bac+evaporative+condensers

8/8/2019 BAC+Evaporative+Condensers

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Overview

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EvaporativeCondensers

Evaporative Condensers

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Product Group Detail

General Information ................................................................................. E2

Principle of Operation .............................................................................. E2

Configuration ............................................................................................. E2

Fan System ................................................................................................. E3

Capacity Range .......................................................................................... E4

Typical Applications .................................................................................. E4

Product Line Overview Table .................................................................. E4

Engineering Considerations ..................................................................... E6


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Bal t im ore A i rco i l

General InformationEvaporative condensers provide heat rejection for many types of systems, and the specificapplication will largely determine which BAC Evaporative Condenser is best suited for a project.The product line overview table in this section is intended as a general guide.Evaporative condensers are used to provide lower condensing temperatures and compressorkilowatts savings of up to 30 percent when compared with air-cooled systems.

Principle of OperationThe vapor to be condensed is circulated through a condensing coil, which is continually wetted onthe outside by a re-circulating water system. Air is pulled or pushed over the coil, causing a smallportion of the re-circulating water to evaporate. The evaporation removes heat from the vapor inthe coil, causing it to condense.

ConfigurationBAC manufactures three types of evaporative condensers: combined flow, counter flow, hybridand adiabatic products.

Combined Flow

Combined flow is the use of both a condensing coil and wet deck surface for heat transfer in anevaporative condenser. The addition of wet deck surface to the traditional evaporative condenserdesign reduces evaporation in the coil section, reducing the potential for scaling and fouling. BACscombined flow evaporative condensers utilize parallel flow of air and spray water over the coil, andcrossflow air/water flow through the wet deck surface.

In parallel flow, air and water flow over the coil in the same direction. In the wet deck section ofBACs combined flow evaporative condensers, air and water interact in a crossflow configuration:water flows vertically down the wet deck as air flows horizontally across it.

Combined Flow: Parallel flow of air and waterover the coil

Combined flow: Crossflow configuration overthe wet deck


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... because temperature matters

Counterflow

In a counterflow evaporative condenser design,the flow of the air is in the opposite direction of thespray water. In BACs counterflow evaporativecondensers, air travels vertically up through theunit while the spray water travels vertically downover the coil.

Hybrid and Adiabatic Products

See description under separate section "HybridWater Saving Products.

Fan SystemThe flow of air through most factory assembled evaporative cooling equipment is provided by oneor more mechanically driven fans. The fan(s) may be axial or centrifugal, each type having its owndistinct advantages.

Axial fan units require approximately half the fan motor kilowatt of comparably sized centrifugal fanunits, offering significant life-cycle cost savings.Centrifugal fan units are capable of overcoming reasonable amounts of external static pressure(125 Pa), making them suitable for both indoor and outdoor installations. Centrifugal fans are alsoinherently quieter than axial fans, although the difference is minimal and can often be overcomethrough the application of optional low sound fans and/or sound attenuation on axial fan units. Fanscan be applied in an induced draft or a forced draft configuration.

Induced DraftThe rotating air handling components of induced draft equipment are mounted in the top deck ofthe unit, minimizing the impact of fan noise on near-by neighbors and providing maximum

protection from fan icing with units operating in sub-freezing conditions. The air being drawnthrough the unit hereby discharges over the inducing fan. The use of corrosion resistant materialsensures long life and minimizes maintenance requirements for the air handling components.

Forced DraftRotating air-handling components are located on the air inlet face at the base of forced draftequipment whereby fresh air is blown through the unit. This base fan position facilitates easyaccess for routine maintenance and service. Additionally, location of these components in the dryentering air stream extends component life by isolating them from the corrosive saturateddischarge air.

Counterflow Configuration

Centrifugal Fans Axial Fans


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Capacity RangeAll capacities shown are for a single unit; multiple units can be applied to achieve larger capacities.

Typical ApplicationsA list of typical applications is provided in the Product Line Overview Table for your reference.

