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Introduction
and the fans when fire is detected. When the alarm
condition is cleared, the reset button on the firestat must
be manually pressed to resume operation.
Note: The smoke detector and firestat are not designed to
operate as room smoke/fire detection systems that
may be required by local or national codes.
Auto Power Transfer Switching
An automatic transfer, main power switching system is
optionally available for critical operations. With this
option, two main power service disconnect switches are
provided on the door of the cabinet to connect two
independent power sources (see the following figure).
Figure 6.
Auto transfer disconnect switches
If the user selectable main power source is interrupted or,
if a phase loss or imbalance occurs, the automatic transfer
switching circuitry immediately transfers operation of the
precision A/C system to a secondary power source. If
power is transferred, the system controller provides an
alarm signal and the alarm display indicates which power
source failed. When the primary power source is
functionally restored, the operation of the A/C system is
automatically transferred back to the primary power
source.
An indicator light is provided above each main power
service disconnect switch (see the above figure). A light
illuminates above the switch that's selected to supply
power to the A/C system, whether the unit is running or
not, indicating that power is available at the switch.
A preferred power selector switch is included with the
auto-transfer switching option. It is mounted inside the
cabinet at the top of the electric box (see
This switch may be used to manually transfer the power
source and/or test the auto transfer switching function.
Dual Cooling Circuits
CyberAir DX systems are designed with two stages of
cooling. The cooling circuits are typically comprised of
one compressor per circuit. The circuits are staged to
operate as needed, based on incremental cooling stage
enable temperature set points as programmed in the
system controller. Each stage is assigned an offset to the
temperature set point for turning the compressors on. The
controller turns each stage on and off as needed based on
12
Front Door of A/C system
Indicator Lights
Dual Service Disconnect
Switches (Location may vary)
Figure 24, p.
28).
the temperature set point plus offset value (reference in
the Microprocessor Controller Manual). The compressor
circuits rotate after each run cycle in an effort to promote
equal run-times.
Tandem Compressor Option
An optional four stage cooling configuration is available
which utilizes three compressors (two small tandem
compressors and one large compressor). The two small
tandem compressors operate as circuit 1 and the large
compressor operates as circuit 2 (see the following figure).
Figure 7.
Tandem compressor configuration
Circuit 1
1A
5
Ton
1B
5
Ton
Tandem Compressors
Four Stage Operation
In the example of a TR-CFU/D-070 (20 ton, 240,000 Btu) A/
C system configured with three compressors, two small (5
ton) compressors are paired together as one, tandem
circuit with a shared suction line and shared discharge
line. The compressor suction and discharge ports are
equipped with back pressure isolation valves so one
compressor may operate independently or both may
operate together as required by capacity staging
demands. One large (10 ton) compressor is also provided
as circuit two.
The controller manages operation of the three
compressors with a unique method of staging which
conserves energy by incrementally matching compressor
capacity against the load. The three compressors are
turned on in various combinations to provide a total of 4
stages of cooling as shown in the table below:
Stage
Cut-in Offset Compressor(s)
1
+2° F
2
+3° F
3
+4° F
4
+5° F
Circuit 2
2
10 Ton
Single Compressor
Capacity
1A
5 tons
2
10 tons
1B+2
15 tons
1A+1B+2
20 tons
SS-SVX002B-EN
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