Chiller Terminal Unit Performance 1

8/3/2019 Chiller Terminal Unit Performance 1

1/79

Dr. A.Dr. A. HammoudHammoud

BAUBAU--20072007

Terminal Unit PerformanceTerminal Unit Performance

ControlControl


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Type of Chilledwater s stem

Air cooled chilled water systemAir cooled chilled water system a er coo e c e wa er sys ema er coo e c e wa er sys em

MiniMini--Chilled Water SystemChilled Water System


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Air Cooled Water Chiller

,,

areaarea)


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Chilled water systemHeavy Duty & Long life cycleHeavy Duty & Long life cycleAir Cooled Lar e Ca acit Chiller Ran eAir Cooled Lar e Ca acit Chiller Ran eEconomical for large systems (highEconomical for large systems (high

Efficiency).Efficiency). ow oiseow oise an coi in ooran coi in oor

Part Load or full load (Part Load or full load (2525--5050--7575--100100%)%)

for capacity control.for capacity control.

Extra control & AccessoriesExtra control & Accessories

Application:Application:, ,, ,

Commercial Centre & Hotel,etcCommercial Centre & Hotel,etc


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ii

Closed area ( basement or very Hot place)Closed area ( basement or very Hot place)


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Water cooled chillerWater cooled chiller

a er coo e c er sys ema er coo e c er sys em


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Hot Air out

Fan stack

,,shaft and motorshaft and motor

Drifteliminator

Spray Nozzle

Spray area

Air InAir In

Cooling Tower Components


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COMPACT DESIGN SHELL AND TUBECOMPACT DESIGN SHELL AND TUBE

WATER COOLERSWATER COOLERS


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Air cooled-Condensingunit chillerwith multi-com ressors

for capacity control.


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Fan coil units

The Fan coil air flow rate in CFM rangesThe Fan coil air flow rate in CFM rangesucte

,, ,, ,, ,, ..

33 speeds (L ,M ,H)speeds (L ,M ,H)


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Chiller E uationsChiller E uations

Summerummer 2004004


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T iT iin Chiller systemin Chiller system

The size of the chiller is rated in tonnage or tons of refrigeration, where

the historic definition of a ton comes from making one ton of ice in 24:

Bth/hr)(TQ(gpm)500qW 11 ton =ton = 1212,,000000BtuIh; tons xBtuIh; tons x 1212,,000000== 500500 gpmgpm TT

2400012

Tons==

This is a good formula for estimating flows versusThis is a good formula for estimating flows versus TT..

T=T=1010..88FF


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In the condenserIn the condenser, the heat transferred to the condenser, the heat transferred to the condenser

wa er nc u es e ea rom e vapora or, p us e eawa er nc u es e ea rom e vapora or, p us e eaof compression.of compression.-- ,,

value ofvalue of 1414,,400400 Btu/h may be used as the total heatBtu/h may be used as the total heat

transferred to the condenser watertransferred to the condenser water..

Bth/hr)(TQ(gpm)500q W

TQ(gpm)50040041

T

Tons28.8gpm

=


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ExampleExample 11::

What chilled water flow will a 100 -ton chiller handle for a12F rise in water temperature and a 8F drop in tower

,(chiller flow):

;24

gpmTons

=

200F12Tgpm ===

T

Tons28.8gpm

=The flow in the condenser:The flow in the condenser:

36000128.8

gpm ==


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Chiller Pump discharge & PipeChiller Pump discharge & Pipesizingsizing

We could also using the basic equation:We could also using the basic equation:

./.. hrBTUinloadcoolingtheisLC

oun

arg edischpumporflowratetheisgpm

oropeempera uresoutinoo

.,


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ExampleExample

Suppose you want to calculate the required flow rateSuppose you want to calculate the required flow rate, ,, ,

required C.L. isrequired C.L. is 11 TonsTons--ref andref and T =T =1010..88 F, ( F, (66 CC ))

24Tons124Tons

;24

TgpmTons

=

o.

F10.8

T

gpm =

OrOr

gpm22.2RateflowThe=

issizepipeingcorrespondThe "2/1

artrom Black steel pipe is recommendedBlack steel pipe is recommended


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er u e ec oner u e ec on

11-- The re uired flow rate & headThe re uired flow rate & head

22-- U feed or down feed , If U feed s stem isU feed or down feed , If U feed s stem is

used ,the shut off head of the pump must beused ,the shut off head of the pump must be

to highest level, However if down feed system isto highest level, However if down feed system isused remember to include gravity assist flowused remember to include gravity assist flow

..


