OpenSprinkler › Forums › OpenSprinkler Unified Firmware › Penmen-Monteith ETo method python script for possible use as weather script › Reply To: Penmen-Monteith ETo method python script for possible use as weather script
Well, I’ve successfully replicated this logic in perl, and track exactly the same results given the same input set. Shawn thanks again for your help!
I think I understand the logic, but just wanted to double check a few things if that’s OK.
– Today’s ET is the amount of moisture change by plants.
– A positive ET means moisture has been lost, and a negative means that there is a net increase of moisture.
– This is where I’m not that clear: After calculating today’s ET value, the previous days ET is subtracted from today’s ET to calculate the current ET. If we can’t run today for whatever reason (too cold, precipation in forecast), then we write 0’s to today’s run time. We take the current ET – todays_rain – yesterdays irrigation – a forecast adjustment. This gives us our mm target.
– Based on the target, we then look to how many seconds are required per zone to net the ‘water balance’ to 0. So if we have an target of 8mm for grass, and it takes 60 seconds to distribute 1mm of water, then we need to run for 4 minutes.
Did I get it right?