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A cooling tower extracts heat from process cooling water. Common applications for

cooling towers provide cooled water for air conditioning, manufacturing, and electric

power generation.

Application Challenges

Energy savings Reduce maintenance requirements (personnel and equipment replacement costs)

recisely control process water temperature sta!ili"ation

Applicable Products

Drives

Products

Features Benefits

E# $rive

%amily

or

# $rive

&uilt'in $ control perate the drive directly with !uilt'in *'+

mA terminals. -aintain temperature and

lower energy consumption.

-aintain a minimum speed. et the frequency reference lower limit.

witch to a line power supply. peration is not interrupted.

Continue running after

momentary power loss.

/he motor continues running even after a (+

sec) momentary power loss.

-otor preheat Eliminate condensation in the motor.

Application Details

A starter and a control unit to provide start0stop control and speed control are required forcooling tower fan operation. 1as2awa AC varia!le frequency drives are equipped with

!uilt'in $ control and speed search technology to restart the drive after a momentary

power loss.

%or maximum energy savings, the drive should provide the coldest temperature that thesystem will tolerate !efore reducing motor speed. 3aria!le frequency drives can !e the

solution in noise sensitive applications. oft starting and gradual speed changes ma2e

cooling tower noise less noticea!le and reduce mechanical wear.

A varia!le frequency drive can correctly identify the cooling tower fan rotation, slow the

motor speed to "ero (when opposite rotation is detected), and accelerate the fan in thecorrect direction. /he 3%$ drive eliminates !ra2es, anti'ratcheting devices, and time

delays. Running the fan slower, which raises tower and water temperatures, can prevent

icing in cold weather. A 3%$ can reverse a cooling tower fan and 2eep the heat in the

tower, if necessary. n warm weather, fans can !e run faster, providing additional coolingcapacity.

Additional Information

http://www.yaskawa.com/site/Products.nsf/productGroup/HVACDrives.htmlhttp://www.yaskawa.com/site/Products.nsf/productGroup/HVACDrives.htmlhttp://www.yaskawa.com/site/Products.nsf/products/Industrial%20AC%20Drives~P7.htmlhttp://www.yaskawa.com/site/Products.nsf/products/Industrial%20AC%20Drives~P7.htmlhttp://www.yaskawa.com/site/Products.nsf/productGroup/HVACDrives.htmlhttp://www.yaskawa.com/site/Products.nsf/productGroup/HVACDrives.html

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/he pdf contains the same information as the we!, !ut in some cases may contain more

and should !e used if a printed version is required.

The greater the range of allowable humidity, the greater the energy savings. As theallowable humidity range increases, the use of energy-efficient indirect-direct

evaporative coolingbecomes more appropriate. Depending upon climate, when alaboratory's required relative humidity range is 4 to ! percent, evaporative cooling

can be used. This approach can consume as little as two-thirds of the energynecessary to provide a range of 4! to 4 percent ".#., assuming this lower humidity

range requires the use of a chiller. $aboratories in warmer climates benefit fromraising the allowable ".#.% laboratories in colder climates benefit most from lower

minimum ".#. specifications as well as a wider range. &ee hapter (and . )$ynn,*++* vaporative cooling systems have been used to condition facilities since before

refrigerated cooling was invented. There are two types of evaporative coolingtechniques indirect and direct. The indirect approach removes sensible energy only

from the air stream with an e/changer that has the air stream flow on one side of a

plate and water on the other. The direct approach removes energy from the airstream adiabatically by adding moisture to the air stream. These approaches can be

combined to provide cooling and humidification that displaces energy from a

conventional compressor-type #0A system. Annual energy savings of more than *percent for a one-stage, direct system and over (1 percent for a two-stage

indirect2direct system can be reali3ed when compared to a conventional #0Asystem. rown 5*++(6 says, 7The use of direct evaporative cooling to humidify

increases the opportunity to recover heat by (8 percent and reduce energyconsumption during the heating season.7 9ne- to two-year paybac:s are possible.

The ;ustification of evaporative cooling should not be based solely on the ability toreplacemechanical cooling but should be considered as an opportunity to displace

mechanical cooling2humidification energy. )rown, *++

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considered when the outdoor wet-bulb temperature is (>? 5**.@>6 or less for(,!! or more hours per year. Direct evaporative cooling of air conditioning

condensers, which are normally simply air-cooled, can reduce electrical energy anddemand consumption by

*++(

Two-stage

Typically, a two-stage evaporative cooling system comprises a direct evaporative

cooler downstream of an indirect evaporative cooler. The two coolers can becombined in a myriad of arrangements to increase energy efficiency. )rown, *++

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0?D controlled cooling tower fans operate over many speeds as opposed to the fans on a single ortwo-speed motor starter. As such, it is a good practice to perform a vibration analysis on the fan

and tower assembly, as a mechanical resonance may develop at certain speeds.

=dentified problem speeds may be programmed into the drive and 7loc:ed out7. 0ibration switches

are often wired into a drive or control system,shutting down the cooling tower if a problem

arises.

A drive may also be able to monitor oil level

and temperature of the gearbo/.

