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Water scarcity is becoming a hot-button issue in the U.S. (and globally), with water managers in 36 states saying they expect freshwater shortages hitting their states by early in the next decade. But the coming shortages could present opportunities for entrepreneurs and investors to develop new water-saving technologies. One ripe area for innovation is the building sector, according to a report, titled “Green Buildings + Water Performance,” released this week by publisher Building Design+Construction.
Buildings account for about 12 percent of water use in the country, according to the U.S. Geological Survey, and green building ratings systems like the U.S. Green Building Council’s LEED encourage more efficient use of water, such as through low-flow toilets, drip irrigation and on-site water reuse. Typically more water is consumed outside commercial buildings and homes (see charts below taken from the report) — for landscape irrigation and cooling towers — than is used inside by things like toilets, faucets and showers, according to the report. With that in mind, we’ve summarized the three areas in green building design noted in the report as the most promising for reducing water use outside buildings:
Smart Landscape and Irrigation: Landscape irrigation can be as much as 60 percent of water use in homes in arid climates and more than a third in more water-rich areas, the report says. Newer technologies, like weather-based irrigation (Rockport Capital-backed HydroPoint is one example), are helping building owners reduce water use. Instead of watering according to a preset schedule, these “smart” systems take into account weather conditions, current and historic evapotranspiration, and soil moisture levels to deliver water based on the needs of the plants. Other water-saving landscape features emerging (besides the low-tech solution of selecting drought-resistant plants) include bioswales and vegetated roofs.
Rainwater Reuse: The bulk of U.S. building projects miss out on one of the most potentially significant water conservation opportunities by failing to put in place rainwater catchment and reuse systems, according to Building Design+Construction. For every inch of rain that falls on 1,000 square feet of roof area, 600 gallons of water can be collected for harvesting — where water is collected either from the roof or the ground and then diverted to storage tanks. If just 10 percent of the roof area in arid Texas were used for rainwater harvesting, 38 billion gallons of water would be conserved each year, says the report. Moreover, rainwater harvesting is relatively simple to execute, especially for irrigation and cooling tower applications.
While many rainwater harvesting systems are custom-engineered from various components, a growing number of packaged systems are now available, such as those from BRAC Systems and Watertronics. One emerging trend in rainwater reuse is the application of siphonic roof drainage technology, in which negative pressure is used to draw water along horizontal piping. Proponents of siphonic roof tech say the process can be less expensive than conventional systems that depend on gravity and require more piping to move water.
Cooling Tower Water Recovery: Cooling towers for chillers are often the largest consumers of water in commercial buildings. (They typically rely on water evaporation to provide cooling for air conditioning.) A large commercial building with 1,000 tons of refrigeration will use 3,000 gallons of water per minutes, the report says.
Newer cooling technologies like variable refrigeration volume systems, which cool individual rooms of a building depending on the need, show promise for reducing water (and energy) use, as do cooling tower water management techniques, such as automated controls. Water treatment technologies (such as Dolphin WaterCare’s system) increase the recirculation rates in cooling towers before the need for a so-called blowdown, when water is removed from the system to reduce mineral concentration and scaling that occurs as a result of the evaporation process.
There is a “potential opportunity” for whole building water savings, according to the report, in the reuse of wastewater (blowdown and condensate) from cooling towers and other mechanical equipment for irrigation. But condensate recovery has not yet caught on all that well in the building industry.
Image courtesy of Wikimedia Commons.