IM 1058-8 • MAVERICK II ROOFTOP SYSTEMS
60
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Condenser Coil Splitter Solenoid Valve Control
(MPS 040 and 050 Only)
Condenser coil splitting is avaialble only on VFD compressor
circuit of a unit with low ambinet option. This feature assists in
maintaining head pressure during low ambient/low modulating
operation. A solenoid valve on each circuit is controlled by a
digital output from the MicroTech III controller.
The coil splitter solenoid valve is controlled based on the
average discharge line pressure equivalent saturation
temperature determined from the corresponding discharge
pressure transducer monitored via an analog input to the
MicroTech III controller.
The splitter solenoid valve on each circuit is normally open
(digital output de-energized). The splitter valve on a circuit is
closed (energized) when that circuit’s saturation temperature
remains below 83.0°F (250 psig) continuously for 60 seconds
and the OAT is less than or equal to 80.0°F. The solenoid valve
is re-opened when the saturation temperature rises above
105.0°F (350 psig) continuously for 60 seconds and the OAT
rises above 80°F or when all the compressors on the circuit are
OFF .
If the average saturated discharge temp falls below 250 PSIG
(83F) for 60 seconds and condenser coil splitter solenoid coil
is energized (closed), the VFD compressor modulation rate is
increased until an average saturated discharge temp of 250
PSIG (83F) is achieved. This operation will raise the lower
modulation limit of the VFD compressor, but is needed to
keep the VFD compressor inside its operating envelope and
maintain head pressure for TEV control.
When the condenser coil splitter is energized (closed) and the
VFD compressor discharge pressure is below 250 PSIG, the
VFD compressor speed is increased by 5rps increments every
30 seconds until the discharge pressure exceeds 250 PSIG.
When the VFD compressor reaches 250 PSIG, this speed
becomes the new minimum speed of the VFD compressor. As
the discharge pressure rises above 250 PSIG, the minimum
allowable compressor speed is decreased in 5 rps increments
every 30 seconds.
If the condenser coil splitter valve is closed and the VFD
compressor discharge remains below 250 PSIG for 15
minutes the circuit is locked out and an alarm is logged in the
unit controller.
If a speed correction was performed to increase the
compressor discharge pressure, there will be a record of the
action in the unit controller under the event log.
VFD Compressor Emergency Stop Control
If the VFD compressor enable output signal has been ON for
30 seconds and the controller fails to receive the VFD run
verification input, VFD Compressor Emergency Stop Control is
activated. When this function is active, VFD compressor enable
output will be turned OFF for 5 seconds and then turned
ON and ramp VFD compressor speed to 60Hz. If controller
receives a VFD run verification input, a log event is set on VFD
Emergency Stop Control. If controller fails to receive the VFD
run verification input after 3 attempts in 30 minutes, the VFD
compressor is locked out and the problem is logged.
Once active the VFD Compressor Emergency Stop Control
function remains active until one of the conditions are met.
• VFD compressor enable output signal has been ON for
30 seconds and VFD compressor status Input is ON
• VFD compressor is OFF
If the controller fails to receive the VFD run verification input
after the VFD compressor enable output signal has been ON
for 30 seconds, the circuit is shut OFF on VFD Compressor
Emergency Stop Control alarm.
Whenever this protection function becomes active a VFD
Compressor Emergency Stop Control event is recorded in the
Event Log with date and time stamp. Whenever this protection
function returns to normal a VFD Compressor Emergency Stop
Control return to normal event is recorded in the Event Log
with date and time stamp.
