Hot water radiator with downdraft compensation (RadHw11)

This application function operates hot water valve(s) for radiator(s) and supports downdraft compensation.

The radiator valve position is calculated based on a request signal for heating (from a room controller).

Multiple radiator control is supported.

Required elements and how to configure them:

Element	I/O	Signal type
RadVlvPos "Radiator valve position"	On-board output, Radiator valve position 1	Water any signal type

Function

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

Radiator heating request (RadHReq) is received and processed into the output signal for radiator valve position (RadVlvPos).

Basic function: Accept request signal from associated room controller and 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

Hot water valve modulation: In response to heating demand, the heating valve is modulated to control the room temperature at setpoint. In response to external triggers for special modes such as warm-up, cool down, or safety conditions, the heating valve 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.

Multiple radiator control: The radiator valve position collection object (RadVlvPosCol) can reference and control multiple radiators.

Radiator valve position objects (RadVlvPos) are referenced by the radiator valve position collection object (RadVlvPosCol); this collection object is a common node for any / all RadVlvPos object(s). The value for RadVlvPos comes from RadVlvPosVal.

Downdraft compensation: The downdraft compensation feature slows the sinking cold air flow at large window surfaces and combats cold wall effect at cold perimeter surfaces. This feature activates the radiator when the outside air temperature drops below a configured value, raising the minimum temperature of the radiator to a value higher than it would be otherwise.

Downdraft compensation is implemented using a linear reset function. The following graphic shows factory default values for X,Y downdraft compensation parameters.

Parameter EnDndft must be set to 1:Yes for downdraft compensation to function (see Configuration).

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

RadDevMod supports the following states:

Off
Control mode (modulation)
Fully open
Ctrl.mode & downdraft (modulation plus downdraft compensation)
Downdraft (downdraft compensation)

Heating available status: When the radiator(s) are available for heating, the binary output signal for "Radiator available for heating" (RadAvlH) will be "Yes" (available). RadAvlH is used by the system to regulate heating resources. For example, if there is a call for heating but the radiator(s) are not available because they are already at maximum capacity (because device mode is fully open), then RadAvlH 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).

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

Configuration

Parameters

Description	Parameter	Default value
Hot water demand
Switch-on point for hot water demand ▶ When the radiant ceiling heating valve position is greater than the switch-on point, the radiant ceiling heating valve enables request hot water for heating.	SwiOnPtHwDmd	4 [%]
Hysteresis for hot water demand ▶ When the radiant ceiling heating valve position is less than the hysteresis value, the radiant ceiling heating valve disables request hot water for heating.	HysHwDmd	2 [%]
Downdraft compensation
Enable downdraft compensation 0:No 1:Yes	EnDndft	0:No
Downdraft characteristics for outside air temperature X1 ▶ Outside air temperature where radiator hot water valve provides full (100%) downdraft control.	X1DndftTOa	-5 [°C], 23.0 [°F]
Downdraft characteristics for valve position Y1 ▶ The radiator valve position that provides 100% downdraft control.	Y1DndftVlvPos	100 [%]
Downdraft characteristics for outside air temperature X2 ▶ Outside air temperature where the radiator hot water valve begins to provide downdraft control.	X2DndftTOa	10 [°C], 50.0 [°F]
Downdraft characteristics for valve position Y2 ▶ The radiator valve position that initializes downdraft control.	Y2DndftVlvPos	25 [%]
Internal settings – do not change
Temperature unit ▶ Defined by selected engineering unit – do not change.	TUnit	[°C] [°F]

Interface

Interface		Description	Type	Ref.	Owned by
RcgVlvPosCol		Collection of radiant ceiling valve position	ColView	●	-
	RcgVlvPos	Radiant ceiling valve position (1...n)	AO	◉	Room segment / Device
RadVlvPosVal		Radiator valve position value	APrcVal	●	-
RadDevMod		Radiator device mode 1:Off 2:Control mode 3:Fully open, heating 4:Control mode & downdraft 5:Downdraft	MPrcVal	●	-
RadHReq		Radiator heating request	ACalcVal	●	-
RadAvlH		Radiator available for heating 0:No 1:Yes	BCalcVal	●	-
RadDndftVal		Radiator downdraft value	ACalcVal	●	-
RadHwDmd		Radiator hot water demand 1:Off 2:Heating demand 3:Warm-up	MCalcVal	●	-
RadSplyHw		Radiator supply chain for hot water	GrpMbr	●	Room segment

Engineering and commissioning

None