Sterling 30RA010-055 manual Operation Sequence, Temperature Limits for, Standard 30RA Units

Table 41 — Temperature Limits for

Standard 30RA Units

UNIT SIZE 30RA	010-030		032-055
Temperature	F	C	F	C
Maximum Ambient	120	49	120	49
Temperature
Minimum Ambient	45	7	32	0

2.Determine maximum deviation from average voltage:

(AB) 243 – 239 = 4 v (BC) 239 – 236 = 3 v (AC) 239 – 238 = 1 v

Maximum deviation is 4 v.

3.Determine percent voltage imbalance:

Temperature
Maximum Cooler EWT*	95	35	95	35

% Voltage Imbalance = 100 x

4

Maximum Cooler LWT	70	21	70	21
Minimum Cooler LWT†	40	4.4	40	4.4

LEGEND

EWT — Entering Fluid (Water) Temperature

LWT — Leaving Fluid (Water) Temperature

*For sustained operation, EWT should not exceed 85 F (29.4 C).

†Unit requires modification below this temperature.

LOW-AMBIENT OPERATION — If operating temperatures below 45 F (7 C) for sizes 010-030 or below 32 F (0° C) for sizes 032-055 are expected, accessory Motormaster® V con- trol must be installed. Refer to separate installation instructions for operation using this accessory. Contact your Sterling repre- sentative for details.

Brine duty application (below 40 F [4.4 C] LCWT) for chiller normally requires factory modification. Contact your Sterling representative for applicable LCWT range for standard water-cooled chiller in a specific application.

VOLTAGE — ALL UNITS

Main Power Supply — Minimum and maximum acceptable supply voltages are listed in the Installation Instructions.

Unbalanced 3-Phase Supply Voltage — Never operate a motor where a phase imbalance between phases is greater than 2%. To determine percent voltage imbalance:

	max voltage deviation
% Voltage Imbalance = 100 x	from avg voltage
	average voltage

The maximum voltage deviation is the largest difference between a voltage measurement across 2 legs and the average across all 3 legs.

Example: Supply voltage is 240-3-60. AB = 243 v

BC = 236 v AC = 238 v

1. Determine average voltage:

243 + 236 + 238

Average voltage =

3

=7173

=239

239

= 1.7%

This voltage imbalance is satisfactory as it is below the maximum allowable of 2%.

IMPORTANT: If the supply voltage phase imbalance is more than 2%, contact your local electric utility company immediately. Do not operate unit until imbalance condition is corrected.

Control Circuit Power — Power for the control circuit is supplied from the main incoming power through a factory- installed control power transformer (TRAN1) for all models. Field wiring connections are made to either terminal block TB5 or TB6.

OPERATION SEQUENCE

During unit off cycle, the control monitors the outdoor air temperature. If the ambient temperature drops below 40 F (4.4 C), cooler and hydronic system heaters (if either are facto- ry installed) are energized. If power is maintained to the chiller and the EMERGENCY ON/OFF switch is left in the OFF po- sition, these heaters are also energized.

The unit is started by putting the ENABLE/OFF/REMOTE CONTACT switch in the ENABLE or REMOTE CONTACT position. When the unit receives a call for cooling (either from the internal control or SCN network command or remote con- tact closure), the unit stages up in capacity to maintain the leav- ing fluid set point. The first compressor starts 11/2 to 3 minutes after the call for cooling.

The lead circuit can be specifically designated on all models or selected based on compressor run hours and starts depend- ing on field configuration. The unit control will override this selection under certain starting conditions to properly maintain oil return to the compressors. In general, on dual compressor circuits, the control will most often start the A1 or B1 compres- sor first, especially after long off periods. The MBB controls fan stages to maintain the head pressure set point and will auto- matically adjust unit capacity as required to keep compressors from operating outside of the specified envelope. There are no pumpout or pumpdown sequences on these chillers.

For all units, if temperature reset is being used, the unit con- trols to a higher leaving-fluid temperature as the building load reduces. If demand limit is used, the unit may temporarily be unable to maintain the desired leaving-fluid temperature be- cause of imposed power limitations. Loading sequence for compressors is shown in Tables 6 and 7.

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