McQuay NC-U Installation Manual

McQuaY”

Operation and

Maintenance Data

Bulletin No. OM 112

March, 1993

FormNo. 573440Y

Absorption Chiller

NC-U Model

NOTESTO USERS

1 . Before operating this chiller, YOUd-mid first thoroughly read this

manual. You may not understand all of the explanations for operation when you firstly read this booklet, however, P1ease strictly follow the directions as shown hereinafter.

2.Besure not toleak theair into thechiller atany cases. (Take care when YOUhandle the manual purge values and service

valves. )

3 . Do not turn off the main supply power to the chiller.

If turn off the breaker, purge unit of the chiller does not work.

4 . Operate chilled water ‘ pump(s) and air handling unit(s) during

dilution cycle operation of the chiller. Chiller has a few cooling capcity during diluted cycle operation.

5. Specifications and eqipment may be changed as required by the manufacture without any notice and obligation to the users.

814-6-0502-452-01

OfIRATIYM4UK

CONTENTS

SKTION 1

i:;

1.3

1.4

SKI’ION 2

2.1 ;::

2.4

2.5

Slxm 3

3.1 ::; ::;

3.6

Page No.

NmEs’m

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OPIRATION---------------------------------------------------------------------58

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CONTENTS

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(1) lUUSIRATION

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(3) DETAROF TYPIC4LC1-HLUR(m VIEW)-----------------------25

(4) ~A~ ~ ~w ~~(R~ V~) ...........-...........26

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(7) TYPEALm CONIROLVALVEANDm ~--.. ..... 30

(8) = ........................................................................3l

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(1)

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-----------------------------23

—l–

1THE PRINCIPLEOFABSORPTION

(1)WHY

DOES A I-EATING CHILL ?

The cooling means keeping the room temperature lower than outside temperature. As shown Fig.l-l, operate tocarry theheat from the room with alowert temperature (28C,

82 F) to the open air with a higher temperature isrequired. heat can not move from low temperature side toahigh temperature side. So, to transmit the heat as opposed to this law (principle), some way (apmratus) is necessary. temperature one asifawater pump isused todraw up the water from a deep well.

That is, aheat pump (chiller) isused topump out the heat from alow

But, in the nature, the

COOLING LOAO

(82 “F) (90 ‘F]

AIR CONDITIONER

FIG. 1-1

HEAT FLOW

HEAT FLoW

–2–

The typical chiller using an electric asa operation power source asaconveyerto curry the heat inFig.1-2 is anelectric turbo chiller and the typical chiller using a

heat energy isanabsorption chiller.

chilled water is made by using the latent heat released by a liquid as it evaporates We can find this principle through our experience in a daily life. having an injection, after applying asalchol fordisinfection onthearm,wefeel thepartofarm cool. heat from thearm when itevaporates. wesweat inahot day orbytaking exerxise. automatically controlled by theevaporation ofsweat which takes theheat from the

body.

necessary toreturn to liquid for using vaporized liquid. compressor isused in an electric turbo chiller and anabsorbent isused inan absorption chiller.

The absorbent decreases the absorption power when itbecomes diluted solution by absorbing thevaporized solution. concentrating process ofthe absorbent isrequired. natural gas, steam or hot water.

A chiller also uses anlatent heat ofevaporation.

Because, the alchol is heated by body’s temperature, took the

And another example is that we feelcool when

bercause, thebody temperature is

But in a chiller, it is

Toreceover theabsorption power, the heating and

Asheat source, itisused by

For example, when

For this purpose, the

INDOOR

A GRAIN OF HEAT=

FIG. 1-2

k!*%

-1=.

HEAT FLOW AT ~ING

HIGHER TEWERATU?E

smE

–3–

(2) J-w PRINCIPLE OF ABSORPTION

Install heat transfer tubes in a closed vessel and put a dry silicagel (Silicagel is

high quality absorbent material) in it as shown Fig.1 -3.

vesselto make avacuum with the pressure

of approx. 6.5mmHg (1/4 inchHg). Drops of water are allowed to fall on the heat transfer tubes (Evaporator). vacuum vessel evaporates at 5C (41F).

