Unit °dH could not be parsed to a known unit for Item Number:AmountOfSubstance

[syntacrsc]

When configuring an item of type Number:AmountOfSubstance and specifying to use unit °dH (by adding unit="°dH" in channel-linkage) openHab keeps using unit "mol" and issues a warning message to the log such as:

2024-07-08 11:28:33.129 [WARN ] [penhab.core.library.items.NumberItem] - **Unit '°dH' could not be parsed to a known unit. Keeping old unit 'mol' for item** 'gruenbeckRawWater'.

Also See:
https://community.openhab.org/t/problem-with-unit-dh-for-item-of-type-number-amountofsubstance-using-mol-instead-of-dh/157079

Expected Behavior

The system should use the specified unit °dH as per current documentation in chapter “SI (base unit symbols)”
of https://www.openhab.org/docs/concepts/units-of-measurement.html

Current Behavior

openHab issues a warning message and keeps using the default(?) unit mol

Possible Solution

no clue since I'm by far to novice of a developer to say ;-)

Steps to Reproduce (for Bugs)

setup an item such as:
Number:AmountOfSubstance gruenbeckRawWater "Wasserhärte Rohwasser [%.2f %unit%]" {channel="mqtt:topic:MQTTMosquittoBridge:gruenbeckSoftliqSd21:rawWater", unit="°dH"}
and link it to any channel providing a pure number value

Context

Encountered the issue while creating a widget for my water softener
for context details: see https://community.openhab.org/t/gruenbeck-water-softener-widget/157104

Your Environment

openHab 4.2.0 release build
Raspberry pi 5b 8GB
Debian GNU/Linux 12 (bookworm)
OpenJDK 64-Bit Server VM (build 17.0.11+9-Debian-1deb12u1, mixed mode

[openhab-bot]

This issue has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/gruenbeck-water-softener-widget/157104/5

[jlaur]

I think there is a bug here:

openhab-core/bundles/org.openhab.core/src/main/java/org/openhab/core/library/unit/Units.java

Lines 94 to 95 in 918b4fa

	public static final Unit<AmountOfSubstance> DEUTSCHE_HAERTE = addUnit(new TransformedUnit<>("°dH",
	(Unit<AmountOfSubstance>) MetricPrefix.MILLI(Units.MOLE).divide(Units.LITRE), MultiplyConverter.of(5.6)));

the type-cast looks suspicious and I think this is part of the explanation. You cannot convert mol to °dH, but you can convert mol/l to °dH. I think the problem is that mole is a unit for the amount of substance:

openhab-core/bundles/org.openhab.core/src/main/java/org/openhab/core/library/unit/Units.java

Line 91 in 918b4fa

public static final Unit<AmountOfSubstance> MOLE = addUnit(tech.units.indriya.unit.Units.MOLE);

but moles per liter is a unit of concentration, indicating the number of moles of substance per liter of solution. So the type-cast is forcing DEUTSCHE_HAERTE into a wrong dimension.

I don't think we currently have a dimension for concentration, but this could be added.

@J-N-K might have some more insights/domain knowledge, I have really just been googling this topic without any prior knowledge, so might be complete nonsense. 😉

[jlaur]

I also found this: https://www.snowate.com/knowledge-calculator/knowledge/water-hardness-introduction.html

[J-N-K]

So it should be dimensionless (like ppm).