Hot water heating coil, external flow control (HclHw13)

This application function generates a water flow setpoint for the pressure independent control valve for a heating coil.

The water flow setpoint is calculated based on a request signal (from the room controller) received for heating.

Required elements and how to configure them:

Element	I/O	Signal type
HclSpWfl "Heating coil setpoint for water volume flow"	On-board output, Heating coil valve position	Setpoint for water volume flow 0…10V

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 valve position (HclSpWFl).

Basic function: Accept request signal from associated room controller and map it to the appropriate water flow setpoint. Pass it through a device mode logic switch; Output the result as a command to the BACnet 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
AirFlHReq	Boolean	Out	Air flow heating request ▶ Initiates air flow (fan turns on or VAV 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".
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. (not active unless EnMonAirFlSta = Yes)	Parameter EnMonAirFlSta must = Yes. See Configuration section for additional information.

Sequence

Hot water flow setpoint modulation: In response to heating demand, the water flow setpoint is modulated/adjusted to control the room temperature at setpoint. In response to external triggers for special modes such as warm-up, cool down, or safety conditions, device mode may be set to off or fully open.

Note
This AF does not perform loop control; its main purpose is to run commands. Loop control processes (for this AF) are managed in the "room" AF(s) that collaborate with this AF to command the end device.

External water flow controller / valve: The water flow setpoint (HclSpWFl) drives the external water flow controller / valve through a 0-10V DC signal.

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

HclDevMod supports the following states:

Off
Control mode (modulation)
Fully open (allows maximum flow for flushing the water circuit)

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).

Supply chain interface, HwDmd: The output signal for hot water demand is a multistate value.

HclHwDmd supports the following states:

Off (no demand signal)
Heating demand (demand signal is active)
Warm-up (Hot water demand is initiated when plant operating mode is set to warm-up)

The following figure(s) illustrates control modulation and related functions.

Configuration

Objects

Description	Object	Type	Default value
Heating coil maximum water volume flow ▶ The desired maximum flow value for the pressure independent flow valve. This value must be ≤ the configured value set in "Process value 2" property of the HclSpWfl object.	HclWflMax	ACnfVal	100.0 [l/h] 0.44 [gpm]

Parameters

Description	Parameter	Default value
Interlocks
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]
Enable monitoring for air volume flow state ▶ Enable monitoring of the fan interlock signal (from fan) that keeps the heating/cooling coil closed unless the fan is running. 0:No 1:Yes	EnMonAirFlSta	0:No
Hot water demand
Switch-on point for hot water demand ▶ When the heating coil valve position is greater than the switch-on point, the heating coil enables request hot water for heating.	SwiOnPtHwDmd	4 [%]
Hysteresis for hot water demand ▶ When the heating coil valve position is less than the hysteresis value, the heating coil disables request hot water for heating.	HysHwDmd	2 [%]

Interface

Interface	Description	Type	Ref.	Owned by
HclSpWfl	Heating coil setpoint for water volume flow	AO	◉	Room segment / Device
HclSpWflRel	Heating coil setpoint for relative water volume flow	APrcVal	●	-
HclDevMod	Heating coil device mode 1:Off 2:Control mode 3:Fully open	MPrcVal	●	-
HclHReq	Heating coil heating request	ACalcVal	●	-
HclAvlH	Heating coil available for heating 0:No 1:Yes	BCalcVal	●	-
HclHwDmd	Heating coil hot water demand 1:Off 2:Heating demand 3:Warm-up	MCalcVal	●	-
HclSplyHw	Heating coil supply chain for hot water	GrpMbr	●	Room segment
HclWflMax	Heating coil maximum water volume flow	ACnfVal	●	-

Engineering and commissioning

The internal AirFlSta interlock signal is optional for HclHw13. If desired, parameter EnMonAirFlSta (Enable monitoring for air volume flow state) must be set to 1: Yes.

The relative water flow setpoint (HclSpWFlRel) is normalized as a percentage (0-100%) of HclSpWFl where 100% represents the value configured in "Process value 2" property for HclSpWFl.