Closed Circuit Coolers

ATW Closed Circuit Cooler

ATW Closed Circuit Cooler

Induced draft axial fan counterflow closed circuit cooler. The ATW cooler is used for cooling of water or water/glycol mixtures. The process fluid remains without oxygen and impurities. Executed as per standard with Z-725 (725 g/m² zinc) galvanized steel panels.

The ATW (Advanced Technology) design combines low energy consuming axial fans with high performance counterflow heat exchange.

EVAPCO's Thermal-Pak® coils feature a patented design which assures maximum cooling capacity. The elliptical tubes of the coil are staggered in the direction of airflow to obtain a high heat exchange coefficient. The coils are manufactured from high quality steel tubing following the most stringent quality control procedures. The assembled coil is pneumatically tested under water in accordance with the European Pressure Equipment Directive (PED) 97/23/EC.

The ATW cooler range is complient with the International Building Code (IBC). Evapco Europe provides with each closed circuit cooler a Thermal Performance Guarantee. ATW-units are constructed for a maximum nominal capacity of 6.2 MW.

Long-lasting corrosion protection is guaranteed with Z-725 heavy gauge mill hot-dip galvanized steel (Z-725 = 725 g/m² zinc). The galvanized steel construction withstands the most difficult environmental and operating conditions.

For special applications, Evapco can produce the units with stainless steel sump, with a water touched stainless steel construction or a complete stainless steel construction (AISI 304 or 316 are possible).

Technical Data 

  • Unit:    Closed circuit cooler
  • Models:    377 Models (ATW 9-2C-2 till ATW 866-6O)
  • Width:    927 / 1.231 / 2.283 / 2.388 / 2.991 / 3.607 / 4.906 / 6.112 / 7.344 mm
  • Design:    Induced draft
  • Capacity:    till 6.206 kW
  • Air Flow:    1,99 till 246,1 m³/s
  • Fan:    Axial
  • Drive:    Powerband-belt driven


  • Low energy consumption
  • Low sound emission
  • Easy maintenance
  • Best choice to avoid Legionaires Disease
  • Dry operation possible
  • Low risk for recirculation

Low energy consumption

The energy consumption of the ATW cooler is minimized due to the optimal heat exchange and the application of axial fans.The heat exchange efficiency of counterflow cooling towers is the highest achievable compared to cross-flow and parallell flow heat exchange. On top of the efficiency advantage, it is generally known that axial fans consume on average more than 50% less motor-power than centrifugal fans. The result is an overall optimized and low engergy consumption.

Low sound emission

The standard wide blade aluminum fan is selected and optimized for high efficiency cooling tower operations. In addition to the standard fans, aluminum LOW SOUND FANS and FRP SUPER LOW SOUND FANS can be installed. Together with water silencers in the sump, sound reductions up till 15 dB(A) can be established.

Easy maintenance

The ATW-design is optimized for easy access to all critical locations and components. The inlet louvers are removable and provide an easy access to the sump. The complete sump can be cleaned from the outside of the unit. Large access doors provide easy access to the eliminators, spray- and drive system.

Best choice to avoid Legionaires Disease

Maintenance is crucial to avoid the proliferation of the LD-bacteria. Avoidance of the penetration of sunlight to the inner part of the cooling tower, no stagnant zones in the sump and cleanable spray systems are of equal importance. The ATW cooler is equipped with WST (Water and Sight Tight) inlet louvers to avoid the penetration of sunlight into the sump via the inlet louvers. The high performance eliminators (0.001% drift rate) avoid the penetration of sunlight via the fan-opening onto the spray system and fill. The sump is sloped and drains completely, stagnant zones are not present. The spray system is completely dismountable (including nozzles) and is executed with a removable end-cap for easy cleaning.

Dry operation possible

The Evapco Thermal-Pak coil is designed for optimized evaporative cooling. But when the cooling load is variable, dry operation might be possible during cold- weather periods. The available dry heat exchange surface is often large enough to cover the heatload during wintertime. Dry operation reduces the water consumption but also creates time for regular cleaning of the sump. This is an important advantage in relation to the avoidence of LD.

