30
OM
AGSB-5
Evaporator Pump State Control
The state-transition diagram shown below controls operation of the evaporator pump.
Figure 4, Evaporator Pump Control
One of two pumps can be automatically selected based on run hours. The run-hour counters
are not visible. When in Auto, the pump with the least hours will start. The options are # 1
only, #2 only, Auto.
The pump output used will be determined by the Evap Pump Control setpoint. This setting
allows the operator to select either pump #1 or pump #2. The selected output will be ON if
the Evap State is set to START or RUN. Both outputs will be OFF if the Evap State is set to
OFF.
Evaporator Heater Control
Evaporator heaters are controlled by the unit controller. This output is turned on when the
evaporator LWT is less than the water freeze se 2
degrees F. The output is turned off
when the LWT is more than the freeze se 4 degrees F.
Leaving Water Temperature (LWT) Reset
The Active Leaving Water setpoint is set to the current Leaving Water Temperature (LWT)
setpoint, unless the unit is in COOL mode, and any of the reset methods below are selected.
The type of reset in effect is determined by the LWT Reset Type setpoint. The Active
Leaving Water variable is sent to all circuits for capacity control after the applicable reset is
applied.
Reset Type – NONE
The Active Leaving Water setpoint is set equal to the current LWT setpoint.
Reset Type – RETURN
The return water temperature adjusts the Active Leaving Water setpoint. When the chiller
mode = COOL, the Active Leaving Water setpoint is reset using the following parameters:
1. Cool LWT setpoint
2. Max Reset Delta-T setpoint
3. Start Reset Delta-T setpoint
4. Evap
Delta-T
OFF
RUN
START
Flow OK for
Evap Recirc Time
[Unit State = AUTO
AND
NOT [OAT low AND LWT > 40 F
OR
LWT < Freeze sp – 1.0 F
[Unit State=OFF
AND
LWT > Freeze sp]
OR
[OAT low
AND
All Comp State=OFF
AND
LWT>70 F]
Power ON
[Unit State=OFF
AND
LWT > Freeze
sp]
OR
[OAT low
AND
All Comp State=OFF
AND
LWT>70 F]
Summary of Contents for AGS 206A
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