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Water: Doing More With Less

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Cooling towers chill buildings by evaporating water. A 100-ton chiller evaporates about three gallons of water per minute (11 lpm), with additional water loss from drift and blowdown. In a typical office building, HVAC equipment accounts for about a third of total water use.

Photo: Advance Cooling Towers

No place is more emblematic of water shortage than Las Vegas. The metropolitan area receives about four inches (100 mm) of rainfall per year and has doubled in population just since 2000 (to 1.9 million). It is 90% dependent on Lake Mead—a half-full (half-empty?) lake whose level has dropped more than 100 feet (30 m) since 1990.

But Las Vegas is not alone in grappling with water shortages. From the uncharacteristically thirsty Atlanta in 2007 to the Pacific Northwest, water shortages are expected to become more and more common in the coming decades. A 2003 report by the U.S. General Accounting Office reported that 36 states are likely to experience water shortages by 2013.

This article looks at strategies for reducing water use in and around buildings, addressing both residential and commercial water uses. This is by no means comprehensive coverage of these products and technologies but should provide an idea of the opportunities available to us.

Water Use In and Around Buildings

According to the U.S. Geological Survey, the United States uses about 400 billion gallons (1.5 trillion l) of water per day. Of this, the vast majority is used for thermoelectric power generation (48%) and irrigation on farms (34%). Water use in and around buildings, from both public water supplies and well water, accounts for about 47 billion gallons (180 billion l) per day, or 12% of U.S. water use.

End Use of Water in Commercial Buildings

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Source: Awwa Research Foundation

The chart to the right conveys how water is used in buildings and their surrounding landscapes. In commercial buildings, the water use for different functions varies significantly depending on building type. Office buildings and hospitals, for example, have very high water use for mechanical systems, while hotels use more water for laundry and kitchens.

Residential indoor water use is dominated by toilets, clothes washers, showers, faucets, and (significantly) leaks, according to a 1999 report from the American Water Works Association Research Foundation. Residential water use from landscape irrigation is highly variable by climate and season.

Plumbing Fixtures

The following sections address the major uses of water in and around buildings and the major opportunities for improved water efficiency. Each section provides a summary of the product or technology area along with information on recent developments and possible future trends. We start with plumbing fixtures.

High-efficiency toilets

 

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Zurn’s EcoVantage Series flushometer-valve toilets use only 1.28 gallons of water per flush (4.85 lpf). Toilets in U.S. commercial buildings consume about 1.2 billion gallons (4.5 billion l) per day.

Photo: Zurn Industries, LLC

Context: The Energy Policy Act of 1992 (EPAct92) mandated a maximum of 1.6 gallons of water per flush (gpf; 6 liters per flush, or lpf) for most toilets beginning in 1994 (and for flushometer-valve toilets beginning in 1997). Despite initial problems, performance has improved dramatically in the past ten years. Desire for even better efficiency now fuels demand for toilets that use at least 20% less water than standard 1.6-gpf models; these are termed high-efficiency toilets (HETs).

State of the art: High-efficiency toilets today are available with gravity-flush, pressure-assist, and flushometer–valve mechanisms. Pressure-assist toilets, which compress air at the top of the refill tank to increase the flush velocity, use as little as 0.8 gpf (3 lpf) and typically achieve excellent performance. Flushometer-valve toilets, which use direct water pressure without a tank, are common in commercial buildings. Dual-flush toilets, pioneered by Caroma in Australia, now dominate Australia and much of Europe. Introduced into North America by Caroma in 1999, most dual-flush toilets use 1.6 gpf for solids and 0.8 to 1.1 gpf (3–4 lpf) for liquids and paper. Caroma recently introduced a model with a full flush of 1.28 gpf (4.8 lpf) and a reduced flush of 0.8 gpf.

In 2006, the U.S. Environmental Protection Agency (EPA) introduced WaterSense, a voluntary program designed to promote the market for water-efficient products and services. Approximately 130 HETs have been certified to bear the WaterSense label. To carry the WaterSense label, HETs must be independently tested using the Maximum Performance (MaP) testing protocol that measures the ability of toilets to remove standardized test media (see EBN Vol. 13, No. 1).

