[CCr21] Cooling circuit, precontrol, dewpoint compensated flow temperature control

Plant example CCr21 is a cooling circuit for precontrol.

Functions

Collects cooling requests
Controls flow temperature
Calculates dew point temperature and shifts the flow temperature setpoint

Plant diagram

Components

Pump
Valve
Flow and return temperature sensor
Room temperature sensor and room air humidity sensor
Condensation monitor
Outside air temperature sensor

Components and functions

Components and functions of the plant example:

Component	Function	BACnet object
	Scheduler program Switches the plant to operating mode: Off \| On	[MSchedule] Scheduler
	Operating mode switch Switches the plant to: Auto \| Off \| On	[MI] Operating mode switch
	Manual operating mode selection Switches the plant to: Auto \| Off \| On	[MCnfVal] Manual operating mode selection
	Present operating mode Reports the present operating mode: Off \| On Plant operating modes and control sequence	[MCalcVal] Present operating mode
	Reason for present operating mode Reports the reason for the present operating mode: Exception \| Operating mode switch \| Manual operating mode selection \| Cooling request \| Scheduler	[MCalcVal] Reason for present operating mode
	Demand Reports demand to heat generation: No \| Yes	[BCalcVal] Demand
	Outside air temperature sensor Measures outside temperature.	[AI] Outside air temperature
	Room functions	Room functions (Folder)
	Room temperature sensor Measures room temperature.	> [AI] Room temperature
	Room humidity sensor Measures room air humidity.	> [AI] Room air humidity
	Dew point temperature calculation Calculates the dew point temperature. Increases the dew point temperature, for example, by 1K and corrects the setpoint for the flow temperature.	> [ACalcVal] Dew point temperature
	Condensation monitor Monitors room air humidity Switches the plant off at too high a room humidity, e.g. in the area of chilled ceilings.	[BI] Condensation monitor
	Flow temperature sensor Measures the flow temperature.	[AI] Flow temperature
	Pump	Pump (Folder)
	Command Switches on/off the pump as needed.	> [BO] Command
	Fault message Reports faults. Switches the plant off.	> [BI] Fault
	Pump run when the outside air temperature is low Pump always operates at low outside temperatures (frost protection).
	Kick function (pump kick) Prevents the pump from seizing during long idle periods. [KICKFNCT] Kick function
	Return temperature sensor Measures the return temperature.	[AI] Return temperature
	Mixing valve Mixes the required amount of water from return to flow to achieve the desired flow temperature.	Valve (Folder)
	Temperature controller Controls the flow temperature.	> [Controller] Temperature controller
	Positioning 0% = Bypass … 100% = Through-port	> [AO] Position

Functions and diagrams

Plant example CCr21 is a cooling circuit for precontrol; the flow temperature can be shifted based on dew point temperature.

Outside temperature

The outside temperature [TOa] is unfiltered.

Signal name	Description	Filter constant	Use
TOa	Outside temperature	Unfiltered	Pump run when the outside air temperature is low

Collect cooling requests

Cooling demand can be collected from different consumers. Binary demand messages and analog demand setpoints can also 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.
[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.

Flow temperature control

The setpoint for flow temperature is derived from the lower setpoint for heat requests (SpHReqX) and the flow temperature setpoint.

BACnet objects

Name	Description	Object type	Default value
PrSpTFl	Present flow temperature setpoint	ACalcVal
SpTFl	Flow temperature setpoint	ACnfVal	16 [°C]
TDwp	Dew point temperature	ACalcVal

The dew point temperature is calculated using room temperature and room air humidity. It is increased by 1K which also increases the flow temperature setpoint (maximum selection).

BACnet objects

Name	Description	Object type	Default value
Vlv'TCtr	Temperature controller Controls the flow temperature.	Controller	N/A
The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint [PrSpTFl] against the flow temperature [TFl] and calculates the valve position [Pos] on the output. The following controller variables are preset: - Controller gain: 2.5 [%/K] - Integral action time Tn: 120 [s]

Name

Description

Object type

Default value

Vlv'TCtr

Temperature controller

Controls the flow temperature.

Controller

N/A

The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint [PrSpTFl] against the flow temperature [TFl] and calculates the valve position [Pos] on the output.

The following controller variables are preset:
- Controller gain: 2.5 [%/K]
- Integral action time Tn: 120 [s]

Plant operating modes and control sequence

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
Cooling request (4)
Scheduler (5), resulting from an active scheduler

There is a normal mode and local exception mode.

Normal mode

Sources for normal mode:

[MI] Operating mode switch
[MCnfVal] Manual operating mode selection
Cooling request
[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
Condensation monitor

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'.

Start-up control and alarm handling

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:

Fixed switch-on delay (can be set on input pin [DlySttUp])
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.
Automatic acknowledge (2x) of possible pending alarms during a fixed switch-on delay.
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:

Automatic acknowledge (2x) after startup
Alarm acknowledgement with a value object
Alarm indication:
- For pending alarms On
- For unprocessed alarms flashing
Ability to connect the acknowledge button [BI]
Ability to connect to an alarm indication [BO], e.g. an alarm lamp through an output block [BO]
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

I/O data points

Name	Description	Type	Signal/connection	State text	Engineering unit
OpModSwi	Operating mode switch	MI	N/A	Auto \| Off \| On	N/A
TOa	Outside temperature	AI	LG-Ni1000	N/A	-70...70 [°C]
TFl	Flow temperature Alarm function: Basic (Notification class 8) Limit high 20 [°C]; limit low 4 [°C] Time deviation 30 [s]	AI	LG-Ni1000	N/A	0...100 [°C]
TRt	Return temperature Alarm function: Basic (Notification class 8) Limit high 20 [°C]; limit low 4 [°C] Time deviation 30 [s]	AI	LG-Ni1000	N/A	0...100 [°C]
CdnMon	Condensation monitor Alarm function: Basic (Notification class 8) Reference value: Tripped Time deviation: 0 [s]	BI	NO contact	Normal \| Tripped	N/A
Vlv-Pos	Valve position	AO	0...10V	N/A	0...100 [%]
Pu'Cmd	Pump command	BO	NO contact	Off \| On	N/A
Pu'Flt	Pump fault Alarm function: Extended (Notification class 7) Reference value: Tripped Time deviation 0 [s]	BI	NO contact	Normal \| Tripped	N/A
TR	Room temperature	AI	LG-Ni1000	N/A	0...50 [°C]
HuR	Room air humidity	AI	0...10V	N/A	0...100 [%RH]