Inches per hour and efficiency questions

I just did my first catch cup tests yesterday in one of my zones. Surprisingly it averages out to about .4” per hour. So that really made my run times go way up! Does anyone else think the default of 1” per hour is a pretty high estimate?

My biggest question is how I should setup efficiency. Doesn’t averaging out the catch cups in/hr essentially take care of the whole efficiency thing by balancing out high and low areas? Should I just adjust the efficiency so that the lowest measured catch cup areas will get the indicated amount of precipitation for the day and others will just get more?
For example, if I set 100% efficiency then to get .4” of precip my system will run 1 hour. For zones that were lower than average in the catch cup test they would get less than called for. So should I lower efficiency to get the amount needed in that zone? Wouldn’t lowering the precip rate to the lowest recorded value essentially do the same thing if I just keep efficiency at 100% ?

I can’t say if Rachio’s default of 1" per hour is high or not, but my 4 zones with rotating heads measure 0.24 to 0.55, based on catch cup measurements. On a custom-designed, properly installed system based entirely on manufacturer’s specs, I’m sure 1" is fine. But on new homes with builder-installed systems, things can be very different. Heck, on my son’s new house which is yet to be built on a 7,000 square foot lot, the builder intends to put in only 2 zones!

Drip cup efficiency is defined as the ratio of the average value of the lowest 1/4 of the catch cup readings divided by the average of all the catch cup readings times 100. It can vary wildly, both due to installation and in catch cup location. Mine for the same zones are 39% to 53%. Again, very low.

Yes, as you say, using the average will simply water some area more, and some less, depending on that location’s efficiency or actual local flow. But Rachio thinks that will under-water the low flow areas. And if you calculate the zone’s flow based solely on the lowest flow areas, it will greatly over-water your lawn. Therefore Rachio, no really the entire irrigation industry, has decided to calculate the efficiency as shown above, and then further to adjust the zone’s time by an “Irrigation Factor” I think it’s called (actually think that’s wrong, but it’s some kind of factor), which is fairly complex calculation. Whereas, for say 80% efficiency you might think you should increase the time by a factor of 1 / 0.8 = 1.25, the formula:

Factor = 1 / (0.4 + 0.6 x Efficiency) = 1 (0.4 + 0.6 x 0.8) = 1.14

I’m sure they do that to help prevent TOO much overwatering due to efficiency. Low flow areas will still be lower than they need to and high flow areas will be higher yet, but it’s what they recommend.

As long as my zone’s grass /looks/ pretty even, I leave the efficiency at a default value, maybe 70-80%. If I can SEE a difference, I try to correct the problem. But yes, setting an efficiency lower will increase the time, as mentioned above, giving you more water. I wouldn’t make the Efficiency 100% and increase the water flow. You’ve /measured/ the water flow, and spent time doing it, you know it’s right. I’d change the efficiency to make the proper correction, which is the right way of doing it.

1 Like