On the horizon: HETs may become standard nationwide. California has passed legislation that will mandate that all new toilets sold or installed in the state after 2014 be HETs (see EBN Vol. 16, No. 11). According to Barbara Higgins, executive director of the Plumbing Manufacturers Institute, the plumbing industry is lobbying to make this requirement the new federal standard—with a clearly defined schedule that gives manufacturers time to modify their products.

Composting and other ultra-low-
water-use toilets

Context: Composting toilets have been around since the 1970s but maintain just a tiny market share in North America. These toilets use no potable water (or almost none) and produce organic mulch for nonfood plantings. The need for extreme water conservation can also be satisfied by other ultra-low-flush toilets, including those relying on centralized vacuum systems and air pressure from compressors—technologies that were developed primarily for specialized uses such as airplanes, boats, and recreational vehicles.

State of the art: While no major manufacturers are known to be developing composting toilets, several smaller companies have gradually improved the technology. Most installations are in recreational settings without running water, though they sometimes appear in urban green buildings. Other types of toilets that use considerably less than a gallon of water per flush include air-pressure toilets made by Microphor that use as little as a quart (one liter) per flush as well as vacuum toilet systems made by Evac that are finding use in prisons, military bases, and other large applications.

On the horizon: With gravity-flush, pressure-assist, and flushometer toilets improving so dramatically in both performance and water conservation, composting toilets and other ultra-low-flush toilets are unlikely to capture much market share, except in unusual situations.

Urinals

Context: The maximum flush volume for urinals in the U.S. is one gallon (4 l), and most urinals today use the full gallon. This profligate waste led to the introduction of waterless urinals in the 1990s, first by the Waterless Company and then followed by at least a half-dozen other companies. In a sizeable office or institutional building, a waterless urinal can save as much as 40,000 gallons (150,000 l) per year. However, most waterless urinals rely on regular replacement of a vegetable-oil-based fluid and a disposable cartridge to maintain performance of the sanitary trap. Keeping waterless urinals clean and preventing the deposition of uric salts in the drain line have proven to be problematic.

State of the art: Waterless urinals are gaining acceptance in many parts of the country and, if properly installed and maintained, should prove satisfactory. Two companies, Caroma in Australia and Ecotech Water in the U.S., have introduced waterless urinals that rely on a rubberized membrane that lets liquid through and then curls up to provide a mechanical seal between uses. That seal allows rinse-water to be poured through the urinal periodically for cleaning without washing away expensive sealant fluid. The track record is very short, however, and, according to John Koeller, P.E., a water conservation specialist and technical advisor to the new Alliance for Water Efficiency, the technology is generally not permitted by code officials, since mechanical seals are not allowed in the U.S. Meanwhile, a new generation of ultra-low-flush urinals is entering the market. These products, available from companies including Zurn Industries, Sloan Valve, and Caroma, use as little as one pint (0.5 l) of water per flush (see EBN Vol. 16, No. 11), and the regular flushing is expected to prevent uric salts from accumulating in drain lines.

On the horizon: As the market gains experience with waterless urinals, we can expect to see installation and operation guidelines that improve performance and user satisfaction. Meanwhile, ultra-low-flush urinals will likely capture some of the waterless urinal market share. EPA plans to offer a WaterSense label for high-efficiency urinals (HEUs), which are likely to be defined as using 0.5 gpf (2 lpf) or less. (BuildingGreen’s GreenSpec Directory standard for urinals is currently 0.25 gpf (0.95 lpf). For more on GreenSpec water-use criteria refer to the relevant section introductions.)

The Ecoblue Cube takes a very different approach to reducing water use in urinals, with a small cube-shaped urinal cake that releases beneficial bacteria. These bacteria line the bowl, trap, and pipes, preventing odors and uric acid deposition (see EBN Vol. 17, No. 1). If this product works (so far so good in trials at BuildingGreen and Veritec Consulting), it could significantly reduce water use in urinals of all types by allowing them to be flushed only periodically.

