Adding temperatures in rule script gives unexpected results

[hdr_jgrade (Jason Grade)]

• Platform information:
  • Hardware: Raspberry Pi 3
  • OS: OpenHABian
  • openHAB version: 3.0.2

I am attempting to create some rules for Nest thermostats to change their setpoints (target temperature) on certain conditions. I can create a basic rule to set the setpoint to a specific input value. However, what I actually need is to change the setpoint by an offset (in this case 5 or 10 degrees F). I couldn’t figure out a way to do that using the Rules GUI, so I’m trying to write is as a script in the rule’s actions. The script is simple: get the current thermostat setpoint, add the offset, and reset the setpoint to the new temperature.

Here’s my current test code:

logInfo("TEST Reset Upstairs - Start", "Attempting to reset Upstairs_Setpoint. Current setpoint state = " + Upstairs_Setpoint.state)
  
var setpoint = Upstairs_Setpoint.state as Number
var offset = Cooling_Offset_degF.state as Number
logInfo("TEST Reset Upstairs - Working", "old setpoint = " + setpoint + ", offset = " + offset)

setpoint = setpoint + offset
logInfo("TEST Reset Upstairs - Working", "new setpoint = " + setpoint)
sendCommand(Upstairs_Setpoint, setpoint)

logInfo("TEST Reset Upstairs - End", "Finished resetting Upstairs_Setpoint. New setpoint state = " + Upstairs_Setpoint.state)

And my log file (from /var/log/openhab/openhab.log) gives:

2021-07-07 22:59:31.321 [INFO ] [odel.script.TEST Reset Upstairs - Start] - Attempting to reset Upstairs_Setpoint. Current setpoint state = 89.999996 °F
2021-07-07 22:59:31.331 [INFO ] [el.script.TEST Reset Upstairs - Working] - old setpoint = 89.999996 °F, offset = 5.0 °F
**2021-07-07 22:59:31.341 [INFO ] [el.script.TEST Reset Upstairs - Working] - new setpoint = 563.522220**
2021-07-07 22:59:31.350 [INFO ] [.model.script.TEST Reset Upstairs - End] - Finished resetting Upstairs_Setpoint. New setpoint state = 89.999996 °F
2021-07-07 22:59:31.849 [WARN ] [binding.nest.internal.sdm.api.SDMAPI] - SDM API error: Temperature setpoint is out of range [10.000000, 32.222301] in FAHRENHEIT.

The script seems to execute without error, but it evaluates the temperature addition incorrectly. It evaluates 89.999996 + 5.0 = 563.522220.

After digging around the forums and documentation, I’m guessing this is some kind of unit conversion issue, even though both setpoint and offset are already in degrees F. However, I didn’t find any resolutions from my forum searches. I tried some of the temperature item state conversion methods shown in the Rules totorial at OpenHAB | Rules #Working with item state conversions as such:

setpoint = setpoint|"°F" + offset|"°F"

But that didn’t work either. How would I revise this script to correctly perform the addition?
Below is the complete rule code:

triggers: []
conditions: []
actions:
  - inputs: {}
    id: "1"
    configuration:
      type: application/vnd.openhab.dsl.rule
      script: >-
        logInfo("TEST Reset Upstairs - Start", "Attempting to reset Upstairs_Setpoint.
        Current setpoint state = " + Upstairs_Setpoint.state)
          
        var setpoint = Upstairs_Setpoint.state as Number
        var offset = Cooling_Offset_degF.state as Number
        logInfo("TEST Reset Upstairs - Working", "old setpoint = " + setpoint + ", offset = " + offset)
        setpoint = setpoint + offset
        logInfo("TEST Reset Upstairs - Working", "new setpoint = " + setpoint)
        sendCommand(Upstairs_Setpoint, setpoint)

        logInfo("TEST Reset Upstairs - End", "Finished resetting Upstairs_Setpoint. New setpoint state = " + Upstairs_Setpoint.state)
    type: script.ScriptAction

[rossko57]

Work with Quantity types.

Working with Number:Temperature Items in rules

openHAB provides Quantity Type features, which can seem baffling. On top of that, Temperature type Quantities have a few quirks all of their own. These notes intend to guide the rules author. I’ve shown work examples in DSL rules language, see below for other scripts examples. All have similar features, if different syntax. Knowing what can be done is half the battle. What is a Quantity Type? Simply, Item states and rule variables may contain Quantities - that just means a number AND a unit …

The cause of your problem -

@hdr_jgrade

var setpoint = Upstairs_Setpoint.state as Number

yields a number with units, but this does not behave like a true quantity type in computations.

[hdr_jgrade (Jason Grade)]

Thanks for the link. I figured it was an issue with units, but I wasn’t finding the method for properly converting them. This was very helpful.
I revised my script as such:

var setpoint = (Upstairs_Setpoint.state as QuantityType<Number>).toBigDecimal
var offset = (Cooling_Offset_degF.state as QuantityType<Number>).toBigDecimal

and it is now working!