McQUAY AIR COOLED FLUID COOLERS The major advantage of a “dry cooler” like the AFC fluid cooler is the reduced maintenance offered by closed loop cooling. Open cooling towers require expensive fluid treat- ment and cleaning of all conditioned water components. A closed tower still requires treatment of the spray water and tower. These water treatment costs are not insignificant. Typical maintenance costs on open and closed circuit towers are shown in Figure 1.

The major limitation to dry coolers, as opposed to cooling towers, is the higher leaving water temperature for a given ambient. This is due to the fact that a dry cooler rejects heat to ambient dry bulb, not wet bulb temperatures. Dry coolers are most commonly applied on smaller heat rejection applica- tions due to the following reasons:

The smaller the job the smaller the magnitude of the energy savings of open and closed towers.

There is a minimum maintenance cost for open and closed towers regardless of size.

Smaller fluid coolers are usually more cost effective than open and closed towers, especially when space and weight considerations are taken into account.

Built to perform The heart of any fluid cooler is the heat exchanger surface. McQuay has been designing and building coils since 1933 and the AFC unit is a continuation of a long, successful line. The latest heat transfer technology, much of which has been pioneered by McQuay, is included in the AFC cooler, in- cluding McQuay’s patented HI-F fin design and staggered tube arrangement.

Built to last Heavy-duty construction throughout insures long and satisfac- tory operation. Thick tube walls and fins, fans with aluminum blades riveted to a zinc plated hub or all steel with enamel paint, weather protected condenser fan motors with inherent protection, and heavy-gauge galvanized steel cabinet all com- bine to give the service you expect.

Table of contents

Figure 1. Annual Water Treatment Costs

$ PER

YEAR

2000 -

lOOO-

0- 0 100 200 300 400

TONS

Introduction ................................. .2 Specification features ......................... .3 Selection procedure, .......................... .4 Performance data .......................... .5-14

Correction factors. .......................... .5 Maximum gpm per unit ...................... .5 Capacity curves (003-025) ................. .6-8

Capacity curves (028-063) ................... S-l 1 Pressure drop curves .................... .12-14

Applications .............................. .14-l 5 Accessories ............................... ..16 Physical data. ............................ .17-20 Wiring diagram. ............................. .21 Engineering guide specifications ............... .22

“McQUAY” and “HI-F” are registered trademarks of McQuay Inc., Minneapolis, Minnesota. The McQuay HI-F fin surface is covered by U.S. Patent No. 3,645,330.

0 1964 McQuay Inc., Minneapolis, Minnesota. “Bulletin illustrations cover the general appearance of McQuay products at time of publication and

we reserve the right to make changes in design and construction at any time without notice.” 165

Page 2 I Catalog 690

Specification featuresGeneral

1.

2.

3.

4.

CABINET - All units are heavy-gauge galvanized steel con-struction throughout and arranged for vertical airdischarge. Full baffles separate individual fan sections toallow capacity control through fan cycling.

MOTORS - All motors are open drip-proof, ball bearingtype with internal overload protection. Permanent splitcapacitor motors are available on Models AFC-003 through025. Three-phase motors are available on all sizes.

FANS & FAN GUARDS - Aluminum direct drive fans areprovided to eliminate sheave and belt maintenance. Thefan blades are mounted on zinc plated steel hubs or areall steel with enamel paint. The fan guards are made ofzinc plated steel and are iridite dipped. Fan motor basketsare made of zinc plated steel.

COIL - Seamless copper tubes (l/z” O.D.) and headersare provided with aluminum fins, threaded steel connec-tions, galvanized steel casing and 5/e” NPT vent and drain.Coil design pressure is 300 PSIG and each unit is leaktested at that pressure.

Rippled finsThe advanced rippled, corrugated HI-F fin surface designcreates a state of continuous turbulence which effectivelyreduces boundary layer formation. The exclusive rippled edgeinstantly deflects the incoming air to create initial turbulence.A succession of corrugations across the fin depth, in con-junction with the staggered tubes, increases the turbulatingeffect and eliminates the “dead spots” behind the tubes.

