Distech Controls ECB-VAVS - Airflow Control and Calibration

11ECB-VAVS Preloaded Applications
Airflow Control and Calibration
In this section, the sequence of operations related to a controller’s airflow control and calibration are
presented.
Airflow Control
There are six airflow configuration setpoint variables described in the following table:
Variable Description
MinFlowSP (AV26) Absolute minimum flow setpoint during occupied mode
MaxFlowCoolSP (AV27) Maximum flow setpoint during cooling mode
MinFlowHeatSP (AV28) Minimum flow setpoint when duct heater is active
MaxFlowHeatSP (AV29) Maximum flow setpoint during heating mode
MinFlowStbySP (AV30) Minimum flow setpoint during standby mode
MinFlowUnoccSP (AV31) Minimum flow setpoint during unoccupied mode
The actual flow setpoint, ActFlowSP (AV2), is calculated based on BoxType (MV20) and other control
variables described in the subsections below.
The system uses DuctInTemp (AV6) and the temperature setpoint average (ActCoolSP and ActHe-
atSP) to evaluate whether the inlet temperature is suitable for cooling or heating the space. If HVAC-
ModeStatus is in morning warm up, the air is by default considered suitable for heating the space.
Cooling Mode
When the air is suitable for cooling the space, ActFlowSP varies between MinFlowSP and MaxFlow-
CoolSP based on terminal load. Otherwise, when the air is too warm, ActFlowSP is by default equal to
MinFlowSP.
When OccupancyStatus is in unoccupied or standby mode, MinFlowSP is replaced by either Min-
FlowUnoccSP or MinFlowStbySP.
Heating Mode
When the air is suitable for heating the space, ActFlowSP varies between MinFlowSP and
MaxFlowHeatSP. Otherwise, when the air is too cold, ActFlowSP is by default equal to MinFlowSP.
Regardless, when duct heating is required, MinFlowSp is replaced by the highest value between Min-
FlowSP and MinFlowHeatSP.
When OccupancyStatus is in unoccupied or standby mode, MinFlowSP is replaced by either Min-
FlowUnoccSP or MinFlowStbySP.
When the VVTMode (BV12) option is selected, ActFlowSP is converted into a percentage, which con-
trols the damper without using a flow reading.
The dual maximum option, DualMaximum (BV19), is available for the ECB-VAVS model. When in
heating mode, ActFlowSP is controlled as follows (see Figure 1): The first 50 percent of the heating
load adjusts the DischAirSP (AV12) between 55°F and MaxDischAirSP (AV56). The second 50 per-
cent of the heating load adjusts the ActFlowSP between MinFlowHeatSP and MaxFlowHeatSP. Note
that the dual maximum option requires a discharge temperature sensor to be configured. This se-
quence of operation respects California Title-24.
DischAirSP
55°F
MaxDischAirSP
50%
Heating Load
100%0%
Discharge air setpoint is adjusted for first 50% of
heating load
ActFlowSP
MinFlowHeatSP
MaxFlowHeatSP
50%
Heating Load
100%0%
Actual flow setpoint is adjusted for remaining 50% of
heating load
Figure1: Heating Control with the Dual Maximum Option
Sequence of Operation