Closed Circuit Coolers

ATWB Closed Circuit Cooler

ATWB Closed Circuit Cooler

Independently certified to withstand seismic and wind load forces at ALL Building locations in North America.

The ATWB is an induced draft, counterflow design closed circuit cooler with a capacity range of 85 to 46,667 MBH (24 to 13,664 kW). Standard construction includes the patented, high efficiency Thermal-Pak® Coil and G-235 (Z-725 Europe)galvanized steel casing and basin. Type 304 or 316 stainless steel construction is available for the basin or the entire unit.

Designed for easy maintenance, the ATWB Closed Circuit Cooler leads the industry in service friendly features. The three most critical areas for closed circuit cooler maintenance are the basin, drive system, and coil. The ATWB basin section is designed to allow quick and easy access from outside the cooler. Just like the basin, all service to the drive system can be safely performed from the side of the cooler, and EVAPCO's Power-Band drive system is the easiest belt drive system to maintain in the industry! The exclusive Thermal-Pak® Coil is designed for trouble-free maintenance and long life straight from the factory.

Click on the features below for more details.

3', 4', 8-1/2' & 17' Wide Models Motor Mount, Power Band Belt Adjustment and Bearing Lubrication

The fan motor and drive assembly are designed to allow easy servicing of the motor and adjustment of the belt tension from the exterior of the unit. The T.E.F.C fan motor is mounted on the outside on these models and is protected from the weather by a cover which swings away for maintenance.

A large hinged access door is located on the side of the unit for easy access to the fan drive system. The belt can be adjusted by tightening the J-Bolts on the motor base and the tension can be checked easily through the access door, all while standing at the side of the unit. 

The bearings can also be lubricated from the side of the unit. The bearing lubrication lines have been extended to the exterior casing and are located by the access door, thus making bearing lubrication easy.

Sloped access ladders and working platforms are available as an option to facilitate maintenance.

Go to Optional Equipment for details.

Easy, Removable Air Inlet Louvers with Quick Release Fasteners (video)

The ATWB features a Quick Release Fastener design consisting of (2) two large thumbscrews and a latch system. By loosening the thumbscrews, the latch pulls up and out of the louver frame, allowing the louver to be removed while the latch and thumbscrews stay on the closed circuit cooler.


Easy Access

The cold water basin section is easily accessible from ground level by simply removing the (2) two Quick Release Fasteners on the inlet louver assemblies surrounding the closed circuit cooler and lifting out the lightweight louver.

The basin can be accessed from all (4) four sides of the cooler. This open basin design enables the ATWB basin to be easily cleaned.

Louver Access Door

  • Hinged access panel with quick release mechanism.
  • Allows easy access to perform routine maintenance and inspection of the make-up assembly, strainer screen, and basin.
  • Available on models with 5 and 6 foot tall louvers.

Clean Pan Basin Design

The ATWB features a sloped basin from the upper to lower pan section. This "Clean Pan" design allows the water to be completely drained from the basin. The closed circuit cooler water will drain from the upper section to the depressed lower pan section where the dirt and debris can be easily flushed out through the drain. This design helps prevent buildup of sedimentary deposits, biological films and minimizes standing water.

12'& 24' Wide Models Motor Mount, Power Band Belt Adjustment and Bearing Lubrication


The T.E.A.O. fan motor is located inside the fan casing on the large ATW Closed Circuit Cooler, and is mounted on a rugged heavy duty motor base. The motor base is designed to swing completely to the outside of the unit through a very large, hinged (14 square feet) (1,3 square meters) access door greatly simplifying motor maintenance.

The unique swinging motor mount designed for these models features easy belt adjustment from the exterior of the unit. The T.E.A.O. fan motor is mounted on an adjustable base which is supported by two heavy duty galvanized steel pipes. The belt is adjusted by tightening an all-thread which runs through the motor base.

The innovative motor base features a unique locking mechanism for a positive belt adjustment and is also used to adjust the belt tension if a wrench is not available.

Bearing lubrication fittings are extended to the side of the unit inside the access door to allow easy application of the bearing lubricant. This external location allows for easy servicing of the bearings and is another important advantage of EVAPCO equipment.

