Two-stage Boiler with Return Temperature Controller (v1.3)
Full Name
Lib.Mervis.v1_3.TwoStageBoilerWithReturnTemp
Description
Block used for controlling the performance of a boiler with a two-stage burner and a circulation pump, where monitoring of the boiler return temperature is necessary.
Required Project References
- Lib.Mervis
Usage Limitations
**Obsolete** - replaced by the block TwoStageBoiler v1.4 and ReturnTempController
Usage in ST
program test
var
twoStageBoiler: lib.mervis.v1_3.TwoStageBoilerWithReturnTemp;
end_var
twoStageBoiler();
end_program
Description of Inputs and Outputs
The function block is derived from the block Lib.Mervis.v1_3.TwoStageBoiler and contains all inputs and outputs that it has. Here, only the added inputs/outputs are listed.
| Inputs | Name | Data Type | Retain | Required Connection | Meaning |
| ReturnTemperature | real | No | Yes | Return water temperature | |
| ReturnSetPoint | real | No | No | Desired return water temperature | |
| ReturnXp | real | No | No | PI controller - proportional band | |
| ReturnTi | real | No | No | PI controller - integral time | |
| ReturnHysteresis | real | No | No | Hysteresis used for switching the short-circuit pump | |
| ReturnControlMethod | ReturnControlMethodType | No | No | Method used to control the return temperature |
| Outputs | Name | Data Type | Meaning |
| SetPointIncrease | real | Calculated increase of the output setpoint | |
| ValveDemand | real | Demand for opening the three-way valve | |
| ShortCircuitPumpDemand | bool | Demand for switching on the short-circuit pump |
Detailed Function Description
The description of burner control is provided in the block Lib.Mervis.v1_3.TwoStageBoiler
This block implements return water temperature control using the following methods:
- Setpoint Increase - The increase is controlled by a simple PI controller which adjusts the setpoint temperature from the cascade controller.
- Three-way valve on return pipe - Here, hot water from the boiler outlet is mixed with cooler water from the heating system, thereby increasing the return water temperature to the boiler.
- Short-circuit pump - The setpoint temperature is increased, and simultaneously, when the difference between the outlet and return water temperatures is less than the set hysteresis, a command to activate the short-circuit pump/valve, connected between the boiler outlet and return pipes, is issued.