OPERATING MODES
The hybrid closed Circuit Fluid Cooler operates under three different operating modes:
1.
Combined Dry-Wet Mode:
During this mode, the process fluid flows through the finned coil bundle (sensible
heat transfer) and then through the wetted prime surface coil bundle (sensible and latent heat transfer). With
lower heat loads and/or ambient temperatures, the evaporative cooling portion (and hence the water usage) is
reduced by keeping the flow fed through the wetted prime surface coil bundle to a minimum. This is
accomplished by a modulating flow control valve, which controls the design outlet temperature.
2.
Adiabatic Mode:
During this mode, the process fluid flows through the finned coil bundle and by-passes the
wetted prime surface coil bundle completely. This entering ambient air is pre-humidified (cooled) by the spray
water before flowing over the high density finned coil bundle.
3.
Dry Mode:
The full process fluid flows through the finned coil bundle and the prime surface coil bundle. Since
the spray pump is turned off, only sensible heat transfer is used.
SEASONAL PERIODS
The optimal operation of the Hybrid Closed Circuit Cooling Tower is obtained by a combination of the above
mentioned operating modes, depending on the thermal load of the process fluid and the ambient conditions.
Typically two different seasonal periods are distinguished from each other:
1. Summer period: During this period all three operating modes are applied and as such the spray pump is
activated during the dry/wet and the adiabatic operating mode. Therefore the cold water basin is filled with
water at all time.
2. Winter period: during this period only the dry operating mode is applied and as such the cold water basin is
drained.
The following table summarises the use of the different operating modes during the seasonal periods.
Summer period
Winter period
Dry mode
Adiabatic
mode
Dry/Wet
mode
Dry mode
Fan motors
Full / Half /
Variable speed
Full speed
Full speed
Full / Half /
Variable speed
Spray pump motor
Off
On
On
Off
Process fluid through finned foil
bundle
100% Design
flow
100% Design
flow
100% Design
flow
100% Design
flow
Process fluid through bare coil
bundle
100% Design
flow (2)
0%
Variable flow
(1)
100% Design
flow (2)
Use of different operating modes during the seasonal periods
(1) Process fluid flow through bare coil bundle is controlled by the three way valve and is in function of the process fluid return temperature.
(2) The three way valve is locked and closes the bypass line completely.
When working dry during winter, the sump can be drained in which case power to the pump and heaters must be
switched off. If the sump is not drained during freezing conditions, heat tracing must be foreseen for pump/piping.
Frequent on/off cycling
of the spray pump should be limited to a minimum operating period of 5 hours.
Rapid on/off cycling
of the fan motors can cause the fan motors to overheat. This should be limited to a
maximum of six on/off cycles/h. If the limit is equipped with 2-speed fan motors, a 15 seconds delay should be
observed when switching from high to low speed.
W W W . B A L T I M O R E A I R C O I L . E U
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2 General information
2 General information
