Navigating Incentives and Regulations for Green Building
When used in combination, incentives and regulations can be a powerful force for encouraging green buildings.
by Allyson Wendt
You catch more flies with honey than you do with vinegar, or so the proverb tells us. That may be why new approaches to design and construction seem to be most successful when they are introduced first as voluntary measures that can be used to garner green credentials, or, increasingly, to benefit from government incentives. But as new approaches gain market acceptance they also begin to show up as mandatory measures via codes or other regulations—quickly in some areas and very slowly in others.
Whereas incentives are welcomed by the private sector, green building requirements are not always greeted with as much enthusiasm. What regulations there are tend to begin in the public sector when governments make their own buildings meet environmental criteria. Now jurisdictions are beginning to extend regulations to the private sector as well, using a variety of approaches to mandate green building in both the commercial and residential arenas.
Green building incentives can offer significant financial benefits, and regulations are becoming increasingly common. This article explores a few of the incentive and regulatory mechanisms currently in place and some on the horizon, and provides tips for incorporating this information into design decisions.
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.
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.
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
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
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.
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
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.
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
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.
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/ft
3 (1300 l/m
3), 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.
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
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
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
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.
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
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.
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.
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
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.
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.
The Challenge of Existing Homes: Retrofitting for Dramatic Energy Savings
by Allyson Wendt
One can hardly pick up a magazine or turn on the television today without hearing something about climate change. The issue finally appears to be gaining traction in our nation’s collective consciousness. Much of the focus of reducing greenhouse gas emissions rightly centers on how we design and construct buildings. Indeed, the 2030 Challenge, adopted by The American Institute of Architects, the U.S. Green Building Council, and others, calls for commercial and residential buildings being built today to use half the fossil fuel of average existing buildings and a gradual increase in performance so that new buildings are carbon-neutral by 2030 (see EBN Vol. 16, No. 6).
This goal is critically important. But it isn’t enough. If we as a society are to achieve the sorts of reductions in greenhouse gas emissions that climate scientists tell us are needed to prevent catastrophic climate change, we also need to tackle our existing building stock, including houses. The 2030 Challenge calls for the renovation of existing building stock equal in square footage to that of newly constructed buildings and achieving the same 50% reduction in fossil fuel use. Achieving this goal with residential buildings would require leading-edge energy retrofits on about 1.5 million existing homes per year—while today there are at most a few thousand energy retrofits per year that achieve such a target, and probably far fewer. This article examines the challenge of existing houses and the potential for dramatically reducing the energy consumption (and greenhouse gas emissions) of these buildings through major renovations.
The Scale of the Challenge
There are 124 million housing units in the U.S., according to the U.S. Census Bureau. Of these, about 85 million are site-built single-family homes, 8.6 million are manufactured or mobile homes, and the rest are units in buildings that house multiple families. If we include single-family, multifamily up to four units (which are similar to single-family in design and performance), and manufactured and mobile homes, there are about 103 million existing houses in the country, and it’s these that we focus on in this article.
The median age of all housing units in the U.S. (including multifamily) is 34 years (built in 1973), meaning that 50% are older and 50% are newer; 77% were built in 1950 or later.
In 2004, residential buildings in the U.S. used 21.1 quads (22 million terajoules) of energy, or 21% of the nation’s total primary energy consumption and 36% of total electricity consumption. (Primary energy is that energy contained in, or used to produce, the fuels and electricity we consume; it includes the fuel that utility companies use to generate electricity rather than the electricity itself.) On a per-household basis in the U.S., total primary energy consumption in 2004 was 185 million Btus (195 gigajoules), and total delivered energy consumption was 101 million Btus (107 gigajoules). Within the residential sector, the largest users of primary energy are shown in the table below. In different regions of the country, this split among energy end-uses is quite different; the share for space cooling, for example, is significantly higher in the South than it is in the rest of the country.
As for impact on global warming, the greenhouse gas emissions associated with residential energy use in the U.S. in 2005 totaled 330 million metric tons carbon equivalent. This represents 20.5% of total carbon emissions for the U.S. and nearly equals the total carbon emissions of Japan, whose economy ranks second to the U.S. but whose carbon emissions rank fourth—well behind China (now number one), the U.S., and Russia. Interestingly, of the carbon dioxide production attributed to our residential buildings, 70% is from electricity use and only 30% is from direct combustion of fossil fuels.
