estimating power demand

7/21/2019 Estimating Power Demand

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Estimating Power Demand

Using IEC MethodsFiled in [Buildings Technology]By Steven on July 27th, 2011

reproduced from

Schneider's 'Electrical Installation

Guide - According to IEC International Standards'Estimating

power demand is combination of science and art. It is an area of

electrical engineering where there is no correct answer. Plug the

gures in your preferred method of calculation and then as an engineer

you need to relay on instincts to say if the answer feels right or not.

Indiidual loads do not necessarily operate at full rated nominal powernor at the same time. Estimating power demand inoles both loo!ing

at the total connected load and the ma"imum e"pected demand on the

system. #s we will see these are not the same.

IEC Method

$epending where you are% di&erent methods% gures and procedures

are used to estimate the power demand of an installation. This is a loo!

at one method inline with what could be considered IE' practice. To get going it is useful to understand some basic denitions(

• oltage ) * the oltage of the electrical system

• load current Ib * the current re+uired to operate an item of

e+uipment

• apparent power !)# * the product of the oltage ) and load

current Ib

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• real power !, * the actual power consumed by the load or

e+uipment

• power factor * the ratio of the real power to apparent power

-!,!)#/

•

utilisation factor !u * see below• simultaneity factor !s * see below

Utilisation factor ku - name plate ratings invariably list higher valuesof current than will be seen in use, motors rarely run at full load, etc. utilisation factor can be applied to these ratings to establish a morerealistic load current, thereby not overestimating the demand.

Simultaneity factor ks - not all e!uipment runs a the same time" fore#ample one motor may be duty and the other standby. $he sameapplies to installations" for e#ample a group of houses or apartmentswill not all consume the full design current at the same time. pplyinga simultaneity factor ta%es care of this. &ften the term diversity isused and has the same meaning.

The diagram illustrates how the utilisation and simultaneity factors are

used to estimate the power demand of an installation. 'lic! on the

image for a larger ersion.

Following the diagram% the apparent power of the load or e+uipment is

multiplied by the utilisation factor to gie a realistic power demand to

be supplied by a distribution board. 0umming these power demand

gures gies the total connected apparent demand -at that board/. Thedistribution board would normally be si1ed for this demand.

#n appropriate simultaneity factor is applied to the connected

apparent demand at the distribution board and this [diersied] load is

carried upstream to higher leels boards. 2epeating this procedure will

lead to an e"pected total demand for the full installation.

In a nutshell% that3s all there is to it * in principal at least. There are

often problems in deciding what simultaneity factor to use and here

e"perience can be really useful.

Tip: estimating power demand this is normally carried out using either apparent or real power. ' prefer real power as it gives me the actual%( re!uired and is an algebraic sum. )any people will use apparent

power, which strictly spea%ing is a vector sum. s we are dealing withestimates *ball par% +gures even, using either real or apparent powerwill yield usable results.



!pical Utilisation " Simultaneit!

#actors

Ideally utilisation and simultaneity factors should be deelopedspecically for each application and based on a !nowledge of how that

particular system will operate. For certain situations it may be

necessary to use factors gien by supply authorities or some other

industry adopted factors.

The factors below are based on those gien in the 0chneider Electrical

Installation 4uide and can be used in the absence of other sources or

to proide reality chec!s on gures being used.

Utili$ation #actor %&u#ctual power used in e+uipment is often less than the rated power. #

utili1ation factor -!u/ is used to gie a more realistic estimation of

ma"imum power.

!pical (alues of Utili$ation #actor &u)

Type of load ku

Motors (Typical 0.75

Lighting Circuits 1

Socket Outlets 0.1 to 0.2

Simultaneit! #actor %&sIf is rare in practice that all loads operate simultaneously. The

simultaneity factor !s is applied to each group of loads -e.g. being

supplied from a distribution or sub*distribution board/. 0imultaneity

factor is sometimes called diersity factor.

!pical (alues of Simultaneit! #actor &s *! circuit function)

Type of load ks

Lighting 1General eating 1

Space eating 0.!

