Chilled water cooling coil, external flow control (CclChw14)

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

The water flow setpoint is calculated based on request signals (from the room controllers) received for cooling and dehumidification.

This application function is ONLY available for:

DXR2x09, DXR2x11 and DXRx18 for FCU-Type.

Required elements and how to configure them:

Element	I/O	Signal type
CclSpWfl "Cooling coil setpoint for water volume flow"	On-board output, Cooling 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:

Cooling coil cooling or dehumidification request (CclCReq / CclDhuReq) is received and processed into the output signal for cooling coil valve position (CclSpWFl).

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
AirFlCReq	Boolean	Out	Air flow cooling request ▶ Initiates air flow (fan turns on or VAV supply damper provides air flow) to satisfy air flow support request for cooling. Signal is sent to fan or VAV supply damper depending on application.	See Configuration section for parameters named "...AirFlCReq".
AirFlDhuReq	Boolean	Out	Air flow dehumidification request ▶ Initiates air flow (fan turns on) to satisfy air flow support request for dehumidification.	See Configuration section for parameters named "...AirFlDhuReq".
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

Chilled water flow setpoint modulation: In response to cooling demand (or a dehumidification request, if configured) the water flow setpoint is modulated/adjusted to control the room temperature at setpoint or to dehumidify the air. 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.

Request signal(s) from a room temperature PID controller and/or a dehumidification PID controller are received from the associated "room" AF. If both a request for cooling and a request for dehumidification are received at the same time, then the larger of the two signals will be used.

Dehumidification control: If dehumidification is used, the cooling coil dehumidification request signal (CclDhuReq) is converted into the analog output signal for cooling coil valve position (CclVlvPos).

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 (CclSpWFl) 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.

CclDevMod supports the following states:

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

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

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

Dehumidification available status: When the cooling coil is available for dehumidification, the binary output signal for "Cooling coil available for dehumidification" (CclAvlDhu) will be "Yes" (available). For the status to be "Yes", device mode must equal "Control mode" (modulation).

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

CclChwDmd supports the following states:

Off (no demand signal)
Cooling demand (demand signal is active)
Free cooling (cooling device is in free cooling mode)

Free cooling can be initiated by the central plant when surplus cooling capacity is available. Under certain conditions, the room can take advantage of surplus cooling capacity in the absence of an explicit cooling demand; the room temperature must be below the setpoint associated with the current room climate mode (Comfort, Pre-Comfort etc.). This type of free cooling is different from "economizer" free cooling, which uses an outside air damper.

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

Configuration

Objects

Description	Object	Type	Default value
Cooling 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 CclSpWfl object.	CclWflMax	ACnfVal	100.0 [l/h] 0.44 [gpm]

Parameters

Description	Parameter	Default value
Interlocks
Switch-on point for air volume flow cooling request ▶ When the cooling coil cooling request (in percent) is above this value, the air volume flow cooling request goes to True.	SwiOnAirFlCReq	4 [%]
Hysteresis for air volume flow cooling request ▶ When the cooling coil cooling request (in percent) is below this value, the air volume flow cooling request goes to False.	HysAirFlCReq	2 [%]
Switch-on delay for air volume flow cooling request ▶ The time after the switch-on point for air volume flow cooling request is True that air volume flow cooling request goes from False to True.	DlyOnAirFlCReq	30 [s]
Switch-on point for air volume flow dehumidification request ▶ When the cooling coil dehumidification request (in percent) is above this value, the air volume flow dehumidification request goes to True.	SwiOnAflDhuReq	4 [%]
Hysteresis for air volume flow dehumidification request ▶ When the cooling coil dehumidification request (in percent) is below this value, the air volume flow dehumidification request goes to False.	HysAirFlDhuReq	2 [%]
Switch-on delay for air volume flow dehumidification request ▶ The time after the switch-on point for air volume flow dehumidification request is True that air volume flow dehumidification request goes from False to True.	DlyOnAflDhuReq	30 [s]
Switch-off delay for air volume flow dehumidification request ▶ The time after the switch-off point for air volume flow dehumidification request is True that air volume flow dehumidification request goes from True to False.	DlyOfAflDhuReq	0 [s]
Enable monitoring for air volume flow state ▶ Enable monitoring of the fan interlock signal (from fan) that keeps the cooling coil closed unless the fan is running. ▶ In an AC unit with a cooling coil and no drain pan, consider setting to 1: Yes to avoid condensing on the coil. 0:No 1:Yes	EnMonAirFlSta	0:No
Chilled water demand
Switch-on point for chilled water demand ▶ When the cooling coil valve position is greater than the switch-on point, the cooling coil enables request chilled water for cooling.	SwiOnPtChwDmd	4 [%]
Hysteresis for chilled water demand ▶ When the cooling coil valve position is less than the hysteresis value, the cooling coil disables request chilled water for cooling.	HysChwDmd	2 [%]

Interface

Interface	Description	Type	Ref.	Owned by
CclSpWfl	Cooling coil setpoint for water volume flow	AO	◉	Room segment / Device
CclSpWflRel	Cooling coil setpoint for relative water volume flow	APrcVal	●	-
CclDevMod	Cooling coil device mode 1:Off 2:Control mode 3:Fully open	MPrcVal	●	-
CclCReq	Cooling coil cooling request	ACalcVal	●	-
CclDhuReq	Cooling coil dehumidification request	ACalcVal	●	-
CclAvlC	Cooling coil available for cooling 0:No 1:Yes	BCalcVal	●	-
CclAvlDhu	Cooling coil available for dehumidification 0:No 1:Yes	BCalcVal	●	-
CclChwDmd	Cooling coil chilled water demand 1:Off 2:Cooling demand 3:Free cooling	MCalcVal	●	-
CclSplyChw	Cooling coil supply chain for chilled water	GrpMbr	●	Room segment
CclWflMax	Cooling coil maximum water volume flow	ACnfVal	●	-

Engineering and commissioning

The internal AirFlSta interlock signal is optional for CclChw14. If desired, parameter EnMonAirFlSta (Enable monitoring for air volume flow state) must be set to 1: Yes.

In an a/c unit with a cooling coil and no drain pan, consider setting EnMonAirFlSta to 1: Yes to avoid condensing on the coil.

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