What is Achievable?
Climate researcher James Hansen, Ph.D., of NASA argued in testimony before the U.S. House of Representatives in April 2007 that the level of carbon dioxide in the atmosphere at which catastrophic climate change would occur is likely about 450 parts per million (ppm), and could be lower. (The current CO2 level is about 385 ppm, up from about 315 ppm in 1958.) Although Hansen did not present any specific reduction in carbon emissions needed to stabilize carbon dioxide levels during that testimony, he has elsewhere suggested that a 60% to 80% reduction would be required. A number of prominent scientific and environmental organizations, including the Union of Concerned Scientists, have called for an 80% reduction in U.S. greenhouse gas emissions by 2050. Both California and New Jersey have adopted that target as a state goal, and legislation recently entered in the U.S. Senate and House of Representatives sets such a target.
The United Nations’ Intergovernmental Panel on Climate Change (IPCC), in a draft of a report to be released in October 2007, finds significant opportunities for carbon emissions mitigation in both new and existing buildings. According to IPCC, 30% of the expected global growth in emissions related to buildings before 2030 could be avoided with economic benefit. The report also finds that, although new buildings present opportunities for the most energy savings per building, existing buildings represent a greater opportunity for energy savings overall.
According to a 1998 study prepared for the U.S. Environmental Protection Agency, about 290,000 buildings are demolished every year, 245,000 of which are residential (about 0.2% of all residential buildings). If all of these demolished houses were replaced with new, carbon-neutral houses and if the energy performance of existing houses was not improved, this turnover rate of housing (0.2% per year) would achieve only about a 6% reduction in total residential carbon emissions by 2030 (10% by 2050)—far less than that called for by climate scientists.
To achieve the carbon emissions reductions called for by Hansen and others, we need to aggressively address existing buildings, including homes. In the 2005 report of the Pew Center on Global Climate Change, Towards a Climate-Friendly Built Environment, Marilyn Brown, Frank Southworth, and Therese Stovall, of Oak Ridge National Laboratory, suggest that with new residential buildings, energy consumption can be reduced 60% to 70% by 2020 compared with conventional practice. With existing buildings, achieving similar energy reduction targets will rarely be possible, but the starting point is often worse, so a reasonable target is to reduce energy use by one-half to two-thirds (the greater savings achievable only with homes that start out with very poor performance). Achieving such a reduction may be both challenging and expensive, but it is possible—and it would reduce loads enough that, with good solar exposure, rooftop solar panels (photovoltaic and solar-thermal) could enable such homes to achieve zero-net-energy performance.
Achieving a Three-Fold Reduction in Energy Use
Taking on such a robust challenge to reduce energy use in an existing home requires significant efforts on multiple levels. Cutting energy consumption by two-thirds or more necessitates addressing equipment for heating, cooling, and water heating as well as lighting, appliances, and electronics (including entertainment and computer equipment). However, one can’t get anywhere close to such a goal without tackling the building envelope: foundation, walls, windows, and roof (or attic floor). We will start there.
How far to go in upgrading the house envelope depends, to a significant degree, on the climate. In cold climates, where heating dominates energy use, it makes sense to start with measures that reduce heating loads: air sealing, adding insulation, and improving the energy performance of windows. According to building energy expert Ambrose Spencer, “a superinsulation retrofit in the Northeast can cut the heating load in half.” In warmer climates, where air conditioning accounts for a significant fraction of total energy use, reducing cooling loads is proportionally more important, with solar control measures and air sealing as key strategies. In any climate, however, tightening a house with insulation and air sealing can cause moisture levels inside the house to rise, so paying attention to the vapor profile of wall and roof assemblies is critically important.
The cost of such retrofits is an impediment—running tens of thousands of dollars per house. As Bruce Harley, technical director for Conservation Services Group, told EBN, “I’d be hard-pressed to find a house where you could do [a major energy retrofit] for less than $50,000.” Other experts EBN spoke with, including builder John Abrams, agree. Using the estimate of $50,000 per retrofit, achieving the near-term 2030 Challenge of retrofitting 1.5 million homes per year in the U.S. would cost $75 billion per year.