Showerheads

Context: Showerheads, like toilets, are regulated by EPAct92, which established a limit of 2.5 gallons per minute (gpm; 9.5 liters per minute, or lpm) at 80 psi of water pressure. Because showers use hot water, reducing water use also saves energy. Replacing an older showerhead, which may flow at 5 gpm (20 lpm) or more, with a unit that uses 2.0 gpm (8 lpm) or less can pay for itself through reduced water and energy use in just a few months. Some early low-flow showerheads atomized the water into tiny, high-pressure droplets that did not wet the body effectively and quickly cooled off through evaporation. Some showerheads today achieve the federally mandated flow with restrictors that can be easily removed by a plumber or user, allowing the flow to be significantly increased—thus circumventing the regulations. Another way people have circumvented requirements is by installing multiple showerheads and body-wash nozzles in one shower system or by creating rain-like water sculptures that manufacturers claim are not showers at all. Kohler and Delta Faucet, among others, market high-end shower-tower systems that use as much as 20 gpm (80 lpm), which is contributing to a measured rise in water consumption in new homes.

State of the art: The best showerheads today have been designed for water efficiency from the ground up. Some models rely on the Venturi effect to aerate droplets and create the feel of a forceful shower while using relatively little water—as little as 1.5 gpm (5.7 lpm); a challenge here is to keep the aeration from making the droplets too small. Manufacturers using this approach include ETL, Bricor, and Hansgrohe with its 1.6 gpm (6 lpm) Croma EcoAir 1-Jet. Other manufacturers, including Delta Faucet, have gone even further in showerhead redesign, creating a pulsed shower with large droplets (see the review of H2Okinetics technology in EBN Vol. 15, No. 5).

On the horizon: EPA’s WaterSense is working on a standard for showerheads that will likely bring us WaterSense-labeled products by the end of 2009 with a maximum flow of 2.0 gpm (8 lpm), or possibly lower. (The GreenSpec standard for showerheads is 1.75 gpm [6.6 lpm].) Plumbing manufacturers are developing methods of measuring the wetting performance and heat retention of showerheads, according to Koeller, and EPA could eventually incorporate such performance attributes into WaterSense standards. Look for the multiple-showerhead loophole to be addressed in some way in the next several years. Also, regulations may prevent showerheads from being modified to increase flow above the legal limit.

Faucets

Context: EPAct92 limits the flow rate of residential kitchen and lavatory (bathroom) faucets to 2.5 gpm (9.5 lpm) at 80 psi, or 2.2 gpm (8.3 lpm) at 60 psi—although some faucets today achieve the federally mandated flow with either aerators or flow restrictors that can be removed, allowing the flow to be significantly increased. EPA’s WaterSense has adopted a more aggressive maximum flow rate of 1.5 gpm (5.7 lpm) at 60 psi for residential lavatory faucets; because of the need to fill kitchen pots with water, however, a WaterSense standard for kitchen faucets has not been adopted. In kitchens, flow controllability tends to be a more significant water-saving feature. While sensors that turn on the flow when a user’s hands are properly positioned—most common in commercial buildings but making their way into homes—might seem like a water-saving feature, studies have shown that they often increase water use because they turn on unnecessarily or stay on longer than needed.

State of the art: Simple, inexpensive aerators can adapt any modern kitchen or lavatory faucet into a water-efficient unit—with flow rates as low as 0.5 gpm (2 lpm). The lower the flow rate, however, the longer it takes hot water to reach the user (see demand-controlled hot water circulators, below). A perception of greater flow can be achieved by aerating the water stream or by creating a laminar flow (essentially a hollow cylinder of water that appears to be solid). Significant savings can be achieved with faucets—and especially kitchen faucets—by installing a foot- or knee-operated control so that users can turn the water on and off without using their hands (and while retaining the desired temperature mix). A less expensive option is a simple lever control on the faucet itself that allows the user to temporarily reduce the flow (though usually not turn it all the way off) with a simple flick of the finger.

On the horizon: Once more people experience the convenience and water savings of foot- and knee-operated controls for faucets, these devices are likely to become more common—especially if less expensive models enter the market. We may also see sensor-activated controls that actually save water. Finally, we may see regulations for faucets that prevent them from being modified to increase the flow above the legal limit.

