Daikin MAGNITUDE WME-D, Установка, эксплуатация и обслуживание, Страница: 28 / 56

OPERATION
MAGNITUDE WME-D MAGNETIC BEARING CHILLER DAIKIN APPLIED
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Unit Enabling/Disabling and
Overrides
There are multiple options that will override normal operation of
the chiller and its compressors:
1 . Manual Button - Located on the outside front of the control
panel. Button needs to be engaged for unit to run. When
disengaged, unit will perform rapid stop. For a controlled
shutdown sequence, use the HMI Enable Button, BAS
command, or Remote Enable signal. This button is the only
method to override other “Control Sources”.
2 . Compressor 1 or 2 Enable Setting - Located in the Settings
menu, Modes tab in the HMI.
The overrides listed above work in conjunction with the “Control
Source” that is selected in the HMI via the Settings/Modes
Screen, see Figure 42 and Table 11 on page 35 . The three
options for “Control Source” are:
1 . HMI Enable Button (Local) - This is the default mode.
When this mode is set, a STOP button and an AUTO button
will appear at the top of the HMI screens. If the “Control
Source” is set to “HMI Enable Button” and a remote switch
is being used, the position of the Remote Enable switch
will be ignored. In that case, only the Manual Button need
to be closed. Once the Manual Button is engaged, press
the AUTO button on the HMI to enable the chiller in “User”
mode. It will also ignore BAS Network commands.
To disable the chiller, press the STOP button on the HMI
screen.
2 . Remote Enable - This mode will ignore BAS enable and
disable commands and requires a physical switch. To
enable the chiller and its compressors, the Manual Button
needs to be closed in the ON position. To disable the unit,
this switch will initiate a normal controlled sequence and
will stop each compressor that is running.
3 . BAS Network - This mode allows BAS to enable or disable
the chiller over a BAS network. To enable the chiller and its
compressors, the Manual Button needs to be closed in the
ON position. When a BAS Network command to disable
is given, the chiller will shutdown the chiller in a normal
controlled sequence and will stop each compressor that is
running.
Variable Fluid Flow Rates
Both excessively high and low fluid flow rates should be avoided.
Extremely high fluid flow rates and high tube velocities will result
in high fluid pressure drops, high pumping power, and potential
tube erosion or corrosion damage. Extremely low fluid flow rates
and low velocities should also be avoided as they will result in
poor heat transfer, high compressor power, sedimentation and
tube fouling.
If it is decided to vary the evaporator or condenser water flow
rate, the flow rate should not exceed the minimum or maximum
limits. Additionally, the rate of change for the evaporator flow rate
should not exceed 10% of the current value per minute.
Water Volume
All chilled water systems need adequate time to recognize a
load change to avoid short cycling of the compressors or loss of
control. The potential for short cycling usually exists when the
building load falls below the minimum chiller plant capacity or on
close-coupled systems with very small water volumes.
Assuming that there are no sudden load changes and that the
chiller plant has reasonable turndown, a rule of thumb of “gallons
of water volume equal to two to three times the chilled water gpm
flow rate” is often used.
A properly designed storage tank should be added if the system
components do not provide sufficient water volume.
Condenser Water Temperature
Control
Condenser water control is an important consideration in chiller
plant design since condenser water temperature will directly
impact chiller operation and efficiency. When the ambient
wet bulb temperature is lower than peak design, the entering
condenser water temperature from the cooling tower can
be allowed to fall, improving chiller performance. However,
operational issues may occur when the condenser water
temperatures are either too high or too low. The WME chiller
provides several options to assist the chiller plant designer in
providing the optimum control of condenser water temperature.
Cooling Tower Control
Control of the cooling tower is required to maintain stability and
avoid operational issues. This can be achieved through a BAS
or by using the MicroTech controller. For systems utilizing a
common condenser water loop for multiple purposes, the BAS
contractor must provide the control but use of the MicroTech
output signal is still recommended.
The preferred cooling tower control utilizes a variable speed fan.
MicroTech will provide a control signal to determine the proper
fan speed. It can also control up to three stages of fan cycling.
Note that fan cycling can cause cooling tower water temperature
to fluctuate as fans stage on/off, potentially adding instability to
the system.
Each of the following acceptable methods can be controlled
by the MicroTech or through a BAS utilizing the MicroTech
output signals :
1 . Three-Way Bypass Valve Operation
A traditional method for building condenser pressure at
startup with colder condenser water is with the use of a
three-way bypass valve. The device blends warmer water
leaving the condenser with cooler water from the cooling
tower at the condenser inlet. The bypass valve position will
change until full flow from the tower to the condenser is
obtained. The MicroTech provides only the valve position
control signal. Main power to drive the valve’s actuator
must be provided by the installer. The three-way valve
should be located close to the chiller within the equipment
room to minimize the volume of water.