ACTS FAQ
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What is
the coldest water temperature an Aggreko cooling tower can
achieve?
The temperature that any cooling tower can
achieve is limited by the wet bulb temperature.
The wet bulb temperature is determined by the ambient humidity and
dry bulb temperature. A cooling tower, in theory, can achieve a
temperature equal to the wet bulb temperature. However, most
experts agree that it is not always practical for a cooling tower
to achieve a temperature colder than 5° F above the wet bulb
temperature. Aggreko employs a custom water distribution system
that makes it very effective at achieving an exceptionally close
approach to wet bulb.
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How do
you handle water treatment for rental cooling towers?
All cooling water treatment programs should
address four things: 1.) scale control, 2.) solids control, 3.)
biological control, and 4.) corrosion control. The water treatment
program should be designed to treat the cooling system, not just
the cooling tower. Aggreko’s industrial cooling towers are
constructed of superior materials (FRP and Stainless Steel) to
minimize the potential for corrosion. Even though Aggreko’s
industrial cooling towers are constructed of superior materials,
proper water treatment is still recommended to prevent scale and
biological growth. When selecting a water treatment program, the
entire cooling system including the cooling tower, pumps, piping,
and exchangers must all be considered. In most cases, the water
treatment program that is in place prior to the rental cooling
towers being placed into service will be adequate. In the case that
no water treatment program is in place, Aggreko can provide water
treatment as a part of our services or can assist the customer in
the selection process.
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What is
the cooling capacity of your largest cooling tower unit?
The cooling capacity of Aggreko’s largest unit is best
referenced by stating capacity in a maximum water flow rate. Our
largest single unit is capable of flowing 4,500 gallons
per minute. However, it is more important to understand that our
industrial cooling towers are modular and can be interconnected to
achieve any cooling requirement from 100 gallons per minute to in
excess of 1,000,000 gallons per minute.
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Do I
need a pump with my rental cooling tower?
Depending on the application, additional cooling tower
pumps may not be required. When being used for the purpose
of supplementing an existing cooling tower, Aggreko cooling towers
do not require pumps. The unique design utilizes an elevated water
basin allowing water to be drained back to the basin/sump of the
existing cooling tower without the aid of pumps. When the towers
are utilized in a stand alone application, Aggreko can provide
pumps that are designed to meet the head and flow requirements
specific to the project.
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How do you predict or measure the capacity of a cooling
tower?
There are five basic temperature measurements used in rating
cooling towers capacity: Hot Water Temperature; Cold Water
Temperature; Wet Bulb Temperature, Range and Approach. The
Hot Water Temperature (HWT) is the temperature of the water
entering the cooling tower and the Cold Water Temperature (CWT) is
the temperature leaving the cooling tower. Wet Bulb Temperature
(WBT) is the lowest temperature that occurs on a surface when water
is evaporated from the surface and is the most powerful variable in
any given cooling tower's ability to reject heat. Range is the
difference between the Hot Water Temperature and the Cold Water
Temperature (HWT—CWT). Approach is the difference between the Cold
Water Temperature and the Wet Bulb Temperature (CWT—WBT). These
formulas calculate the cooling tower’s ability to get the CWT down
to the WBT.
Generally speaking, a cooling tower will have a tighter approach
when there is less water flowing and a bigger approach when there
is more water flowing. The difference between the Hot and Cold
Water Temperature is an element in the process of the water being
cooled, and is not dependent on the cooling tower (except in a
once-through discharge system like pond/river cooling). It is
interesting to note that when cooling, the process will add a
certain amount of energy in the form of heat regardless of the
cooling tower's capability.
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What is meant by cooling tower performance?
A cooling tower is designed to produce certain results based on
specific conditions, with variables due to conditions presented as
curves. Standard conditions for a cooling tower are 95 degree Hot
Water Temperature (HWT), 85 degree Cold Water Temperature (CWT), a
78 degree Wet Bulb Temperature (WBT), a 10 degree Range (HWT—CBT)
and 7 degree approach (CWT—WBT). If a cooling tower is designed to
be able to flow 3,000 gallons per minute at standard conditions and
is flowing 3,000 gpm, then it is said to be performing at 100%.
However, varying conditions will change what the cooling tower is
able to produce, with the largest factor being the wet bulb
temperature.
An Example: A process is delivering 105 degree HWT to the
cooling tower. The cooling tower is producing 90 degree CWT with an
80 degree WBT (with a 15 degree Range and 10 degree Approach). If
the tower's curves say it should deliver 3,000 gpm but it is
measured at those conditions and is only producing 2,700 gpm; the
tower is performing at 90%. If conditions change again, the tower’s
flow rate is measured at 3,300 gpm, it performing at 110%.
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