Sequence control damper / heater coil / cooler coil¶

SequenceControl is used to control three sequences - heater coil, RCA damper and cooler coil.

RCA damper - 0% (maximum outdoor air) .. 100% (would be: no outdoor air)

This is about to utilize mixed air or outdoor air energy as much as possible to heat / cool.

In case you want to trade comfort (in this case control deviation and it’s duration) a bit higher to energy consumption, you might want to set mc_rDamperCoilOverlap to a value < 0.0, making the RCA damper sequence and the coil sequences overlap thus forcing the coils to jump in before maximum RCA ratio is reached. Set mc_rDamperCoilOverlap to -1.0 (K) will make the coil open 25% (because rXP = 4.0) if recirculation air damper reached maximum.

Recirculation air admixing and energy selection¶

RCA admixing is done using the RCA damper as primary control sequence thus minimizing heat / cool energy consumption. Please see m_energySelection for the energy selection aspect.

Minimum outdoor air ratio¶

Minimum ODA ratio is achieved by rMax2 := 100% - rMinOdaRatio Remember: RCA damper is controlled by sequence 2. rOut2 = 0% means maximum ODA ratio (100% in this case).

Water side anti-freeze for heater coil¶

Water side anti-freeze for heater coil is done with two separate sub-functionalities

• a controlled startup procedure

• continuous anti-freeze during control

The startup procedure is done using HVAC_AntiFreezeControlStartup if ODA temperature < startup threshold:

1. preload (the heater coil):

• ODA / ETA damper closed

• RCA damper open (maximum recirculation air ratio - 100%)

• forcing the heater coil to open

• check heater coil return temperature to reach a threshold

2. after preload - wait for system to become settled (HVAC_AntiFreezeControlStartup.tFollowUp):

• open ODA / ETA damper to minimum ODA ratio

• set RCA damper accordingly to minimum ODA ratio

3. take over to normal control actions

SequenceControl.xForceEnable and .rForcedValue is used to force the heater coil sequence, thus providing smooth control takeover after sucessfull startup.

The continuous anti-freeze during control is done using a CommandVariable setting the heater coil sequence minimum.

Air side anti-freeze¶

Air side anti-freeze is done using a frost monitor HVAC_AntiFreezeControlMonitor. The frost monitor simply does shut-off the whole plant, but keeping the heater coil opened to maximum.

Hints¶

Unused pins of function block instances are hidden, so refer to the function block documentation for more details.

Caveats¶

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

• configuration missing (configuration of m_energyLevelSetpoint, m_sequenceControl, m_antiFreezeControlStartup and m_antiFreezeCont is not exposed on the ExampleAirConditioning1 VAR_INPUT section)

• ignoring the subtle differences between indoor air control vs. extract air control (assuming extract air temp. = indoor air temp.)

• no indoor air / supply air cascade control (control quality)

• no supply air minimum enforced (physiological problems caused by low supply air temperature)

• ramping up/down the ODA / EHA damper after anti-freeze control preload is done (our impl. does simply switch to rMinOdaRatio or 100%)

• cooling is not blocked if continuous anti-freeze during control is opening heater coil

InOut:

Scope	Name	Type	Initial	Comment
Input	xEnable	BOOL	TRUE	Enable
	eLevel	EnergyLevel	EnergyLevel.COMFORT	Energy level
	rEtaTemp	REAL	22.0	Extract air temperature
	rSetptHeatComfort	REAL	21.0	Heat setpoint comfort level
	rSetptCoolComfort	REAL	23.0	Cool setpoint comfort level
	rOdaTemp	REAL	10.0	Outdoor air temperature
	rMinOdaRatio	REAL	20.0	Minimum outdoor air ratio, 0..100%
	rHeaterCoilReturnTemp	REAL	20.0	Heater coil return temperature
	xFrost	BOOL	FALSE	Heater coil frost indication
	xReset	BOOL	FALSE	Reset to proportional control / reset detected input error
	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	eModeOut	HeatCoolOperationMode	HeatCoolOperationMode.INACTIVE	Operation mode.
	rHeatOut	REAL		Heat valve signal (0..100%).
	rCoolOut	REAL		Cool valve signal (0..100%).
	rOdaDamperOut	REAL		Outdoor air damper signal (0..100%).
	rRcaDamperOut	REAL		Recirculation air damper signal (0..100%).
	rEhaDamperOut	REAL		Exhaust air damper signal (0..100%).
	xFan	BOOL		Extract air / supply air fan
	xAntiFreezeStartup	BOOL		Anti-freeze control startup indication
	xAntiFreezeStartupError	BOOL		Anti-freeze control startup error indication
	xFrostAlarm	BOOL		Frost alarm indication
	xError	BOOL		Error indication
	eErrorID	Error		Error ID