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.
Methods of commercial water tracking
Now that we have a good idea of how we can conserve water in commercial buildings, how do we track it and make sure water is being used appropriately and efficiently?
In the past, metering of a typical commercial building would only be provided by the incoming domestic water service. This approach gives facilities a good overview of what the building uses as a whole, but it doesn’t give good information on exactly where and how the water is being used. With so many functions requiring water throughout a typical commercial building, it quickly becomes apparent that a more localized and robust method of tracking needs to be implemented. This is where sub-metering and enhanced data-retrieval technologies come into play. These methods also allow the facility to pinpoint issues more easily. When we dissect the separate functions, this is where sub-metering and enhanced data retrieval can more precisely track water consumption.
Separately leased or rented spaces: Providing water sub-metering on separate tenant spaces gives building managers the ability to individually track water consumption from tenant to tenant or space to space. This also will help educate tenants on their individual water usage as compared to others, and may prompt them to not only save themselves a bit of money, but also to conserve for the greater good.
HVAC: Any HVAC equipment such as cooling towers, evaporative coolers, boilers, and anything that requires a single pass make-up water connection provides an opportunity for metering. As stated earlier, HVAC systems can account for upwards of 30% of commercial buildings’ total water consumption. Installing sub-meters on HVAC equipment gives the facility owner/manager the ability to individually track this water-intensive equipment, and to make sure the equipment and systems are functioning as designed without any issues such as leaks or blockages.
Irrigation: This is an obvious area where water can be more effectively tracked. How many times have visited a park or common area that has automatic sprinkler/dripper systems to sustain the vegetation, and noticed that a geyser is streaming from the ground? Because exterior irrigation is usually out of sight, it tends to be forgotten—and eventually becomes so dysfunctional that it is not operating anywhere near its optimal efficiency. Sub-metering of irrigation systems can provide a very quick indication where there is potential waste.
Special systems: Kitchens, laundry, lab equipment, or any large water-using process also stand to benefit from sub-metering. Reuse systems such as greywater, stormwater, and condensate collection systems also offer sub-metering options. Metering these systems will allow a building to not only track what they are using, but also track what they are gaining or offsetting.
Data retrieval and evaluation: Remote metering or automatic meter reading (AMR) capabilities allow all metered information to be easily collected and analyzed. Analog meters tend to be forgotten about because they are buried or are high above an inaccessible ceiling. If they are not being read, they provide no useful function. Remote metering and AMR allows for all of the information to be compiled in a single location and ensures that design conditions are being met.
Meter data-collection systems also are available to track daily and even hourly usage of water at meters and sub-meters. Data storage systems have the capability of storing data for prolonged periods. This helps with building maintenance, commissioning, measurement and verification, and comparing certain functions from time to time to make sure operation is consistent.
Dashboards are also making a strong surge onto the scene of commercial building tracking. They are monitors located in high-visibility areas of a building that show actual energy and water usage. They are usually tied directly to the sub-meters or the building-management system. This approach allows building occupants the ability to see how their habits are contributing to, or hindering, water conservation. For example, college dormitories have held contests between students where water-conservation challenges are featured and incentives are given for the group that saves the most water. This approach reaches the core element of improving water conservation: education of users.
Additionally, any system that uses water can benefit from sub-metering and enhanced reading capabilities. Many other water-intensive systems such as kitchen, laundry, and lab equipment will undoubtedly benefit from the ability to see where the water is actually going. Plumbing engineers should check specific code requirements for metering, sub-metering, and data retrieval as there tends to be specific requirements in some areas.
Mark Graf is a senior associate at CannonDesign. As a plumbing and fire protection engineer, Graf provides engineering leadership across all markets and building typologies. He established CannonDesign’s water use unit to examine and develop water-conservation solutions.