Conserving, tracking commercial buildings’ water use
The immediate interest in a building’s energy efficiency typically focuses on heating and cooling systems, and with conserving nonrenewable resources like power and gas. Throughout the world, however, there is increased pressure to track and conserve water in nonresidential buildings.
- Review the current water-management options, such as using greywater and rainwater, and look at less traditional management options, such as wastewater and condensate reuse.
- Understand the codes and standards that govern water use in nonresidential buildings
- Understand how water use potentially differs between building typologies.
Water consumption and conservation have become front-page news in recent months, and building owners and plumbing engineers are frequently being tasked with doing everything they can to conserve water in commercial buildings. You may have heard the statement, “water is the next energy crisis.” When considering recent events such as the California droughts, water shortages in developing countries, mandatory cuts focused on reducing water use, and efforts to conserve fresh water supplies, it makes you realize that there may just be something to that statement.
An increased stress on available supplies coupled with increased sanctions on water consumption has continued to thrust water toward the top of the list of resources to be conserved. Building owners and managers are increasingly focused on reducing their buildings’ water footprints in an effort to not just meet present and future restrictions, but also to conserve precious water supplies for future generations. The ideas outlined here establish a good starting point for designers, engineers, and anyone involved in the building industry to reduce, conserve, and track water for generations to come.
Energy efficiency has always taken the spotlight as the more pertinent issue in the AEC community. However, engineers continue to see an increase in emerging directives, prescriptions, and regulations aimed toward tracking and conserving water in commercial buildings, from local municipalities and governing bodies, code requirements, and organizations and programs that promote sustainability. Several programs promote water conservation and tracking water use, including U.S. Environmental Protection Agency (EPA) WaterSense, U.S. Green Building Council, Green Globes, and Energy Star.
It has been estimated that less than 1% of the world’s freshwater is accessible for direct human use, and buildings could potentially consume roughly 20% of that freshwater supply. Residential and commercial buildings use about 12% of the freshwater consumed in the United States. Figure 1 represents general figures as they pertain to specific areas of water consumption for different commercial building types. Building details such as siting, construction period, and size may not be exactly the same, but for the sake of this article they will give you an idea of the functions in various building types that tend to use more or less water.
A reduction in any one of these types of water use can have a profound effect on overall building water consumption. Figure 1 shows where these categories could potentially add up to a large portion of a building’s water use.
Methods of water conservation
Water collection systems such as those that collect rainwater from rooftops and stormwater basins, greywater from plumbing fixtures, and HVAC condensate discharge help conserve water supplies. There are many avenues to consider when conserving water in commercial buildings, such as kitchen equipment, laundry equipment, and process equipment. Each can be carefully analyzed and, most likely, some conceivable water savings can be realized. Code implications always should be analyzed for each individual approach. And remember, just because it is beneficial in one place doesn’t necessarily mean it will be beneficial somewhere else.
Plumbing and reuse options: Because restrooms alone can potentially account for 25% of a given building’s water consumption (see Figure 1), there is a big opportunity to track and conserve this amount. A low-consumption or high-efficiency plumbing fixture is the most popular and obvious place to begin. Even minor adjustments to standard fixture flow values—as prescribed in the Energy Policy Act (EPAct) of 1992 standards for plumbing fixture usage—can result in a 20% to 40% savings in water consumed by building plumbing systems. Significant gains in respect to lower water consumption also can be realized by adding WaterSense appliances.
Water reuse in the form of greywater, black water, stormwater, and recycled water also are viable options to help conserve water use and supplement the potable supply for nonpotable uses. Typical sources for greywater in a commercial building are sinks, showers, and lavatories, from which the water can be collected and used as a water supply for toilet flushing, irrigation, laundry, and HVAC make-up. Stormwater harvesting, or capturing rainwater from the roof, is also an option for supplementation.
Recycled water is becoming more prevalent with many municipalities offering recycled water supplies. To clarify, recycled water—often referred to as “purple pipe”—is water that is collected from stormwater runoff, snowmelt, and byproducts from water treatment plants. This can be confused with “reclaimed” water, but, in context to this article, we will differentiate each as such. The uses for recycled water are much the same as greywater and rainwater.
Keep in mind there are many different approaches and regulations for each type of water reuse system, such as the type of treatment required and when and where it may be implemented. For example, there are differing requirements for a greywater system in the International Plumbing Code (IPC) versus the Uniform Plumbing Code (UPC). Local authorities may have further stipulations associated with the implementation of one of these systems. Building siting, geographic location, and weather conditions (i.e., average rainfall rate) could also have a large impact on the feasibility of using one of these systems.All system types, regulations, and general applicability must be carefully considered and evaluated during the design process.
HVAC methods: As we saw with plumbing systems, HVAC systems in certain building types can potentially account for upwards of 30% of the building’s total water consumption. Specialized facilities have the potential to consume significantly more water. Careful consideration and focused selection of HVAC systems can offer significant water savings.
A thorough investigation of make-up water supplied to HVAC systems and equipment is crucial to water conservation. Results should be incorporated into system design and selection requirements. Designers also can select make-up water valves for precise delivery of make-up water and basin level control.
Once-through potable water systems for cooling in labs or equipment are highly inefficient. Closed-loop systems, where the water is circulated through an additional medium, help eliminate water that would otherwise be discharged to a drain.
The use of air-cooled equipment in the form of dry cooling towers and chillers, like in an institutional setting such as a health care facility, may translate to less water use than more conventional water-cooled equipmentAlthough air-cooled equipment may not be as efficient as water-cooled equipment with regard to energy, air-cooled systems can offer advantages in water conservation and should be evaluated.
When water-cooled equipment is required, “blowdown” and “drift” should be considered. Blowdown is recirculating water that removes all minerals, chemicals, and bacteria that are in a cooling tower. Historically, this controlled water-removal process may not have been tracked, but due to its advanced system controls it should absolutely be monitored and regulated to conserve as much water as possible. Drift is water that is carried out of the tower by the force of the air moving through the cooling tower. Drift is essentially an uncontrolled loss, usually listed as a percent of cooling tower recirculating flow.
Thermal storage systems such as cold thermal energy storage, partial thermal storage systems, thermal ice storage, and chilled water storage may allow for a reduction in smaller system equipment, which will reduce the amount of water required along with the potential to save energy and costs.
Similar to the reuse systems that we touched on under plumbing methods, condensate discharge and blowdown from air conditioning equipment can be collected, treated, and reused for irrigation purposes.
Landscape and site methods: Water for landscaping use is often the most pervasive consumer of water on any type of building—and up to as much as 70% for some building types (see Figure 1). Many older U.S. cities and towns consider and dispose of rainfall as waste, which is funneled directly from roof gutters and paved surfaces to combined sewer systems (wastewater and stormwater), leading to increased cost in stormwater management. Rather than getting rid of stormwater as quickly as possible, a sustainable approach to stormwater management involves finding ways to harvest it on-site and using it for irrigation and groundwater recharge.
To maximize irrigation efficiencies, landscape designers should group plants with similar water needs together and use native or non-native vegetation appropriate for site conditions and climate. Plumbing engineers should specify efficient irrigation systems and choose climate-based and “smart” controllers for irrigation systems.
Wetland sites can help capture and treat wastewater for nonpotable water reuse while providing a natural ecosystem for plants and animals. These microsystems efficiently remove nutrients and solids from black wastewater, resulting in high-quality effluent. The effluent is then filtered and disinfected, leaving it ready for reuse in the form of greywater.