Evaluating Variables- How?

[CFUG]

Looking for some creative guidance on how to program off of variable delta. Example could be to watch for 2 degree difference between initial room temperature and current room T and kill-off furnace.

[pstuart]

On temp change (thermostat program event), set variable "temp" to value of t-stat temp

On temp variable change, check to see if greater than initial temp (+2) (another variable either preset or set at a predefined time) then turn off furnace.

Can do reverse as well.

So, if the initial temp or preset temp is 72 and the current temp is 72 or below, nothing is executed...

If preset temp is 73+, then furnace shuts off

Otherwise, you might need to do a quick custom driver to do some math for you to get your 2 degree math calculation if you want it to always be 2 degrees above the a given temp.

[CFUG]

It's the "plus two" part that is not sinking in. I have all that you mentioned and that works with a +1 degF over final T situ. I need a Tinit + XdegF feature.

[pstuart]

I think you can do that by setting the variable as a number and the action can be a "+ 2" on variable set. Under actions, variables "Var Name" Type of number has simple math as an action. Insert that in your initial temp set action and that should work.

This is on 2.3, didn't check other versions...

[CFUG]

Let me redefine what it is I'm trying to accomplish. Starting room T is var Tinit. Bring the room T up and turn off the heat after a 2 degF rise from Tinit. All of this is being measured at a remote CA relay. I currently do this as a time-based operation but this is too crude to handle even light climatic changes.

Ideally, I would be looking for a "when Tfinal=Tinit+2, set stat to off" to simply state.

[cdnDesigner]

Sounds like you’re almost there.

Create a variable, let’s say Tmax, set it to Tinit then add 2 to it.

When Tinit changes

Set Tmax to value of Tinit

Set Tmax to value of Tmax + 2

When Tcurrent changes

If Tcurrent >= Tmax

Set stat to off

To set Tmax to Tinit and to add 2 to it, select Tmax from the list of variables in the actions pane in the programming page. Below it, also in the actions pane, there's option to set Tmax to value of other variables and just above that there's option to add 2 to it.