In any climate, major improvements to the envelope are easiest—and cheapest—when other major renovations are happening at the same time. “If someone’s planning on replacing their siding anyway,” said Harley, “that’s the time to add one, two, or three inches of foam insulation.” Adding insulation to the exterior of a house also allows occupants to live in the house while the work is being done, which can reduce costs. Air sealing, which also improves performance, can occur at the same time. Spencer argues that this is one of the easier ways to improve existing houses. “Every time a siding replacement is done, I’d like to see extra exterior insulation added,” he said.
Meeting Energy Loads with Renewables
If energy loads have been reduced enough, or if the house is located in an extremely sunny climate, it may be possible to meet those loads with renewable energy systems—achieving zero-net-energy performance. Solar-thermal heating systems, solar water-heating systems, and photovoltaic (PV) power systems are typically the most viable options for homes, and true net-zero-energy homes generally require a combination of these systems.
Spencer and others argue that renewable energy systems should be considered only after the building envelope has been addressed. “If you have the opportunity to deal with the envelope and you spend your money on photovoltaics instead,” he told EBN, “you’ve made it nearly impossible to improve the building later.” If the energy loads are brought low enough, however, a renewable energy system may make sense financially.
Occasionally, the economics point towards putting money into renewable energy rather than lowering demand. Eric Doub, a builder of low-energy homes in Boulder, Colorado, is working on a zero-net-energy retrofit that is nearing completion. According to Doub, “we didn’t have far to go to get this home to be superinsulated,” which meant that more money could be put into renewable energy sources. Doub added a $30,000 evacuated-tube solar thermal system and a 6.5-kW PV system that cost $25,000 after rebates. By comparison, the envelope improvements to the house cost $15,000. Although Doub admitted that “the PV system will be nowhere near cost-neutral at current electricity costs,” his clients’ desire to be able to provide all of their energy needs, including those for a plug-in electric car when one becomes available, with renewable energy made the PV system worth the money.
Case Study: Pettit Four-Square House, Massachusetts
When Betsy Pettit, AIA, of Building Science Consulting, bought a house for her daughter, she wanted to make it easy to live in. “I wanted to make a house where there would be no energy bills to worry about, and little maintenance,” she said. Pettit also saw an opportunity to use the retrofit project as a pattern for others: the 2,000 ft2 (190 m2) house, built around 1916 and located near Boston, follows the common “four-square” pattern made popular by Sears Roebuck kit homes, so many of the techniques used by Pettit could be replicated in similar houses throughout the U.S.
“Most houses that are 100 years old need all of their systems replaced,” said Pettit, “and this house hadn’t been touched since 1916.” The $300,000 renovation included added living space (finished basement and attic) and upgrades to existing spaces as well as added insulation throughout the house, new windows, a new roof, a new boiler and hot water heater, and a new ventilation system. The renovation increased the living space by 80%—to 3,600 ft2 (330 m2).
The work started in the basement, where Pettit installed a drainage mat and a layer of extruded polystyrene (XPS) rigid foam insulation on the existing slab, followed by a new reinforced concrete slab. Four inches (10 cm) of high-density polyurethane foam were sprayed onto the basement walls, then covered with non-paper-faced gypsum board to create the finished basement.
On the upper floors, the aluminum siding was stripped down to the existing board sheathing, and cellulose insulation was blown into the uninsulated wall cavities. Pettit chose to have the insulation blown in from the exterior, both to preserve the historic trim and plaster on the interior and to allow her daughter to live in the house while the work was being done. Because she was working with a trusted contractor, she told EBN, she did not feel the need to perform a thermographic analysis to ensure that the walls were properly insulated—but that can be a useful step with blown-in insulation and many insulation contractors offer the service. In the attic, 4” (10 cm) of high-density polyurethane was sprayed into the exposed rafters and covered with gypsum board. On the exterior walls, Pettit added a draining housewrap and two staggered layers of 2” (5 cm) foil-faced polyisocyanurate rigid insulation, covered by cedar siding. On the roof, the old shingles were removed and the same thickness of polyiso insulation was installed as on the walls, followed by plywood sheathing and roofing (without an air space). Pettit prevented moisture problems by installing a continuous air barrier to limit air leakage and a continuous drainage plane on the exterior wall.