"irCon#itioning

1

Socket Outlets 0.1 to 0.2

Building

Installations

ks

$scalator 0.5

$le%ator 0.&

Sanitary syste's 0.5

Sprinklers 0.1

eating 0.!

Apartment

Blocks

ks

2 to 1

5 to ) 0.7!

10 to 1 0.*&

15 to 1) 0.5&

20 to 2 0.)



Type of load ks

Li+ts,oists Most po-er+ul

'otor

1

Secon# 'ost po-er+ul

'otor

0.75

or all 'otors 0.*

Assemblies -Number of Circuits ks

2 an# & 0.)

an# 5 0.!

* to ) 0.7

10 an# 'ore 0.*

"ir con#itioning 0.!

Cooling -atersyste'

0.7

/e+rigeration 0.7

25 to 2) 0.*

&0 to & 0.

&5 to &) 0.2

0 to ) 0.1

50 an# 'ore 0.0

+asic Demand Data and Preliminar!

Planning

0iemens produce a series of publications proiding typical demand

gures for arious building functions [see 0teen5s Technical 6ist%Buildings Technology for a list of these]. The following tables are based

on alues gien in these publications(+uildings according to theirt!pe of use)

Building Use Average

Power

emand

!imultaneity

"actor

ank 070

-,'7

0.*

Lirary 200

-,'7

0.*

O++ice &050

-,'7

0.*

Shopping centre &0*0

-,'7

0.*

Di,erent functional and *uildingareas

"unctional Area#

Building Area

Average

Power

emand

!imultaneity

"actor

all-ay3 anteroo'

or loy

515 -,'7 0.&

Staircase 515 -,'7 0.&

General utilities 515 -,'7 0.&

oyer 10&0-,'7

1.0

"ccess -ays(e.g. tunnel4

1020-,'7

1 .0

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otel &0*0

-,'7

0.*

epart'ent store &0*0

-,'7

0.*

S'all hospital(0!0 e#s4

25000-,'7

0.*

ospital

(200500 e#s4

50!0

-,'7

0.*

6arehouse (no

cooling4

220 -,'7 0.*

Col# store 500 13500

-,'7

0.*

"part'ent

co'ple(-ithoutnight storage or

continuous+lo-

-ater heater4

10&0

-,'7

0.*

Museu' *0!0

-,'7

0.*

8arking garage &10 -,'7 0.*

8ro#uction plant &0!0-,'7

0.*

ata centre 50023000-,'7

1 .0

School 10&0-,'7

0.*

Gy' hall 15&0-,'7

0.*

Sta#iu'(03000!03000

seats4

70120-,seat

0.*

Ol# people9s

ho'e

15&0

-,'7

0.*

Greenhouse

(arti+icial

lighting4

250500

-,'7

/ecreation

roo',kitchenette

2050

-,'7

0.&

Toilet areas 515 -,'7 1 .0

Tra%el centre *0!0

-,'7

0.!

O++ice areas 200-,'7

0.!

ookstore !0120-,'7

0.!

lo-er shop !0120-,'7

0.!

akery,utcher 250&50-,'7

0.!

Groceries !0120-,'7

0.!

istro,ice crea' parlour

150250-,'7

0.!

Ca+e 1!0220-,'7

0.!

iner,restaurant 1!000-,'7

0.!

Toacco shop !0120

-,'7

0.!

air#resser 2202!0

-,'7

0.!

rycleaner9s or

laun#ry

700)50

-,'7

0.7

Storage area 515

-1,'2

0.&



.ce E/uipment Demand0ecommendations

$%uipment Average

Power

emand

ata

!ource

"ll in one 8rinter,

a,Scanner

75 - C:S$

Ceiling 8ro;ector Li+t 50 - $sti'ate#

Ceiling 8ro;ectorScreen

!0 - $sti'ate#

Colour 8rinter,Copier 200 - C:S$

Colour Scanner 50 - C:S$

Co'puter 8eripherals 00 - $sti'ate#

Con%enience Sockets 200-,socket

$6"

