LEED and Irrigation Efficiency

There is no shortage of confusion when it comes to LEED requirements and what will or will not be acceptable to the reviewer. Though the credits may appear clear cut at first, allowable products and methods can be a bit subjective. That is certainly true in our corner of the LEED world, Water Efficient Landscaping.

Meeting the LEED Requirements

In both WE 1.1 (50% reduction of potable water in the landscape) and WE 1.2 (100% reduction), the designer is asked to supply a baseline case and a design case for their proposed irrigation system.

The baseline case is the amount of water used by a traditional landscape with a standard irrigation system while the design case details the methods or materials employed to achieve the required water savings. The design case landscape may include plants that do not need supplemental irrigation after establishment, though this isn’t always practical. Many clients aren’t willing to forego lush manicured lawns, annuals for color, or even less hardy trees and shrubs. In that case, a different approach is necessary.

The good news is that irrigation and LEED credits aren’t mutually exclusive. In fact, with only a few relatively inexpensive modifications to the irrigation design, credits for WE 1.1 are all but guaranteed. Or they should be.

Sprinklers and Controllers

One popular change is the use of drip irrigation in landscape beds instead of traditional sprinklers. Because USGBC considers drip to be 90% efficient but “sprinklers” to be only 62.5% efficient, the benefit is obvious.

The problem is that not all sprinklers are the same and not all are 62.5% efficient. For example, fixed spray sprinklers with integral pressure regulators – designed to make sure that every sprinkler operates at optimum pressure – are very often more efficient than 62.5%. The same is true for stream-spray type nozzles which are less affected by wind drift and therefore provide more uniform (and efficient) coverage. But how do we prove it to the satisfaction of the reviewer?

Controller Efficiency

Even more nebulous is the Controller Efficiency (CE) part of the spreadsheet. According to the LEED reference guide, CE is “the percent reduction in water use from any weather-based controllers or moisture sensor-based systems.” A standard controller will have a CE of 1.0 while a smart controller’s CE will be 0.9-0.7 or even lower.

Sounds easy enough but the guide continues with “This number must be supported by either manufacturer documentation or detailed calculations by the landscape designer”.

There is the problem.  Historically there has been little in the way of quantifiable date provided by the manufacturers of irrigation controllers (or sprinklers for that matter). The reason was that independent testing is expensive and until the green building movement gained popularity, there wasn’t much demand for the information.

 

A few proactive manufacturers sent their products to the Center for Irrigation Technology in Fresno, CA for testing and the information provided by CIT proved invaluable when compiling LEED documentation. The concise testing results including average efficiencies gave reviewers the undeniable proof they wanted. Unfortunately, such results were available for only a handful of controllers.

Fortunately, times are changing rapidly. Due to the high demand for efficient controllers – and proof of their efficiency – independent entities such as the Irrigation Association together with the EPA’s Watersense program have started offering manufacturers more affordable testing options.

A review of the IA’s Smart Water Application Technologies or SWAT page shows dozens of climate- and soil moisture-based controllers as well as rain sensors and the list is sure to grow. Each product listed is linked to test results as well as a complete disclosure of the testing procedure. The information isn’t quite as concise as that supplied by CIT and the designer must still make some assumptions when completing the LEED work sheet, but it is a giant step in the right direction.

LEED Bottom Line

So when all is said and done, which efficiency numbers are correct? Or more importantly, which numbers will the reviewers accept? That’s still the $25,000 question and there is still no definite answer.

However, upgraded sprinklers with high-efficiency nozzles can easily reach 65%-70% efficiency and ET-based controllers are routinely around 0.7 or better (sometimes much better). The trick is to pick a number that is defensible and then to gather as much support as possible from CIT, IA or the product manufacturer.

On the bright side, more useful efficiency information is becoming available every day. Even better, there is no reason to choose either irrigation or LEED credits, so feel free to use every plant in the palette and let your creativity flow! For more information about SWAT or products tested by the Irrigation Association, please visit; the Irrigation Association SWAT site here or the EPA Watersense Partners site here.