Functional Control ESIE10-01
2–30 Part 2 – Functional Description
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2.2.6 Evaporator Pump Control
For control of the evaporator pumps, three evaporator pump control states are possible:
■ Off – No pump on.
■ Start – Pump is on, water loop is being recirculated.
■ Run – Pump is on, water loop has been recirculated.
The control state is Off when all of the following are true:
■ Unit state is Off.
■ LWT is less than the Evap Freeze set point or LWT sensor fault is active.
■ EWT is less than the Evap Freeze set point or EWT sensor fault is active.
The control state is Start when any of the following are true:
■ The unit state is auto.
■ LWT is higher than the Evap Freeze set point plus 0.6°C and LWT sensor fault isn’t active.
■ EWT is higher than the Evap Freeze set point plus 0.6°C and EWT sensor fault isn’t active.
The control state should be Run when the flow switch input has been closed for a time greater than
the Evaporator Recirculate time.
Pump selection The pump output used will be determined by the Evap Pump Control set point. This setting allows the
following configurations:
■ #1 only – Pump 1 will always be used.
■ #2 only – Pump 2 will always be used.
■ Auto – The primary pump is the one with the least run hours, the other is used as a backup.
■ #1 Primary – Pump 1 is used normally, with pump 2 as a backup.
■ #2 Primary – Pump 2 is used normally, with pump 1 as a backup.
■ Primary/Standby Pump Staging
The pump designated as primary will start first. If the evaporator state is start for a time greater
than the recirculate timeout timer and there is no flow, then the primary pump will shut off and the
standby pump will start. When the evaporator is in the run state, if flow is lost for more than half of
the flow proof set point value, the primary pump will shut off and the standby pump will start. Once
the standby pump is started, the flow loss alarm logic will apply if flow cannot be established in the
evaporator start state, or if flow is lost in the evaporator run state.
■ Auto Control
If auto pump control is selected, the primary/standby logic above is still used. When the evapora-
tor is not in the run state, the run hours of the pumps will be compared. The pump with the least
hours will be designated as the primary at this time.
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