Department of Defense Energy Manager’s Handbook phần 7

root zone, rather than a sprinkler system, which will lose a much greater portion of the water to evaporation. Possibly, a subsurface irrigation system could also prove beneficial. Consideration should also be given to reusing water from other applications such as laundries, vehicle and aircraft wash facilities, cooling towers, or industrial processes. Utilizing reclaimed water from the local sewage treatment plant should also be investigated. Many localities have recently modernized their plumbing codes to allow such reuse, and some water districts require it. Refer to EPA Manual “Guidelines for Water Reuse” for detailed information. 13.4.3. Industrial Water Use 13.4.3.1. Cooling/Boiler Water One often-overlooked area with substantial potential for water conservation is boiler and cooling tower use. Water is lost from recirculating cooling towers in two ways: (1) evaporation, which provides the cooling; and (2) blowdown, which removes scale-causing constituents from the recirculating water. Blowdown provides the opportunity to conserve water. As water evaporates, scale-causing impurities are left behind (and concentrated) in the recirculating water. When the impurities are concentrated beyond their saturation point, they settle out of the water as scale. Blowdown is used to remove the impurities before they settle out. By chemically treating the recirculating water, these impurities can be concentrated beyond their normal saturation point without settling out. Thus, cycles of concentration can be increased and blowdown reduced. (Cycles of concentration refers to the number of times a given constituent is concentrated in the tower.) In some applications, injection of ozone for biocidal treatment will make further blowdown reductions possible. A similar situation exists for boilers. The calculations, however, can be somewhat simpler, since there is no evaporation to consider. Cycles of concentration can be easily calculated from the conductivities of the blowdown and the feedwater. 13.4.3.2. General Tips for Industrial Water Efficiency The following tips are taken from the U.S. EPA’s web site. Additional resource information can be found at the web site as well as referenced at the end of this chapter. 3 Jan 05 144 For equipment: • Install high-pressure, low-volume nozzles on spray washers. • Install in-line strainers on all spray headers; inspect nozzles regularly for clogging. • Replace high-volume hoses with high-pressure, low-volume cleaning systems. • As equipment wears out, replace with water-saving models. • Equip hoses with spring loaded shutoff nozzles. • Install ultra-low flow toilets, or adjust flush valves or install dams on existing toilets. Other measures: • Detect and repair all leaks. • Identify discharges that may be re-used and implement re-use practices. Some discharges with potential for re-use are: o final rinses from tank cleaning, keg washers, fermenters o bottle and can soak and rinse water o cooler flush water, filter backwash o pasteurizer and sterilizer water o final rinses in wash cycles o boiler makeup o refrigeration equipment defrost o equipment cleaning o floor and gutter wash • Use fogging nozzles to cool products. • Handle waste materials in a dry mode where possible. • Adjust overflows from recirculation systems by controlling the rate at which make-up water is added: install float-controlled valve on the make-up line, close filling line during operation, provide surge tanks for each system to avoid overflow. • Turn off all flows during shutdowns. Use solenoid valves to stop the flow of water when production stops. • Adjust flow in sprays and other lines to meet minimum requirements. • Wash vehicles less often, or use a commercial car wash that recycles water. • Discontinue using water to clean sidewalks, driveways, loading docks, and parking lots. 13.4.4. Leak Detection and Repair The DoD Components shall continue to concentrate on early leak detection and repair. The American Water Works Association estimates that 10 to 20% of the water treated at a typical plant is lost to distribution system leaks or other unaccounted uses. Some of this water may be used for beneficial purposes, such as flushing mains, but much of it is lost to the ground. 