RTAA-SVX01A-EN 95
Controls Interface
Current Overload Protection
The UCM continually monitors compressor current to provide unit protection
in the event of an overcurrent or locked rotor condition. Protection is based on
the phase with the highest current and, if limits are exceeded, the UCM will
shutdown the compressor and will display an MMR diagnostic.
Leaving Chilled Water Temperature Control
If the Auto key is pressed and a remote chilled water setpoint has been
communicated, the UCM will control to the Remote Chiller Water Setpoint.
Otherwise, it will control to the front panel setpoint. Control is accomplished
by both staging compressors and modulating the slide valves on each
compressor.
Upon start-up, if the leaving chilled water temperature is dropping 5 F per
minute or faster, the chiller will not load further.
Chilled Water Reset (CWR)
As an option, the UCM will reset the chilled water temperature setpoint,
based on either the return water temperature, zone air temperature, or
outdoor air temperature. The 1U2 Module is necessary to preform CWR.
The following are selectable:
1. One of three RESET TYPEs, from top to bottom in order of reset:
no CWR
RETURN WATER TEMPERATURE RESET
OUTDOOR AIR TEMPERATURE RESET
The Clear Language Display will not permit more than one type of reset to be
selected in the Operator Settings Menu.
2. RESET RATIO Setpoints. For OUTDOOR AIR TEMPERATURE RESET,
there are both positive and negative reset ratios.
3. START RESET Setpoints
4. MAXIMUM RESET Setpoints. The maximum resets are with respect to
the chilled water setpoint.
No matter which type of reset is selected all parameters are factory set to a
predetermined set of values. Field adjustment of 2,3,or 4 above, is usually not
required.
Table 16 Compressor(s) Current Limit Setpoints
vs. Chiller Current Limit Setpoint (CLS)
System
CLS
(70 - 125)
Number of compressors
in operation
One Tw o
120% 120 120
100% 120 100
80% 120 80
60% 120 60
40% 80 40
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