Trouble with Zimmerman Method

[Greenthunder]

I’m using the Zimmerman method for weather adjustments. I have some questions on setting it up:

1) My temp and rain amounts are in Celcius, the directions for settings show in english units, will it still work for me?

2) In the Weather Adjustments Options show you can set baseline conditions. What should these be set at?

3) There are sensitivity adjustments, how should these be set? The documentation doesn’t mention these.

4) My Weather Underground account is in F but in opensprinkler the values are metric. How to change? Does it matter?

5) What does the response from this mean: http://weather.opensprinkler.com/weather1.py?loc=XX.XXXXX,XX.XXXX&key=XXXX (filled in my GPS and WU key). Just wondering?

Thanks,

Jeff

[Peter]

Jeff,

I added the zimmerman baseline parameters to the OS firmaware a while back and happy to try and answer your questions as below:

1) My temp and rain amounts are in Celcius, the directions for settings show in english units, will it still work for me?

The web app uses the user’s location to determine whether to display weather parameters in imperial or metric in the user interface dialog. So provided I have the location logic correct then you can enter in your baseline settings in locale specific units which the UI will convert to imperial before sending on to the OS Firmware to do its magic.

2) In the Weather Adjustments Options show you can set baseline conditions. What should these be set at?

The basic zimmerman logic is based on shortening/lengthening watering duration depending on whether the weather conditions are above or below an “average” or baseline day. In the default set-up the baseline day is set as 21C, 30% humidity and 0 rainfall. Unfortunately, in London this is not a great match to our average day. Here the weather is colder and more humid so it makes more sense for zimmerman to adjust watering times based on variation from an average London day which is 15C, 70% humidity and 0 rainfall. By configuring a more locally relevant baseline, zimmerman will operate in a more intuitive manner. So the recommendation would be to set the baseline to be your average weather conditions and then set the watering duration for your programs to be the right amount for an average day. Zimmerman will then increase/decrease watering duration based around the local baseline.

3) There are sensitivity adjustments, how should these be set? The documentation doesn’t mention these.

The sensitivity options allow you to further customise the water duration calculation. If you find that the zimmerman logic is not increasing water duration enough in hot weather then you might increase the temperature sensitivity. Alternatively, if you wanted to ignore any change in humidity then you could set the humidity sensitivity to zero. This is where trial and error comes in as you calibrate the system to your specific watering needs/conditions.

4) My Weather Underground account is in F but in opensprinkler the values are metric. How to change? Does it matter?

The weather underground api provides access to both imperial and metric values. As it happens, OpenSprinkler always draws from the imperial values behind the scenes and only converts units back and forward for display purposes in the user interface. So whether you set weather underground to imperial or metric should not matter.

5) What does the response from this mean: http://weather.opensprinkler.com/weather1.py?loc=XX.XXXXX,XX.XXXX&key=XXXX (filled in my GPS and WU key). Just wondering?

The response from the weather server (weather.opensprinkler.com/weather1.py) contains 6 parameters the first and most relevant for here is the “scale” parameter which is the output of the zimmerman calculation as a percentage multiplier that gets applied to the zone water duration (a number between 0-200%). This is what the firmware uses to adjust the watering times when running a watering programme. Another interesting parameter is “rd” or rain delay that tells OpenSprinkler to defer watering if raining. Other parameters help OpenSprinkler understand sunrise/sunset times as well as timezone.

Let me know if any other questions. I am quite interested to hear if people are using the baseline parameters and have any feedback on the way it is setup.

Cheers, Pete

[Steve]

I need help to understand the Zimmerman method in OS. I have done manual calculations on both the “std” default adjustment numbers and my own inserted numbers (I’m on FW 2.1.6 (2)). I am receiving accurate wunderground updates too.

Weather pull:
Min Humidity: 63%
Max Humidity: 97%
Mean Temp: 84.3 F
Precip yesterday and today: 0

on default numbers:
-50% for humidity
+57.2% for temp
0 for rain
Adjusted Watering percentage: 7.2%
What OpenSprinkler calculates: 106%

My real numbers (70 temp, 0 rain, 67 humidity)
-13% for humidity
+57.2% for temp
0 for rain
Adjusted watering percentage: 44.2%
What Opensprinkler calculates: 143%

So does the “adjustment” simply adjust from 100%?

[Ray]

Yes, the adjustment is from 100%. The specific algorithm is explained in this support article:
https://opensprinkler.freshdesk.com/solution/articles/5000017312-using-weather-adjustments

It’s assumed that your water times you set in programs are the typical water times for an ‘average’ day, defined as 30% average humidity, 70 degree F temperature, and no rain fall. Hence if humidity is 30%, temperature is 70 F, and there is no rain, then it would calculate 0% adjustment, and hence the actual water time is 100% (no change) of your programmed water times. As the weather condition deviates from the baseline, the adjustment will change according to the algorithm. In sum, the formula calculates an adjusted percentage that deviates from 100%.

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