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Exam leExam le

Su ose ou want to calculate the re uired flow rateSu ose ou want to calculate the re uired flow rate

for a chiller centrifugal pump ,assuming that, the C.L.for a chiller centrifugal pump ,assuming that, the C.L.

.. . .. . --

included in the calculation of the total Cooling Load.included in the calculation of the total Cooling Load.

o ut on:o ut on:

F.810gpm50012000180 o

=

=

sizei encores ondiThe

gpmsc argeumpe


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y ca an co arrange eny ca an co arrange en


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The Fan coil inlet cold water temperature isThe Fan coil inlet cold water temperature is

..

water temperature inlet is aboutwater temperature inlet is about 4040 C.C.

Practically, the temperature change across thePractically, the temperature change across the

Fan coil varies fromFan coil varies from 55 --77 C C in the summer.in the summer.

difference is aboutdifference is about 1111CC..

Maximum water operating pressure is aboutMaximum water operating pressure is about 33 Bars.Bars.


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e an co a r ow rate n ranges rome an co a r ow rate n ranges rom

200200 300300 400400 600600 800800 andand12001200..

The Fan coil m is about =The Fan coil m is about = 22..44 m/tonm/ton. Based. Based

on temperature difference betweenon temperature difference between inin && outout

1010 F,F, which is aboutwhich is about 55..55 C.C.


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Pipe Systems

Two pipe Systems Three pipe Systems Four pipe Systems

23


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TwoTwo--pipe systemspipe systems

BoilerBoiler -- OffOff

Consists of one supply and one return pipe for eitherConsists of one supply and one return pipe for either

chilledchilled oror hot water su l . The twohot water su l . The two-- i e s stem is limitedi e s stem is limitedduring changeover season.during changeover season.

24


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TwoTwo--pipe systemspipe systems

ChillerChiller -- OffOff

25


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Three-Pi e S stem

It has three pipes to each terminal unit. These pipes are aIt has three pipes to each terminal unit. These pipes are a,, ..

The return pipe has a mixture of chilled & hot water duringThe return pipe has a mixture of chilled & hot water during

26

..

because they consume excess energy.because they consume excess energy.

F P


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Four-Pipe System

FourFour--pipe systems have a cold water supply, cold waterpipe systems have a cold water supply, cold waterreturn, ot water supp y, an ot water return. ereturn, ot water supp y, an ot water return. eterminal unit usually has two independent secondaryterminal unit usually has two independent secondary

27

,,

cold watercold water..

C iC i


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ComparisonComparison

TheThe fourfour--pipepipe systemsystem hashas thethe followingfollowing advantagesadvantages::

11-- RespondingResponding quicklyquickly toto loadload changeschanges..

-- pera espera es ww ee summersummer--w n erw n er c angeoverc angeover..

,,

initialinitial costcost isis generallygenerally higherhigher..

44--TheThe systemsystem cancan bebe designeddesigned withwith nono interconnectioninterconnection ofof thethe

hothot andand coldcold waterwater secondarysecondary circuitscircuits..

28


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Two & Three way -valve

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Types of valvesTypes of valves


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Types of valves.Types of valves.Control of water flow through the coil is typically

accomp s e us ng e t er two-way va ves or t ree-way va ves.Two-way valves are available in single-seat or double-seat.

but require adequate actuator size to overcome water system

differential ressures.

-Figure 1-b

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ThreeThree--way valveway valveTwoTwo--way valveway valve


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ThreeThree--way valvesway valves,, available as a mixing or a diverting pattern,available as a mixing or a diverting pattern,

are somet mes cons ere w ere cont nuous system ow sare somet mes cons ere w ere cont nuous system ow sdesired (seedesired (see FigureFigure 11--bb). However, this will have increased). However, this will have increased

load. Another application is where flow diversion is required,load. Another application is where flow diversion is required,

such as condenser flow to or b assin a coolin tower. Threesuch as condenser flow to or b assin a coolin tower. Three--way control valves used in this manner throttle the flowway control valves used in this manner throttle the flowthrough the coil fromthrough the coil from 100100% down to minimum and increase flow% down to minimum and increase flown e ypass rom m n mum up on e ypass rom m n mum up o ..A balancing valve is provided in the bypass to set a pressureA balancing valve is provided in the bypass to set a pressure

..controlling the flow through the terminal should be chosencontrolling the flow through the terminal should be chosen

with an e ual ercenta e characteristic and the b ass ortwith an e ual ercenta e characteristic and the b ass ortselected with a complimentary linear characteristic toselected with a complimentary linear characteristic tomaintain nearly constant total flowmaintain nearly constant total flow..

