Dear all,
We are consulting for a big retail shopping mall. The project is aiming to achieve this prerequisite and the WEc3 by installing sanitary fixtures close to the baseline values, but complementing it with a full graywater recycling system which will collect water from all lavatories and kitchen sinks (non-greasy water of course).
The Mechanical Engineer performed calculations based on typical projects of the same size / type, and calculated around 200 cubic meter of graywater recycled per day.
We did the same calculations as per the LEED guidance , and found that the total amount of graywater is around 20 cubic meter per day (almost 10% of the Engineer's estimated value). We assumed the same flow rates of lavatories / sinks, but it seems that the Engineer has assumed more uses and also included water consumption for activities which LEED doesn't take into consideration (washing food in restaurants, water for cleaning the floor, etc).
My question is:
If I provide sufficient calculations by the Mechanical Engineer to the USGBC, would this be enough to assume the Engineer's graywater volumes in the LEED Credits? If I use the Engineer's numbers, I would be able to achieve the full 4 credits of WE Credit 3 (plus 1 ID point), in addition to the 4 credits of WE Credit 1 (Water Efficient Landscaping) as no potable water would be used for irrigation.
Anyone had a previous experience of a similar situation?
Thanks!
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
September 5, 2014 - 6:03 am
I've not checked this for a while, but I must caution not to lump credit requirements together. For the prerequisite, you may only account for those elements listed and still must reach the minimum...that means regardless your greywater use, you still must have efficient taps, etc.
For greywater calcs. I think the engineer's numbers are good to use if you include them with a narritive.
Maya Karkour
EcoConsulting872 thumbs up
September 5, 2014 - 7:14 am
Thanks Jean,
Looking at the USGBC's "Water Use Reduction Additional Guidance" version 8 (pages 4 & 5), and quoting the below:
***
"Overall, the focus of Water Use reduction prerequisite and credit is water efficiency of the installed fixtures and fixture fittings regardless of the water source, but projects are still allowed to use on-site alternative sources of water to achieve water use reduction through an alternative compliance path.
Examples of on-site non-potable water sources that apply to the Water Use Reduction prerequisite and credit include: graywater, captured rainwater, air conditioner condensate, cooling tower blow-down/bleed-off water...
To document the use of on-site non-potable water to reduce water use for flush and flow fixtures, use the Alternative Compliance Path (ACP) section of the applicable LEED Online forms, WEp1 and/or WEc3"
***
Back to my initial question:
Can we consider the Engineer's estimated collected graywater volume from usages such as commercial kitchen sinks (which are not included for LEED purposes), knowing that the while the baseline scenario does not account for these volumes? I do not see why we can’t do it, as we need to be realistic and reflect the actual design / actual consumption rates in our calculations: the graywater system will be operational and will provide water to cover 100% of the WC flushing demand and 100% of the irrigation demand. So why not explain this to the USGBC?
Michelle Rosenberger
PartnerArchEcology
522 thumbs up
September 5, 2014 - 10:45 am
Hi Omar,
We have a project that is using captured rainwater to offset WC flushing and irrigation. And we are using the alternate compliance to document additional reduction in WEcr3. Though our source is rainwater and not greywater, the issue would be the same I believe. The non-potable water source is not directly part of the baseline vs. proposed fixtures calculation. It is solely a calculated volume that you use as an additional input to modify the results of WEpr1 and WEcr3.
I do not believe your greywater sources need to match up with the low flow fixtures regulated by the WE credits, and I don't see why you would not use the Engineer's greywater calcs to establish your annual non-potable volumes, just like we are using the civil's cistern calcs to establish ours. Obviously profuse explanations are always a good idea. If you are a Proven Provider, you can always confirm this in a presubmittal call. Good luck.