Commercial buildings are made up of many systems that rely on water. With today’s desire to design green systems, the engineer’s goal has become not only to provide a functional design, but also to keep usage and energy savings in mind. With or without the need to achieve U.S. Green Building Council LEED points, water conservation can be incorporated into a design, even if it is just at the fixture level. Providing a system that reduces water usage will not only lower energy costs, it will also ensure future availability of resources and convey a corporate message that the environment matters.
For the purposes of this article, we are categorizing commercial buildings as office buildings, hospitality, institutional, sports complexes, and retail. Some of the solutions presented also apply to single- and multi-family residential buildings, but they are not the focus of this article. Additionally, the article does not directly reference water usage costs because the costs vary significantly around the country.
One of the best ways to identify suitable water conservation measures is to establish a water savings plan to create a benchmark with which to rate and prioritize them. However, before we can determine and incorporate a water savings plan, we must first look at where water is used within a building. Water conservation will vary in a commercial setting depending on the building type. While hospitals and office buildings require a large water volume for mechanical systems, hotels and restaurants require high usage in laundry and food service applications, respectively. In sports complexes with large playing fields and stands, the usage is driven by large public toilets and the irrigation system. Determining the applications that have the greatest water consumption is critical to prioritize the overall goals and budget. Once the systems have been determined, a water savings plan can be developed.
Water savings opportunities
1. Low-flow plumbing fixtures
Many breakthroughs have been made in building water systems. These results have led to the replacement of large water-consuming fixtures with low-flow water fixtures (see Figure 1-3). Aerators for faucets, reduced-flow shower heads, and high-efficiency toilet and urinal flush valves are available with an initial capital investment; they often pay back the investment in less than a year, especially when they are used often. Low-flow fixtures in themselves are not a remedy as they don’t save you water if you are filling a pot, getting a glass of water, or doing other things that require a fixed volume of water. They do, however, save a significant amount of water when the number of usages is held constant.
In 1992, the National Energy Policy Act mandated the use of water-conserving plumbing fixtures. Since the law’s inception, low-flow plumbing fixtures—including flush valves for water closets, urinals, faucet aerators, and showerheads—have been further developed to save substantial amounts of water compared to conventional fixtures while providing the same utility through design features such as improved bowl, aerator, and flush valve design. Payback is not addressed here because water rates vary widely across the United States. See Table 1 for the evolution of water-conserving fixtures. Although no one is specifying the pre-1992 fixtures, the percentage of pre-1992 fixtures in existing commercial building stock is fairly significant, though specific data to quantify this is hard to come by.
|Table 1: Fixture Water Usage Reduction Since 1992|
|Fixture type||Usage rate (gallons/flush (gpf) or gallons per minute (gpm))|
|Pre-1992||1st generation||2nd generation||3rd generation high-efficiency||% Reduction from pre-1992|
|Water closet||3.5 gpf||1.6 gpf||1.28 gpf1||Dual flush (1. 6/0. 8 gpf)||63.43%2|
|Urinal||2.0 gpf||1.0 gpf||0.5 gpf1||0.125 gpf3||93.75%|
|Shower||5.5 gpm||2.5 gpm||2.0 gpm1||1.75 gpm||68.18%|
|Faucet||3.0 gpm||2.2 gpm||1.5 gpm1||0.5 gpm||83.33%|
1 EPA WaterSense Program Compliant
2 Based on 1.28 gpf. Dual flush can significantly reduce flow to an average 0.96 gpf based on 5 flushes/day/person with only one 1.6 gpf flush and four 0.8 gpf flushes.
3 No-flow urinals are not considered, as many municipalities and codes do not allow these fixtures.
However, one major caveat to using low-flow fixtures is in effectively moving solids great distances in horizontal sanitary lines. Particular care must be applied in the design process to avoid buildups and backups due to decreased water flow and the resulting reduction in the effective transport of solids. This is particularly important in retrofitting low-flow fixtures in existing facilities with rough pipe and minimal pitch in sanitary lines. Another is that low-flow faucets lead to less hot water flowing through pipes, resulting in water waste due to longer wait times until hot water reaches faucets.
