PKG-SVX029A-EN
31
Figure 15. Fixed speed compressor protection
module (MCSP)
Compressor Staging
Fixed speed compressors cycle 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 condenser,
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.
This user-definable feature allows the user to select a
purge schedule to 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 defined at the TD-7.
Water Piping Options
Water piping is factory-installed with left-hand (standard)
and right hand (optional) connections on units.
If equipped, the unit water cooled condenser uses 24 VAC
powered water regulating ball valve to control flow through
the condenser. the unit controller modulates the condenser
flow to limit discharge pressure, help prevent high pressure
cutout trips, and maintain a circuit minimum differential
pressure.
The valve can also be used for condenser system chemical
purge and condenser cooling loop system balance.
This option provides condensing temperature control when
the unit is configured (user defined at the HI) for variable
water flow with or without a waterside economizer. A two-
way modulating control valve is wired and installed in the
unit to maintains a specific range of water temperature rise
through the condenser when entering fluid temperature is
less than 58°F (15°C).This option allows the compressor to
operate with entering fluid temperature down to 35°F (2°C).
The minimum valve position to maintain minimum
condenser flow rates is user-defined at the HI. This valve
drives closed if the unit shuts down or if a power failure
occurs.
With Compatible piping configurations, the unit can be set
to the following control schemes at the TD-7.
• Constant water flow
or
• Variable water flow
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.
Water Flow Switch Option
A water flow switch is factory installed in the condenser
water pipe within the unit. Whenever the flow switch
detects a water flow loss prior to or during mechanical
cooling, compressor operation locks out and a diagnostic
code displays. If water flow is restored, the compressor
operation automatically restores.
Water-Cooled Condensers
Units that are set up for variable water flow will modulate a
water valve to maintain a user-defined condensing
temperature setpoint. Condensing temperature will be
referenced utilizing factory installed sensors located at
each condenser.
Table 11. Condenser water piping connection sizes
20 to 40
tons
45 to 70
tons
75 to 110
tons
Water Pipe (inlet and
outlet)
2.50 NPT 3.00 NPT 4.00 NPT
Operating Principles
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