equipment room piping practice

8/12/2019 Equipment Room Piping Practice

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Equipment RoomPiping Practice

TECHNICAL MANUALTEH-1275A


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' ' ' . N "OINT

WR,O. . ,G,~ T I I PU I I ~ D -

"0 Oft,,,,,l i l YV ;JR 0 N -

~ Tc\JIt 'VI D-t40 01.,.,. ..... UTV

Figure 2 - RIGHT AND WRONG PUMP SELECTIONS

System d i s t r i bu t i on pumps should be selected for system needs .

The l a r ge mult i - c i r cuited hydron i c system needs a pump se l ect ion that

wi l l help overcome c i rcu i td i s t

r ibu t i on problems .3 . PIPING SIZE AT PUMP SUCTION AND DI SCHARGE

Pipe s ize a t the pump suct i on and discharge should conform to

di s t r ibut ion main size; not to suct io n and discharge pump opening size.

TO D ' . . TII t"UTIO"l'1 INa. ~ Z

~ V","I / I I l l t D

,. .....01"l 'NIN6.W R O N , G P Il M " "'IPI"" So . . . . VIS'MST"'LL.O 'TO P'\,I _ ...... 1

NO I N C " . . . S S .

wt9NafTf t . \p \ ' . Wl'1' INnMllO'To 11'1,) , . . OfIIIt 'N. Slloa .

F I GURE 3 - RIGHT AND WRONG PUMP PIPE AND VALVE SIZING

Suction and di s charge p i ping (and va l ve s ) s ized to the pump

opening wor ks against system f l ow d i s t r i bution needs because of unwarranted

i ncreases in eq u i pment r oom pressu r e drop .


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4 . PUMP SUCTION PIPE LENGTH

The pump suct ion s t ra igh t" run pipe length shou l d be a t le a s t

S OIA. of suct ion pipe size t o insure good pump entry conditions ,

IG H T . '~ o o ' U M ~e.Nifty.

PIPING S U P P O RT .

W g O N G .I&It..C PUMP t N ~. .' NO ' P I IN,. ~ P O R 1

FIGURE 4 - RIGHT AND WRONG PUMP ENTRY CONDITI ONS

5 . PUMP PIPING SUPPORT

Pump piping suppo r t shou ld be provided as shown in Fig u re 4.

The pump should not serve as a piping anchor.

6. MULTIPLE PUMP CHECK VALVES

Check valves (c onvent ional , Triple Duty or Fl o Control)

shou l d be in s t a l led a t each pump discha r ge when mor e than one pump i s

u se d in the equipment r oom. This appl ies whether the addi t io na l pumps

are for standby, para l le l ope r a t ion or zone pumping.

RIQt= T J

INST '1.1. C"'l.e'll:. 011M U I . I ~, "UM., .S .

'N ONftlc. ,.c:.w.to I . . ' T QI IT .~ ~ M&J.NS T l t O w t U

FIGURE 5 - MULTIPLE PUMP CHECK VALVES

Trouble wi l l develop when check valves are not ins ta l led

because of reve r sed flow through non-operating pumps . When these pumps

are s t a r t e d, they must overcome a heavy flow ine r t i load and wi l l over-

load.


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* Piping arrangements with 3-Way control valves shown within this technical manual are provided by Bell & Gossett as referenceinformation of existing systems only. As an active participating member of ASHRAE, it is Bell & Gossetts recommendation thatengineers and system designers consult with the most current ASHRAE Standards for design guidance on Variable Flow Systemsor Constant Flow Systems as indicated in ASHRAE Standard 90.1 Section 6.5.4.

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F I GURE IV - Z -

UNWIU


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Figu r e V- 8 - MU LTIPLE INJECTIONPUMP RESET

On cold s t a r t up, the pumps a r e gradua l ly sequenced in u n t i l r e s e t

cond i t ions a re reached .

Mult ip le sma l l b o i l e r s are a l so used fo r r e s e t cont r o l . This p a r t i e -

u l a r method has the advantage of reducing b o i l e r standby l o s s dur ing l i g h t

loads .