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Controlling Water Flow

Figure 1-a

Two way-Valve

32


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Fi ure 1-b

Three wa -Valve

33


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Figure 1-b

Three wa -Valve

34


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Figure 1-b

Three way-Valve

35

Fl ff


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Flow coefficient Cv

The flow coefficient Cv is defined as the volume flowrate of water at 60 F, in gallons per minute (gpm), that

Psi across the valve.

Where:

PCvQ

=Q= flow rate gpm

=Sg = Specific gravity of water =1

Now

eetindwhered

Cv4300

2=36

Kv

Th Fl h h h l l


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The Flow rate through the control valve

Where:

. = ow rate gpm

H= Pressure drop ft

Note that ; the control valve size is not necessaril the same as the i esize, but is based on the control valve Cv and may be one or two sizes smallerthan pipe size.

The Cv is based on the control manufacturer's valve test data. This Cv rating mayvary when comparing different manufacturers' valve sizes.

37

PP dd


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PrimaryPrimary Secondary pumpingSecondary pumping

systemsystem

38


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-

39


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Primaryrimary-secondary pumpingecondary pumpingControlling water temperature in a primaryControlling water temperature in a primary--secondary pumpingsecondary pumpingarrangement with a two way valve is another approach toarrangement with a two way valve is another approach to

improving valve coil control, as shown figure (improving valve coil control, as shown figure (33--a )in thea )in therev ou gurerev ou gure .. erm con an ow a a me a aerm con an ow a a me a avariable temperature in the coil circuit, at the design velocity,variable temperature in the coil circuit, at the design velocity,

..

A common pipe (aA common pipe (a--b )is connected to both the primary andb )is connected to both the primary andsecondary circuits with no pressure drop. This commonsecondary circuits with no pressure drop. This common--pipe ispipe isusually located in a bridge between the supply and returnusually located in a bridge between the supply and returnmains of the primary.mains of the primary. The common pipe is selected with "noThe common pipe is selected with "no--

"" ..

40


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gure -

42

The primary-secondary concept allows the distribution


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The primary-secondary concept allows the distribution.

(see Figure4-a) or distributing the pumping to remotebuildings or zones of a large facility (see Figure4-b).

The primaryprimary--secondary concept allows continual flowsecondary concept allows continual flow

throu h the source and still ermits twothrou h the source and still ermits two--wa valve control inwa valve control inthe loads. There is flexibility in dedicating a pump to athe loads. There is flexibility in dedicating a pump to achiller or boiler or manifolding the pumps. This mightchiller or boiler or manifolding the pumps. This mights mp y t e nee or av ng ac up pumps or every system.s mp y t e nee or av ng ac up pumps or every system.Pumps, manifolds, accessories and associated pumpingPumps, manifolds, accessories and associated pumping

,,or can be factory prepackaged as an assembly for aor can be factory prepackaged as an assembly for a

desi nated mountin location. The desi ner must wei h thedesi nated mountin location. The desi ner must wei h thepros and cons of cost, flexibility and installationpros and cons of cost, flexibility and installationrequirements of the various concepts to determine the bestrequirements of the various concepts to determine the best

43

arrangemen .arrangemen .


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gure -a

44


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45

-


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46


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Chiller PumpsChiller Pumps&&

Cent r i fugal Pum p Basic s


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Closed Syst emBalancing

Valve

3-Way

Control Valve

Isolating

Valve

LOAD

LOAD

LOADBUILDINGHEIGHT

LOAD

EXPANSION

SOURCE



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Closed Syst em Resis t anc e Cur ve

