Please explain exactly how the Total watering inches in a zone is calculated

So I have had my controller three weeks now and I absolutely love it. Now I am starting to try to improve the watering estimates. So…first of many questions I will ask and couldn’t get a clear answer that I could find in previous posts:

I have two zones that are spray heads at 180 degrees and completely overlap the opposite zone in a long outlawn by the road. How does Rachio determine how many inches of water that area received? What is the best way for me to set it up? Following notes for more clarity:

1 - right now I told Rachio that the area is half of what it really is. Does Rachio use the area of the zone in the calculation based on a volumetric flow of the number of heads? Or am I missing how it calculates the amount of water delivered?

2 - when the corner heads are 90degrees and the middle heads are 120 degrees so I need to tell the controller that for any assumption on water volume?

3 - does the yard map at all figure into the calculations? It seems to feed total area in but is that it? Is yard map mainly for show😊

4 - does Rachio just assume the heads were installed perfectly and that the amount is inches per hour of the head design in an average diameter? This would seem to be a poor assumption for a smart system but if I can modify my settings to correct, I can do that.

Thank you for any help and clarifications for me on this question and my comments and understanding.

Using Flex Daily, the watering inches each time Rachio waters is calculated only from the Soil Available Water, the Allowed Depletion and the Root Depth for each zone. For mine, that’s 0.17" x 6" x 0.5 = 0.42".

Once the amount of water desired is known, the time to water is then based on the zone’s spray head Efficiency and the Nozzle Inches per Hour entry. For 80% efficiency and 1" per hour the time would be 0.42 (above) / (0.4 + 0.6 x Efficiency) / 1"/hr = .477 hours = 29 minutes. This will change depending on the zone’s Sunlight, but I’m not sure how.

With Flex Daily, then, the Frequency of watering the determined amount is determined by the Crop Evapotranspiration value, determined by the Crop Coefficient and the Weather.

While times will be proportional, Flex Monthly may/will water a different amount, as it determines how much and how often to water differently.

Notice that none of this depended on the Area of the zone (not used by Rachio except in calculating savings), number or spacing of sprinkler heads (water flow is determined only by the Nozzle Inches per Hour factor, based on head type or fine-tuned based on your measurements).

The Yard Map will input the zone’s area, but again, that is not used directly by the program. It helps if you want to fine-tune Nozzle Flow Inches per Hour which can be calculated from the actual gallons or cubic feet of water used during a given time divided by the area of the zone. You can also calculate it from catch cups.

For spray head Rachio uses average flow Nozzle Inches per Hour and Efficiency for different spray head types. I have found that my actual values differ greatly from their assumed values, probably because my irrigation system is not very well done.

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Thanks for the help. So basically I need to just put some cups out and get actual water rates then and I put that in the zone.

Anyone ever try to measure total GPM by watching your city meter while the zone is running and then calculate over the zone area?

One more question: since there are two zones that overlap, does it work correctly to set the rate at twice what it really is so it doesn’t double the water to the area because the two zones overlap completely?

It can be simple, but usually calibrated catch cups are used, usually at least 12 per zone, spaced at specific locations, and input into an online or other calculate that does all the calculations including efficiencies. I’ve done that with my zones, but found that the exact placement of the cups can greatly affect the results, so don’t care for it.

Yes, in fact I prefer this message. Using your water meter, you can measure gallons over a given number of minutes to calculate total GPM (PER ZONE). Then, if you measure the area of the zone, either manually, using a mapping program or using the app, you can calculate Nozzle Inches per Hour from:

Nozzle Inches per Hour = Gallons / Minutes / Area (in sq ft) x 96.25.

This method doesn’t give you efficiency, but it’s not as critical (to me) and can be guessed at.

If two zones overlap completely, that is two zones water the exact same area, then it can approach double the rate. But normally, zones just slightly overlap, so I just try to judge the best outline of the zone where they overlap and estimate area based on that.

It might be worth posting exactly how the zones overlap for a better answer.

