Retrotec USACE - Manual (Page 205)

Appendix D D75
D.4.2.22 Control of Fans and Pumps Not Based on Cooling Tower
Water Temperature (Ineffi ciency)
Figure D125. Multiple cooling
towers having cold well or basin
in ground that serve a chilled
water system. The fi rst two towers
on the left share a common basin.
Note the vertical turbine pumps
adjacent to each tower.
It is common to have more than one cooling tower servicing a chilled water
system or some other process. They are set on a basin, which is often common
to all towers (Figure D125). Thus the cooling water fl ows over the tower and
is collected and, to some degree, stored in a tank or basin below. In these large
systems, a group of pumps draw water from the basin and send it to the as-
sociated equipment that requires cooling. To obtain more cooling out of the
cooling tower, more water can fl ow over the towers, or additional towers can
be brought online. If that does not provide the desired cooling, the cooling
tower fans can be energized to increase air fl ow by increasing the fan speed or
by adjusting the fan blade(s). If it is cool outside, the fans may not be needed,
or they can run on low speed. If it is a variable condenser water fl ow system,
less water fl ow is required during low-use periods. The best way to control the
cooling tower is to operate the fans and pumps to achieve a determined cooling
water temperature. The controls can be set to maintain the desired basin water
temperature, so as not to waste extra energy by overcooling the water. Control
of this temperature can be varied to optimize the operation of the total system,
thereby achieving additional energy savings.
D.4.2.23 Cooling Tower Fan Blades Not Adjusted for Load or
Season (Ineffi ciency)
The air fl ow through a cooling tower is accomplished by running the cooling
tower fans. When more cooling is desired from a cooling tower, air fl ow is in-
creased by having a greater fan speed or adjusting the fan blades. Propeller type
fans with diameters of 0.6–309.1 m (2–30 ft) are normally used especially on
the larger towers. Fans with a diameter greater than 1.2 m (4 ft) typically would
have adjustable-pitch blades enabling the fan to produce the desired amount of
air with the least energy use. If the outside air is cool, the air fl ow through the
tower can be reduced for the same water cooling. If the required water cooling