Comparative study of a steam jet refrigerationsystem and compression refrigeration

systems for a central cooling plant

Item Type text; Thesis-Reproduction (electronic)

Authors Vachhani, Vasantrai Ambavi, 1936-

Publisher The University of Arizona.

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V COMPARATIVE STUBI OF A STEAM JET REFRIGERATION SYSTEM AND. COMPRESSION REFRIGERATION SYSTEMS FOR A GEITRAL

COOLING PLANT

Vasantrai Ao Vachhani

A Thesis"Submitted to the. Faculty of the DEPARTMENT OF MECHANICAL ENGINEERING

In Partial Fulfillment of the Requirements . For the Degree of ■. : /mSTER :pF; SCIENCE V

In the Graduate CollegeTHE DNIVERSITT OF ARIZONA

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of the requirements for an advanced degree at The Univer­sity of Arizona and is deposited in The University Library to be made available to borrowers under the rules of the Library.

Brief quotations from this thesis are allowable with­out special permission, provided that accurate acknowledg­ment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or dean of the Graduate College when in their judgment the proposed use of the material is in the inter­ests of scholarship. In all other instances, however, per­mission must be obtained from the author.

This thesis has been approved on the date shown below:

SIGNED: VaVfrvOkkAji. A - V g J ^ W u ^ c'

APPROVAL BY THESIS DIRECTOR

HELIODORE A. MARCOUXProfessor of Mechanical Engineering

The author wishes to express his appreciation for the assistance' given by ®r0 A 0 E0 Hamilton, Chief Operating Engineer in power plant s The fmiyersity of Arizonaj who provided information concerning operational costs of the refrigeration units, cooling towers$, heating equipment and other accessories, and statistical records for the last several years0

i

TABLE OF CONTENTS

I v pfTROBUGTlON « „ 0 » =. = „ . » . '. o = ■ 0 1, lo Preliminary Statement » » » « . o „ „ . 1' 2C Objective of the Study „ » . oy = » o » 1

3 o Scope and Limitations of This Stndy „ 2II • COMPARATIVE STUDY OF THE ADVANTAGES OF A

STEAM-JET REFRIGERATION SYSTEM. OVER OTHER■ p o - o p

60 Total Operating and Maintenance Costs of the Refrigeration System » .» , o <> ,

3lo The Applicatipn of a Stearn-Jet Refrig­eration System to The University of Arizona o o @ o o o. o. o © o o © © © © V

III A BRIEF STUDY OF A NEWLY.MODIFIED AND IM­PROVED . STEAM-JET REFRIGERATION . SYSTEM . © © 101©: Operational: Details of. a Steam-Jet

■ RefrigeratIbn System © V ©,© © © © © © 10. 2©, Thermodynamic Principles of Operation 11

3 © ' An%:iliary Equipment © © © © © © © © © 124= Temperat'iire-Entropy Diagram of the

Steatii-Jet Refrigeration Cycle © © © © 175<> Operating Characteristics of St earn-Jet

Ejectors © © ©•© © © .© © © © © © © © © 20IV COMPRESSION REFRIGERATION SYSTEMS

■ 1© Initial Cost.of the Present Centrifu-\ gal RefrigeratIon System of The Univer­

sity of Arizona. © © © © © ©: © © © © © 302© Average Cost of Centrifugal Ref rigera-t>ion Pi,ant © © © © © © © © © © © © © © 3 C

3 © Cost of Building for Centrifugal • . Refrigeration System © © © © © .© © © © 40

4© Total Initial, and Installation Cost of ' \ the Centrifugal Refrigeration System © 40

5© Operating and Maintenance Cost of the40

T m i^ of m m rm rs \. . (Gont do ), .

m $ T E R PAGEV 8TATI8T1GAE EPG# OF A Wsm-JET - . •:

BEFBTGEMTZOl, SYSTEM A » > » » 0 = 0 . = „ 47 ■1« . Initial and.Installation Gost of aStearn-Jet Refrigeration System = •„ 0 0 47

2= Operating and Maintenanoe Gost ofSteam-Jst Refrigeration System <. » = ,»■ 55

3 o Maintenanoe Gost of the Meohanioal and 1. Electrieal Equipment o; <, , 9 - « 0 0 6 » 64

4o Maintenanoe and Repair Costs „ » , = » 655= Cost, of Electrical Power = o o « o » => 666 0 Wages and Salaries , 0 » = » . . » o . 677= Goolihg Tower Galeulations = = o o „ = 6784 Gost ofVluferioation for the Water

Pumps and Repair Gharges o 0 « » o » >' 749 o Miscellaneous Expenses 0 » » 0 o = 6 o 7o

VI RECOMMENDATION 9 SUMMARY, AND CONCLUSIONS „ . 78lo Recommendation t, » . o 0 0 0- « 4 . » 0 0 782o Summary of the Gomparison and Reoom-

mendations o o o a o o © © © © © © © © ^13 © Conclusions © © © © © © © © © © © © © 3

REFERENCES © © © © © © © © © © © © © © © © ©■ © © © 9 4

iii

cmPTER, I

■ ' \ :; - :' HTtOMGTIOI ;

10 Preliminary StatementThe University of Ariaotia*s'aireoaditioning.sys-

teai was selected for comparison with steam-jet refrigera­tion and other compression refrigeration aireonditioning systems» This was a theoretical investigation„ Initial and operational costs of the present centrifngal refriger­ation system were collected from the physical plant office of The University of Arisona? Since some of the refriger­ation units are ten years old9 the initial costs of these emits was translated into current cost of similar units for purposes of comparison0

20 Objective of the StudyThe objective of this study was to investigate

the feasibility of a central steam-jet refrigeration system for The University of Arizona to meet the increasing demands of this institmtion on its aireonditioning system* Installation of such a system would make it possible for the university to utilize its present heating boiler cap­acity on an economical year-round basis0

' ' v / : y : ■ y': y ' :':' ' ;;' 2 '3 o Scope and Limitations of this Study

Although based on the airconditloning needs of The University of Arizona$, the results of this study could be applied to any other similar situation after . giving due consideration to. loeai operating conditions 0 Galcuiations were based bn the A 0SoHȴoS? design data for the city of Tucsonj, Arizona<,

GOMPAR&TITE STUDY OF THE ADVANTAGES OF A .STEAM- JET REFRIGERATION SYSTEM OVER OTHER COMPRESSION

' ; REFRIGERATIONv SYSTEMS

The followihg types of refrigeration systems are in common uses

lo Compression refrigeration 1 t o Stearn-jet refrigeration

Absorption refrigeration •4o Thermoelectric refrigeration Absorption and thermoeleotrio refrigeration sys­

tems were not included in this study0 The centrifugal^ reciproeating9 air cycle, steam-jet expansion, and rotary compression are all compression refrigeration systems<»The steam-jet refrigeration system is, however, treated as a separate system in this airconditioning systems evaluation program?

Stearn-jet refrigeration was first investigated ■some time prior to 1901 by La Blank and Parsons (7)* and received limited application at that timeo During the

Parenthetical numbers: refer to references at end

early 1930*3 steam-jet refrigeration units experienced their first wave of popularity for airconditioning large buildingso Currently, the steam-jet unit is finding increasing popularity for the cooling of buildings and in the process industrieso / v

: When chilled--water temperatures of 40 degrees .Fahrenheit temperature or higher are required? steam-jet refrigeration may be the most economical answer» Cornpar- ,

, atire adrantages of the steam-jet refrigeration system are § ' ■■ . : "

lo Haring no raoring parts, except for condenser- pumps, maintenance costs are rery low<> One such refriger­ation plant claimed a maintenahce expense of only $30 a

■ year o . : _ •

2 o The design of a steam-jet refrigeration unit is relatirely unsophisticatedo Therefore, less skillful labor is required for maintenanee and repairso

- 3° From the standpoint of initial cost, the cost of a steam-jet refrigeration system is lower than that of any other comparable system=

4° Steam-jet refrigeration systems do not need protective housing and may, therefore, be exposed to the elements without deterioration6 This is an important factor when considering expansion of an existing plant„

. Steam-jet refrigeration units are quite flexible

as far as installation is concerned0 Whenever it is neces­sary to move them* they are easily handled* and quickly installedo This reduces labor costs in moving and handlings Steam-jet units can be installed .at any required location* indoors or outdoors* and the weight permits elevated loca­tion oh light steel' frameworke Special ejectors and assem­blies can be provided to suit unusual installation require­ments o " t v

As they have no moving parts* except water pumps* there are no maihtenanoe costs for adjustments or lubrica­tion* no cooling is required for the lubricating oilo Wear in ejectors is confined to erosion by high velocity steam and to corrosion by the corrosive vapors being handled0 This eah/ be minimized by the use-of special materials0 '

Replacement costs for worn parts are low*' •: One special advantage of steam-jet units is thatthey work efficiently for any load from low to high0 In other systems* operational costs at Tow load are very higho The wfill® in the Condensers is non-flammable j there is* therefore* no off-season fire hazard,,

■ The absence of moving parts on the low side of the system mbans that there will be no vibration at either.the high or low frequency level* Noise levels are also low* less than that of fan and water on a cooling tower* There is no ®hunting^ nola e such as can.becur on other systems

; when operating at light loads„ ■ ,If steam is available from excess boiler capacity

and water from, stream or well at .reasonable costs opera­ting costs are lower or competitive with other systems=

Water, the refrigerant in steam-Jet refrigeration systems, is inexpensive and easily available from nature« Water is free from strong chemical action, and has most of the characteristics of a good refrigerant (such as chemical stability), is non-explosive* non-toxic, low in costj, and is non-flammable = Water has the highest known latent heat 0 Ammonia, its closest industrial competitor, has a maximum latent heat of 543=1 btu at 32°F; water, oh the other hand, has a latent heat of 1075»8 btu at 320Fo

The compression ratio for steam-jet refrigeration is approximately 8 to lo ,

Life expectancy has been excellent due to the absence of moving parts„ The use of special materials to reduce the effects of wear, erosion, and corrosion has prolonged the useful life of these systems0

Failure of the simple, economical, automatic con­trol device cannot damage the system? nor can faulty oper­ation of the control system result in damage0 Damage from freege-up is virtually impossibleo

When used for the cooling and storage of leafy vegetables, it evaporates the small portion of water con-

; ; : / - ^ ..;- ;: \ r :..'' ?tained in the vegetables0 The highly penetrating effect of vaeuuin cooling makes it possible to eool produce, not only quickly and completely, but more effectively and ; economicallya

1 o The Application of a Steam-.let Refrigeration System to The University of Arizona