Exclusive HI-FFin Surface

Nomenclature

Staggered tubes mean HI-PerformanceStaggered tube design exposes all the tubes to the turbulentairstream created by the fin surface design, thus producinghigher performance.

The combination of the McQuay HI-F high efficiency fin sur-face and tubes in a staggered arrangement produces asubstantially higher heat transfer rate per square foot of coilsurface than coils with conventional fins and in-line tubearrangement.

0’0

McQuay offers control and piping packages to minimize fieldinstallation requirements. A fan cycling control option includesfan contactors and thermostats factory mounted in a weather-proof enclosure for capacity control. Merely connect powerto the main control terminal block and a time clock oc-cupied/unoccupied signal to the unit and you are ready to go.

A surge tank kit is also offered to protect against water ham-mer and a fill valve kit is offered with a gate valve and hosebib for filling the water system.

For more details on these options see page 16.

ReliabilityAll basic units are U.L. listed. Units with factory installed op-tions such as FANTROL are NOT U.L. listed. Field installedkit options are also NOT U.L. listed.

Catalog 690 / Page 3

Selection zwocedure I

Select a fluid cooler to cool 60 gpm of 40% ethylene glycol solution from 130°F entering fluid temperature (EFT) to 120°F leaving fluid temperature (LFT) at an ambient air temperature of 95°F. Fluid pressure drop not to exceed 15 feet of water.

Procedure: A. Find the capacitv required.

Find average-fluid’ temperature (AFT).

AFT = (EFT + IIT) t -7 = (1jOF + 1,7OF) i .? = 125F

Enter Chart A with the AFT (125”) to find the N factor (ethylene gylcol conversion factor).

N = +to

Calculate the required capacity.

Q = N x CPM x (EFT - LFT). Bfuh = -t’ic) x 60 x (l.WF - ItOF) = 2h9.d MBH

B. Find the fluid cooler with sufficient capacity and accep- table pressure drop.

1. Find the initial temperature difference (ITD) between the entering ambient air and the entering fluid temperature.

ITD = EFT - aznbient = 1jOF - 95F = .?5F

2. Find the required QIITD.

269.4 MBH i 35F = 7. ‘0 MHH/ITIl

Example Selection

Page 4 / Catalog 690

Enter Chart B with the AFT to find the unit capacity con- version factor.

‘.‘O MHH/ITD + 1.00: = -.65 MBH/lTD

With the QllTD and the gpm, select the fluid cooler with sufficient capacity and acceptable pressure drop from the capacity rating curves on pages 6 through 11. Model AFC-014 is the proper selection at 8.8 feet of pressure drop. Pressure drop is found in curves on pages 12 and 13. The actual unit capacity is:

tJ = (r;md MBHhTD) x 17‘1) x CCF. MBH = -.‘5 x $5 x l.OO- = r-.3. I MBH

Verify that the actual fluid pressure drop is acceptable. Enter Chart C with the AFT to find the pressure drop correction factor.

8.X x 0. Yt = 8.2’2 fixt of' prcwzr~ drop

Verify that the leaving air temperature (LAT) does not exceed the maximum limitation of 140°F to avoid possi- ble motor overheating. CFM can be found in Tables 3 and 4 in the Physical Data section.

Table 1 gives maximum gpm for each unit. In some cases. this is greater than shown on the tables. Con- tact your local sales representative for these selections.

60 60 100 120 140 160 180 GPM

50% Ethylene glycol

Application

40 80 120 160 200 1GPM

Application range1. Leaving air temperature from the coil must not exceed

140°F due to fan motor limitations.

2. Heat is rejected to the ambient dry bulb temperature. Leav-ing fluid temperature has ambient dry bulb temperatureas a low limit.

3. Maximum and minimum gpm per unit is shown in Table 1.

Cooling tower for water cooled condensersDry coolers cannot maintain the lower compressor headpressures typical of open and closed towers (85” F to 95” Fwater and 105°F SCT at design) but approach the headpressure of typical packaged air cooled equipment. Their ma-jor application for compressor heat rejection is for reducedmaintenance, higher reliability and when air cooled con-

Page 14 / Catalog 690

densers are not practical.The practical limitations of air cooled condensers are most

evident on small, indoor compressor applications whererefrigerant piping would be excessive. Computer room airconditioning units are an excellent example. A dry cooler of-fers several advantages over a remote air cooled condenserssince:

Water piping is generally less expensive than refrigerantpiping.

