Control points#

Control points are used to control processes with P/PI/PID-controller. Control points ideology is always “heating”. Cooling stage is done by reversing the max and min values of stage. e.g Min value = 100, Max value = 0.

Point info#

  • Pointname: Unique name for the point inside the FX-controller. Any other point cannot have the same name.

  • Description: Used to describe the point.

Point levels#

Point levels are part of user rights management. Value is minimum user level to be view, set or program the point. If user level is under the value, they are not able to see, set or edit the point.

Main controls#

  • Main measurement: Pointname of measurement used as input for PID-controller.

  • Outdoor measurement: Select a outdoor temperature measurement. This is used for outdoor temperature limiting function.

Basic settings#

  • Indication point: Indication point that decides if controller is on or off. Indication points value 1 or bigger sets controller on and value 0 sets controller off.

  • Unit: Letter or symbol displayed after the value of this point.

  • Decimal: Number of decimals displayed on value of this point.

  • Statetext: Select state text group for displaying point state in text mode states instead of numbers.

  • Picture: Select a process picture that will be opened when clicking graphics symbol on point settings of this point.

  • Control mode: Either PI or PID. Note! P-controller can be used by selecting control mode PI and giving value 0 to integration time parameter.

  • Slow speed factor: While indication point has value 1 the controller is at “slow” state and at value 2 the controller is at “fast” state. The P-band of controller is multiplied by the slow speed factor when controller is at “slow” state. Use case of this is to control 2 speed AHU’s, where the temperature control differs at the different speeds.

  • Integration time: Integration time. Increasing integration time will slow down the controlling of the process and vice versa.

  • I term sensitivity: Disables effect of I term if difference between setpoint and measurement is smaller that this value.

  • Cooling deadzone: Creates setpoint for cooling which is calculated by Setpoint + Cooling deadzone value.

  • Execution interval (sec): Defines how often control point is executed. Value 0 = ‘do as often as possible’.

Balance point

Balance point of P control and starting point of controller when point state is changed to ON. Select the stage and value for this function. Value is the percentage value of the selected stage.

Control stages#

  • Stage count: amount of stages in use 1-6.

Stage1…6

  • Name: Name for stage.

  • Stage P-band: P-band for stage, increasing the P-band will slow down the controlling of the process.

  • Type: Type of stage. None, Cooling, Recovery and Heating.

  • Min output: Minimum output value of the stage. Output of the stage is limited between Min output and Max output.

  • Max output: Maximum output value of the stage.

  • Off state: Define fixed value for stage when control point is in Off state. This value is not limited to Min and Max values of the output.

  • AO-point: If defined, the value of the point is set according to output of the stage. If the process is more complicated, you can leave this empty and read the stage output value in code.

Outdoor temperature

With outdoor temperature it is possible to control the selected stage with P-controller.

  • Temperature limit: When outdoor temperature is below this value, the functionality starts working.

  • P-Band: Define the temperature range of the functions control steps.

Example:

Temperature limit is -5°C and the P-Band is 10°C. Start point is the temperature limit -5°C and the end point is calculated by this equation: Temperature limit – P Band. Which is -5°C - 10°C = -15°C. Functionality works between temperatures: -5°C -> -15°C.

Output of the stage is linear, below is table that shows few example values.

Title#

Temperature measurement

Output of the stage

-5°C

0%

-7°C

20%

-10°C

50%

-15°C

100%

Limit measurement

You can select a limiting measurement for each stage. Limiting function is a P-controller and it’s setpoint is the stages limit value.

  • Limit measurement: Select a measurement point for this functionality.

  • Limit value: Limiting functions starts working when limit measurement is at this value.

  • P-Band: Define the temperature range of the functions control steps. Value can be positive or negative. In case negative P-Band, maximum value of stage is limited. Example usage is to prevent return temperature of glycol heat recovery to drop too cold.

Example:

Heating battery stage has temperature after battery as limiting sensor, temperature limit is 12°C and the P-Band is 6°C means that the functionality works between outdoor temperature of 12°C -> 6°C.

At temperature value of 10°C all stages below heating stage (Cooling, heat recovery) will be forced to max heating state and minimum value of heating battery will be 33%. If temperature drops to 8°C the heating battery stage will be at 67%.

AHU heating#

  • Stage value: Select the stage number you want to put as return water stage.

OFF state

When control point is in Off state, this function controls temperature of return water of heating battery. This is P type controller.

  • Set value: Set value of controller during its off state.

  • P-Band: Define the temperature range of the functions control steps.

On state

This is P type controller for freeze protection at On state. If temperature of return water of heating battery drops below ‘limit value’ value of return water stage of main control and value of this controller are compared and higher one is set to stage value.

  • Set value: Set value of controller during its on state.

  • P-Band: Define the temperature range of the functions control steps.

  • Return water measurement: Measurement point for the functionality.

Control type#

Constant set value

  • Default value: Default setpoint value for controller.

  • Copy manual set value to default: If point value gets manually set to different than “Default value” then it can be copied as new default value with this setting.

Cascade control

  • Control point: Select a control point that gives the setpoint to this controller.

  • Stage: Select the stage of the control point that gives the setpoint to this controller.

Compensation control

Controller type compensation control reads measurement as input and adjust the setpoint of controller based on the lookup table.

  • Lookup table: Lookup table used to adjust the setpoint of controller based on measurement.

  • Compensation AI: The measurement point used as input for lookuptable.

Control point operating mode

Cooling / heating control has four possible operating modes.

Night mode

When point is in OFF state. (indication OFF)

  • If return water stage is defined it is controlled.

  • Set value is return water set value.

  • Measurement is return water measurement.

Energy saving

When main input is between set values and heating and cooling are OFF

  • Set value is average of heating and cooling set values.

  • Only heat recovery stage is controlled

Heating

Only heating stages are controlled, others are in maximum heating position

Cooling

Only cooling stages are controlled, others are in minimum heating position

Note

When dead zone of room control point is zero then operating mode is always “Heating”.