In summertime, the University^s heating boilers are idle* They could be utilized on a year-round basis if a steam-Jet refrigeration system was installed, thus shar­ing in the initial cost of the heating system^ There are currently three boilers at the heating plant of The Univer­sity of Arizonao Two of these would be sufficient to operate the steam-Jet refrigeration system0 Another im­portant consideration i.s that the present refrigeration units work day and nightQ Actually, during the night, refrigeration is required in only the working areas ' of Very few buildings« But, refrigeration is maintained in all of the buildings throughout the nightb If taken off the line during that peribd, the present system carinbt, pick up the cooling load in the morning because the plant does not have the reserve capacity necessary; to pick up the heavy initial load0 The initial cost of centrifugal refrigeration units is high, making it difficult to pro­cure the necessary extra load carrying capacity» On the other hand, the initial cost of steam-Jet refrigeration is

low, the wits work efficiently at partial loads, and they can be installed outdoors, thus eliminating the increased building space, and comparative operational costs are low when operated for twenty-four hours a day„

Curves of steam consumption vs. wet bulb tempera­ture indicate that steam consumption decreases as wet bulb temperature decreaseso From the table of summer design conditions of the major cities of the United States, Tucson was found to have a high dry bulb tempera­ture but a low wet bulb temperatureo Steam consumption, therefore,.would be low in the Tue son area„

In summer, the relative humidity in Tucson is low, which is desirable for. cooling towers« St earn-jet refrigeration requires more cooling water than compression systems« Low humidity helps in the: cooling of water and saves the cost of additional cooling towers»

Very recently; refrigeration by solar energy was developed» Stearn, produced by solar energy, is used in this refrigeration system<, At present, this is done by the absorption refrigeration method using steam as a source of energy? : Ihen -;steam- becomes economically avail­able bn a large scale through the medium of solar energy, steam-jet refrigeration should supersede absorption re­frigeration » The climate of Arizona is ideal for the engineering application of solar energy. The application

: a./ \ ^ 9

of solar energy to st earn-j et refrigeration would permit the eGonomieal operation,of such units dmring daytime and by steam from toilers dm^ing the nighto

OMFTER/HI

4 BHIEF STUDY OF A NEWLI MODIFIED AND IMPROVED STM-JET REFRIOERATIOU SYSTEM

- • Ifheii ehilled Wat@r at a iiemperatmre of 35®“’0°F is neededj, steam-jet refrigeration can be the answer0

lo Operational Details of a Steam-.jet Refrigeration . System \ \

If water is heated to a temperature of 175°F at sea level and then earried to the summit of Pikers Peaky the water will boil instantly and eontinme boiling until its vapor pressure is,equal to the pressure of the sur­rounding rarefied atmosphere^.A required forboiling comes from the water itselfP along with a small amount from the container= Some of the sensible heat of the water is used to supply the latent heat of vaporiza­tion for boilingo This heat loss causes the water tem­perature to dropo

The rarefied atmosphere at high elevations cor­responds to a partial vacuum created artifieally at sea levelo .If the pressure is lowered .sufficientlys any evaporative temperatures down to the freezing pointy can be produced* It is even possible to sub-cool ice from

10

; ■ ■ ■' . . , ; ' ■ 11 the solid to the vhpor phase by means of direet evapora­tion o This process is used eommeroially and is called ^freeze drying®0' ,,f.x , .

ITaouum refrigeration finds its widest application in chilling water for air conditioning,, food processing, and many ether industrial uses» The principle of the partial vacuum is used in this system0 The vacuum is created by means of a steam-jet ejectoro Water is usual­ly chilled to temperatures in the range of 35° to 6G0Fo However, in many processes, liquids are cooled to much lower temperatures than by the use of brine or ofchemical: additives in the water=

2o Thermodynamic Principles of Operationit 2120F water boils at an atmospheric pressure

of 14o7 psiaf decreasing the pressure on the surface of the water results in a lowering of the boiling point» it 10.psia,'water boils at 193#F, at 5 psia, at 1620F| and at 1 psia, at 101°F= Dropping the pressure down to 0o25 inch of.Hg0 will result in the water boiling at 40°F0 This is sufficiently low for most industrial re­frigeration applications and is the pressure and tempera­ture at which steam-jet refrigeration units operate*

Until recently, steam-jet refrigeration found only limited applieationo Improved design and controls have widened its,adaptiono Well-designed steam ejectors

are available for a variety of pressures» Automatic con­trols are reliable, and economical 0 Manufacturers have started to produce steam-jet units for chilling water0 Steam-jet refrigeration experienced its first wave of . popularity during the early 1930*8 for the aireendition- ing of large buildingso .

Atypical steam-jet refrigeration system is shown schematically in Figo 3 do The corresponding tempera­ture-entropy diagram is reproduced in Pig. 3 °2°

High pressure steam supplied to the nozzle inlet is expanded in the booster compressor, where it draws vapor from the flash chamber» The velocity of steam is then decreased, the pressure increased, and the mixture discharged to the condenser* If a surface condenser is used, the condensate from the condenser is returned to the boilero If a barometric condenser is used, the steam is rejected with the cooling water=

3 ° Auxiliary Icuipment .The Float Valves The function of the float valve

is to maintain the water level in the flash chamber and in cooling towers,, allowing additional water into the system as neededo The water ih the flash chamber is cooled by absorption of the latent heat of that portion of water flashed into vappf and removed-by the ejector= The amount of water flashed In the cooling process is smallo The

Steam Supply

8Feed Valve

-Ad-

Booster CompressorEH

Return Warm Water (x

Flash Chamber

Water from

Condenser vChilled Water

.PumpAir Conditioner

Conden­ser First

Stage Ejec- frorondenseyjI

Conden­sate Pump— rK

SecondStage Ejector Condenser!

Air VentCirculating Water to Condenser

Fig. 3*1 Steam-jet Refrigeration System for Air Conditioning

High pre ssure ste am source

Condenser

_Flaab Ghamhar

218770 1 0Entropy Fig. 3.2

V ' , ; 15remaining water is then recirculated from the chamber as the primary cooling medium to the point of the load» Upon ■ return, it is sprayed-into the flash chamber to provide exposure Of the maximum surface areao

The required operating pressures are extremely low., since an evaporator temperature of approximately 45°F requires an absolute pressure in the flash chamber of : Qp3;inch of Hg. If condensation is to be accomplished at . approximately 101°Fy the condenser pressure must be 2 in of mercury absolute« Operation under this, condition results in a compression ratio of 6«67, which -is suffi- ’cient for efficient operation.

Condensers: Two types of condensers are used.in asteam-jet refrigeration system:

1, The surface condenser,.which has the contact coils; the condensate from this unit returns directly to the boiler,

> 2o The barometric condenser, in which the cool- ing water and vapor are mixed and then returned to the cooling tower.

Barometric condensers are used for this second . function because surface condensers add to the mainten­ance charges in the cleaning of the tubes and, in addition, increase the overall cost of the installation by at least 50 per cent . Barometric, condensers are installed at a .

height sufficient to overcome the prevailing barometric pressure and thus permit removal of the cooling water and condensed vapors by means of a tail pipe without mechan­ical assistance. The amount of elevation of the condenser above the tall well is neeessarily dependent upon the maximum barometric pressure and the maximum vacuum obtain­able in the condenser. For most installations operating at a reasonably high vacuum, at or near sea levels a ver­tical height.of at■least 34 foot is required. Although a barometric condenser will lift the injection water by reason of the vacuum in the condenser9 the maximum lift obtainable is usually insufficient in most cases due to the location of the water supplys thus requiring that the water be pumped to the condenser. To provide the neces­sary pressure differential and to insure stability, the maxitnum permissible injection water lift is limited to about 18 feet for most installations at or near sea level»; • In a count erflow barometric condens er, the in­

coming vapors enter the lower part of the shell and the air and noncondensable vapors leave at the top. Water distribution is aceomplished effectilrely by an overflow ' dam in combination with a sebies of splash trays which produce a rain-like effect in the falling, water, thus re­sulting in intimUte contact between the cooling Wat er and condensing vaporso /'-I'' '' : - - ■lb - -

■■ 17Air and ;non-condensing; .gases passing upward through

the condenser are cooled to a temperature close to that of the incoming water with the result that these condensers are capable of operating on close terminal difference under a wide range of operating conditions with respect to load and cooling water temperatureP thereby keeping the water requirements to a minimumo , .

Air Ejectorsg The air and non-condensable gases and vapor remaining in the condenser are removed by meansof air ejectors * This is done in.two stages c The air

; . ■■■■■ ■;. ■■ load is relatively small compared to the booster compressorload but the compression is so greats from 2 inch of Egoto about 29o92 inch of Ego (14»7 psia) or atmosphericpressures that it is more economical to do this in twostages than, in oneo

4o Temp eratur e-° Entropy Diagram of the St earn-.jet Refriger­ation Cycle

In Fig o' 3 o2> point A represents the initial condi­tion of fhe motive steam before passage through the nozzle and B, the final condition= For the refrigeration system of The University of Arizona^ steam pressure is available at 100 psia or more and make-up water at 70°Fo Point C represents the initial condition of the water vapor flashed in the chamber and Es the resultant condition of the mix-

tmre of high-veloeity steam, and entrained water vapor be­fore eempressibn= If the compression'were isentropic, the final condition womld then be at the discharge of the mixture to the condenser» Make-up water is available at GP slightly lower in temperature than the condenser con­dition and is throttled, to point H in' the flash chamber= Because of unavoidable losses encountered in expansion, entrainment, and compression9 the actual path of expansion and entrainment of the motive steam is AB?D0 The motive steam, at B and the water vapor flashed at G mix to give a resultant condition shewn as Eo Gompression of the mix­ture actually occurs along EF8„

The nozzle efficiency, Y)nfl is the ratio of the actual enthalpy drop to the isentropie enthalpy drop of the motive steam passing through the nozzle„ .Numerical­ly, this may range from 85 to 90 per cento The entrain­ment efficiency, e, indicates the losses that originate in the transfer of a portion of the kinetic energy of the motive steam to the flashed vapor« This process, in ,which the flashed vapor is brought into motion at the ex­pense of a loss of the kinetic energy of the motive steam, is inherently insufficient and, according to Kalustian in ^Analysis of the Ejector. Cycle,^ (6), should be taken as 65 per cento The loss of kinetie energy, 1- e, is dissi- . pated as heat added to the mixtureo The compression

- ; ■ - ■■ 19 effieiency, y)qs indicates the loss encountered in utiliz­ing the kinetic energy of the; mixture for the compression in the diffuserc The ratio between the isentropic enthal­py increase:theoretically required to the actual enthalpy increase needed, to accomplish this compression is the com­pression efficiency^ which may be taken as 75 to 80 per cento By definition of nozzle efficiency, '

• ' ■ HB? - Hb.); (3ol)

The quantity Hr s is equivalent to the kinetic energy of the motive steams now available for entrainment of the vapors in the flash chambere This process, however, is not an efficient one, and the portion of the original motive force available for compression to the condenser is

hi/ - = <r|e(H£ - Hge) (3° 2)

However, the actual energy required for compression of the mixture is

■ . ■ ’ hpg. - . Eg =. Hp ^ Hg . •; (3 »3): / '■ ' , ' ' ,, ¥lc ' , - ' ;Since the required work of compression must be equal tothe available energy for compression, the members of equa­tions 3*1 to 3=3 must be equal when adjusted for the weight involved» Thus,

Where W. is the weight of motive steam iti pounds per pound of flashed vapor0 For each pound of vapor flashed from ' the evaporator.