For windows, Pettit chose double-glazed, argon-filled, low-emissivity (low-e) windows from Andersen. Pettit kept the existing trim on the interior, extending the exterior windowsills around the added insulation and protecting the assembly from moisture with metal flashing and housewrap. Expanding foam sealant prevents air leakage around the perimeter of the window. “We didn’t go to the very best window,” Pettit said, because the glazing accounted for only about 12% of the surface area of the house and she felt that its contribution to heat loss did not warrant the expense of a further performance upgrade. Although Pettit chose the Andersen windows because she could order them in custom sizes, she told EBN that she “wasn’t as thrilled with them as I should be for the price.” If approaching the same decision again, she said she would probably put the cost premium toward windows with better energy performance.
Overall, Pettit is happy with the results: the house performs well (the energy loads dropped by two-thirds: from 360 million Btu to 120 million Btu per year) and is comfortable. While Pettit originally planned to add solar systems to achieve net-zero-energy, she has not yet done so. Parsing out the costs of the project, Pettit estimates that the extra insulation cost about $10/ft2 ($100/m2) in materials and $10/ft2 ($100/m2) in labor, or 10%–15% of the total project cost. Because the house needed major renovation anyway and the energy improvements could be done as part of that work, Pettit felt that the cost of the added insulation was reasonable. She cautioned, however, that “for someone who doesn’t have to do any other work, it would be a different story.”
Case Study: The Raritan Inn, New Jersey
Bill Asdal of Asdal Builders in Chester, New Jersey, bought a 24-acre (10 ha) property in nearby Califon, knowing the two 100-year-old buildings (the inn and the cottage) on the property would need extensive renovations. Neither house had been occupied for at least ten years, and both had some structural damage. Since the renovations would be extensive anyway, moving to a net-zero-energy retrofit seemed feasible. The National Association of Home Builders Research Center expressed interest in one of the buildings, the cottage, for a case study for its Strategies for Energy Efficiency in Remodeling program. (Several manufacturers donated materials and expertise, but, according to Asdal, this did not affect the decisions he made about materials or technologies.)
After repairing some structural damage to the buildings’ foundations, Asdal began the work of insulating them. He tore down the interior wallboard and added blown cellulose to the walls. He stripped the existing siding before adding sheathing and housewrap and covering it with R-4 foam-backed insulated vinyl siding. This work brought the total insulation value of the wall assembly to R-22. Simply adding insulation does not go far enough, however: as Asdal points out, “the magic is not always in the R-value, but in the tightness of the house.” Therefore, Asdal’s crew used air-sealing techniques throughout the house, caulking the window openings, foaming around floor and wall penetrations, and gluing both wallboard and exterior sheathing to the framing.
Asdal added a room to the cottage, and went with structural insulated panel (SIP) construction. He worked with Techbuilt of Cleveland, Ohio, to design the addition using expanded polystyrene (EPS) foam panels with steel supports. Techbuilt created the panels and worked with Asdal and his crew to assemble the addition in under six hours. The 7” (20 cm) wall panels achieve an R-38 insulation value, and the 12” (30 cm) roof panels achieve R-50. Ground-source heat pumps were added to both houses, feeding off of a single horizontal piping loop installed on the property.
After thoroughly insulating the houses, the next step for Asdal was to introduce several renewable energy systems to achieve net-zero site-energy performance (see EBN Vol. 14, No. 10 for more on defining net-zero energy). In the cottage, a solar-thermal collector preheats domestic hot water that is then fed through a tankless water heater and delivered to the fixtures. In the inn, a desuperheater (an optional energy-saving feature on many heat pumps) extracts waste heat from the heat-pump cooling cycle to preheat the water. Asdal also installed a 14.2 kW PV system; the panels are divided among the cottage roof, a garage roof, and a barn roof. Because the onsite PV system generates more power than the houses need, Asdal received $232 back from the utility in 2006, in addition to funds from the utility that were provided to replace government rebates on the PV system (which New Jersey no longer offers).
According to Asdal, both buildings are “overperforming, in a number of ways.” The energy savings are greater than expected, he said, and public interest in the project continues to grow. He cautions, however, that such an extensive retrofit might not work for every project: “consumers and contractors should not touch renewables” until they’ve changed occupant behavior and performed an extensive weatherization job, he said. Despite the challenges of such extensive renovations, Asdal is hopeful about the potential for net-zero retrofits. “If we can go out and do a full gut rehab on a lot of these houses, we can avoid some of the barriers of new building,” he said. “I see this as the ultimate form of recycling.”