Pre-rinse spray valves

 

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This Fisher Ultra-Spray pre-rinse spray valve uses just 1.2 gallons of water per minute (4.5 lpm), well below the 2006 federal maximum of 1.6 gpm (6.1 lpm).

Photo: Fisher Manufacturing

Context: Commercial kitchens use pre-rinse spray valves to rinse dishes before they go into the dishwasher. These units consist of a spray nozzle, a squeeze lever controlling water flow, and a dish-guard bumper. (Note that pre-rinse spray valves are different than spray valves used for filling cooking pots, which have higher flow rates.) Pre-rinse spray valves have flow rates as high as 5 gpm (20 lpm)—with an average of about 3.2 gpm (12 lpm), according to Pacific Gas & Electric’s Food Service Technology Center in San Ramon, California. In a typical commercial kitchen, more water is used rinsing dishes than washing them in dishwashers. The Energy Policy Act of 2005 (EPAct2005) established a maximum legal flow rate of 1.6 gpm (6.0 lpm) for pre-rinse spray valves manufactured after January 1, 2006. Compared with a spray valve using 3.2 gpm, a 1.6 gpm model in a small, quick-serve restaurant will save about 50,000 gallons (190,000 l) of water and $1,000 in energy costs per year.

State of the art: At least three manufacturers produce pre-rinse spray valves that use no more than 1.28 gpm (4.8 lpm; 20% less than the federal maximum) and meet a stringent standard for performance of 21 seconds per plate, based on a standard test procedure. (These criteria for pre-rinse spray valves have been adopted by GreenSpec.)

On the horizon: EPA had been planning to adopt voluntary Energy Star criteria for pre-rinse spray valves but decided against that after the new federal standard was adopted as part of EPAct2005. With clear performance metrics and demonstrated savings from the replacement of older models, we can expect to see more water conservation programs offering rebates for such replacements.

Demand-Controlled Hot Water Circulators

Context: Waiting for hot water in bathrooms and kitchens wastes a tremendous amount of water nationally. The amount of waste depends on the pipe diameter and the distance between the fixture and the water heater; the flow rate of the end-use fixture may also affect the waste slightly and it significantly affects the wait time for hot water. Continuous-circulation systems, which maintain a loop of circulating hot water, can save water while eliminating the wait for hot water. Such systems are very common in hotels and are becoming more common in homes. The problem with continuous-circulation systems is that they waste tremendous amounts of energy because they turn hot-water pipes into low-temperature radiators—increasing energy use for water heating year-round and for air conditioning in warmer months. Timer-controlled circulators reduce this energy waste by turning off the pump during certain periods of day or night.

State of the art: Demand-controlled hot water circulators can solve these problems. The D’Mand system is marketed by three companies: ACT Metlund, Taco, and Uponor (formerly Wirsbo). With these systems, a user activates a small pump, by either pushing a button or tripping an occupancy sensor, that quickly delivers hot water. Cold water that had been sitting in the hot-water pipes, meanwhile, returns to the water heater instead of running out of the tap. When hot water reaches the fixture, a temperature sensor turns off the pump. (For more detail, see EBN Vol. 12, No. 5.)

A less expensive and simpler (though less effective) strategy for reducing water waste while waiting for hot water is to insulate all hot water pipes. With insulation, hot water in the pipes will cool down more slowly, so that the next user may not need to let the water run while waiting for hot water. Pre-slit, closed-cell polyurethane foam pipe insulation, sized to the pipes being insulated, is generally the most convenient option.

On the horizon: “Home-run” systems that deliver water separately to individual fixtures and appliances through cross-linked polyethylene (PEX) tubing sized to the flow-rate requirements can reduce waste and reduce the wait time for hot water. The rising popularity of PEX has brought greater use of such home-run systems, and it’s likely that demand-controlled hot water circulators will become much more common.

Appliances

A number of residential and commercial appliances are addressed below, providing a sampling of savings that can be achieved.

Residential clothes washers

 

Residential Clothes Washer Energy- and Water-Efficiency Standards

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Source: CEE and EPA Energy Star

Context: Vertical-axis (top-loading) clothes washers require two to three times more water than horizontal-axis (H-axis) washers because the former almost fully submerge laundry, while H-axis washers dip laundry in and out of the wash water as the inner drum rotates. Because most people wash with hot water, the H-axis machines save significant energy. The market share of H-axis washers has been increasing rapidly: from 9% of sales in 2001 to 29% in 2006, according to the Association of Home Appliance Manufacturers.

