lecture 11 air exchange

8/10/2019 Lecture 11 Air Exchange

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Importance of this Lecture to

the Simulation of BuildingsAir is critical to sustaining life and also to thethermal environment inside a building (comfort)While a zone is de ned by a common air mass

at a particular temperature, air is not staticwithin a buildingUnintended ow into out of the building!urposeful ow into out of the building"#change between interior spaces

Air movement may result in energy transferfrom one area to another and thus has anenergy impact on the zone and or buildingUnderstanding the energy impact of airmovement is critical to our understanding of

how much energy is re$uired to maintainthermally comfortable conditions within a space


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Purpose of this Lecture

%ain an understanding of how to&'e ne air movement between interior

spacesAppro#imate the e ect of ventilatinga building (naturally or mechanically)

!erform detailed air movementcalculations using the "nergy!lus linto *+ -.


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Keywords overed in this

Lecturei#ing

*ross i#ing/entilation*+ -. -nput .ynta#


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Mi!ing

Used to move air from one zone to another+nly has an impact on the receiving zone0user must account for energy impact onsource zone through i#ing, -n ltration, etc1*an be used to set2up multiple air ow pathsor a 3circular4 path between more than two

zonesUser must specify ow rates and schedule


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Mi!ing "cont#d$

-'' 'escription& MIXING, A1 , \field Zone Name

A2 , \field SCHEDULE Name N1 , \field Design Level of Ai !lo" in m#$s A# , \field So% &e Zone Name N2 ' \field Del(a )em*e a(% e in deg ees Celsi%s

%&elta 'emperature( controls when mi!ing

air from the source )one is sent to receiving)one* if positive+ the temperature of )onefrom which air is drawn must ,e ' warmerthan receiving )one air or no mi!ing occurs* ifnegative+ the temperature of source )onemust ,e ' cooler than receiving )one air orno mi!ing occurs* if ' is )ero+ mi!ing occursregardless of the relative )one temperatures


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ross Mi!ing

Used to e#change e$ual amount of airbetween two zones5as an (e$ual) energy impact on bothzones+nly needs to be de ned once for one ofthe two zones+nly one cross mi#ing statement per zone-f mi#ing occurs with more than one zone,must use i#ingUser must specify ow rates and schedule


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ross Mi!ing "cont#d$

-'' 'escription&C+ SS MIXING,

A1 , \field Zone Name

A2 , \field SCHEDULE Name N1 , \field Design Level of Ai !lo" in m#$s A# , \field So% &e Zone Name N2 ' \field Del(a )em*e a(% e in deg ees Celsi%s

&elta 'emperature controls when mi!ing air from

the source )one is sent to the receiving )one-* ifpositive+ the temperature of )one from which air is,eing drawn "%source )one($ must ,e ' warmerthan the )one air or no mi!ing occurs* if )ero+mi!ing occurs regardless of the relative airtemperatures* negative values for %&elta'emperature( are not permitted


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Mi!ing and ross Mi!ing

.!amples

/one 1 /one 0

/one /one 2

mi!ing

m i ! i n g

mi!ing

m i !

i n g

/one 1 /one 0

/one /one 2

crossmi!ing crossmi!ing

/one 1 /one 0

/one /one 2

mi!ing

/one 1 /one 0

/one

crossmi!ing

3K 3K

3K

Illegal


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4entilation "Simple$

-ntent is to allow simple mechanicalventilation without specifying an 5/A*system or natural ventilationAmount of ventilation determined by userde ned design ow rate, schedule, ande$uation similar to in ltration (allows forvariation based on temperature di erence

and wind speed) 6ype and control of ventilation determinedby ventilation speci c parameters


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4entilation "Simple+

cont#d$*ontrol !arameters&

inimum 6emperature& indoor (zone) air temperature belowwhich ventilation is shut o 'elta 6emperature& temperature di erential between inside(zone) and outside air below which ventilation is shut o(negative values allowed)