Product Line Overview Table

For VXC, VCL, HXC, CXV, CXV-D: 1. Air in; 2. Air out; 3. Vapour in; 4. Liquid out; 5. Wet deck surface; 6. Cold water basin; 7. Water

distribution system; 8. Coil; 9. Spray Water Pump; 10. Eliminators; 11. Optional Extended Surface. 12. Dry finned coil; 13. Modulating air inlet

dampers; 14. Servo motor; 15. Pressure transmitter.

HXC and DCV water saving and hybrid wet-dry products are available to meet these specificdesign requirements. Refer to the Water Saving Products section for more details onthese products.

VXC VCLHXC

(For more information refer to SectionHybrid Water Saving Products)

Principle ofOperation

Configuration Counterflow Counterflow Combined flow

Fan System Centrifugal Fan, Forced Draft Centrifugal Fan, Forced Draft Axial Fan, Induced Draft

Capacity RangeNominal R717

kWs50 to 6470 kW 160 to 1290 kW 710 to 2460 kW

TypicalApplications

Sound sensitive industrial refrigerationprojects

Installations with limited plan areaIndoor Installations

Sound sensitive industrial refrigerationprojects.

Installations with extremely low heightrequirements

Indoor InstallationsSkid packages

Industrial refrigeration applications in geo-graphical regions where water cost is high.

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For TrilliumSeries Condenser: 1. Dry heat exchanger; 2. Fluid in; 3. Fluid out; 4. Axial Fans; 5. High efficiency evaporative coolingpad; 6.

Water inlet connections; 7. Water outlet connections; 8; Adiabatic cooling ot ambient air; 9. Air Discharge; 10. Air In.

CXV CXV-D

DCVTrilliumSeries Condenser

(For more information refer to SectionHybrid Water Saving Products)

Combined Flow Combined Flow Counterflow

Axial Fan, Induced Draft Axial Fan, Induced Draft Axial Fan, Induced Draft

410 to 2730 kW3500 to 5140 kW 340 to 1030 kW

Industrial refrigeration applicationsVery large industrial refrigeration and processprojects requiring low energy consumption and

low sound

Small to medium industrial refrigeration projectsLocations with limited water and limited space

availability

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Engineering Considerations

Location

Units must have an adequate supply of fresh air to the air inlet(s). When units are located adjacentto building walls or in enclosures, care must be taken to ensure that the warm, saturated dischargeair is not deflected off surrounding walls or enclosures and drawn back to the air inlet(s).

Warning: Each unit should be located and positioned to prevent the introduction of the warm discharge air and the

associated drift, which may contain chemical or biological contaminants including Legionella, into the ventilation

systems of the building on which the unit is located or those of adjacent buildings.

Note: For detailed recommendations on layout, please consult your local BAC Balticare Representative.

For VL and VX products, bottom screens or solid bottom panels may be desirable or necessary forsafety, depending on the location and conditions at the installation site.

Piping and Valves

Piping should be adequately sized according to standard refrigeration practice and arranged to

allow flexibility for expansion and contraction between component parts of the system. Suitablysized equalising lines must be installed between the condenser and high pressure receiver toprevent gas binding and refrigerant backup in the condenser. Service valves should be installedso that the component parts may be easily serviced.

On multiple evaporative condenser installations, evaporative condensers in parallel with shell-and-tube condensers, or single condensers with multiple coils, refrigerant outlet connections must betrapped into the main liquid refrigerant header. The height of the trapped liquid legs must besufficient to balance the effect of the unequal coil pressures without backing up liquid refrigerantinto the condensing coil. This type of liquid line piping permits independent operation of any oneof the parallel circuits without manually closing inlet and outlet valves.

Although equalising lines can be used to balance water levels between multi-cell evaporativecondensers, the spray water for each cell must be treated separately, and a separate make-upmust be provided for each cell. Note that a common remote sump for multi-cell installations cansimplify make-up and water treatment. See section "Technical Resources, Application Guidelines"or the appropriate Operating and Maintenance Instruction Manual for more information on watertreatment.

