Rev 3.1 01/11/23 - 19 - Model 600 User Guide
4.5 Heating Mode
The Model 600 Controller has two setpoints for heating mode. Heating stage 1 will be enabled when
the controlling temperature is below the heating setpoint. If the temperature continues to lower to
where the controlling temperature is below the heat 2 threshold (heating spt – heat 2 delta) then heat
stage 2 will be enabled. Once a stage of heating is active, it must stay on until the controlling
temperature is greater than the heating setpoint + heat off delta.
The same minimum on and minimum off time delays apply for heating stages. These timers must elapse
before there can be a change of state on the output relays. For example, if heating stage 1 is off, it must
be off for the minimum delay time before it is turned on. Once it is turned on, it must continue to stay
in the on state for at least the minimum on time. The only exception is if there is an alarm condition that
requires the heating to be turned off such as a smoke alarm.
Also, note that the unit won’t ever “jump” a heating stage based on controlling temperature. As in, if
the unit is off and calculations would like the unit to be in heat2, the unit will first try heat1 for the
normal on time before moving to heat2.
4.6 Economizer Control
The unit supports two types of economization plus the option for no economizers. The options are
“Quest” which requires an Outside air sensor connected to the Model 600 and integrated. Integrated
will rely solely on the settings of the economizer controller inside the HVAC unit. When “Quest” mode is
selected, the HVAC economizers (enthalpy controller) should be set to max OSA value so that the Model
600 can operate properly in econ mode. In Quest mode, the controller will use the outside air
temperature reading and compare to setpoints that can automatically adjust based on successfully
cooling with outside air.
The outside air temperature Modbus point will have write capability to allow the ESB2 (remote
controller) to write a value to the point. This way a single Outside air sensor can be used and shared
amongst multiple controllers when Modbus is deployed. The Model 600 Controller will use the written
value for control unless a communications fault is detected. When a communications fault occurs, the
controller will default back to the defined controlling temperature sensor mode.
4.6.1 Quest Econ Mode
The Model 600 Controller will use Quest’s patented economizer control algorithm to maximize the
amount of time outside air can be used for cooling the facility and will automatically adjust based upon
changes to the facility or HVAC equipment. OSA temperature greater than L2 setting for the dwell delay
will disable economization. OSA temperature between L1 and L2 for the dwell delay will enable econ
mode in both the lead and lag unit at the same time when there is a call for econ stage 1 mode. The
reason for this is assuming both units are required to provide necessary airflow for cooling when the
outside air is at a higher value. OSA temperature below L1 for the dwell delay will allow the economizer
for the lead system to be active when in Econ stage 1 and then will bring on the lag unit in econ mode if
the inside temperature is above the econ setpoint plus the value in the stage 2 cooling delta. Floating of
OSA setpoints is only available with Quest Econ mode and a valid OSA sensor reading.
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