CET hot water heating coil, thermal power control, supply air temperature control (CetHclHw12)

Overview

The application function "CET room pressurization hot water heat.coil 12, with thermal power control, cascaded supply air temperature control" (CetHclHw12) operates a hot water valve for a heating coil. The main output is a modulating output for valve position.

This AF has its own PID controller(s) for cascaded supply air temperature control and quicker response. A supply air temperature sensor is required.

Main features:

Hot water valve modulation
Cascaded supply air temperature control
Thermal power control with BTU compensation
Heating available status
Interlocks
Supply chain interface

Function

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

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.

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

	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 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.

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).

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

Parameters

Description	Parameter	Default value
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 [%]
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 changes 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 (REQUIRED as this enables supply air temperature cascade control loop).	EnMonAirFlSta	1:Yes
Maximum supply air temperature setpoint for heating ▶ To be compliant with ASHRAE 90.1 and Title 24; the maximum supply air temperature for heating must be no more than 20°F (10°C) above the room temperature heating setpoint.	SpTSuHMax	32 [°C] 89.6 [°F]
Minimum supply air temperature setpoint for heating ▶ Must be sufficiently below heat supply air temperature so that the heating can turn off completely when heat is not needed.	SpTSuHMin	16 [°C] 60.8 [°F]
Temperature unit ▶ Defined by selected engineering unit – do not change.	TUnit	[°C] [°F]

Interface

Interface	Description	Type	Ref.	Owned by
HclVlvPos	Heating coil valve position	AO	◉	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	●	-
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

Engineering and commissioning

Parameter EnMonAirFlSta (Enable monitoring for air volume flow state) must be set to 1: Yes. This is the default setting for HclHw12 (unlike HclHw11 where this setting is optional). It is important to understand that this setting is NOT optional for HclHw12.