State of the art: Most of today’s water- and energy-efficient clothes washers are H-axis, and all but one of these are front-loading. New federal energy standards for residential clothes washers—top-loading and front-loading—went into effect January 1, 2007, raising from 1.04 to 1.26 the modified energy factor (MEF), which is the capacity of the washer divided by the sum of the machine’s electrical energy, water heating energy, and energy required to remove remaining water for a wash cycle, expressed in ft3/kWh/cycle. At the same time, EPA increased MEF standards for Energy Star certification (from 1.42 to 1.72) and added a water factor (WF) maximum of 8.0. The water factor is the number of gallons used for a full wash and rinse cycle per cubic foot of drum capacity. Given average usage, a one-unit reduction in a clothes washer’s water factor (from nine to eight, for example) will save about 1,000 gallons (4,000 l) per year. Meanwhile, the Consortium for Energy Efficiency (CEE), whose standards are often used as a basis for rebates, also increased the performance requirements on January 1, 2007, for its Tier 1, 2, and 3 designations for washers, as shown in the table below.

On the horizon: The recently signed Energy Independence and Security Act of 2007 (see 2007 Energy Bill Promotes High-Performance Buildings) establishes, for the first time, a maximum water factor for clothes washers. The legislation establishes a limit of 9.5 gal/ft3 (1300 l/m3), effective January 1, 2011, and sets the stage for further tightening energy- and water-use standards in 2015 and 2018. The average water factor of top-loading, vertical-axis washers today is about 11.5, so this change will hasten the industry transition toward H-axis machines.

Commercial clothes washers

Context: Residential-style H-axis clothes washers have been the norm in laundromats for some time and are addressed by both federal standards and Energy Star. Larger commercial laundry systems, often called washer-extractors, are common in hotels, hospitals, and nursing homes. Although these systems are not addressed by federal standards or Energy Star, they outperform the smaller machines in both energy efficiency and water savings. Washer-extractors are available with capacities of hundreds of pounds and often include an option for water reuse.

State of the art: Prior to 2007, there was no federal standard for residential-style commercial clothes washers, while there was an MEF threshold of 1.42 for Energy Star listing. Effective in 2007, the federal standard of MEF 1.26 and WF 9.5 was adopted, and the Energy Star threshold was tightened to MEF 1.72 and WF 8.0.

On the horizon: Look for continued reductions in water and energy use with residential-style clothes washers as well as advances in onsite water recovery and reuse, which are already common with washer-extractors.

Residential dishwashers

Context: The water and energy use of residential dishwashers have dropped considerably since federal energy performance standards first went into effect in 1994. While standard-sized dishwashers used 11–15 gallons (42–57 l) of water for a full cycle in 1978, today’s models typically use just 3–10 gallons (11–38 l). (By comparison, washing and rinsing an equivalent load of dishes in the kitchen sink, according to John Koeller, uses about 18 gallons (68 l) of water.) More than 60% of the total energy use by dishwashers goes to heat water, so efforts to improve energy efficiency focus on reducing water use. The energy factor for dishwashers is defined as the number of wash cycles per kWh, accounting for both the dishwasher’s electrical energy use and the energy required for heating water.

State of the art: With residential dishwashers, many top-of-the-line models, such as the Bosch 800-series Evolution SHE98 (which BuildingGreen recognized as a 2007 Top-10 Green Building Product—see EBN Vol. 16, No. 12), are the most resource-efficient. This product has an energy factor of 1.14, compared with the federal minimum of 0.46 and the Energy Star minimum of 0.65. Among the features used to achieve this water savings are controls that adjust wash conditions, including water use, according to how dirty the dishes are.