To facilitate motor removal, an optional motor davit is available.

Go to Optional Equipment for details.

Stainless Steel Strainers

The EVAPCO standard for many years, the stainless steel strainer is one component of the closed circuit cooler subject to excessive wear and corrosion. With stainless steel construction, this component will last the life of the cooler.

The ATWB Closed Circuit Cooler features the highly successful EVAPCO POWER-BAND Belt Drive System engineered for heavy-duty operation. The POWER-BAND Drive System has consistently provided trouble-free operation in the most severe duty closed circuit cooler applications. In addition, the complete drive system including the fan motor is standard with a (5) Five Year Warranty.

Click on the features below for more details.  

Fan Motors

All ATWB Closed Circuit Cooler models utilize heavy duty totally enclosed (T.E.F.C. or T.E.A.O) fan motors designed specifically for closed circuit cooler applications. In addition to the standard motors offered on each cooler, EVAPCO offers many optional motors to meet your specific needs, including:

  • Premium Efficiency Motors 
  • Multi-Speed Motors
  • Inverter-Duty Motors for VFD Applications

3', 4', 8.5' & 17' (0,9; 1,2; 2,6 & 5,2 m) wide ATWB models feature T.E.F.C. motors are located on the outside of the unit, protected by a hinged, swing away cover. 12' & 24' (3,7 & 7,3 m) wide ATWB models have T.E.A.O. motors located inside the fan section on a heavy duty motor base which swings to the outside for repair or removal.





(5) Five Year Warranty

EVAPCO provides a standard (5) five year motor and drive warranty on all direct drive Power-Band belt drive and optional gear drive ATWB Closed Circuit Coolers. This unique warranty is designed to offer the end user optimum protection against fan drive and motor failure. It is a comprehensive plan which includes the fan, fan shaft, belts, sheaves, fan bearings, gear box, flexible coupling, driveshaft and the motor.

Fan Shaft Bearings

The fan shaft bearings on the ATWB Closed Circuit Cooler are specially selected to provide long life, minimizing costly downtime. They are rated for an L-10 life of 75,000 to 135,000 hours, making them the heaviest duty pillow block bearing in the industry used for Closed Circuit Cooler duty.

Drive System Sheaves

Drive system sheaves located in the warm, moist atmosphere inside the closed circuit cooler are constructed of an aluminum alloy. Those located externally are protected by a hinged cover.

Power-Band Belt Drive

The Power-Band drive is a solid-back multigroove belt system that has high lateral rigidity. The belt is designed for closed circuit cooler service, and is constructed of neoprene with polyester cords. The drive belt is sized for 150 percent of the motor nameplate horsepower ensuring long and trouble free operation.

The ATWB Closed Circuit Cooler is an Advanced Technology, induced draft counterflow design closed circuit cooler featuring EVAPCO’s patented THERMAL-PAK® COIL – the most efficient in the industry. The counterflow design provides the ATWB Closed Circuit Cooler with inherently better operational and maintenance features.

Click on the features below for more details.

Principle of Operation

The process fluid is circulated through the coil of the closed circuit cooler. Heat from the process fluid is dissipated through the coil tubes to the water cascading downward over the tubes. Simultaneously, air is drawn in through the air inlet louvers at the base of the cooler and travels upward over the coil opposite the water flow. A small portion of the water is evaporated which removes the heat. The warm moist air is drawn to the top of the closed circuit cooler by the fan and is discharged to the atmosphere. The remaining water falls to the sump at the bottom of the cooler where it is recirculated by the pump up through the water distribution system and back down over the coils.

Thermal-Pak® Coil

EVAPCO's Thermal-Pak® coils feature a patented design which assures maximum cooling capacity. The airflow through the coil is counter to the fluid flow, providing the most efficient heat transfer process. A special coil design is utilized to reduce the air pressure drop through the unit while maximizing tube surface area and increasing its heat transfer capabilities. The uniquely shaped tubes of the coil are staggered in the direction of airflow to obtain a high film coefficient.