The water take anevaporation heat from the

water intheheat trasnfer tubes, when itbecome vapor.

Take out anairinthe

The water in the

(Such liquid is called a

refrigerant and shown as a refrigerant liquid or a refrigerant vapor for the following.) silicagel, a vacuum is kept inside the vessel.

As this evaporated refrigerant vapor is absorbed immediately by a

(Ontheother hand, thewater inthe heat transfer tubes becomes chilled becasese the heat eqiovalent to the evaporation heat is taken.

immpossibleto keep a vacuum

But, when the silicagel reaches the limit of absorption, it is

in the vessel and chilled water can not be obtained.

WATER

(REFRIGERANT)

CHILLED

WATER

MATER

6EA7

TRANSFER TUBE

FIG. 1-3

SILICAGEL

—4–”

Therefore replacing a silicagel as an absorbent in the vessel with new one at all times permits to get chilled water continuously.

For this purpose, instead of the

solid absorbent such as a silicagel, a liquid absorbent suchaseasy-to-handle lithium bromide (LiBr) solution, etc. is used

(Such liquid is called an absorbent.) This

case is shown Fig.1-4.

CHILLED WATER

WATER

CONCENTRATE SOLUTION

EAT TRANSFER TUBE

REFRIGERANT

[

PUHP

bILUTED

VAPOR

S(MJTION

FIG. 1-4

–5–

drops of LiBr solution areallowed tofall (Absorber) inside thevessel. The LiBr solution absorbs refrigerant vapor.

But,when theabsorbent once absorbes the

refrigerant vapor, it is diluted and dereases ability to absorb. Resulting in the chilled water can not be obtained.

in continuously. At this stage, thediluted solution is hinted by driving heat

This means that concentrated solution must befed

source (natural gas, steam or hot water:Generator). The heat causes the solution to release the absorbed refrigerant and also

reconcentrates thesolution.

The refrigerant vapor which is released from the solution when heated,

separate vessel (Condenser) liquid refrigerant. Drops of again introduced into the vacuum vessel andrecycled

This is shown

is cooled in a

this. water are.

Fig.1-5. ‘

FIG. 1-5

–6–

(3) SINGLE EFFECT TYPE (BASIC CYCLE)

Asshown Fig.1-6, absorption chiller.

this is the basic operational cycle

Part (l)shows agenerator,

shows anevaporator

Cooling water flows

condensor cools the cooling water intheabsorber absorbs the heat when the bythe absorbent.

The generator (1)heats the diluted solution bydriving solution releases the refrigerant vapor and becomes the

transfers tubes ofevaporator (3). Drops

The water through the heat transfer tubes

ofvaporized refrigerant.

of the single effect type

sbows acondenser, part (3)

The cooling water in the

back into refrigerant. The

regrigerant vapor is absorbed

heat source.

The diluted

concentrated solution.

COOLING

WATER

CHILLEO WATER

WATER

----- .-

DRIVING HEAT SOUCE

FIG. 1-6

–7–

(4) DOUBLE EFFECT TYPE

In case of the single effect type absorption chiiller mentioned above, all condensation heat whn the refrigerant vapors coming from generator iscooled and condensed atthe condensor, is released in the cooling water.

The double effect type absorption chiller is used The generator section is divided into a high

-- generator.

generator is used to heat the LiBr solution in the the pressure (hence the boiling point) is lower.

As mentioned in the single effect type, the refrigerant vapor produced by the low temperature generator issent tothecondensor

other hand, therefrigerant vapor produced bythehigh temperature generator turns to water as it released heat to the intermediate LiBr solution. heat transfer tubes in the low temperature generator.

byboth low and high temperature generators turns to liquid refrigerant and mixes in thecondenser before returning totheevaporator.

