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Sprinkler Systems, Irrigation Controllers, and Sensors
An irrigation controller is the clock that runs a sprinkler system. A good controller can make the difference between a landscape that is efficiently managed and one that is not. It can also have a strong effect on a business's monthly water bill.
Property managers who inadvertently water their landscapes too much or at inappropriate times of the day nearly always end up with high water bills. The newer controllers, like Hunter or Toto irrigation controllers, take into account local weather conditions. They make it easier to have a healthy landscape and a healthier water bill, too.
Really large sprinkler systems may have more than one controller. Each controller has several stations (timers), depending on its size, that control different parts of the landscape, each station with its own timer. Older controllers and their stations are programmed by hand, with the landscaper guessing how much water each section will need. Newer ones take weather and other factors into account, modifying programmed schedules to water only when plants are thirsting.
What are Weather Based Irrigation Controllers?
There are several different kinds of "Weather Based Irrigation Controllers" (WBIC) or Smart Controllers, and all of them work by using input about the site from local sensors or satellite weather stations to modify the watering schedule. Examples of information WBIC's can take into account are: Weather readings, moisture in the air, moisture in the soil, solar radiation, plant types, soil types, slopes, and water pressure. Each of these factors affects the amount of water needed by plants in a landscape, and alters the amount of water the controller will allow through the sprinkler system.
How a controller works.
Each controller has several stations hooked up to valves that feed water to sets of sprinklers in different locations or zones. Controller sizes can vary from four to 200 stations, each with its own timing. Since stations are designed to match the watering needs of whatever plants are in its relevant zone, having a number of them provides a lot of flexibility with watering.
The size and number of controllers chosen for a sprinkler system depends on the size and complexity of the landscape. As mentioned, each landscape zone is watered by sprinklers controlled by a valve. Station timers control the valves and controllers host the stations. Since controllers/stations are hooked up electronically to the valves, they have to be located near enough to allow for a hookup.
A six acre site with valves spread out through the landscape with many different types of plantings could have 8 controllers with 64 stations each, whereas a one acre landscape may need only one or two controllers with 8 stations each. A station could be set up to water trees and bushes on one side, another for grass in front, a third for a drought tolerant section, another for medians or parkway, one for a shady section, or another for grass in a far corner.
Controllers vs. nozzles.
There are some situations in which problems with watering have been blamed on improper controller programming, when in fact that may not be the case. The most common of these is really a problem with irrigation nozzles.
Different types of plants require different speeds and lengths of watering, and so do different soils. For best watering, different plant types should not be watered by the same station, nor should they be watered by the same types of nozzles (see "Irrigation Nozzles"). Because different types of nozzles allow for different amounts of water through them, if you mix them on the same station, you will cause one area in a section to be either shorted or flooded.
The reason a controller has a number of stations with their own timers is so that a landscaper can take the difference in nozzles and plant types into account when programming watering schedules. The stations and their valves give much needed control. But a landscaper that bypasses that control by mixing nozzle types or plant types on the same station loses the flexibility that a good controller gives.
WBIC scheduling assists - like rain & soil sensors.
When first installing a new WBIC, the landscaper will be entering the soil type, types of plants, water pressure, and location of property (latitude and longitude or zip code), among other data, as detailed by installation directions. Additional information will be provided by additional accessories that support more efficient watering with a WBIC:
Weather (rain) sensors connected to irrigation controllers have proven to be the most accurate controller systems so far, according to a study conducted by the University of Texas. This system does not rely on state weather data or soil moisture, but measures moisture in the air of your landscape. When it starts to rain, felt pads inside the sensor swell, triggering the sensor to turn off the controller automatically. When the rain stops and the pads dry out, they shrink, and the controller is reactivated.
The State of California has a CIMIS system, run by the Department of Water Resources, that gathers weather information from all over the state. (CIMIS stands for California Irrigation Management Information Systems.) The state set up the system originally to collect its own weather data, but then realized landscape companies and private homeowners could benefit from it too.
Readings come from a multitude of weather stations, like the one on the right, that are placed all over the state, high and low. These stations feed weather data into a central compiler monitered by the state. WBIC-controlling websites draw local weather information from the CIMIS system, and use it for their subscribers to control the irrigation timers on their properties (see link below).
Reviewers say that this rain sensor is easy to set up. Rainbird also has a great website with instructions on how to use and install rain sensors and other pieces of equipment they sell.
Soil moisture sensors - You can also hook up soil moisture sensors to a regular controller or Smart Controller. These sensors measure the moisture in your soil, then signal the controller (or valve) when it needs watering. Using this type of sensor makes for very efficient watering, but it does take some initial checking and adjustment.
Purchasing a WBIC.
The type of Smart Controller you choose to buy will depend on conditions onsite. Here are some things to look for:
- Is it user-friendly? Easy to understand and program?
- Does it allow for sensors to be attached and read?
If you have a large property, or one with controllers watering areas that can't be seen from its location, does it have a remote control function?
Are there enough stations on each controller to cover all the planting zones the property has? You will need to count how many zones there are. Sunny areas will be one zone, shady areas another, since they require different amounts of water, due to heat and evaporation. Other factors that form "zones" are: Sandy vs. clay soils, slopes vs. flat land, flower beds vs turf areas, tropical vs desert plantings, and mixtures of any of these.
Does it have a manual shutoff capability for valve and sprinkler maintenance purposes?
Can each station be programmed with multiple start times or does it have a "Cycle and Soak" feature? This is especially crucial in locations with heavy clay soils or steep slopes, where applying too much water at once will flood or cause erosion.
If you have several properties whose sprinkler systems you want to run from a single location (like a school district headquarters), you can choose a controller that has the capability to be run by a central control. You can buy the whole system together - the central control and controllers that go with it. Or, if you already have a central control system, you might only need to purchase extra controllers to add another property to it.
Here are a number of links that show different brands of Smart Controllers:
- Southern California's Water Smart list of approved controllers: PDF download
- From California's Metropolitan Water District: Weather Based Irrigation Controllers
Enjoy the shopping, but remember that the real benefits of your new controllers will depend on how well you set up, test, and adjust them. Make sure you and/or your landscaper follow the controller's written instructions, then check the results several times afterward to make sure they are operating efficiently for the sprinkler system on your site.
- California Irrigation Management Irrigation System (CIMIS)
Calculation of Evapotranspiration (ETo) from sensor readings at over 100 weather stations throughout California.
- How to Practice Water Conservation
One of the threats most common to much of the world is the drying up of water. Here are ways individuals can use water efficiently, so there is enough for everyone.