Cost /eco%ery e%ices &3000 - $sti'ate#

esktop 100 - C:S$

< 8layer 70 - $sti'ate#

ie# Ca'era &0 - $sti'ate#

Laptop 100 - C:S$

Large S'art oar# &00 - $sti'ate#

Monitor 200 to 006

C:S$

8aper Shre##er 50 - C:S$

8ersonal 8rinter,a 50 - C:S$

8ortale 6ireless

Controller

20 - $sti'ate#

8ro;ector &00 - C:S$

/ack $=uip'ent in

Cre#en>a

00 6 $sti'ate#

Shre##er 1)0 - $sti'ate#

Technology 6ells in

Tale Top

200 - $sti'ate#

Telecon+erence Mo#ule 50 - $sti'ate#

6all Mounte# 20 - $sti'ate#

ther areas)

Area Average power

demand

$lectric +loor heating

e#roo's

*51 00 -,'7

$lectric +loor heating

athroo'

1&0150 -,'7

?ight storage heating@

Lo-energy house

*070 -,'7

?ight storage heating@

house -ith Astan#ar#B

insulation

100110 -,'7

S'all air con#itioning

unit

*0 -,'7

8hoto%oltaic

('ai'u'

output o+ the 'o#ules4

1001&0 -,'7



Controller

6all Mounte# LC 200 - $sti'ate#

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Ma1imum Demand for

+uildingsFiled in [Buildings Technology]By Steven on June 1th, 2010

2anitas with a Cr!stal +all

2incent 3aurens$ (an der 2inne

%4567 8 49:6Estimating ma"imum demand is a topic fre+uently

discussed. ,or!ing out how much power to allow for a building can be

ery sub8ectie . #llowing too much power results in additional

e+uipment% increased space re+uirements% greater system losses and

e"tra cost. 9n the other side% not enough power results in operational

problems. Trying to nd the right amount of power is li!e ga1ing into a

crystal ball and eeryone will see something di&erent.

Early in a pro8ect power demand is estimated on a wm7 basis. Each

building needs to be considered on it merits and appropriate

allowances wor!ed out -for e"ample a o:ce designed for high end

ban!ing clients will re+uire more power than a general purpose o:ce/.

,hile there are no "ed guidelines it is good to hae some sort of

starting point. The table below proides an initial set of demand gures

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Courthouse Con+ine'ent Cells 10 0.!5 0 0

Courthouse Courtroo' 20 0.!5 20 0.!

Courthouse u#gesD Cha'ers 1 0.!5 20 0.!

ining "rea ar Lounge,Leisure ining 15 0.!5 10 0.&

ining "rea a'ily ining 2& 0.!5 10 0.&

ining "rea General 10 0.!5 10 0.&

ining "rea otel 1 0.!5 10 0.&

ining "rea Motel 1& 0.!5 10 0.&

ining "rea 8enitentiary 1 0.!5 10 0.&

or'itoryLi%ing Euarters 12 0.!5 1! 0.*

ressing,Locker,itting /oo' * 0.!5 10 0.&

$lectrical,Mechanical 1* 0.!5 15 0.&

$terior Stair-ays 10.! 0.!5 0 0

$terior uil#ing aca#es (illu'inate#4 2.2 0.!5 0 0

$terior uil#ing aca#es (nonillu'inate#4 0 0.!5 0 0

$terior Canopies,O%erhangs 1&.5 0.!5 0 0

$terior $ntrances,:nspection Station 1&.5 0.!5 0 0

$terior Loa#ing "reas 5. 0.!5 0 0

$terior Sales "reas 5. 0.!5 0 0

$terior Fnco%ere# 8arking "rea 1.* 0.!5 0 0

$terior 6alk-ays ( &' -i#e4 ).) 0.!5 0 0

$terior 6alk-ays (H& ' -i#e4 2.2 0.!5 0 0

ire Stations $ngine /oo' ) 0.!5 15 0.&

ire Stations Sleeping Euarters & 0.!5 1! 0.*

oo# 8reparation 1& 0.!5 &!7 0.!

