IOMM AGR AGR 055A through 100A 51
When Return Water Reset is chosen, a Fail Smart Logic option is also available. This option works
as follows. If the Leaving Water Sensor (AI-1) becomes unreliable, the controller switches from
Leaving Water control to Return Water control. Actual Return Water Setpoint equals Leaving Water
Setpoint (AI-4) plus an adjustable Leaving Water Setpoint Offset. This value takes into account the
temperature differential between Leaving and Return water temperatures, which is typically about
10
o
F. If both the Leaving and Return water sensors are unreliable, the compressor is forced to 0%.
Zone Temperature (optional Zone Temperature Sensor )
When selected, a Zone Temperature Sensor is connected to TB-7 terminals #134 and #135. Four
variables are used to setup the reset ramp that calculates the Actual Leaving Water Setpoint. These
are: Leaving Water Dial Setpoint (AI-4), Reset Band SP selected with the Zone Terminal, Zone
Temperature High Limit (ZTHL), and Zone Temperature Reset Band (ZTRB).
Figure 30, Zone Temperature Reset
LWRB
LWSP
ZTLL ZTHL
ZTRB
(ZTLL=ZTHL - ZTRB)
As the Zone Temperature increases above the Zone Temperature Low Limit (ZTLL), the controller
decreases the Actual Leaving Water Setpoint from its Leaving High Limit (Leaving Water Setpoint
plus Leaving Reset Band) to the Leaving Water Setpoint. When the Zone Temperature reaches the
ZTHL, the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the Zone
Temperature sensor is missing or unreliable, no reset occurs and the Actual Leaving Water Setpoint
equals the Leaving Water Setpoint. If the Leaving Water Sensor (AI-1) becomes unreliable, the
compressor command is forced to 0%.
The Zone Terminal is required to activate and change the reset values.
Remote Reset (2 to 10VDC input)
When selected, a 2 to 10 Vdc signal is connected to TB-7 terminals #134 and #135. This input can
be achieved by using a 4-20mA signal and conditioning it with a 500 ohm resistor. This input resets
the leaving water temperature to a higher value based on the reset input signal magnitude. At a 2
Vdc (4mA) chiller signal input, the controller uses the Setpoint Dial setting. At a 10 Vdc (20mA)
signal input, the controller adds the reset value to the Dial Setpoint for the controlling temperature.
Between 2 Vdc and 10 Vdc, a proportional value is added to the Dial Setpoint for the controlling
temperature. The leaving water temperature can be reset upwards an additional 15
o
F. The Zone
Terminal is required to change the reset values.
Demand Limit (0 to 10VDC input)
When selected, a 0 to 10 Vdc signal is connected to TB-7 terminals #134 and #135. This input
limits the cooling capacity (0 to 100%). At 0 Vdc signal input, the controller does not limit
compressor staging. At 10 Vdc signal input, the chiller would be off. Between 0 Vdc and 10 Vdc, a
proportional percentage capacity is available.
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