Advantage& can ta e e ect of natural or simpleforced ventilation into account without a lot of input'isadvantage& user must de ne the air ow rate (willnot gure out how much air ow there will be)Use *+ -. for more serious studies of air movementwithin the building and between inside and outside


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4entilation "Simple+

cont#d$A few thoughts on how to get the design ow rate fornatural ventilation8

A*5& consider how many air changes per hour you mighte#pect for natural ventilation (somewhere betweenin ltration and fan driven ow, probably closer to in ltration)Window area and velocity& area times velocity is volumetric

ow rate'etermine window opening area (not necessarily the same aswindow area0depends on window type)

ultiply by some 3standard4 velocity (you will use the velocitycoe9cients so consider :1;m s)


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3MIS Multi)one Air6ow

*+ -. *on=unction +f ultizone-n ltration .pecialists*+ -. model incorporated into "nergy!lus

ultizone air ow driven by e#ternal windand stac e ect'oes not model 5/A* system impact

*omputes in ltration and interzone owswhich are passed to the thermal simulation.ee -nput +utput


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3verview of the

3MIS7.nergyPlus Lin5 *+ -. was developed in :>>? as a stand2alonemultizone air ow program with its own input andoutput processors1 -n the *+ -. "nergy!lus lin , *+ -.is called each time step by the "nergy!lus program1

Using inside and outside temperatures and the windpressure distribution at the beginning of a time step,*+ -. calculates air ows through crac s and largeopenings (such as open windows) between outside andinside and from zone to zone1 6hese are then used by

the "nergy!lus thermal calculation to determine surfacetemperatures and zone air temperatures for that timestep (which are then used in the ne#t time step tocalculate new air ow values, and so on)


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'he 3MIS Input 3,8ects

Air6ow Model3MIS Simulation3MIS /one &ata3MIS Surface &ata3MIS Standard onditions for rac5 &ata3MIS Air 9low: rac5 3MIS Air 9low:3pening3MIS Site ind onditions

3MIS .!ternal ;ode3MIS P Array3MIS P 4alues


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Input 3,8ect &escription3MIS Simulation de nes basic run parameters for the airow calculation and speci es whether wind pressure

coe9cients are input by the user or, for rectangularbuildings, calculated by the program (@ew 7eature for/ersion :1:1:)1

3MIS /one &ata ob=ect speci es the ventilation controlthat applies to all of the openable e#terior windows anddoors in the corresponding thermal zone1

3MIS Surface &ata indicates whether a heat transfersurface (wall, window, etc1) has a crac or opening andreferences a 3MIS Air 9low: rac5 or 3MIS Air9low:3pening ob=ect that gives the air ow characteristicsof that crac or opening1 *+ -. .urface 'ata can also beused to specify individual ventilation control for openablee#terior windows and doors1


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Input 3,8ect &escription

" ont-$3MIS Standard onditions for rac5 &ata is used to normalize crac information that isbased on measurements of crac air ow1-f wind pressure coe9cients are input by theuser, 3MIS Surface &ata also has anassociated 3MIS .!ternal ;ode , that, via the

3MIS Site ind onditions , 3MIS PArray and 3MIS P 4alues ob=ects, gives thewind pressure distribution vs1 wind direction forthat node and, implicitly, for the crac s andopenings in the e#terior surfaces associatedwith that node1


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hat 3MIS7.nergyPlus

an &oAir ow through crac s in e#terior or interzone surfacesAir ow through crac s around windows and doors@atural ventilation, i1e1, air ow through open (or partiallyopen) e#terior windows and doors

*ontrol of natural ventilation based on inside outsidetemperature or enthalpy di erenceodulation of natural ventilation to prevent large temperature

swings-nterzone air ow, i1e1, air ow through open interzonewindows and doors, and through crac s in interzone surfaces

Account for how air ow depends on buoyancy e ects andwind pressureAccount for how wind pressure depends on wind speed, winddirection and surface orientation


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hat 3MIS7.nergyPlus

annot &oAccount for the e ect of supply2air and or return2air owsin a zone when an 5/A* air system is present and isoperating1 6his means that the *+ -. air ow simulationwill give reliable answers only if there is no 5/A* system,the 5/A* system is o , or the 5/A* system is hydronic1Air ow through crac s around windows and doors1

