Does anybody know where USGBC / WE TAG came up with Table 1? I've not been able to find it anywhere, except where it is referenced as coming from LEED. For example, the EPA WaterSense Water Efficiency Management Guide for Mechanical Systems linked below has the table, but cites the source as LEED. This credit is really poorly developed / explained in the LEED Reference Guide and over they years they still haven't addressed many basic technical questions. It also doesn't have any good citations or reference standards the way most LEED credits do. All of the federl / non-vendor best practice guides I can find talk about maximizing COC and monitoring conductivity, but don't include suggested maximum concentrations.
The reason I ask today is we have a large office site with cooling towers in Illinois and the water treatment vendor says conductivity of 2,000 μS/cm is too high. They won't push conductivity past 1,350 μS/cm stating that anything higher causes scaling on our heat exchangers, reduces efficiency, etc. We're currently at 4.5 COC and would save a good amount of water if we set our conductivity limit closer to 2,000, but we'd have to ignore the warnings from our vendor and absolve them from responsibility for scaling.
https://www.epa.gov/sites/default/files/2017-12/documents/ws-commercialb...
Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
530 thumbs up
August 13, 2021 - 12:09 pm
per the credit language 'Limit cooling tower cycles to avoid exceeding maximum values for any of these parameters.' listed in the table. If project teams blowdown / makeup prior to the maximum limit, then this still meets credit language.
So in your instance if you blowdown/makeup when the conductivtiy reaches 1,350 you have demonstrated that you 'limited cooling tower cycle so that maximum value of 2,000 is not exceeded'.
My 'head scratcher' on this one is that there are some cooling tower requirements hidden within the Indoor Water Use Reduction prerequisite...why not make a Cooling Tower prereq? (and aren't cooling towers located outside? .. so wouldn't it be a better fit to put this in the Outdoor Water Use prereq??)
Nathan Gauthier
August 13, 2021 - 1:45 pm
I don't think that response is accurate. If we limit our COC to 4.5 to keep our conductivity below 1,350 then we're using much more water than if we set our limit at 2,000 (6.7 COC). The 1 point is for setting your COC to the "maximum without exceeding". Step 4 in the Reference Guide is a little clearer.
STEP 4. SET COOLING TOWER OR EVAPORATIVE CONDENSER CYCLES
Adjust the cooling tower or evaporative condenser settings for the maximum number of cycles without exceeding concentration levels or affecting condenser operation.
Either way, in this case I'm not trying to go for LEED, just trying to save water in an existing facility. I'm wondering if I should push back on our water treatment vendor and ask them to increase the setpoint (and save water) or if their concerns are valid enough that we shouldn't risk it. If the LEED maximum value was backed by a study or reference standard, that would help.
Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
530 thumbs up
August 16, 2021 - 8:34 am
you are correct, Nathan. Thank you for bringing this to my attention.
I have been lucky to submit, and be approved by GBCI, with blowdow/make-up prior to the upper limit(s) listed by the credit requirements.
Would the equipment manufacturer provide a study or some research/evidence supporting the reduced thresholds? If so I would guess GBCI would accept this.
Perhaps ask other water treatment vendors if they concur with the 1,350 conductivity threshold.