In this step, the diluted solution is heated by driving heat source and by the latent heat in the refrigerat vapor which otherwise would be released into the cooling

water. Moreover, less heat being discarded into the cooling water translates into a snail cooling tower.

This combination means a lower energy consumption of driving heat source.

As shown Fig.1-7.

The refrigerant vapor

the condensation heat effectively.

temperature generator and alow

produced by thehigh temperature

low temperature generator in which

to become liquid refrigerant. On the

This occurs inside the

The refiigerant vapor produced

FIG. 1-7

–8–

(5) COOLING WATER

The lower temperature of cooling water

The absorption power ofLiBr solution isstrong atthe lower temperature ofthe cooling water. condensed temperature ofregrigerant downs.

low.

As the boiling temperature (generator temperature) oftheLiBr solution downs

when thecondensed pressure islow,

When thetemperature ofcooling water in thecondenser is

Therefore condensed pressure becomes

calolific value of driving heat source can

decrease. This means save energy.

It is not acceptable

As shown Fig.1-8, a LiBr solution of

temperature For

that the temperature of cooling water is too low.

few LiBr dissolves with water at low temperature.

That is, the high concentration becomes crystallization under the lower example, it is crystallized with concentration of 65% at the

temperature lower then 42C (108F), with concentration of 60% at the temperature lower than 17C (63F).

Chiller has some problems when cooling water temperature becomes too high

When thetemperature of thecooling water becomes tohigh, theabsorption power of the LiBr solution decreases.

temperature and wastes much fuel.

The chiller can not get the normal chiller water

Therefore, to prevent this, the maintenance for

cooling water SYStem (epuipment and control) and water treatment are required.

Water treatment of cooing water

The water treatment of the cooling water is an inportant factor for the chiller. If thewater quality isno good, scale adheres totheinside ofthe heat transfer tubes,

resulting in the

decreases transfer heat effect and waste fuel. Astheheat transfer

tubes may become corroded, itisrequired to fully take care ofthe water treatment.

–9–

(6) VACUUM

Onthe earth, wearepressed bythe air. pressure (1kg/cm, 14.2psi).

the vacuum.

When explaining the vacuum for the absorption chiller, it is required to

This pressure is called atmospheric

The pressure less than atmospheric pressure

is called

know the relation between the pressure and the evaporation pressure o the water.

lt is experienced in a daily life that the water is boiled (evaporated) at 100C (212F) in the atmospheric pressure.

When the pressure

pressure (vacuum), the water boiled below 100C (21OF).

between the pressure and the evaporation temperature.

is lower than the atmosheric

Table 1-1 shows the relation

The water isevaporated atlower temperature, when thepressure is lower and lower. Therefore, the inside the chiller should be always kept in high vacuum.

Since the

refrigerant is evaporated at 5C (41F) to get the chilled water of 7C (45F) by an absorption chiller, it is required to keep a high-vacuum condition with pressure

6.54mmHg (1/4 inchHg) in the evaporator.

Table 1-1

Gauge Absolute pressure

W“2G

m=me *

(psig)

Atmospheric

pressure

t 0.5 ( 7.2)

1 ata.

{o (o) 760(29.9)

vacullB

(inch&)

10 (142)

8 (114)

Driving pressure for double effect type

5 ( 71) 1 (14.2) Driving pressure for single effect type

Atmospheric pressure

525.9 (20-3/4)

61.0 ( 2-3/8)

Pressure in the cmdenser

9.2 ( 3/8)

6.54( 1/4)

Pressure in the evajxmtor

–lo–

(7) LITHIUM BROMIDE (LiBf : ABSORBENT)

Lithium bromide (LiBr) isamedicine made from lithium obtained fromlithium ore and bromide obtained from theseawater. with sodium chloride (NaCl).

Because lithium (Li) and sodium (Na) are alkali while

bromide (Br) and chloride (Cl) are halgen.