Refrigerating effect = HG - Hq btu per lbo (3 <= 5) and .. -

Weight of motive steam per ton-hour is- ;• . . V' .. ; , , ■ .: ' \ . := 12.000W , : (3 »6)

; : ; ; He E G ^ :.r. ; .

The expressions from 3=1 to 3 06 are used in evaluating the stearn consumption and the efficiency of a steam-jet refrig­eration system 0 They are used in the next chapter for the calculations of a steam-Jet refrigeration system»

5® Operating Characteristics of St earn-.let E.iectorsSteam -Pressure; It is imperative that an ejector

be designed to operate satisfactorily at a .predetermined minimum operating pressure„ If the steam pressure at the inlet to the nozzle falls below the minimum designed opera­ting pressure^ the ejector will not operate satisfactorily and will lose vacuum rapidly0 In establishing the minimum operating pressure to use in the design» it is therefore

extremely important that careful consideration be given to possible oceasicnal drops in the boiler or header pres­sure and normal pressure drop between the header and the ejector steam inlet0

If an ejector is operated with a higher pressure than that for which it is designed, the steam consumption will increase by an amount proportional to the increase in the absolute steam pressure above the designed value« Although an ejector will perform satisfactorily with excess steam pressure, there is ordinarily no accompany­ing, increase in capacity and, as a general rule, a slight decrease in capacity occurs particularly with single- and two-stage non-condensing unitso In some types of inter- condenser units, an increase in capacity may be obtained from the use of excess steam pressure if the unit is oper­ating beyond the designed pointo In such cases, excess steam pressure may occasionally be of value for partially overcoming temporary conditions of load or cooling water temperatures in excess of designed values c,

Condition of the Stearns The use of dry steam is essential to the proper Operation of ejectors and while superheat is of no particular valuie economically, a nomin­al degree of superheat is. very desirable as it provides added assurance of a supply of dry steam to the ejector nozzleso Wet steam seriously interferes with the operation

" - V : 22of ejectors, particularly in the smaller sizes, and also causes rapid erosion of the nozzle throats with consequent increase in maintenance costs^ Where wet steam is pres­ent, an efficient steam line separator should be installed close to the ejector steam inleto

Load Variation: In ejector is a fixed capacitYmachine and normally any variation in load will result in an increase or decrease in vacuum» In those cases where a variable capacity is required at the designed point,. two or more ejectors must be installed in parallel with isola­ting valves, thus permitting operation of one or more ejectors as required by the variation in load. In steam- jet vachum cooling systems, two or more booster ejectors are installed in parallel to obtain partial load operation at the designed chilled water temperatureo

Refrigerant? Water is the only refrigerant used in stearn-jet refrigeration systems, since It is always circulated for cooling purposes at temperatures above 32°Fd Each pound of water evaporating in the flash chamber ab­sorbs approximately 1,000 btuW This vapor is removed from

• the circulating waberv ;: ' %One ton of refrigeration is the heat removed at

the rate of 12,000 btu per hr| thus, the evaporation of a little less than 121 lbso of wafer per hr* in the flash chamber produces a unit with a one-ton capacity* .

>Powers To operate a steam-jet refrigeration plant, steam is needed for ejectors, steam or electricity for the cold water and condenser water pumps, and cooling water for the condenser„

With steam and water available at reasonable cost, the main advantages of the steam-jet unit are as followss only two moving parts - the pumps, ease of control, low cost, flexibility of installation, and overall safety=

Plants having, lightly loaded boilers in summer, or off season utility rates for steam, can often make steam-jet refrigeration pay off«, Chilled water temperature needs should be of the order of 3 or higher for best application

Control: Part load regulation is easily obtainedby running the booster ejector on a start and stop basis by automatic controls» Chilled water temperature is kept to within plus or minus 1°F. by the normal control setting» The thermostat in the chilled water discharge actuates a relay supplying air to a pneumatically operated valve in a booster steam-supply line.

In large units, multiple booster ejectors are oper­ated in parallelo -.Where' water; must be cooled over large temperature ranges, two-stage evaporators may be used5 cost is only slightly more and there are large savings in steam and water consumption when the cooling range is 20°F

■ . . : . ; 24or moreo Two-stage evaporation reduces steam and water needs about 20 per cent when the temperature reduction is 20°JV

Pumpsg The chilled water pump removes the cooled liquid from the evaporator0 A circulating water pump is needed for the condenser when the water supply pressure is not high enougho A condensate pump is used when the con­densers are of the surface typeo Pumps are also needed for barometric condensers when the vacuum is not suffi- .ciento ' /

Pumps are of the conventional centrifugal type with chilled watero The condensate pumps are selected to operate with a net suction head of 4 to 5 feet»

Performance’ of .Steam--.jet Refrigeration g A quali­tative prediction of performance trends can be made from an analysis of performance curves„ Fig„ 3 °3 shows the effect of wet bulb temperature on steam consumption.These are standard curves for a. .constant pressure of motive steam. As ambient wet bulb temperature increasesj, the steam consumption also..increases.. Fig. 3.4 indicates the effects of steam pressure yariation on steam consumption; the consumption decreasing as the pressure rises. Steam nozzles give good results at designed pressure| they are, therefores always operated at a fixed designed pressure. Pig. 3.5 indicates that steam;consumption.increases with

Ambien

t Wet Bulb

Temper

ature,

25

o

17 2.0

Steam Consumption LB/M.R./T.R. Fig. 3-3

Steam

Consum

ption

LB/H.R

./T.R.

26

l3o76oSteam Pressure PSIA

Fig. 3.4

Chilled

Water

Temperature,

27

o

50

4-0

5050U

Steam Consumption LB/H R./T.R. Fig. 3-5

\

a decrease in chilled water temperature. M l of these curves are useful for calculating operation costs and for comparing results obtained with those obtained by calcu­lation (see Chapter If)o

e W T E B IT

COMPRESSION REFRIGERATION SISTMS

Host of the practical systems of refrigeration that utilize mechanical equipment for the recovery of the refrigerant may be broadly classified as compression systemso Ihether this compression is accomplished by reciprocating, rotary, or centrifugal devices by high pressure steam ejectors, or by evaporation from a secondary fluid (absorption system) makes no fundamental difference; all are basically compression systems=

By far the most important systems, commercially, are those which use a refrigerant alternating between the vapor and the liquid phase„ (hie exception, not in­cluded in this group, is the air^compression refrigeration system. Reciprocating, rotary, centrifugal, steam-jet, and absorption systems operate cyclically with two pres­sures and use a two-phase working medium| therefore, in the broadest terminology, they may be classed as wvapor compression systems,^ From the practical stand-point, however> such an all-inclusive classification is undesir­able , Therefore, the absorption and steam-jet systems are, for clarity, almostalways so designated, and the:v,; :v 29 "T'.

terra ^vapor compression systems® is reserved for recipro­cating and rotaa^y : sy st eras rasing a two-phase refrigerant = The centrifugal system is commonly used, differing from the reciprocating and rotary.units.only in that it is not positive in displacements and iss therefore9 classi­fied separately for convenience0 The refrigeration plant of The University of 4rizo,ma has all centrifugal units 0 For this reason9 this system is discussed here for com­parison with stearn-jet refrigerationo

There is no meed to describe the centrifugal refrigeration systemo Howevers some of its advantages are as follows.i its use for operating temperatures below the freezing point of water at atmospheric pressure| requires less'cooling water than the absorption and steam- jet refrigeration systems| ands compressors are available up to 3$000 tons of refrigeration capacity*

1o Initial Cost of the Present Centrifugal Refrigeration : System of The University of Arizona

General Tnformationg y ' :The information given in the following sec- '

tions is based on the actual cost of all the equipmentand machinery» H&wever, the ebst of the refrigerationunits is based on the current price figures quoted by the manufacturerso This was made necessary because the price

of refrigeration units has decreased*B* Centrifugal Compression Refrigeration Units?

The cost of the refrigeration units is depen­dent upon the capacity of the single unit* This cost does not ihclude the cost of the foundation nor of any hecessary external piping*

The current required refrigeration capacity for the cooling of the buildings on the campus of The University of Arizona is 295O0,tons* At present* the re­frigeration plant has the following refrigeration units:

Capacity Cost per unit Present age Makein tons . when •purchased of unit -

100 $ 12,700 12 Trane100 , 12,700 12 Trane500 . 56,500 10 . York500 . 56,500 10 York

1,200 y ' 1 ■ Trane

2,400 tons #203,824 ' '; The original cost was aboilt #84= 5 per ton of

refrigeration* . The present cost, available from the manufacturers, is ahout #55 per ton of refrigeration for large capacity unite of oyer 1,000 tons and about $60 per ton for smaller units * On the basis of present costs, the cost of 2,500 tons of refrigeration should be broken

d o w as follows g- , / -There shemld be more than one unit, so that smaller

units may carry the parallel loads, and thereby affect a saving on overall oostSo In modern plants, large units are always preferred because they inherently require less maintenance6 Two units, one of 1,300 tons and another of1,200 tons of refrigeration, should be selected*

The plant now has one unit of 1,200 ton capacity, which cost $65,424° On the same basis, the cost of a 1,300 ton unit is $71,500* Total cost of proposed units for 2,500 tons, of refrigeration §

$65,424 -h $71,500 = $136,924 Go Oost of the Gooling Towers s

There are three cooling towers with the fol* lowing.datas : :

Gooling tower Cost of the tower Capacity in gpm. ■ . ■ ■ of circulated ■

' v . . - . . ' water . • -Lili-Hoffman . : $29,850 3,600 ,Fluor §orp0 8,300 2,100Pritchard & Go* 8,300 2,100

■ ; $46,450 7,800The cost of the above cooling towers had increased

by the time the new Lili-Hoffman cooling tower was in-

... . : " • ' .. 33eooling water for their condensers= Where water is expen­sive and scarce, cooling towers are used to cool water*

When air is used to cool water, the rate of heattransfer depends on the followingg

(1) The difference between the air wet-bulb temperature and water temperature

|2) The area of water surface exposed to the: . ' / ■. . air 'W" '

(3) Tk® relative velocity of air and water Secondary factors also influence the performance

of various types of systems0: The size of equipment re­quired for the cooling of a given water quantity is af­fected by2 , _.'

