Load Control

A Load Control object lets a utility, a demand-response system or another controller ask a device to shed electrical load for a set time. The device decides how to shed; the client only sees whether it is complying. It suits building controllers that take part in demand response.

Typical uses

• Shed 20 percent of a building’s load during a peak event
• Let a utility gateway start a demand-response event
• Schedule a shed for a later start time
• Report whether the building met the requested shed

Key properties

Property	What it holds
Present_Value	The shed state: inactive, request pending, compliant or non-compliant.
Requested_Shed_Level	How much to shed, as a percent, an amount or a level.
Start_Time	When the shed should begin. Writing it starts a request.
Shed_Duration	How long the shed lasts, in minutes.
Expected_Shed_Level	The level the object expects to reach for the pending or active request.
Actual_Shed_Level	The level currently achieved.

How it behaves

Present_Value follows a state machine as requests arrive, start, finish or cannot be met. The object keeps its request across a restart. The standard pairs it with the CHANGE_OF_STATE algorithm on Present_Value. It also sends change-of-value notices for Present_Value.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_LOAD_CONTROL build option and add each object with BACnetStack_AddObject. Arm change-of-state alarms with BACnetStack_SetAlarmsAndEventsForObjectEnabled and then BACnetStack_SetIntrinsicChangeOfStateAlgorithmEnum; the alarm values are shed states. CASBACnetStackDLL.h declares no function that is specific to Load Control.

Related object types

Schedule, Command, Notification Class

Properties

The properties ASHRAE 135-2024 clause 12.28 defines for this object type.

How to read the table:

• Conformance is what the standard asks of every object of this type: R is required, W is required and writable by a client, O is optional. A digit after the letter marks a condition in the standard that decides when the property is present or writable, such as support for intrinsic reporting.
• Present by default: yes means the stack presents the property as soon as you add the object; no means it is optional and you turn it on with BACnetStack_SetPropertyEnabled. This is the stack’s starting setup, so it can differ from the conformance code.
• Writable is whether a client can write the property by default. Change it with BACnetStack_SetPropertyWritable.
• not in profile means the stack does not offer this property for this object type.
• Value when your callback does not answer: “Held by the stack” means the stack stores and serves the value itself and does not ask your callbacks. Otherwise it is the value the stack answers when your callback declines or is not registered.

Property	Datatype	Conformance	Present by default	Writable	Value when your callback does not answer
Object_Identifier	BACnetObjectIdentifier	R	yes	no	Held by the stack.
Object_Name	CharacterString	R	yes	no	"Object <type>,<instance>", such as "Object 0,1" for Analog Input 1.
Object_Type	BACnetObjectType	R	yes	no	Held by the stack.
Description	CharacterString	O	no	no	""
Present_Value	BACnetShedState	R	yes	no	No default: value-not-initialized.
State_Description	CharacterString	O	no	no	""
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	R	yes	no	0
Reliability	BACnetReliability	O	no	no	0
Requested_Shed_Level	BACnetShedLevel	W	yes	yes	No default: the read fails.
Start_Time	BACnetDateTime	W	yes	yes	No default: the read fails.
Shed_Duration	Unsigned	W	yes	yes	0
Duty_Window	Unsigned	W	yes	yes	0
Enable	Boolean	W	yes	yes	false
Full_Duty_Baseline	Real	O	no	no	0.0
Expected_Shed_Level	BACnetShedLevel	R	yes	no	No default: the read fails.
Actual_Shed_Level	BACnetShedLevel	R	yes	no	No default: the read fails.
Shed_Levels	BACnetARRAY[N] of Unsigned	W1	yes	yes	0
Shed_Level_Descriptions	BACnetARRAY[N] of CharacterString	R	yes	no	""
Notification_Class	Unsigned	O2,4	no	no	0
Time_Delay	Unsigned	O2,4	no	no	0
Event_Enable	BACnetEventTransitionBits	O2,4	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O2,4	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O2,4	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O2,4	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O4	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O4	no	no	""
Event_Detection_Enable	Boolean	O2,4	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O4	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O4,5	no	no	false
Time_Delay_Normal	Unsigned	O4	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O6	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Value_Source	BACnetValueSource	O7,8,9	no	no	No default: the read fails.
Audit_Level	BACnetAuditLevel	O10	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O10	not in profile	not in profile	No default: the read fails.
Tags	BACnetARRAY[N] of BACnetNameValue	O	no	no	No default: the read fails.
Profile_Location	CharacterString	O	no	no	""
Profile_Name	CharacterString	O	no	no	""