SPX Cooling Technologies MARLEY CLASS 800 - Manual (Page 13)

13
Temperature Control and Energy
Management
➠
The wet-bulb temperature of the ambient air varies significantly on a daily
basis, and considerably from season to season. As the wet-bulb temperature
reduces, the tower becomes capable of producing colder and colder water—or
it becomes capable of producing a given cold water temperature at reduced
airflow through the tower. These characteristics are the “opposing forces”
referred to on page 4.
Maximizing Tower Performance
If your operating system is one which benefits from the coldest possible water;
that is, if colder water allows you to increase your output—or allows you to
operate your system at significantly lower cost, then continuous full speed
operation of the fan(s) may be your best mode of operation.
In this mode of operation, concern for the cold water temperature level would
be limited to the potential for the tower to form ice during freezing weather.
(See Caution note on page 8 and Freezing Weather Operation on pages
11 and 12.) Although the 70°F (21°C) cold water temperature indicated on
page 11 is appropriate for cold weather start-up and operation, acceptable
temperatures during full operation in spring, summer, and fall may be appreciably
lower, perhaps as low as 50°F (10°C) or less. Refer to your performance
curves for expected tower cold water temperatures at varying flow
rates, ranges, and wet bulb temperatures.
Minimizing Tower Energy Use
Most systems gain no operating or production benefits from water temperatures
below a certain level, and that level is not usually below the aforementioned
70°F (21°C). When a reducing ambient wet-bulb permits the tower to reach
that target cold water temperature level, further reductions in the wet-bulb
temperature permit manipulation of fan speeds or operation to maintain that
temperature level.
Single-speed fans can be cycled on and off for cold water temperature control,
with the steps of control depending upon the number of fan cells in the tower.
Two-speed motors offer twice as many control steps—with the added bonus
that half-speed (which produces half of the normal airflow through the tower)
requires less than 20% of the full-speed power requirement.