Air circulation and or air temperature strati cation withina thermal zone1 7or e#ample, you should not try to dividea high space, such as an atrium, into subzones separated

by arti cial horizontal surfaces that have crac s oropenings with the e#pectation that *+ -. "nergy!lus willgive you a realistic temperature in each subzone and or arealistic air ow between subzones1


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hat 3MIS7.nergyPlus

annot &o " ont-$i2directional ow through large horizontalopenings1 .ee discussion below under *+ -.Air 7low&+pening1

7low through ducts or other elements of an5/A* air system1!ollutant transport1 6here are some pollutant2related inputs but they are not used1

Air2 ow networ s that are not connected1 6hismeans you cannot model air ow in two ormore separate groups of zones1


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Simple 3MIS Air 9low

;etwor5

Zone-1

indo%,-

Zone-2

Zone-3

indo%,.

indo%,/

"oor,.-

"oor,-/

ExternalNode,.

ExternalNode,-


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Illegal 3MIS Air 9low

;etwor5 indo%,. indo%,-

indo%,/indo%,0

"oor,-/

Zone-1 Zone-2

Zone-3

ExternalNode,.

ExternalNode,-

ExternalNode,/


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orrecting the Illegal

3MIS Air 9low ;etwor5 6he previous slide shows an Air2 ow networthat is illegal in *+ -. because there are twoseparate groups of zones with air ow (one

group is Bone2C plus Bone2D and the other isBone2:)1 6o ma e this legal a lin (a crac oropening) between Bone2: and Bone2C wouldhave to be added or the zones in one of thegroups would have to be 3turned o 4 as *+ -.zones1


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;ew 3MIS 9eature

4ersion 1-1-1


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3MIS Input

AI+!L ; M DEL, C MIS' ./ Ai !lo"Model-al%e

C MIS SIMULA)I N, -EN), ./ -en(ila(ion sim%la(ion &on( ol N B L, ./ Boll%(ion sim%la(ion &on( ol N C NC, ./ Con&en( a(ion sim%la(ion &on( ol 1?>>, ./ Unde / ela a(ion fa&(o dimensionlessF 1?>E/> , ./ A sol%(e flo" (ole an&e @g$sF 1?>E/> , ./ +ela(ive flo" (ole an&e dimensionlessF 1?>E/> , ./ E o es(ima(e fo (o(al flo" *e :one @g$sF 1, ./ S(a ( n%m e of i(e a(ions 1?>E/> , ./ Limi( fo lamina flo" a** o ima(ion BaF

1, ./ !lag fo %sing old * ess% es >, ./ !lag fo * ess% e ini(ia(ion >>, ./ Ma im%m n%m e of i(e a(ions 1>?>, ./ +efe en&e 0eig0( fo e&o ded "ind da(a mF >?1 , ./ ;ind velo&i( * ofile e *onen( dimensionlessF Eve #> Deg ees' ./ C MIS CB A++AJ Name


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3MIS Input " ont-$C MIS SI)E ;IND C NDI)I NS, >?>, ./ ;ind di e&(ion degF >?2>, ./ Blan a ea densi( dimensionlessF >?1K, ./ E *onen( of ;ind velo&i( * ofile dimensionlessF >?>' ./ S% o%nding %ilding 0eig0( mF

C MIS SI)E ;IND C NDI)I NS, 1K>?>, ./ ;ind di e&(ion degF >?2>, ./ Blan a ea densi( dimensionlessF >?#2, ./ E *onen( of ;ind velo&i( * ofile dimensionlessF 1 ?>' ./ S% o%nding %ilding 0eig0( mF

C MIS EX)E+NAL N DE, N!a&ade, ./ Name 1?>' ./ %(side Boll%(an( Con&en( a(ion !a&(o dimensionlessF ? ? ? C MIS EX)E+NAL N DE, ;!a&ade, ./ Name 1?>' ./ %(side Boll%(an( Con&en( a(ion !a&(o dimensionlessF