Friction

CAPACITY



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g p

Open Syst em

Static Head

StaticSuction Head

CONDENSER



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g p

Open Syst em Resis t anc e Cur ve

System Head Curve

D

Losses

HE

TotalStaticHead

CAPACITY



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g p

Closed Syst em w i th

BALANCINGVALVE

2 WAY CONTROLVALVE

ISOLATINGVALVE

LOAD

LOADBUILDING

LOAD

HEIGHT

EXPANSION

SOURCE



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g p

Closed Syst em Res ist anc e Cur ve w i t h

Friction

Losses

HEA

MaintainedPressure

CAPACITY


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Refer to the Fundamental of pumps by Dr. Hammoud

Each pump operatesEach pump operates


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Each pump operatesEach pump operatest is pointt is point

Both pumpsBoth pumps--ONON

ystem operat ngystem operat ng

pointpointBoth pumpsBoth pumps--ONON

SingleSingleumum

OperatingOperatingpointpoint

Parallel pump operationParallel pump operation

Single pumpSingle pumpSystemSystem

O i P iO i P i


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Single pumpSingle pumpO eratin PointO eratin Point

opera ngopera ng

PointPointOne pump isOne pump is

Both pumpBoth pump --OnOn

--

Each pumpEach pumpoperates @ thisoperates @ this

pointpoint

o pumpo pump -- nn


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with Speed?with Speed?

So:

ow c anges near w

Head changes as a SQUARE of RPM

Power is proportional to Flow times Head it changes as CUBE of

RPM

Q ~ RPMQ ~ RPMH ~ RPMH ~ RPM22

SP ~ RPMSP ~ RPM33


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Affinity laws (For the same pump)


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ff y w (F m pump)


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AffinitAffinit lawslaws

Doublin the um rotational s eedDoublin the um rotational s eed

leads to:leads to:-- ..

22-- Increase the total head value by aIncrease the total head value by a

ac or oac or o ..33-- Increase the power by a factor ofIncrease the power by a factor of 88..

TwoTwo Speed pumpingSpeed pumping


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Multiple-speed motors can be used to reducesystem overover--pressure at reduced flowpressure at reduced flow. Inthis example standard two-speed motors areavailable in models with speeds of 1750/1150rpm, 1750/850 rpm, 1150/850rpm and

3500/1750 rpm. The corresponding figures ows t e per ormance o a system wit a1750/1150 rpm multiple speed pump. In thefigure, curve AA shows the system's responsew en e pump runs a rpm. en e

pump runs at 1150rpm, operation is at point1 and not at point 2 .

shown in curve B, the pump would operate ator above the shut-off , it will be damaged if

.designer must analyze the system carefullyto determine the pump's limitations and the

.

Two multiTwo multi--speed pumps in parallelspeed pumps in parallel


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It can Replace the use ofIt can Replace the use of MultiMulti--speed (speed (33 speeds)speeds)manual ad usted circulated um b VFDmanual ad usted circulated um b VFD


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operation in heating system. (operation in heating system. (heating systemheating systemcirculated um

He

H u y po n

22ndnd duty pointduty point

33ndnd duty pointduty point

Q1

Radiators OnRadiators On--off !!!off !!!

Refer to the VFD by Dr. Hammoud


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reductionreduction

PumpsPumps

powerpower

Pump & System curvesPump & System curves


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A lication of chiller um sA lication of chiller um s

4 pipe systems


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own ee pump systemDown - feed pumping system

Operating point

stat c = egat ve

Shut off headFan Coil Shutoffhead


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pera ng pon

Qstat c = zero

Up Fee pump systemUpUp--feed pumping systemfeed pumping system

Standb uStandb u


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a way goo rac ce o con er a ac u um o equaa way goo rac ce o con er a ac u um o equacapacity and proper valves to permit operation when the normal pumpcapacity and proper valves to permit operation when the normal pumpis inoperable. Usually this is an application for a parallel pump.is inoperable. Usually this is an application for a parallel pump.

ai ure can occur in extreme y co weat er or eating or in t eai ure can occur in extreme y co weat er or eating or in t emiddle of a hot spell during the cooling season, and the originalmiddle of a hot spell during the cooling season, and the originalinvestment cost of a by ass will be trivial com ared to theinvestment cost of a by ass will be trivial com ared to theinconvenience for the building occupants or the operator.inconvenience for the building occupants or the operator.

Depending on the system curve and the pump curve and how manyDepending on the system curve and the pump curve and how manyum s are in the full s stem a standb um can rovide u toum s are in the full s stem a standb um can rovide u to 8080%%

of design flow.of design flow.