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Thank you very much, I think I understand it all now.

Here is a picture of the outlawn I mean:image|375x500

The cups are there in the picture because I tried that as it ran overnight in early morning. But in this outlawn there are ten spray nozzles on each side of lawn placed exactly across from each other. Each nozzle basically reaches the other side and the next nozzle. I will do the water meter next time to validate but for now I did this cup method.

I put cups out with a rock to hold steady, then both sides ran around 4:00 am. Then in morning, I weighed the water out of each cup and used the 3” diameter top as the collection area. There was a large deviation but I averaged 1.66 in/hr per cup which would be both zones watering. Then dividing by the zone efficiency number to ensure it doesn’t apply to this actual measurement, I get 2.08 in/hr. I put this in for each zone and then I assume it will run half the time on each zone to get this full amount.

I then used the water meter method on another zone that overlaps with each other and has rotors this morning and used the cups at same time. I ran them for ten minutes and measured the city meter volume. Then based on the area of the total zone calculated by me drawing on the yard map, I get 0.43 in/hr by the meter. Then by weighing the mass of water in cups (1cc/g), I got 0.69 in/hr with both zones total, dividing by efficiency number I get 0.98. Since this is both zones running, dividing by two is 0.49 which I think is surprisingly close correlation between actual meter and cup measurements.

So for this zone I will use the meter number and leave the standard efficiency and put 2x in for each zone (0.86 in/hr) so it will accurately estimate total when they both run.

I think this should be correct.

I would recommend Rachio clearly articulate this in their documentation because it is easy to assume the calculations are more rigorous than they are (in fact I wish they were more rigorous). I know some people complain. It is too complicated but, in my opinion, it needs to be to be so accurate in moisture, I bought it for that, if I want simple I would buy a rain bird.

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All good information, mdtelgen. Thanks for posting that.

I have a concern with your situation, and I’m not sure how to solve it. The main problem is that you have two zones watering the same grass area. Admittedly, the two cooperate to give better and more even coverage, but for the most part, they water the same grass.

My concern is if the two zones get unsynchronized, that is, not occurring the same day. (Bear with me, I’m just thinking about it here, so not sure where this is going). Even seemingly identical zones don’t always water on the same day. While a heavy rain will sync them, over time, especially long dry times, 2 zones can end up watering different days. In your case, that would mean watering the same zone twice as often, with half the water, but not overall distributed as well. So instead of watering a good amount say every 2 days, it might water half that amount every day, which is bad for the grass.

Thinking further on that, as long as the zones start out the same, and ALL your zone settings on these two zones be IDENTICAL. This will force Rachio to water the exact same amount at one time, and will result in a calculating ET value being the same as well, so frequency should be the same. I would also keep Nozzle Inches per Hour and efficiency are the same, so they’ll run the same amount of time. If they differ actually, I’d use an average number. And I’d double the average Nozzle Inches per Hour you get, so that each zone will run half the time needed in total.

Hope this helps. Confusing myself a bit at this point.

I have two zones with this exact same problem (where the zones almost totally overlap} and I did what @rraisley recommended. That seems to work pretty well for me, but it’s not perfect as each zone has one head on it that doesn’t totally overlap with the other zone. I decided it was best just to let that bit of grass have a little less water rather than too much water on the majority of the two zones. Why the installer set it up this way is totally beyond me!

I did set up the two zones exactly the same and have had installed for a few weeks now and the two zones seem to follow each other exactly so I think it should work okay. One had only slightly more in/hr than the other when measured by the city water meter so I just averaged them and set for both of them.

Thanks for all the help this was really good.

P.S. going through the actual measurements, I found my backyard zone default parameters from Rachio was almost 3X actual so I have been significantly under watering. In fact I am sure I have for many years even with my manual controller I used to have.

I found that as well. I think that many irrigation systems installed by builders are not up to snuff (I know mine isn’t), so don’t obey the same rules that well designed systems do.