Temperature

The temperature control is an optional part of the Pressure Control application algorithm. Reaching and maintaining the temperature setpoint is achieved by adjusting the reheater and/or perimeter based on the current space temperature measurements and occupancy status.

The application’s algorithm includes a number of variables referring to the temperature:

• temperature setpoints,

• temperature setpoint’s offset,

• space temperature,

• discharge temperature.

Space Temperature

To enable the temperature control in the Pressure Control example application, it is required to select the temperature measurements source. The available options are:

• Control Point VAV panel,

• dedicated universal input, U2 (connected sensor),

• network.

Automatic Detection

Additionally, the Pressure Control application has a mechanism to provide an automatic temperature detection in case the selected temperature source does not provide any value. First, the application checks for the Control Point VAV panel availability. If the value cannot be read from the panel, the algorithm checks the dedicated U2 input and if no sensor is connected, it proceeds to check the value from the network. In case all these steps fail to provide the measured temperature, the algorithm uses the calculated effective heating setpoint value, which forces the application to work in minimal ranges.

Discharge Air Temperature

Discharge air temperature sensor is measured temperature in the duct after a reheater: acting as regulation and high limit for discharge air temperature, the reheater is indirectly controlled by the space temperature and directly by the discharge air temperature with high limit the reheater when the discharge air temperature is too hot.

The universal input U1 is dedicated for the sensor of the discharge air temperature.

Automatic Detection

Similarly, as in case of the space temperature, the application has a mechanism providing an automatic discharge temperature detection in case the sensor is not available or its value cannot be read from it. In such an event, the algorithm takes the MinDischTempSetpoint component’s value to calculations (located in the TemperatureSetpointSelector folder of the Pressure Control example application).

Temperature Setpoint

Temperature setpoint is a fundamental for an optional heating setting in Pressure Control example application’s algorithm. It determines the temperature setpoint calculations depending on the area’s occupancy status. The algorithm will work to achieve the temperature setpoint according to the set HVAC mode.

Heating Setpoint

The heating setpoint is used for heating control with high limit in systems with the reheater.

For heating control with electrical reheater, information on the discharge air temperature from the discharge air temperature sensor connected to the U1 input or from the network is required. Generally, in systems with the reheater, if there is no discharge air temperature measurement, heating is based on the space temperature control loop. In systems with the discharge air temperature measurement, heating is based on the discharge air temperature control loop.

In systems with the perimeter, the discharge air temperature sensor is not necessary because heating is based on the space temperature control loop only.

The application starts heating if the space temperature falls below the actual heating setpoint temperature for the corresponding occupied state.

Effective Setpoint

The actual heating temperature setpoint for the occupied mode are further adjusted by:

• offset: the value is added or subtracted from the occupancy setpoint;

• panel-derived setpoint temperature depending on the setting (offset or setpoint) of the PanelSetpointMode variable (TemperatureSetpointSelector folder of the Pressure Control example application):

  • offset: added or subtracted from the occupancy setpoint,

  • setpoint: the setpoint set on the Control Point VAV panel is corrected by half the difference between the default cooling occupancy setpoint (not used) in component and OccHeatTempSetpoint values, added or subtracted from the panel’s setpoint providing setpoint for heating.

This selection, impacting the effective setpoint temperature, is made with the HVAC Mode slot (set in the HeatLoop folder):

• Auto: effective setpoint equals the heating setpoint depending on the occupancy mode:

  • occupied: effective setpoint equals the OccHeatTempSetpoint value,

  • bypass: effective setpoint equals the OccHeatTempSetpoint value,

  • standby: effective setpoint equals the StandbyHeatTempSetpoint value,

  • unoccupied: effective setpoint equals the UnoccHeatTempSetpoint value;

• Heat: effective setpoint equals the heating setpoint depending on the occupancy mode:

  • occupied: effective setpoint equals the OccHeatTempSetpoint value,

  • bypass: effective setpoint equals the OccHeatTempSetpoint value,

  • standby: effective setpoint equals the StandbyHeatTempSetpoint value,

  • unoccupied: effective setpoint equals the UnoccHeatTempSetpoint value;

• Cool: the heating control loop is disabled;

• MorningWarmUp: effective setpoint equals the heating setpoint depending on the occupancy mode:

  • occupied: effective setpoint equals the OccHeatTempSetpoint value,

  • bypass: effective setpoint equals the OccHeatTempSetpoint value,

  • standby: effective setpoint equals the StandbyHeatTempSetpoint value,

  • unoccupied: effective setpoint equals the UnoccHeatTempSetpoint value;

• PreCool: the heating control loop is disabled;

• NightPurge: the heating control loop is disabled;

• Fire: the heating control loop is disabled;

• Off: the heating control loop is disabled.

Discharge Air Temperature Setpoint

The discharge air temperature setpoint is obtained by a linear function from the current value of the effective heating setpoint temperature to the effective heating setpoint increased by a value of 15 degrees with a low limit MinDischTempSetpoint and high limit MaxDischSetpoint. The value is calculated based on the output value from the heating control loop. The x value is based on the heating demand and depending on whether the DualHeat options is turned on (50-100% default for a secondary source or 0-50% for primary source) or turned off (0-100%).

Temperature Setpoint Offset

The offset value for the temperature setpoint can be set from the Control Point VAV panel or using a resistance adjuster like SP connected to the U3 input. It is possible to select a leading offset source in the Input Selector variable (SetpointOffsetSelector in the OffsetCalculator folder of the Pressure Control example application).

From the Control Point VAV panel and iSMA Configurator, the user has the option to change the range in the SetpointOffsetRange variable for a resistance adjuster connected to the U3 input, which by default is set to 3°C (from -3 to +3) or 5°F (from -5 to +5). Changing the variable also triggers a change in the offset setpoint range in the Control Point VAV panel.

Temperature Control Loop

The temperature control loop in the Pressure Control example application determines the demand for heating only based on the space temperature measurement and the corresponding actual heating temperature setpoint.

Space Temperature Control Loop

The space temperature control loop for heating is based on the space temperature sensor measurements (Control Point VAV panel or connected to the U2 input). It operates according to the HVAC Mode settings (HeatLoop folder):

• Auto: the heating control loop is always active,

• Heat: the heating control loop is always active,

• Cool: the heating control loops is disabled,

• MorningWarmUp: the heating control loop is always active,

• PreCool: the heating control loop is disabled,

• NightPurge: the heating control loop is disabled,

• Fire: the heating control loop is disabled,

• Off: the heating control loop is disabled.

Space temperature control loop settings are only available from iC Tool and must be adjusted to the current room:

• Kp: default 20.0,

• Ki: default 0.33,

• Kd: default 0.0.

Discharge Air Temperature Control Loop

The discharge air temperature control loop for heating and cooling is active when there is the discharge air temperature sensor connected to the U1 input or there is the discharge air temperature value available from the network. It operates according to the HVAC mode set in the HVAC Mode settings (HeatLoop folder):

• Auto: the heating control loop is always active,

• Heat: the heating control loop is always active,

• Cool: the heating control loop is disabled,

• MorningWarmUp: the heating control loop is always active,

• PreCool: the heating control loop is disabled,

• NightPurge: the heating control loop is disabled,

• Fire: the heating control loop is disabled,

• Off: the heating control loop is disabled.

Discharge air temperature control loop settings are only available from iC Tool and must be adjusted to the current room:

• Kp: default 10.0,

• Ki: default 0.33,

• Kd: default 0.0.