Wednesday, December 3, 2014

Make it work: Methodologies for successfully implementing smart irrigation controllers

Encouraging the use of smart technologies for residential landscapes has become a popular trend in water conservation and rebate programs by water utilities and agencies looking for ways to decrease waste due to inefficient irrigation.  Generally, these technologies can be separated into two categories (Figure 1):
  •  evapotranspiration-based irrigation controllers (ET) The ET controller uses weather data, inputs chosen by the user based on landscape characteristics, and proprietary algorithms to determine when to irrigate and how much to apply. 
  • soil moisture sensors (SMS). The SMS measures the amount of moisture in the soil and skips irrigation if the soil is too wet.  

Figure 1. Examples of ET controllers and SMS systems (clockwise from top left): Rain Bird ESP-SMT, Weathermatic SL1600, Rain Bird SMRT-Y, Toro Precision Wireless, Toro Intelli-Sense, and Baseline WaterTec S100.
If at once you don’t succeed
A recent ET controller study was planned and implemented in Hillsborough County, FL.  A community-wide analysis of water billing data was completed for the county and the three communities that showed the highest estimated irrigation were Apollo Beach, Riverview, and Valrico.  A total of 36 volunteers were selected across the three communities with 21 of them receiving Toro Intelli-sense ET controllers.  All ET controllers were programmed with UF/IFAS-recommended program settings (ET+Edu).  The remaining volunteers were monitored, but did not receive an ET controller (comparison).

Unfortunately, results were not as positive as anticipated.  Though the ET controllers decreased irrigation application by 23% to 41%, irrigation increased by 14% for homes in Valrico and 54% for homes in Riverview when compared to the respective volunteers without technologies. Irrigation was high within these two communities, but the volunteers were not necessarily over-irrigators.  It was clear that there must be a better way to identify the utility customers that would benefit from smart technologies. 

More technology, bigger canvas
A new study was planned for Orange County, FL, that would evaluate the water conservation potential of both types of smart technologies when installed on homes with excessive irrigation habits.  Instead of focusing on communities, all customers in the Orange County Utilities service area were evaluated individually for trends in over-irrigation.  The UF/IFAS recommendation for irrigation is based on a soil water balance approach where the change in soil moisture depends on evaporation, transpiration, rainfall, and irrigation (Figure 2).  

Figure 2. The soil water balance is used to estimate the amount of irrigation needed to account for evaporation and transpiration losses when rainfall is not sufficient.
Landscape Irrigation Ratios (LIR) were calculated for every month over a five year span for each utility customer.  The LIR is a ratio of measured irrigation to UF/IFAS recommendations for the same month.  An LIR greater than 1 indicates over-irrigation whereas an LIR less than 1 indicates conservative irrigation practices.  Customers were considered for the study when a minimum of three months in three consecutive years had ratios greater than 1.5.  Out of 140,000 accounts analyzed, there were only 7,408 accounts that exhibited this behavior and out of these accounts, there were 843 volunteers willing to learn more about the study. 

After a detailed evaluation of many of the volunteering homes, the study included 139 participants located in seven communities across the county.  There were 28 that did not receive a technology (comparison), 55 that received a Rain Bird ESP-SMT (ET), and 56 that received a Baseline WaterTec S100 (SMS).  There were 28 homes of each technology that received additional educational opportunities and UF/IFAS recommended program settings (+Edu). 

Figure 3. Average landscape irrigation ratios from before the Orange County smart controller study began.  Irrigation trends were high with 6-8.3 times the recommendation.
The average historical LIRs (five years of monthly irrigation application to monthly UF/IFAS recommended irrigation) for Orange County study subjects ranged from 6.0 to 8.3, meaning that these volunteers were applying 6 to 8.3 times the amount of irrigation needed (Figure 3).  When considering historical LIRs in the aforementioned Hillsborough County study, they ranged from 1.5 to 2.4 indicating that they were also over-irrigating but were already much more conservative than the Orange County participants (Figure 4).

Figure 4. Average landscape irrigation ratios from before the Hillsborough County ET controller study began.  These volunteers had some over-irrigation, but did not exhibit signs of excessive water use.
Diving into the numbers
Irrigation by the comparisons in Orange County decreased from historical trends (6.9 before the study, 4.3 during the study).  Though the real reason is unknown, possibilities for the behavior adjustment include highly publicized droughts encouraging water conservation, awareness of being monitored for the study, or even repairing leaks discovered during their initial system evaluation.  Implementing the technologies had a larger effect, reducing the LIRs to 2-3.3 (Figure 5).  The additional education and programming was important for the SMS, reducing the ratio significantly from 2.9 (SMS) to 2.0 (SMS+Edu).  However, all of these treatments are still well above a value of 1, which is the goal, so more savings are possible.

Figure 5. Average landscape irrigation ratios that occurred during the smart controller study in Orange County.  The technologies were effective at reducing water use, but there’s room for improvement.
The takeaway
Smart technologies should be focused on homes that exhibit habitual excessive irrigation.  In situations where marginal water savings are possible, such as in the Hillsborough County ET controller study, a soil moisture sensor with UF/IFAS recommended installation and programming is recommended.  These sensors can be used in situations of deficit irrigation schedules whereas ET controllers can increase water use to maintain a well-watered landscape.  Both technologies were effective when used in the right situations.

Thanks to Hillsborough County Water Resource Services, Tampa Bay Water, Orange County Utilities, Water Research Foundation, St. Johns River Water Management District, and South Florida Water Management District for providing the support to complete these projects.  These studies were co-authored by Michael D. Dukes.

About the author:
Stacia L. Davis, Ph.D. is an assistant professor of irrigation engineering with the Louisiana State University Agricultural Center located at the Red River Research Station, Bossier City, LA.  She studied the water conservation potential of smart technologies at the University of Florida prior to moving to Louisiana.


  1. Awesome research! Thanks Stacia!! We should look at publishing multi-state extension documents!