(1) The cooling temperature range of the :. water "'

{2). The difference between the entering and leaving air wet-bulb temperature

(3) The design wet-bulb temperature itself(4) Time of contact of the air and water

Three types of cooling towers are used for cool­ing waters atmospheric spray, forced-draft, and induced- draft cpplimg towers. For large plants, forced or in­duced- draft cooling towers are preferable» Induced-draft cooling tower is quite similar to a forced-draft cooling tower with the exception that the fan is located at the

top instead of at the bottom af the tower, drawing the air upward through the tower - a more efficient principle of operation^

The cooling towers described above, in general, operate under the .followihg conditiohs at The University of Arizona| f

Initial temperature 91°FFinal temperature ’ 81°F

. ' Bo temperature y ; v V 760F ,,.-;.y':%-.;;Type “ spirodome upspray ’Do ,Cost of the Water Pumpsg

Seven water pumps serve the condensers and cooling towers o Four.of- the# are new? the other three are old. These cost as followss

$ 6,536 for the large pump of 5,400 gpm, 250 H0P0,serving the condensers •.y

3,338 for the smaller pump of 3^750 gpm, 125 HoPo, serving the cooling towers

.6,000 for three additional water pumps of2,200 gpm, 75 H?Po each, serving the con- demsers , 0 t ,

4#000 for two additional water pumps of 2,200gpm, 75 HoPo each, serving the coolingtowers

< Total oost of the wat.er: pumps = $19,874° lo Foundatioia Oost s

/ Estimatid oost pf tha Toundatiom was $10 per . eubio ft0 for reinforeed concrete laid im forms= Present foundatiom eosts were as follows:

$ 500.V for „ Mli-loffiaan , oo.oling tower .; 65OOO for Flmor Gorpv oodling tower

5*500 for Pritchard & Co.o ooollBg tower49500 for two 5OQ ton refrigeration units and

two 100 ton refrigeration units 000 for l5)200 ton refrigeration unit - '

- #23,500 ; ;l /' .

Total oost = #23,$00o ;■ Fo Oost of Automatic .Controls:

Every plant should have an automatic control room, for all the aireonditioning and refrigeration equip­ment o The present plant has one automatic eontrol room for heating and cooling0 This control room has eight reoording meters for the controls. This cost includes both heating and cooling of the plant, Half of the cost will be for the refrigeration system. Estimated cost of the control room for the heating and refrigeration systems is #20p000} of the refrigeration equipment controls -

■: ' 36 CL Co$t of Gomtml # the Buildings s

Constant temperature is controlled in the buildings by pneumatic controls operated by compressed air* Compressed air f o r control is furnished by four air compressors= Total cost of these compressors will be divided between the heating ard cooling, systems» The total cost of the four.compressor units is estimated at $5,000*

Cost as shared by the refrigeration system will, therefore, be

Ho Cost of Electric Equipment, Meters, Starters, ,.L.' and Transformer: : ; v • : .

There is one switch gear for the electric motors of the refrigeration units, condenser pumps, and cooling tower pumpsi There is one meter to measure the water flow and the total cooling load in btu» Each re­frigeration unit has a starter for the electric motor, but the new refrigeration unit will hot have this starter.A separate starter will, therefore, have to be installed for this 1,200 ton unito One time-delay panel for 1,200 ton unit will be needed. 66,000 V is available from the main supply line of electricity.v The electric motors of the refrigeration units are operated on 4,160 V. But, to run the equipment on 220 V, voltage should be further stepped down to 220 Y. One transformer is frequently in­stalled for this purpose. All these costs are listed as

follows S < '■ ■ ' ', ■ $13 95GG swi.toto gear oost ■

SgOGO eost of water flow and Bt;m meter lOgOOO, bost of: starter Of the 1,200 ton urn it

: 92000 transformer.cost210 cost of delay panel

: Total eost of eleetrio ©qmlpmentg Btu, and waterflow meter, and transformer == $38,710o

iv/,-o % :f = - Oost #f :Maokine' and Repair ShopsEvery large plant needs a repair shop for the

repair and maintenance ofVthe plant» 'The University of■ t-; --- . ■ - r-;. ■ :.Arizona has. one machine shop and one plnmhing shop 0

These shops are .used for the maintenance and repair ofpiping, of the airconditioning and refrigeration machines,of the cooling towers, and general maintenance work,insidethe Wildings a

In the machine shop there are fomr enginelathes of different sizes (most of these are old)s fourvertical drill presses, one cutting hacksaw, one grinder,and several small pieces of equipment«

Total price of all the machines and equipmentis available from the machine shop, and is estimated at

The total, cost of tools is estimated at $3*$00„ The plumbing shop costs about |5>000o

The total cost bf machine and plumbing shopwa s i ;

$20,000 cost of machine shop 3?500 cost of tools3,000 dost of plumbing shop

$28,500 *= Total cootApproximately 25 per cent of the work schedule

of the machine and plumbing shop is allocated to the repair and maintenance of the refrigeration and airconditioning system in the summer=

The cost of additional machine and plumbing shop facilities for the refrigeration system is estimated at $28j,500 x Oo25 = $7P125o

The average post of the eehtrifugal refrigeration system of 2,500 ton capacity was a guide for the compari­son of both systemso This was the actual cost of the air- conditioning and refrigeration plant of The University of Arizona* The Post of another plant may differ materially from that listed below:

fl36»924 for the refrigeration units465,450. for the cooling towers19,874 cost of the water pumps23 9 500 for the foundation of the cooling towers

v and refrigeration unitslOyOOO for the automatic controls2,500 for the control system of the buildings

38,710;for the meter and electric equipment 7,125 for the repair and plumbing shop

$285,083 - Total costThis cost does not include the cost of the build­

ings and tunneled underground piping leading to all the buildings on the campusI , Both systems can make use of the same pipe-lines since the temperature of the chilled water of both systems is the same» Piping costs were $145,000, This is included here for general information.

4 centrifugal refrigeration system requires an engine room to protect the units from the elements. But a stearn-jet refrigeration system does not require housing for protection because there are no moving parts which might deteriorate if exposed to the weather. Generally, centrifugal refrigeration systems are installed indoors and steam-jet refrigeration systems outdoors,

3o 6ost of Building for Gentrifugal Refrigeration System The building occupied by the present refrigera­

tion system is 80 feet wide and 140 feet long* This type of industrial building costs approximately $15 per square foot of area. Cost of this, building would then be as fol­lows 2 . ■ ' 1 : , \ _

80 x 140 x 15 = $168,000 'i.gain this cost will be. divided between the heat­

ing and refrigerafibnAsysteja'as bhe boilers for heating and the control room occupy half of the; area. Therefore, the portion of the building cost to be assessed to the centrifugal refrigeration system is2

4, Total Initial and Installation Cost of the Centrifugal

$294,484 total cost of all of the refrigeration equipment .

84,000 cost of the building

$378,484 - Total cost

5d Operating and Maintenance Cost of the Centrifugal

Fixed charges are not included in this comparative study because they do not differ: much for both systems.

\ .■■■' : ■ 4 v f ^ \ ^ ', ', ::':. aThese fixed eharges are interest ©n the total capital in­vestment s taxesp insurances and depreciationo

' The operating -charges for the centrifugal refrig­eration plant for ©tie season will be made up of the follow- ing principal itemsg ,

Power costGosh of Imhricant and refrigerant Gost of repairsMaintenance of electric and mechanical equipment

, WageSs salariesg and all incidental labor costs The total gross operating cost for one complete

season will be the sum of the fixed charges and the opera­ting and niaint ehamce costs« Imterest g taxes 9 and insurance are charged foh all capital investments of the air condi­tioning and refrigeration plant0

Operational and maintenance costs are collected from the plant office of The University of Arizona and are based oh the average of the last three yearso

The refrigeration plant works for twenty-four hours a dayo luring the night9 in most of the buildings9 cooling is not required| but s if it is stopped during that time, it is impossible to pick up the heat load in the morning= This is due to inadequate refrigeration capacityo

The average heat load is as followsg ' :

Kay 19 <33,7 ions of refrigerationJmne 1,010 tons of refrigerationJuly 1,069 tons of refrigerationAugust 1,497 tons of refrigerationSeptember 1,526 tons of refrigerationOctober 719 ions of refrigeration

Total 6,858 tons of refrigerationThis 6,858 toils Of refrigeration represents the season ;ioad for ©me year» v /. -: r - " " ; : '

y Ao Power '■ ■ ■ . _: • ’ ’ The centrifugal refrigeration compressors, .

condenser water pumps, the cooling tower fans, and the cooling tower water pumps are operated by electric motors»

1 1 Power' and water -costs. averaged 40^/ton of re- frigeration/24 hrSb

Total load = 6,858 x 30 4 One day of Kay,July, August, and::8etober0 yi ' '1'' '. . ;:

= 205,740 t 4,322 :■ : : 21Q,062;t©ns-days

; yOperating oost. :;y;:

Total power cost averages,$84p025°00 per seasono Bo Cost of Inbrioant and refrigerant

Cost of Inbrioating,oil: per:year - $150«00 Cost, of refrigerant;;* {Freon). = #800 000

\ Total = $950o00Co Maintenanee eost of the mechanical and elec­

trical equipmentsProgressive maintenance requires that every

year one of the refrigeration nnits gets a change of packings and seals» Cost of the seals is approximately

The repair and maintenance costs of the auto­matic control system and of the electric equipment per year average $ls000o00» . .

Cooling towers are protected from oorrosioh by adding chemicals to the watero This amounts per year to $19500o00o , 't .t . .

The electrie motor of the 500 ton units are rewound once every ten years at a cost of $1,500<,00*

The electric motor of the 100.ton units was rewound twice in ten years at a cost of $29800„00 =

‘ Coils of the condensers of the two 100 tonunits were replaced for $69800o00o

When averaged out on the basis of one year, these costs amount to #1«500 t 2«8Q0 -K 6«,800 = $l5110o00/y

Total maintenance cost of the mechanical and electrical equipment is as follows:

S 6OO0OQ padking and sealsl.OOOoOO for repair of automatic control system Ig^OOoOO dhemioals for the cooling tower water • 150000 rewinding of the electric motor of the

500 ton unit 280o00 rewinding of the electric motor of the

100 ton unit 680a00 condenser coil replacement charge

.$,:210' ^ . '

Total maintenance cost of the mechanical and electrical equipment for the refrigeration system was $4s£lQt,0© per year,, >

Do Maintenance and repair expenses of the main­tenance and plumbing shops Average charges of the machine shop on the

refrigeration units and cooling towers are estimated for a year at |19500000sand the charges of the plumbing shop are estimated at $2g500o00o These costs may vary slightly from year to year*

Total repair and maintenance costs amount to #lg5 0 0 ^ #,0OOoOO<, ;

Eo lages5 salaries9 and labor costsSeven employees work in the air conditioning

and. refrigeration, plant 0 Five of these work on the refrig­eration systemo It is not necessary to inelude the labor of the thief operator and draftsman because they work for

. the airconditioning arid refrigeration plant and also on piping and the buildings 0 Both of them are required • also for the steam-jet refrigeration system0 Two of them do additional work on the campus„

The remaining three workers are paid a total of; \. $15,500 = 00 per month = ' : .