Low risk for recirculation

Due to the large distance between the high speed air outlet and the multi-sided low speed air inlet, the risk for recirculation is minimized.

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.

1. Casing and basin design

High Performance drift eliminators

The drift eliminators remove entrained water droplets from the air stream to limit the drift rate to less than 0.001% of the recirculating water rate. The unit can be located in areas where minimum water carryover is critical. 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.

Water Sight Tight air inlet louver (WST)

The air inlet louvers are both water and sight tight to ensure that the water stays in and sunlight stays out of the cold water basin. The water tight design maximizes thermal performance while minimizing water loss. The sight tight design also inhibits algae growth more effectively than previous designs.

Z-725 Galvanized steel panels

EVAPCO has developed the ultimate system for corrosion protection in galvanized steel construction - the EVAPCOAT Corrosion Protection System. Z-725 is the heaviest level of galvanizing available for manufacturing evaporative condensers and has a minimum of 250 % more zinc protection than competitive designs using Z-275 steel.

2. Heat transfer system

Thermal-Pak® evaporative coil

EVAPCO’s patented Thermal-Pak® condensing coils feature a design which assures maximum condensing capacity. The airflow thru the coil is counterflow to the refrigerant flow, providing the most efficient heat transfer.This 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 elliptical shaped tubes of the coil are staggered in the direction of air flow to obtain a high film coefficient. In addition, all tubes are pitched in the direction of refrigerant flow to give good drainage of liquid refrigerant. The coils are manufactured in accordance with Pressure Equipment Directive “PED” 97/23/EC. High quality steel tubing is used following the most stringent welding and 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 air pressure tested under water at the appropriate pressure, in accordance with the Pressure Equipment Directive. To protect the coil against corrosion, it is placed in a heavy-duty steel frame and the entire assembly is hot dip galvanized at a temperature of approximately 430°C.

3. Mechanical design

Power-Band Drive System 

The ATW Closed Circuit Cooler features the highly successful, easy maintenance, heavy duty Power Band Drive System. It consists of Standard heavy-duty pillow block bearings with a minimum L10 life of 75,000 hours, extended lube lines, external motor/belt adjustment, aluminum alloy sheaves, solid-back multi-groove Power- Band belts and totally enclosed motors.

Single speed fan motor 

Each Evapco unit is equipped as per standard with a heavy duty, single speed IP55 TEFC / TEAO electrical motor.

Standard axial fan

The standard fans are heavy duty  statically balanced axial propeller type. The fans are constructed of extruded aluminum alloy blades, installed in a closely fitted cowl with venturi air inlet for maximum fan efficiency. Each fan blade is individually adjustable. The fan cowl is covered with a heavy gauge hot dip galvanized wire fan guard.

4. Water distribution

Spray pump

The spray pump is optimized for high waterflow at relative low pressure. The motor is totally enclosed and protected with an end-cap to ensure a long trouble free operation.

Spray-water distribution system 

The water distribution system is enclosed and completely protected by the casing panels and drift eliminators. The water distribution system is made with non-corrosive materials including schedule 40 PVC pipe and durable ABS plastic nozzles. The spray branch piping is easily removed and designed with threaded end-caps for easy cleaning. Evapco’s design avoids the problems of biological growth and clogging.

ZM II ™ Zero-Maintenance spray nozzles 

Even and constant water distribution is paramount for reliable, scale-free evaporative cooling. EVAPCO's Zero Maintenance ZM II™ Spray Nozzle, mounted in a PVC distribution pipe with end-caps remains clof-free under the toughest conditions to deliver approwimately 4 l/s tovery square meter of coil paln area. The heavy-duty nylon ZM II™ Spray Nozzles have a 33 mm diameter opening and a 38 mm splash plate clearance, enabling EVAPCO to use 75 % fewer nozzles.

5. Maintenance and inspection

Large access door

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 tensioning-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.

6. Operational control

Mechanical water level control

Simple but reliable water level control system with adjustable mechanical float and brass float-valve.