1-9 basic flow regulation

8/18/2019 1-9 Basic Flow Regulation

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PART 1

Module 1/9

Basic Flow Regulation


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Objectives:

• To study the methods of regulating airows

• To study the methods of regulatingwater ows

• To study the checks that must becarried out on a system before it is

balanced / commissioned• To study the principles of proportional

balancing


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INTRO!"TION TO MO!#$Any air or water system installed in a building will have beendesigned to give a specic performance. By regulating owwithin a system we can set up the system so that it gives there!uired design performance. This principle is known asproportional balancing.

"n this module we shall#• $iscuss the methods used for air ow rate regulation

• $iscuss the methods used for water ow rate regulation

• $iscuss the checks that should be carried out on a systembefore it is balanced.

• $iscuss the method of proportionally balancing a system


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1% AIR F#O& R$'!#ATION

'ene(al

Airow is regulated by a device called adamper. "magine blowing down a small piece oftube. "f you put your nger completely over theend of the tube no air will come out. "f you put

your nger partly over the end the tube someair will come out. "f you take your nger awayall of the air that you are blowing into the tubewill come out. "n this instance your nger isacting as a damper.


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T)*es o+ a,*e(s• The simplest form of damper is basically a plate mounted on a

spindle as shown in the sketch in %igure & below.• 'hen the plate is in the hori(ontal position there is virtually no

resistance to air ow. As the plate is moved from the hori(ontal to thevertical air ow is progressively regulated until virtually no ow isallowed past the plate.

• The plate damper is commonly used in small diameter circularductwork. )nfortunately due to its simple construction the platedamper is crude and can give downstream distortion of air ow when

it is partly closed. %or that reason various other types of damperhave been developed. The main types of dampers in common use inair systems are#

* O**osed blade

* I(is

* #ouv(e

• +et us look at each type in turn.

Figu(e 1: Plate a,*e(


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T)*es o+ a,*e(s

O**osed Blade a,*e(

• As you can see this type of damper is made up of a series ofplate dampers arranged so that they will swivel in alternatedirections.

• This type of damper is particularly recommended forrectangular ducts because it gives a wide setting range.

• Blades can either be at plate or aerofoil section the lattergiving less turbulence of the airow note however that theregulating mechanism usually has an arrow which must point inthe direction of airow.

Figu(e -: O**osedBlade a,*e(


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T)*es o+ a,*e(s

I(is a,*e(

• "t is made up of a diaphragm of overlapping leaves connectedto an e,terior ring.

• Turning the ring in one direction opens the diaphragm whilst-turning the ring in the other direction closes the diaphragm.This is also the principle used in the aperture control in a

camera lens.• This type of damper is particularly recommended for circular

ductwork because it gives a very wide setting range.

• This type of damper can be calibrated and graphs are producedby manufacturers. A pressure drop can be measured and this

plotted on the graph to give an airow rate.

Figu(e .: I(isa,*e(


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T)*es o+ a,*e(s

#ouv(e a,*e(

• A louvre damper is made up of a series of blades ,ed to apivoted frame.

• As the frame is pivoted into the air stream the blades willcreate a resistance and hence a lower air ow.

• This type of damper is particularly useful to deect air ow

from a main duct to a grille.


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O(ice Plate

• An alternative method of regulating air ow in a duct

is the orice plate.• The main disadvantage with an orice plate is that it

will not give variable ow regulation0 it must be si(edto give a particular air ow.

• 1ipe line mounted orice plates were described inmodule 2. A duct mounted orice plate is identical toa pipeline mounted plate. Alternatively a perforatedplate can be used.

• This type of device is usually installed in ductbranches close to the fan in order to reducee,cessive static pressures hence simplifying thebalancing procedure.


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a,*e( Positions$ampers should be installed in the following positions to enable asystem to be correctly regulated#

&. At each air handling unit or fan in the main duct.

3. "n each branch duct.

4. At each grille or terminal. "deally the damper should be inthe connecting duct to the grille however this is not always

possible due to lack of space. "n this instance grilles andterminals should have an in-built damper which can bead5usted without undue e6ects on the terminal itself.

%igure 7 below gives a schematic layout of an air system showingthese recommended damper positions.

Figure 4: RecommendedDamper Positions


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Fi(e a,*e(s• 8arious walls within a building can be protected with a type of

insulation to prevent the spread of re.

• 'hen a duct passes through a protected or re rated wall it can forman easy passage for re.

