Trane SCXG-SVX01B-EN Input Devices and System Functions, general Operation information, Notice

general

Operation information

Input Devices and System Functions

Following are basic input device and system function descriptions used within the UCM network on IntelliPak self- contained units. Refer to the unit wiring diagrams for specific connections.

Water Purge

NOTICE

ProperWaterTreatment!

The use of untreated or improperly treated water in coils may result in scaling, erosion, corrosion, algae or slime. It is recommended that the services of a qualified water treatment specialist be engaged 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.

During the unoccupied mode, water- cooled units will periodically circulate water through the condensers and waterside economizer if the user has enabled the purge function at the HI. The water purge function circulates water to introduce fresh water-treatment chemicals and help prevent water stagnation.The number of hours between each periodic purge, or purge duration, is user-defined at the HI between 1-999 hours. If the periodic purge timer expires while the unit is in occupied mode, it will wait for the next available unoccupied time before initiating water purge. Contrary, if a request for cooling occurs during a purge sequence, purge will terminate and cooling will commence.

Compressor Circuit Breakers

The compressors are protected by circuit breakers that interrupt the compressor power supply if the current exceeds the breakers “must trip” value. During a request for compressor operation, if the compressor module (MCM or SCM) detects a problem outside of it’s normal parameters, it turns any operating compressor(s) on that circuit off, locks out all compressor operation for that circuit, and initiates a manual reset diagnostic.

Compressor MotorWindingThermostats

A thermostat is embedded in the motor windings of each compressor. Each thermostat opens if the motor windings exceed approximately 221°F.The thermostat resets automatically when the winding temperature decreases to approximately 181°F. Rapid cycling, loss of charge, abnormally high suction temperatures, or the compressor running backwards could cause the thermostat to open. During a request for compressor operation, if the compressor module detects a problem outside of it's normal parameters, it turns any operating compressor(s) on that circuit off, locks out all compressor operation for that circuit, and initiates a manual reset diagnostic.

Low Pressure Control

Low pressure (LP) control is accomplished using a binary input device. LP cutouts are mounted on the suction lines near the compressors.The LP control contacts close when the suction pressure exceeds 27 ± 4 psig. If the LP control is open when a compressor starts, none of the compressors on that circuit will operate.They are locked out and a manual reset diagnostic initiates. The LP cutouts open if the suction pressure approaches 7 ± 4 psig. If the LP cutout opens after a compressor starts, all compressors operating on that circuit will turn off immediately and will remain off for a minimum of three minutes.

If the LP cutout trips four consecutive times during the first three minutes of operation, the compressors on that circuit will lock out and a manual reset diagnos- tic initiates.

Evaporator Temperature Sensor Frostat™

The evaporator temperature sensor is an analog input device used to monitor refrigerant temperature inside the evaporator coil to prevent coil freezing. It is attached to the suction line near the evaporator coil with circuits 1 and 2 connected to the SCM/MCM and circuits

3and 4 connected to theWSM.The coil frost cutout temperature is factory set at 30°F. It is adjustable at the HI from 25-35°F. The compressors stage off as necessary to prevent icing. After the last compressor stages off, the compressors

will restart when the evaporator temperature rises 10°F above the coil frost cutout temperature and the minimum three minute “off” time elapses.

Saturated CondenserTemperature Sensors

The saturated condenser temperature sensors are analog input devices.They are mounted inside a temperature well located on a condenser tube bend on air- cooled units, and in the condenser shell on water-cooled units.The sensors monitor the saturated refrigerant temperature inside the condenser coil and are connected to the SCM/MCM for circuits 1 and 2 (air or water cooled), and WSM for circuits 3 and 4 (only water- cooled).

Head Pressure Control

Head pressure control is accomplished using two saturated refrigerant temperature sensors on air-cooled units and up to four sensors on water-cooled units.

Air-cooled units: During a request for compressor operation when the con- densing temperature rises above the lower limit of the control band, the compressor module (SCM/MCM) sequences condenser fans on. If the operating fans cannot bring the condens- ing temperature to within the control band, more fans turn on. As the satu- rated condensing temperature ap- proaches the lower limit of the control band, fans sequence off. The minimum on/off time for condenser fan staging is

5.2seconds. If the system is operating at a given fan stage below 100% for 30 minutes the saturated condensing temperature is above the efficiency check point setting, a fan stage will be added. If the saturated condensing temperature falls below the efficiency check point setting, fan control remains at the present operating stage. If the fan stage cycles four times within a 10 minute period, the lower limit tempera- ture is redefined as being equal to the lower limit minus the temporary low limit suppression setting.The unit will utilize this new low limit temperature for one hour to reduce condenser fan short cycling.

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