Accepting the premise that a significant stock of existing buildings has pre-1992 fixtures, fairly significant water savings can be obtained through an engineered retrofit program that takes the above-mentioned flow through horizontal pipes into concern.
While water-conserving devices are generally low-maintenance items, they cannot simply be installed and forgotten. Technicians should check all units regularly and make periodic adjustments to flow-control devices. Automatic flow controls that are not hardwired require battery replacement, and flow-control openings should be checked for dirt and contaminants in the water system that can easily clog the smaller flow ways. Building owners and operators also need to establish a schedule for inspecting and testing all water-conserving devices. In setting up a program as the devices are installed, building operations teams can ensure that the low-flow fixtures will achieve their greatest potential.
2. Grey water
The idea behind grey water reclamation is simply getting the most out of water through reuse (see Figure 4). The water used in most commercial buildings has long been thought of in terms of clean clear water coming in, and sewage—or black water—going out. Grey water, however, is something in between. By most definitions, grey water is tap water soiled by use in washing machines, tubs, showers, and bathroom sinks that is not sanitary, but it’s also not toxic and generally disease-free. Grey water reclamation is the process that capitalizes on the water’s potential to be reused instead of simply piping it into a sewage system. Engineers are advised to consult with the local authority having jurisdiction (AHJ) to verify that grey water systems are allowed and determine if any special accommodations must be included in the design.
In commercial settings where bath, dish, and laundry water is available—excluding toilet wastes and free of garbage-grinder residues—grey water can provide a reasonable payback of investment. The grey water treatment process consists of a combination of solids separation, biological treatment, and ultraviolet disinfection. This system of water conservation uses simple diversion from the main plumbing system in which the water can be treated by sand filters, aeration, electroflotation (the removal of pollutants from water through the generation of bubbles that collect and carry pollutants to the surface), and pressure filtration ultimately being stored in above- or below-ground storage tanks. Once this process has taken place, the stored water can then be reused for applications such as toilet flushing, condenser water, and site irrigation. Grey water systems are not approved for storing and delivering potable drinking water. To minimize the possibility of cross-contamination, these systems must be in a separately piped system and specifically identified as a nonpotable source. This system also may prove to be problematic to vegetation and HVAC condensing water as harmful chemicals can be used to treat the reclaimed water. Consult with vendors of the receiving grey water systems to make them aware of the water source and quality.
Grey water systems require significant design effort and initial costs. They also bring the risk of contamination and pollution if mismanaged. Running costs for more involved systems can be high, with system payback potentially extending for many years. System maintenance and upkeep also play important factors in choosing this water conservation method. Filters, pumps, and treating stations all require attention. Grey water reclamation can be a difficult sell, but its potential can be fulfilled with the right application. Grey water systems are typically cost-effective in hospitality and similar buildings with high-volume, regular nonbiological contamination usage, such as laundry plants coupled with large nonpotable loads like toilet flushing and landscaping irrigation. Grey water systems are not cost-effective when the available grey water is not on par with demand. The upfront costs can be so high that the water savings just do not produce viable return on investment.
3. Rainwater harvesting
Commercial rainwater harvesting systems (see Figure 5) can be a viable option for owners and designers where a building with a large roof area also requires a high demand for nonpotable water. Again, this is based on the AHJ’s guidelines. Capturing and storing rainwater is an easy and effective way to conserve water through a commercially viable payback period. Obviously, in areas where rainfall is more prevalent, it is easier to capture and store rainwater for meeting demands, thus providing payback of investment much earlier than in areas that have limited rainfall. With a design and components that are simple and a system that is generally easy to operate, upfront and operating costs can be an attractive proposition to the owner. A payback study can be accomplished by defining an area’s annual rainfall and using the availability to compare demand savings based upon local water costs versus system upfront costs. The demands for a system of this type lie with irrigation and cooling tower makeup loads as the primary considerations behind implementing this method of water conservation. Therefore, the on-site requirements and performance of the storage components should be designed to meet the demand needs of the target load. Other uses of stored rainwater include laundry, toilet and urinal flushing, car washing, and ornamental water features.
