[HGen22] Heat generation, 2 boilers with external boiler control (on/off command, setpoint, feedback, common fault)

Overview

The following diagram is a simplified illustration of plant example HGen22.
Sequencing energy generators

Key

Step up/down (1)

Key

Important settings:

• Neutral zone (Nz) = 3 K
• Delay for up impulse (DlyUp) = 10 min
• Delay for down impulse (DlyUp) = 10 min

If the function is enabled, the higher value of the two temperatures in main flow 'TMnFl' and main return 'TMnRt' is selected as the controlled variable. If the measured temperature exits the neutral zone 'Nz' by setpoint 'SpT', an impulse "Step up" or "Step down" is sent over output 'StepUp' or 'StepDn' to power balance. The impulse is sent with a delay. The delays are determined using the settings 'DlyUp' and 'DlyDn'.

There are two cases:

• One or both temperatures drop. Pulse "Step up" is generated.
  Heat generation supplies too little power and/or flow in the consumer circuit is higher than in the generation circuit.
• One or both temperatures increase. Pulse "Step down" is generated.
  Heat generation supplies too much power and/or flow in the consumer circuit is lower than in the generation circuit.

To prevent continued switching prematurely, the evaluation logic is held after each impulse. The enabled heat generator returns its 'TraSta' to "Step up/down". The evaluation logic restarts once the transition state expires.
Step up or step down

Power control and compensation (2)

Key

Important settings:

• Automatic power control and compensation for a loss of power (EnCmpLack) = 1 (see below)

Power control and compensation receive the request from "Step up/down" for more or less power as a result of the pulse "Step up" or "Step down". In this way, Power control and compensation" triggers a change to the following or previous line in the profile table.

"Power control and compensation" then checks whether the change in row in the "profile table" resulted in the desired increase or reduction to the currently produced output. It receives the feedback on input [PwrCap] on the power currently produced and compares it against the value in internal memory [PrPwrCap].

In the event that the desired result does not arrive, "Power control and compensation" changes the row until the desired increase or reduction to current power is reached.

Automatic power compensation in the event of a power shortage [EnCmpLack]: Power shortage is detected based on input [PwrCap] and balanced by sequential steps, e.g. due to a loss of a heat generator due to a fault.
Power control and compensation

Profile table (3)

In the profile table, the sequence is determined for switching on the heat generators. Four different profiles can be created. The entries are entered in each profile so that total power of the enabled heat generators or stages increases as the row number increases.

Function block SELP_8MS determines the profile table.
[SELP_8MS] Profile and table value selection for 8 multistate values

Two profiles are prepared in the example:

Profile 1: Boiler 1 is switched on first.

Boiler 1 (100 KW) is a boiler with own control.

Boiler 2 is added in the following 2 cases:

• The power for boiler 1 is not sufficient
• Boiler 1 is in fault

Profile 2: Boiler 2 is switched on first.

Boiler 2 (100 KW) is a boiler with own control.

It changes over to boiler 1 in the following 2 cases:

• The power for boiler 2 is not sufficient
• Boiler 2 is in fault

A profile changeover is planned in the example, based on the boiler operating hours.

Manual profile selection is also possible.
Profile table

The profile changeover is implemented in function block ROT_8.
[ROT_8] Rotation switch with 8 outputs

Heat generator (Boiler 1 and 2) (4)

The heat generators enabled by the profile table report on available power [PwrCap] to power control and compensation.

They also report in the event of an active change of the power stage, the transient state [TraSta] to "Step up/down". No further "Step up" or "Step down" is triggered during an active transient state.

Key

Boiler 1/2 with external control, single-stage pump, shutoff valve

Operating modes: Off, On, Min.

Settings for power feedback:

Complete the power settings on function block SELMS_R

1 Off = 0 KW

2 On = 100 KW

Settings for feedback of the transient state on the nested chart BoTraSta(1):

Components, sequence, and functions in CMDSEQ_B (Bo1/2)

[CMDSEQ_B] Command sequence for binary

Start sequence

1. The shutoff valve opens. It is further switched if an operating message comes from the shutoff valve on the input pin for CmdSeq(Bo1).
2. The pump and external control coil switch on at the same time (function AND, Group with next aggregate).

Stop sequence

1. External control switches off. It waits for 2 minutes (function Delay).
2. The shutoff valve closes and the pump switches off (Function AND, Group with the next aggregate).

Main pump group, consumer side

The example implements two main pumps, each with a fault message.

The changeover occurs:

• Every 168 hours regardless of operating hours
• Regardless of fault

The changeover is implemented in function block ROT_8.
[ROT_8] Rotation switch with 8 outputs

Setpoint generation and temperature control

Individual heat consumption transmits its heat request and forms the temperature setpoint for main flow as per this heat request. The setpoint is increased slightly and sent to the heat generators.
Setpoint generation

Key

Plant operating modes:

• Off (1)
• On (2)

The operating modes are reported on [MCalcVal] object 'Present operating mode'.

At the same time, the reason for the present operating mode is reported to another [MCalcVal] object:

• Exception (1)
• Operating mode switch (2), resulting from an active (not equal to Auto) operating mode switch
• Operating mode (3), resulting from an active (not equal to Auto) manual operating mode selection
• Heat request (4)

There is a normal mode and exception mode.

Normal operation

Sources for normal mode:

• [MI] Operating mode switch
• [MCnfVal] Manual operating mode selection
• [HReq (1)] Heat request

In normal operation, operating mode 'On', the main pumps are switched on and the logic for boiler sequence operation (step up/down, power control and compensation and profile table) is enabled. The logic for boiler sequence operation controls the individual energy generators using their function blocks CMDSEQ_B.
[CMDSEQ_B] Command sequence for binary

Exception mode

Sources for exception mode:

• Fire detection contact
• Fault to expansion vessel
• Faults to both pumps in the main pump group
• Fault to both boilers

In exception mode, all outputs are switched off directly at priority 5 and the present operating mode is set to 'Off'.

It is reported on input [RpdOff] from all CMDSEQ_B on the energy generators.

Start-up control (nested chart SttUpAlmHdl)

The following functionality is available for an automatic startup of the plant, e.g. after a loss of power and return of power:

1. Fixed switch-on delay (can be set on input pin [DlySttUp])
2. The plant remains off to ensure communications are reliable and cross-check references are triggered. 'Exception' is reported as the reason for the present operating mode.
2. Automatic acknowledge (2x) of possible pending alarms during a fixed switch-on delay.
3. Additional adjustable delay for staged plant ramp-up (can be set on input pin [DlyOn])

Alarm handling (nested chart SttUpAlmHdl)

The state of events on the plant is acquired by BACnet object 'Plant state'. The state is mapped on function block CMN_EVT.
[CMN_EVT] Common event

The following functions are available:

1. Automatic acknowledge (2x) after startup
2. Alarm acknowledgement with a value object
3. Alarm indication:
   - For pending alarms On
   - For unprocessed alarms flashing
4. Ability to connect the acknowledge button [BI]
5. Ability to connect to an alarm indication [BO], e.g. an alarm lamp through an output block [BO]
6. Ability to connect to other alarm handling functions on other plants, e.g. acknowledge button and alarm indication for multiple plants in the same control cabinet

Startup function and alarm handling for flat plants