Device Discovery and COV in BACnet

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      One of the main features of the BACnet protocol is a service called device discovery. This service allows the Building Automation System (BAS) operator to poll the networked devices for their identifying information, operational status, and values. Devices are identified by their device object name and unique instance number (ObjectID). A device name is optional, while the ObjectID serves for the controls to identify devices. Unlike all other object types, each device may contain only one Device object. The instance number of this Device object must be field-configurable so that it may be assigned a unique instance number among all of the Device objects of all of the devices on a given BACnet internetwork.

      Additionally, a field may exist for the location in the building or on the network. These can also be recorded in programming notes and do not necessarily reside on the module. A password is another feature that may exist but is not critical to function.

      When setting up the Energy Valve for BACnet communications, either BACnet MS/TP or BACnet IP must be chosen based on the desired BACnet network topology. In addition to this setting, the Energy Valve must be assigned a unique Instance ID. Using BACnet MS/TP, the user must choose the appropriate baud rate and MAC address. It is advisable, but not necessary, to set the Max Master to that of the BAS network on which the EV is being installed. Using BACnet IP, the user will have to assign a UDP port. This port should default to 47808 but must match the port used by the BAS system. Entering a device name that describes the EV location is also a good practice.

      After device discovery is performed, the next task is integrating object data to exchange and report information between devices. There is a lot of information, and values don't frequently change in many cases. Most BASs' monitor data object values by continuous polling, which wastes network bandwidth by increasing network traffic. Change Of Value (COV) schemes are one way to mitigate this traffic. A COV involves the client subscribing to the server device containing the value of interest and specifying the change amount. After the subscription is accepted, the server device monitors the object's value. The server issues a COV notification if the value has changed by more than the defined increment amount since the last reported value. Only values that exceed the defined COV increment get reported, saving network bandwidth by decreasing traffic.

      Mind Mapping Design Thinking Infographic Graph

      The Belimo Energy Valve™ supports up to six active BACnet COV data subscriptions, in which the client subscribes for notifications from the server with a lifetime of 1… 28'800 seconds. Below is a list of available object values for COV subscription.

      BACnet Object Description

      Object Name

      Object Type
      [Instance]

      Description Comment Status_Flags

      Values

      COV Increment

      Access

      Device

      Device [Inst.Nr]

       

      0… 4'194'302
      Default: 1

      –

      W

      RelPos

      AI[1]

      Relative Position in %
      Overridden = true, if the gear is disengaged

      0...100

      0.01...100
      Default: 1

      R

      SpAnalog

      AI[6]

      If SetpointSource MV[122] is not 1: Analog then Out_Of_Service is TRUE
      Overridden = true, if forced control (bus, tool and analog forced control) is active

      0...100

      0.01...100
      Default: 1

       

      Sens1Active_Volt

      AI[20]

      Sensor 1 as Voltage in V
      If Sens1Type MV[220] is not 2: Active then Out_Of_Service is TRUE

      0...15

      0.01...15
      Default: 1

      R

      Sens1Passive_ Ohm

      AI[21]

      Sensor 1 as Resistor in Ohm
      If Sens1Type MV[220] is not 4: Passive then Out_Of_Service is TRUE

      0.1... 1'000'000

      0.1... 1'000'000
      Default: 1

      R

      T1_UnitSel

      AI[22]

      Temperature 1 (remote) in selected unit
      Unit can be selected with object MV[127]

      -20…120

      0.01…252
      Default: 1

      R

      T2_UnitSel

      AI[23]

      Temperature 2 (Flow Body) in selected unit
      Unit can be selected with object MV[127]

      -20…120

      0.01…252
      Default: 1

      R

      SpRel

      AO[1]

      Setpoint Relative in %
      The set point is related to either the position, the flow (of V'min, Vmax) or the power (of Pmax).
      See also MV[90], MV[94], MV[100], MV[110]
      Overridden = true, if forced control (bus MV[1], tool and analog forced control) is active

      0...100
      Default: 0

      0.01…100
      Default: 1

      C

      RelFlow

      AV[10]

      Relative Flow in %

      0…150

      0.01…150
      Default: 1

      R

      SpAbsFlow_ UnitSel

      AV [17]

      Setpoint Absolute Flow in selected unit
      Unit can be selected with object MV[123]
      Overridden = true, if forced control (bus, tool and analog forced control) is active

      0…1,5*Vnom

      0…1,5*Vnom

      R

      AbsFlow_UnitSel

      AV[19]

      Absolute Flow in selected unit
      Unit can be selected with object   MV[123]

      0…1,5*Vnom

      0…1,5*Vnom

      R

      Sens1Temp_ UnitSel

      AV [20]

      Sensor 1 as Temperature in selected unit
      Unit can be selected with object MV[127]
      If Sens1PassiveType MV[221] is 1: None or Sens1Type MV[220] is not 3: Passive then Out_Of_Service is TRUE

      -20…248

      0.01...252
      Default: 1

      R

      DeltaT_UnitSel

      AV[22]

      Delta Temperature in selected unit
      Unit can be selected with object MV[128]

      0...140

      0.01…810
      Default: 1

      R

      RelPower

      AV[40]

      Relative Power in %

      0...300

      0.01…300
      Default: 1

      R

      CoolingPower_ UnitSel

      AV[45]

