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PKG-SVX027D-EN
Figure 41. 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
NOTICE
Proper Water Treatment Required!
The use of untreated or improperly treated water
could result in scaling, erosion, corrosion, algae or
slime.
Use the services of a qualified water treatment
specialist to determine what water treatment, if any, is
required. Trane assumes no responsibility for
equipment failures which result from untreated or
improperly treated water, or saline or brackish water.
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.
Water Flow Switch Option
A water flow switch is required to be installed in the
condenser water pipe within the unit; it can be supplied
Operating Principles
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