Selecting a rainwater harvesting system is dependent on the collection area of the commercial site and the intensity of rainfall in the particular region of the country. Once the availability and demand are calculated, the system should be designed to meet the daily demand throughout the dry season. The system tank should be sized to be filled during conventional rain events with an overflow connected to the stormwater draining system. Additionally, the system should have a connection to the potable water system, through a break tank or some other form of physical air gap, to provide a supplemental water source during periods of low precipitation. Typically, direct rainwater collection systems intercept roof drain risers before they leave the building. The storage tanks can be located above or below ground. Site stormwater runoff can be collected through catch basins and site storm drainage at paved parking surfaces. Typically, there must be a system to separate oils and grit from the water before storing it. Significant coordination between the plumbing engineer and the civil engineer is crucial for a coordinated system. An effective rainwater harvesting system benefits not only the owner but also a municipality with an overburdened combined sewer system by diverting rainwater runoff. However, as with grey water, the inclusion of a rainwater harvesting system in a building’s design may require the engineer to meet with governing authorities for approval.
4. Pressure reduction
In many high-rise and commercial settings, domestic water booster pumps are necessary to overcome the loss of pressure due to increases in elevation and to maintain water supply in water towers and supply tanks. With these higher pressures, water flows through the system with resulting greater flow through terminal fixtures beyond rated flow capacities, and this additional water is wasted as it serves no additional benefit to the rated performance. Most plumbing codes require pressure-reducing valves on systems where pressures exceed 80 psi. In most cases, these pressures could be lowered by the implementation of additional pressure-reducing valves. Additionally, the higher pressures can rupture pipes and damage fixtures. This leads to even greater waste in the domestic water system. When it comes to the domestic heating plant, if less water flows through the system, then less energy is needed to heat the domestic hot water in the first place.
5. Insulate piping
For a domestic hot water system, clearly it is better—and now an energy code requirement—to insulate all piping and storage tanks. In many existing commercial buildings, domestic hot and hot water return piping is either uninsulated or not insulated properly. As a result, when there is a demand for hot water, the user will wait at faucets and showers for the hot water to flow, resulting in significant water waste. Properly insulating return piping also ensures that warmer water will be supplied back to the hot water plant, thus reducing the energy demand at the heating plant. By properly insulating hot water pipes, heat losses can be reduced and terminal fixture water temperatures can be effectively raised without any additional energy usage. When hot water is immediately available, the user is less likely to waste.
6. Leak proofing/leak repair
Leaking pipes can go unnoticed, sometimes for years. Water distribution piping is inevitably installed in every nook and cranny, crawlspace, and chases throughout all types of buildings. Pipes are concealed out of sight, and more times than not, leaks are not found until water damage is evident on chase walls and ceilings. Rates of water loss vary significantly depending on the type and severity of the leak. Dripping water taps and leakage from toilet cisterns can lose gallons of water per day. Proper preventive maintenance, proactive approaches, and quick fixes are necessary for water conservation, but there are steps that can be taken prior to installation that can potentially discover future leaks prior to the inevitable failure.
Design modifications that can reduce leaks or find leaks prior to waste and damage Include checking water usage through metering and submetering. Leak detection systems in critical or remote locations tied to a BAS to notify maintenance staff of water leaks ensure a quick response before building walls, ceilings, and equipment are permanently damaged. Piping dedicated lines to high-usage areas ensures that pressure is maintained at the point of use. Isolating zones in buildings also gives the end user the ability to shut down areas where leaks have occurred without interrupting the overall building usage. The fundamental idea is ease of maintenance and inspection. Leaks are inevitable, but with methods and procedures in place and—don’t forget—an upfront cost, damage and water wastage can be reduced.