Types of Pumps neededTypes of Pumps needed


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entire characteristic curve. Centrifugal pumps are available with steep curves thatdrop from high head at low flow to low head at high flow versus those with flat

Some designers like to limit this to a 15% to 25% rise-to-shut off curve. Theseflat curve pumps are always recommended where two-way valves are applied to

unit terminals. At part-loads, the valves will be operating at lower flows and thiswill move the system operating differential pressure up the pump curve.


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Pum s selectionPum s selection

When selecting a pump for chiller application,When selecting a pump for chiller application,the ollowin uestions actors should bethe ollowin uestions actors should beconsidered:considered:

Pumps selectionPumps selection


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11-- h i h h i ih i h h i i


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(Water or antifreeze liquids , cold or hot etc.. ).(Water or antifreeze liquids , cold or hot etc.. ).22-- hat is the re uired volu e low rate dischar e ?hat is the re uired volu e low rate dischar e ?

What is the diversity factor?, what is theWhat is the diversity factor?, what is the

maximum and minimum amount of liquid to bemaximum and minimum amount of liquid to bepumped?pumped?33-- What is the head required from the um and theWhat is the head required from the um and the

pipe system curve ?. For circulating pump the headpipe system curve ?. For circulating pump the headrequired from the pump is to overcome the totalrequired from the pump is to overcome the totalea oss on y.ea oss on y.

44--What are the conditions on the suction (inlet) sideWhat are the conditions on the suction (inlet) side

o e pump an on e sc arge ou e s e oo e pump an on e sc arge ou e s e othe pump? check the NPSH. That is to saythe pump? check the NPSH. That is to say ..

55-- Check the specific speed. Read the correspondingCheck the specific speed. Read the corresponding. .. .


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66--Flat curve pumps rather than steep curve pumps is selectedFlat curve pumps rather than steep curve pumps is selected77--Plot the i e s stem curve on each selected umPlot the i e s stem curve on each selected umcharacteristic curve and then compare the headcharacteristic curve and then compare the head --discharge relationship, efficiency and power of thedischarge relationship, efficiency and power of thei erent pumps rom cata ogues . T e pump, w ic isi erent pumps rom cata ogues . T e pump, w ic is

operating at or near the point of B.E.P, (operating at or near the point of B.E.P, ( maximummaximum. ,. ,

able to identify one or two pumps that are suitable.able to identify one or two pumps that are suitable.88-- Choose theChoose the lowestlowest initial and runnin cost of the um i.e.initial and runnin cost of the um i.e.(power requirements).(power requirements).99-- What is the type of power source (electric motor, dieselWhat is the type of power source (electric motor, diesel

engine, etc. ?engine, etc. ?1010-- Check the space, weight, and location ( indoors or outdoorsCheck the space, weight, and location ( indoors or outdoors

..

1111-- Refer to the governing codes and standards.Refer to the governing codes and standards.

--

Remember thisRemember this

..


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with trimmed impellerwith trimmed impeller Optimizing pump capacityOptimizing pump capacity forforaaspecific application. . Single pump with backup pumpspecific application. . Single pump with backup pump-- InIn,, ..

TwoTwo--speed pumpspeed pump -- Provides limited variable flow steps withProvides limited variable flow steps withan added investment.an added investment.

ara e pumpsara e pumps-- exi e capacity contro wit out increasingexi e capacity contro wit out increasingsystem head; goodsystem head; good forfortwotwo--way valve control. Series pumpsway valve control. Series pumps-- Stee head chan e with limited flow chan e; twoStee head chan e with limited flow chan e; two--wawavalves would require high differential pressure operationvalves would require high differential pressure operation

and capability.and capability.- - ,,

minimum pumping energy.minimum pumping energy.Distributed pumpsDistributed pumps -- Special application of primarySpecial application of primary--secondarysecondary

..Variable speed pumpsVariable speed pumps-- Applied to pumping systems to reduceApplied to pumping systems to reduce

ower b lowerin um s eed to meet control differentialower b lowerin um s eed to meet control differentialpressure in se ecte ocations; usua y app ie to para epressure in se ecte ocations; usua y app ie to para e

pumping distribution systems employing primarypumping distribution systems employing primary--secondarysecondaryor distributed um in , with twoor distributed um in , with two--wa control valves.wa control valves.


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nd o t e lect rend o t e lect re

Documents

Chiller Terminal Unit Performance 1