OPERATION
MAGNITUDE WMT CHILLER
DAIKIN APPLIED
36
Description
Default
Range
PW
Comments
Tower Con-
trol Mode
Auto
Effi-
ciency
Manual,
Auto, Auto
Efficiency
O
Manual: Activate
manual control of
tower control outputs
Auto: Set tower con-
trol outputs to reach
set point
Auto Efficiency:
When set point can
not be reached,
reduce fan output if
possible
Response
Speed
Slow
None,
Slow,
Medium,
Fast
O
Tower control output
rate of change when
not on set point
Manual Control
Manual Fan
Stages
1
0 – 3
O
Set the number of
running fan stages
when Manual Con-
trol is enabled
Manual Fan
VFD
50
0 – 100
O
Set fan VFD speed
when Manual Con-
trol is enabled
Manual
Valve /
Cond Pump
VFD
90
0 – 100
O
Set bypass valve
/ cond pump VFD
when Manual Con-
trol is enabled
Tower Stages
Cooling
Tower
Stages
2
1 – 3
O
Number of available
tower fan stages
VFD Mini
-
mum Speed
0
0 – 70%
O
Minimum tower fan
VFD speed
Tower Control Setup
Setup for tower control settings in
Table 17
will be accomplished
on the HMI using the Tower screen under Settings. See
. Using the chiller unit controller, up to three digital outputs of
tower staging and two analog outputs (0-10 VDC) are available.
The two analog outputs are as follows:
1 .
Bypass Valve or Condenser Pump VFD signal.
2 .
Tower Fan VFD signal.
Tower Control Strategies
There are four possible tower control strategies that can be
selected with the Cooling Tower Control (Temp, Lift) and Tower
Control Mode (Manual, Auto, Auto Efficiency) settings:
1 .
Manual: Tower control outputs are set to operator
configured values.
2 .
Temp, Auto: Tower control is reactive to the delta between
set point and process value (CEWT), and the process
value rate of change. This allows the set point to be
reached by adjusting tower output over time, if possible,
given the cooling tower capability as well as outdoor air
temperature and humidity.
3 .
Lift, Auto: Tower control is reactive to the delta between
set point and process value (Lift), and the process value
rate of change. This allows the set point to be reached
by adjusting tower output over time, if possible, given the
cooling tower capability as well as outdoor air temperature
and humidity.
4 .
Temp, Auto Efficiency: Operates the same as Auto, except
that when tower fan output is at 100%, after 15 minutes
has elapsed, tower fan output is slowly reduced until
CEWT increases to find where increasing tower fan output
would no longer be effective in reducing CEWT. Fan output
control will return to normal if the process value increases
by more than 0.2°F or drops below the set point.
5 .
Lift, Auto Efficiency can be selected but will operate the
same as Lift, Auto. Cooling Tower Control by temperature is
recommended.
For all strategies, the chiller unit controller can control up to three
tower fan stages, as well as a tower fan VFD and either a tower
bypass valve or condenser pump VFD. See
Within each variation of the Auto and Auto Efficiency, a PD loop
determines a tower capacity loop output (TCLO) value that goes
from -100 to 100, where -100 is reducing tower capacity as
quickly as possible, 0 is leaving tower capacity unchanged, and
100 is increasing tower capacity as quickly as possible.
•
Tower bypass valve
•
steps open above 10 TCLO
•
steps closed below -40 TCLO
•
Tower fan on/off events limited in frequency by timers for
staging up and staging down
•
For a given number N of tower fan stages, all VFD
controlled:
•
all stages run at the same speed
•
VFD speed steps up from minimum speed setting to
maximum speed setting when above 15 TCLO and
tower bypass valve position is > 90% of Valve Control
Range - Max
•
VFD speed steps down below -5 TCLO
•
For a given number N of tower fan stages, where one stage
is VFD controlled:
•
VFD speed steps up from minimum speed setting to
maximum speed setting above 0 TCLO and tower
valve > 90% of Valve Control Range - Max
•
speed steps down below 0 TCLO
•
VFD speed -100%/N stages when adding 2nd and or
3rd stage
•
VFD speed +80%/N stages when dropping 2nd and or
3rd stage
•
For one tower fan stage
•
turn on at 90 TCLO if tower bypass valve position is >
90% of Valve Control Range - Max
•
turn off at 20 TCLO
•
For multiple tower fan stages:
•
(E)nable threshold = 90 / N stages
•
(D)isable threshold = 20
