Electric heating coil with supply air temperature control, modulating output (HclEl12)

This application function operates an electric modulating heating coil.

The request signal for heating (from the room controller) is transformed into supply air temperature setpoint and is provided to the own PID controller for cascaded supply air temperature control. The modulation results from the output of the PID-controller.

There is an optional binary input for overtemperature detection.

Another optional binary output can be used to enable the modulation.

Required elements and how to configure them:

Element	I/O	Signal type
HclElPos "Heating coil electric position"	On-board output, Heating coil valve position	Electric modulating
TSu "Supply air temperature"	On-board input, Supply air temperature	any signal type

WARNING

Electric heat coils require safety limit thermostat

Improper installation of electric heating coils can result in fire and cause destruction of life and property.

Install a high temperature cut-out switch on all electric heating elements.
Ensure that all wiring and installation conform to applicable safety codes and regulations.

Function

The figure below shows BACnet objects associated with this application function. Primary signal flow is summarized as follows:

Heating coil heating request (HclHReq) is received and processed into the output signal for heating coil electric position (HclElPos).

Basic function: Accept request signal from associated room controller and map it to appropriate control setpoint; Compare setpoint to present value of supply air temperature sensor; Pass result through a device mode logic switch prior to outputting as a command to the object that controls the device.

	Command or request (or related)
	Notification of condition or status, or availability
	Device mode
	Interlock (internal signal, not a BACnet object; see Interlocks section for additional information)

Interlocks

Room automation interlocks are internal signals that coordinate interaction between HVAC devices. They are not visible in ABT Site or web interface, but parameters associated with them are. See comment column for hints on parameters that affect interlock functionality.

Signal	Type	Direction	Description	Comment
AirFlSta	Boolean	In	Air flow status ▶ Interlock signal, from a fan or a supply damper, that keeps the coil locked at equipment protection priority (PrPrio = 5) unless that same fan or supply damper provides air flow.	No related parameters in electric coils. AirFlSta is hard-coded.
AirFlHReq	Boolean	Out	Air flow heating request ▶ Initiates air flow (fan turns on or VAV supply damper provides air flow) to satisfy air flow support request for heating. Signal is sent to fan or VAV supply damper depending on application.	See Configuration section for parameters named "...AirFlHReq".
AirFlHldH	Boolean	Out	Air flow hold for heating ▶ Interlock signal to fan or supply damper requesting equipment protection air flow support for a period of time, such as when the electric heating coil has just turned off.	See Configuration section for parameters named "...AirFlHldH".
AirManOff	Boolean	In	Air manual off ▶ Interlock signal to turn off electric heating element if air source (fan or damper) is manually turned off. If AirManOff is True, HclDevMod =1:Off at priority 4 (protection mode 1).

Analog control of electric heating coil: In response to heating demand, the heating coil electric position (HclElPos) modulates to control the cascaded supply air temperature at setpoint. In response to external triggers for special modes such as warm-up, cool down, or safety conditions, the heating coil electric may be set to off or fully open.

Cascaded supply air temperature control: The heating demand signal (HclHReq) from room temperature PID is mapped to a setpoint value for supply air temperature (HclSpTSuH), and used as input to the cascaded supply air temperature PID located in this AF. The supply air PID compares the setpoint value to the present value of the supply air temperature sensor, and any difference is used to increase or decrease the analog output signal to the command object.

If the supply air temperature sensor is not valid, temperature control is performed by the room temperature PID.

Device mode: The input signal for device mode is a multistate value.

HclDevMod supports the following states:

Off
Control mode (modulation)
Fully open

Heating available status: When the heating coil is available for heating, the binary output signal for "Heating coil available for heating" (HclAvlH) will be "Yes" (available). HclAvlH is used by the system to regulate heating resources. For example, if there is a call for heating but the heating coil is not available because it is already at maximum capacity (because device mode is fully open), then HclAvlH will signal "No" and the next available heating resource in the temperature control sequence will be activated.

For heating available status to be "Yes", device mode must equal "Control mode" (modulation).

High temperature cut-out switch: This AF has a heating coil over-temperature detection input (HclOvrTDet) from a high temperature cut-out switch. When the switch activates, the coil is commanded off at equipment protection priority and a signal is sent to the source of air flow to hold / maintain air flow. A timer prevents the source of air flow from stopping until after the timer expires.

Parameter EnOvrTDetIn must be set to 1:Yes for the cut-out switch to function (see Configuration).

