Hello Everyone,
I am seeking further clarifications and suggestions regarding the clacuation for the use of grey water for irrigation and rainwater for our project. We have a large retention pond where we will be collecting rainwater to purify for drinking and other potable water use. We also have a Waste water treatment plant that will treat our water and recylce it for irrigation and toliets.
The project is located in Phuket, Thailand. For 6 months of the year it is rainy season. The other 6 months are relatively dry. Irrigation demands on the grey water will be less if not zero some dry months.
We are trying to claim Non potable water used equal to the design case water total. The project is a net zero water project, no potable water from offsite. GBCI feedback is they would like to get more details on the calculations that determine the amoubt of non potable used. My engineers seem to not understand what is needed. Is there an online resource somewhere with examples of these calculations?
I am assuming we have to show two things. One would be a rain fall water balance chart thast would show the irrigation demands for a year (by month) with rainfall factored in. The other item would be a daily or monthly output of the grey water produced by the WWTP and how much gets used by irrigation. And to factor in any treated rainwater use if that is required in the hotter months of the dry season.
Any feedback on what is needed to document non potable water use and where I might find examples of this is appreciated. Thanks.
Melissa Merryweather
DirectorGreen Consult-Asia
245 thumbs up
February 4, 2017 - 1:17 am
John, hi. You are nearly there. You want to be sure that the irrigation demands match what you've put into the existing credit sheet of course, but the other months can vary according to seasonal needs. Output of grey water is correct, and there should be an annotated schematic or other proof that irrigation needs are either prioritised, or that all needs, including cooling towers if they are using treated grey water, are accounted for within the amount available. Depending on the interactivity of this, you may want to show the cycle over longer than 1 year--for instance I found that with large seasonal variations (my projects are in Vietnam with the same weather patterns) I needed to show a 2-year cycle to show how the lag worked between having large amounts of rainwater available and virtually none. Finally, I would estimate the size of your retention pond. If its really large, a rough estimate is all that you'll need. But you need to show that you have that storage capacity to satisfy all needs.
John Covello
Senior Sustainability ManagerUL Solutions
9 thumbs up
February 4, 2017 - 1:49 am
Hi Melissa,
Thanks for your feedback.
We have drawings showing how the grey water is distributed. So you are saying we should have an estimate of the daily (monthly?) output from the WWTP creating grey water and how it is distributed? I have drawings with the size of the retention pond so that is covered. And we should do a rain balance chart for irrigation as well? We usually have enough water each year. Actually this year we have more water due to El Nino.
No cooling towers. We are a VRV AC project.
Melissa Merryweather
DirectorGreen Consult-Asia
245 thumbs up
February 4, 2017 - 2:16 am
Disregard this year since it is unusual. Its easiest if you put all the values into either daily or monthly figures--for instance if you have monthly irrigation but daily output from WWTP, put all into monthly values. Make sure its easy for the reviewers to compare. Not sure what you mean by rain balance chart for irrigation, but you need to show estimated irrigation needs per month for a full year cycle, similar to the calculation you would have made for Credit WEc1 on line. If you need to use a lot less irrigation due to heavy rainfall, estimate the amount you do need and make a comment in the documentation or the narrative, offering whether this is already measured on site or what other justification you can provide. However, it sounds to me as though you have so much available non-potable water that you might prefer to take the simplest route, and show that even without calculating rainfall, your worst month x 12 is satisfied. I've used that solution on 2 projects so far where I had enough storage, and was successful. With my latest project (also successful) the storage area was much smaller and I needed to show competing uses for treated water and how inputs matched required outputs across the spectrum. Always find the simplest, most consistent and "provable" calculation possible.