Sequences of Operations
Page 51 of 67
eZV-440 Version 2.1 Application Guide
Document Edition 2.5
Heating and Cooling
Heating load is present when the HeatCoolLoad (AV802) value is between 0 and 100.
The available heating stages in the algorithm are sequential and are as follows: Heat1, Heat2,
and Heat 3. The heating load is evenly divided by the number of heat stages that you’ve set up.
Also, when the duct heater is turned on but still can’t meet the heat demanded by the system,
an ECM fan can act as an extra and final heat stage by ramping up its fan speed from its
minimum setting to its maximum setting based on the heat load.
When AirFlowStatus (BV800) is off, all stages of duct heating are disabled.
Cooling load is present when the HeatCoolLoad (AV802) value is between 0 and -100.
“Box” mode in the algorithm detects if there is hot or cold air in the duct. As a result, Box mode
decides whether opening the damper acts as a heating stage or as a cooling stage. The
algorithm, unless manually commanded, controls box mode by monitoring the inlet air
temperature and comparing it to the current space temperature.
Box mode object (MV801) can be commanded to its manual states: CoolCmd_ or HeatCmd_.
The following table summarizes how damper heating or cooling stage is determined by Box
mode.
Space demand
Box Mode detects:
Damper stage
Heating demand
Hot air in the duct, or HeatCmd in
manual mode
Damper is the first stage of heat.
Heating demand
Cold air in the duct, or CoolCmd in
manual mode
If there is a duct heater and it is not
a series or parallel fan VAV box, the
damper is the last stage of heat.
Otherwise the damper will act as a
first stage of cooling.
Cooling demand
Hot air in the duct, or HeatCmd in
manual mode
Damper is the first stage of heat.
Cooling demand
Cold air in the duct, or CoolCmd in
manual mode
Damper is the first stage of cooling.
Note: If an inlet air temperature has not been configured, the default state for box mode is
AutoCool_.
If outdoor air temperature (AV9) rises above outdoor air temperature heating lockout setpoint
(OATHtgLockout), then all heating is disabled. The outdoor air temperature will have to drop by
1.0 °C below this setpoint before the heating is re-enabled.