0?D's are usually not mounted close to the

cooling tower, resulting in long lead lengthsbetween the drive and the motor. ?or oldermotors with lead lengths greater than 8! feet,a long lead 5d02dT6 filter is recommended.

Gew motors may be approved for 0?Doperation with motor lead lengths in e/cess of

(! feet, without the need for an output filter.onsult the motor manufacturer for motor leadlength and carrier frequency restrictions.

AC! "## - T$e %erfect C$oice for Cooling

ToersBell suited for the rigors of an industrialenvironment, the A& 1!! was designed withma/imum reliability in mind. &tandard features

include (F impedance A line reactors. Additionally,capacitor ban:s and cooling fans have a lifee/pectancy of *!!,!!! 8!,!!! hours respectively.

A wide operating voltage range 5(1!-!! 0A H

*!F6 in con;unction with an over-voltage controller,eliminate over-voltage trips. y utili3ing the load

inertia, an under-voltage controller providese/tended ride thru capability.

The common loo: and feel of the A& 1!! minimi3estraining requirements as well as helps to :eep thecost of spare parts down. The ma;ority of components are the same, regardless of the #C or voltage

ratings.

DT 5Direct Torque ontrol6 provides features found only in 0?D's fromA. ?or e/ample, an Automatic &tart feature will immediately start into arotating load, with no delay - regardless of direction. The motor is then

smoothly accelerated to commanded speed.

Advanced ?lu/ 9ptimi3ation yields up to a *!F increase in efficiency at

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side of molded plastic indirect evaporative cooling plates. Separate wet and dry passages troug tose

plates are facilitated by a uni$ue means for clamping te upper ends of te plates. "ese clamping means

also add to te structural integrity of an array of plates so tat te array can be inserted in and removed

from a ousing containing oter operational components of te IDEC suc as fan! direct cooling plates and

water distribution means. #pplicants IDEC utili&es improved porous piping tat allows uniform and

continuous distribution of water to all wet passages witin bot te indirect and direct stages of te IDEC.'perational controls for te system limit te potential water damage caused by overflow of water from te

IDEC ousing.

A variable-frequency drive (FD!is a system for controlling the rotational speed of analternating current(AC) electric motor!y controlling the frequency of the electrical

power supplied to the motor. A varia!le frequency drive is a specific type ofad4usta!le'

speed drive. 3aria!le'frequency drives are also 2nown as ad4usta!le'frequency drives

(A%$), varia!le'speed drives (3$), AC drives, microdrives or inverter drives. ince thevoltage is varied along with frequency, these are sometimes also called 333% (varia!le

voltage varia!le frequency) drives.

VFD system description

3%$ system

A varia!le frequency drive system generally consists of an AC motor, a controller and an

operator interface.

[edit] VFD motor

/he motor used in a 3%$ system is usually a three'phaseinduction motor. ome types of

single'phasemotors can !e used, !ut three'phase motors are usually preferred. 3arioustypes of synchronous motors offer advantages in some situations, !ut induction motors

are suita!le for most purposes and are generally the most economical choice. -otors that

are designed for fixed'speed mains voltage operation are often used, !ut certain

enhancements to the standard motor designs offer higher relia!ility and !etter 3%$performance.

Now that we have covered the basics of the indirectanddirectevaporative cooling processes,

it's time to consider one more wrinkle--putting them together.

In the IDEC cooling discussion, I made the point that not onl do we get a reduction in dr-bulb

temperature as our airflow passes through the IDEC unit, but we get a reduction in wet-bulb

temperature, also. !nd since we now have seen that the direct evaporative cooling process

depends criticall on the wet-bulb temperature of the air it is cooling, it seems we should get

http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Adjustable-speed_drivehttp://en.wikipedia.org/wiki/Adjustable-speed_drivehttp://en.wikipedia.org/wiki/Adjustable-speed_drivehttp://en.wikipedia.org/w/index.php?title=Variable-frequency_drive&action=edit&section=4http://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Single-phasehttp://jbarrownews.blogspot.com/2007/09/introduction-to-indirect-evaporative.htmlhttp://jbarrownews.blogspot.com/2007/09/introduction-to-indirect-evaporative.htmlhttp://jbarrownews.blogspot.com/2007/09/introduction-to-direct-evaporative.htmlhttp://jbarrownews.blogspot.com/2007/09/introduction-to-direct-evaporative.htmlhttp://jbarrownews.blogspot.com/2007/09/introduction-to-direct-evaporative.htmlhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Adjustable-speed_drivehttp://en.wikipedia.org/wiki/Adjustable-speed_drivehttp://en.wikipedia.org/w/index.php?title=Variable-frequency_drive&action=edit&section=4http://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Single-phasehttp://jbarrownews.blogspot.com/2007/09/introduction-to-indirect-evaporative.htmlhttp://jbarrownews.blogspot.com/2007/09/introduction-to-direct-evaporative.html

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some advantage b running the air through the IDEC section, and then running it through the

direct section. !nd we do"

#click for larger image$

!s ou can see, the resultant leaving dr bulb is on the order of %&, which is better than the

resultant of () from the indirect section alone, or %* for the direct evaporative section alone.

