achieve excellent illumination levels using well below 1.0
> watts per foot.
>     Thomas E. Anderson
>     President
>     Cx Associates, Ltd.
>     Building Commissioning Specialists
>     http://www.cx-assoc.com
>     933 Road 101
>     Jeffersonville, Vermont 05464 USA
>     hvac at cx-assoc.com
>     Tel: 802-644-5616 Fax: 802-644-6797
>   Samuel Hassid wrote:
>       what is the accepted value for internal loads in a
>       high tech building
> ?
>     ======================================================
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