Sterling 882.00440.00 SC6-610.6 specifications Operation, Bleed-Offand Evaporation Rates

Chapter 4: Operation

4-1 Bleed-Off and Evaporation Rates

A proper bleed-off rate is important to limit the concentration of minerals and foreign materials in re-circulated water. A bleed-off equal to the evaporation rate, normally about two gallons per hour per ton (7.57 liters per hour per 3,780 Kcal/hr), is sufficient for many makeup water conditions. Refer to the suggested bleed-off arrangements in Figure 3 and Figure 4 on pages 14 and 14 for more information. For automatic bleed rate control, a conductivity controller is available through the Sales department.

4-2 Winter Operation Considerations

All cooling towers are subject to ice formation in sub-freezing weather. Your cooling tower requires a certain amount of attention and maintenance to prevent damage during these operating conditions.

Follow these guidelines to reduce the chance of ice buildup:

•Maintain full design flow. Any reduction in water flow greatly increases the probability of ice forming on and around the air inlet louvers.

•Do not use free cooling applications during freezing weather. Reduced water temperatures or loading dramatically increases the chance of ice formation. Make sure that the leaving water temperature is set above 80ºF (27ºC) during sub-freezing weather so heat from the water warms the air inlet louvers and reduces ice formation when the fan is off. Using a thermostat to control fan cycling by leaving water temperature is mandatory.

•Do not run fans backward to thaw ice. Ice can form on the fan ring, fan guard, and support structures, and can severely damage fan blades. Reversed airflow can also blow water vapor out onto the roof and create ice fields around the cooling tower.

•Maintain a heat load of at least 60% of tower capacity at all times during operation in freezing weather. A lack of substantial load can create uneven temperatures in the tower and cause freezing.

•If you shut down your cooling tower during freezing weather, you must drain it completely. We recommend that you use an indoor reservoir tank to permit water to drain into the tank on system shutdown, whether for emergencies or actual planned shutdowns.

•An alternative is to use basin heaters if a tower basin is used as a sump. Basin heaters are available as an option. However, basin heaters can permit freeze-up during power failures if water remains in the sump. The customer is responsible for determining risk factors for each specific application.

Fiberglass Cooling Towers Chapter 4: Operation Page 17 of 25