UBC’s Earth Sciences Building uses acid scrubbers to treat fume hood exhaust prior to the fumes entering the exhaust fans. The original fume hood exhaust design utilized fans with metal blades, which were susceptible to corrosion and required water scrubbers to prevent corrosion from the exhaust stream. The fans were replaced with plastic fans that are corrosion resistant and don’t require the scrubbers. Since each scrubber uses 5gpm of water constantly, significant water savings could be realized by disabling the scrubbers that were no longer needed. As it turned out, disabling the scrubber system was much more involved than originally anticipated.
The scrubbers drain to an acid neutralization tank, which is used to ensure the water leaving the facility is at a neutral pH level. Safety and Risk Services raised the concern that, with less water going to the neutralization tank, there is less dilution, and the remaining water would be at a higher concentration of acid even though there is a neutralizing agent in the tank. To verify tank outlet acidity, UBC Facilities’ Energy and Water Services staff purchased a pH monitor to test the water in the neutralization tank before and after disabling the scrubbers. The results were well within acceptable limits.
Another concern brought forward from UBC Facilities’ Building Operations was that the scrubbers would have less air resistance after the water was disabled, as air flowing through wet media is more restricted than flowing through dry media. To address this concern, a plan was put into place to test a sample of fume hoods after the scrubbers were disabled to check if the face velocity was affected by drying out the scrubber media. The fume hood testing showed that the resulting face velocity of the fume hoods was still within the safe range prescribed by WorksafeBC.
With the above concerns addressed, UBC Facilities’ Energy and Water Services was given the green light to disable the scrubbers to the fume hoods (while retaining operation of the perchloric fume hood scrubbers and washdowns). It was simply a matter of using the Building Automation System (BAS) to close the electronic valves that control the water flow to each scrubber. However, when attempting this, it became clear that the valves seen on the BAS did not correspond to the correct valves on site. Therefore, all valves would need to be manually isolated at the branch isolation valves.
Finally in May 2024, the valves were manually isolated after satisfying the concerns of all stakeholders consulted and overcoming the roadblocks encountered. In order to determine the actual amount of water savings, UBC Facilities’ Energy and Water Services staff used a portable flow meter connected to the common pipe serving the scrubbers to record water flow data before and after the scrubbers were isolated. The result was a water consumption reduction of 24gpm for all 8760 hours of the year. That’s equivalent to 19 Olympic sized swimming pools and about $66,000 per year in annual water cost savings!
Photo 1: EWS staff on site marking which valves to isolate
Photo 2: pipe branches serving acid scrubbers