Documenting Controller Efficiency

Michael, there are two good previous discussion threads that cover this issue. Please start there and come back with any followup questions you have.

Michael, you sum up the situation well. Given that, it seems like there is simply not a lot of collectice knowledge out there to evaluate your plan. But i would say that it sounds pretty good, as long as you are confident in the data being provided.

I'm going to try this on a project, let me know what y'all think:

1. ETo used for LEED calcs is based on July. My project is located in inland Southern California, where July precipitation is near zero. This should mean I can claim all annual precipitation against the total TWA (where CE = 1).

2. Assume that the controller reduces/halts irrigation whenever precipitation is available to replace it. Not sure if this is legit, but the controller is just as likely to reduce irrigation when it shouldn't as it doesn't when it should (if that makes sense), so maybe it averages out.

3. Calculate annual rainfall in gallons (ft/year precip x landscape area [sf] x 7.48 gal/cf).

4. CE = 1 - (annual rainfall [gal] / TWA [where CE = 1])

This is a pretty inaccurate approach, since it doesn't account for controller accuracy, or runoff from landscape areas when water volumes are too high, or runoff into landscaping from adjoining impervious surfaces, or probably a dozen other factors. However, it doesn't seem any less accurate than the LEED TWA calculation procedure.

I'd love to hear what anyone thinks of this approach. I'll try submitting it and report back the results.

Hi Eric, did you succeeded? We are using soil moisture sensors for irrigation from vegetronix.com that just do that. They only start the irrigation if the soil is dry. The manufacturer can't help with any value for the controller efficiency CE. So our only way to justify a value of CE different from 1 is to provide a similar approach you were thinking as well.

We took a different approach, and used the rainbird document cited above (we are using the rainbird system) and simply averaged the savings. Here is the resulting response to the GBCI comment. I will try to remember to update on whether or not it is accepted:

"The design team has revised the CE value for the design case based on the attached “ETManagerWaterSavings.pdf” document which profiles savings in six projects over two years, resulting in twelve years of data. These values were averaged two ways, one by taking the percentage savings for each project each year and dividing by twelve. That calculation is as follows:

(43+70+49+60+35+28+30+44+35+37+33+35)/12 = 41.5% average savings unweighted

Additionally, we took a weighted average of the savings by multiplying the “Usage before ET Manager” for each project and multiplying by 2 since two years of post-installation savings are documented to develop a baseline consumption rate with conventional controllers. We then added the total consumption of each project post-installation and found the difference overall. That calculation is as follows (all calcs in 1000’s of gallons):

(2296+416+2604+1510+640+1228)*2 = 17,388 kgals baseline

(1310+699+214+164+1642+1885+1057+851+417+402+827+804) = 10,272 kgals proposed

(17388 – 10272) / 17388 = 40.9% average savings weighted

We then took the lesser of the two savings, 40.9%, and converted that to CE by taking 1 - .409 savings = .591 CE.

Harvard University,
Was this approach to CE accepted? The form specifically states that CE value must be between .7 and 1, so I'm curious to hear if something this low was ok, given your backup. Thanks!

We received this comment and are unsure how to respond, has anyone seen this and had an acceptable response? going to the manufacturer and asking for all their testing data and deep details of proof seems a bit ridiculous? are we now required to do this for filters and bathrooms fixtures as well? Do we need to prove same species of plants grown in different climates may react differently to water and soil and thus need to prove their water requirements?