Total wages during the summer season would, there-' fores amount to §lp5O©:=00;.x 6 = f9s00©o00/=

Salaries and. wages, for the refrigeration system in summer total $9,000=00 per summer seasono

F= Miscellarieous escpenses.Every plant experiences unexpected expenses=

This varies from year to year = The plant of The Univer-. sity of Arizona has experienced miscellaneous expenses ranging from $1,000.00 to $2,000.00 per year for the refrigeration units and cooling towers. Basing our esti- \ mate on the average, the cost of miscellaneous expenses =

Total Operating -and'Maintenance’.Costs of the Refrig­eration System f"

I 84s025o00 power oost950o00 labrieants and refrigerant

4s210o00 maintenance; of the mechanioal and electrical eqmipment

4s000o00 repair costs of the machine and plumb­ing shops

9s00©oOO salaries and wages 1„50Qq0Q miscellaneous expenses

$103s685o00 total

STATISTICAL STUDY OF A STEAM-JET REFEIGERATIOW SYSTEM

In this chapter, a statistical study of a steam- get refrigeration is matio This inelmdes initial and installatleh costs, operating and maintenance cost of the refrigeration units, cooling towers, and repair and plumb­ing shopSo A theoretical study of a steam-jet refrigera­tion system is made, and its results compared with standard data which is available from manufacturing companies and from some technical paperso .lo Initial and Installation Cost of a Steam-Jet Refrig­

eration SystemA 0 Stearn-jet refrigeration units

Price, available from the manufacturer, Croll- Reynolds Coo, Inc*, is as followss

, 1,000 ton refrigeration capacity unit withthree jet compressbrs listed at |4O,O©C)oO0o

2,000 ton refrigeration unit would costS75,OOOo0©y

Prices for capacities between this range are found accbrdimglyo A-,;

, >: ' . .. . ; " . ■ . ■ . 48TMe above-listed steam-jet refrigeration unit is

oOmplete witb jet compressors^ barometric condenser, inter­connected pipes, supports, and automatic controls»

Present requirement of the plant for cooling is 2 s 500 tons of refrigeration One unit of 1,000 tons capacity and another unit of 1,50© tons.capacity would produce the required cooling0 Stearn-jet compressors also work effectively -on very lew load o',

, Cost of 1,000 ton unit = $40,000„00„Oost of 1,500 ton unit = $57,5000000 Total cost of the two units - #40p000„00 +

$57,500.00 = $97,500.00. : : .B. Oqst of cooling towers :

The steams jet refrigeration, unit requires approximately 4 gpm of cooling water per ton of refrigera­tion. For 2,500 tons of refrigeration, the cooling water required will amount to 2,500 x 4 = 10,000 gpm.

. The University refrigeration plant has three cooling towers. Total capacity of cooling water circulated per minute is 7,800 gallons.

Gooling water to be circulated in the fourth cool­ing, tower will be the difference -

- . 10,000 - 7,600 > 2,200 gpm.Hew cooling tower of the capacity 2,500 gpm will be

'■ selected...

■ - 49Costs of the cooling towers are listed below:

. Cooling towers 'Cost of tower Circulating water. : : 1'' - canacitv in gpm' - '

Lili-Hoffman:- < ' |299850-C)0 ' ' 3,600FlWr Cor^o 8,300.00 2,100

, -Pritcha^ > 8,3^0.00 2,100New tower 20.000.00 2.500

Total^ $66,4$0.00 . 10,300Costs of the cooling towers are.increasing. Pres­

ent, costs average"$8.00 per gpm -of circulated cooling water6 ^

0. Cost of boilersThere are three boilers in the heating plant.

Two are of large capacity and one is small. In cold weather, the large boilers are operated while the small remains idle. ;

Required steam for a steam-jet refrigeration system is derived later in this chapter. According to these calculations, this amounts to 47»300 lb/hr.

The . combined' capacity of the large boilers is 72,800 lb/hr; the capacity of the small boiler is 3,500 lb/hr. For a steam-jet refrigeration unit both large boilers would be needed. About 10 per cent of the steam of one boiler is used as process steam in the Student Union cafeteria. Cost of operation will be divided between

; . 50the heating and eooling season0 The refrigeration system works abomh. six to seven months a year = So it will share approximately fifty per-eent' of the: eesto

Each of the large boilers cost $22 $,500000„ Both of these are new and were manufactured by Babcock and Wilcox0Oo V _ . : .

Cost for ;the> bbilers of^ the steam~ jet refrigera­tion system ares therefore/,estimated at $22$,500o00o

Bo installation cost of the steam-jet refrigera- - :tion mnits ; / -

Fommdation costs and labor charges for instal­lation of the steam-jet mnitsP cooling towers$, and boilers world be as listed belows '-

$5$,500o00 foundation and labor costs for a Lili- Hoffman cooling tower

6$,00PoQ0 foundation cost for a Fluor Corp.cooling tower

59500o00 forhdation and labor Cost for a- Pritchard and Coo cooling tower

' . 2,000p00 fonndation cost for one boiler2$, 500o00 estimated foundation cost and labor

Charge for the 1$, 00© ton refrigeration ; ' ; mnit . '

3,0O0oO0 estimated fomhdation cost arid labor chargefor' the 19 500 ton refrigeration mit

■■■■■■.' : : ' 51• | 59500o00 ©stimated f©mndatioii cost of the new

pooling tower$30,000,00 - totalE, Machine and plumbing shops

Maintenance and repair costs of the steam-jet refrigeration <system are very low, &s mentioned earlier^ one plant experieneed a maintenanee charge of only $30,00 for one year. Actually$, hdweyer9l the central refrigera­tion system, requires only a small repair shop; but, the repair and plumbing shop is needed for the maintenance of piping and the buildings.,

.jit would hardly exceed fifty per cent of the initial cost of the centrifugal refrigeration system.

The initial cost of the centrifugal refriger­ation system was figured out as $7,125,00, This was only for the central cooling equipment,.

The initial cost of the steam-jet refrigera­tion system would be $7,125,00 = $3,562,50,' ; . a : ' ■, ■■

* This.is only an approximate cost, becauseevery plant installs its repair shop as it is needed. Machines and tools are added from time to time according to their need,

F, Cost of water pumps; Pumps would be required, just as they were

/ . ' ' \ ' ' - . 5 2 'B.eeded. in the centrifugal refrigeration system. Actually^ the ©onlensers require leAs pumps of cooling water due to the partial Taeiroiii created in ’barometric condensers. Buta this system has one additional cooling tower which requires water pumps for the: circulation of water through the pipes ’and condensers. This calls for the same amount of circu­lated water as do the other systems. Water is circulated in the condensers, cooling towers, and through the pipe­lines to the b u i l d i n g s . /

dost ;of these water pumps was determined previously to be $29* 275 *00 totalo V '

Cost of water pumps.- $29.s275oO0oG. Cost of automatic control room

Cost of the control room for the centrifugal refrigeration system was previously computed to amount to ■.

■ $10,000.00. ■ ::' ^ vf Cost bf w $10,000.00.H. Cost of the buildings8 control system■ Automatic thermostats in the campus buildings

are operated by compressed air. Compressed air is sup­plied: from the plant house by five small compressor units.

: Cost of these five; air compressors is $5,000.00.These ■ control both the heating and cooling.Cost for cooling only will be $2,500.00.

lo Cost of* piping from boiler to ejectors, and st ep-dowi transformer

, ,* Pipe-lines should be installed to supplysteam to tbe ejectors and air ejection unitso The cost will depend upon the size and length of the pipe-limes* •It is only possible to estimate an approximately correct figure after tracing out the exact path of the lines at the,time of inStallatioho The east side of the power- house building looks like a proper place for the installation of the stearn-jet Units0 length of this steamline would be approximately eighty feeta including elbows* Cost would be $5,000,00 including labor charges,

'A description of the step-down transformer was given previously® Its cost was estimated at $9,000,00,

Total cost $14,000*00,J* Misoellaheous expenses

,/This is a new system and there is always the possibility of unexpected expenses for installation, labor, and other incidentals, ;■

$9,000,00 will be, allocated to cover these anticipated costs*;.' \ : /

K, BuildingThis system does not require any type of

housing for the refrigeration units, but the boilers and the automatic Contrbls require cover for protection and

; ■■ . 54malnteiaaneeo The same boilers and controls are used for heating in the winter time* The steam-jet refrigeration system would share fifty per cent of the cost of the

; building with the cost for heating*Cost of building for heating was $84?000*00*Obst of building for.the steam-jet refrigeration

• system would? therefore? be $42?O0Qo00* . ;Total Initial and Installation Post of the Steam-

Jet Refrigeration Systems $ 97?000*00 cost of refrigeration unit 66?45©*00 cost of cooling towers 22?500*00 cost of boiTers - shared with heating >0?000*00 installation costs of steam-jet units and

cooling towers 3?562*50 initial cost shared for the machine and plumb-

; ing/;ShOpsV-v;;;.,-'.■ '■ . •29?275*©0 cost of the circdlatlng water pumps 10?000*00 cost of the automatic control room 2?500*00 cost,of the automatio control system of the

buiidingg this is only for the air .compressors l4?00Go0© piping for steam-lines and step-down trans-

___________ formers$275?287*50 - total :

Oost of the building, is now added and the total cost of the completely installed steam-jet refrigeration

system adds Ap to g : ; "r" '; x-|275p2B7o50 total cost of complete equipment

, it.2o000o00 cost of the building$317,287*50 ~ total cost of steam-Jet refrigeration

; system * ; / ',7, ' ^

2o Operating and Maintenance Cost of Steam-Jet Refriger­ation System

A* Oost of the steamSteam is the major source of energy to operate

the refrigeration system* The required steam for a sea­son's operation, according to the design and local condi­tions of the oity of Tucson, is found as followst

1eSign eomditlohs of Tucson: 105oF dry bulbtemperature, 720F wet bulb temperature*

Steam pressure to the ejectors is 100 psia ■ for more efficient performance|:this pressure is available from the boilers* { /

Chilled water temperature, 45 F*Temperature of make-up water, 70°F*Condenser pressure^ 2 in? of Hg* absolute* lozsle effieiency is estimated at 80 per cent* Diffusion or compression efficiency, 80 per

' cent'*. - , ■Bntraimment effioiehcy, 70 par cent*

. ■ / ■ ■ : 56 fhe theoretieal disemssiOB given in Chapter II

will mow be applied t© the final,ealemlationssReferring to Fig* B»2 -%3.ality of the steam at point Bs

\ r . lo#26 0*0262 ^ ~B ”* 2o 1429 ®c.0262 ■ ' ' : '

' = lo2o1167

r • : = 0,745Throughout the calculations;, all the values are

taken from the steam table by Keemam and Keyes,By equation 3,1,

% - % » - hb >

,2 - HD,- = 0.88(1187.2 - 808,■ ■ ' ■■■■' - BV , ; . - , ' ' ' - ■

■ HB9 = 1187»2 W ©088 x 379.14" = 1187o2 w 333,7= 853 =5 btm/lb o

,1. .

