SPX Cooling Technologies CoolingTower Marley MCW - Manual (Page 13)

13
Tower Operation
general:
The cold water temperature obtained from an operating cooling tower will
vary with the following influences:
1. Heat load: With the fan in full operation, if the heat load increases,
the cold water temperature will rise. If the heat load reduces, the cold
water temperature will reduce.
Note that the number of degrees (“range”) through which the tower
cools the water is established by the system heat load and the amount
of water being circulated, in accordance with the following formula:
The cooling tower establishes only the cold water temperature attain-
able under any operating circumstance.
2. air wet-bulb temperature: Cold water temperature will also vary with
the wet-bulb temperature of the air entering the louvered faces of
the tower. Reduced wet-bulb temperatures will result in colder water
temperatures. However, the cold water temperature will not vary to the
same extent as the wet-bulb. For example, a 20°F reduction in wet-
bulb may result in only a 15°F reduction in cold water temperature.
3. Water flow rate: Increasing the water flow rate (GPM) will cause a
slight elevation in cold water temperature, while reducing the water
flow rate will cause the cold water temperature to decrease slightly.
However, at a given heat load (see formula), water flow reductions also
cause an increase in the incoming hot water temperature. Use care
to prevent the hot water from exceeding 125°F in order to prevent
damage to the tower components.
4. air flow rate: Reducing air flow through the tower causes the cold
water temperature to rise. This is the approved method by which to
control leaving water temperature.
If your tower is equipped with a single-speed motor, the motor may
be shut off when the water temperature becomes too cold. This will
cause the water temperature to rise. When the water temperature then
becomes too warm for your process, the motor can be restarted.
Operation
Range – °F =
Heat Load (Btu/hr)
GPM x 500
or — in SI units
Range – °C =
Heat Load (kilowatts)
Liters/sec x 4.187
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