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I.
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 (CRSTl)
-
allowable range
0”
to 20” F (0” to
1
I”
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 mA 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 mA 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
mA
depending on which method was selected at the field
configuration step.
IO
9
18
8
16
7
Example 5
-
Using Return Water
Temperature Reset
KEYPAD DISPLAY
ENTRY
RESPONSE
FLD CFG
CSPTYP X
CRTYP 0
CRTYP 1
SET POINT
CPSl 44.0
CPSl 45 6
RESET
CRST2 0 0
CRST2 10 0
CREF2 0.0
CREF2 1.0
CRSTI
0 0
CRSTI 2.0
CREFl 0.0
CREFl 8 0
COMMENTS
Field configuration
subfunction of
service function
Scroll past single/dual
Display shows no reset
type has been selected
Return water temperature
is selected and activated
System set points
Present occupied chilled
water set point
Enter new chilled water
set point
Reset set points
F;li;g
maximum reset
0
Cooling maximum reset
is 10 F
Cooling maximum reset
reference is 0” F
Cooling maximum reset
reference is 1 F
Cooling minimum reset
is
0”
F
Cooling minimum reset
is 2 F
Cooling minimum reset
reference is 0” F
Cooling minimum reset
reference is
8
F
f73c=)
-- /
35.3
MIN RESET REFERENCE (CREF
I
)
q 13
100
80
60
0
2 3 4 5 6 7 8 9
IO
RESET REFERENCE TEMPERATURE (COOLER EWT-LWT)
Fig.
4
-
Cooling Return Water Reset
40