# Zone Area

I’m configuring my new Iro for the first time and when setting up zones, I see the Area option in the advanced settings. I did some reading on the website and it basically said that if you don’t know what you are doing, don’t change any of the advanced options.

I was thinking that zone area would be one of the most important factors in determining how long to run a zone. For instance, my front yard is half the size of my side yard. Naturally, running both for the same amount of time would result in twice the amount of water per square foot in my front yard than it would be in my side yard.

Am I thinking about this the wrong way? Is the square footage of grass in a zone not that important in the calculations? If it is important, then why is it tucked away under Advanced Settings?

@Ed3120 The zone square footage is used for estimating your water usage. One of the more important data points for calculating duration (and usage) is the nozzle inches per hour which you can select a default nozzle from, or even create your own custom nozzle type in your personal nozzle library!

The equation we use to estimate water usage is based on this article (Total Area Method Formula)

http://www.sprinklerwarehouse.com/DIY-Calculating-Precipitation-Rate-s/7942.htm

Would it be possible/worthwhile to provide an option for the user to measure the actual usage and use that number to configure the water Iro software?

Out here in CA they are going to be severely restricting water usage so I’ve got familiar with reading my meter. Its not hard, the dial measures CCF (748 gallons) in white digits and hundredths of a CCF in black. If you want to be real accurate there’s a dial that makes 1 revolution per 7.48 gallons, but I didn’t use that. I just ran a zone for 4 minutes and saw how many hundredths of a CCF I used, divided by 4, and voila. Meters probably differ around the country, but the local water company usually provides the details on how to read them online.

Hi @mikeT, good evening. Great idea! I’d like to brainstorm them a bit with you if you’re open to it…

Could you share this number with us? I’d like to run a few numbers.

Thanks, Emil

If I set my zone square footage to 2000 sq ft and create a new watering time, it defaults to 25 minutes. If I set my zone square footage to 200 sq ft and create a new watering time, it still defaults to 25 minutes. In the second case, my lawn would get 1/10th the water per sq ft.

What is driving that 25 minute number and why doesn’t it change based on area?

Hi @emil,

My water meter looks like the one in figure 2 of http://h2ouse.org/resources/meter/index.cfm I read it as 424.17 and after 4 minutes as 424.24. The difference is .07 which is 52 gallons, so dividing by 4 that gives 13 gallons per minute.

That number could be off by a gallon or two, as it turns out. I watched my meter run for a minute and the black hundredths position works like the date on a watch; it stays the same until almost 7 gallons is used, then quickly transitions to the next digit. So I only know the amount used to the nearest 7 gallons, which over 52 gallons is an error of about 15%. This error would go down if the measurement was made over a longer time.

However there is a more accurate way, at least for the type of meter I have. The “second hand” sweeps around once for every hundredth of a CCF, or 7 gallons. I watched it and thats when I noticed the digit changes when it approaches 0. However each .1 measured by that dial is .7 gallon. So a better procedure would be to run each zone for 1 minute, noting the position of the second hand at the start and end and including any full revolutions past the starting point. A bit tedious, but with the Iro allowing easy manual runs while you are at the meter its not hard. For low flow zones with drip on them would probably have to be run for a few minutes to get a decent measurement.

Hi @Ed3120, thanks for reaching out.

I’m going to look into this for you this week. Thanks for brining it to our attention.

Hi @mikeT, I appreciate your feedback and detailed description.

Perfect! Assuming your zone is 1000 square feet, your custom nozzle should be setup as 1.25 in/hour. If you know the exact square footage of the zone, please let me know and I’ll recalculate the precipitation rate in inches per hour for you.

Agreed. I think every meter type will have it’s variables to figure out, but it’s a pretty simple process in general.

Thanks for sharing and experimenting for us! We always love trying new ideas to make the Ior better.

Best, Emil

@Ed3120 The zone square footage is only used in determining water usage.

It will not modify your run time. Thanks and have a great day.

My lawn area is 22’ x 24’ which is 528 sq ft. so applying a ratio to the 1.25" value I get 2.37 in/hr. Sound right?

