OpenSprinkler Forums OpenSprinkler Unified Firmware Do people use Zimmerman?

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    I’m curious, do people really use the option to modify watering times based on the Zimmerman algorithm? The reason I ask is that right now, the system is chopping my watering times all the way back to 12% due to average 60 degree temperature (we are sunny and high of 70 right now, but gets cool at night), and average humidity of around 65%. I’m worried that my lawn in particular isn’t getting enough water.



    I recently installed OpenSprinkler and set it up for the Zimmerman algo. I saw a similar effect where the length of watering is reduced. My solution was to lengthen the run times for the stations, which makes the reduced run times a bit longer. Seems to be working OK for now.



    @Cosmacelf: if the default parameters don’t work for you, you can adjust the zimmerman baseline parameters until the watering percentage it calculates matches your expectation.



    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 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 The forwarded information is stored and evaluated by 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 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.



    When you are determining the initial watering times for your particular location and vegetation take note of the daily averages for temperature and humidity from a nearby weather underground personal weather station.

    For instance you’d like it to water for 10minutes everyday at sunrise, this will be your idealist baseline time. Then the weather for the last week has averaged about 62F and 55% humidity if you exclude “outlier” days. Please note it is important to not include weather that should have been adjusted for. Now use the temp and humidity you found for your location in the adjustment settings with the program set for ideal times. As the weather drifts from your measured data it will adjust the time more appropriately.

    The important thing to remember is the Zimmerman method needs to be set for ideal conditions initially and may take a couple of tries to nail down. Once you’ve tweaked the settings it will down a pretty good job of making adjustments for weather that would be considered abnormal, like high temp low humidity, or random afternoon thunderstorms. It isn’t perfect, but, it’s trade-off is in simplicity of setup. Just check on things once in a while and you’ll find you won’t have any problems after those first few tweaks.

    I spent a while setting up an ET method that is a lot more complicated and it probably just barely outperforms the Zimmerman method in most locations. Where I live in Colorado I did see some nice water savings with ET, however, virtually no where else do they have the incredible unpredictability and crazy swings in weather patterns that we get here. End of the day, I’d recommend the Zimmerman method to anyone, and I’d encourage them to do the small amount of homework needed to see the gains they expect.



    Shawn, thanks for sharing your knowledge. You are right and I see my first adjustment (humidity baseline 65%) as a starting point.

    I have started last year with an OSBee controlled by IFTTT and applets: weather-controlled-sprinkler-system-with-osbee/. I learned from this expierience that the weather forecast is not the best way to control the water times. For example, we have had a lot of afternoon thunderstorms in the last two weeks, resulting in heavy rainfall in nearby places, but no rainfall at all at my home. This means Zimmerman or the ET method are a much more better solution to do sprinkler control than using weather forecasts.

    For the time being I suffer a little bit from the changed Weather Underground policy of not supporting my Netatmo station anymore. I am still investigating nearby weather stations that are still reporting to Weather Underground, but it takes some time to find out if I can rely on their data. That was also the reason for me to make use of my own rain gauge to pause any watering in case of more than 5 mm rainfall measured at my home location.

    It is good to hear that the Zimmerman method needs to be setup for ideal conditions. I will follow your advice and try to find out what are this ideal conditions for my place and what parameters need to be tweaked to make the best out of the Zimmerman method.



    I have changed my and IFTTT applets to reschedule the watering program in case of a rainy day with sufficient rainfall. Instead of setting a custom rain delay time, which stops the watering for e.g. 24 hours, I changed the program to restart the following day. The API command used for this purpose is:


    (Modify existing program, program enabled, use weather adjustment, no restriction, interval day schedule, fixed start time type, runs every 2 days, starting from tomorrow, start at 7:00 AM and the running stations are 1st station – 30 minutes, 2nd station – 30 minutes, 3rd station -30 minutes, program name is Summer2018)

    This seems to be a more realistic approach, as it avoids non-watering periods of more than two days, if there are no further rainy days with ample rainfall. Unfortunately there exists no simple API command to delay (reschedule) a watering program by one day, which makes it necessary to use the Change Program Data command with all parameters for this purpose.

    Again, I carefully have to look at the changes made to my automated sprinkler system. But for the time beeing it looks very promising.



    Please find attached the Excel Sheet (Workbook) I have prepared to visualize the Zimmerman Method %-Watering calculations. It helped me to understand the possible parameter settings available by OpenSprinkler when using the Zimmerman weather adjustment method.





    Very good, You live in Germany, I live in Nord-est Italy
    usually in summer it is hot and there is a lot of humidity. perhaps the temperature value of 21 ° C at 100% is a bit low. I should try to put 24 ° C at 100%
    Then I water the lawn for 3 days with 15mm of water, practically 37 minutes per zone.

    I could try to insert:
    temperature 24 ° = 100%
    rain 7mm = 50%
    humidity 65% = 100%

    what do you think about it?



    I would be careful with the rain parameter and leave it as is 0mm = 100%. It is maybe better to find out if there is enough watering in sunny conditions? If there is a certain amount of rain it’s maybe not necessary to water at all? You can also play with the Excel Sheet to see what will happen.

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OpenSprinkler Forums OpenSprinkler Unified Firmware Do people use Zimmerman?