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THE BENEFITS OF HARVESTING HVAC CONDENSATION

It is a typical, muggy August afternoon in Houston, but Erik Knezevich, P.E., is feeling super-chilled. The former Rice University facilities project manager is standing inside the massive air conditioning unit that cools Brockman Hall for Physics on the north end of campus. The incoming air registers a toasty 88 degrees, but in the instant it takes for it to blow through water-chilled air conditioner (A/C) coils and reach him, it is decreased more than 30 degrees — cold enough to travel inside the building’s ductwork and keep labs, classrooms and offices comfortable.

Anyone who knows Houston understands that high temperatures are just part of the reason air conditioners run feverishly nearly year-round. Couple an average August thermometer reading of 94 degrees with an average relative humidity of 75 percent, and it is easy to see why “air you can wear” is not just a meteorologist’s fanciful turn of phrase for residents of the Bayou City. Under those combined conditions, sweat drenches people, and condensation nearly pours off A/C coils. On a hot, humid day, the amount of condensate produced from the Brockman Hall A/C system equals an astonishing 15 gallons per minute.

In many Houston buildings, HVAC condensate is discarded, simply sent down the sewer. However, at Rice University, a long history of environmental stewardship makes that kind of waste unacceptable.

Instead, the condensate from Brockman Hall and six other buildings is captured and pumped back for reuse on campus, primarily as makeup water for the central plant’s cooling towers. Knezevich figures that Rice recovers about 14 million gallons of water per year, and that is probably a conservative estimate. That means that instead of buying 14 million gallons of treated, potable water from the city to replenish its cooling towers or tapping the university’s own well, Rice saves a precious resource and a considerable amount of money.

According to Knezevich, HVAC condensate recovery has been underway at Rice for about eight years. Some of the buildings were retrofitted to make the process possible; for newer buildings, including Brockman Hall and the BioScience Research Collaborative Building, condensate recovery was incorporated into the design. Knezevich admits that retrofitting is not always economically viable. Of 12 campus buildings considered for HVAC condensate recovery, it only made sense for seven.

“If you have a pipe going from the attic to the basement in an existing building, you’re going to rip up too much of the structure to justify the return on investment,” he says.

In addition, the reused condensate does not totally replace the water required by the cooling towers. Some fresh water will still be needed. According to a report by the San Antonio, Texas, cooling water system, the figure typically ranges from as little as 5 percent to as much as 45 percent with the latter figure reflecting a high-ventilation building such as a laboratory.1 At Rice, the total cooling tower makeup water for the university is about 68 million gallons per year, so the recycled amount represents about 20 percent.

Knezevich, who now operates Galaxy Consulting Engineers, expects that as construction continues on campus, condensate harvesting will be part of the plan. Water recovery, he explains, is part of Leadership in Energy & Environmental Design (LEED) certification — which is administered by the U.S. Green Building Council (USGBC), the benchmark in green building — and Rice is aiming for the LEED Silver level.

As he notes in a YouTube video that promotes Rice University’s condensate recovery efforts, using HVAC condensate instead of potable water in cooling towers is, “putting good water to good use.”