September 2012

Volume 21, Number 9

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Smarter Irrigation for a Parched Landscape

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Rain Bird’s ESP-SMT system uses a tipping rain bucket to measure site-collected rainfall; this data is combined with information on soil and plant type, landscape slope, and other factors to minimize water waste during irrigation.

Photo: Rain Bird Corporation

By Brent Ehrlich

Nearly 7 billion gallons of water are used in the U.S annually for outdoor residential applications, primarily for landscape irrigation, with up to 50% of this wasted due to overwatering, according to the U.S. Environmental Protection Agency. These numbers stand in stark contrast to the droughts that have devastated much of the U.S. through 2012, but there are signs of hope amidst the parched landscape. Water-conscious property owners and landscape contractors are now going beyond simple water-conservation strategies and are employing “smart” irrigation controllers that automatically adjust irrigation schedules and maximize water efficiency. WaterSense is now certifying both residential and commercial products using its Specification for Weather-Based Irrigation Controllers.

Smart irrigation controllers are like thermostats that manage water consumption instead of heat, but rather than using just rainfall or soil moisture data, they use complicated evapotranspiration (ET) algorithms based on temperature, humidity, sunshine, wind, and other factors to calculate the amount of water transpired by vegetation and evaporated from the soil. The controllers use ET data to adjust irrigation schedules and provide just the right amount of water to maintain the health of different plant species and avoid overwatering.

ET calculations used by WaterSense-labeled irrigation controllers incorporate data on specific soil types, slope percentages, sun exposures, vegetation types, water storage at plants’ root zones, sprinkler heads and irrigation system type, and precipitation rates. The weather data used to determine the irrigation schedule and prevent overwatering can be gleaned from a number of sources.

WaterSense’s specification is based on the Irrigation Association’s Smart Water Application Technologies (SWAT) testing protocol. According to Ben Jamison, vice president of marketing for Cyber Rain, “SWAT was designed to certify products that meet certain water-efficiency standards that would allow them to qualify for rebates across the country.” But, Jamison says, while Water-Sense is based on SWAT, “it is far more difficult to pass WaterSense.”

WaterSense-Labeled Irrigation Controllers


Source: U.S. Environmental Protection Agency

For WaterSense, a controller is tested by a third party on six different zones representing real-world planting scenarios and weather conditions. To be certified by WaterSense, an irrigation controller has to perform at 80% or better efficiency for each test zone with an average of 5% or less overwatering. The test conditions also have to be met within a 30-day window, according to Jed Price, controller product manager for Rain Bird, another company with certified irrigation controls. He says, “If you aren’t in an area of the country with weather conditions necessary for the test, then it can take six months or more to pass.” Rain Bird, located in Tucson, Arizona, had its products tested in Alabama.

Though the data and software are complicated, WaterSense-certified systems actually simplify water conservation by automatically calculating ET information that used to have to be input by hand on a regular basis. Smart controllers still require the end user to input initial data—slope, sun exposure, and plant type, for instance—but just once, and many factors, such as root depth, can be calculated by the program. In fact, most of the data are gathered automatically. Cyber Rain, for instance, uses a Web-based interface from Weather Underground to gather climate and weather data. A zip code or GPS coordinates pinpoint the location of the irrigation system to provide accurate weather information.

Rain Bird relies instead on eight years of weather data based on the local zip code, along with site-collected rainfall and temperature information. Controllers can also access weather signals from other sources, such as weather stations, and many can accommodate freeze, rain, or soil moisture sensors. (Soil moisture sensors provide an extra level of protection against overwatering in some instances, but experts EBN spoke with agreed that they are more expensive to install and maintain, and the small performance gains may not justify the added cost.)

Currently, WaterSense irrigation controllers are available in sizes ranging from six-zone models used for residential and small commercial operations to 36-zone professional models, but significantly larger models are now undergoing testing for certification. Many of these systems offer central controls that allow property managers or landscaping firms to monitor and adjust irrigation on a site as needed from any Internet-connected computer. See an adjustment that should be made while walking the grounds? On the road, and the mowing schedule has changed? Cyber Rain also allows mobile devices to adjust irrigation on the fly. Most systems can also be connected to flow meters that detect and pinpoint breaks in the irrigation lines and can send notifications via email, saving water and the time required to find and fix the leak.

Prices for these controllers range from as little as $150 for a six-zone Rain Bird SST 600s to more than $5,000 for a Rainmaster Eagle, from Irritrol. Jamison claims a one- to two-year return on investment for Cyber Rain products, with up to 40% water savings.

So far, only Cyber Rain, Rain Bird, Irritrol, and Toro have products certified to WaterSense’s weather-based specification. But because the standard is so new and a number of established companies, such as Calsense, have products that easily meet SWAT standards, we’ll likely see more WaterSense-labeled irrigation products in the near future. And hopefully we’ll see some more rain, too.

For more information:

Cyber Rain

Rain Bird Corporation


The Toro Company

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