• A re damper is a special type of damper that is used to prevent this.

• %igure 9 below shows a typical re damper. :ou can see that it consistsof a folding shutter section and a fusible link. "f the temperature within

the duct rises above a certain temperature the fusible link will meltand the shutter will drop. ;nce the shutter has dropped it will preventthe spread of re through the duct. This type of damper is known as amanual re damper.

• Automatic re dampers are also available where the fusible link isreplaced by a solenoid linked to the building re alarm system. 'hen

a re alarm occurs in the building the re alarm system will releasethe solenoid and the shutter will drop.


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Access• "t is important that all re dampers are

accessible for resetting purposes.• "t is also highly desirable for duct access

doors to be tted ad5acent to all multi-bladeregulating dampers.

• "t is essential if the damper is motorised.


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T$T 2OOT)*es

• The usual method of measuring air ow from a grille is to use either an anemometer ora velometer discussed in module 2 however it can be very di=cult to obtain anaccurate reading. By using a test hood air from a grille can be directed through a ,edarea opening where the air velocity can be measured and hence an air volume ow ratethrough the hood and the grille can be obtained.

• The simplest form of hood is a stub duct si(ed to cover the grille. Air velocity ismeasured across the duct opening using an anemometer hence the volume ow of the

air through the duct and hence the grille can be obtained. This type of hood is usuallymade from strong cardboard or plastic sheet and can be easily fabricated up on site.

• A far more accurate type of hood is the calibrated hood. "n this type of hood all of theair from the grille is directed into a circular >Throat> via a converging cone theanemometer head being located in the centre of the throat. The anemometer reading isproportional to the volume ow rate through the hood. ?anufacturers of these types ofhood supply a calibrated curve from which the volume ow corresponding to the

velocity can be read. This type of hood imposes a resistance on the grille. @owever thisdoes not normally cause a problem with proportional balancing because relativereadings are taken. @owever to prevent this occurring velocities through the throatshould be limited to between & and 7 metres per second to avoid undesirable e6ect ofhood resistance.

• +arge hoods whether calibrated or of the stub duct type can be very di=cult to handle.


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T$T 2OO"alib(ation

• The performance of a hood whether a simple or calibrated type mustbe checked to ensure that the readings obtained are meaningful. Theusual method of checking hood performance is#

&. "dentify a grille which is served by a straight length of ductwork.

3. Take a reading at the grille using the hood and obtain a volume ow rate forthat grille.

4. arry out a pitot scan in the branch duct serving the same grille and againobtain a volume ow rate.

7. ompare the hood volume ow rate and the duct volume ow rate.

9. "f the two readings are not identical divide the duct ow rate by the hoodow rate and use the obtained gure as a conversion factor for calculatingthe actual volume ow rate for all velocity readings taken on the system

using the hood.• Always ensure that the scan is taken in the duct serving that grille only0

if a reading is taken in a branch serving two grilles a useful comparisoncannot be made.

• "f the conversion factor is greater than &.3 or less than .C the hoodshould not be used0 a factor outside this range implies an inaccurate

reading at the hood.


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-% &AT$R F#O& R$'!#ATION Flow Regulation evices

•'ater ow rate in a system is regulated by means of valves. Themost common valve used in a pipework system is the gate valvehowever although this type of valve is good for isolation it is notparticularly suitable for regulation. This is because#

* The gate valve cannot be locked in position once a ow rate has been set

* The regulation o6ered by a gate valve is very crude. A lockable type of

gate valve known as the lockshield valve is often used at radiators andin sub-branches but as stated already the regulation o6ered is crude.

• The double regulating valve is normally used in pipework systemsfor ow regulation. This type of valve is a double regulating globevalve.

• "t can be tted with a pressure tapping either side of the valve seat toform a measuring device known as a variable orifce doubleregulating valve. $ouble regulating valves without pressuretappings can be close coupled with an orice plate to form ameasuring station. A far more accurate pressure drop reading can beobtained across the combination than by using a variable oricedouble regulating valve alone.


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-% &AT$R F#O& R$'!#ATION Position o+ Flow

Regulating andMeasu(ing evices

• The positioning of owregulating and measuring

devices is criticallyimportant. "f they areincorrectly positioned it canbe almost impossible toobtain a correct proportional

balance on a system.

•%igure D shows a typicalsystem schematic whichindicates the usual positions.