The coils are manufactured from high quality steel tubing following the most stringent quality control procedures. Each circuit is inspected to assure the material quality and then tested before being assembled into a coil. Finally, the assembled coil is pneumatically tested at 400 psig (2758 kPa) under water to ensure it is leak free.

To protect the coil against corrosion, it is placed in a heavy steel frame and then the entire assembly is dipped in molten zinc (hot-dip galvanized) at a temperature of approximately 800°F (427ºC).

Note: Closed circuit coolers should only be used on sealed, pressurized systems. Continual aeration of the water in an open system can cause corrosion inside the tubes of the cooler leading to premature failure.

Easy Field Rigging

  •  A new field assembly seam design which insures easier assembly and reduced potential for field seam leaks.
  •  Self guided channels guide the fan casing section into position improving the quality of the field seam.
  •  Eliminates up to 66% of fasteners.

IBC Compliant  



What is IBC?  

  • The International Building Code requires that evaporative cooling equipment must meet the same seismic or wind load forces as the building to which they are attached.

How does it apply? 

  • Based on project zip code and site design factors, calculations are made to determine the equivalent seismic "g force" and wind load on the unit.

What does EVAPCO offer?

  •     Standard Structural Design

                    -Projects with ≤ 1.0g seismic or 145 psf wind loads

  • Upgraded Structural Design

                    -Projects with > 1.0g seismic or 145 psf wind loads

  • The upgraded structural design package for the New ATWB is designed for 5.12g and 145psf, making it applicable to ALL building locations in North America.

Efficient Drift Eliminators

An extremely efficient drift eliminator system is standard on the ATWB Closed Circuit Cooler. The system removes entrained water droplets from the air stream to limit the drift rate to less than 0.001% of the recirculating water rate. With a low drift rate, the ATWB Closed Circuit Cooler saves valuable water and water treatment chemicals. The ATWB Closed Circuit Cooler can be located in areas where minimum water carryover is critical, such as parking lots.

The drift eliminators are constructed of an inert polyvinyl chloride (PVC) plastic material which effectively eliminates corrosion of these vital components. They are assembled in sections to facilitate easy removal for inspection of the water distribution system.

Fast, On-Time Shipments

The ATWB is completely factory assembled and manufactured by a dedicated professional workforce, expert in building closed circuit coolers. Factory trained mechanics and EVAPCO's strict quality control and inspection procedures guarantee the quality of every unit shipped.

EVAPCO's controlled factory environment ensures fast on-time shipments, allowing the ATWB to be available WHEN THE CUSTOMER WANTS IT!

Superior Air Inlet Louver and Screen Design

The air inlet louver screens on the ATWB are constructed of corrosion-freePVC. They are a two pass design that minimizes splashout and reduces the potential for algae formation inside the cooler.

In single pass louver systems used by other manufacturers, circulating water droplets tend to splashout, especially when the fans are shut off. With the two pass louver system, the water droplets are captured on the inward sloping pass, minimizing splashout problems.

This unique louver design completely encloses the basin area. Direct sunlight is blocked from the water inside the cooler, thereby reducing the potential of algae formation. Water treatment and maintenance costs are substantially reduced.

While effectively containing the recirculating water and blocking sunlight, the louver design has a low pressure drop. The low pressure drop results in lower fan energy consumption, which reduces the operating costs of the cooler.

Maintenance Free ZMII® Water Distribution System

EVAPCO’S Zero Maintenance ZMII® Spray Nozzle remains clog-free while providing even and constant water distribution for reliable, scale-free evaporative cooling under all operating conditions.

The heavy duty nylon ZMII® Spray Nozzles have a 1-5/16” diameter opening and a 1-1/2” splash plate clearance enabling EVAPCO to use 75% fewer nozzles. Furthermore, the fixed position ZMII® nozzles are mounted in corrosion-free PVC water distribution pipes that have threaded end caps. Together, these elements combine to provide unequaled coil coverage and scale prevention, and make the industry’s best performing non-corrosive, maintenance-free water distribution system.

The water distribution is designed to provide a minimum 6 GPM over each square foot (4 liters per second over each square meter) of unit plan area to ensure proper flooding of the coil.

