HVAC (concept)

KNX standardized HVAC Functional Blocks

The arrows have according to these Functional Blocks the following meaning :

• Green
  • HMI output : User Setpoint
  • HC output : Actual Setpoint
• Blue
  • RTSM input : HVAC Mode, e.g. time-based
  • RTSM output : Effective Setpoint
• Red
  • HC output : valve settings
  • HMI output : room temperature
• Black
  • HE output : heat/cool status
  • HE input : outside temperature
• Orange
  • window status (optional)
  • presence status (optional)

The HVAC buildings functions of KNX Virtual are based on these KNX standardized Functional Blocks, i.e. this means that the following devices are involved :

1. A push button (HMI) in order to send :
   • the 'User Setpoint', i.e. to send the expected temperature of the room in question to the bus:
     
     • D4 for room1
     • D21 for room21
     • D22 for room22
     • D23 for room23
     • D24 for room24
     • each push button compares the User Setpoint with the Actual Setpoint, any difference is indicated with cyan as back color
     • D4 can also indicate the outside temperature (via D12)
     • D21, D22, D23 & D24 cannot indicate the outside temperature
   • the actual temperature in the room as feedback for the heat controller (D16)
2. The setpoint manager (D15) :
   
   • in order to define per channel the 'Effective Setpoint' based on:
     • the User Setpoint
     • window status (optional)
     • presence status (optional)
   • 1 channel represents 1 room
3. The heat controller (D16) :
   • in order per channel to:
     • set & send the valve positions and 'Actual Setpoint' based on
       • the Effective Setpoint
       • the actual temperature in the room
     • each Actual Setpoint sent serves as feedback for the push buttons (HMI)
   • the heat/cool status (1 per channel) is directly influenced by the heat exchanger (D17)
   • 1 channel represents 1 room
4. The heat exchanger (D17) :
   • this device produces the required energy in order to exchange heat in each room and consists out of 5 separate units (1 per room)
   • each individual heat exchanger unit :
     
     • is controlled via 2 valves which are connected to the valve actuator (D6)
     • one valve serves the purpose of adding heat to the room
     • one valve serves the purpose of extracting heat from the room
   • the heat/cool status of this device depends on the outside temperature (D12)
     
     • if the outside temperature < 22° C : heat/cool status = heat
     • if the outside temperature > 22° C : heat/cool status = cool
5. The valves of the valve actuator (D6) are connected as follows :
   • channel 1 controls the valves of the heat exchanger unit in room1
   • channel 2 controls the valves of the heat exchanger unit in room21
   • channel 3 controls the valves of the heat exchanger unit in room22
   • channel 4 controls the valves of the heat exchanger unit in room23
   • channel 5 controls the valves of the heat exchanger unit in room24
   • channels 6, 7 & 8 are not used
6. The weather module (D12) in order to send the outside temperature to the bus

Further details:

• A User Setpoint involves 3 objects (per device/room) :
  • HVAC Mode : DPT 20.102
  • Temperature Room Setpoints - Heat : DPT 275.100
    • contains 4 values : comfort, standy, economy (*) and protection
  • Temperature Room Setpoints - Cool : DPT 275.100
    • contains 4 values : comfort, standy, economy (*) and protection
• An Effective Setpoint involves 3 objects (per device/room) :
  • HVAC Mode : DPT 20.102
  • Temperature Room Setpoint - Heat : DPT 9.001
  • Temperature Room Setpoint - Cool : DPT 9.001
• An Actual Setpoint involves 3 objects (per device/room) :
  • Heat/Cool Mode (**) : DPT 1.100
  • HVAC Mode : DPT 20.102
  • Temperature Room Setpoint : DPT 9.001

• (*) not implemented in KNX Virtual, i.e. value is set to zero
• (**) not to be confused with Heat/Cool Status of the heat exchanger, i.e. heat/cool mode is a link between a push button (HMI) and the heat controller whereas heat/cool status a link is between the heat exchanger and the heat controller