7. Rain sensor on irrigation
One of the quickest and simplest ways to address water conservation in irrigation systems is to add a rain sensor. Rain sensors are designed to identify when precipitation is present and lock-out a controller so it does not run its program and irrigate when watering is unnecessary. After the rain event, the sensor automatically resets, allowing the controller to resume its schedule without losing any program information.
8. Cooling tower water recovery
Cooling towers remove heat from a building’s air conditioning system by evaporating some of the condenser water. Since all cooling towers continually lose water through evaporation, drift, and blowdown, they can consume a significant percentage of a building’s total water usage. Towers that are in good condition, operated properly, and well maintained allow chillers to operate at peak efficiency. Some cooling towers can use recycled water like stormwater or grey water if the concentration ratio is maintained conservatively low. Similarly, blowdown water may be reused elsewhere on-site.
In an attempt to reduce water usage at cooling towers, the designer should focus on the two factors that can be controlled: drift (water droplets that are carried out of the cooling tower with the exhaust air) and blowdown (the removal of circulating water to maintain the amount of dissolved solids and other impurities at and acceptable level designated by the electrical conductivity of the water). Evaporation is integral to a cooling tower performance and cannot be reduced without an acceptable reduction in performance. Reducing blowdown to the minimum level consistent with good operating practice can conserve significant volumes of water. Treating the condenser water by chemical means usually reduces water loss. Installing conductivity meters on blowdown lines helps reduce water usage during the bleed/feed cycles. Drift can be reduced by baffles or drift eliminators. Not only do these devices reduce water loss from the system, they inherently contain water treatment chemicals within the system to improve operating efficiency and reduce environmental impacts.
These subtle improvements and modifications to the condenser water system should be incorporated into the installation at the design level to save significant amounts of water from the onset and provide an efficient system. Minimizing the condenser water loss, ensuring proper chemical levels, and constant system service will save valuable amounts of water.
9. Steam boiler blowdown
Boiler blowdown is the removal of water from a boiler to control boiler water conditions within prescribed limits to minimize scale, corrosion, carryover, and other specific problems. Blowdown is also used to remove suspended solids present in the system. Poor quality feedwater will result in more frequent blowdown.
A typical strategy used to reduce the need for blowdown is to use automated controls and treatment. Water can be conserved by controlling the amount of water lost due to excessive blowdown. Updated control equipment will prevent wide fluctuations in blowdown, which will reduce water loss and the energy used to heat that water. The rate of blowdown required depends on feedwater characteristics, load on the boiler, and mechanical limitations. Variations in these factors will change the amount of blowdown required.
10. Educate users
Water conservation is not only about innovation and good design practices, but also about building an understanding among water consumers to work together to achieve a greener and more energy-efficient environment. It is important to educate users about water scarcity issues and the impact of water conservation practices through signage and awareness campaigns at the point of use. The conservation of water reduces water waste and energy costs too, on both operation and production. Educated consumers will be better able to identify problems and think innovatively about ways to conserve or reuse water within the facility. Not only will the work environment benefit, but these tools can be taken back to the home, where individuals and families can use these practices to play an even larger role in the preservation of rapidly dwindling fresh water resources.
Water is a necessity for the sustenance of life on earth. While the supply may seem abundant, water is not an infinite resource, particularly fresh potable water necessary to our survival. Without our acknowledgement in the design and construction industry and in our everyday consciousness, this vital supply of water may be threatened. We, as owners, developers, and engineers, play a vital role in looking beyond our building codes and budgets to achieve higher levels of water efficiency. New technologies that use less water are becoming more important than ever, but our common sense and realization that our planet cannot give forever will ensure that future generations will enjoy the benefits of abundant fresh water because of the decisions that we make now.
Spigarelli is senior plumbing engineer with CCJM Engineers. His experience includes highly efficient plumbing designs in a number of LEED Gold certified schools and commercial buildings.