Refrigerant piping requires careful design especially whenlengthy runs are involved. Considerable time will be re-quired in selecting line sizes, double risers, charge re-quirements, etc.

Even a well-designed refrigerant split system has poten-tial reliability problems from lengthy runs.

Industrial applicationsThe following considerations have helped make dry coolersa logical alternative over open or closed towers for rejectingheat from industrial applications.

1.

2.

3.

Generally, open towers are not acceptable for industrialapplications unless an intermediate heat exchanger isused. Otherwise, fouling of the conditioned fluid would in-volve expensive maintenance of the industrial machinery.

Leaving water temperatures from industrial fluid cooler ap-plications are often in the 100°F to 140°F range. This isa temperature range where dry coolers are most effectivebecause 95°F ambient is typically the design ambient anda dry cooler can generally provide 100°F leaving watertemperature at 95°F ambient.

High reliability is the major requirement of the coolingtower on many industrial applications. With a dry coolerthere is no need to shut down the system for cleaning orto provide extensive water treatment.

Economizer for air cooledchilled water systemsEconomizers have proven to be a cost effective energy saver.However on larger buildings, especially multiple story, an air-side economizer involves elaborate and expensive ductworkand control. A waterside economizer often is a superior alter-native. If water cooled condensers are used for rejectingsystem heat, the economizer is usually tied in with the cool-ing tower.

The best economizer application for a dry cooler is withair cooled chillers. A significant amount of free cooling canbe obtained at minimal cost in precooling the chilled waterbefore it goes to the chiller. A typical installation is shownin Figure 2.

The system shown in Figure 2 can be particularly cost effec-tive on the following applications:

1. Year-round cooling.a. Process application.b. High internal cooling load.

2.

3.

4.

5.

6.

7.

Northern climate.

Ethylene glycol is already being used to protect the chillerbarrel.

Chilled water reset can be employed at lower ambients.

A large number of operating hours are required.

A chilled water delta-T greater than 10°F can be accepted.

The chiller requires an expensive low ambient option suchas fan speed control, dampers, or condenser back floodingwhich is eliminated by the free cooling.

Why a dry cooler?A dry cooler is superior to open or closed towers for the follow-ing reasons:

1.

2.

3

4.

Open towers are impractical without using an intermediateheat exchanger. This is because contaminants cannot bebrought into the chilled water system without involving ex-pensive maintenance of the chilled water coils. An in-termediate heat exchanger usually makes an open towertoo expensive on smaller applications.

Pre-cooling of chilled water is only required at lower am-bients where a variation between dry and wet bulbtemperatures are minimal as shown below.

DRY AND CORRESPONDING WET BULB TEMPERATURESAT 60% RELATIVE HUMIDITY

Dry Bulb .5O”F Dry Bulb .95OFWet Bu lb .440F Wet Bulb .83OFDelta-T. 6°F Delta-T.. .12”F

The extra energy savings that an open or closed towercould provide is usually not of a very large magnitude. Thewater treatment costs usually would cancel the majorityof the economizer energy savings.(See Figure 1, page 2.)

On smaller tonnage applications, typical of air cooledreciprocating chillers, a dry cooler will require less space,have significantly less weight, and usually is more effec-tive on a first cost basis.

Figure 2.

Fd I1

AA .’

NOTES:1. Fan cycling controls (FANTROL) sensing LWT from AFC unit.2. Balancing valve opens below 50°F (60°F with chilled water reset.)3. Isolation valves may be required.

Catalog 690 I Page 15

Optional accessories The following optional features are available with the McQuay AFC fluid cooler. Extended lead time may be required for fac-

based on ambient temperature or leaving fluid temperature. The fans are cycled off in sequence by field adjustable

tory mounted options thermostats in the following manner:

Surge tank kit This option is field installed and serves as an expansion tank, partially filled with air, to protect against water hammer. The kit is connected to the coil header.