The lithium bromide has the same characteristic

The sodium chloride (NaCl) is salt. It

is well known that when salt is left in a high-humidity atmosphere, it becomes sticky.

This means itabsorbs moisture intheatmosphere.

The lithium bromide has the same

characteristics and its absorption power is stronger than that ofsalt.

its concentration and the lower its temperature of liquid. thestronger the absorption

power.

The higher

Fig.1-8 shows the lithium bromide Fig.1-9 shows the lithium bromide Fig.1-10 shows the lithium bromide the condition of the cooling cycle

equilibrium diagram. concentration diagram.

during diagram.

This chart is convenient to show “

of lithium bromide solution.

Fig.1-l1 shows the lithium bromide enthalpy diagram.

Lithium bromide has corrosive action to a metal under existing oxygen

But, asthe

absorption chiller is a vacuum vessel, almost no oxygen is in a vessel. However, to make more complete, corrision inhibitor is added in the absorbent and further alkalinity is adjusted.

So, attention should be taken to handle the absorbent and it

is neccessary to keep the amount of inhibitor bY performing thechemical analysis for

theabsorbent.

Chemical formula : LiBr molecular weight : 86.856

Component

: Li= 7.99%

Br=92.OI% specific gravity : 3.464 at25C (77°F) Meltingr

point :

549C. (1 ,020 .2F)

Boiling point : 1.265C (2,309F)

–1 l–

21 20

12!

100

10(

-25

-40

-50

-75

LX5R-21+2

-40

-60

-1oo

-80 0

CONCENTRATI~ (%)

EOILIBRIUM DIAGRAM

TEk!.!ERATURE

32 50 75

1.9C

1.85

1.8C

1.75

1.70

1.65

10 20 30 40 50 60 70 80 90

100

125

150

175 200

—

—.-.

100[”(!

1.60

1.55

1.50’

1.45

1.40

32 50

---r--t-”

—

3=1

10 20 30 40 w 60 70 80 go

I I

100

TEMPERATURE

125

150

175

100[’C)

200 212[”F)

58 57

56 55 54

52 51 50

FIG.

1-9 CONCENTRATI~

–1”3–

760 700

600

400

300

200

160

100

60 40

3240 60 80 100 120 140

10 20 30 40 60 60 70 80 90

I 1, 1 1

FIG. t-10 DUHRING DIAGRAM

160

TEMPERATURE

180 200

100

220

110

120

240

260

.130

140 I 1.

280 300 320

I 50

160

170(” C:

338(” F

150

140

130

120

110

- 160

100

-l

~ 130

—

I I

I I ---

(

—

120

70 60 50 40 30 20 10 0

CONCENTRATION (%)

FIG.1-11 ENTMU_PY DIAGRAM

–15–

(8) COOLING CYCLE

An example for the actual driving cycle of double effect Duhring diagram.

a) A-B shows theabsorption process in theabsorber.

tration of 63.62 at point A absorbs the refrigerant vapor cooled until 36.3C (97.3F) by cooing water, then becomes diluted solution with

concentration of 58.1% at point B.

The pressure of this point is 6.3mnHg(torr) which is equal to the saturation vapor pressure of water at 4.3C (39.7F) (cross point on the saturation liquid line), so, the chilled water at 7C (44.6F) can be produced in the evaporator.

Therefore, the higher the temperature of thecooling water, thehigher the absorber

internal pressure evaporation obtained.

b) B- C-

the diluted

temperature ofrefrigerant becomes high and chilled water can not be

D' shows the temperature rise process under the fixed concentration when

solution pass through the low and high temperature heat exchangers.

(equal to the evaporator internal pressure .

type is explained using the

The absorbent with concen-

from the evaporator asitis

)

As a result, the

generator the refrigerant vapor and is concentrated. solution of 61.1% at point E and finishes the first stage of concentrating.