Weld Byproduct CleaningThe installation and manufacturing processes commonly used for field assembly of steel-pipedsystems may leave weld byproducts inside coils and connecting piping (especially in refrigerationsystems). It is common practice to install filters and/or strainers that remove contaminants during

initial system operation. Shortly after system startup, the filters and/or strainers should be cleanedor replaced.

Capacity Control

Variable Frequency Drives (VFD)Installations which are to be controlled by Variable Frequency Drives (VFD) require the use of aninverter duty motor as designed IEC 34.1, which recognizes the increased stresses placed onmotors by these drive systems. Inverter duty motors must be furnished on VFD applications inorder to maintain the motor warranty. Fan motors must be furnished with thermal protection (eitherPTC sensors or coil thermostats normally open, or normally closed). The motor protection consists

of temperature sensitive cutout devices embedded in the motor windings (minimum 3 per motor).


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The minimum fan motor speed during normal operation should be not below 30% of the speedindicated on the motor nameplate. This corresponds with 15 Hz for a 50 Hz supply and 18 Hz fora 60 Hz supply.

BAC offers factory installed motor control packages including VFD drives. Refer to the section"Technical Resources, Motor Controls". Check with your local BAC Balticare representative foravailability.

Warning: When the fan speed is to be changed from the factory-set speed, including through the use of a variable

speed control device, steps must be taken to avoid operating at or near fan speeds that cause a resonance with the

unit or its supporting structure. At start-up, the variable frequency drive should be cycled slowly between zero and

full speed and any speeds that cause a noticeable resonance in the unit should be locked out by the variable speed

drive.

Fan CyclingFan cycling is the simplest method of capacity control. The number of steps of capacity control canbe increased using the BaltiguardFan System, the independent fan motor option, or two-speedfan motors in conjunction with fan cycling (see the Custom Features & Options section of theappropriate product line to determine whether the BaltiguardFan System or the independent fanmotor option are available; two-speed motors are available for all products). These options provide

substantial energy savings when compared to simple fan cycling.

Warning: Rapid on-off cycling can cause the fan motor to overheat. It is recommended that controls be set to allow a

maximum of 6 on-off cycles per hour.

Note:Spray water pump cycling should not be used for capacity control. This method of control often results in short

cycling of the pump motor as capacity changes substantially with pump cycling. In addition, alternate wetting and drying

of the coil promotes scaling of the heat exchanger coil surface.

Capacity Control DampersOn centrifugal fan models, modulating capacity control dampers are available to provide closecontrol of head pressure. See Section "Accessories" or contact your local BAC Balticare

representative.

Vibration Cut-out Switch

Vibration cutout switches are recommended on all axial fan installations. Vibration cutout switchesare designed to interrupt power to the fan motor and/or provide an alarm to the operator in theevent of excessive vibration. BAC offers both electronic and mechanical vibration cutout switcheson all evaporative condensers.

Water Treatment

As water evaporates in the unit, the dissolved solids originally present in the water remain in the

system. The concentration of these dissolved solids increases rapidly and can cause scale andcorrosion. In addition, airborne impurities and biological contaminants, including Legionella, maybe introduced into the circulating water. To control all potential contaminants, a water treatmentprogram must be employed. In many cases, a simple bleed-off may be adequate for control ofscale and corrosion.However, biological contamination, including Legionella, can be controlled only through the use ofbiocides. Such treatment should be initiated at system startup, after periods of equipmentshutdown, and continued regularly thereafter. Accordingly, it is strongly recommended a biocidetreatment be initiated when the unit is first filled with water and continued regularly thereafter. Formore information, consult the appropriate Operating and Maintenance Manual.

When a water treatment program is employed, it must be compatible with construction materials.