Fill valve kit This option includes a tee, gate valve and hose bib and is field connected to the header connection. This can be a very practical option since the fluid cooler typically is at the top of the water system.

FANTROL fan cycling capacity control The FANTROL fan cycling capacity control package can be field or factory installed to automatically cycle the fans

Figure 3.

e-fan units . .I cycled 3-fan units. .2 cycled in sequence 4-fan units . .l pair cycled 6-fan units .2 pair cycled in sequence

The FANTROL package includes a weatherproof enclosure, fan motor operating contactor( a line voltage terminal block, a 24 volt transformer, an auxiliary terminal block (24V) and thermostats. The thermostats are bulb-type with a setpoint range of 50 to 130°F. Consult your local representative on applications outside of this range.

NOTE: Capillary tube for thermostat bulb is 8 feet long max- imum. Units with opposite end connections must be piped to allow for limited capillary tube length.

Fill Valve Assembly

Surge Tank Kit

Coil data

DESCRIPTIDN

s

dd

Page 16 / Catalog 690

Wihg diagram Refer to Figure 4 for a typical schematic representation of required field electrical hookups for AFC units with the op- tional FANTROL control package. (Units without the optional FANTROL have the motor leads simply terminated in a junc- tion box at the end of the unit.) All wiring must be done in accordance with applicable local and national codes.

Figure 4. Wiring Diagram

Electrical connection location (standard unit)

- NCTION BOX

I AFC Unit

Catalog 690 I Page 21

Engineering guide specificationsFurnish and install as specified and shown on the plans, McQuay type AFC air cooled fluid cooler(s) arranged for verticalairflow. The fluid cooler shall be multiple fan design (AFC-010 and larger) and shall perform as scheduled. Each fluid coolershall consist of a casing, coil, multiple direct drive propeller fans with independent fan motors, fan guards and mounting legs.All fan motors shall be wired to a common electrical junction box. The basic unit (less optional controls and kits) shall be UL listed.

COIL - The coil shall be constructed of seamless copper tubes on a staggered tube pattern. Tubes shall be mechanicallyexpanded into continuous, rippled (aluminum) (copper) plate type fins for permanent metal-to-metal contact. The fins shallhave full depth fin collars completely covering the copper tube. Copper tubes shall be attached to headers with heavy wallfittings for maximum resistance to piping strain and vibration due to fluid pulsation. Coils shall have a working pressure of300 psig. Coils shall be factory leak tested and sealed for shipment. Coils shall have vents and drains and shall have threadedconnections as scheduled.

CASING - The condenser casing shall be of heavy-duty, reinforced construction utilizing continuous galvanized steel. Cas-ing shall be divided into individual fan sections by full width galvanized partitions. Structural support members, including coilsupport frame, and legs shall be 7- and lo-gauge continous galvanized steel for strength and corrosion resistance.

FAN AND FAN GUARD - Fans shall have aluminum blades riveted to zinc plated steel hub or all steel with enamel paint.The maximum fan diameter shall not exceed 26 inches. Direct drive fans are required to eliminate the maintenance requirementsof belt-driven fans. Fan guards shall be heavy-gauge, close meshed, steel wire, zinc plated and iridite dipped. The guard shallbe contoured for maximum rigidity.

MOTORS - Fan motors shall be weather protected, have ball bearings and built-in overload protection. The units shall be fur-nished with required power as indicated.

0 380/50/30 208-230/60/l0 208160110 230/60/30 460/60/3

OPTIONSFANTROL FAN CYCLING CONTROL PANEL - Unit shall be supplied with factory installed line voltage terminal block, 24volt transformer, time clock terminals, fan cycling thermostats, sensors, and fan contactors, all mounted in a weatherproofcontrol panel. Fan motors are wired through the contactors back to the main unit terminal block.

SURGE TANK KIT - A surge tank kit will be provided to protect against water hammer and shall be for field installation.

FILL VALVE KIT - A pipe tee, gate valve, and hose bib shall be supplied for field installation.

Page 22 / Catalog 690