Technology Bulletin
Adiabatic Cooling Towers
By: Jim Fisher, Sales Manager, Heat Transfer
Open-loop cooling towers have their drawbacks
For decades, many plastics processors have relied on open-
loop cooling towers to meet the bulk of their process cooling
requirements. These structures typically cycle warm, process-
return water through baffles to expose it to ambient air. As a portion
of the warm water evaporates into the air, the rest is cooled as it
falls back into the cooling tower reservoir, ready for recirculation.
For all of its simplicity and effectiveness, however, tower-based
process cooling systems have their costs: Because cooling
capacity is based on evaporation, water consumption is
continuous and fresh water must be continually replenished.
And, because these systems are open to ambient air, cooling
water quality must be continually monitored and maintained.
Multiple forms of chemical treatment are necessary, not only to
prevent the growth of harmful bacteria but also to prevent the
accumulation of harmful particles or deposits in cooling lines,
molds, or machinery linked to the cooling system.
These concerns, together with increased water-use regulations,
the drive to conserve energy and natural resources, as well
as rising water, sewer, and electrical costs, make tower-based
cooling less attractive than it used to be.
In open-loop towers, hot process water falls over
baffles and is exposed to ambient air. Evaporation
lowers the temperature of the water before it
returns to the process.
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200 West Kensinger Drive | Cranberry Township, PA 16066 724.584.5500 | www.conairgroup.com
Closed loop, energy efficient, environmentally friendly
Now, an increasing number of processors are recognizing the
potential of adiabatic cooling towers, a closed-circuit cooling
system design that dramatically reduces water usage, energy,
and maintenance costs and evaporation, while they are cooled
by the ambient air.
The only water consumed in an adiabatic cooling system is that
which is applied onto evaporative cooling pads mounted at the
front of the cooling tower, ahead of the cooling coils through
which the process coolant flows. As ambient air passes through
these wetted panels, the water within them evaporates, increasing
the cooling capacity of the tower by reducing the temperature of
the air flowing through the cooling coils.
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200 West Kensinger Drive | Cranberry Township, PA 16066 724.584.5500 | www.conairgroup.com
Understanding the adiabatic process
Adiabatic cooling is a simple, natural process that has long been
used as a low-cost way to cool volumes of air. Scientifically, here
is how it works: When warm air is exposed to moisture – such as
when warm air is drawn through the wetted pads in an adiabatic
tower – the air is cooled as the water evaporates. In that process,
water absorbs heat from the air and uses that energy, in the form of
latent heat, to change its state from liquid to vapor (evaporation).
The water or water vapor itself does not undergo any temperature
change during this process.
Interestingly, the total amount of heat in the volume of air, or
air plus humidity, does not change due to adiabatic cooling.
However, the measured temperature(dry-bulb, or thermometer
temperature) of air flowing through an adiabatic cooling tower
is reduced because of the latent heat that is bound up with the
water vapor.
Adiabatic towers are cost-effective because, in many cases, they
are capable of cooling very effectively without the need to utilize
the adiabatic process at all. When air temperatures are low, the
flow of ambient air alone – drawn upward through the adiabatic
panels and the cooling coils – is often sufficient to meet process
cooling requirements. “Dry” or water-free operation is often
possible during the cool months that occur in many climates,
minimizing or eliminating the need and costs of supplemental
mechanical chilling. Compared to conventional cooling towers,
an advanced adiabatic cooling tower can reduce water usage by
as much as 80%.
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200 West Kensinger Drive | Cranberry Township, PA 16066 724.584.5500 | www.conairgroup.com
Adiabatic control systems optimize water and energy
efficiency
The efficiency and performance of the today’s adiabatic cooling
towers, including the latest EarthSmart™ towers from Conair, are
optimized with the help of advanced control systems, managed by
application-specific PLCs. All feature variable-speed, electrically
commutated fans and circulating motors that ensure precise
regulation, making it possible to coordinate motor speeds,
match specific cooling load requirements, and minimize energy
consumption.
EarthSmart adiabatic cooling towers offer three programmable
operating modes that give processors the flexibility to manage their
water and power consumption costs as needed to meet changing
costs and plant operating requirements:
In dry (normal) mode, the control system regulates fan speed,
air flow, and process coolant flow to achieve the desired process
cooling set-point. No adiabatic cooling water is used.
In water-saving mode, the control minimizes water consumption
in favor of increased airflow to achieve the desired process-cooling
set-point. In this mode, the tower makes maximum use of fan
speed and ambient air flow to provide process cooling capacity.
The control system allows for use of water on the adiabatic cooling
pads only if airflow at maximum fan speed is insufficient to achieve
or maintain the process cooling set-point.
In energy-saving mode, the control system reduces electrical
consumption by activating use of adiabatic cooling as soon as
power consumption reaches a user-defined set-point. Adiabatic
cooling is then increased until process cooling needs are satisfied
or adiabatic capacity is up to 100% before power consumption is
increased.
The closed-loop design of adiabatic cooling towers not only
minimizes the consumption of water due to evaporative cooling
requirements, but also dramatically reduces the possibility of
coolant contamination, coolant fouling, and the related costs of
water monitoring and chemical treatment. In place of water as a
process coolant, processors may adopt a mix containing 35%
propylene glycol mix, which will also help prevent freezing during
cold weather. Reduced water consumption also dramatically
reduces sewage costs.
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200 West Kensinger Drive | Cranberry Township, PA 16066 724.584.5500 | www.conairgroup.com
Adiabatic coolers serve a range of cooling capacity
requirements
Conair offers eleven models of EarthSmart™ adiabatic cooling
tower (ESTW Series), to handle nominal process coolant flow rates
from as little as 45 gal/min (170 l/min) up to 510 gal/min (1930 l/
min), with cooling capacities ranging from 17 tons to 195 tons.
Model ESTW-12 ESTW-13 ESTW-14 ESTW-22 ESTW-23 ETSW-24 ESTW-25 ESTW-26 ESTW-27 ESTW-28 ESTW-29
Nominal flow rate
45 70 105 107 165 210 280 290 333 400 510
(gpm)
Nominal cooling
17 26 40 41 63 81 107 111 128 153 195
(tons)
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200 West Kensinger Drive | Cranberry Township, PA 16066 724.584.5500 | www.conairgroup.com