Gy'nasiu',$ercise Centre $ercise "rea 10 0.!5 20 0.*

Gy'nasiu',$ercise Centre 8laying "rea 15 0.!5 15 0.*

ospital $'ergency 2) 0.!5 &*0 0.*

ospital $a',Treat'ent 1* 0.!5 &*0 0.*

ospital Laun#ry6ashing * 0.!5 &*0 0.*

ospital Me#ical Supply 15 0.!5 &*0 0.*



ospital ?ursery * 0.!5 &*0 0.*

ospital ?ursesD Station 11 0.!5 &*0 0.*

ospital Operating /oo' 2 0.!5 &*0 0.*

ospital 8atient /oo' ! 0.!5 &*0 0.*

ospital 8har'acy 1& 0.!5 &*0 0.*

ospital 8hysical Therapy 10 0.!5 &*0 0.*

ospital /a#iology 0.!5 &*0 0.*

ospital /eco%ery ) 0.!5 &*0 0.*

otel,Motel Guest /oo's 12 0.!5 1! 0.*

Laoratory 15 0.!5 &*0 0.*

Lirary Car# ile an# Cataloguing 12 0.!5 &! 0.*

Lirary /ea#ing "rea 1& 0.!5 &2 0.*

Lirary Stacks 1! 0.!5 &2 0.*

Loy General 1 0.!5 1 0.&

Loy otel 12 0.!5 1! 1

Loy Motion 8icture Theatre 12 0.!5 1! 1

Loy 8er+or'ing "rts Theatre &* 0.!5 1! 1

Lounge,/ecreation General 1& 0.!5 2 0.&

Lounge,/ecreation ospital ) 0.!5 * 0.&

Manu+acturing Control /oo' 5 0.!5 72 0.*

Manu+acturing etaile# Manu+acturing 2& 0.!5 72 0.*

Manu+acturing $=uip'ent /oo' 1& 0.!5 72 0.*

Manu+acturing igh ay (H7.* '4 1! 0.!5 72 0.*

Manu+acturing Lo- ay (7.* '4 1& 0.!5 72 0.*

Museu' General $hiition 11 0.!5 *) 0.*

Museu' /estoration 1! 0.!5 *2 0.*

O++ice $nclose# 12 0.!5 2! 0.!

O++ice Open 8lan 12 0.!5 2! 0.!

8arking GarageGarage "rea 2 0.!5 ! 0.*

8enitentiary Con+ine'ent Cells 10 0.!5 0 0

8enitentiary Courtroo' 20 0.!5 20 0.!



8enitentiary u#gesD Cha'ers 1 0.!5 20 0.!

8olice Station Con+ine'ent Cells 10 0.!5 0 0

8olice Station Courtroo' 20 0.!5 20 0.!

8olice Station u#gesD Cha'ers 1 0.!5 20 0.!

8ost O++iceSorting "rea 1& 0.!5 72 0.*

/eligious uil#ings ello-ship all 10 0.!5 5 0.&

/eligious uil#ings 6orship 8ulpit3 Choir 2* 0.!5 5 0.&

/estroo's,Toilets 10 0.!5 5 1

/etail Mall Concourse 1! 0.!5 2 0.*

Sales "rea (+or accent lighting4 1! 0.!5 0 0

Sports "rena Court Sports "rea 25 0.!5 5 0.*

Sports "rena :n#oor 8laying iel# "rea 15 0.!5 5 0.*

Stairs * 0.!5 ) 0.&

Storage "cti%e General ) 0.* * 0.&

Storage "cti%e ospital 10 0.* * 0.&

Storage :nacti%e General & 0. * 0.&

Storage :nacti%e Museu' ) 0. * 0.&

Transportation "ir,Train,us aggage "rea 11 0.!5 1) 1

Transportation "irport Concourse * 0.!5 2 1

Transportation Ter'inal Ticket Counter 1* 0.!5 1 1

6arehouse ine Material Storage 15 0.!5 5 0.*

6arehouse Me#iu',ulky Material Storage 10 0.!5 5 0.*

6orkshop 20 0.!5 72 0.*

An Alternati(e Energ! +ased

Approachsing wm7 gures -including some sort of diersity/ to estimateelectrical demand% may not be the best approach for future buildings.

