ExampleHeating (FB)¶

FUNCTION_BLOCK ExampleHeating

Example heating circuit

This example function block implements a simple outside temperature dependent water heating circuit to demonstrate how to:

implement a plant / an aggregate in CFC using CODESYS Building Automation library function blocks
SequenceControl can be used for one sequence as well
use DailyMeanTemperature to enable / disable heating circuit in “atomatic”-mode
use HeatingCharacteristicCurve to compute supply temperature setpoint

This example involves:

heating circuit operation enabled / disabled in “auto”-mode using DailyMeanTemperature or outdoor temperature
computation of supply temperature setpoint using HeatingCharacteristicCurve
night time setpoint reduction vs. switching off heating circuit operation
economy mode - switching off circulation pump and mixing valve if supply temperature to low to provide sufficient energy
optional anti-freeze

Watch out for comments in the implementation where those aspects are covered.

outdoor air temperature sensor
indoor air temperature sensor
supply temperature sensor
circulation pump
mixing valve

Heating circuit operation¶

Heating circuit operation could be enabled / disabled manually setting eOnOff accordingly. Heating circuit operation could be determined automatically setting eOnOff to Auto. In “auto”-mode the operation is enabled if either the daily mean temperature or the outdoor temperature (xUseOdaTemp = TRUE) is below rTempLimitEnable.

Night time setpoint reduction vs. switching off heating circuit operation¶

ExampleHeating allows to use either a reduced supply temperature setpoint (rSupplyTempSetpt) at night, or to switch off operation at all.

Economy mode¶

Economy mode is switching off circulation pump and mixing valve if rSupplyTempSetpt is to low to provide sufficient energy. It differentiates low / high temperature heating systems by HeatingCharacteristicCurve gradient. Gradient < 1.0 assumes a low temperature heating system (for example floor heating).

Gradient <= 1.0 - low temperature heating system:

rSupplyTempSetpt < rIdaTempSetpt => switch off rSupplyTempSetpt > rIdaTempSetpt + 2.0K => switch on

Gradient > 1.0 - high temperature heating system:

rSupplyTempSetpt < rIdaTempSetpt + 5.0K => switch off rSupplyTempSetpt > rIdaTempSetpt + 7.0K => switch on

Optional anti-freeze¶

If anti-freeze is activated, there are three separate measures activated:

low outdoor temperature (rOdaTemp < rAntiFreezeOdaTempLimit) cause the circulation pump to be enabled
low supply temperature (rSupplyTemp < rAntiFreezeSupplyTempLimit) cause the heating circuit operation to be enabled anyway
low indoor air temperature (rIdaTemp < rAntiFreezeIdaTempLimit) cause the heating circuit operation to be enabled anyway

Caveats¶

To keep complexity as low as possible this example omits - amongst others - the following real world application aspects worth mentioning:

configuration missing (configuration of m_heatingCharacteristicCurve, m_circulationPump, m_sequenceControl, m_mixingValve, etc. is not or not completely exposed on the ExampleHeating VAR_INPUT section)
sensors missing (circulation pump service / error indication, …)
input consistency checks (implausible measurement values, …)
day / night operation does often fullfill more complex needs
scheduling (for example via BACnet scheduler) might set setpoint instead of day / night
ramping up/down the setpoint instead of switching over between day / night setpoint
xError / eErrorID not computed at all, see ExampleAirConditioning2 how to do this
sensor / actuator process I/O not mapped (FB sensor inputs, m_circulationPump, m_mixingValve)

InOut:

Scope	Name	Type	Initial	Comment
Input	`eOnOff`	AutoOnOff	AutoOnOff.Auto	Operation mode preset
	`rSupplyTemp`	`REAL`		Supply temperature
	`rOdaTemp`	`REAL`		Outdoor temperature
	`rIdaTemp`	`REAL`	21.0	Indoor air temperature
	`rIdaTempSetpt`	`REAL`	21.0	Indoor air temperature setpoint
	`rTempLimitAutoEnable`	`REAL`	16.0	Temperature limit to enable operation in “auto”-mode
	`xUseOdaTemp`	`BOOL`	FALSE	Decides whether to use daily mean temperature or outdoor temperature to enable operation in “auto”-mode. xUseOdaTemp := FALSE => use daily mean temperature. xUseOdaTemp := TRUE => use outdoor temperature.
	`xDayNight`	`BOOL`	TRUE	Decides whether to use day / night operation
	`rGradient`	`REAL`	1.2	HeatingCharacteristicCurve gradient.
	`rShift`	`REAL`	0.0	HeatingCharacteristicCurve parallel shift
	`rMinimumSupplyTemp`	`REAL`	20.0	Supply temperature minimum
	`rMaximumSupplyTemp`	`REAL`	80.0	Supply temperature maximum
	`xNightSetptReductionEnable`	`BOOL`	TRUE	Decides whether to use night time setpoint reduction vs. switching off heating circuit operation
	`rNightSetptReduction`	`REAL`	-12.0	Night time setpoint reduction
	`xEconomyEnable`	`BOOL`	TRUE	Enables economy mode
	`xAntiFreezeEnable`	`BOOL`	TRUE	Enables anti-freeze
	`rAntiFreezeOdaTempLimit`	`REAL`	4.0	Anti-freeze outdoor temperature limit
	`rAntiFreezeSupplyTempLimit`	`REAL`	10	Anti-freeze supply temperature limit
	`rAntiFreezeIdaTempLimit`	`REAL`	14.0	Anti-freeze indoor air temperature limit
	`xReset`	`BOOL`	FALSE	Reset
	`itfDateTimeProvider`	`Util.IDateTimeProvider`	Globals.g_dtpDateTimeProvider	Source for the current date and time information in milliseconds since 1.1.1970 00:00:00.000
Output	`xOn`	`BOOL`		Heating circuit is activated / enabled
	`xHeat`	`BOOL`		Heating circuit in operation
	`rSupplyTempSetpt`	`REAL`		Supply temperature setpoint
	`xEconomy`	`BOOL`		Economy mode active
	`xFrostAlarm`	`BOOL`		Frost alarm indication
	`xCircPump`	`BOOL`		Circulation pump running
	`rValve`	`REAL`		Mixing valve