On the horizon: One of the technologies being researched is ultrasonic washing, in which high-frequency sound generators create cavitation bubbles in the dishwasher that surround the dishware. According to a November 2007 U.S. Department of Energy technology assessment, “these bubbles implode upon contact with a surface, effecting a mechanical scrubbing action that removes soil from the dishware.” Sharp introduced a countertop dishwasher for the Japanese market in 2002 that uses a somewhat different ultrasonic process to create a fine mist and hardens water with table salt to help remove protein-based stains. These more radical innovations aside, dishwasher cleaning performance should continue to improve even with continued reductions in water and energy use.

Commercial dishwashers

 

Energy Star Efficiency Requirements for Commercial Dishwashers

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Source: Energy Star

Context: Commercial dishwashers are divided into several categories, based on configuration, means of sterilization, and size. High-temperature models use hot water—typically boosted to about 180°F (82°C)—to sterilize dishes, while lower-temperature models use water at 140°F (60°C) or lower plus chemical additives to sterilize dishes. The smallest undercounter models work like residential dishwashers, except that they operate at higher temperatures and with much shorter wash cycles—as short as 90 seconds. Larger kitchens and institutional cafeterias use warewashers, which pass racks of dishes through multiple tanks on a conveyor belt. Energy Star standards for commercial dishwashers went into effect in October 2007 (see EBN Vol. 16, No. 9).

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Hobart’s revolutionary Opti-Rinse spray nozzle reduced rinse water use in the company’s conveyor-type commercial dishwashers by half.

Photo: Hobart

State of the art: Considerable attention has been paid to commercial dishwashers in recent years. The Energy Star product list includes more than 120 commercial dishwasher models from ten manufacturers. Water consumption for the multiple-tank conveyor systems is as low as 0.28 gallons (1.1 l) per rack. Energy Star limits are shown in the table below.

Many technologies have contributed to the improved water efficiency of commercial dishwashers. Hobart, for example, introduced an Opti-Rinse System in 2004 with spray nozzles that cut water use in half. This technology alone reduced the water use per rack from 1.49 to 0.74 gallons (5.64 to 2.80 l) on certain Hobart products.

On the horizon: With Energy Star standards in place, continued reductions in energy and water use by commercial dishwashers are likely.

Commercial steamers

 

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A standard commercial steamer consumes about 80,000 gallons of water per year—most of it tap water to cool the condensate. AccuTemp’s Steam’N’Hold, shown here, is a boilerless (or connectionless) steamer that dramatically reduces water use.

Photo: AccuTemp Products, Inc.

Context: In commercial food-service establishments, food steamers use significant amounts of water and energy. Steam contains six times the energy of boiling water and quickly heats food when it condenses on its surface, transferring its latent heat to the food. Older steamers inject steam into the cooking cavity at a constant rate from a boiler or steam generator; steam not condensing on the food escapes as a mixture of steam and condensate through a drain line. This escaping steam and hot water directly wastes water and energy, and the need to cool off the condensate (to a maximum of 140°F, or 60°C, according to most codes) with tap water before it enters the sewer line indirectly wastes a great deal more. A 2005 California study found an average flow rate of over 40 gallons (150 l) per hour in these condensate lines. In many restaurants, steamers are turned on in the morning and left on until closing. The study estimated that 250,000 commercial steamers operate nationwide, each consuming about 80,000 gallons (300,000 l) per year.

State of the art: Boilerless, also known as connectionless, steamers do not have condensate drain lines, so do not require cold water flow to cool the condensate. Because most of the steam is retained, they require significantly less heat input. Beginning in August 2003, Energy Star began qualifying commercial steamers that achieve a cooking energy efficiency of at least 50% for electric models and 38% for gas models. Some electric steamers achieve efficiencies as high as 73% with convection fans to improve steam circulation, vacuum pumps to lower the cooking temperature, improved insulation, an efficient standby mode, and advanced controls. In a corporate cafeteria case study in the California study, replacing an older boiler-based steamer with stacked, boilerless steamers cut water use from 479 to 33 gallons (1,810 to 125 l) and energy use from 104 kWh to 29.9 kWh per day, resulting in annual water and energy cost savings of $3,284.

