> For the complete documentation index, see [llms.txt](https://support.powerio.com/hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.powerio.com/hub/codesys-hvac/en/hvac-library/functionblocks/energy/wetbulbtemperature.md).

# WetBulbTemperature

## `WetBulbTemperature` (FB)

FUNCTION\_BLOCK WetBulbTemperature

### Short description

> Calculation of the wet-bulb temperature in degrees Celsius\
> Quantities: temperature, relative humidity\
> Typical application: calculation of the wet-bulb temperature for adiabatic cooling

### Representation

<figure><img src="/files/3a3c114cd738f18b537a392bc5c903574c538cb3" alt=""><figcaption></figcaption></figure>

### Interfaces

#### Inputs

| Name                | Data type | Value range    | Initial value | Function                       |
| ------------------- | --------- | -------------- | ------------- | ------------------------------ |
| *rTemperature*      | REAL      | -20.0 to +50.0 | 0             | Temperature in degrees Celsius |
| *rRelativeHumidity* | REAL      | 5.0 to 99.0    | 5             | Relative humidity in percent   |

#### Outputs

| Name                  | Data type | Value range | Initial value | Function                                                                                        |
| --------------------- | --------- | ----------- | ------------- | ----------------------------------------------------------------------------------------------- |
| *rWetBulbTemperature* | REAL      |             | 0.0           | Wet-bulb temperature in °C (error: +/- 1.0 percent in the specified temperature/humidity range) |
| *xError*              | BOOL      |             | FALSE         | Output for indicating error states (TRUE = error)                                               |
| *sErrorCode*          | STRING    |             | ‘’            | Output for indicating error messages                                                            |

### Function description

#### General

This function block is used to calculate the wet-bulb temperature in degrees Celsius.\
For this purpose, the current values of air temperature in degrees Celsius and relative humidity in percent must be provided.

> **Temperature range in degrees Celsius&#x20;*****rTemperature***
>
> The temperature in degrees Celsius may only take values between -20.0 and +50.0 degrees Celsius (inclusive).\
> Values outside this range generate an error state ('xError' = TRUE) and a corresponding error message ('xErrorCode').\
> No calculation of the wet-bulb temperature is performed.
>
> **Relative humidity range in percent&#x20;*****rRelativeHumidity***
>
> The relative humidity in percent may only take values between +5.0 and +99.0 percent (inclusive).\
> Values outside this range generate an error state ('xError' = TRUE) and a corresponding error message ('xErrorCode').\
> No calculation of the wet-bulb temperature is performed.

#### Output for indicating error states *xError*

This output is used to indicate error states (= TRUE):

1. Temperature outside the allowable range of temperature in degrees Celsius *rTemperature*
2. Relative humidity outside the allowable range of relative humidity in percent *rRelHumidity*
3. Wet-bulb temperature 'rWetBulbTemperature' > temperature 'rTemperature'
4. Wet-bulb temperature 'rWetBulbTemperature' < (temperature 'rTemperature' - 50.0)

\
In all other situations the output is not active (= FALSE).

#### Output for indicating error messages *sErrorCode*

This output is used to display context-dependent error messages in plain text.

### CODESYS

InOut:

| Scope  | Name                  | Type          | Initial |
| ------ | --------------------- | ------------- | ------- |
| Input  | `rTemperature`        | `REAL`        | 0       |
| Input  | `rRelativeHumidity`   | `REAL`        | 5.0     |
| Output | `rWetBulbTemperature` | `REAL`        | 0       |
| Output | `xError`              | `BOOL`        | FALSE   |
| Output | `sErrorCode`          | `STRING(255)` | ‘’      |


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