Batch feeding of chemicals into the unit is not recommended. If units are constructed with optional


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corrosion resistant materials, acid treatment may be considered; however, the water quality mustbe maintained within the guidelines set forth in the Operating and Maintenance Instructions.

Note:Unless a common remote sump is utilised, each cell of a multi-cell installation must be treated as a separate

entity, even if the cold water basins are equalized.

For complete Water Quality Guidelines, see the appropriate Operating and MaintenanceInstruction Manual, available at www.baltimoreaircoil.com. For specific recommendations on watertreatment, contact a competent water treatment supplier.

Sound Levels

Sound rating data are available for all BAC models. When calculating the sound levels generatedby a unit, the designer must take into account the effects of the geometry of the tower as well asthe distance and direction from the unit to noise-sensitive areas. Whisper Quiet fans and intakeand discharge sound attenuation can be supplied on certain models to provide reduced soundcharacteristics (see the Custom Features and Options section of the appropriate product line fordetails). The BaltiguardFan System, two-speed motors, or variable frequency drives can also beused to reduce sound during periods of non-peak thermal loads. For more information on sound

and how it relates to evaporative cooling equipment, see Section "Technical Resources,Fundamentals of Sound". For detailed low sound selections, please consult your local BACBalticare Representative.

Winterization

When a unit is shut down in freezing weather, the basin water must be protected by draining to anindoor auxiliary remote sump tank or by providing supplementary heat to the cold water basin.Supplementary heat can be provided by electric immersion heaters or in some cases, hot water,steam coils, or steam injectors. All exposed water piping, make-up lines, and spray pumps (ifapplicable) that do not drain at shutdown should be traced with electric heater tape and insulated.When dry operation is planned for low ambient conditions, centrifugal fan units should be supplied

with oversized fan motors to prevent motor overload when the spray water is not operating. Forremote sump applications, the spray water pump must be selected for the required flow at a totalhead which includes the vertical lift, pipe friction (in supply and suction lines) plus the requiredpressure at the inlet header of the water distribution system (14 kPa). A valve should always beinstalled in the discharge line from the pump to permit adjusting flow to the unit requirement. Inletwater pressure should be measured by a pressure gauge installed in the water supply riser at thespray water inlet, and adjusted to the specified inlet pressure.

Indoor Installation (applicable to VXC and VCL models only)

Many indoor installations require the use of inlet and/or discharge ductwork. Units installed withinlet ductwork must be ordered with solid-bottom panels. Generally, intake ducts are used

only on smaller units while the equipment room is used as a plenum for larger units. Dischargeductwork will normally be required to carry the saturated discharge air from the building.Both intake and discharge ductwork must have access doors to allow servicing of the fanassembly, drift eliminators, and water distribution system. All ductwork is supplied and installed byothers and should be symmetrical and designed to provide even air distribution across the face ofair intakes and discharge openings. Such ductwork may increase the external static pressure onthe unit, requiring a larger fan motor to be installed. This external static pressure must be quantified(in Pa) to BAC to allow for suitable fan motor sizing.

Warning: The discharge opening must be positioned to prevent the introduction of discharge air into the fresh air

intakes serving the unit or the ventilation systems of adjacent buildings.

Note:Axial fan units are not suitable for indoor installations.


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Safety

Adequate precautions, appropriate for the installation and location of these products, should betaken to safeguard the public from possible injury and the equipment and the premises fromdamage. Operation, maintenance and repair of this equipment should be undertaken only bypersonnel qualified to do so. Proper care, procedures and tools must be used in handling, lifting,installing, operating, maintaining, and repairing this equipment to prevent personal injury and/orproperty damage.

Code Requirement

All evaporative condenser coils supplied from Europe, including desuperheater coils, are certifiedaccording to the European Pressure Equipment Directive 97/23/EC. Since November 1999 thisPressure Equipment Directive has been adopted by the national legislation of all EU and EFTAmember states. The PED 97/23/EC specifies the design, manufacturing, quality anddocumentation requirements for pressure vessels and replaces previous national coderequirements. BAC evaporative condenser coils fall under Category IV of the PED 97/23/ECreglementation and require a CE Declaration of Conformity which is supplied by BAC at time ofshipment.

