Hi Shawn
thank’s for your immediate and comprehensive answer.
Since you have been very detailed your explanations , I would like to describe to you what I have done in my code , hoping to get some advice and suggestions.
I have started last year to try to automatize my garden irrigation system consisting in several units about 100mt away from my home.
I was thinking to use Arduinos that I normally use and program. Then I discovered ESP8266 and OpenSprinkler and I understood that porting OpenSprinkler to ESP8266 was the way to go! I have completed the porting 3-4 month ago and I have now 5 units running 24h a day.
But I am missing a tool to manage those units (checking status and functions of the units and regulate intervals depending on weather).
I started that my OpenSprikler Manager that will be ready for first upload to GitHub soon. The code measure the water flow from the main supply valve and is WiFi connected to all the units, with Api calls. This way if the flow for a certain interval is not correct will warn that the unit or the irrigation devices are not working correctly.
Coming to the weather controls routines ….I am reading WU json /conditions/pws:XXXXXX output and recording temperatures,humidity,wind,rain and sun radiation.
I have followed tightly the Allen-Pereira :Crop evapotranspiration – Guidelines for computing crop water requirements – FAO Irrigation and drainage paper 56. It provide all needed info to compute irrigation needs. A comprehensive database is included of different crop behaviours and assumptions to be taken.
According to the above I have evaluated actual daily ET0 and used Kc parameters for the areas with different (from grass) vegetations.
The ET0 equations are straight forward…. but measured sunrad is sometime unreliable…therefore I have corrected the reading if are very far from clear sky radiation . This lead to good result that shown daily values ranging fro 1.9 to 4.5 ( I live in Italy!).
I was thinking anyhow to get some local measurement to verify those values or using a solar panel or using the “pan evaporation” method applied to my swimming pool.
Those calculations are used to draw a water balance versus time plot of the different zone so that water shortages can be easily seen and corrected .
The programs correction can be done automatically , but I prefer supervision and manual controls of the units ( at least at this time!).
I look forwards to your welcome comments
Paolo