Carrier 040-420 - Manual (Page 40)

Maximum Reset Amount (CRST2) allowable range
0” to 20” F (0” to 11” C). This is maximum amount leav-
ing chilled water
set point is to be increased.
2. Maximum Reset Reference (CREF2) allowable range
0” to 20” F (0” to 11” C). This is the cooler temperature
drop at which reset reaches its maximum value.
3. Minimum Reset Amount allowable range
to F (0” to C). This is minimum amount leav-
ing chilled water set point is to be increased when reset
is initiated.
4. Minimum Reset Reference (CREFl) allowable range
0” to 20” F (0” to 11” C). This is the cooler temperature
drop at which reset is at its minimum value. (Reset be-
gins here
NOTE: Reset set points are not accessible unless the reset
function is enabled first. This is done as a field configura-
tion. Select one of the 3 choices for type of reset: Return
Fluid Reset, External Temperature Reset, or 4-20
Ex-
ternal Signal (with a loop isolator) Reset.
If dual set point control is enabled (see Field Wiring sec-
tion on page 7 1), the amount of reset is applied to which-
ever set point is in effect at the time.
Example 5 demonstrates how to activate reset. Example
6 demonstrates how to change the type of reset. Assume
that reset is to be based on return water temperature, the
desired reset range is to be 2” to 10” F (1” to 5.5” C) and
full load is a 10” F (5.5” C) drop across the cooler. See
Fig. 4.
Activating reset based on external temperature or
4-20 signal is done the same way, except the reference
set point range is 20” to 125” F (-6.6” to 5 1.6” C), or 4 to
20
depending on which method was selected at the field
configuration step.
9
8
7
Example 5 Using Return Water
Temperature Reset
KEYPAD DISPLAY
ENTRY RESPONSE
FLD CFG
C S P T Y P X
CRTYP 0
C R T Y P 1
S E T P O I N T
44.0
45 6
R E S E T
C R S T 2 0 0
C R S T 2 1 0 0
CREF2 0.0
CREF2 1.0
0 0
2.0
CREFl 0.0
8 0
COMMENTS
F i e l d c o n f i g u r a t i o n
subfunction of
s e r v i c e f u n c t i o n
S c r o l l p a s t s i n g l e / d u a l
Display shows no reset
type has been selected
Return water temperature
is selected and activated
System set points
P r e s e n t o c c u p i e d c h i l l e d
water set point
Enter new chilled water
set point
Reset set points
maximum reset
Cooling maximum reset
is 10 F
Cooling maximum reset
reference is 0” F
Cooling maximum reset
reference is 1 F
Cooling minimum reset
is
F
Cooling minimum reset
is 2 F
Cooling minimum reset
reference is 0” F
Cooling minimum reset
reference is F
I q 13
8 0
6 0
0
2 3 4 5 6 7 8 9
RESET REFERENCE TEMPERATURE (COOLER EWT-LWT)
Fig. 4 Cooling Return W a t e r Reset
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