hxChart (FB)

FUNCTION_BLOCK hxChart

Short Description

Calculation of state variables of humid air on the basis of the mollier-h, x-diagram

Sizes: enthalpy, dew point temperature, absolute humidity

Typical application: Calculation of the dew point temperature in a zone

Portrayal

Interfaces

Inputs

Name	Datatype	Range	Init-Value	Function
rT	REAL	0.0 bis 50.0		Temperature in degrees Celsius
rH	REAL	0.0 bis 100.0		Relative humidity in percent

Outputs

Name	Datatype	Range	Init-Value	Function
h	REAL			Enthalpy in kJ/kg
x	REAL			Absolute humidity in grams of steam / kilograms of dry air
t	REAL			Dew point temperature in degrees Celsius
xErr	BOOL			Collective fault

Setpoints / Parameters

Name	Datatype	Range	Init-Value	Function
rP	REAL		980.0	Air pressure in mbar

Functional description

General

This function block is used to calculate essential state variables of humid air on the basis of the Mollier-h, x-diagram.

For this purpose, the current values of the air temperature in degrees Celsius and the relative humidity in percent must be transferred.

Ideally, the current air pressure in mbar is available for high accuracy, but it can be adjusted by one of the following methods

Altitude of the measurement location (barometric height formula).

Range of values of temperature in degrees Celsius rT

The temperature in degrees Celsius may only be between 0.0 and +50.0 degrees Celsius (included in each case).

Values outside the value range are automatically corrected to the appropriate limit value.

Range of relative humidity in percent rH

The relative humidity in percent may only assume values between +0.1 and +100.0 percent (each inclusive).

Values outside the value range are automatically corrected to the appropriate limit value.

Collective fault xErr

This output is used to display exceeding of the permissible value ranges.

It is activated (= TRUE) if the temperature in degrees Celsius falls below the limit value +0.0 and / or

or exceeds the limit value +50.0. It is also activated if the relative humidity in percent falls below the limit value +0.1

and / or exceeds the limit value +100.0.

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

Visualization

Information

Element	Authors	Date	Version	Note
Function	Adam Bartod	02.2017	1.0	Initial version
Programming	Adam Bartod	02.2017	1.0	Initial version
Test	Jochen Reu	11.2017	1.0	Initial version
Documentation	Jochen Reu	11.2017	1.0	Initial version

Codesys

InOut:

Scope	Name	Type	Initial	Comment
Input	rT	REAL		Temperature in degrees Celsius
	rH	REAL		Relative humidity in percent
	rP	REAL	980.0	Air pressure in mbar
Output	h	REAL		Enthalpy in kJ/kg
	x	REAL		Absolute humidity in grams of steam / kilograms of dry air
	t	REAL		Dew point temperature in degrees Celsius
	xErr	BOOL		Collective fault

• hxChart.mEx (METH)