York SSS 14L-B, Руководство по эксплуатации

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JOHNSON CONTROLS
13
SECTION 1 – THEORY OF OPERATION
FORM 160.00-O2
ISSUE DATE: 04/30/2019
1
SOLID STATE STARTER COOLING LOOP
The SCRs in the LCSSS generate heat during normal
running conditions and become very hot during start-
up of the chiller. This heat is generated by the fact that
all of the current flowing to the motor is conducted
through the SCRs. The SCRs are very reliable, but
they do have a slight resistance value when they are
turned on. The resistance, along with the load current
of the motor, generates the heat.
The heat must be dissipated, or the SCRs will fail from
an overheating condition. Two methods are commonly
used to dissipate the heat. The first method, which was
employed on older solid state starters was forced air
cooling. This method works well, but requires a larg-
er cabinet and the addition of many fans. The second
method for dissipating the heat is to employ a water
cooling system similar to that used in automobiles.
The cooling system for the LCSSS is different from
the system in an automobile. In automobiles, heat is
transferred to the air, but the starter transfers heat to
the condenser water.
Condenser water is used to cool the starter for many
reasons. One, the condenser water will always be avail-
able since it is part of the chiller system. The cooling
is free since the condenser water will be cooled in the
cooling towers for the chiller needs, and does not add
any load to the chiller. If the chilled water was used to
cool the starter, this would add to the chiller load and
add cost to the customer. In a few applications where
chilled water is being used because of extremely high
condenser water pressure, a temperature regulating
valve must be used. The temperature regulating valve
should be set to 85°F so that condensation does not
occur inside the starter cabinet. Using condenser wa-
ter eliminates the concern for condensation occurring
inside of the starter cabinet, which could damage the
starter. The reliability of the starter is improved from
the standpoint that the three forced air fans are re-
placed with one circulating pump.
The SCR assemblies are cooled by a pump circulating
coolant in a closed loop through the SCR’s heatsink
and the outer tube of the tube-in-tube heat exchanger.
When the coolant passes through the heatsink, it ab-
sorbs heat from the heatsink. As the coolant passes
through the heat exchanger, it gives up its heat to the
system condenser water that is flowing through the in-
ner tube of the tube-in-tube heat exchanger. The design
of the heat exchanger prevents the closed loop coolant
from mixing with the condenser water. The condenser
water is forced through the heat exchanger by the pres-
sure differential across the condenser shell input and
output.
The cooling loop is filled with coolant
at system start-up commissioning by the
service technician. Refer to start-up in-
structions. As maintenance, the coolant
must be changed every year. If the coolant
is not replaced within this time interval,
a potential for corrosion of the SCR’s
heatsink is greatly increased.
The Logic/Trigger Board constantly monitors the tem-
perature of the three SCR heatsink assemblies with a
thermistor attached to each assembly. The temperature
of each thermistor is sent to the Micro Board in the
OptiView Control Center via the serial communica-
tions link. Refer to ASSOCIATED LITERATURE on
page 3 for details on where this data can be viewed on
the OptiView Control Center.
If the temperature of any assembly exceeds a high
value during a running condition, the Logic/Trigger
Board will initiate a shutdown. Further, anytime the
temperature of any assembly exceeds a high value and
the starter is not running, the chiller will be prevented
from starting and the closed loop coolant pump will be
operated until the temperature has fallen. Also, if the
temperature of any assembly falls below a preset val-
ue, the Logic/Trigger Board will initiate a shutdown.
Changes have been made to the OptiView Control Cen-
ter software to improve the restart time of the starter.
These changes allow for the control of the condenser
water pump when a style ‘B’ LCSSS is used with the
following OptiView Control Center software. On a YK
chiller, the software is C.MLM.01.04 or later. On a YT
chiller, the software is C.MLM.02.01 or later. On a YS
chiller, the software is C.MLM.03.01 or later.
The condenser water pump will be turned on any time
the chiller is started, and will continue to run until
coastdown is complete. After coastdown is completed,
the condenser water pump will continue to run if any
one of the three thermistors indicated that the SCR as-
semblies are too hot. Once the temperature has fallen
to a specified level, the condenser water pump will
turn off.
This new control will cool down the SCR assemblies
more quickly after the chiller has been stopped. Then
the LCSSS can be started sooner, as long as the anti-
recycle timer has been satisfied.