      Cooling Power in selected unit
      Unit can be selected with object MV[124]

      0… 74'150'000

      0.1… 73'361'050
      Default: 1

      R

      HeatingPower_ UnitSel

      AV[46]

      Heating Power in selected unit
      Unit can be selected with object MV[124]

      0… 74'150'000

      0.1… 73'361'050
      Default: 1

      R

      CoolingEnergy_ UnitSel

      AV[47]

      Cooling Energy in selected unit
      Unit can be selected with object MV[125]. See also MV[200]

      0… 2'147'483'641

      1…1.35E12
      Default: 1

      R

      HeatingEnergy_ UnitSel

      AV[48]

      Heating Energy in selected unit
      Unit can be selected with object MV[125]. See also MV[200]

      0… 2'147'483'641

      1…1.35E12
      Default: 1

      R

      VolumeDecimal_ UnitSel

      AV[50]

      Decimal Number of the Volume_m3 Object
      Resolution of 0.01m3 of the Object PIV[50]. See also MV[200]

      0.01-0.99

      0.01-0.99
      Default: 0.1

      R

      Volume_UnitSel

      AV[52]

      Accumulated Volume in selected unit
      Unit can be selected with object MV[126]. See also MV[200]

      0… 2'147'483'641

      1…4.2E10
      Default: 1

      R

      GlycolConcentration

      AV[60]

      Glycol concentration in %
      Measured value or override value in settings

      0…100

      0.01…100
      Default: 1

      R

      Vmin

      AV[90]

      Minimum Flow Limit in %

      0…100

      0.01…100
      Default: 1

      W

      Vmin_UnitSel

      AV[93]

      Minimum Flow Limit in selected unit
      Unit can be selected with object MV[123]

      0… 360'000

      0… 360'000
      Default: 1

      W

      BACnet Object Description

      Object Name

      Object Type
      [Instance]

      Description Comment Status_Flags

      Values

      COV Increment

      Access

      Vmax

      AV[94]

      Maximum Flow Limit in %

      0…100

      0.01…100
      Default: 1

      W

      Vmax_UnitSel

      AV[97]

      Maximum Flow Limit in selected unit Unit can be selected with object MV[123]

      0… 360'000

      0… 360'000
      Default: 1

      W

      Vnom_UnitSel R

      AV[100]

      Nominal Flow in selected unit
      Unit can be selected with object MV[123]

      0… 360'000

      0… 360'000
      Default: 1

      R

      Pmax

      AV[110]

      Maximum Power Limit in %

      0…100

      0.01…100
      Default: 1

      W

      Pmax_UnitSel

      AV[113]

      Maximum Power Limit in selected unit
      Unit can be selected with object MV[124]

      0... 74'150'000

      0.01… 73'361'050
      Default: 1

      W

      Pnom_ UnitSel

      AV[116]

      Nominal Power in selected unit
      Unit can be selected with object MV[124]

      0… 21'500

      0.01… 73'361'050
      Default: 1

      R

      SpDeltaT_UnitSel

      AV[120]

      Setpoint Delta Temperature in selected unit
      Unit can be selected with object MV[128]

      0…99

      0.01…99
      Default: 1

      W

      SpAbsFlowDeltaT_ UnitSel

      AV[127]

      Setpoint Absolute Flow at Delta T in selected unit
      Unit can be selected with object MV[123]

      0… 360'000

      0… 360'000
      Default: 1

      W

      BusWatchdog

      AV[130]

      Timeout for Bus Watchdog in s
      Non functional. Reserved for future extension

      0…3600
      Default: 0

      0.01…120
      Default: 1

      W

      ErrorState

      AV[140]

      Error State
      No communication to actuator: Communication with actuator not possible.
      Gear disengagement: Gear disengaged button is pressed Actuator cannot move: Mechanical overload due to blocked valve, etc.
      (only available for EV..R+KBAC)
      Reverse flow: Reverse flow is detected
      Flow setpoint not reached: Setpoint cannot be reached within 15 min during flow control
      Flow actual exceeds flow nominal:   Actual flow exceeds the designed nominal flow
      Flow measurement error: Air in the system, error occurred during flow measurement
      Remote temperature not OK: No connection to external temperature sensor
      Flow body temperature not OK: Error with embedded temperature sensor
      Communication to sensor interrupted:   Internal communication to flow sensor interrupted
      Freeze warning: Measured temperature & glycol concentration indicate that grease ice can build up
      Glycol detected: Glycol was detected in a MID application Power setpoint not reached: Setpoint cannot be reached within 15 min during power control

      Bit   0: No communication to actuator
      Bit 1: Gear disengaged Bit 2: Actuator cannot move
      Bit 3: Reverse flow
      Bit 4: Flow setpoint not reached
      Bit 5: Flow with closed valve
      Bit 6: Flow actual exceeds flow nominal
      Bit 7: Flow measurement error
      Bit 8: Remote temperature not OK Bit 9:   Flow body temperature not OK
      Bit10: Communication to Sensor interrupted Bit11: Freeze warning Bit12: Glycol detected
      Bit13: Power setpoint not reached
      Bit14: not used Bit15: not used

      1… 16'383
      Default: 1

      R

      Refer to the Energy Valve Technical Documentation for the energy valve setup instructions.
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