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3MIS Input " ont-$

C MIS S)ANDA+D C NDI)I NS ! + C+AC DA)A, 2>?>, ./ S(anda d (em*e a(% e fo & a&@ da(a CF 1>1?#2, ./ S(anda d a ome( i& * ess% e fo & a&@ da(a @BaF ?>' ./ S(anda d 0%midi( a(io fo & a&@ da(a g$@gF

C MIS AI+ !L ;3C+AC , C+/1, ./ Name >?>1, ./ Ai mass flo" &oeffi&ien( @g$sF >? , ./ Ai mass flo" e *onen( dimensionlessF 1?>, ./ C a&@ leng(0 mF >?>, ./ Boll%(an( 1 !il(e Effi&ien& dimensionlessF >?>, ./ Boll%(an( 2 !il(e Effi&ien& dimensionlessF >?>' ./ Boll%(an( # !il(e Effi&ien& dimensionlessF


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3MIS Input " ont-$ C MIS AI+ !L ;3 BENING, ;i *en1, ./ Name >?>>1, ./ Ai Mass !lo" Coeffi&ien( ;0en ;indo" o Doo Is Closed @g$s/mF >? , ./ Ai Mass !lo" E *onen( ;0en ;indo" o Doo Is Closed dimensionlessF 1, ./ ) *e of la ge ve (i&al o*ening 6L- < >?>, ./ E ( a & a&@ leng(0 fo L- ( *e 1 "i(0 m%l(i*le o*ena le *a mF 2, ./ N%m e of *ening !a&(o -al%es

>?>, ./ *ening fa&(o 1 dimensionlessF >? , ./ Dis&0a ge &oeffi&ien( fo o*ening fa&(o 1 dimensionlessF >?>, ./ ;id(0 fa&(o fo o*ening fa&(o 1 dimensionlessF 1?>, ./ Heig0( fa&(o fo o*ening fa&(o 1 dimensionlessF >?>, ./ S(a ( 0eig0( fa&(o fo o*ening fa&(o 1 dimensionlessF 1?>, ./ *ening fa&(o 2 dimensionlessF >? , ./ Dis&0a ge &oeffi&ien( fo *ening fa&(o 2 dimensionlessF 1?>, ./ ;id(0 fa&(o fo fo *ening fa&(o 2 dimensionlessF 1?>, ./ Heig0( fa&(o fo fo *ening fa&(o 2 dimensionlessF

>?>, ./ S(a ( 0eig0( fa&(o fo fo *ening fa&(o 2 dimensionlessF >, ./ *ening fa&(o # dimensionlessF >, ./ Dis&0a ge &oeffi&ien( fo fo *ening fa&(o # dimensionlessF >, ./ ;id(0 fa&(o fo fo fo *ening fa&(o # dimensionlessF >, ./ Heig0( fa&(o fo fo fo *ening fa&(o # dimensionlessF >, ./ S(a ( 0eig0( fa&(o fo fo fo *ening fa&(o # dimensionlessF ?

??


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3MIS Input " ont-$C MIS Z NE DA)A, ;ES)OZ NE, ./ Name of Asso&ia(ed )0e mal Zone ;indo"-en(S&0ed, ./ -en( )em*e a(% e S&0ed%le )em*e a(% e, ./ -en(ila(ion Con( ol Mode >?#, ./ Limi( -al%e on M%l(i*lie fo Mod%la(ing -en(ing *en !a&(o dimensionlessF ?>, ./ Lo"e -al%e on Inside$ %(side )em*e a(% e Diffe en&e fo Mo del(aCF 1>?>, ./ U**e -al%e on Inside$ %(side )em*e a(% e Diffe en&e fo Mo del(aCF

>?>, ./ Lo"e -al%e on Inside$ %(side En(0al* Diffe en&e fo Mod%l P$@gF #>>>>>?>, ./ U**e -al%e on Inside$ %(side En(0al* Diffe en&e fo Mod%l P$@gF *(ional -en(ing S&0ed%le'

