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Water consumption in the United States increased by an estimated 12 percent between 1990 and 2000 – an increase of over 5 billion gallons per day. Of the water consumed, only about 14 percent is lost to evaporation, transpiration, or use in products or crops; most water is used, treated, and discharged into the nation’s water bodies. Discharged water contaminates the receiving waters by increasing solids, nitrogen, bacteria, and toxic metals. Much has been done to help protect our rivers, lakes, and streams, but we have only begun. This article explains how water is used and produced in buildings and how to conserve it.
In 1992, Congress passed the Energy Policy Act (EPAct 1992), which set a benchmark for water consumption and prohibited the manufacture, import, distribution, sale, or installation of plumbing fixtures that exceeded this mark. In creating LEED, USGBC took a cue from EPAct. Under LEED for New Construction and LEED for Existing Buildings: Operations and Maintenance Water Efficiency (WE) Prerequisite 1, all commercial toilets, urinals, lavatories and faucets must meet the water efficiency benchmarks set by the EPAct 1992.
The legislation was tightly written and effective in eliminating the manufacture and use of high-consumption fixtures, but it preceded proven technology. Users soon found that the new plumbing fixtures did not function, water closets were inadequate on a single flush, and drain lines were becoming clogged. As a result, water use increasedSaving Water Means Saving Energy
Today, technology has caught up with the EPAct 1992 and LEED Water Efficiency requirements. High Efficiency Toilet (HET) fixtures consume only 1.28 gpf. Also available are single-flush, pressure-assisted 1.0 gpf water closets; dual-flush water closets (1.6 gpf full-flush and 1.1 gpf low-flush); foam-flush closets consuming 0.05 gpf; and non-water toilets consuming 0.0 gpf.
In the offices of mechanical and electrical engineering consulting firm Jaros Baum & Bolles (JB&B), engineers who work on projects seeking LEED certification installed and tested 1.28 gpf water closets. In the JB&B tests, the 1.28 gpf fixtures outperformed the 1.6 gpf fixtures with a metered savings of greater than 20 percent. This means that in an existing commercial building with older fixtures consuming 3.5 gpf or more, conversion to the newer water closets with electronic flush could result in water savings greater than 60 percent. The engineers found that the 1.28 gpf fixtures not only use less water, but also the fixtures’ flushing performance is as good, if not better, than the 1.6 gpf fixtures necessary to meet WE Prerequisite 1.
New urinal designs also save water. Older urinals require upwards of 2 gpf or more per flush. Urinals that perform better than 1 gpf, which include waterless urinals, must be used in order to achieve maximum water-use reduction and meet the baseline of 1 gpf required by WE Prerequisite 1 in both the LEED for New Construction and LEED for Existing Buildings: Operations & Maintenance. Use of waterless urinals may also take a project one step closer to achieving WE Credit 3: Water Use Reduction.
Waterless urinals utilize a chemical that seals off the trap while allowing waste to pass through. Concerns that low-flow or waterless urinals may crystallize or not carry waste at adequate velocity can be alleviated with good installation. For example, placing water closets at the beginning of the run with urinals closer to the stack allows wastelines with non-water or ultra low-flow urinals to be cleared every time water closets are flushed.
In New York City’s One Bryant Park, a 1.8 million-square-foot commercial building that is the first skyscraper to receive LEED Platinum Certification, non-water urinals resulted in a savings of over 5.5 million gallons of water over a year. [For more information on One Bryant Park, see the article on page 34 of this issue.] After almost a year of occupancy, the only complaint seems to be “Where is the flush button?”
New technology and LEED evolution have increased the efficiency of faucet fixtures, enabling projects to save water and achieve LEED WE requirements. The EPAct 1992 mandates that lavatory fixture faucets pass no more than 2.2 gallons per minute (gpm). Earlier versions of LEED rating systems (v2.0, v2.1, and v2.2) awarded points to projects for meeting the baseline set by the EPAct 1992, but projects were not required to meet this baseline as a prerequisite. In LEED 2009, all faucets and aerators must meet 2.2 gpm for private facilities and 0.5 gpm for public facilities at a flowing water pressure of 60 pounds per square inch (psi) under WE Prerequisite 1. Electronic metering faucets may increase water savings further by limiting water to 0.25 gallons per cycle (gpc). In the case of One Bryant Park, this results in a water savings in excess of 1.5 million gallons per year.
Low-consumption fixtures also reduce the energy needed to bring potable water to occupants and heat it. In One Bryant Park, electronic metering faucets resulted in an energy savings in excess of 8,000 therms annually. When looking to implement strategies that meet LEED WE prerequisites and credits, the following requirements should be taken into consideration: Energy & Atmosphere (EA) Prerequisite 2: Minimum Energy Efficiency Performance, EA Credit 2: Existing Building Commissioning, and EA Credit 3: Performance Measurement.