1187*2 - Hd » 0,70(33307)% = 1187^2 - 23*5 ., '

■ — 953 o7 btu/lbo

Quality :0f the' St earn, and flash yapor at the be­ginning of compression is expected to be about 0,90 to

570o92 per isento Here it is taken as 0O92 per eento

HE *= 13o06 + 0=92(I©85o5- 13o06)/ ' = 13 0 Q6 + 0 a 92 (1072 o 44) "

- 99#o36 btm/iboA s vapor is compressed adiabatieally from E to F,

entropy remains the sameo

SE '©o©2S2 .+ 0o92(2ol429 4 0<= 0o©262 4 0.92(2.1167)- I.9732 btm per dego Fo per lb0

SE = Sp = lo973 btu per dego F0 per lb,

%p /== %mallty, of steam at F.= 1.973 - Odl3l6 1.9797 - 0.1316= 1.

. . 1.!= 0,9919

% = 0c992 ;

From equation 3o3s IF = 69olO 0.992(1105.7 -5- 69o 10) ' = 69.10 4 Od992(l©3606)= 1101.16 btm/lb. '

58999=36 + A1101010 . 999

0.80999=36 + 1 2 o7©II26.36 btu/lb

By eqmatloB;3.SW

( % -1101.10-999=3' )0.88x0.65x0.

= 101=74 ■ ' ' ,

= 1.42 lb. motive steam per lb. of flashed vapor.

Hq + W(Hd ) = (1+1)1E . ' ;Hg = (1.42 +1)(999=36) - 1=42(953=7)

IO64 btm/lb

994 btm/lb

Weight of motive steaM per (ton)fhr.).V '/ \ ^ - W 8 8 S U i : "' : ■ ; , ' . HQ - %

■■ : ■ a : , /■■■ .. . : 59= 12.000 x 1042 ^

989 , „ .

1%, 18 lb, , ■■, .

Weight of motive steam per (ton)(hr») ^ 17018 lb0 Comparison of,Calculated Steam Consumption with

Standard Results from the Curves for Standard Practises Three standard omrves are available from which

steam consumption at various local conditions can be deter mined„ ■ /. .'.v. ; . : \

From curve (Fig® 5ol) for steam consumption at 100 psia, % . ', .

= 17<.2 Ibo per (tom) (hr.o) of refrigeration•»Design conditions for the city of Tucson in

summer ares 10$®Fo dry bulb temperature and 72°F0 wet bulb temperatureo

From curve (Fig0 502) steam consumption at 72®F0 WBo = 17o2 Ibo per (ton)(hro) of refrigerationo Steam, pressure for this curve was kept constant at 108 psiao . ’

From curve (Figo 5»3) steam consumption at 45°F temperature in the flash chamber

- 17,10 Ibo per (ton)(hro) refrigeration,From the calculations based on the design condi­

tions for Tucson and from the curves, the steam consump­tion was found to be almost identical.

Steam

Consumption

LB/H.R./T.R.

60

31

21

150760Steam Pressure PSIA

Fig. 5.1

61

20

Steam Consumption LB/HR./T.R. Fig. 5.2

Chilled

Water

Temperature,

62

&4O

4o

18 1%Steam Consumption LB/H.R./T.R

Fig. 5.3

■ ' ■ - ' ; 63Steam e nsiunpt;ion. - vl^olSl Ibo per (ton) (hr0) of

Usually the water pumps of the condensers and eool= ing towers are operated by eleotrio motorso But' air-ejeot* ors are operated: by steam* Approximately ten per cent of the steam eonsumption may be Qharged to the operation of the ejeotors* .

Steam used in the air~ejeotors = 17=18 x 0*10= lo72 lb* per (ton"

(hr*) of re­frigeration*

Total steam consumption ~ 17*18 -f 1*72= 18*90 lb* per (ton)(hr*)

of refrigera­tion*

Steam consumption could be taken as 19*00 lb* per (ton)(hr*) of refrigeration^ thus accounting for leakages and other losses* , .

Steam required per (ton)(lb*) of refrigeration= 1 9 lb*

Cost of the steam for one seasonsThe total refrigeration load for one season was

calculated previously as,. 210 s 062 ton-days= 21©,062 x 24 ton-hrs*

ATerage eost o £ the steam ean be e'btained from the heating season in the winter0 Fignres obtained from the plant ©fficle are as follows"

> Month : Priee per 1,000 lb, of steam

,November Deeember

MarchApril

Oo533 0*592 0,00.1,

Total eonsnmp- tion in lb.13,300,0001?,600,00016,562,00012,000,00014,100,000

Total ,237 * 9 p 'Average cost of the steam is 70^ per 1,000 lb*

for an average, steam eonsnmption of 12,677,000 lb* per month * ; ; : ’ ; :v 6 , / : ,

Gost of steam" for one season= 210,1,000 x

,000,

x 24 x 70 x 19

3 Maintenance Gost of the Mechanical and Electrical Equipment

The iWaimt enam# e cost of the St earn-Jet units is very low* This, however, can be figured ©mt only approxi­mately* The centrifugal system, on the other hand, has experienced additional costs in changing the windings of electrical motors, change of condenser coils, make-up

Imbricating ©1:1 aad, refrigeramt j, and cooling of the lubri­cant o In addition^ the fomr eo©ling towers require chemi­cal additions every year, totalling $230000GO per year*

Maintenance costs of the refrigeration units can be assumed at approximately $1,000o00o Sometimes this would be very low, but it is assumed that, sooner or later, packings and seals shodld be changed to cheek leak­ages o At that time, seal costs would amount to about $1,000o00o Operation and maintenance costs of controls was about $1,000o00 in the centrifugal refrigeration systemo This same charge would have to be assessed for the steamrjet: refrigeration systemo

; . Maintenance costs of the; automatic control system for all units and recorders = $1s0000000

Total maintenance and operating costs of the mechanical and electrical«equipment are as follows °

$t,OO©o0O for chemical additions to the cooling

1,000tod for automatic controlsl.OOOoOO for packing: and seals $4j>000o00 - total

4= Maintenance and Repair PostsRepair costs and charges for plumbing and repair,

or for the machine shop, will decrease as the maintenance costs for this type of system are very low0 Some expense

on the 'boiler» howevers - may be antieipatedo The present plant spends $l,50Qo©C) a year for the maintenanee of its boilersp An equal amount would be in order for the refrigeration plant * It may further be assumed that the charges for the machine and plumbing shop would average $l,8QGip#: per yearo

Total eo st = $1s 500 o 00 ^ .ll9 80©,00 = $3,300.00.

5o Post of Electrical PowerFans for the cooling towers, the water pumps for

the condensers and cooling towers, the air compressors of the control system, and recorders and meters are operated by electric motors and require electrical power0 The horsepower requirement of. all the equipment is listed

^ t I , j :120 hp for the fans of the five cooling towers40 hp for the air Compressors

. 300 hp for the,water pumps of the condensers150 hp for the water pumps of the cooling towers

^ pThese electric mbhors do not work at full load

capacityo Usually, they operate between 60 to 70 per cent of their capacityo Therefore, the total power re­quirement would be reduced to approximately 400 hp0

Cost of'electric power' is.io250/kwhp Cost = kwhx cost of power x hrso of running in one season; 100

= 400 x 0,746 x 180 x 1.25 x 241 0 0 - - ; :. : '

= #16,125.00 .6. Wages and Salaries

Since maintenance and repair is a minimum, labor costs are also low. Seven workers maintain the steam-jet refrigera.tion system:. Five of these would be required for maintenance and office work; two of these will be needed in the plant office. Labor costs will amount to #6,000.00 for the total cooling season.7. Cooling Tower Calculations

Conditions and data available for cooling towers in Tucson are as follows? •

mospheric design condition in summer is 105°F dry bulb and 72°F wet bulb

Cooling water range in the cooling towers 91®F

Condition of air leaving the towers is 90 per cent.saturated and 93°F

Total load 2,500 tons of refrigeration The amount of water to be circulated in gpm for

2,500 tons of refrigeration is calculated as follows?

'■■■' . ■ . . ■- " 68 SolutionsPreviously calculated results are used wherever

they are required0; .Steam is condensed to 91°F in the barometric con-

denserSj, where the steam and water mix together»Beat gained by the cooling water = heat lost by

steam =0,992(11050 7 - 69o10) + (101o14 -91}= 1032 ^ IO0I4 = 1042o14 btu/lbow(91 - 81) = ■ ■

■ ;' / ’V;: ... .... 8 33 . : . . 'liherej, Iff = water to be circulated in gpm

w = weight of steam per minute to be eon- ' .:; .' ’ densed

H = heat to be given away in btu8033 conversion factor for gallon from lb,

11(91 ~ 81) == -8o33; :3c .60'.'' /V = 3,94 gpm per ton of refrigeration»

Gomparison of calculated result with the standard curve available from Groll-Eeynolds. Go, is made in Fig,

From the cuhve of steam vso water consumption in gpm, ; ' s ;'. ■v'"1/ . -

Water consumption for 19,0 lb/ton hr,, 3«96 gpm.

G.P.M./Ton

of Refrigeration

69

45FTemper Chilled

atureWater

604*00 30to 20LB/H.R. Steam Per Ton of Refrigeration

Fig. 5.4

Calculated water consumption is close to the value found from the plot 0 '

For practical consideration, it is estimated that 4 gpm of water are required per tom of refrigeration»

Water required for 2,500 tons of refrigeration = 4 x 2,500 = 10,000 gpm to be circulated*The University of Arizona has three cooling

towers with a total circulating capacity of 7,800 gpm*• ,, The fourth cooling tower should have a circula­

ting capacity of 10,000 - 7,800= 2,200 gpm*Total air to be handledSThis is necessary in order to determine the capa­

city of the blowers of the cooling towers, and to find out the make-up water requirements of the towers*

Cooling towers cool water primarily by adiabatic saturation of the air, although there is some cooling of the water as a result of flow of sensible heat from the warm water to the cooling air*- Heat lost by the water is equal to the sum of thelatent heat gained by the air plus the sensible heat gained by the air* This heat balance can be expressed by

:: "v;:' '; : ■ 7 1(5oi)

mere; /'. '" 7'" . : : ' "■ : , ; ' : Ww = weight of water leaving the tower ■ .

