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Reusing Air Conditioning Condensation To Save Water

Over eighty percent of Texas is in the worst drought stage, and last month, Houston set a record for consecutive days at 100 degrees or more. While forecasters predict the drought to persist through at least November, one university is actually saving water by reusing condensation from air conditioning systems.



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For years, Houston has been known as the most air conditioned city in the world. As warm air is cooled by an air conditioning system, humidity in the air forms condensation. Accessing this condensate or graywater, is not new, but it’s been a priority of Rice University’s Department of Facilities, Engineering and Planning.

Project manager Erik Knezevich says on a nice humid day, it’s not unusual for an air conditioned building on campus, to put out 15-gallons per minute of water that would normally be wasted.

“You’ll hear people doing that on their home air conditioning. They’ll try to capture that little bit of water that comes off which is helpful, but when you scale it up to a university level, the numbers really start to get big.”

PH: “What kind of numbers are we talking about?”

Knezevich: “Between the various buildings, we’ve got about eight of them that we’re reclaiming most of all the condensate, it can add up to 12-million gallons a year here at Rice University.”

Rich Johnson is director of Energy and Sustainability at Rice. He says that represents about 5 percent of the University’s total water consumption in a typical year.

“This was an idea that we’ve had for several years, but we didn’t know exactly the volume of water that we were going to get to. So once we got the figures for how much water was actually coming out of these systems, we immediately started thinking what other buildings can we implement this project on, and that’s why we had the project this past summer, and we’re looking at other locations as well, to capture even more water.”

After it’s collected, the water is pumped to the central plant’s cooling towers for use as makeup water, instead of having to buy water from the City of Houston.

Project Manager Erik Knezevich
Project Manager Erik Knezevich shows how air conditioning condensation is recycled.

Johnson says the water being collected is not dirty.

“The water that comes from the air conditioning units is pure, distilled, cold water. It doesn’t need any further treatment. When it goes into the cooling towers it’s already cool, so it reduces our energy consumption. It doesn’t need any further treatment, it’s ready to use.”

Project manager Knezevich took me underneath Brockman Hall of Physics, where the condensate-harvesting initiative is now underway.

“These are the chilled water pipes that feed into the air conditioning unit that actually do the cooling of the air. It brings in water that’s about 42 degrees, runs it through the coils that absorbs the heat out of the air, and causes the moisture to condense out on the coil, and run down to the pan for collection.”

While the older buildings are being retro-fitted to collect the graywater, Knezevich says the newer buildings will include the condensate-harvesting initiative.