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IO ILI II:

0_IoOll.fII

0 -

Figure V-9 - MULTIPLE BOILER RESET

In mul t ip l e b o i l e r r e s e t , only the opera t ing b o i l e r s are a t

temperature. Standby loss i s el iminated fo r the non-opera t ing bOi lers

r e s u l t i n g in lower opera t ing c o s t . During l i g h t load , only one b o i l e r i s

on as load o r r e s e t t empera ture requi rements i nc rease a d d i t i o n a l b o i l e r s

a r e sequenced on.

Boi le r c i r c u i t pumps a re o f t en used to provide cons tan t b o i l e r

f low, reduce c o n t r o l valve s i z e and provide a g a i n s t b o i l e r shock .


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VI. EQUIPMENT OR BOILER ROOM PIPING PRACTICE - CHILLER

1. CONSTANT CHILLER FLOW

I t i s important , for most c h i l l e r s , tha t a f a i r l y constant c h i l l e r

f l ow r a t e be es tab l i shed fo r good c h i l l e r load contro l . Unless precaut ions

are taken c h i l l e r sh or t cycle can occur with resu l t ing c h i l l e r problems .

Changing ch i l l er flow ra tes wil l occur with 2 way valve system

con t ro l .

Figure VI-l -

The c h i l l e r con t ro l i s temperature sens i t ive only and wil l goin to the same load con t ro l r ega rd less of flow r a te . Fo r a system design

t o f u l l load a t 300 GPM the temperature control wil l load the c h i l l e r

properly only a t 300 GPM. At 100 GPM flow past the c h i l l e r contro l pOin t ,

only 1/3 load i s r equi red for any given l oad tempera ture s igna l . The

c h i l l e r control cannot r ecognize the change in load caused by flow change,

however, and c h i l l e r l oad control i s upset .

The solut ion i s to provide a r e l a t i v e ly constant f low r a t e past

the c h i l l e r temperature load r eg i s t r a t i o n point . This can be accomplished

by e i ther of two methods.

1. Separate c h i l l e r pump

2 Diffe ren t ia l pressure con t ro l l ed bypass valve.


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Figure V I ~ 2~

l. W .. VV I . . V.c.oW rfilOI..

In Figure V I ~ l a cons tan t c h i l l e r flow r a t e i s e s t a b l i shed by

d i f f e r e n t i a l pressure con t ro l ac t iva t ion of a two way bypass valve . The

pressure d i f f e r e n t i a l cont r o l l e r i s s e t to mainta in a r e l a t i v e l y cons tan t

pressu r e drop constant f l ow) .

The d i f f e r e n t i a l pressure con t ro l i s of ten taken across a c a l i ~

brated o r f i c e mete r , r a t he r than the c h i l l e r i t s e l f .

The sepa r a t e c h i l l e r pump i s a l so employed t o provide cons tan t

c h i l l e r flow r ega rd les s of system f l ow change.

: K O I S T f I I I 6 ' T I ~ NP u ~ COMMON P IP I , e..,."II..5 o

CHII.LIIt 'N

t WAYVA I.V I

C O N ~ t r O I

1 0AO C.ONTROI.

Figure VI - 3


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The separa te chi l l er pump provides constant flow r a t e through the

c h i l l e r r ega rd less of system flow r a t e .

When system flow ra te r educes to l e s s than c h i l l e r flow r a t e , bypass

flow from c h i l l e r discharge to c h i l l e r re tu rn occurs through the common piping.

A mixture of system re tu rn with c h i l l e r discharge water occurs so tha t a t r ue

load s ta tement i s made to the c h i l l e r cont r ol device in terms of en te r ing

c h i l l e r temperature.

The sepa r a t e c h i l l e r pump removes c h i l l e r P.O. from system pumping

cons ide ra t ions . Removal of the c h i l l e r P. O. increases 2 way valve con t ro l

effec t iveness because of a reduct ion in t he main d i s t r i but i on pump head.

