[HCcr21] Heating/cooling circuit, precontrol, changeover for heating or cooling

Components and functions of the plant example:

Plant example HCCr21 is a heating/cooling circuit for precontrol and with changeover heating/cooling.

Outside temperature

The outside temperature [TOa] can be unfiltered and filtered.

Function changeover heating/cooling

Changeover is based on three criteria that are prioritized in this sequence:

1. Manual selection (Switch heating/cooling or manual selection heating/cooling)
2. External changeover signal (is read using an input block of type R_B (HCReq))
3. By outside temperature (using the adjustable changeover point to cooling)

The result is mapped as heating/cooling state. Both changeover valves are changed over accordingly.

The plant is stop for the runtime of the changeover valves during changeover.

BACnet objects

Collection of heat requests

The heat request can be gathered from different consumers. Binary demand messages and analog demand setpoints can be collected.

The program receives an input block of type R_B (HReq(1)) that can be linked to a binary demand message via BACnet and an input block of type R_A (SpHReq(1)) for an analog demand setpoint.
[R_B] Read binary
[R_A] Read analog

Additional demand signals can be connected in parallel: Binary to an OR and analog to a MAX block.

Collects cooling requests

The cooling demand can be gathered from different consumers. Binary demand messages and analog demand setpoints can be collected.

The program receives an input block of type R_B (CReq(1)) that can be linked to a binary demand message via BACnet , and an input block of type R_A (SpCReq(1)) for an analog demand setpoint.

Additional demand signals can be connected in parallel: Binary to an OR and analog to a MIN block.

A request that matches the heating/cooling state is processed and switches on the plant.

Controls flow temperature

The plant heating/cooling state determines the flow temperature setpoint and is comprised of the following values:

• The higher setpoint for heat requests (SpHReqX) and the flow temperature setpoint heating
• The lower setpoint for cooling requests (SpCReqX) and the flow temperature setpoint cooling

BACnet objects

BACnet objects controller

If plant power must be reduced, e.g. during charging of the hot water storage tank, connect input [YCtrMax] of the temperature controller heating to a limitation signal, e.g. via BACnet.

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
• Manual operating mode selection (3), resulting from an active (not equal to Auto) manual operating mode selection
• Heat request (4)
• Cooling request (5)
• Scheduler (6), resulting from an active scheduler

There is a normal mode and local exception mode.

Normal operation

Sources for normal mode:

• [MI] Operating mode switch
• [MCnfVal] Manual operating mode selection
• Heat request
• Cooling demand
• [MSchedule] Scheduler

In normal mode, components are simultaneously switched on and off as per the operating mode.

Exception mode

Sources for exception mode:

• Pump fault
• Overtemperature detector

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

Local exception mode (special case for overtemperature detector)

The pump remains on, for example, for 10 minutes if the overtemperature detector is triggered. The pump is then switched off. The outputs [AO] valve position and [BO] pump command are switched at priority 4.

The overrun described above may need to be adapted in the program depending on the application and installation. For example, it may have to be set to 0 for floor heating.

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