Now %& degrees ma not seem cool enough for tpical cooling applications--and for most

pro+ects it probabl isn't #although it is important to not that !!E comfort conditions canbe

met with this leaving air condition in a predominantl sensible load application given enough

air$. /ut keep in mind that this is the performance on a design day. ow man hours a ear

would ou be able to meet the traditional suppl air temperature of 001 2ets look at

pschrometric chart with eattle bin data loaded into it"

#click for larger image$

! 3uick note of e4planation" 5he vertical line at 00 is the economi6er line--an climactic

conditions to the left of that line can be used to create cooling air directl using 7! alone #or

mi4ing 7! with !$ and thus re3uire no additional cooling at all. 5he blue diagonal line along

the 08 wet-bulb line is a conservative mapping of the direct evaporative regime. !t an bin

hours under this line, direct evaporative cooling can be applied to the ambient 7! to achieve

cooling air directl. !nd lastl, the red diagonal line above that is the indirect-direct

evaporative cooling regime, where the application of both cooling techni3ues will provide

acceptable suppl air conditions #assuming about (9: effectiveness on the IDEC$. !nd above

that line, the indirect evaporative sstem can still be applied to greatl reduce the load on an

supplemental mechanical cooling sstem, if used to meet the same 00 leaving air condition.

http://img115.imageshack.us/my.php?image=indirectdirect55degreesmy6.jpghttp://img511.imageshack.us/my.php?image=indirectdirectexampleeh1.jpg

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5wo things +ump out of this analsis" ;irst, the vast ma+orit of the hours are satisfied without

using mechanical cooling. In fact, in eattle, most hours are met with simple economi6ers--

which e4plains the emphasis in our local codes on this cooling technolog.

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#click for larger image$

It looks prett similar to eattle, as we might guess. ow about a hot, dr climate like

pokane1"

#click for larger image$

5hat's a real winnerA 5here's onl a small fringe of hours outside of the range where

indirectBdirect evap works alone. o if pokane works, surel

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Indirectdirect evaporative coolinguses te pysics of water evaporation to cool wit reducedlevels of compressor cooling! wic is an energy intensive process. Evaporative coolers can save*-+*, of te cooling energy for spaces suc as classrooms. In addition to saving energy! directevaporative coolers also add needed moisture to te conditioned air.

en a pound of water evaporates! almost *** /tu0s of cooling is associated wit te process.If warm dry air is blown across a medium torougly wetted wit water! te air is cooled and itsumidity is raised. If te process were **, efficient! te temperature drop of te air would bete difference between dry bulb and wet bulb temperatures. In practical systems suitable forcommercial! industrial! and agricultural use! efficiencies of +*-+1, are routinely acieved. InColorado0s climate &ones! wet bulb temperatures are lower tan dry bulb temperatures by anaverage of over 2* degrees 3areneit for 44, of te cooling season! so evaporative cooling is$uite feasible. Since te only energy it consumes is tat associated wit fan power for moving airand pump power for moving relative small amounts of water! evaporative coolers save botenergy and demand by a factor of almost tree versus conventional compressor-based cooling.

#ltoug direct systems li%e te one sown below wor% well wit small commercial structures and

most agricultural buildings! directindirect systems are more prevalent wit larger buildings li%eoffices and retail establisments. #ir tat is cooled evaporatively from te exaust stream fromte building (or from outside air! depending on circumstances) is used to cool incoming air via anair-to-air eat excanger. "us! incoming air is cooled! but not umidified wit a directindirectsystem. # variation! %nown as a ybrid system! includes a modicum of compressor-based coolingfor periods of ig umidity in wic evaporative cooling systems become less effective.5owever! te conventional cillers wit suc ybrid systems may be downsi&ed by a factor of fiveor more from a ciller used to supply all of a building0s cooling needs.

Directindirect and ybrid systems are more costly tan simple direct evaporative coolingsystems! but tey routinely cost less tan conventional compressor-based systems and avesubstantially lower energy and demand costs over teir lifetimes. "e best units utili&e ig-efficiency fans driven by variable speed drives on premium-efficiency motors. 6arying fan speed

wit load not only raises overall system efficiency! but also extends te life of te wetted pad andoter %ey components. 7ifetime is also extended by te selection of pads tat use treated glassfiber seets (instead of conventional excelsior made of aspen wood)! and ousing of fiberglass orstainless steel. 8outine maintenance is not costly but necessary to ensure good air $uality andlong life.

Direct Evaporative Cooling(Source: Platts/E SOURCE)

Direct/Indirect Evaporative Cooling(Source: Platts/E SOURCE)

Specifying ig-efficiency! water-cooled cillers wenever appropriate saves energy and demandcarges. In te case of facilities wit cooling loads of more tan 9** tons! it is generally cost-

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effective to install a water-cooled chiller! particularly in Colorado0s dry climate. In all events! ahigh-eiciency electric chillercan reduce energy consumption by 9*, or more compared wita standard-efficiency ciller. Consider evaporative coolers in ot! dry climates. Specify smalldirect or indirect evaporative coolers instead of vapor-compression units.