Submetering of large users within buildings is another strategy to save water and achieve WE Credit 1: Water Performance Measurement (Option 2). Areas and systems where submetering is recommended include cooling towers, kitchens, landscape irrigation systems, and health club areas. The purpose of this metering is twofold: first, to help gather more information about the quantities of water being consumed within a building; and second, to allow the building engineer or manager to observe unusual water consumption and correct a potential problem (e.g. a float valve that might be stuck in an open position). Submeters should be connected to an electronic data gathering system (such as the building management system) in order to create trend logs and alert building personnel in the event of unusual consumption.
Cooling Towers – The Biggest Culprit?
Depending on the climate, a building’s cooling tower may consume more water than any other use. Blowdown – the process of removing water to reduce mineral concentration and scaling – is a necessary process within a cooling tower. As water evaporates, minerals left behind become more concentrated. This concentration can lead to scaling, fouled chiller tubes, lower heat transfer rates and increased energy usage for cooling. Cooling towers with constant blowdown will generally consume more water because evaporation rates are linked to heat loads.
To control blowdown, conductivity meters can be used to measure the water’s electrical conductance, adjust the bleed rates on the basis of evaporation rates, and thus ensure a higher concentration ratio or cycles of concentration. Using conductivity meters along with automatic controls is one option to achieve WE Credit 4: Cooling Tower Water Management through Option 1: Chemical Management.
Because the blowdown has the same chemical concentration as the recirculation water, the cycles of concentration are a comparison of the dissolved solids in the blowdown vs. those of the makeup water. More cycles result in less blowdown and less makeup water. For example, in a 2,000 TR cooling tower circulating 6,000 gpm with a 10ºF ΔT, the makeup water reduction would be 18 gpm (from 90 gpm to 72 gpm) or a savings of 20 percent.
Once-through cooling systems, in which potable water is used as the cooling medium, must be avoided in order to save water and meet LEED requirements. Both the new LEED 2009 Guidelines, as well as the proposed ASHRAE standard 189.1, prohibit the use of once-through cooling systems.
Harvesting Water within Buildings
Stormwater harvesting, or collecting the rainwater that falls on a building’s roof, is a proven strategy that can save potable water use and help achieve a number of LEED credits, including WE Credit 1: Water Efficient Landscaping, WE Credit 3: Water Use Reduction, and Sustainable Sites requirements related to stormwater management. Stormwater requires minimal filtration and perhaps minor sterilization depending on its future use. Stormwater is typically used for cooling tower makeup, but it can also be used for irrigation and the flushing of plumbing fixtures. At One Bryant Park, stormwater harvesting from a roof area of approximately 80,000 square feet resulted in a potable water savings of 2.3 million gallons per year.
Buildings produce water as well as consume it. In the case of buildings in New York City, both cooling coils and Consolidated Edison’s steam produce condensate during a building’s normal operation. At One Bryant Park, steam condensate was harvested to save approximately 3.5 million gallons of water annually. The harvesting of the steam condensate also saves energy by passing it through a heat exchanger that preheats domestic hot water in the building.
Wastewater from fixtures within a building can also be captured and reused. “Gray water” is untreated wastewater from bathroom sinks, bathtubs, showers, clothes washers, and laundry sinks. Depending on its assumed or measured contaminants, this water should be filtered and sterilized for cooling tower makeup, flushing toilets, or irrigation. Gray water can help a project achieve WE Credit 1, WE Credit 2: Innovative Wastewater Technologies, and WE Credit 3.
Gray water harvesting saves approximately 2.1 million gallons of water annually at One Bryant Park. It does require some additional piping systems, and the added cost for this piping must be weighed against the potential savings. The cost of this piping was minimized by working with the architect on One Bryant Park’s core toilet room design.
Groundwater can be harvested for some buildings with high water tables that require pumping to protect the foundation,. Typically, this water is pumped through a silt basin and then to the storm sewer, but it can instead be harvested and, depending on its quality, used for cooling tower makeup, fixture flushing, and irrigation.
Black water – or the wastewater from toilets, urinals, dishwashers and kitchen fixtures – can also be captured and reused. However, treatment is much more detailed and costly. Nevertheless, it may be justified by a rate-of-return analysis for some buildings, particularly high-rise residential buildings.
Other areas that consume water within buildings are landscape irrigation and building cleaning. In order to meet WE Credit 1, native and drought-tolerant plant species must be used to limit the water required for landscaped areas. For building cleaning, non-potable water is encouraged through use of mechanized cleaning tools and “dry” cleaning equipment.
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Robert Benazzi is a consultant and a former partner with Jaros Baum & Bolles, an electrical and mechanical engineering firm.