The pressure atpoint Ebecomes approx. 707.1mmHg(torr). the pressure of 55.7mmHg(torr) in the condenser temperature ofcooling water. That is,thepressure generator has to be performed at the temperature higher than 91.1C (196F) of the

concentrated solution obtained from the cross point with the concentrated solution

of 63.6%.

pressure of the high temperature generator becomes 707.mmHg (torr).

The diluted solution at point D’ is healed until point D.

Then it becomes the intermediate

(This pressure depends on

determining it according to the

inside the low temperature

Whensetting to 97.9C (208.2F) bymaking this as^ 6.8C (12.2F), the

It releases

—16-

F-F-G shows theconcentrating process in thelow

temper

absorbent with 61.1% atpoint F'isheated bythe refrigerant vapor from the

temperature generator.

concentration rises, and it becomes theconcentrated solution of63.6%. Thus, the second stage oftheconcentration isfinished.

The pressure atpoint Gisdetermined bythe temperature ofthe cooing water. With thecondensation temperature of40.2C (104.4F) thepressure pressure ofthis temperature, 55.7mmHg (torr).

G-A’shows theprocess ofthe heat exchanger with the diluted solution while the

concentrated solution goes out from low temperature generator and passes through the

As a result, the refrigerant vapor isgenerated, the

isthesaturated vapor

Asdescribed above, itcanbeunderstood that the cycle of the absorption cooling

system depends onthe

taking out temperature

temperature condition (partially determination element from the

of the chilled water).

theabsorber and iscooled bythe

starts toabsorb therefrigerant

–17–

“\

-\ \

\ i

;

\ .

H h.

3tJf7SS3Ud

–18–

1$2(XIMGcm DEsowTnt”l

(l) COOLNG CYUE

IA.J

!&---+ i--------i------$----%--:

w—

-1

.-1.

-r

1LtY

t :

z 0

‘5

Z a w

[

-d

1!1

Q-

-w

-IA

ol03 00

11 [3!,, I,!!,,,,,!!< Ii II :

o-l

II II

—

——— ——— ———

C!Y

lilt

111[

1111

—

—19—

a) Evaporator

The refrigerant isdispersed onthe heat transfer tubes ofevaporator.

Chilled water

through the heat transfer tubes of evaporator is cooled by the latent heat of

vaporized

b) Absorber

refrigerant.

FIG. I-14

—2 o—

c) Heat exchanger

The diluted solution from the absor$er passes through the low temperature heat exchangerss, where it is heated by concentrated solution.

The diluted solution after

leaving the low temperature heat exchanger passes through thehigh temperature heat

exchanger, where it is heated by intermdiate solution.

The diluted solution after

leaving the high temperature heat exchanger flows to the high temperature generator.

d ) High temperature generator

FIG. I-15

The diluted solution from the heat exchangers is heated in the high temperature generator. It releases the refrigerant vapor

and is concentrated.

It becomes

intermediate solution.

FIG. 1-16

—21—

e) Low temperature generator

The refrigerant vapor from thehigh temperature generator passes through theheat transfer tubes oflowtemperature generator.

The intermediate solution in the low

temperature generator is heated by the refrigerant vapor. refrigerant vapor and is concentrated.

It becomes concentrated solution. The condensed refrigerant intheheat transfer tube oflow temperature generator flows to the condenser.

Condenser

It releases the

The refrigerant vapor from thelowtemperature transfer tubes of condenser.

Cooling water

condensation heat.

generator iscondensed ofthe heat

from the absorber is heated by

FIG. 1-17

—22–

103MIERlMRATl$i

(l) UlJSTRATI14

9’ 2.1

‘L=’

n < > w

-1

Z 0 c-l

II I

w’

111

-1

l-!

D----r&”#--”

—23–

( 2 )DETAIL OF TYPICAL

(Fret view :

Steam

CHILLER

inlet side)

-lx

an >

:“

U-J

II \ \

m z

-1

: <

—w

-I-I

ol-

03 00

0 wt-

-lW

-l_l

-t- --l

-ii-

-lW

cl-

–24–

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