Tracking and conserving facility water use
Plumbing and mechanical engineers are frequently being tasked with doing everything they can to conserve water in commercial buildings.
- Outline the codes and standards that govern water use in nonresidential buildings, and understand how water use potentially differs between building typologies.
- Appraise the current water-management options, such as using greywater and rainwater, and look at less traditional management options, such as wastewater and condensate reuse.
A large portion of the U.S. West Coast has been experiencing a drought for a number of years now. California, in particular, is experiencing a "D4 Exceptional Drought" (the highest drought-intensity rating on the United States Drought Monitor) and the worst in the state's history, which has led to mandatory water restrictions. Other parts of the country also are experiencing moderate drought or abnormally dry conditions.
These conditions place enormous pressure on potable-water storage and water supply networks. This not only creates water-supply uncertainties, but also brings about a realization in the broader community that water is an extremely valuable and finite resource that should not be taken for granted.
According to the U.S. Geological Survey Circular 1405, Estimated Use of Water in the United States in 2010, the total water withdrawals for public supply was 42,000 million gpd (nearly 14% of the total freshwater withdrawals). The majority of the remaining water withdrawals are primarily for thermoelectric power (45%) and irrigation (33%).
This article relates to tracking and conserving water in a range of commercial buildings including office buildings, retail developments, public and government buildings, educational and research institutions, health facilities and hospitals, and hotels and resorts. The breakdown of water use across these building types varies considerably (refer to U.S. Environmental Protection Agency's WaterSense—Types of Facilities page); however, the three major uses of water are generally restrooms, HVAC (heating and cooling), and landscape irrigation. Kitchen, laundry, or washdown activities also can consume significant amounts of water for certain facilities. The commercial and institutional sector accounts for approximately 17% of withdrawals from public water supplies in the U.S., so significant savings can be made in this sector.
To achieve resilience in the face of water shortages, builders, engineers, and designers of new commercial buildings are looking to implement water-efficiency measures. These measures include using water-efficient fixtures and fittings—i.e., low-flow faucets and showerheads, low-flush toilets and urinals, dual-flush toilets, low-flow lavatory faucets—and adhering to maximum flow levels that have been mandated under the Energy Policy Act (EPAct) of 1992.
In the past, the difficulty with many low-flow fixtures was that without good fixture design, the performance was often compromised. For instance, low-flow toilets that fail to fully clear waste can result in double flushing, which potentially wastes more water than the higher-flow fixtures. To help protect against this, the U.S. Environmental Protection Agency (EPA) created the WaterSense Program in 2006, which is a national voluntary program that certifies products that use 20% less water than the national standards without sacrificing performance. Many states have individually established their own fixture-efficiency standards that, in most cases, match or exceed WaterSense standards.
In April 2015, the California Energy Commission approved standards that exceeded those of the WaterSense program in an effort to save more water and ease the effects of drought. California and a number of forward-thinking states are now leading the nation in water-efficiency standards. A comparison of the flow standards is listed in Error: Reference source not found.
Water-efficient fixtures are now common, relatively inexpensive, and one of the most cost-effective ways to reduce water use within new commercial buildings. However, caution should be applied when retrofitting older buildings with low-flow fixtures, as the older drainage pipe systems often have horizontal pipe gradients that are not designed to move solids with such low water flows, resulting in serious blockages.
No-flow or flushless urinals also can save considerable amounts of water. However, correct and continual maintenance is necessary to prevent odor and formation of solid precipitates, such as struvite or uric acid scale within the drainage pipe. The risk of formation of the latter can be alleviated through installation of higher-flow systems, such as lavatory sinks or showers upstream that drain into the same pipe. The flows from these other fixtures dilute the urine and help keep the pipe flushed. While the claims are "no-flow" or "waterless," there is an amount of water required for cleaning and maintenance; although, admittedly, the volume required is greatly reduced as compared with its low-flush equivalents.
Vacuum toilets, such as those used in shipping and aircraft applications, also are being considered in some specific building developments as a water-saving measure. These systems use, on average, 0.26 gallons per flush (gpf) and approximately 2 watts per flush; they can be particularly useful in developments where gravity drainage is problematic (for example, developments over water, marinas, etc.). Continued operation can be challenging with these systems; there are noise issues and ongoing maintenance by specialty contractors is required to maintain efficient vacuum operation. The system results in a much more concentrated flow for disposal to the sewer drainage network, which may be a consideration for the controlling authority or service provider.
Error: Reference source not found shows an example of a typical office building. Potential water savings have been modeled in toilets and lavatories where low-flow units were installed. We have begun with an assumed population of 5,000 with a 50:50 mix of males to females. While the mandatory standards set by EPAct 1992/EPAct 2005 have reduced typical fixture flow rates from pre-1992 levels, the modeling shows that the savings that can be achieved through the tighter standards adopted in California are still quite considerable and, in this case, resulted in approximately 3 million gallons/year—or a water-usage reduction of 39%. Dual-flush toilets with an average water use of 1 gpf; (the average of one 1.6-gpf flush and three 0.8-gpf flushes) offer even greater savings.
Metering for water management, leak detection
Another simple and often underrated method to achieve water savings is through metering (see "Case study: Royal Society for Prevention of Cruelty to Animals" on page xx). A well-designed metering system can perform a number of highly valuable functions including assessment of water use across functional areas or zones and identification of high-water-use appliances or activities. It also can assist with the early detection of leaks.
Detailed knowledge of water used for various functions of the building allows water-management schemes to be developed that can identify areas of significant water usage and enable development of strategies targeted to achieve greater reductions in water use. The installation of meters alone does not save water and requires the appropriate infrastructure to provide monitoring, analysis, and reporting of water use and identification of unusual water use. Most building management systems (BMS) have become quite sophisticated in how they can process and report on acquired data. Once baselines are established, the BMS allows water-use setpoints and alarms that can be triggered to alert building managers of unusual events or abnormal operation.
One meter installed on the incoming water supply (usually for billing purposes) gives very limited information with regard to water use throughout the building. While leaks and inefficient water use may be detected, a large amount of investigation is then required to locate them. Currently, there are no requirements for submetering of water use within commercial buildings within the Uniform Plumbing Code (UPC) or the International Plumbing Code (IPC), which are the two major plumbing codes adopted across the U.S. Local and state codes and requirements may vary and should be consulted if in doubt.