The standard design of the EVAPCO ATWB provides the customer with the most efficient and easiest Closed Circuit Cooler to maintain in the industry. There are additional options which can make maintenance easier, extend the life, or enhance the performance capabilities of the Closed Circuit Cooler.

Click on the features below for more details.

Evapco Manufactured 304 Stainless Steel Coils

The Evapco manufactured Stainless Steel Coil is an elliptical tube, continuous return bend, 304 stainless steel coil. It is available in both the Patented Thermal Pak Coil design used on AT, UB, LR and LS coolers and condensers and in the patent pending SensiCoil design used in the ESWA. This option has superior corrosion  resistance for Open Systems and Hostile Environments and is available with the Standard Evapco Lead Time! For more detail on the corrosion resistant properties of 304 stainless steel, see Evapco's Maintenance Instruction Bulletin, 112AA. The Evapco 304 SST coil option can be manufactured as an ASME coil and is CTI certified on the ESWA and ATWB closed circuit cooler.

Stainless Steel Water Touch Basin

The ATWB Closed Circuit Cooler has a modular design which allows specific areas to be enhanced for increased corrosion protection. The basin area of the cooler experiences turbulent mixing of air and water, in addition to silt build-up. In conjunction with the EVAPCOAT Corrosion Protection System, EVAPCO offers an optional Stainless Steel Water Touch Basin. This option provides Type 304 or Type 316 stainless steel for the entire basin area including the support columns of the closed circuit cooler and the louver frames.

The basin section provides the structural support for the unit and is a critical part of the closed circuit cooler. The Stainless Steel Water Touch Basin provides maximum corrosion protection.

Discharge Hood with Positive Closure Dampers

When a closed circuit cooler is used in a water-to-air heat pump system or in certain process cooling applications, a method of reducing the heat loss during idle periods of wintertime operation may be required. For these cases, an optional discharge hood with positive closure dampers and damper actuator is available.

The discharge hood with dampers is designed to minimize the heat loss from convective airflow through an idle cooler. Further reductions in heat loss may be obtained with the addition of insulation to the hood and casing, minimizing conductive heat losses. Insulation may be factory installed on the hood and casing or field installed by an insulation contractor.

The discharge hood and dampers are constructed of hot-dip galvanized steel. Hoods are equipped with access panels to facilitate maintenance of the eliminators and water distribution system. The dampers, damper actuator and linkage are all factory assembled. Actuator controls and wiring are field supplied by others. Damper actuators require 120 volt power supply.

The system control sequence should provide for dampers to be fully open before the fans are running and closed when the fans are off; the damper actuator must be interlocked with the temperature control system for this purpose.

See ATWB catalog (pg. 55) or contact the factory for heat loss data. Table ratings are based on 50°F(10ºC) water in the coil, -10°F(-23ºC) ambient and 45 MPH(72 kMPH) winds (fan and pump off).


Sloped Access Ladders

A sloped access ladder is available for 8.5', 12', 17' and 24' (2,6; 3,7; 5,2; 7,3 m) wide ATWB models. A vertical access ladder is available on 3', 4' (0,9 m; 1,2 m) wide ATWB models. The EVAPCO designed access ladder features a sloped "ships type" ladder arrangement which provides fast and easy access to the water distribution system and drive components. A grab bar is attached to the sloped ladder for safe and easy ascent and descent. There is no need for safety cages or railings with this design. The ladder(s) will ship loose and must be field mounted. The sloped ladder meets all applicable OSHA requirements.

Electric Water Level Control

EVAPCO closed circuit coolers are available with an optional electric water level control system in place of the standard mechanical makeup valve and float assembly. This package provides very accurate control for the basin water level and does not require field adjustment, even under varying operating conditions.
The control was designed by EVAPCO and is manufactured exclusively for EVAPCO. It consists of multiple heavy duty stainless steel electrodes. These electrodes are mounted external to the unit in a vertical stand pipe. For winter operation, the stand pipe must be wrapped with electric heating cable and insulated to protect it from freezing.
The weather protected slow closing solenoid valve(s) for the makeup water connection is factory supplied and is ready for piping to a water supply with a pressure between 25 and 50 psig (138 kPa and 345 kPa).