Heating, Ventilation, and Air Conditioning (HVAC) Systems

HVAC systems in commercial buildings use a lot of water. The bulk of this water use is by cooling towers, which water conservation specialist Bill Hoffman of Austin, Texas, describes as devices “to get rid of unwanted energy with wanted water.” For every ton-hour (3.5 kWh) of cooling, according to Hoffman, 1.44 gallons (5.45 l) of water are evaporated. “The first and foremost water conservation practice you can follow is energy conservation,” he told EBN. While general energy-conservation measures are not described here, strategies like energy-efficient lighting and optimized glazing should top any project’s list for reducing water use.

Cooling towers

 

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Evapco’s WDW hybrid cooling tower has an extremely low drift rate of just 0.001% and further saves water by operating dry much of the year.

Photo: Evapco

Context: Cooling towers chill buildings by evaporating water. With a typical cooling tower, warm water from the heat source (such as an air-conditioning system or process equipment) is pumped to the top of a cooling tower and is either sprayed or dripped through fill material called wet decking. Air blown through the falling water evaporates and chills the water. Water is lost in the cooling tower through three processes: evaporation through the top of the tower, which amounts to about three gallons per minute (11 l/min) in a 100-ton (350 kW) chiller; drift losses, or droplets of water (mist) carried out of the tower by the airflow; and blowdown, the regular removal of water from the bottom of the cooling tower to lower concentrations of dissolved minerals and other contaminants. To compensate for these losses, makeup water is continually added to cooling towers. The higher the acceptable concentration ratio, or level of dissolved minerals in the blowdown water, the greater the water savings, because less makeup water is needed. For this reason, considerable effort is warranted to reduce the problems caused by high levels of dissolved minerals and contaminants, such as scaling and bacteria-laden biofilms.

State of the art: Various features in cooling towers can reduce the amount of makeup water required. First, both the makeup and blowdown water flows should be metered so that operators can gauge performance and water use. Conductivity controllers should be used to maintain the desired concentration ratio in the cooling-tower water. Overflow alarms should be installed to prevent waste. Finally, efficient drift eliminators should be used to keep drift losses to a minimum. In the proposed Standard 189, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers [ASHRAE] calls for limiting drift loss to 0.001% of the circulated water volume for counter-flow towers and 0.005% for cross-flow towers.

On the horizon: There are a number of water-treatment technologies claimed by their manufacturers to prevent scaling and protect water quality in cooling towers. Some rely on magnets that apparently alter the surface charge of dissolved or suspended particles and prevent deposition; others rely on electrostatic field generation, accomplishing the same result (see EBN Vol. 14, No. 4 for a review of one such system, the Dolphin). While such systems have avid believers—and growing sales—the unusual chemistry and physics involved, and a paucity of third-party testing, has produced skepticism. If testing can verify performance claims, such systems offer significant water- (as well as energy- and chemical-) saving potential.

Commercial boilers

Context: Commercial steam boilers and steam distribution systems, especially older systems, are inherently leaky and require large quantities of makeup water. Some old steam-based district heating networks, in fact, are single-pipe systems with no condensate return lines—the condensate simply drains to sewer pipes.

State of the art: At a minimum, older steam systems without condensate return pipes should be retrofitted to recover both water and heat; this measure can reduce operating costs by as much as 50% to 70%, according to Amy Vickers in her Handbook of Water Use and Conservation. A better solution is to convert steam distribution systems to hot water. Operating at lower pressure, hot water piping is much less prone to leakage, and the lower temperature significantly cuts heat loss from the piping. Other good practices include using well-insulated piping designed for district heat, installing flow meters on blowdown discharge valves and makeup water inlets, and providing automated controls for blowdown discharge and makeup water. Blowdown (boiler bleed-off) should be based on water-quality testing rather than timers.

Process Equipment

Context: A lot of process equipment used in industry, laboratory, and healthcare settings generates heat that has to be dissipated. Often, this is done with once-through cooling. A 20-horsepower (15 kW) vacuum pump used around the clock in a small manufacturing plant may use 12 gpm (45 lpm) of water for cooling—more than six million gallons (20 million l) per year.

State of the art: Recirculating cooling systems can save a tremendous quantity of water, compared with once-through systems. Providing a chiller or cooling tower to chill water for process equipment usually results in even greater savings. Alternately, water-cooled equipment can be replaced with air-cooled equipment, coupled with proper ventilation to prevent significant increases in cooling loads.