3 Jan 05 145 Accurate determination of the position of leaking water pipes within a supply system and subsequent repair serves to conserve water as well as energy. Water that is lost after treatment and pressurization, but before delivery to customers, is money and energy wasted. Municipalities can usually determine their unaccounted water use by subtracting customer meter readings from the production meter readings. On many military installations, this is not possible because end-use of water usually is not metered. AWWA publication M36, “Water Audits and Leak Detection,” can be used as a guide to determine if you need leak protection. An alternate means to determine if leaks are likely to be a problem is presented in Public Works Technical Bulletin (PWTB) 420-46-2, “Procedure to Detect Water Distribution System Leaks.” The procedure consists of measuring flow into and out of the distribution system over a 24-hour period and during the time of "minimum-night flow," usually between 0000 - 0300 hours. If the ratio of minimum night flow to average daily flow is more than about 0.4 -0.5, it is likely that leaks are a problem in the distribution system. In this case, it is probably worthwhile to contract for a leak detection survey with a local firm. As noted in the PWTB, the Construction Engineering Research Laboratory has a spreadsheet to help installations estimate the cost effectiveness of a leak detection survey. The Spring 2002 issue of Water Conservation News (accessed through the California Department of Water Resources web site at http://www.owue.water.ca.gov) discusses the methodology for conducting leak detection surveys. It also cites a new technology currently in production which includes a single unit comprised of audible leak detection hardware coupled with a data logger, radio transmitter and extended life battery (10+ years). Multiple units are permanently installed at multiple pipe locations within the water supply system and continually monitor for sounds characteristic to pipe leakage. When a unit detects an audible reverberation indicative of leakage, the onboard radio transmitter sends a signal to an above ground receiver. The survey team now has only to drive about the survey area with the receiver to identify locations in which to return with a noise correlator for pinpointing or discounting potential leakage spots. The primary drawback to such a system is that large quantities of data loggers are necessary to accommodate a large water system. 13.4.5. Industrial Water Audit Industrial processes are so specialized that it is not possible to provide general recommendations for effective water conservation at 3 Jan 05 146 industrial facilities. The best approach is to conduct an individual water audit of the facility in question. One prime area of consideration in industrial facilities is water reuse. In some cases, water discharge for one process can be reused, without treatment, in another. 13.4.6. Public Information Programs Public information programs can be used in conjunction with all other water conservation measures. Recent environmental concerns have provided some emphasis on water conservation. Many people are motivated to save water, not only because of the potential money savings but also because it is environmentally responsible. Information programs can take the form of handouts to housing residents, posters in administrative buildings, school programs, etc. Some installations have provided water conservation kits, including informational packets and retrofit devices, to new housing residents. Information packets can be developed to provide installation-specific information, or brochures from EPA or other sources can be used. 13.5. References 1. American Water Works Association. Water Audits and Leak Detection. Publication M36, 1990. 2. US Environmental Protection Agency. Guidelines for Water Reuse. Manual EPA/625/R-92/004, Sept. 1992. 3. US Navy Facilities Engineering Service Center. Navy Water Conservation Guide for Shore Activities. NFESC UG-2017- E&U, August 1996. 4. California Department of Water Resources. WaterPlan™ Water Conservation Assumptions. Sacramento, California, October 1989. 5. US Department of Housing and Urban Development, Office of Policy Development and Research, Building Technology Division. Survey of Water Fixture Use. Brown and Caldwell Consulting Engineers, March 1984. 6. Corbitt, Robert A., Standard Handbook of Environmental Engineering. McGraw-Hill, New York, 1990. 7. US Environmental Protection Agency, Office of Water. Xeriscape™ Landscaping - Preventing Pollution and Using Resources Efficiently. EPA-840-B-93-OOl, April 1993. (Xeriscape™ is the registered trademark of the National Xeriscape Council, Inc.) 8. Metropolitan Water District of Southern California. Alternative Flushing and Retrofit Devices for the Toilet. Stevens Institute of Technology, Department of Civil, Ocean and Environmental Engineering, June 1992. 9. Department of the Army, Army Science Board. Report of the Ad Hoc Subgroup on Water Supply and Management on Army Installations in the Western United States. February 1988. 10. US Army Construction Engineering Research Laboratory. Distribution of 3 Jan 05 147 Water Use at Representative Fixed Army Installations, August, 1983. 11. US Army Center for Public Works. Facilities Engineering and Housing Annual Summary of Operations, Fiscal Years 1989-1993. 12. California Department of Water Resources. “Leak Detection Technologies,” Water Conservation News, Spring 2002. 3 Jan 05 148 ... - tailieumienphi.vn