Hi @Mike_Maxwell,
Here is an excerpt from a conversation I had with the engineer in charge of the device handler code on the topic of pressure:
----- October 4th -----
engineer:
The pressure is measured as an absolute barometric pressure at each device
To give meaning to that value, you need the values from the rest of the system, as well as information like barometric pressure in the area due to weather, altitude, etc.
So that’s something that our analytics platform is going to be using, but honestly, using it in SmartThings in a SmartApp may prove difficult
A number that get’s thrown around a lot in HVAC circles is 0.5 inches of water for the maximum static pressure of a system
Which (according to a wolfram alpha serach just now), is 125 Pascals
----- October 5th -----
yracine [9:48 AM]
Just trying to relate the 125 Pa to the measure I get from the vents: I usually get around 102312 Pa or 102.312 kPa which is close to the normal barometric measure of 101.325 kPa at 20 degrees Celsius (NIST) . Should I then subtract the NIST standard measure from the smart Vent’s pressure to compare the difference with the 125 Pa? This doesn’t seem to compute well as I see a difference of around 987 Pa which is well above 125 Pa…
engineer [9:50 AM]
No, like I said, absolute barometric pressure will change with weather and altitude
So it may be hard to use that value in SmartThings because it needs outside data to be useful
yracine [10:49 AM]
I can get outdoor data from my weather station… So, what should I do to translate the 125 Pa and the measure at the vents to something meaningful?
engineer [11:34 AM]
Honestly, I’m not sure you’re going to be able to… You can try subtracting barometric pressure outside from the vent pressure, but even then the number is going to be dependent on altitude (as in, floor vs ceiling vs second story, etc)
As well as inherent offsets in the sensors themselves
It would require baseline readings while the system is on vs off, as well as how closing the vents affects the pressure in that part of the system
We’ve got a lot of data science and analytics going into this, and it’s part of the reason we ended up building our own system instead of just relying on SmartThings
The short version of it is, just make sure you don’t close all the vents in one zone
And for common safety problems the temperature sensor may be what you should be paying attention to
Especially as we get into winter, as a furnace that’s burning too hot is a thing that happens and is easily detectable
I’d have to dig them up but I can get you common temperature values for the air stream coming from the heat exchanger
Regards.