Cascade control with comfort zone

This macro provides supply air temperature control with room temperature reset and room temperature comfort zone, using both room temperature and supply air temperature sensors.

The P-controller for the room temperature control sequences the output signals of the energy recovery equipment within the comfort zone.

Outside the comfort zone, setpoint adjustments will be provided for the supply air temperature and fan speed.

The supply air temperature will be controlled with two PI-controllers.

Fan speed can be controlled, based on the room temperature deviation or CO2 (air quality) override.


Cascade control of supply air temperature

This macro provides supply air temperature control with room/ return temperature reset and comfort zone. For this function, it is absolute necessary to have a temperature sensor connected to the input RoomRetAirTemp of the macro.

The room temperature setpoint can be reset by the FilteredOATemp because of the summer compensation and/or the ContrPtAdj value.

The supply air temperature setpoint and fan speed is shifted by the room temperature deviation.


The application uses one P-controller for the room temperature, to reset the setpoints for the two supply air temperature PI-controllers (heating and cooling) in order to sequence the supply air temperature and the fan speed, with respect of the comfort zone between, which is defined by parameter RMT-05. With parameter RMT-03 the respective end-points of the supply air temperature setpoint-shifting for heating and cooling can be adjusted.

The P-band for the room temperature P-controller is defined by parameter RMT-01.


Description

Default value

RMT-01: room temperature control P-band

4 K

RMT-02: room temperature control I-time

0 sec

RMT-03: span for SAT-setpoint shift

60 %

RMT-05: room temperature comfort zone

2 K


Next figure shows the comfort zone around the compensated room temperature setpoint and the way the room temperature deviation affects the supply air temperature setpoints.



The P-band and I-time adjustments for both supply air temperature controllers are respectively defined by parameters SAT-03 and SAT-04. Each controller uses ½ RMT-01 as P-band.

The supply air temperature setpoint is always limited by the low and high temperature values as defined by the parameters SAT-01 and SAT-02.


Description

Default value

SAT-01: supply air temperature low setpoint

14 °C

SAT-02: supply air temperature high setpoint

35 °C

SAT-03: supply air temp. control P-band

200 K

SAT-04: supply air temp. control I-time

50 sec


Winter compensation of supply air temperature setpoint

To eliminate increased building transmission losses and from the comfort point of view (during the winter period), a higher supply air temperature is desired. With decreasing outside temperatures, the supply air temperature setpoint is reset as defined by parameters WCS-01 and WCS-02.

The winter compensation raise is defined by parameter WCS-03, shifting the supply air temperature setpoint between the respective minimum and maximum limit setpoints SAT-01 and SAT-02 upwards.


Note: If parameter WCS-03 is set to “0”, there will be no winter compensation.



Description

Default value

WCS-01: start point OAT winter comp. SAT

-10 °C

WCS-02: end  point OAT winter comp. SAT

10 °C

WCS-03: supply air temperature setpoint  raise

4 K


Comfort zone

In case of cascaded control with comfort zone and unoccupied periods (PlantMode equals 0, 1, 2 or 3), the OptimEnable output will be transmit the following values to the plant strategy:


Note: The OptimEnable will be connected to the plant strategy module, which will recognise this code and prevent undesired optimum start activities for heating during the cooling season, or undesired optimum start activities for cooling during the heating season.


Next figure explains the procedure during the unoccupied periods



Description

Default value

RMT-05: room temperature comfort zone

2 K


Minimum supply air temperature control

The minimum supply air temperature controller uses the supply air temperature sequencer, defined by the parameters SAT-05...SAT-12. The output signals of the sequencer are used to override the heating, energy recovery and cooling control signals.

When the supply air temperature falls below the minimum supply air temperature setpoint, defined by CalcDischAirTmpSP_Low, then the cooling coil will be closed first, energy recovery control signal will be raised, dampers will be closed and finally the heating coil will be opened. This prevents the opening of the heating coil, while the dampers are still open.  Next figure, showing the minimum supply air temperature override sequencer.



Note: The end-point parameters must always have a higher value then the start- point parameters. If both start- and end-point parameters are set to “0”, then that particular sequence function will be inactive.


Maximum supply air temperature control

The maximum supply air temperature controller uses the supply air temperature sequencer, defined by the parameters SAT-05...SAT-12. The output signals of the sequencer are used to override the heating, energy recovery and cooling control signal.  

When the supply air temperature becomes above the maximum supply air temperature setpoint, defined by CalcDischAirTmpSP_High, then the heating coil will be closed first, energy recovery will be closed and finally the cooling coil will be opened. This prevents the opening of the cooling coil, while the dampers are not fully open. Next figure, showing the maximum supply air temperature override sequencer.



Note: The end-point parameters must always have a higher value then the start- point parameters. If both start- and end-point parameters are set to “0”, then that particular sequence function will be inactive.


Description

Default value

SAT-05: sequence start point heating valve

0 %

SAT-06: sequence end point heating valve

50 %

SAT-09: sequence start point energy recovery

50 %

SAT-10: sequence end point energy recovery

75 %

SAT-11: sequence start point cooling valve

75 %

SAT-12: sequence end point cooling valve

100 %