Standard PED Coil design (hot-dip galvanised)All BAC evaporative condenser coils, including bare serpentine coils, split circuit coils, extendedsurface coils and desuperheater coils are designed as standard for a maximum operating pressureof 23 bar (minimum -1 bar). Design temperatures are minimum: -20C and maximum +120C. Allstandard PED coils are pneumatically tested at 34 bar after fabrication.

Optional High pressure PED coil design (hot dip galvanised)For specific refrigerants or applications requiring higher operating pressures (> 23 bar), the highpressure coil option is available for all hot-dip galvanised condenser coil types (see above understandard PED coil design). The high pressure coils are designed for a maximum operatingpressure of 28 bar (min. -1 bar) and are pneumatically tested at 40 bar. Design temperatures are

minimum -20C and maximum +120C.

Optional Stainless Steel PED coil designBare serpentine coils only (with or without split) are available in stainless steel AISI 304 or AISI 316execution. All stainless steel coils are designed for a maximum operating pressure of 23 bar (min.-1 bar) and are pneumatically tested at 34 bar. Design temperature limits are minimum -20C andmaximum +120C.

Checking the refrigeration system for non-condensables and purging

Source of Non-Condensables

Air and other non-condensables gases collect in refrigeration systems from several sources :

1. Poor evacuation of a new system low side if operation is at pressures below atmospheric.2. Failure to evacuate completely after part of a system has been open for repair.3. Chemical breakdown of oil and/or refrigerant.


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Test on Non-Condensables

Check the system for non-condensable gases is done during system operation. First close thevalve (V3) in the liquid line running from the receiver to the evaporator (king valve).

Keep the compressor running and start pumping down the system. The compressor pressure willdrop as the ammonia supply has been shut off and will finally cause the compressor to fall out(security). When this happens, simultaneously close the discharge valve V1 of the compressor.

The condenser is now fully pumped up with the ammonia refrigerant (which is captured betweenvalves V1 and V3 and cannot escape).

Operate the evaporative condenser for at least two hours and measure the 5 temperatures (listedbelow) every 10 minutes until the pan water temperature is equal to the entering wet bulbtemperature (T pan = WB in).When this happens, an equilibrium has been reached in the condenser and all 5 measuredtemperatures should be identical to each other.If the temperature (T1, T2) corresponding to the pressure in the evaporative condenser is higher

than the entering wet bulb temperature by more than 1C, the system has an excessive amount ofnon-condensables (make sure that all gauges are accurate when checking for non-condensables).

Five temperatures to be measured : Entering wet bulb temperature at the condenser air inlet (WB in).

Discharge wet bulb temperature at the condenser outlet (WB out).

Pan (or remote sump) water temperature (T pan).

Temperature (T1) equivalent to refrigerant inlet pressure of the condenser.

Temperature (T2) equivalent to refrigerant discharge pressure of the condenser.


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Purge ConnectionsThe several recommended piping arrangements each show purge valves at two different locations,i.e. at the high point of the system and at each condensing coil outlet.

Purging at the high point of the system can only be effective when the system is down. Duringnormal operation the non-condensables are dispersed throughout the high velocity refrigerantvapour and too much refrigerant would be lost when purging from this high point.

However, purging at the condenser coil outlet can be effectively accomplished during system

operation. The non-condensables will carry through the condenser coil with the refrigerant liquidand vapour and tend to accumulate in the condensing coil outlet header and connection where thetemperature and velocity are relatively low.

Purge PipingAll of the purge connections on the condenser coils plus the purge connection in the receiver maybe cross connected to a single purge line, connected to an automatic purger. However, only onepurge valve should be open at a time. Opening two or more valves tied together equalises the coiloutlet pressures and the effect of the vertical drop legs is lost.

