I live in a suburb, not far away from the cities Fuerth and Nuremberg in Germany and have an OpenSprinkler DC 3.0 running since mid of May 2018. It operates each day at 7:00 AM and every 2nd day thereafter. It switches three Gardena 24VAC valves in order to water the zones Backyard Lawn, Backyard Flowers and Frontyard Flowers of my garden.
The typical German garden season lasts from mid-March to end-October. There is no need to water the garden during the winter months. To avoid any frost damages to the water system it is also necessary to empty it from any water and to store the valves inside the house in a dry place.
To make use of the Zimmerman algorithm the typical water times for an ‘average’ day have to be defined. For this reason last year’s temperature, humidity and precipitation values as collected by my Netatmo weather station are analyzed in more detail. Please see Attachment “Weather Data 2015”.
The Zimmerman formula assumes a baseline of 21 °C (70 °F), 30% Humidity and 0 mm precipitation. As can be seen from the diagram above this does not represent my typical garden season. The baseline temperature of 21 °C is sufficient. The baseline for the humidity needs to be adapted to 65%. Please see Attachment “Weather Specific Methods”.
If humidity is 65%, temperature is 21°C (70 F), and there is no rain, then it would calculate 0% adjustment, and hence the actual water time is 100% (no change) of the programmed water times. As the weather condition deviates from the baseline, the adjustment will change according to the algorithm. For example, if there is an average humidity of 85%, this results in 65% – 85% = -20% humidity adjustment and 80% actual water time.
There is also a reasonable amount of rain during the year and there should be no watering at all if todays and yesterday’s precipitation sums up to more than 5 mm (0.2 inch) rainfall. For this reason, the Netatmo rain gauge measurements, together with the IFTTT and apilio.io cloud services will be used to compare the measured rainfall against a certain threshold. IFTTT allows for actions when connected to e.g. Time or Netatmo apps. The actions to perform are controlled by applets which forward information and create triggers to apilio.io. The forwarded information is stored and evaluated by apilio.io. The outcome of this triggered evaluation is again handed over to IFTTT applets in order to modify the Open Sprinkler watering program.
The following logic diagram explains the IFTTT applets in combination with the apilio.io Variable, Condition and Logicblock. Please see Attachment “Ample Rainfall Detection”.
Please note that the Logicblock ample_rainfall fires for positive results, even if there are no changes in the result. This allows for multiple rain delays, if there are consecutive days of rain.