Electric Heaters

Electric immersion heaters are available as an option and are located in the basin of the cooler They are sized to maintain a +40° F (4,4º C) pan water temperature at 0°F (-18º C) ambient with the fans off *. They are furnished with a thermostat and low water protection device to cycle the heater on when required and to prevent the heater elements from energizing unless they are completely submerged. All components are enclosed in rugged, weather proof enclosures for outdoor use. Heater control packages that include contactor, transformer or disconnects are available.
(*) - Electric heater selection based on 0°F (-18º C) ambient temperature. For alternate low ambient heater selections consult the factory.

Extended Surface Coil

Closed circuit coolers can be provided with spiral fins on the heat exchanger coil to increase the dry performance of the unit. Dry performance is accomplished by rejecting heat to the atmosphere without the use of the spray pump and the evaporation process. Dry operation can be practical in cold climates and/or when reduced winter loads exist. The number of fins per inch and and quantity of rows finned can be varied to obtain different dry performances.

Working Platform & Ladder with Davit

ATWB Closed Circuit Coolers are available with an external working platform and ladder to allow easy servicing of the fan motor and water distribution system. Providing a convenient platform to perform work, the heavy duty galvanized steel platform is self-supporting which eliminates the need for any external support. A less expensive alternative to field erected catwalks, the working platform option uses a straight ladder as standard and ships in sections for easy installation. The davit option eliminates crane rentals and facilitates the removal of motors and gear drives. The davit and bracket are constructed of heavy duty galvanized steel and are mounted on the side of the unit. The optional fan motor and gear davit ships loose and is installed in the field. (The working platform and ladder meet all applicable OSHA requirements.)

Other Options

  • Hot Water or Steam Coils
  • Steam Injectors
  • Vibration Switches
  • Remote Sump Connections
  • Insulation on Hood and Casing
  • Motors– Energy Efficient / Inverter Duty /2S/1W and 2S/2W / Mill and Chem Duty Automotive Duty and Many More, Consult the Factory

Super Low Sound Fan

9 - 15 db(A) Reduction versus Standard Fan!

The Super Low Sound Fan offered by EVAPCO utilizes an extremely wide chord blade design available for sound sensitive applications where the lowest sound levels are desired. The fan is one-piece molded heavy duty FRP construction utilizing a forward swept blade design. The Super Low Sound Fan is capable of reducing the unit sound pressure levels 9dB(A) to 15dB(A), depending upon specific unit selection and measurement location. The fans are high efficiency axial propeller type and operate with no loss of thermal performance and provide CTI Certified Performance.

The Super Low Sound Fan is available on all 8.5ft and 12ft (2.4m and 3.6m Europe) wide ATWB Closed Circuit Coolers.

View Product Video

Super Low Sound Fan

ATWB specification57.5 KB

ATWB Specification

Furnish and install as shown on the plans an EVAPCO Model_________ induced draft counterflow closed circuit cooler. Each unit shall be CTI Certified and have the capacity to cool _________ GPM of_______ from ______ °F to ______ °F with a _____ °F entering wet bulb temperature.

IBC 2006 Compliance

The closed circuit cooler shall be designed and constructed to meet the International Building Code (IBC 2006) specifications for installed components per ASCE 7-05. The manufacturer shall provide a certificate of compliance to demonstrate that the equipment/unit has been independently tested and certified in accordance with the IBC program.

Basin and Casing

The basin and casing shall be constructed of G-235 hot-dip galvanized steel for long life and durability. Standard basin accessories shall include overflow, drain, type 304 stainless steel strainers, and brass make-up valve with plastic float.

Belt Drive Models 3', 4', 8-1/2' & 17' Wide

Fan Motor

_________ horsepower totally enclosed fan cooled motors with1.15 service factor shall be furnished suitable for outdoor service on _________ volts, _________ hertz, and _________ phase. Motor(s) shall be mounted on an adjustable base which is accessible from the outside of the unit for service. A swing away protective cover shall shield the motor and sheave from the weather.


