Adiabatic cooling first was used in the Roman Empire. For 2000 years, people have been using water evaporation to cool down the surrounding air in all types of climate systems, including modern, highly advanced cooling systems for data centers, where engineers combine the ancient principle with modern technologies.
Adiabatic cooling for freecooling applications: the benefits
Adiabatic cooling technology is now used in many solutions and has even more exciting opportunities. For example, are air-cooled chillers, and, in particular, free cooling chillers. In addition to reducing the condensation temperature, the time interval for the operation of the free cooling system is significantly extended, because the adiabatic approach helps to reduce the inlet air temperature, and this temperature decrease is not associated with any significant energy expenditure.
Wet pads vs. water spray
Discussions have recently centered around two different evaporative solutions – wet pad cooling and water spray systems. The pros and cons of each solution are shown in the below table:
Water spray systems can be applied when the air resistance is the issue. However, Kaltra uses low air-resistant microchannel heat exchangers in its equipment and additional pressure drop caused by evaporative pads can, therefore, be avoided.
Evaporative cooling pads: real-life experience
Let’s look at real situations where adiabatic cooling systems proved its benefits.
For two weeks, the daytime temperature was never below +30°C with peak values of up to +37°C and did not fall below +24°C at night, the humidity was between 10 and 40%. Lightstream Freecool chiller with a capacity of 1MW and return/supply water temperatures of 12/18°C worked around the clock with an active adiabatic cooling system based on wet pads. On this basis, condensation temperature was reduced by 7 degrees, which allowed a saving of 120kW/h electricity on an hourly basis. Within two weeks, investment in the adiabatic cooling system not only paid off, but also allowed the customer to save a substantial amount of money.
During the last summer season, despite the constantly high air temperature and high humidity of the coastal territory, the evaporative cooling system installed on the Lightstream Screw chiller reduced condensation temperature by an average of 7 degrees. Every hour, the five-hundred-kilowatt chiller saved 60kW/h, thereby reducing electricity costs each season by EUR 19,500.
Cooling plant of four Lightstream Freecool chillers with a total cooling capacity of 2.5MW for a year worked in freecooling mode, on the hottest days, using compressors in parallel. Mechanical cooling worked only for 15% of the time, and the savings amounted to more than 65% compared to chillers installed before the modernization of the chiller plant.
In all cases, the evaporative cooling system did not require water treatment for its operation and worked on the potable water.
A significant advantage of evaporative pads over the water spray system lies in the possibility of recirculating water, and as a result, it’s saving. In the spraying systems, water consumption dictates constant supply, while using evaporative pads water can be used repeatedly, circulating in a closed loop system. Also, with pads water temperature does not affect system efficiency.
Evaporative pads in details
The evaporative environment used in pads design is a water retaining finned aluminum structure which prevents the buildup of mould and dirt and does not require droplet eliminators for air velocities of up to 3m/s. Water is distributed over the length of evaporative pads by spraying through orifices located on the header pipe and collected into a drip tray. Intake air flows through the wetted environment and cools down due to adiabatic evaporation process.
Optionally, the system can be equipped with a water recirculation/management module which consists of immersed-type circulation pump, water tank, water quality monitor, and control unit housed in a weatherproof enclosure. A recirculation module connects to the domestic water system to top-up fresh water when needed.
Evaporative cooling systems in air-cooled chillers make it possible to achieve the efficiency inherent in such complex and expensive cooling systems as Kyoto cooling while remaining inexpensive and easy to use.
PUE (power usage effectiveness) of this type of system is not more than 1.10 for Central European countries, which guarantees their popularity and further distribution. Free cooling chillers, which were previously popular in hot climates due to almost constant operation in mechanical cooling mode, have every possibility of becoming a daily solution thanks to modern adiabatic cooling systems. For regions with a hot climate, this solution is revolutionary.
Not limited to chillers, we use this solution for air-cooled condensers and dry coolers, and wherever energy efficiency is required together with the conservation of natural resources. A combination of cutting-edge technologies, such as evaporative cooling and microchannel heat exchangers, allows Kaltra to lead in the field of energy efficient products for cooling and refrigeration.