Case Study: 1926 Austin Bungalow
In February 2007, a crew from the television show This Old House began work on a 1926 bungalow in Austin, Texas. The homeowners wanted to expand the 1,500 ft2 (140 m2) house to make space for their growing family, and they wanted a green renovation. Architect David Webber, AIA, of Webber + Studio in Austin, Texas, designed a second-floor addition that added two bedrooms and only 6’ (2 m) to the roofline. With such major renovations happening, making improvements to the energy performance of the house was fairly easy.
Adding a second floor gave builder Bill Moore a chance to add 7.5” (20 cm) of closed-cell sprayed polyurethane insulation between the attic rafters. Moore decided to insulate the entire attic, including the unfinished portion that would house the air-conditioning equipment. He also added TechShield, a radiant barrier roof decking product from LP Building Products, to keep the attic cool. Although the addition offered the greatest opportunity for envelope improvements, Moore also added dry-pack cellulose insulation to the existing wall cavities on the first floor.
Adding large amounts of extra insulation to the house did not make sense for the climate, according to Moore. In the hot, humid climate of Austin, he said, “the biggest bang for the buck is to seal the air leaks, because that’s effective for heating and cooling.” Similarly, replacing all of the original single-pane windows with high-performance windows didn’t make sense financially. “There’s not a payback down here for high-performance windows” in renovation situations, Moore said, because the energy savings are not great enough to justify the cost of replacement. He admitted that “comfort is a different issue,” saying that insulating windows make a house more comfortable in the winter. He used double-glazed, argon-filled, low-e windows from Andersen in the second-floor addition.
Moore focused on other ways to lower the energy demand of the house, replacing the old furnace with a high-efficiency model from Trane and adding a gas-fired tankless water heater with an on-demand recirculator. The air-conditioning system was upgraded from a 10 SEER unit to a 16 SEER unit, and all of the ductwork was placed in conditioned space. The largest energy savings for cooling, however, came from occupant behavior: the homeowners wait as long as possible to turn on the air-conditioning, according to Moore, and rely on natural ventilation and shading to cool the house, making even their pre-renovation energy use low compared to other area homes.
According to Moore, a computer simulation showed that, despite increasing the square footage of the house 50%, the energy loads were cut by 10%. Rebates for a 2.45-kW PV system, which is expected to provide 40% of the home’s energy needs, made it financially feasible to offset the small gains in efficiency with onsite renewable generation.
Final Thoughts
Significantly reducing the energy consumption of existing homes is a critical priority if we are to stem greenhouse gas emissions and global warming. It is also very challenging. Achieving 50% energy savings in an existing home is not as easy as it might seem—but it can be done.
Checklist:Low-Energy Retrofits–Priority Checklist
The biggest challenges are cost and skilled labor. To address these, EBN’s editorial this month (see An Environmental Service Corps for America) presents the concept of an Environmental Service Corps to focus on home energy retrofits along with such other activities as ecological restoration and invasive species control. A program like this—as bold and unlikely as it seems—would provide only part of the answer to bring about widespread energy retrofitting. We will also need to encourage the use of energy-efficient mortgages and home loans, subsidized low-interest loans, outright grants, and performance-based tax incentives.
The costs of committing our nation to a cutting-edge program to retrofit a significant percent of our nation’s housing stock would be huge—hundreds of billions of dollars, if not trillions of dollars, over the coming decades. The cost would be on the scale of what we are spending on the Iraq War but arguably with more return on investment for the people footing the bill. The hope is that our political leaders would see the benefits that this investment would provide in the way of energy security, protection against rising energy costs, and environmental stewardship.
You catch more flies with honey than you do with vinegar, or so the proverb tells us. That may be why new approaches to design and construction seem to be most successful when they are introduced first as voluntary measures that can be used to garner green credentials, or, increasingly, to benefit from government incentives. But as new approaches gain market acceptance they also begin to show up as mandatory measures via codes or other regulations—quickly in some areas and very slowly in others.
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.
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.
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).
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.
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.
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
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.
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.
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
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
