6
Operating Modes
•
Adiabatic Mode (Balanced Water and
Energy Savings):
The spray water
circulating pump distributes water
over the fill surface. The fans draw
air over the wetted fill where it is
adiabatically pre-cooled resulting is a
significantly lower air temperature and
greatly increasing the rate of sensible
heat transfer. The process fluid is
only circulated through the dry finned
coil. To enable this mode, a customer-
supplied three-way valve is needed.
Table 1.
Sequence of Operation
Sequence of Operation with a 3-way Valve
Conditions
Operation
No Heat Load
Spray pump OFF; Fans OFF
Peak (design) operating conditions -
Ambient wet bulb ≥ Design wet bulb
Energy Saver Mode:
Spray pump ON; Fan motors ON with VFD - fan
motors ramp up and down together. 3-way valve fully closed to allow
full flow through evaporative coil.
Fan speed is reduced based on load and reaches
customer-defined fan speed switchpoint
OR
Ambient dry bulb ≤ Design adiabatic operation
switchpoint temp
Adiabatic Mode:
Spray pump ON; Fan motors ON with VFD - fan
motors ramp up and down together. 3-way valve opens to bypass
evaporative coil, thereby saving water.
Fan speed is reduced based on load and reaches
customer-defined fan speed switchpoint
OR
Water Saver Mode:
Spray pump OFF; Fan motors ON with VFD - fan
motors ramp up and down together. 3-way valve fully closed to allow
full flow through evaporative coil to maximize dry performance.
NOTE:
LWT= Fluid Cooler Leaving
Water Temperature
Sequence of Operation
The following is applicable to all sequences of operation:
• All fan speed control operation is based on leaving fluid temperatures.
• Basin heaters are interlocked with the spray pump, and only operate when the spray
pump is off and the basin temperature is less than 40°F.
• For extra coil freeze protection, spray pump can be locked out if ambient temperature
is less than 32°F
Figure 2c:
Adiabatic Mode
Sequence of Operation without a 3-way Valve
Conditions
Operation
No Heat Load
Spray pump OFF; Fans OFF
Peak (design) operating conditions - Process
fluid leaving temperature ≥ Customer setpoint
Energy Saver Mode:
Spray pump ON; Fan motors ON with VFD - fan
motors ramp up and down together. Process fluid flows through dry
coil and evaporative coil in series.
Fan speed is reduced based on load and reaches
customer-defined fan speed switchpoint
OR
Ambient dry bulb ≤ Design dry operation switch-
point temp
Water Saver Mode:
Spray pump OFF; Fan motors ON with VFD - fan
motors ramp up and down together. Process fluid flows through dry
coil and evaporative coil in series to maximize dry performance.
Table 1a:
Sequence of Operation with a 3-way Valve
Table 1b:
Sequence of Operation without a 3-way Valve
