iWorX CCU1
505-022, Effective: September 23, 2010
17
© 2010 Taco Electronic Solutions, Inc.
To prevent the integral component from becoming too large, there is anti-wind up reset protection. This protection
clamps the integral value when all of the components add up to more than 100% or less than 0%. The following equa-
tions are used for P+I control:
K
P
= Proportional Gain
K
i
= Integral Gain
Error
=
Inputs
-->
Cond Rtn Temp
-
All Settings --> Cool Tower Valve SP
I
=
I
+ (
K
i
x
Error
)
Outputs --> Cooling Tower Valve (%)
= (
K
P
x (
Error
+
I
)) + 50.00%
The valve can be set for reverse action by exchanging the maximum and value settings during configuration. That is, if
the default maximum of 10 Volts and default minimum of 0 Volts are being used for reverse action, set the minimum to
10 Volts and the maximum to 0 Volts.
Cooling Tower Variable Speed Fan Control
The cooling tower variable speed fan is controlled when the CCU1 is configured for a water cooled chiller. The cooling
tower fan speed is calculated by a P+I control loop based on the condenser water return temperature and the cooling
tower water setpoint. The fan speed control loop is activated 15 seconds after the cooling tower bypass valve has mod-
ulated to its 100% position (full flow through tower).
As the temperature increases above the cooling tower water setpoint, the fan speed is increased. The fan speed is
decreased as the water temperature decreases below the
Chiller settings --> setpoint
. The fan speed control loop is
selectable for direct or reverse acting operation.
To prevent the integral component from becoming too large, there is anti-wind up reset protection. This protection
clamps the integral value when all of the components add up to more than 100% or less than 0%. The following equa-
tions are used for P+I control:
K
P
= Proportional Gain
K
i
= Integral Gain
Error
=
Inputs
-->
Cond Rtn Temp
-
All Settings --> Cool Tower Valve SP
I
=
I
+ (
K
i
x
Error
)
Outputs --> Cooling Tower Fan (%)
= (
K
P
x (
Error
+
I
)) + 50.00%
Figure 6: Cooling Tower Sequence
0%
100%
Condenser Return
Water Setpoint
Tow
er
W
at
er
By
pa
ss
Va
lve
Co
ol
ing
To
we
r Fa
n
Supply Water Temperature
The valve can be set for reverse action by exchanging the maximum and value settings during configuration.
Chiller Low Limit Control
The CCU1 provides low limit control. When the outside air temperature drops below the low limit setpoint as sensed by
the ASM on the network, the CCU1 energizes the chiller low limit output and starts the chilled water pump. The chiller
low limit output is interfaced to the factory supplied chiller controls to signal the chiller to not start in response to the
chilled water pump operation in the low limit condition. The chilled water pump and chiller low limit output de-energizes
when the temperature rises 1 °F above the low limit setpoint.
