ACR Journal

CMYK / .ai CMYK / .ai CMYK / .ai acrjournal.uk 21 ADVERTORIAL Because blowdown of the basin water is reduced on closed-loop systems, water conservation also is improved when compared to open-loop systems. Because evaporative coolers can oftentimes run dry when ambient conditions are favorable during reduced load conditions, water consumption is eliminated entirely during these periods of operation. Hybrid coolers Hybrid coolers combine dry and evaporative cooling to maximise energy e ciency while simultaneously reducing water consumption. These units provide heat rejection in dry mode until the load exceeds dry rejection capacity. At this switch-over point, the unit enters evaporative mode to increase cooling capacity. Operating in wet mode only when needed can reduce annual water consumption, sewer expense and eliminate plume (while in dry mode). Hybrid cooling solutions include a dry cooler with wet trim and an evaporative cooler that runs both wet and dry. Dry coolers with wet trim are suitable where saving water is the top priority. In these systems, the dry cooling coil is placed in series with the evaporative cooling coil. It plays an integral role as part of the cooling system rather than simply having an on/o role. Alternatively, wet coolers with dry trim are capable of running in wet and dry mode simultaneously by having separate spray sections above the coils. The coils can utilise either evaporative or dry cooling - rather than both at once - which also helps to minimise water consumption. Depending on capacity needs, such units are capable of running in dry mode, partially in wet mode or completely in wet mode. Compared to wholly evaporative cooling units, both systems reduce water consumption. Space savings is also a benefit of hybrid coolers when compared to adiabatic and dry cooling equipment. Hybrid coolers are frequently used in critical chilled-water applications where minimising both water and energy are important. They also are found in data centers and battery plants. Dry coolers Dry coolers are best specified where water conservation and reduced aintenance are the key considerations. Because dry coolers do not utilise any water or evaporative cooling, dry coolers eliminate water treatment, plume and Legionella concerns. Dry coolers will use more energy and require a larger footprint than evaporative or hybrid fluid coolers of the same capacity. In a dry cooler, heat from the process- loop fluid dissipates via heat transfer to the coil-tube surface and out to the fins – not through evaporation. Ambient air is drawn over the coil surface by a fan located at the top of the unit. Heat from the process fluid transfers to the air via sensible cooling and discharges to the atmosphere. Adiabatic coolers Adiabatic coolers function in a similar fashion to dry cooling systems but with the addition of pre-cooling pads. Water runs over porous media while air is drawn through the pads, lowering the dry bulb temperature of the incoming air. The influence of reduced dry-bulb temperatures at the coil provides greater heat rejection. As a result, adiabatic systems are most e ective in hot, dry environments. Adiabatic coolers use up to 80 per cent less water than traditional evaporative units. Adiabatic units also deliver the required cooling capacity in a smaller footprint and/ or lower fan motor horsepower than a completely dry cooler. Similar to hybrid units, some manufacturers o er coolers that can operate in dry mode, adiabatic mode or partial-adiabatic mode, in which only a portion of the adiabatic spray pumps are energized. The thermal performance of these units is also fully rated. It is critical that specifying engineers understand that fully rated dry coolers and fully tested pad e ciencies will impact the sizing of units. Inadequately sized equipment will result in greatly increased water usage and energy consumption compared to a fully rated unit. In conclusion, when determining the type of heat-rejection equipment that should be used on a given project, the specific needs of the facility should dictate whether a closed- or open-loop design is most suitable. Given the growing sensitivity to water conservation, and the ever-increasing cost to maintain mechanical systems, closed-loop technology is seeing wider implementation. Also called fluid coolers, closed-circuit coolers provide aheat-rejection solution for engineers or end userswhowant to reducewater consumptionand equipmentmaintenance.