52
PKG-SVX027C-EN
Figure 37.
Variable speed compressor drive I/O
Compressor Staging
Fixed speed compressors cycle and the variable speed
compressor loads/unloads to maintain the operating
state required by the temperature controls. In the event
of a compressor failure, the next available compressor
turns on. During normal conditions, compressors will
not turn on until they have been off for at least three
minutes. Normal operating conditions are established
on an individual compressor basis. When a compressor
starts, its timer also starts.
Compressor Control
Steps of mechanical cooling are control based on
supply air or zone temperature. Compressor staging is
based upon a proportional, integrating (PI) control
algorithm.
Waterside Components
Waterside components consist of water piping, water
valves, water flow switch option, water cooled
condensers, and the economizer option.
Water Purge
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Automatically circulate water through the economizer
and condensers periodically during non-operational
times. This allows fresh chemicals to circulate in
waterside heat exchangers. This feature is on all units
and is controlled at the HI.
Water Piping Options
Water piping is factory-installed with left-hand
(standard) and right hand (optional) connections on
units. Also, units with waterside economizers can be
set for either variable or constant water flow at the HI.
See for detailed piping configuration information.
With compatible piping configurations, the unit can be
configured to provide:
•
Constant water flow with basic or intermediate
piping
or
•
Variable water flow (head pressure control)
Constant water flow is for condenser pumping systems
that are not capable of unloading the water-pumping
system. Variable water flow maximizes energy saving
by unloading the water pumping system.
Basic Water Piping
This option is available on units without a waterside
economizer and with condenser water applications
above 54°F (12.2°C) that do not require condensing
pressure control. Left hand water connections and
piping are extended to the unit exterior. Manifold
piping is factory installed.
Water Regulating Valve (WRV) optional
If equipped, each compressor (Fixed or VS) uses a 24
Vac powered water regulating ball valve to control flow
through the condenser. The UC600 controller
modulates the condenser flow to limit discharge
pressure, help prevent high pressure cutout trips, and
maintain a compressor minimum differential pressure.
The valve can also be used for condenser system
chemical purge and condenser cooling loop system
balance.
