Heating / Cooling coil 4-pipe system with supply air temperature control (HCcl4Pipe12)

Required elements and how to configure them:

Element	I/O	Signal type
HCclVlvPosC "Heating/cooling coil valve position for cooling " [%] HCclShofC "Heating/cooling coil shutoff for cooling " [0/100%] HCclVlvPosH "Heating/cooling coil valve position for heating " [%] HCclShofH "Heating/cooling coil shutoff for heating " [0/100%]	On-board output, Heating/cooling coil valve position	4-pipe any signal type
TSu "Supply air temperature"	On-board input, Supply air temperature	any signal type

Function

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

H/C coil heating or cooling request (HCclHReq / HCclCReq) is received and processed into the output signals for the H/C coil valve positions for heating and cooling (HCclVlvPosH / HCclVlvPosC) and the H/C coil shutoff valve positions for heating and cooling (HCclVlvShofH / HCclVlvShofC).

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
AirFlCReq	Boolean	Out	Air flow cooling request ▶ Initiates air flow (fan turns on or VAV 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".
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/Chilled water valve modulation: In response to heating or cooling demand, this application function modulates the control valve(s) 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 control valve(s) may be set to off or fully open.

Cascaded supply air temperature control: The heating (or cooling) demand signal (HCclHReq, HCclCReq) is received from the respective room temperature PID. It is then mapped to a setpoint value for supply air temperature (HCclSpTSuH or HCclSpTSuC), and used as input to the respective cascaded supply air temperature PID (one heating, one cooling) 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 objects (HCclVlvPosH, HCclVlvPosC; HCclVlvShofH, HCclVlvShofC).

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.

HCclDevMod supports the following states:

Off
Control mode (modulation)
Fully open, heating
Fully open, cooling

Heating available status: When the H/C coil is available for heating, the binary output signal for "Heating/cooling coil available for heating " (HCclAvlH) will be "Yes" (available). HCclAvlH is used by the system to regulate heating resources. For example, if there is a call for heating but the H/C coil is not available because it is already at maximum capacity (because device mode is fully open), then HCclAvlH 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).

Cooling available status: When the H/C coil is available for cooling, the binary output signal for "Heating/cooling coil available for cooling" (HCclAvlC) will be "Yes" (available). HCclAvlC is used by the system to regulate cooling resources. For example, if there is a call for cooling but the H/C coil is not available because it is already at maximum capacity (because device mode is fully open), then HCclAvlC 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).

Supply chain interface outputs

HCclHwDmd 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)

HCclChwDmd 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.

Supply chain interface inputs

The input signals for hot water availability / chilled water availability are binary values [No|Yes] determined by central command. They are commanded via supply chain group communication for the purpose of TOa-dependent device lockout. The relinquish default value for each is Yes.

HCclHwAvl: If the outside air temperature is above the hi limit value, HCclHwAvl is set to No and the heating valve is closed. (see Central AF SplyHwxx for additional information)

HCclChwAvl: If the outside air temperature is below the low limit value, HCclChwAvl is set to No and the cooling valve is closed. (see Central AF SplyChwxx for additional information)

If for some reason HCclHwAvl and HCclChwAvl are both "No", then device mode (HCclDevMod) is set to Off at priority 9.

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

Configuration

Parameters

Description	Parameter	Default value
Manual control mode ▶ Configured during commissioning of system to define the control mode provided by the heating/cooling coil: 1:Auto 2:Heating 3:Cooling	CtlModMan	1:Auto
Supply air temperature setpoints
Maximum supply air temperature setpoint for cooling ▶ Must be sufficiently above cooling primary air temperature so that the cooling can turn off completely when cooling is not needed.	SpTSuCMax	32 [°C] 89.6 [°F]
Minimum supply air temperature setpoint for cooling ▶ To be compliant with ASHRAE 90.1 and CEC Title24: the controls shall reset the supply air temperature "at least 25% of the difference between the design supply air temperature and the design room temperature".	SpTSuCMin	16 [°C] 60.8 [°F]
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.	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]
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 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]
Switch-on delay for heating/cooling changeover ▶ Switch-on delay for heating/cooling changeover from heating to cooling or from cooling to heating. This is to prevent equipment damage to the central heating and cooling systems that supply the heated/chilled coil.	DlyOnHCChovr	2 [min]
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	1:Yes
Hot/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 [%]
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 [%]
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
HCclVlvPosC	Heating/cooling coil valve position for cooling	AO	◉	Room segment / Device
HCclVlvShofC	Heating/cooling coil shutoff valve position for cooling	AO	◉	Room segment / Device
HCclVlvPosH	Heating/cooling coil valve position for heating	AO	◉	Room segment / Device
HCclVlvShofH	Heating/cooling coil shutoff valve position for heating	AO	◉	Room segment / Device
HCclSpTSuC	Heating/cooling coil supply air temperature setpoint for cooling	APrcVal	●	-
HCclSpTSuH	Heating/cooling coil supply air temperature setpoint for heating	APrcVal	●	-
PrSpRu	Present setpoint for room operator unit	APrcVal	●	-
HCclDevMod	Heating/cooling coil device mode 1:Off 2:Control mode 3:Fully open, heating 4:Fully open, cooling	MPrcVal	●	-
HCclTSuCtrC	Supply air temperature controller cooling for heating/cooling coil	Controller	●	-
HCclTSuCtrH	Supply air temperature controller heating for heating/cooling coil	Controller	●	-
HCclCReq	Heating/cooling coil cooling request	ACalcVal	●	-
HCclCReqMin	Heating/cooling coil cooling request minimum	ACalcVal	●	-
HCclHReq	Heating/cooling coil heating request	ACalcVal	●	-
HCclHReqMin	Heating/cooling coil heating request minimum	ACalcVal	●	-
HCclAvlC	Heating/cooling coil available for cooling 0:No 1:Yes	BCalcVal	●	-
HCclAvlH	Heating/cooling coil available for heating 0:No 1:Yes	BCalcVal	●	-
HCclChwDmd	Heating/cooling coil chilled water demand 1:Off 2:Cooling demand 3:Free cooling	MCalcVal	●	-
HCclHwDmd	Heating/cooling coil hot water demand 1:Off 2:Heating demand 3:Warm-up	MCalcVal	●	-
HCclChwAvl	Heating/cooling coil chilled water available 0:No 1:Yes	BPrcVal	●	-
HCclHwAvl	Heating/cooling coil hot water available 0:No 1:Yes	BPrcVal	●	-
HCclSplyChw	Heating/cooling coil supply chain for chilled water	GrpMbr	●	Room segment
HCclSplyHw	Heating/cooling coil supply chain for hot water	GrpMbr	●	Room segment

Engineering and commissioning

Device capacity configuration

The H/C coil must be configured to provide one of the following conditions: Auto (provides both heating/cooling), Heating, or Cooling. To configure the H/C coil set CtlModMan to the appropriate control mode (e.g., heat) for the room segment.

When concerned with operation of a coil in a changeover system, remember to check:

Changeover state of the central system

Local indication of the changeover state.