How do I use catch cup and nozzle data correctly?


#1

I have the GPM rate for all nozzles in my zones as well as data from catch cups.

How do I use this data to correctly enter 1. nozzle types, 2. efficiency and 3. area so it accurately calculates water usage?

For example, one of my zones is as follows:
I have 6 nozzles with a combined output of 14.5gpm.
Total area is 133.97 m2
Cup data in ml with a 16.25in coverage area: 38 25 40 31 35 48 50 41 28 27 32 42 which averages 20.84mm/hour. Is this calculation correct? https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=36.4166ml%2F16.25+square+inch with a 10 minute runtime so multiply by 6.

Right now I just made a custom nozzle for 20.84mm/hour and set the efficiency to 100%, but I know that’s not going to calculate runtimes very well and water usage is not accurate as some of the water gets sprayed outside of the “total area”.

This seems way more complicated than it should be!


#2

Since you have the total GPM for the zone you can get very close in to the precip rate by using this formula:

(96.25 x total GPM) \ Total zone area = precip rate

You could also use this website:


It will calculate everything for you as long as you have the catch cup size in sq in.

Me I just looked at my water meter, ran it for 10 min and calculated precip rate that way, faster than catch cups and probably a little more accurate. I wasn’t to concerned with effic. since I can tweek that and the depletion % to get the results I want.

I do agree with you that this entire process should be much easier to use or at the least much easier to find instructions on how to use it. My hope is that in the next release that they make this entire thing a behind the scenes calculation and you just put in numbers and it does it for you. That way for all the newbie’s it will be easier.


#3

Surprisingly that formula gets close to what I measured with catch cups. Nozzle output should put me at 24.58mm/hour and catch cups measured 21mm/hour on average across the yard.

The calculated efficiency (using the online calculator) does not take into account what the nozzle precipitation rate should be. So I’m confused as to what nozzle rate to enter so that its data is accurate if I enter the calculated 73% efficiency rate.


#4

Great questions! I’ll do my best to address them below:

  1. Nozzle type: I assume you might be referring to the nozzle’s precipitation rate. If so, the equation @cbetguy1 mentioned is correct. I recommend breaking the equation up into a few variables that are easier to calculate. For details, please refer to this support article: http://support.rachio.com/article/316-precipitation-rates
    If you need help determining the nozzle type, please refer to this support article: http://support.rachio.com/article/218-sprinkler-system-components
  2. Efficiency: I also recommend using the website @cbetguy1 mentioned. The Efficiency, also also referred to as Application Efficiency or Distribution Uniformity (DU), tells us how efficient the water is being distributed by the sprinklers. The lower the DU the higher the run time needs to be to deliver enough water to the area with the weakest coverage. For additional information on variables that affect Efficiency, please refer to this support article: http://support.rachio.com/article/304-advanced-zone-setttings. You should calculate the Efficiency on a zone by zone basis, not system wide. A 73% efficiency rating is acceptable, but should not be factored against the precipitation rate calculated in #1 (above) as the app does this for you using the Irrigation Association’s scheduling multiplier (SM=10.4+0.6×DUlq) over distribution uniformity as the basic for determining gross water to apply. The reason for this is that the scheduling multiplier reduces overwatering in cases of very poor distribution uniformity, and it takes into account the capillary movement of water through soil.
  3. Area (square footage): This is also a separate calculation that only affects the water usage reports in the app. For details, please refer to this support article: http://support.rachio.com/article/383-how-we-calculate-water-usage. For a quick, easy way to calculate your zone’s square footage without having to drag around the tape measure, I recommend using this free website: http://www.findlotsize.com/

Sorry for any confusion, these should be entered as separate values on a zone by zone basis. I believe you mentioned you calculated a nozzle output of 21-25 mm/hour & efficiency rate of 73% …do you have one zone? Or multiple zones?

Hope this helps! Let me know if you have any questions.

Best, Emil


#5

Thanks @emil. So when entering the nozzle precipitation, if I use the calculated one based on GPM, it’s actually higher than what is actually sprayed on the lawn. I may be splitting hairs as this point for real world results, but the 73% efficiency doesn’t indicate how much water is put on the lawn.

Would it be more accurate to reduce the nozzle precipitation rate to match what the catch cup data is or adjust the efficiency down?