C MIS SU+!ACE DA)A, S% fa&eO1, ./ Name of Asso&ia(ed Ene g Bl%s S% fa&e C+/1, ./ Ai !lo" C a&@ o *ening ) *e S!a&ade, ./ E (e nal Node Name 1' ./ C a&@ A&(%al -al%e o ;indo" *en !a&(o fo -en(ila(ion dimensionlessF

C MIS SU+!ACE DA)A, ;indo"1, ./ Name of Asso&ia(ed Ene g Bl%s S% fa&e ;i *en1, ./ Ai !lo" C a&@ o *ening ) *e S!a&ade, ./ E (e nal Node Name >? ' ./ C a&@ A&(%al -al%e o ;indo" *en !a&(o fo -en(ila(ion dimensionlessF


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3MIS Input " ont-$C MIS C* A++AJ, Eve #> Deg ees, ./ Name 1>?>, ./ +efe en&e 0eig0( fo CB da(a mF >, ./ ;ind di e&(ion 1 degF #>, ./ ;ind di e&(ion 2 degF ? 2 >, ./ ;ind di e&(ion 1> degF

#>>, ./ ;ind di e&(ion 11 degF ##>' ./ ;ind di e&(ion 12 degF

C MIS C* -ALUES, Eve #> Deg ees, ./ C MIS CB A++AJ Name N!a&ade, ./ E (e nal Node Name >? >, ./ C* val%e 1 dimensionlessF >? K, ./ C* val%e 2 dimensionlessF >?> , ./ C* val%e # dimensionlessF

/>? , ./ C* val%e dimensionlessF />? , ./ C* val%e dimensionlessF />? 2, ./ C* val%e dimensionlessF />?# , ./ C* val%e dimensionlessF />? 2, ./ C* val%e K dimensionlessF />? , ./ C* val%e Q dimensionlessF />? , ./ C* val%e 1> dimensionlessF >?> , ./ C* val%e 11 dimensionlessF >? K' ./ C* val%e 12 dimensionlessF


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4entilation ontrol ModeVentilation Control Mode * ? types of natural ventilation control)

6 out E outside air temperature 6 zone E previous time stepGs zone air temperature 6 set E /ent 6emperature .chedule value5 zone E speci c enthalpy of zone air

5out

E speci c enthalpy of outside air'emperature & 6he windows doors are opened if 6 zone H 6 out and 6 zone H 6 set and /enting .chedule allows venting1.nthalpic: 6he windows doors are opened if 5 zone H 5 out and

6 zone H 6 set and /enting .chedule allows venting1onstant & Whenever /enting .chedule allows venting, the

windows doors are open, independent of indoor or outdoorconditions1;o4ent & 6he windows doors are closed at all times independentof indoor or outdoor conditions1 /enting .chedule is ignored inthis case1


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4entilation Schedules9ield: 4ent 'emperature Schedule

6he name of a schedule of zone2air temperature set points thatcontrols opening of a window door to provide natural ventilation1

6his schedule consists of wee s and days, with the days containingthe ventilation temperature setting in I* for each hour of the day1

6his ventilation temperature is the temperature above which thewindow door will be opened if the conditions described under thefollowing /entilation *ontrol ode are met1 J6his opening controllogic does not e#ist in the original *+ -. program1K

9ield: 4enting Schedule 6he name of a schedule that speci es when venting through thiswindow door is available1 A zero schedule value means venting isnot allowed1 A value greater than zero means venting can occur ifother venting control conditions (speci ed by /entilation *ontrol

ode and /ent 6emperature .chedule) are satis ed1 6his scheduleshould not be confused with /ent 6emperature .chedule1


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Summary

Air movement between spaces in"nergy!lus can either rely on user2de ned $uantities or more detailedcalculations.imple modeling statements&mi#ing, cross mi#ing, and ventilation*+ -. lin provides more detailedanalysis of interzone air ow as wellas more sophisticated calculation ofin ltration

lecture 11 air exchange

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