Sequence Of Operation - BAC HXV Operation & Maintenance Manual

NOTE: LWT= Fluid Cooler Leaving
Water Temperature
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Figure 2c: Adiabatic Mode

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
Conditions
No Heat Load
Peak (design) operating conditions -
Ambient wet bulb ≥ Design wet bulb
Fan speed is reduced based on load and reaches
customer-defined fan speed switchpoint OR
Ambient dry bulb ≤ Design adiabatic operation
switchpoint temp
Fan speed is reduced based on load and reaches
customer-defined fan speed switchpoint OR
Table 1a: Sequence of Operation with a 3-way Valve
Conditions
No Heat Load
Peak (design) operating conditions - Process
fluid leaving temperature ≥ Customer setpoint
Fan speed is reduced based on load and reaches
customer-defined fan speed switchpoint OR
Ambient dry bulb ≤ Design dry operation switch-
point temp
Table 1b: Sequence of Operation without a 3-way Valve
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.
Sequence of Operation with a 3-way Valve
Spray pump OFF; Fans OFF
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.
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.
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.
Sequence of Operation without a 3-way Valve
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.
Water Saver Mode: Spray pump OFF; Fan motors ON with VFD - fan
motors ramp up and down together. Process fluid flows through dry
Table 1. Sequence of Operation
coil and evaporative coil in series to maximize dry performance.
Operation
Operation
Spray pump OFF; Fans OFF