> 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/hxchart.md).

# hxChart

## `hxChart` (FB)

FUNCTION\_BLOCK hxChart

### Short description

> Calculation of state variables of moist air based on the Mollier h,x diagram\
> Quantities: enthalpy, dew point temperature, absolute humidity\
> Typical application: calculation of the dew point temperature in a zone

### Representation

<figure><img src="https://2592874069-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FQR4vCFzt6ixgsqlR3pdR%2Fuploads%2Fgit-blob-906072320167f8c1fe8ee104657d5c457c8d5019%2Fimage.png?alt=media" alt=""><figcaption></figcaption></figure>

### Interfaces

#### Inputs

| Name  | Data type | Value range    | Initial value | Function                       |
| ----- | --------- | -------------- | ------------- | ------------------------------ |
| *rT*  | REAL      | -20.0 to +50.0 |               | Temperature in degrees Celsius |
| *rRH* | REAL      | 0.1 to 100.0   |               | Relative humidity in percent   |

#### Outputs

| Name   | Data type | Value range | Initial value | Function                                                        |
| ------ | --------- | ----------- | ------------- | --------------------------------------------------------------- |
| *rH*   | REAL      |             |               | Enthalpy in kJ/kg                                               |
| *rX*   | REAL      |             |               | Absolute humidity in grams of water vapor / kilogram of dry air |
| *rDP*  | REAL      |             |               | Dew point temperature in degrees Celsius                        |
| *xErr* | BOOL      |             |               | Collective fault                                                |

#### Setpoints / Parameters

| Name   | Data type | Value range     | Initial value | Function             |
| ------ | --------- | --------------- | ------------- | -------------------- |
| **rP** | REAL      | 800.0 to 1200.0 | 980           | Air pressure in mbar |

### Functional description

#### General

This function block is used to calculate essential state variables of moist air based on the Mollier h,x diagram.\
For this, the current values of air temperature in degrees Celsius and relative humidity in percent must be provided.\
Ideally, for high accuracy, the current air pressure in mbar is available; however, it can be replaced by a constant adjusted to the altitude of the measuring location (barometric formula).

| Sea level (m) | Air pressure (mbar) | Constant |
| ------------- | ------------------- | -------- |
| 0             | 1013                | 10130    |
| 300           | 980                 | 9800     |
| 400           | 966                 | 9660     |
| 600           | 943                 | 9430     |
| 800           | 921                 | 9210     |
| 1000          | 899                 | 8990     |
| 1500          | 842                 | 8420     |
| 2000          | 795                 | 7950     |

> **Temperature range in degrees Celsius&#x20;*****rT***
>
> The temperature in degrees Celsius may only take values between -20.0 and +50.0 degrees Celsius (inclusive).\
> Values outside the range are automatically corrected to the appropriate limit.
>
> **Relative humidity range in percent&#x20;*****rRH***
>
> Relative humidity in percent may only take values between +0.1 and +100.0 percent (inclusive).\
> Values outside the range are automatically corrected to the appropriate limit.

#### Collective fault *xErr*

This output is used to indicate exceedances of the permitted value ranges.\
It is activated (= TRUE) if the temperature in degrees Celsius falls below the limit -20.0 and/or exceeds the limit\
+50.0. It is also activated if the relative humidity in percent falls below the limit +0.1 and/or exceeds the limit +100.0.\
In all other situations the output is not active (= FALSE).

### CODESYS

InOut:

| Scope       | Name   | Type   | Initial |
| ----------- | ------ | ------ | ------- |
| Input       | `rT`   | `REAL` |         |
| Input       | `rRH`  | `REAL` |         |
| Input Const | `rP`   | `REAL` | 980.0   |
| Output      | `rH`   | `REAL` |         |
| Output      | `rX`   | `REAL` |         |
| Output      | `rDP`  | `REAL` |         |
| Output      | `xErr` | `BOOL` |         |


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