Sterling 30RA010-055 manual Typical Space Temperature Sensor Wiring

SPT (T10) PART NO. 33ZCT55SPT
	SENSOR
SEN	TB5
	SEN
	5
	6

Fig. 9 — Typical Space Temperature

Sensor Wiring

		T-55 SPACE
		SENSOR
		6
	SCN+	5
TO SCN	SCN GND	4
COMM 1
BUS (PLUG)		3
AT UNIT
	SCN-	2
		1

Fig. 10 — SCN Communications Bus Wiring to Optional Space Sensor RJ11 Connector

Energy Management Module (Fig. 11) — This factory-installed option (FIOP) or field-installed accessory is used for the following types of temperature reset, demand limit, and/or ice features:

•4 to 20 mA leaving fluid temperature reset (requires field-supplied 4 to 20 mA generator)

•4 to 20 mA cooling set point reset (requires field- supplied 4 to 20 mA generator)

•Discrete inputs for 2-step demand limit (requires field- supplied dry contacts capable of handling a 24 vac, 50 mA load)

•4 to 20 mA demand limit (requires field-supplied 4 to 20 mA generator)

•Discrete input for Ice Done switch (requires field- supplied dry contacts capable of handling a 24 vac, 50 mA load)

See Demand Limit and Temperature Reset sections on pages 44 and 43 for further details.

Care should be taken when interfacing with other manufac- turer’s control systems due to possible power supply differences, full wave bridge versus half wave rectification. The two different power supplies cannot be mixed. ComfortLink™ controls use half wave rectification. A signal isolation device should be utilized if a full wave bridge signal generating device is used.

Loss-of-Cooler Flow Protection — A proof-of-cooler flow device is factory installed in all chillers. It is recommended that proper operation of the switch be verified on a regular basis.

Thermostatic Expansion Valves (TXV) — All units are equipped from the factory with conventional TXVs. Each

refrigeration circuit is also supplied with a factory-installed liquid line filter drier and sight glass.

The TXV is set at the factory to maintain approximately 8 to 12° F (4.4 to 6.7° C) suction superheat leaving the cooler by metering the proper amount of refrigerant into the cooler. All TXVs are adjustable, but should not be adjusted unless absolutely necessary.

The TXV is designed to limit the cooler saturated suction temperature to 55 F (12.8 C). This makes it possible for unit to start at high cooler fluid temperatures without overloading the compressor.

Capacity Control — The control system cycles com- pressors, and minimum load valve solenoids (if equipped) to maintain the user-configured leaving chilled fluid temperature set point. Entering fluid temperature is used by the Main Base Board (MBB) to determine the temperature drop across the cooler and is used in determining the optimum time to add or subtract capacity stages. The chilled fluid temperature set point can be automatically reset by the return fluid temperature, space, or outdoor-air temperature reset features. It can also be reset from an external 4 to 20-mA signal (requires Energy Management Module FIOP or accessory).

The control has an automatic lead-lag feature built in which determines the wear factor (combination of starts and run hours) for each compressor. If all compressors are off and less than 30 minutes has elapsed since the last compressor was turned off, the wear factor is used to determine which compres- sor to start next. If no compressors have been running for more than 30 minutes and the leaving fluid temperature is greater than the saturated condensing temperature, the wear factor is still used to determine which compressor to start next. If the leaving fluid temperature is less than the saturated condensing temperature, then the control will start either compressor A1 or compressor B1 first, depending on the user-configurable circuit lead-lag value.

The TXVs will provide a controlled start-up. During start- up, the low pressure logic will be bypassed for 21/2 minutes to allow for the transient changes during start-up. As additional stages of compression are required, the processor control will add them. See Table 6 and 7.

If a circuit is to be stopped, the compressor with the lowest wear factor will be shut off first in most cases. Certain override conditions may shut off the smaller of two compressors on a circuit first.

The capacity control algorithm runs every 30 seconds. The algorithm attempts to maintain the Control Point at the desired set point. Each time it runs, the control reads the entering and leaving fluid temperatures. The control determines the rate at which conditions are changing and calculates 2 variables based on these conditions. Next, a capacity ratio is calculated using the 2 variables to determine whether or not to make any changes to the current stages of capacity. This ratio value ranges from –100 to +100%. If the next stage of capacity is a compressor, the control starts (stops) a compressor when the ratio reaches +100% (–100%). If installed, the minimum load valve solenoid will be energized with the first stage of capacity. Minimum load valve value is a fixed 30% in the total capacity calculation. The control will also use the minimum load valve solenoid as the last stage of capacity before turning off the last compressor. If the close control feature (CLS.C) [Configura- tion, OPT2] is enabled the control will use the minimum load valve solenoid whenever possible to fine tune leaving fluid temperature control. A delay of 90 seconds occurs after each capacity step change. Refer to Tables 6 and 7.

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