Desuperheaters

The discharge gas from ammonia reciprocating compressors is highly superheated. Adesuperheater removes a portion of this superheat prior to the gas entering the condensing coil,and thereby reduces the load on the evaporative condenser. Within the normal range of single-stage compressor operation, discharge gas temperatures at 13 bar discharge pressure (36C)may run from 120C to 150C depending on the compression ratio, amount of suction gassuperheat, and the compressor design. This represents up to 15% of the total heat rejection load.Other refrigerants and compressor types generally have much lower discharge gas temperaturesthan the ammonia reciprocating system so a desuperheater is usually impractical for theseapplications.

An enhanced surface coil encased by galvanised steel panels will be fitted onto the evaporativecondenser in the discharge air stream. The coil has a design for low pressure drop and is incomplete compliance to the PED code requirements for a 23 bar design pressure. Optional highpressure PED coils are available designed for 28 bar operating pressure. The coil is a two passarrangement with the entering and leaving gas connections at the same end; thus keeping all coilconnections at the same end of the evaporative condenser. The coil is hot dip galvanised afterfabrication and mounted into a completely enclosed plenum with access doors to allow inspectionand maintenance of the drift eliminators and spray section. The piping between the desuperheater

coil and the condenser coil is to be field fabricated and installed by the contractor.

Ammonia Reciprocating Compressorsgenerate significant superheat

The desuperheater coil is located on top of thecondenser, above the drift eliminators.


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Refrigerant Liquid Subcooling

The pressure at the expansion device feeding the evaporator(s) can be substantially lower thanthe receiver pressure due to liquid line pressure losses. If the liquid line is long or the evaporatoris above the receiver, which further reduces the pressure at the expansion device, significantflashing can occur in the liquid line.

To avoid liquid line flashing where the above conditions exist, it is necessary to subcool the liquid

refrigerant after it leaves the receiver. The minimum amount of subcooling required is thetemperature difference between the condensing temperature and the saturation temperaturecorresponding to the pressure at the expansion device. To determine the degree of subcoolingrequired, it is necessary to calculate the liquid line pressure drop including valves, ells, tees,strainers, etc., and add to it the pressure drop equivalent to the static head loss between thereceiver and the expansion device at the evaporator, if the evaporator is located above thereceiver.

Some compressor manufacturers publish their compressor ratings based on a fixed amount ofsubcooling at the expansion device. Subcooled liquid at the expansion device of the evaporatordoes increase system capacity since it increases the refrigeration effect per litre refrigerant

circulated. But the increase is relatively small and seldom justifies the cost of the subcooling deviceand piping for this reason alone. However, where compressor ratings based on subcooled liquidare used, the specified amount of subcooling must be added to that required for liquid line pressuredrop and static head loss.

Note: Increasing the evaporative condenser size over the capacity required for the system will not produce liquid

subcooling. The increased condenser capacity will result only in lower operating condensing temperatures. The same

result will occur if the condensing coil is piped directly to the subcooling coil.

Low temperature, multistage ammonia (R-717) refrigeration systems often use liquid subcoolingbetween stages for more economical operation. However, subcooling coils in an evaporativecondenser are seldom, if ever, used with an ammonia refrigeration system for several reasons and

are not available from BAC:

1. Design condensing temperatures are generally lower with ammonia, thus limiting the amount ofsubcooling that can be obtained.

2. The density of ammonia liquid is approximately 37 pounds per cubic foot, less than half that ofthe normally used halocarbons, and static head losses are proportionately less.

3. The expansion devices and system designs normally used for ammonia systems are lesssensitive to small amounts of flash gas.

4. The high latent heat of ammonia (approximately 7110 kJ/kg versus 163 kJ/kg for R-22) resultsin comparatively small amounts of flash gas with a liquid line properly sized for low pressuredrop.

Note:Subcooling coils are not available from BAC.

Warranties

Please refer to the Limitation of Warranties applicable to and in effect at the time of the sale/purchase of these products.

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