Page 344 - HVAC Pump Handbook

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Open Cooling Tower Pumps

Open Cooling Tower Pumps 341

the cooling tower sump to a higher temperature for the absorption
machine. Use of any of these procedures should be approved by the
chiller manufacturer under consideration.
Chiller manufacturers are evaluating many different effects that
variable flow through the condensers have on their equipment. It is
obvious from the preceding examples that the optimal pumping
arrangement for a specific installation requires analysis of several
different pumping arrangements.

11.6.2 Avoiding ice in cooling towers
Ice in certain forms and quantities can be disastrous to cooling tower
performance and to its structural integrity. Some ice is acceptable in a
cooling tower that is designed for operation in freezing climates.
Heavier amounts of ice that impair the cooling tower’s performance or
jeopardize the tower structure must be avoided.
Ice formation varies directly with the amount of air flowing and
indirectly with the amount of water flowing through the tower. There-
fore, pumps and pumping rates can be used to help control ice forma-
tion in a tower. Constant flow in a tower is obviously important in
freezing weather. The primary-secondary pumping of Fig. 11.7 main-
tains a steady flow of water over the tower, regardless of the flow
through the equipment using cooling tower water. The bypass valve
that is used to eliminate flow from the tower should be a two-position
valve for most towers and not be throttling, where the flow rate over
the tower is reduced from the design rate.
Ice control techniques vary between cooling tower manufacturers.
The recommendations of the manufacturer whose tower is under con-
sideration should be the basis of design for the cooling tower pumping
system.

11.6.3 Cooling tower plume abatement with pumps
Cooling towers have exit air plumes that can become quite visible,
particularly in the winter. They can be reduced or their elevation
above the ground can be increased by several techniques. Decreasing
the temperature of the entering water can have some effect on the
size and location of the plume. This can be accomplished by recircu-
lated pumping that lowers the total return water temperature. Often,
there is excess pumping capacity when the plumes occur, and some of
the water can be bypassed around the chiller condensers or process by
special valving back to the cooling tower.
The use of pumps to control these plumes should be as recom-
mended by the cooling tower manufacturer.

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