====== Return Temperature Controller for Boiler Blocks (v2.0) ======

{{:en:mervis-ide:35-help:returntempcontroller.png}}

==== Full Name ====

Lib.Mervis.v2_0.ReturnTempController

==== Required Project References ====

  * Lib.Mervis

===== Description =====

Auxiliary block for boilers used for controlling the return water temperature.

===== Usage in ST =====

<code>
program test
    var
        returntempctrl: lib.mervis.v2_0.ReturnTempController;
    end_var

    returntempctrl();
end_program
</code>

===== Inputs =====

|Name                                                         |Data Type|Retain|Mandatory to Connect                                   |Meaning|
|Demand           |[[..:025-two-stage-boilers:stagecontroltype_v2.0.htm|Lib.Mervis.v2_0.StageControlType]]|No        |Yes   |                                                 |      |
|State            |[[..:025-two-stage-boilers:stageinfotype_v2.0.htm|Lib.Mervis.v2_0.StageInfoType]]      |No        |Yes   |                                                 |      |
|ReturnTemperature|real                                                          |No        |No    |Return water temperature                              |      |
|SetPoint         |real                                                          |No        |No    |Desired return water temperature                       |      |
|Xp               |real                                                          |No        |No    |PI controller - proportional band width                       |      |
|Ti               |real                                                          |No        |No    |PI controller - integral time constant              |      |
|Hysteresis       |real                                                          |No        |No    |Hysteresis used for switching the short-circuit pump|      |
|ControlMethod    |[[..:025-two-stage-boilers:returncontrolmethodtype.htm|ReturnControlMethodType]]       |No        |No    |Method used for controlling the return water temperature       |      |

===== Outputs =====

|Name|Data Type                                |Meaning|
|MinimalSetpoint       |real |Calculated minimum desired output temperature|      |
|SetPointIncrease      |real |Calculated increase in desired output temperature |      |
|ValveDemand           |real |Request to open the three-way valve|      |
|ShortCircuitPumpDemand|bool |Request to activate the short-circuit pump  |      |

===== Detailed Function Description =====

The block implements control of the return water temperature using the following methods:

  * //Increasing Desired Temperature// - The increase is controlled by a simple [[..:025-two-stage-boilers:simplepicontrollerwithen_v1.2.htm|PI controller]], which adjusts the desired temperature from the [[..:025-two-stage-boilers:cascadecontroller_v2.0.htm|cascade controller]].
  * //Three-way Valve in the Return Line// - Here, hot water from the boiler output is mixed with cooler water from the heating system, thereby increasing the return water temperature to the boiler.
  * //Short-circuit Pump// - Used to increase the desired temperature, and simultaneously, when the difference between the output and return water temperatures is less than the set hysteresis, it activates the command for the short-circuit pump/valve connected between the boiler output and return lines.

===== Versions =====

{{indexmenu>.010-returntempcontroller#2}}