Figu(e 3: T)*ical &ate( )ste, c4e,atic


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-% &AT$R F#O& R$'!#ATION Position o+ Flow Regulating and Measu(ing evices

• %low regulating devices with corresponding ow measurement devicesshould be installed in the following positions as a minimum#

* "n the main pipe

* "n each branch pipe

* "n each sub branch

* At each terminal. +ockshield valves are normally used at radiators

however double regulating valves and measuring devices should beused in all other instances.

• The principal re!uirement for the positioning of a ow measurementdevice is a certain minimum length of straight pipework both upstreamand downstream of the device in order to minimise uid turbulence. Theupstream pipework is by far the more critical0 all local ttings which could

cause disturbances should be positioned downstream wherever possible.Advice should be obtained from the ow measurement devicemanufacturer regarding the minimum straight lengths upstream anddownstream of the device. Typical values are & pipe diameters upstreamand 9 pipe diameters downstream. These gures are recommendedalthough manufacturers say that a 9 up and 3E down should be regardedas absolute minimum. Below this measurement accuracy cannot be

guaranteed.


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.% PR$ "OMMIIONIN'"2$"5

• 1re-commissioning checks are a very

important part of the balancing andcommissioning procedure. By carrying outthese checks you will be able to ensure thatthe system has been installed correctly andcan be balanced e6ectively.

• Feneral lists of pre-commissioning checks forair and water systems are given below. The

pre-commissioning checks listed are notdenitive0 they are a minimum. 8ariouscommissioning companies will have their ownin-house check lists.


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AIR 6T$M esign In+o(,ation

The following design information is needed#* +ayout drawings of systems showing all ductwork runs and e!uipmentlocations including dampers and other ow measuring devices.

* Gchematic drawings of systems showing -design air volume ow ratesand cross sectional areas at air handling units supply fans e,tract fansmain branch and sub branch ducts and all terminals0 also design staticpressure loss across lters cooling coils heating coils and silencers.

* %an characteristic curves including full details of fan design speed.* "dentity of lter media.

* ontrols schematic wiring diagram and description of system operationincluding details of all interlock arrangements fuse ratings design timesfor staged starting and motor run up control design values for fan speedcontrol.

Important Note:I, or any reason, system schematic drawings are notavailable, ull details o system design ow rates and static

pressure drops must still be obtained. Duct cross sectionalareas can be calculated rom the duct sies given on thesystem layout drawings. N!"# that these must be confrmedby actual on site measurement, do not assume that the duct

sie shown on the drawing is correct.


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AIR 6T$M Ins*ections to be "a((ied Out on ite

"he ollowing checks and inspections should be carried out on site prior to starting a an.

• "4ec7 t4at t4e building is co,*lete8 +alse ceilings *a(titionsdoo(s and windows s4ould 4ave been installed windows s4ould beglaed and t4e building s4ould be a(c4itectu(all) sealed%

• "4ec7 t4at all ai( 4andling units +ans da,*e(s (e da,*e(slte(s and te(,inals 4ave been co((ectl) installed%

• "4ec7 t4at t4e ductwo(7 s)ste, is co,*lete and clean%• "4ec7 t4at all access doo(s at ai( 4andling units +ans and

ductwo(7 a(e co((ectl) tted%

• "4ec7 t4at ai( lea7age tests on t4e ductwo(7 4ave been co,*leted%

• "4ec7 t4at t4e(e is ade;uate access to all e;ui*,ent%

• &al7 a(ound t4e s)ste, and +ull) o*en all da,*e(s (e da,*e(s

and te(,inals% F(es4/(eci(culation ai( da,*e(s s4ould be set ineit4e( t4e +ull +(es4 ai( o( +ull (eci(culation ai( *osition%

• "4ec7 t4at local isolato(s at *lant a(e +ull) o*e(ational%

• T4at all +use (atings a(e co((ect%

• "4ec7 t4at ,oto( sta(te( ove(loads 4ave been co((ectl) set%

• "4ec7 t4at cont(ols s)ste, is co,*lete and +ull) o*e(ational andt4at t4e(e is an elect(ical su**l) to t4e cont(ol *anel%


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AIR 6T$M Once t4e above c4ec7s 4ave been ca((ied out t4e +ollowing *(ocedu(e s4ouldbe +ollowed:

• Note +an and ,oto( t)*e se(ial nu,be( ,anu+actu(e( *ulle) and belt t)*eand sies%• "4ec7 sa+et)


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&AT$R 6T$M esign In+o(,ation

The following design information is needed#* +ayout drawing of systems showing all pipework runs and

e!uipment locations including valves and ow measuring devices.