The fan drive shall be multigroove, solid back V-belt type with taper lock sheaves designed for 1.5 service factor of the motor nameplate horsepower. The belt material shall be neoprenere inforced with polyester cord and specifically designed for evaporative cooler service. Fan sheave shall be aluminum alloy construction. The fans and the fan sheaves shall be mounted on the shaft with a specially coated bushing to provide maxi-mum corrosion protection. Belt adjustment shall be accomplished from the exterior of the unit. Bearing lube lines shall be extended to the exterior of the unit for easy maintenance.

Belt Drive Models 10', 12', 20' & 24' Wide

Fan Motor

_________ horsepower totally enclosed air over ball bearing fan motor(s), with 1.15 service factor shall be furnished suitable for service on _________ volts, _________ hertz, and _________ phase. Motor(s) shall be mounted on an adjustable base which allows the motor to swing to the outside of the unit for servicing.


The fan drive shall be a multigroove, solid back V-belt type with taper lock sheaves designed for 1.5 service factor of the motor nameplate horsepower. The belt material shall be neoprene reinforced with polyester cord and specifically designed for evaporative cooler service. Fan and motor sheaves shall be aluminum alloy construction. The fans and fan sheaves shall be mounted on the shaft with a specially coated bushing to provide maximum corrosion protection. Belt adjustment shall be accomplished from the exterior of the unit. Bearing lube lines shall be extended to the exterior of the unit for easy maintenance.

Axial Propeller Fans

Fans shall be heavy duty axial propeller type statically balanced. The fans shall be constructed of aluminum alloy blades, installed in a closely fitted cowl with venturi air inlet. Fan screens shall be galvanized steel mesh and frame, bolted to the fan cowl.

Fan Shaft Bearings

Fan shaft bearings shall be heavy duty self-aligning ball type with grease fittings extended to the outside of the unit. Materials shall be stainless steel balls with chrome steel races and zinc plated housing for corrosion resistance. Bearings shall be designed for a minimum L-10 life of 75,000 hours.

Water Recirculation Pump

The pump(s) shall be a close-coupled, centrifugal type with mechanical seal, installed vertically at the factory to allow free drainage on shut down. _________ horsepower totally enclosed motor(s) shall be furnished suitable for outdoor service on_________ volts, _________ hertz, and _________ phase.

Heat Transfer Coil

Cooling coil(s) shall be all prime surface steel, encased in a steel framework and hot-dip galvanized after fabrication as a complete assembly. The tubes shall be arranged in a self-spacing, staggered pattern in the direction of airflow for maximum heat transfer efficiency and minimum pressure drop, without the use of additional spacers between the coil tubes. The coil(s) shall be pneumatically tested at 400 psig, under water.

Water Distribution System

The system shall provide a water flow rate of not less than 6GPM over each square foot of coil face area to ensure proper flooding of the coil. The spray header shall be constructed of schedule 40 polyvinyl chloride pipe for corrosion resistance. All spray branches shall be removable and include a threaded end plug for cleaning. The water shall be distributed over the entire coil surface by heavy-duty molded nylon ZM spray nozzles with large 1-5/16" diameter openings and internal sludge ring to eliminate clogging. Nozzles shall be threaded into the spray header to provide easy removal for maintenance.


The eliminators shall be constructed entirely of inert polyvinylchloride (PVC) in easily handled sections. The eliminator design shall incorporate three changes in air direction to assure complete removal of all entrained moisture from the discharge air stream. Maximum drift rate shall be less than 0.001% of the circulating water rate.


The air inlet louvers are constructed from UV inhibited polyvinyl chloride (PVC) and incorporate a framed interlocking design that allows for easy removal of louvers for access to the entire basin area for maintenance. The louvers have a minimum of two changes in air direction and are of a non-planar design to prevent splashout, block direct sunlight and debris from entering the basin. (Patent Pending)


All basin and casing materials shall be constructed of G-235heavy gauge mill hot-dip galvanized steel. During fabrication, all panel edges shall be coated with a 95% pure zinc-rich compound for superior protection against corrosion.

Thermal Performance

Flow tables699.08 KB
Flow tables 30%PG571.96 KB
Flow tables 30%EG701.42 KB