On the horizon: With some process equipment, newer technology generates less heat. Digital x-ray machines in hospitals, for example, can save thousands of gallons per day, compared with film-based technology; more efficient pumps and motors generate less waste heat, and better engineering can allow waste heat to be captured from heat-generating processes and transferred to a heat-requiring processes, saving energy at both ends.

Outdoor Water Use

This section addresses water use for the landscapes around our buildings. Swimming pools, fountains, and other outdoor water features can also be very significant water users but are not covered in this article; nor is agricultural water use.

Xeriscaping and native plants

Context: Irrigation practices vary widely by region. The American Water Works Association Research Foundation (AWWARF) reports that in dry places, such as Phoenix and Scottsdale, outdoor water use accounts for 59%–67% of total residential water use, while in wetter places, such as Seattle and Tampa, outdoor use accounts for 22%–38%. AWWARF reported outdoor water use in Phoenix at over 440 gallons (1,700 l) per household per day. The vast majority of this outdoor water use is for lawns; nationwide we plant mostly variations of Kentucky bluegrass, which was cultivated from a species native to the British Isles and requires about 40 inches (1 m) of rain per year to prosper.

State of the art: Landscaping with climate-adapted plants, which require little or no irrigation, should be a top priority. Often called xeriscaping, this practice is gradually gaining acceptance, though many municipalities mandate green lawns and prohibit xeriscaping. In some areas, we are seeing growing use of artifical turf, which can save a lot of water but raises lots of other issues (see EBN Vol. 13, No. 4).

On the horizon: In drier and drought-prone regions, we can expect an end to regulations requiring lawns. In their place will be incentives to convert high-water lawn areas to xeriscaping. Xeriscaping and associated products and services should become more common.

Water-efficient irrigation

Context: In drier parts of the country, not only is landscape irrigation common, but standard irrigation practices often waste a significant portion of the water that is used. Evaporation, uneven distribution and pooling, piping leaks, poorly targeted spray nozzles, and irrigation when the water isn’t needed can waste a tremendous amount of water —75% or more.

driphose.jpg

Subsurface drip irrigation delivers water directly to the root zone and significantly reduces evaporation. This system is being installed in Colorado.

Photo: Denver Water

State of the art: Drip irrigation, soaker hoses, and microspray heads can reduce evaporation, overwatering, and improperly targeted delivery. The greatest savings can often be achieved with newer, more advanced controllers that adjust water delivery according to soil moisture and weather predictions. (The WeatherTRAK irrigation control system, for example, was a BuildingGreen Top-10 Green Building Product for 2006—see EBN Vol. 15, No. 12.) Potable water use can be reduced or eliminated by using harvested rainwater, graywater, and treated wastewater for irrigation.

Final Thoughts

There are strong indications that water will become a more limited resource over the coming decades, and it is important for building professionals to pay close attention to these trends and build up the expertise needed to reduce water consumption in and around buildings should supply become further constrained. The good news is that the U.S. has become significantly more water-efficient in the past several decades—showing that a lot can be achieved—and there are still plenty of opportunities for further improvement.

Alternative water sources—and the separation of potable and nonpotable water uses—will also play an important role in satisfying water needs. Look for coverage of this topic in a later issue of EBN, along with information on the policy side—incentives, fee structures, regulations, and other strategies to encourage wise management of our water resource.

Finally, fairly simple changes in behavior by building occupants can significantly reduce water use. Homeowners can avoid running the water while rinsing dishes or take shorter showers. Commercial building managers can maintain higher temperature set points on evenings and weekends to reduce cooling needs and be more frugal with irrigation. Technology has a huge role to play in saving water, but so do our actions. Educating building occupants about water conservation can make a big difference.

with research support from Rachel Navaro

For more information:

Alliance for Water Efficiency

www.allianceforwaterefficiency.org

American Water Works Association

www.awwa.org

Consortium for Energy Efficiency

www.cee1.org

EPA Energy Star Program

www.energystar.gov

Food Service Technology Center

www.fishnick.com

Plumbing Manufacturers Institute

www.pmihome.org

 

 

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February 3, 2008