But without using the zone area or knowing the number of heads in a zone, how does the Iro know how much long to water? I have Rainbird 5000 heads, which state 0.76-9.63 gpm here: http://www.rainbird.com/documents/turf/ts_5000Series.pdf

That’s a huge range. Even if I knew the correct flow rate for one of those heads, the Iro doesn’t know if I have 1 or 5 of them running simultaneously in one zone. It also doesn’t know if I’m using one head to water 100 sq ft in at 30 degree arc, thus the head is going back and forth across the zone quickly and throwing down more water per sq ft per minute, vs one head doing a 270 degree arc on a 1000 sq ft zone and taking a long time to get across it, thus, not throwing down as much water per sq ft per minute.

I’m just confused how watering times can be calculated without knowing these variables. Maybe I’m looking at this wrong.

Spot on! However, we need to account for the number of heads as @Ed3120 has mentioned. Do you happen to know how many you have in that zone?

Hi @Ed3120,

Valid concerns and we’re addressing this.

Can you email us your zone square footage, # of heads and precip rate per zone [to support@rachio.com, attention Emil?] – I’d like to do some testing with you if you’re open to it.

Thanks, Emil

I’ll measure and count the heads in each zone. How do I figure out the precipitation rate per zone?

This is dependent on the nozzle or outflow of your heads.We can find this by referencing the nozzle type(s), performing a catch cup test, or measuring your water meter on a zone by zone basis.

Hope this helps.

well, the iro assume that your irrigation system was not installed by asshats. its a bold assumption, yes, but:
if you know the accumulation rate of a head,
all heads in the zone provide the same flow rate.
not mixing misters and rotors in the same zone
then the controller can make the assumption that “accumulation rate of your head” / “desired accumulation rate” = minutes of runtime (over simplified i know).

for me, it gave me a solid starting point. after 7 years of tweaking my hunter pro c, the iro controller recommend 1 extra minute of runtime on my zones, and 3 extra minutes of soak/rest. that was pretty damned closed to my 7 years of tweaks.

more specifically, "It also doesn’t know if I’m using one head to water 100 sq ft in at 30 degree arc, thus the head is going back and forth across the zone quickly and throwing down more water per sq ft per minute, vs one head doing a 270 degree arc on a 1000 sq ft zone and taking a long time to get across it, thus, not throwing down as much water per sq ft per minute."
this is improper irrigation design, more heads should be added to the zone, or the different arcs should be in a different zone. each zone should in my opinion should have heads that are homogeneous. unless you are doing a drip system, you will always end up with too much/little water in areas of a zone.

@plainsane, thanks for the great feedback to @Ed3120’s question. My comments below:

This is very important to keep in mind as mixed nozzle types in the same zone are very difficult to build automation for. The math becomes very messy on the back end. There are work arounds, but if you have a zone with mixed heads, I’d recommend correcting the problem with your zone design to yield long term water savings.

Awesome to hear! I’m glad we got it so close on the first try

Agreed. The Iro can control the flow of water by is limited by the infrastructure of the system it’s working with. Improper head placement, head selection, etc might force the Iro to overwater to satisfy the water needs of the plants give the delivery system it has to work with.

Best, Emil

sorry for the delay in responding, didn’t have time until now to run and count. I have 10 heads in the zone. However, to bring up something mentioned above, they are not all the same. Some in the center of the lawn are 360 degree sprinkers, those along the middle against the edge are 180 degree spray, and there are 90 degree ones in corners.

hi @mikeT, no need to apologize.

Great point to bring up. This is a sprinkler head case study. It’s important to remember that to water an entire area evenly with rotor heads, you should not use the same gallon per minute (GPM) nozzles in every rotor head. You can save between 10 and 40 percent of the water used in a rotor irrigation zone by proportionally matching the precipitation/application rate of the rotor nozzles. For example, a rotor only covering a 1/3 circle should have a nozzle installed in it that is roughly applying 1/3 of the GPM that the nozzle in a full circle rotor in the same zone is applying – or if a rotor is only covering a 90 degree area, it should have a nozzle installed in it that is roughly applying 1/4 of the GPM that the nozzle in a full circle rotor in the same zone is applying.

Thanks for double checking. I made an error in my request for this data in that we already knew the total precip rate of the zone from your initial calculations when you measured volume from your water meter. As such, your custom nozzle should be set to 2.37 in/hr. as you already calculated.

I hope this helps. Let me know if you need any help setting this up on your account.

Best, Emil

Why isn’t it used in the watering time calculation?