* Gchematic drawings of systems showing design water volumeow rates at pumps main branch and sub branch pipes and allterminals0 also design static pressure loss across e!uipment and

terminals.* 1ump characteristic curves including full details of pump design

speed.

* ontrols schematic wiring diagram and description of systemoperation including details of all interlock arrangements fuseratings design times for stages starting and motor run up control..

Important Note:

I or any reason system schematic drawings are notavailable, ull details o system design ow rates andstatic pressure drops must still be obtained.


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&AT$R 6T$M Ins*ections to be "a((ied Out on ite

"he ollowing checks and inspections should be carried out on site prior to starting a an.

• "4ec7 t4at t4e building is co,*lete8 +alse ceilings *a(titions doo(sand windows s4ould 4ave been installed windows s4ould be glaedand t4e building s4ould be a(c4itectu(all) sealed%

• "4ec7 t4at all boile(s *u,*s (adiato(s c4ille(s +an coil units andan) ot4e( te(,inals 4ave been co((ectl) installed%

•"4ec7 t4at 4)d(aulic tests on t4e *i*ewo(7 4ave been co,*leted• "4ec7 t4at t4e *i*ewo(7 s)ste, is co,*lete 4as been us4ed inacco(dance wit4 t4e s*ecication=and 4as been lled%

• ent t4e s)ste,% ee ,odule 3 +o( details%

• "4ec7 t4at t4e(e is ade;uate access to all e;ui*,ent%

• &al7 a(ound t4e s)ste, and +ull) o*en all valves w4ic4 a(e designedto be no(,all) o*en w4et4e( isolating o( (egulating%

• "4ec7 isolating valves designed to be closed du(ing no(,al o*e(ationa(e closed%

• "4ec7 t4at local isolato(s at *lant a(e +ull) o*e(ational%

• "4ec7 t4at all +use (atings a(e co((ect%

• "4ec7 t4at ,oto( sta(te( ove(loads 4ave been co((ectl) set%

• "4ec7 t4at cont(ols s)ste, is co,*lete and +ull) o*e(ational and t4at

t4e(e is an elect(ical su**l) to t4e cont(ol *anel%


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&AT$R 6T$M Once t4e above c4ec7s 4ave been ca((ied out t4e +ollowing *(ocedu(e s4ouldbe +ollowed:

• Note *u,* and ,oto( t)*e se(ial nu,be( ,anu+actu(e( and i+ tted *ulle)

and belt t)*e and sies%• "4ec7 all sa+et) as*ects%• "4ec7 t4at *u,*>s? (otate in t4e co((ect di(ection%• ta(t t4e *u,*%• Pa(tiall) close t4e s)ste, ,ain valve%• "4ec7 cu((ent d(awn b) *u,* and ensu(e t4at it is not e@ceeding t4e C design

+ull load value%• O*en ,ain valve until t4e *u,* ,oto( cu((ent is close to its design valve%

• "4ec7 *u,* and ,oto( s*eed%• Measu(e t4e total ow (ate at t4e *u,* b) using t4e s)ste, ,ain ,easu(ing

device% T4e +an s4ould be delive(ing at least 11CD o+ design%• I+ t4e total ow (ate is less t4an 11CD o*en t4e ,ain valve w4ilst ensu(ing t4at

t4e *u,* ,oto( design +ull load cu((ent is not e@ceeded until a**(o@i,atel)11CD is ac4ieved% I+ t4e *u,* will not delive( at least t4e design volu,e wit4t4e ,ain valve +ull) o*en t4e cause s4ould be investigated and (esolved% T4ist)*e o+ investigation will be cove(ed in a late( ,odule%

• Measu(e t4e *(essu(e diGe(ential ac(oss t4e *u,* using *(essu(e gauges andca(() out a closed 4ead test to *lot t4e actual *u,* cu(ve%• Measu(e t4e wate( ow (ate at eac4 te(,inal using t4e tted ,easu(ing device%• "a(() out a *(o*o(tional balance in acco(dance wit4 t4e ,et4od detailed in *a(t

E o+ t4is ,odule%• Be *(e*a(ed to sto* t4e *u,* and vent t4e s)ste, a nu,be( o+ ti,es i+ ai( is

slow to clea(% Onl) co,,ission and (eco(d t4e nal (eadings w4en t4e s)ste, isco,*letel) +(ee o+ ai(%


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E% PRIN"IP#$ OF PROPORTIONA# BA#AN"IN'

'ene(al

• The >@arrison Fibbard> method ofproportional balancing is recognised as beingthe simplest and most e6ective way to

regulate an air or water distribution system.;ne of the great advantages is that once adamper or valve has been set it should notneed to be altered again.

