Compressor Staging; Compressor Control; Waterside Components; Water Purge - Trane SCWM Series Installation, Operation And Maintenance Manual

Figure 38. 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.
PKG-SVX027A-EN

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
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.
Operating Principles
Figure 39, p. 48 for
47