Search
MENU
  • Expressions
  • System architecture by project type
  • Users and Permissions
  • Regulation of Boiler Cascade

    Use this setup if you want to achieve desired temperature of hydronic circuit using 2 or more boilers connected in cascade.

    In the example scenario, we will show configuration for 3 boilers, that can be controlled by digital outputs.

    Preparations

    You should already have following devices defined:

    Thermostat with temperature of returning water, measured on the pipe

    Thermostat

    Digital outputs for each boiler (Boiler A, Boiler B, Boiler C)

    Boiler ABoiler BBoiler C

    Create virtual Analog Output that will be used as a variable for calculating overall heat output.

    Overall Output

    Basic configuration

    Create Smart Rule Temperature PID Controller that will calculate Overall Output based on difference in Thermostat Set point and Actual temperature

    Input device

    → Smart Rule →

    Output device

    Thermostat

    → PID Controller→

    P = 2
    I = 0.2
    D = 0

    Overall Output

    Based on overall output ranges, 3 (or more) boilers will be turned on
    Configuration for mode where priority of boilers is: Boiler A → Boiler B → Boiler C

    Input device

    • Overall Output

    → Smart Rule →

    • Equation

    Output device

    • Boiler
    <1%

    --

    --

    >1%

    Equation:
    If Overall Output > 0.01

    Minimum duration: 5min

    TRUE: Turn on Boiler A
    FALSE: Turn off Boiler A

    >45%

    Equation:
    If Overall Output > 0.45

    Minimum duration: 5min

    >90%

    Equation:
    If Overall Output > 0.90

    Minimum duration: 5min

    Cycling of boilers

    In order to achieve even usage of boilers, extra configuration needs to be applied.

    Create Multi-value switch with N+1 states, where N is number of boilers. Last state can be defined as Heating Inactive system with zero heating.

    Name: Boiler Priority


    States:

    • Priority A (Boiler A → Boiler B → Boiler C)
    • Priority B (Boiler B → Boiler C → Boiler A)
    • Priority C (Boiler C → Boiler A → Boiler B)
    • Heating Inactive


    Create Smart Rule Sequencer that will rotate priorities (A → B → C → A → ... )

    Input device

    → Smart Rule →

    Output device

    Virtual push button to start the sequencer

    Sequencer
    Step 1: Priority A
    (duration 18 hours)
    Step 2: Priority B
    (duration 18 hours)
    Step 3: Priority C
    (duration 18 hours)



    (tick) 

    (/) Rotate sequence

    Boiler Priority


    Define separate set of smartrules limited for each Boiler Priority. See Smart Rules for Priority A in table below:

    Input device

    • Overall Output

    → Smart Rule →

    • Equation

    Output device

    • Boiler

    Limiting Condition

    <1%

    --

    --


    >1%

    Equation:
    If Overall Output > 0.01



    TRUE: Turn on Boiler A
    FALSE: Turn off Boiler A

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority A
    >45%

    Equation:
    If Overall Output > 0.45



    TRUE: Turn on Boiler B
    FALSE: Turn off Boiler B

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority A
    >90%

    Equation:
    If Overall Output > 0.90

    TRUE: Turn on Boiler C
    FALSE: Turn off Boiler C

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority A

    Similar set of Smart Ruless should be applied with Limiting Condition for Priority B and Priority C:

    Input device

    • Overall Output

    → Smart Rule →

    • Equation

    Output device

    • Boiler

    Limiting Condition

    <1%

    --

    --


    >1%

    Equation:
    If Overall Output > 0.01



    TRUE: Turn on Boiler B
    FALSE: Turn off Boiler B

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority B
    >45%

    Equation:
    If Overall Output > 0.45



    TRUE: Turn on Boiler C
    FALSE: Turn off Boiler C

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority B
    >90%

    Equation:
    If Overall Output > 0.90

    TRUE: Turn on Boiler A
    FALSE: Turn off Boiler A

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority B

    Input device

    • Overall Output

    → Smart Rule →

    • Equation

    Output device

    • Boiler

    Limiting Condition

    <1%

    --

    --


    >1%

    Equation:
    If Overall Output > 0.01



    TRUE: Turn on Boiler C
    FALSE: Turn off Boiler C

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority C
    >45%

    Equation:
    If Overall Output > 0.45



    TRUE: Turn on Boiler A
    FALSE: Turn off Boiler A

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority C
    >90%

    Equation:
    If Overall Output > 0.90

    TRUE: Turn on Boiler B
    FALSE: Turn off Boiler B

    Type: Multi-Value Switch
    Smart Rule will only work if...

    • Boiler Priority is set to Priority C