This topic contains 13 replies, has 6 voices, and was last updated by  Ray 4 years, 3 months ago.

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  • #38471

    geewizard
    Participant

    Are there any references on the Zimmerman method? I understand what parameters it’s based on but I’d like to know if there are scientific references from which Rich Zimmerman came up with his formula.

    • This topic was modified 4 years, 4 months ago by  geewizard.
    #38473

    Samer
    Keymaster

    Richard Zimmerman is a forum member here who first introduced the weather adjustment feature in his code (explained here: https://github.com/rszimm/sprinklers_pi/wiki/Weather-adjustments) and we have since incorporated it into the main code base (Unified firmware) due to the feedback from users. As far as references go, I don’t think either one of us could provide much past what Richard Zimmerman has documented.

    #38493

    ShawnHarte
    Participant

    Though I don’t know if he based his calculation method on any one scientific source, if you take a look at the Hargreaves papers, a lot of the methods are similar. So whether or not, he used the information as a source he ended up on the same path.

    #38522

    geewizard
    Participant

    Do you have any links to the Hargreaves papers you refer too?

    The MAJOR reasons I bought an OpenSprinkler are the option to use my own WU weather station for input with the Zimmerman Method, the web interface, and the security of NOT having a device depending on the cloud like the Rachio and Blossom controllers.

    I assumed the Zimmerman method was based on scientific study of irrigation using past and present weather data. I sure would like to know what Richard Zimmerman based his code on.

    Don’t get me wrong, OpenSprinkler is wonderful and I wouldn’t trade it for anything. I just want to know more about the Zimmerman Method.

    • This reply was modified 4 years, 3 months ago by  geewizard.
    • This reply was modified 4 years, 3 months ago by  geewizard.
    #38533

    ShawnHarte
    Participant

    http://agsys.cra-cin.it/tools/evapotranspiration/help/Hargreaves.html There is a link, to the original works there, and a derivative work from Allen. Both are used to estimate ET with missing information. You would need an ASCE login for access to the papers there, if you don’t want to pay for that, http://www.iwhr.com/download/li080827-yoder.pdf is a nice abstract comparing and defining the evolution of a standard ET calculation. If you work out the base equations with a bit of dummy data, you will see a trend that is close to what the zimmerman method provides with the same data and his base weighting of inputs.
    Zimmerman uses 3 pieces of data: Mean humidity ( defined as (min+max)/2 ), mean temp, and precipitation.
    They are weighted in the following manner:
    30 – mean humidity
    (mean temp – 70)*4
    Precipitation * 200
    Those are all divided by 100 and added together, then 100 is added for a scale, which is then bound to 0 to 200.
    Scientifically it appears to have no direct supporting work, however, it works out close to a couple ET calculations for inland areas free of high humidity influence. It is quite close to Hargreaves formula using only temperature, the formula is in the first link provided.

    #38543

    geewizard
    Participant

    That helps a lot, thanks.

    #38549

    aruzsi
    Participant

    I want to ask why my weather adjustment percent is 137% if the parameters are:
    min hum.: 46%; max. hum.: 77%, temp.: 20,8C and percipitation: 0mm/–
    I tried to evaluate and I think it is -31,5% (I used 20,8C/~70F.)

    I have never seen other percipitation value except 0.0mm/–.
    Humidity and temperature values are changing.
    I use Weather API, Budapest Soroksár XXIII.

    Usually the adjustment percent remains the same many days and the weather conditions
    were changed (sunny and hot days after rainy and cold period or opposite).

    TIA,

    #38550

    aruzsi
    Participant

    I changed my weather info source to Taksony.
    Values are:
    min:56%
    max:83%
    temp:20,3C
    perc:0.0/–
    Counted percentage: 137%! Is that correct?

    TIA,

    #38552

    Ray
    Keymaster

    If you are using a recently firmware, can you also report the ‘Last Successful Weather Call’ time stamp? The 137% is the number reported by the controller, so if the controller hasn’t successfully received updated weather data that number may be outdated.

    #38563

    aruzsi
    Participant

    My version is 2.1.3.

    #38564

    Samer
    Keymaster

    Then can you please update to the latest version? As the latest forum posts have indicated there is a bug in firmware prior to 2.1.5 that would cause the weather not to update after a period of time. If you can’t update, a reboot of the controller will update the values.

    #38565

    aruzsi
    Participant

    OK.
    I try it.
    Upgrading firmware is very unconvenient over USB. It was hard for me last time.

    #38840

    joe
    Participant

    I created a key and selected the zimmerman formula.

    I live on Long Island NY.

    With regards to the weather adjustments, how is this used?

    I have the defaults of 100,100,100 temp,rain,humidity.

    How and for what are these values changed? Sorry confused.

    #38862

    Ray
    Keymaster

    The three numbers are used to adjust the relative weight of each factor: temperature, rain, humidity. In the past users have reported that the default weights used by the Zimmerman method is too aggressive (e.g. the watering level reduces too dramatically with respect to temperature change). Therefore we provided the ability to change the weights. You can leave them as is (100%), but if you feel any of the factors should have less influence on the watering level, you can suitably reduce the weight.

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