A Cooling Tower also commonly known as an evaporative heat rejection equipment is a specialized heat exchanger in which air and water are brought into direct contact with each other in order to reduce the water's temperature. As this occurs, a small volume of water is evaporated, reducing the temperature of the water being circulated through the tower. A factory packaged cooling tower is classified as a unit that is of series production from a manufactures factory (shipped complete or knocked down shipped for ease of transportation). Knocked down shipped products shall be installed by skilled personnel trained / supervised by the certified company. Field erected cooling towers are deemed outside this scope.
Water, which has been heated by an industrial process or in an air-conditioning condenser (Water -cooled chiller), is pumped to the cooling tower through pipes. The water sprays through nozzles onto banks of material called "fill," which slows the flow of water through the cooling tower, and exposes as much water surface area as possible for maximum air-water contact. As the water flows through the cooling tower, it is exposed to air, which is being pulled through the tower by the electric motor-driven fan. When the water and air meet, a small amount of water is evaporated, creating a cooling action. The cooled water is then pumped back to the condenser or process equipment where it absorbs heat. It will then be re-cycled back to the cooling tower to be cooled once again.
There are two main types of Cooling Tower, these being:
These cooling tower types have the same design system purpose as described above, however the Closed circuit cooling towers operate in a manner similar to open cooling towers, except that the heat load to be rejected is transferred from the process fluid (the fluid being cooled) to the ambient air through a heat exchange coil. The coil serves to isolate the process fluid from the outside air, keeping it clean and contaminate free in a closed loop. This creates two separate fluid circuits: (1) an external circuit, in which spray water circulates over the coil and mixes with the outside air, and (2) an internal circuit, in which the process fluid circulates inside the coil. During operation, heat is transferred from the internal circuit, through the coil to the spray water, and then to the atmosphere as a portion of the water evaporates.
The configuration of a cooling tower can generally be grouped into two design configurations based on the air-flow direction to water-flow direction, these being counter-flow and cross-flow:
- Counter-flow water cooling tower design is where the air flow is vertically upwards, counter current with the hot water falling downwards. The coldest water comes in contact with the coolest and most dry air, optimizing the heat transfer and obtain-ing the maximum performance
- Cross-flow water cooling tower design is where the air flows horizontally and the water falling downwards meets the air at different temperatures. Therefore the heat transfer is not always optimized
Induced draft or forced draft configuration
Further characteristics that differentiate the design of a cooling tower is based on the fan. Cooling Towers fans can be applied in an Induced draft or a Forced draft configuration:
- Induced Draft: Axial fan units require approximately half the fan motor horsepower of comparably sized centrifugal fan units, offering significant lifecycle cost savings. The rotating air handling components of induced draft equipment are mounted in the top deck of the unit, minimizing the impact of fan noise on near-by neighbours and providing maximum protection from fan icing if units operate in sub-freezing conditions.
- Forced Draft: Centrifugal fans are also inherently quieter than axial fans, although the difference is minimal and can often be overcome through the application of optional low sound fans and/or sound attenuation on axial fan units. The rotating air handling components are located on the air intake face at the base of forced draft towers, facilitating easy access for routine maintenance and service. Additionally, locating these components in the dry entering air stream extends component life by isolating them from the saturated discharge air.
Value Added Benefits
- Encourages honest competition between manufactures
- All players can be benchmarked from a common playing field, using one industry standard, therefore increasing consumer confidence.
- Reduces costly unforeseen system operating costs, based on certified data
- Eliminates the need for costly on site performance tests, what happens if the equipment fails an acceptance test, who pays in the end?
- Certification of evaporative cooling equipment guarantees thermal performance prior to shipment of the equipment
Compare to make the right choice
It is very easy to make the right choice: just compare the products. But when product performance is not certified, this becomes impossible.
Certification makes it possible to compare objectively.
- The product performance is evaluated according to the same criteria, and the results are expressed in the same unit of measurement, regardless of the country where the products are manufactured or marketed.
- A certified product has its performance verified by an impartial, independent and competent accredited body.
- Certified products comply with standards.
- A product whose performance is certified will work according to the specifications stated by the manufacturer.
The performances we certify
- Certified characteristics shall be per CTI STD-201
- Entering wet bulb temperature
- Cooling range
- Cooling approach
- Process fluid temperature
- Barometric pressure