Electric power usage: The nominal electric power usage of the electric heating coil is provided for energy monitoring and coordination with other devices. The following equation calculates the coil's electric power usage when on (HclElPos > 0%):

HclElPwr = HclElPos * NomElPwr (zero power is used when coil is off)

Supply Air Coordination: Additional setpoint logic is possible if a central function with HVAC capability is present and connected to the room segment controller. If enabled, this central function makes available the TPa object (primary air temperature from the air handling unit), allowing for dynamic adjustments to the minimum supply air temperature setpoint. For additional information see

SpTSuHMin
TPa object: CenFnct11 ->SplyAir11

Configuration

Parameters

Description	Parameter	Default value
Nominal electric power ▶ The nominal electric power (kW) for the electric heating coil. The total power for the electric heating coil can be found on manufacturer's data sheet.	NomElPwr	0.4 [kW]
Enable overtemperature detector input ▶ Enable input, must be set to 1:Yes when an electric heating coil over temperature detector (binary input) is present. When electric heating coil overt temperature detector is closed, the heating coil device mode will turn Off at priority (4:Protection 1). When heating coil over temperature detector is open, the heating coil device mode will be released to 15: Automatic mode 6). 0:No 1:Yes	EnOvrTDetIn	0:No
Supply air temperature setpoints
Maximum supply air temperature setpoint for heating ▶ Per CEC Title24, the maximum supply air temperature setpoint for heating must be no more than 95°F (35°C). Note: the system will limit the supply air temperature setpoint to the lesser of SpTSuHMax and (present room temperature setpoint + DiffSpTSuHSpR).	SpTSuHMax	32 [°C] 95.0 [°F]
Minimum supply air temperature setpoint for heating ▶ Must be sufficiently below heating supply air temperature so that the heating can turn off completely when heat is not needed. If an HVAC supply air central function is connected, the plant will limit the minimum supply air temperature setpoint to the greater of: SpTSuHMin Primary air temperature from the air handling unit minus one temperature unit (TPa – 1 Kelvin [1.8 F]) If there is no central function present, the setpoint minimum will always be SpTSuHMin.	SpTSuHMin	16 [°C] 50.0 [°F]
Supply air temperature setpoint heating differential to room setpoint ▶ To be compliant with ASHRAE 90.1 the maximum supply air temperature for heating must be no more than 20°F (10°C) above the room temperature heating setpoint. Note: the system will limit the supply air temperature setpoint to the lesser of SpTSuHMax and (present room temperature setpoint + DiffSpTSuHSpR).	DiffSpTSuHSpR	10 [K] 20.0 [°F]
High outside air temperature lockout
Enable lockout heating coil at high outside air temperature ▶ IF EnLockHclTOaHi is Yes AND the outside air temperature is greater than LockHclTOaHi and is valid, the device mode is set to Off. IF EnLockHclTOaHi is False OR the outside air temperature is less than LockHclTOaHi minus HysTOaLockHcl OR is invalid, this function has no effect on the device mode. 0:No 1:Yes	EnLockHclTOaHi	0:No
Lockout heating coil at high outside air temperature ▶ See EnLockHclTOaHi for functionality.	LockHclTOaHi	13.0 [°C] 55.4 [°F]
Outside air temperature hysteresis for lockout heating coil ▶ See EnLockHclTOaHi for functionality.	HysTOaLockHcl	1.0 [K] 1.8 [°F]
Interlocks
Switch-on point for air volume flow hold heating ▶ When the heating coil position (in percent) is greater than the switch-on point for air volume flow hold heating, the airflow volume hold heating interlock to the fan goes to True.	SwiOnAirFlHldH	4 [%]
Hysteresis for air volume flow hold heating ▶ When the heating coil position (in percent) is less than the hysteresis value, the air volume flow hold heating interlock goes False.	HysAirFlHldH	2 [%]
Switch-off delay for hold signal for air volume flow heating ▶ The time after the switch-off point for air volume flow hold heating is True, then the air volume flow hold heating goes from True to False.	DlyOffAflHldH	30 [s]
Switch-on point for air volume flow heating request ▶ When the heating coil heating request (in percent) is above this value, the air volume flow heating request goes to True.	SwiOnAirFlHReq	4 [%]
Hysteresis for air volume flow heating request ▶ When the heating coil heat request (in percent) is below this value, the air volume flow heating request goes to False.	HysAirFlHReq	2 [%]
Switch-on delay for air volume flow heating request ▶ The time after the switch-on point for air volume flow heating request is True that air volume flow heating request goes from False to True.	DlyOnAirFlHReq	30 [s]
Internal settings – do not change
Temperature unit ▶ Defined by selected engineering unit – do not change.	TUnit	[°C] [°F]
Temperature difference unit ▶ Defined by selected engineering unit – do not change.	TDiffUnit	[K] [°F]

Interface

Interface	Description	Type	Ref.	Owned by
HclElPos	Heating coil electric position	AO	◉	Room segment / Device
EnHclElPos	Enable heating coil electric position 0:No 1:Yes	BO	◉	Room segment / Device
HclOvrTDet	Heating coil overtemperature detector 0:Off 1:On	BI	◉	Room segment / Device
HclSpTSuH	Heating coil supply air temperature setpoint for heating	APrcVal	●	-
HclDevMod	Heating coil device mode 1:Off 2:Control mode 3:Fully open	MPrcVal	●	-
HclTSuCtrH	Supply air temperature controller heating for heating coil	Controller	●	-
HclHReq	Heating coil heating request	ACalcVal	●	-
HclHReqMin	Heating coil heating request minimum	ACalcVal	●	-
HclAvlH	Heating coil available for heating 0:No 1:Yes	BCalcVal	●	-
HclElPwr	Heating coil electric power	ACalcVal	●	-

Engineering and commissioning

Troubleshooting tip: Why is the coil off at high priority?

Probably because there is no air flow. Check fan or damper. Maybe because of high temp safety input. (Confirm function of safety switch.)