Particularly with regards to encouraging innoation in the design with a

focus on improing oerall energy consumption and a buildings carbon

footprint.

#n alternatie approach would be to set design targets on how much

electrical energy indiidual systems can use. This would be done at



the beginning of the pro8ect. $esigners for each system% would then

be tas!ed with producing designs to meet these targets. Tight energy

targets would encourage a more innoatie and integrated design as

well as proiding performance indicators to monitor the design.

The electrical engineers 8ob is clearly made easier by this approach asthe ma"imum demand is "ed by the energy targets.

This approach does re+uire commitment from the design team to a

more integrated design approach. There are companies already

utilising the approach and initial feedbac! has been good. ;ow useful

and productie it will be in the long run still remains to be seen.- See more at: http://myelectrical.com/notes/entryid/!/ma"imum-demand-for-

uildings#sthash.i$%&'(().dpuf

2oltage Drop in Installations -ConceptsFiled in [Buildings Technology]By Steven on eptember 27th, 2011

Problems on achieing ma"imum oltage drop within an installation

come up often. $epending where you lie% local regulations will hae

di&erent limits on ma"imum allowable oltage drop% howeer the

intent of all of these is to ensure su:cient oltage is aailable at the

e+uipment so that if functions correctly. 0pecied oltage drops aregenerally not for an indiidual cable but for the full installationC from

the point of supply connection to the nal e+uipment. Thus the oerall

oltage drop is a combination of indiidual oltage drops across

multiple cables.

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The gure shows a typical

installation. # transformer feeds a main distribution board -@$B/%

which in turn feeds one or more sub main distribution board -0@$B/.

Each 0@$B feeds one or more nal distribution board -F$B/% which in

turn supplies the connected e+uipment. It is apparent that the total

oltage drop at the nal e+uipment is the sum of following oltage

drops(

• )oltage drop -)>/ in the cable from the transformer to the @$B

-which is carrying the current for all the loads on the system/

• )oltage drop -)7/ in the cable from the @$B to the 0@$B -which

is carrying the current for all loads in all F$B connected to the 0@$B/

• )oltage drop -)D/ in the cable from the 0@$B to the F$B -which is

carrying the current for all loads connected to the F$B/

• )oltage drop -)/ in the cable from the F$B to the load -which is

carrying the current for the load only/

,hat becomes obious is that the oltage drop is a function of the

oerall system and not triial to calculateC particularly for a large

system. In order to accurately determine the oltage drop to any load%

a complete understanding of the system is re+uired. $ue to this%



design is often carried out using computer software which can +uic!ly

ealuate the full system and proide a eriable solution.

'onsideration of a common problem where the oltage drop e"ceeds

the allowable% may help illustrate some of the issues li!ely to be

encountered. 4ien a oltage drop which is too larger% this couldpotentially be resoled by increasing the si1e of the cable from the F$B

to the load. Increasing this cable may wor! or could possibly result in a

cable which is too large to be practical. #n alternatie would be to

consider increasing the si1e of one or more of the cables in the

upstream circuits% with the possible benet of reducing cable si1es on

multiple other circuits downstream of this.

)oltage drop and the installation cabling system are integrated and

tied together. The e"ample illustrates that consideration of the

oltage drop re+uires a full understanding of the system. 9theraspects of the design complicated this further. These include

consideration of the cost of the installation% system losses and carbon

footprint. By minimi1ing the amount of copper [cable] used these

aspects are reduced% but this needs to be tied in with achieing

satiable oltage drops. #ttempting to address all these aspects with

numerous combinations of di&erent cables and what*if type scenarios

can only be realistically addressed by using some sort of computer

program.- See more at: http://myelectrical.com/notes/entryid/87/*oltage-drop-in-

installations-concepts#sthash.+,en0.dpuf

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estimating power demand

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