Carrier 30GX - Page 20

20
0
0
0
8
1
0.0
8 0.0
8
8 6.6
0.1
8 6.6
9 0.0
9 0.0
9
9 5.0
0.1
9 5.0
9 5.0
12 0.0
12 0.0
12
12 3.0
0.1
12 3.0
Let us assume that the 0-10 V d.c signal
comes from a calibrated outside temperature
probe (configuration accessible to Carrier
Service only) with the following
parameters:
• The probe delivers 0 volts at -20°C.
• The probe delivers 10 volts at 40°C.
Based on this information:
• The probe delivers 5.0 volts at 10°C.
• The probe delivers 6.6 volts at 20°C.
The active cooling setpoint reset curve is
then as follows:
Cooling setpoint voltage reset
MAXUMUM RESET VALUE
BUILDING LOAD
ZERO RESET VOLTAGE
MAXIMUM RESET VOLTAGE
RESE T VALUE
% BUILDING LOAD
VOLTAGE RESET REFERENVE VALUE
EQUIVALENT TEMPERATURE REFERENCE VALUE
OPERATION PRESS BLOCK 3 BLOCK 1 BLOCK 2
KEY LED DISPLAY DISPLAY
Hold down the MENU button until
the LED for SETPOINT lights.
Press or until block 1
displays item number 8; this item
shows the zero reset voltage in
cooling mode. The default value (0
volts) is displayed in block 2.
Press the button to authorise
modification of the value
associated with item 8. The
SETPOINT menu LED flashes
indicating that modification mode
is active and the value can be
modified.
Press the until the value 6.6 is
displayed in block 2. The
SETPOINT menu LED in block 3
keeps flashing.
Press the button again to
validate the change. The new value
for item 8 is 6.6 volts. The
SETPOINT menu LED stops
flashing, indicating that
modification mode no longer
applies.
Press until block 1 displays
item number 9; this item shows the
maximum reset voltage in cooling
mode. The default value (0 volts)
is displayed in block 2.
Press the button to authorise
modification of the value
associated with item 9. The
SETPOINT menu LED flashes
indicating that modification mode
is active and the value can be
modified.
Press until the value 5.0 is
displayed in block 2. The
SETPOINT menu LED in block 3
keeps flashing.
Press the button again to
validate the change. The new value
for item 9 is 5.0 volts. The SET-
POINT menu LED stops flashing,
indicating that modification mode
no longer applies.
Press until block 1 displays
item number 12; this item shows
the maximum reset value in
cooling mode. The default value
(0°C) is displayed in block 2.
Press the button to authorise
modification of the value associat-
ed with item 12. The SETPOINT
menu LED flashes indicat-ing that
modification mode is active and
the value can be modified.
Press until the value 3.0 is
displayed in block 2. The
SETPOINT menu LED in block 3
keeps flashing.
Press the button again to vali-
date the change. The new value for
item 12 is 3.0°C. The SETPOINT
menu LED stops flashing, indicat-
ing that modification mode no
longer applies.
Items 10-11-12 D T reset - Cooling mode reset values
Items 15-16-17 D T reset - Heating mode reset values
This function is only active if an reset
based on water returning to the
evaporator (cooling mode) or condenser
(heating mode) has been selected (see
section 4.2.10). In the following descrip-
tion, ‘ D T’ represents the temperature
difference between water entering and
leaving the evaporator in cooling mode
or the condenser in heating mode.
Since the difference between the leaving
water temperature and the return water
temperature is a measure of the building
load, a setpoint reset based on the return
water temperature is actually an reset
method based on the average building
load. As the building load falls from
100% to 0%, so the entering evaporator
water temperature falls in proportion to
the load. Thus a drop in temperature in
the evaporator which is in general 5.5°C
at full load would theoretic-ally become
0°C at zero load. In this event, the reset
parameters are generally configured to
deliver an reset with a negative slope:
• In cooling mode, the controller automa-
tically resets the chilled water setpoint
upwards in response to a drop in D T.
• In heating mode, the controller
automatically resets the chilled water
setpoint downwards in response to a
rise in D T.