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

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 per kilogram of dry air
rDP	REAL			Dew point temperature in degrees Celsius
xErr	BOOL			Aggregate fault

Setpoints / parameters

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

Function description

General

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

Altitude above 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 rT

The temperature in degrees Celsius may only take values between -20.0 and +50.0 degrees Celsius (inclusive). Values outside the range will be automatically corrected to the appropriate limit.

Relative humidity range in percent rRH

The relative humidity in percent may only take values between +0.1 and +100.0 percent (inclusive). Values outside the range will be automatically corrected to the appropriate limit.

Aggregate fault xErr

This output is used to indicate violations of the permissible 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