' Sw = specific heat of watertwi = temperatmre: of water into tower two = temperature of water leaving tower W© = weight of water evaporated

: .■;; X. L: = 'latent:■ heat v:o;f:,'evapomf-idn. at a temperature midway Between twi and tWG '

Wa ^ weight of airh = enthalpy of air out of tower ,

- ■ ■ ■ ' 0 ; ... .

h^ = enthalpy pf air into tower

: Shslyzing; :the; eqmatioiis it would at first seemthat two unknowns- are involved and that the solution would be impossible* However9 it is possible from the use of a psyehrometriG eharts

weight of water evaporated ' , specific humidity of air out of tower - specific

humidity of air into tower = 0.031 - 0=0094= 0o02l6 lb* of water per lb* of air handled

L = latent heat at 86°F. ' / r :

Evaluating the right side of equation for 1 Ibo of circulated air.

I = 0c216 x 1045^ - 3508)' = 22.6 + 19-0

' = 41o6 btu are tramsferred from the water to each• pound of air handled.

low eoBsidering the left side of the equation for the total 2,508 tons of refrigeration

v S: = : 500 X ' 3 »<S' ± '8 33;t;9l - 81) ",= 2)300 x 300 htu/min.

2.500 x 300 41.6; ; . =18)000 Ih/min.

, fhis is the air circulat ed in the four cooling towers. This is useful to find out the capacity of the fans for the cooling towers.

Amount of evaporated water= 0.0216 x 18.000

■■■■ :• 8.33 .4&»48 gpm. ; ' ' ;

, . Intrainment or drift loss will fee about 0.10 per cent of the ©irculated water for each degree of cooling.

Brift loss = 10)300 x 0.001(91 - 81)= 10.3 gpm.

Where

. . . ; ' . 73Make~mp water required = Evaporated loss + drift

: lOSS

= 46.48-1" 10.30' = 56.78 gpm.

Iffeetiveness of the cooling towers of the Waiver*

\Iffeotlveness of the cooling tower will he,: Y|e = ; , :

^t ^ w b

t. = temperature of water at the top tg = temperature of water-at the bottom t_ , = design wet ,bulb temperature ef tower

== 66.67 per cent,.Cost of watersIt was previously calculated that make-up water

is required due to evaporation and drift loss. Loss of vapor in the exhaust from the air ejectors is about IQ per cent of the steam used in the stearn-ejectors. This will amount to 3,300 lb/hr. ■ .

-up water per year will bes

Water required for the exhaust steam= 3 *300 % 24 x 180

8o.33 , ' -- : ' '

= 1071 x 10^ gallons .

Totalmake-up water required:

= 14.7 X 106 + 1.71X iq6 . '^ l6«4i x 10°, galloms \

Average load for the season, is about 50 per cent j, therefore, the total make-up water will beg

80205 x k A gallons

Cost of water is 5# per 1,000 gallons, therefore, the total cost for the make-up water

= 80^05 x 106 x 5 ', • : 100 X 1,000 , :

80 Post of Lubrication for the Water Pumns and Repair Charges

Cost of lubrication for the water pumps is about $5©oQ0V This is the same for both systems, because they

have the same water pimps,Eepair charges for the electric motors will amount

to $200o00 per year* This is estimated from the experi- enee of the refrigeration plant of The University of Ari­zona » ' ' : - " .

Usmally maintenance costs of the recording meters are negligible since they do not give trouble regularly. Average cost should not exceed $10(^00 per year*

Total cost = $50*00 4* $20©,o©0 -k $100*00 = $350b00*

9* Miscellaneous Expenses ;;There is no mechanical break-'down in this system

due to the absence of mechanical vibrations and moving parts* However, $1,000*00 should be provided for unfore­seen or unexpected incidental expenses*

Total operating and maintenance cost of the steam- jet refrigeration systems

$67,000*00 cost of steam4,000*00 maintenance and operating cost of

mechanical and electrical equipment 35300*0© maintenance and repair costs of the

machine and plumbing shops 16,125 *00 cost of electrical power 6,000*00 salaries and wages

410*25 cost of water

35QoG€) ©©st of lubrication and repair ©barges of pumps and meters miscellaneous expenses

M 5185o2 5 ^ total ' .

GliUPTER;, VI

BEGOMEEroAf 101 „ SIMBli, M B C0HGLUSI01S

lo ReoommendationThe air cohditl©ming and refrigeration plant of

The University of Arizona is continually expanding as the campus of the University growso A steam-jet refrig­eration system would be an economical addition to the refrigeration plant of the Universityo If new units of this system were installed as it expands? this would prove economical and could utilize the steam from the otherwise idle boiler capacity in the summer0 This sys~

• tern is feasible in Tucson where cooling towers operate efficiently due to the low humidity0

In the next two years, the refrigeration plant would install a new centrifugal refrigeration unit of 1,20© ton capacity and a. cooling tower to serve it»Stearn-jet refrigeration systems and absorption refriger­ation systems use steam as a major source of energy to drive them* After analyzing the various systems according to the performance of the current cooling plant, it would be quite possible to determine what the most economical

78

system womM be for the refrigeration plant of The Univer­sity of Arizonao Often, operational and maintenance costs of a refrigeration system depend on the geographic locale, the condition of the air in summer5, velocity of the wind, and temperature difference between day and night» 'Where cooling towers are used t© supply cooling water to the condensers and to the chiller units, the humidity of the air and the velocity of the wind are important factors for satisfactory operationo These conditions are favor­able in the Tucson areao

There is am important point about the continuous operation of the current centrifugal refrigeration sys­tem 0 This system works continuously twenty four hours a day. During the might, most of the buildings remain closed, but the refrigeration system remains at work in all of the buildings o This is due to the fact that the capacity of the current system is not sufficient to pick up the high initial heat load from all of the buildings o Because of this, the units must work continuously without shut-down* If extra units are installed to assist carry the load, they could be stopped during the night* This would save on the operational cost of the refrigeration units and electrical power to run the fans of the chiller units inside the rooms* The author suggests a combination of stearn-jet and centrifugal refrigeration system to solve

the problem of shut-doMi during the nighto The present refrigeration unitsGouldbe stopped.during the might, and them started'again in the mormimg with the assistance of the extra units = These are.the advantages of combin­ing the two systems:

Ao Extra mnits save .Operational costs» The extra mnits will work only for a few homrs in parallel with the current refrigeration system* For that reason, the initial cost of installation should be as low as possibleo A steam-jet refrigeration system makes this possiblec

Bo Stearn-jet-units do not need housing for pro­tection and could be installed outdoors» This is a saving in the cost of„ the building and its insurance and taxes«

Go Gombimatiem of the two systems will give the advantages of both systemso The steam-jet refrigeration system has the advantage of low initial cost, low cost of installation, saving on protective housings, and use of idle boilers| the centrifugal refrigeration system has the advantage of low temperature chilled water and better control o ,

lo iShen a unit fails to operate, extra units can be used without adverse.effects on the refrigeration sys­tem of the buildlngSi‘ Sbmetimes the temperature goes up beyond the design temperature, add the current refrigera-

: ' * ■ ' . '■ ' ,y ' ‘ : ; ■ . ' 81 tioii system fmils to pr#ylde the required refrigeration.At that times the extra units can be used to. assist the present mnitSo v- ■

E0 Sayings which would be effected in the opera­tional costs of the present system are greater than theinstallatipn costs of the steam-jet units 0 How much would be saved can be determined in the following manners Initial and installation costs of the extra units g

Ao Cost of extra refrigeration units• . Two units of the steam-jet type should be selected

to work harmoniously with the present centrifugal unitSo Total initial cost was determined previously to be $97s000oOOo dost of the installation was computed at

.■ SSoOOOoOO ;f©r the;two^ ' " ;v , : ;.•Bo Cost of the cooling towers; Extra cooling towers should be installed to serve

the extra unitSo There is no need for very efficient cooling towers since they will cool the water.for only a few hours of the day. Again it would require a detailed study to find out what type of cooling tower should be installed at the time of installationc The current price of induced-draft pooling towers is $8000 per. gallon of circulated water for about,10oF of cooling„ Forced-draft cooling tower costs are almost the same» Atmospheric cooling towers are also possible, but require more space?

82however, they are also cheaper to operate. The low humi­dity of the air makes it possible to use atmospheric eooliug towerso The cost does not differ from the cost of the otherso The author recommends that a future analysis of the possible use of atmospheric cooling tower ia the Tucson, area be made,

lOpGOG gpra of the circulated cooling water will be required for the steam-jet units. Cost of cooling towers =|1O9'00.Q x 8 = |8Gp0GObOG,

instailation costs for one cooling tower were $5,000,00, Total cost of the four cooling towers = $5,000,00 x 4 = $20,000,00,

C, Cost of the water-pumps of the condensers and of the cooling towers

Cost was estimated previously at |>19,275=00 for 1025 B,P, capacity, : _

D,..Cost of pipingCost of the piping of the cooling towers and steam-

pipes should, be considered. Photographic view 6,1 showsthe building of the current refrigeration units, boilers,and control room, and shows the space for future expansion.Photographic view 6,2 Shows the cooling towers, refriger­ation :and heating building equipment, stepdown transformer station, and available space. Fig, 6,1 shows the complete air conditioning and refrigeration plant with available

83

Photographic View 6.1

Photographic View 6.2

Plant Office

Central Heating and Refrigeration Plant

Plant Ware­house

QT.G.L.& P. Substation

Future Cooling Tower Space__

1200 Tons Cooling Tower No. 1

General Storage Building

700 Tons Cooling Tower No. 2

700 TonsCoolingTowerNo. 2

PhysicalPlantShop

The University of Arizona Central Heating and Refrigeration PlantFig. 6.1 ®

space for futmre, expansion» Two photographic views and a plan of the plant give a picture of the current plant, utility building, and space for future expansipm. After considering all factors, the exact location of the new steam'"jet units and the cooling towers can be traced out« From this, it is possible to trace out the path and length of the piping for the cooling towers and the steam-* line Of the stea.m*jet units o •

Ho matter where the steam-jet refrigeration units might be installed, the cost would be estimated at approx­imately $6,000o00o Cost of piping of the cooling towers would be around $7,00©o00o Total cost of piping would be approximately $11,000*00„

\ ■ :The/;iactm l;\spst:pf;/th® piping will be greater or less than.the estimated costa depending on the exact location selected at the time of installationo

Eo Miscellaneous expenses ■Additional machines of steam-jet units do hot need

an additional machine and plumbing shop or machine toolso But they will require control and recording meters, flow meters for steam and water, and various other small equip­ment 0 This may be reasonably estimated at $5,00©600o This is estimated on the basis of the price of current recording meters and other small accessory equipment»

Total cost of tke extra Steam-jet equipmentg $ 97s000o00 for the steam-jet units / 8s@©0oQ© for the installation of steam-jet

; ': v V mmits ’ • ■■ ; ; 'V;. ■ ;: .• 80 P Q0© 0 00 for the eoolimg. towers • '

20s000oQG for tke installation of pooling ■ ’ towers : ' • ■v; v. '' •

19p275«00 gost of water pumps ■-vv-' 13 s 00©»00 eOst of stea$a and water piping

5*000o00 miscellaneous expenses; total:.':’,:': /

Operating and Maintenanoe OOsts of tie Current Refrigera­tion System during the Might; - . . .r. ■

•Records of the refrigeration load during the night, after 10 o®clock, show that about twenty-five per cent of the total load for the twenty-four hour period'is; experienced oh Oo many of the rooms of the build­ings are closed before 10 o®clock,, Only a few reading rooms in the library, and in some of the other buildings

, remain open to midnight : Total operating' and • maintenance cost of the centrifugal reffige^ution system was previous­ly computed at $103,#@5 pOO* The portion of this cost for

•. ' 87IIeet»rlc Power Cost for Might Operation , .