The separa te ly c i r cu la ted chi l le r with s l ight modif ica t ion, pe r

mits use of the c h i l l e r to cool down hot d i s t r i b u t i on mains while con t ro l l ing

i n l e t ch i l l er water temperatures.

2 . Immediate cool down of hot d i s t r i bu t i o n ma i n, Primary-Seconda r y - Separate

Chi l l e r Pump.

A common operat ion a l prob l em with combination heat ing - cooling

systems concerns switch ove r f r om heating t o cooling when res idu a l system

water temperatures are too high (ove r 90) to permit i n s t a n t c h i l l e r s ta r t up.

The separa te ly c i rcu la ted c h i l l e r can be used to cool down the

hot sys t em water by mi x ing of c h i l l e r discharge wate r with main system water

to provide al lowable c h i l l e r entry temperatures.

Ei ther of two methods can be used:

1. Const a nt c h i l l e r flow; reduced mai n flow.

2. Const a nt chi l l e r flow; constant system flow with

cont r ol led b l eed flow.


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P '

.sIoYoU1W V ' ~

StoI"1..1.. (J l .... 6E OVU, , . , p COIJTiItOl. . OM -.T

TlIo'I1 OY 0 ~ O I I 'TTeM UIoIDf. t o

Figu r e VI-6

cw n I .. 1t

The changeove r pump i l l u s t r a t ion above wil l gene r a l l y be a small

booste r pump pr oviding a system flow r a t e l e s s th an c h i l l e r f l ow r a t e .

Since system flow r a t e i s l e s s t ha n c h i l l e r flow a continuous

bypass f l ow occ u r s i n the Pri.mary - Seconda r y bypass mi xing wi th sys tem water

to provide mixed c h i l l e r entry water tha t i s less than 90

When system water temperature decrease s to 90 the ma in d i s t r i -

but ionpump

i s energized and normal system Oper a t ion

takes place .

VII. EQUIPMENT ROOM PUMPING HEATING/COOLIN G

1. S ta ndby Pump Prov i s io n

Most l a r ge he a t ing-cool ing systems have standby pump provis ion .

A common standby method i s i l l us t ra ted b e l o ~ :

Figure VU-l -

, M A I N . 01 STRI& V TION PUMP

TOWER P U MP

1 - - " I-l:


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The common standby pump i s se l ected to the g r ea te r f l ow requi r ement;

usual ly tower pump and i s checked aga ins t d i s t r i bu t i on head r equ i r eme nt by

use of system curve a naly s i s fo r actua l s t andby system d i s t r i bu t ion flow.

2 . Para l l e l ed Chil l e r ; Each Ch i l l e r with i t s own Pump.

On some l a r ge r systems. ch i l l e r s a r e placed in para l l e l ; each

ch i l l e r having i t s own c i r c u l a t io n pump . which i s a l so applied to system

d i s t r ib u t ion. As l oa d inc r eases ch i l l e r s are p l aced on the l ine , as l oa d

dec r eases chi l l e r s and th e i r pumps are cut of f .

CHILLER

C UT1 0 N IN PUMP S e.l.S.CTIOH

C H I L L e R

Fi gu re VI I -2 -

Cau t i on must be a ppl ied in pump se l ec t i o n an d op e r a t i o n f o r th i s

arrangement. The pump se l ec t ion can be ea s i l y made f o r f u l l load op e r a t ion ;

with both c h i l l e r s and th e i r pu mps in ope r a t i on. As an example :

Pu mp se l ec t ion i s t o be mad e for pa r a l l e l chi l l e r s ; eac h with i t s

own pump . Each ch i l l e r has 20 f t . P.O. at 200 G PM . The pip ing system , ex -

e lus ive of th e ch i l l e r s has 80 f t . P.O . a t 400 GPM

The se l e c t i on point for each pu mp i s then 100 f t . head a t 200 GPM

A system curve can be s t r uck f o r eac h pump using the point 100 f t .

@ 200 GPM


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Xylem Inc. 8200 N. Austin AvenueMorton Grove, Illinois 60053Phone: (847) 966-3700Fax: (847) 965-8379

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