Carrier 040-420 Example 3 Using Test Function, Keypad Display Comments Entry Response

	Example 3 - Using Test Function
KEYPAD	DISPLAY	COMMENTS
ENTRY	I RESPONSE

C O M P Factory/field test of compressors subfunction of test function

CPA 1 OFF Circuit A, Compressor 1A test

CPA 1 ON Pressing ENTR starts the test:

when the compressor should be running the display shows CPA1 on

CPA 1 OFF If the test is allowed to time out (10 sec- onds) the display will show CPA1 off

cl+ CPA 2 OFF Pressing the down arrow key advances the system to Circuit A, compressor 2 test

	NOTE: Once a compressor has been run using the EST							function, it
	is not allowed to run again for 30 seconds.						E l
	HISTORY FUNCTION - Keystrokes mb] and sub-
	sequent [ keystrokes display total unit run time and total
	run time for each circuit.
.	Keystrokes		m m		and subsequent m		keystrokes		dis-
	play total unit		starts	and the total starts for each circuit.
	Keystrokes	Fi b[ and			subsequent	q	keystrokes		dis-

play the last 5 alarms along with a description of each alarm.

SET POINT FUNCTION - Set points are entered through the keypad. Set points can be changed within the upper and lower limits, which are fixed. The ranges are listed below.

Chilled Water Set Point

Water:

38 to 70 F (3.3 to 21 C)

Brine:

15 to 70 F (-9.4 to 21 C)

Pulldown Set Point

0.2 to 2.0 F (0.11 to 1.1 C)/min.

Reset Set Points

Maximum Reset Range:

0” to 20” F (0” to 11” C)

Maximum Reset Reference Range: Return Fluid Reset 0” to 20” F

(0” to 11” C)

External Temperature Reset 20 to 125 F (-6.6 to 51.6 C)

External Signal Reset 4 to 20 mA

Minimum Reset Reference Range: Return Fluid Reset 0” to 20” F

(0” to 11” C)

External Temperature Reset 20 to 125 F (-6.6 to 51.6 C)

External Signal Reset 4 to 20 mA

Demand Limit Set Points

Switch Input:

Step 1 - 0 to 100% Capacity Reduction Step 2 - 0 to 100% Capacity Reduction

External Signal:

Maximum Demand Limit 4 to 20 mA Minimum Demand Limit 4 to 20 mA

Set points are grouped in subfunctions as follows:

Displaysm Fl chiller water and cooling ramp set points.

a. The first value shown is the occupied chilled water set point.

b. The next value displayed depends on how the sched- ule function has been programmed. (See pages 45- 47.) If dual set point has been selected, the next set

point after m has been pressed is the unoccupied chilled water set point. If single set point or inactive schedule has been selected in the schedule function,

then when q	is pressed, the display shows the
modified chilled water set point.		q
c. The final value	displayed when the		is pressed

is the cooling ramp loading rate. This is the maxi- mum rate at which the leaving chilled water is al- lowed to drop, and can be field set from 0.2 to 2.0 F (. 11” to 1.1” C)/minute. This value is not displayed unless the function is enabled (see Adjustable Field Configurations on page 45).

Reading and Channinrr Set Points - Example 4 shows how to read and change the chilled water set point. Other set points can be changed by following the same procedure. Refer to Table 9 for the sequence of display of set points in each subfunction.

Example 4 - Reading and Changing

Chilled Water Set Point

KEYPAD	DISPLAY				COMMENTS
ENTRY	RESPONSE
	SET POINT		System set points
	CSPl	44.0	Present occupied chilled water
			set point is 44 0 F
	CSPI	420
			~~~~~~~h~!$w~cupied
			chilled water set point is 42 0 F
	CSP2	44.0	Present	unoccupied chilled				water
			set point is 44.0 F
	CSP2	50.0	Press the FiD iris F[p l				a	y
			shows new			chilled
					unoccupied
			water set point is 50.0 F
	RESET		Displays the maximum reset and
			minimum reset set points The
			minimum		and maximum		reference
			reset set points can also be
			displayed.
			These set points are not
			accessible when reset type has
			been configured for NONE in
			the service function

Temperature Reset Based on Return Water TemDerature - The control system is capable of providing leaving water temperature reset based on return water temperature. Be- cause the temperature difference between leaving water tem- perature and return water temperature is a measure of the building load, return water temperature reset is essentially an average building load reset method.

Under normal operation, the chiller maintairis a constant leaving water temperature approximately equal to chilled water set point. As building load drops from 100% down to O%, entering cooler water temperature drops in proportion to load. Thus, temperature drop across the cooler drops from a typical 10 F (5.5 C) at full load to a theoretical 0” F (0” C) at no load. See Fig. 4.

At partial load, leaving chilled water temperature may be lower than required. If this is allowed to increase (reset), the efficiency of the chiller increases. Amount of reset can be defined as a function of cooler temperature drop, as shown in Fig. 4. This is a simple linear function that requires 4 pieces of input data for the set function:

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