The refrigeratioB. system works during the night to keep the buildings eomtiraomsly cooled0 Refrigeration is provided by Trane air conditioning units installed in all of the roomso These units consume electric power during the off-timeo It is not possible to determine the exact number of Trane units working at any one time, or how many units are not operated in the class rooms, and whether they are set on high, medium, or low tappings o It has been observed, that in the buildings, some units are turned'' offj a1 few of them may be working on a medium setting, or on higho 1 data book by the Trane Company supplies some required Information about this situation= The following table is useful in calculating the power costs of the air GOnditidhing unitss

; ; ■ ' : ’ TABLE 6.1 ■ ■Model bmitrane Maximum efm Total lominal ■ Motor

Size of ventila- efm capacity H.F.' - , ■ tion.air range .: . " ' : . '; " . . Btu/hr. , - ' : .Vertical 22 5© :: ■ 200 2,000-

7,000 1/3©

32 : 75 300 5,000-10,000 1/25

42 100 400 7,000-14,000

1/20

62 150 600 10,000-20,000

1/12

: ■ . ■■ . 88 If Table 6.1 is observed, the 42 and 62 Unitrane

sizes are capable of handling one ton of refrigeration load. This.Trane 'bnlletin mentions that usually 600 ofm of air should be handled per ton of sensible load of refrigeration0 Air eonditioning units are operated on low, medium, and high tappings, so, usually, a large unit is selected. Model 62 is oapable of handling one ton of refrigeration load»

Model 62 has dimensions of 60® x 25® x 9®, and requires.a 1/12 H.P. motor. Usually, the motor is de­signed for overload dap58ity, drawing less eurrent on a low setting and high current on a high setting. Because of this, it is difficult to determine the exact nature of the yariabie electrical power consumption. It is safe to assume that at least 50 per cent of■the H.F. is used when they are chilling cool night air.

Total H.i.= 1/12 x 2,50© for 2,500 tons of ■refrigeration.

Power consumed in 8 hours = 1/12 x 2,500 x 8 x 0.5 x 0.746 = 622 K1H.

The University of Arizona operates its own step-down transformer of 6,600 ¥ - 110 ¥, and 110 ¥ is dis­tributed to the buildings. Power costs $1.25 per ICIH. Power consumed by the air conditioners in an 8-hour period

of the day will be 622 x il025 - $7o775o' ' : - : : -;." ^ 100 ; ■■ . ■

Power eost for a yearns operation = $7=775 x 180 : :;':vv , = $1,400.00

Bleqtrie p p W for oonditionere for an ''S^homr1 day per year, will be $1 s 4@Po0Go This is the cost of the electrical power eonsnmed by the Traine air condi­tioners to cool the air.and eirculate it inside the roomso This cost is estimated for the eight hours of hight-time operation when the cool air is hot required at all,Biis is the estimated minimum saving effected, .

Operating and maintenance costs of the 8 hours of night-time operation will be as follows:

$25$921,25 for the operation and maintenance of the central refrigeration system

lg4.00,00 for the electrical power used in the ____ air conditioners in the rooms$27,321,25 r total

Operating and Maintenance Cost of the Combined SystemsIt is necessary to determine the additional cost

of operation of the combined centrifugal and steam-jet refrigeration systems. In the .United States where extraunits of refrigeration are used, they are of the samesystem. These experience less than 15 per cent of the operational cost which results from running for a twenty-

fomr komr‘da io In the mornings extra units are turned on to assist the main units:tw absorb the leadI them, gradu­ally, they are taken off the line= luring this period, ' they work from full load to'partial load. Fifteen per eemt of the total.-operation and maintenance cost is assumed by the additional steam-jet units0

,; fhese' extha ;uhits: will-;hot .require' extra machine and maintenaneb shops * Eoreoyer, steam-let refrigeration units require less maintenanoe and attenti©n0 .' Extra operating and maintenance costs are estimated in the. .followihg itemso \ ■- - --.Z : v: |S7o©OOo0© east of the steam \ ' . rr 4sOOQoOO maintenance and operation costs of the

: ' ; mechanical and electrical equipment 16,125o0© cost of electrical power : ;v ■,

; 410=00 cost of water■ 350o00 cost of lubricant and aimer water pump

; ^repairs, " V-'v;. ; " i-: ■■ l/OOOoOO miscellaneous expenses " 'r : ; :v v |8$g883o00 » total . V vt

Fifteen per cent of this operation and maintenance cost is expected to drive the additional unitso This aBiounts to |8@9885t.ob x 0o15 ™ $13,312075»■<

. Savings in operating and maintenance costs due tothe combination of the two systems will be:

• ■ ■ V ■' ' ' ■ 91#2??3210^5 - $13,332=75 = $13,988,50, or approxi­

mately $l4,0Wo00*This saviaS is dme to the extra refrigeration

mmits and to the Goolihg towers which cost $242s275«00 for their installationo This amount can be paid off in 17o35 years from the savings effected by the operation and maintenanee costs of the present system„ Considering interest end taxes on the investment of the capital, it Ywill be effected in 20 years, After 2© years, this Gombined. system will, sav® $14,000,00 per year. Compara­tively spea&img, this Saving is not much for a centrifu­gal or mechanical refrigeration system because of its relatively short working life, However, steam-jet refrig­eration units have been known to give more than forty years of satisfactory service. From this angle, this is a considerable saving,

2, Summary of the Comparison and RecommendationsThe following is a summary of the results obtained

in this comparative study and recommendations for future action,

A, Initial cost of the steam-jet refrigeration unit is about 1,5 times less than the cost of a comparable centrifugal refrigeration-unit,

B, The total initial and installation costs ofa stearn-jet refrigeration eystem are also lower than those

of a centrifugal refrigeratiom system» This cost .inolud.es the refrigeration unit9 cooling towers controls, measur­ing and recording facilitys water pump* repair shops and the buildingo This excludes only the tunnel piping of the chilied water0 Ratio of the cost is 0„838d

Co Maintenance and operation costs are slightly lower for the steam-jet refrigeration system» These can he assiamed to be substantially the same because for a large plantj, small differences do not mean a great dealo Operating and maintenance costs vary from plant to plant and differ due to different design conditions o Taking into account all these factorsoperating and mainten­ance costs of both systems are approximately the sameo

1 0 Considering the initial costs, cost of instal­lations, and operation and maintenance costs, the steam- jet refrigeration system comes put advantageously over the compression refrigeration plant of The University of Arizonao This also decreases the initial and installa­tion costs of. the steam boilers of the heating system0

Eo The combination of a centrifugal and steam- jet refrigeration system is practical and economically desirablea This will effect a saving Of |14»000o00 a year for The University of Arizonac,

F0 The steam-jet refrigeration system may use solar energy in the future = Steam can .be generated by

' . : , ; . 93 solar energy<, This could be used in the ejectors; of therefrigeration uaitSp and would .parallel and supplementthe energy supplied by tke steam boilers<,

Go A, ©areful and detailed study of the exactplan for the utilization of space for bbe installationof the refrigeration units and coblihg towers will providean a ©urate picture of the proposed system <,

3 o OonelusionsComparison of the steam-jet refrigeration system

and She/centrifugal refrigeration system revealed that a supplemental steam-jet refrigeration system would be econbmi©ally feasible for The University of Arizona> Moreoverj, the steam-jet refrigeration system would, use the idle boiler capacity in the summer and would share the installation costs of the heating system=

Uewly^developed stearn-jet refrigeration units could play an economical part in the future expansion plans of the refrigeration plant of The University of Arizonao . . . . . ,

REFERENCES

lo Burgess Ho Jenuings and Samuel Ro Lewisa Air Condi"* ti©ming and Refrigeration , pp0,5 5 \ ^ 5 5 Q q

2 o Stockern Refrigeration and Air Conditioningn Chapter 13, SteamsJet Refrigeration^ pp. 194-204=

3= Air Conditioning and Refrigeration Bata Book, 10th edition9 3.957"58o

A, Bo Go Skorotzkis Assoeiate Editor5 Power, Vol. 105$August 1961 o

5o Plant dffioe of the Refrigeration and Air Condition- . ing Plant of The University of Arizona=

60 Jordan,and Priester$ Refrigeration and Air Condition­ing, pp, 116-124 and pp. 154-155° •

7o ASiRAl Journal No, 3_$ Hofemfeer 1961$ pp, 59-65 =80 lorman C o Harris $ .Ref rigeration and Air Conditionings

Chapter 13 s Refrigeration System Equipmentppo - ##269,%/ ; : _

9o Co Fo Sweet, lh.gineer, ,Ingerso 11-Rand Company, Power, .Volo: of Sdptemher 1952, ,,

100 Jo Ho Keenan and Keyes, Thermodynamic? Properties ofSteam, : :V;"; ... - ; '...

11o A hulletin. Chilled Vector, of Groll-ReynoIds Company, v Inc,

14, Bulletin DS-42C April 1955, of Trane Manufacturing

£s,. for Vaouum Service p of Co Ho Wheeler Manu-

A detailed letter from B, H, Co o ahout St earn-jet.refr

13 0 A detailed letter from B, H, Jackson, Groll-Reynolds Co o ahout St earn-jet.refrigeration units,

Company94

■/ , "■ ,; :■ ■ ■' 9515o; 4 btilXetiris, Comparative.Performance of a Warm-ilir

■ Geiling; Panel System, and a Convection System0 of the University of Illinois0

16 <, Po Ho Hyland, M, 1=, The Design of a Steam ElectrioGenerating Stationo .

17 o national Academy of Seience Group T~38, RefrigeratedStorage Installation»

18 o John Ho Perry <, Chemical Engineers^ Handbook* 1950°