• 'ith this method it is not necessary to workwith actual design ow rates percentages areused instead.


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Basic P(inci*les

• To balance one terminal against each other therefore it is only

necessary to ad5ust the regulating devices to ensure that theterminals share the total ow in the correct proportions.

• "t does not matter within limits what the actual system volumeow rate is. After a system has been proportionally balancedand the correct system ow rate is established the design ow

rate will be delivered to each terminal since each has been setto take itsI correct share.


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Balancing P(ocedu(e&. arry out system checks described in part 4 of this module.

3. %ully open all valves in the system.

4. ?easure the ow to each terminal and the total system ow using owmeasuring devices and a manometer. onvert the ow rates to percentages ofdesign. Jemember to use the volume s!uare law. see module 2 for watersystems.

7. "f the total ow rate measures greater than &4H throttle the system main owregarding valve until a ow rate of below &4H of the design value.

9. +ocate the terminal that is discharging the least percentage of design. This is

generally the last terminal in the run. "f it is. not ad5ust the regulating device atthe last terminal until it is working with the same percentage as the lowest one.

D. The last terminal is then used as an inde, to which the ows from the otherterminals are compared.

2. ?easure the ow from the terminal ne,t to the inde, and calculate thepercentage ow. Ad5ust the regulating device at this terminal to make thepercentage ow as close as possible to that of the inde,.

C. Jepeat 2 above for the ne,t terminal and so on until the proportions through allterminals have been brought into line. As regulating devices are closed downthrough the system more ow will be driven towards the downstreamterminals and the volume to the inde, terminal will rise. This does not a6ectthe balancing procedure since each terminal being ad5usted is related in turnwith the inde,.

K. 'hen all the terminals have been balanced to the inde, carry out a total scanof readings. The terminals should have an e!ual percentage of the design owrate.


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$@a,*le• +et us look at a simple e,ample having four fan coil units and a

pump.

• A measuring station has been installed at each fan coil unit andin the main pipe. The design system ow rate is 3.7 kg/s eachfan coil unit re!uired .D kg/s.

An initial scan reveals the following#1 2 3 4

Main 1 - . E

$esign%low

3.7 kg/s .Dkg/s .D kg/s .D kg/s .D kg/s

Actual%low

3.D kg/s &.3 kg/s .C kg/s .7 kg/s .3 kg/s

H $esign%low

&CH 3H &44H D2H 44H


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$@a,*le

• "n this case the inde, terminal is at the end of the run. 'enow need to balance the ne,t least favoured terminal to beinde,ed to bring it in line with the inde,. Because we areclosing the regulating device at this terminal the ow willrise through the inde,#

• 'e now need to balance the ne,t least favoured terminalalong to bring it in line with the inde,#Balance

3 to 7&44H

Throttled toD4H

77HD3H

Main 1 - . E

Balance4 to 7 D2H Throttled to 79H 44H77H


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$@a,*le

Main 1 - . E

Balance& to 7

3H Throttled to

&&H

D3H&H

• 'e can nally bring the last terminal into line with theinde,#-

• "f we take a system scan now we would nd the following#%inalGcan H

&&H &&H &3H &&H &H

Actual%low Lg/s

3.73 kg/s .DD kg/s .D&3 kg/s .DD kg/s .D kg/s


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$@a,*le

• :ou can see from the e,ample that once a terminal has beenbalanced to the inde, terminal itIs ow rate will rise inproportion with the inde,.

• The procedure given is also used for large systems withbranches and sub-branches. "n this case each sub-branch istreated as a separate circuit that is if the sub-branch isproportionally balanced. ;nce each sub-branch has beenbalanced the branches are proportionally balanced againsteach other again by comparing against the inde, branchuntil the system has been nally balanced.

• 'hether you are balancing an air-system or a waste systemyou must always work from the inde, terminal back towardsthe fan or pump.

1-9 basic flow regulation

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