DOS DÍAS DEL MES DE SEPTIEMBRE DEL AÑO DOS MILTRECE

Familiarity with the drivers and pathways within the building site is prerequisite for water assessment. A building is a system operated by multiple subsystems, including energy and water, and the movement of resources to, within, and from the building site creates individual resource cycles (Cole et al., 2012). The subsystem created by the movement of water throughout the site can be described as the building water cycle. Historical management of the building water cycle mirrors a paradigm shift in water resources management that can be compared to the natural hydrologic cycle. The building system boundary that houses its water

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cycle includes the building structure in addition to applicable vegetation and hardscapes. Both the natural and building water cycles map water flows throughout the system. In the natural cycle, water is contained within the global system boundary representing the net-zero goal. Recycling within the natural cycle ensure that water consumption is matched by water production. Conventional building design imports potable water flows from environmental sources for consumption within the building. Once used, water is labelled as waste and discharged from the building site. Managing water using linear processes results in higher environmental impacts through resource depletion. Sustainable design encourages conservation measures in order to decrease overall water use. Water reuse and recycling techniques that mimic natural processes further reduce the need for potable water supplies. Both conservation and the creation of balanced water feedback loops are necessary in order to achieve the same net-zero efficiency as the natural cycle.

The building energy framework consists of individual loads that exert a demand, as well as available energy sources that serve the loads. Similarly, the building water cycle is formed by water fixture demands served by available water sources. Opportunities to increase water efficiency or create closed loops towards net-zero water accomplishment depend on the existing components of the building water cycle, such as building demands, available water sources, and occupant behavior patterns.

2.3.2.1 End-uses and Water Sources

Designed water demands (Table 2.3), or end uses, and their magnitude depend on the type of building and affect the overall quantity of consumption (Dziegielewski et al., 2000). For example, a residential home includes water demands related to cooking and showering that may be non-existent in commercial or industrial facilities, and a shower in an office building will likely demand less water than showers in a multi-family residence. Demand existence and magnitude also varies among buildings of the same type, such as the presence of swimming pools in certain homes or aesthetic water features in specific office complexes. Therefore,

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demands found in the building water cycle are site-specific, and the varying magnitude of water consumption by demand causes outcomes from similar water efficiency strategies to also be unique to the building site. Multiple demand-based conservation measures exist that decrease overall building water use and guide the building water cycle toward the net-zero ideal (Inman and Jeffrey, 2006).

Table 2.3: Potential building water demands and associated fixtures.

Water demands Fixtures

Irrigation Sprinklers Hoses Underground drip-systems Drinking Faucets Water fountains Water dispensers

Hygiene Bathroom sinks

Kitchen sinks Showerheads Bath faucets

Cooking Kitchen faucets

Dishwashers

Cleaning Faucets

Clothes washers

Sanitation Toilets

Urinals

Process water Mechanical cooling Boilers

Steamers

Industrial dishwashers Ice machines

Pre-rinse spray valves

Safety Fire sprinklers

Recreation and aesthetics Swimming pools Fountains

Ornamental ponds

Accessibility to individual water sources (Table 2.4) is necessary to meet the unique building water demands dependent on the supporting infrastructure, climate at the location of the building site, and building demands. Centralized sources supplied by extensive infrastructure networks include potable water and reclaimed water. Climate at the building location affects the availability of rainwater and stormwater supplied by precipitation. In

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addition to driving overall consumption, demands within the building also determine the availability of wastewater sources (greywater or blackwater) generated on-site. Meteorological conditions and the presence of a mechanical cooling demand affect the availability of condensate as an alternative water source. Condensate is ideal for non-potable water demands due to its high quality and limited treatment requirements (Licina and Sekhar, 2012). Potable water has traditionally been utilized for all building demands; however, net-zero water buildings need to incorporate additional alternative sources within the building’s water source portfolio.

Table 2.4: Potential building water sources and origins.

Source Origin

Potable water Centralized treatment of groundwater, surface waters, or desalinated water Reclaimed water Treated wastewater from centralized wastewater treatment facilities Rainwater Precipitation intercepted before interacting with the ground

Stormwater Precipitation collected after interacting with ground surfaces; runoff Condensate Condensed water vapor resulting from cooling processes

Greywater Wastewater from faucets, showers Blackwater Wastewater from toilets and urinals

2.3.2.2 Influencing Factors and Uncertainty

Identifying the magnitude of demands and available sources within the building water cycle allows for simple demand-source matching in order to fulfil the building water functions, but uncertainty affects demand and source profiles thereby introducing variability into the actual building water cycle performance and impeding consistent net-zero accomplishment. The vast variability in climate greatly affects the potential for alternative water use, such as rainwater harvesting and condensate production, thereby reducing the options available to offset potable water (Licina and Sekhar, 2012). Further imbalance results when climate increases the water required for weather-sensitive demands such as irrigation, cooling, and water features (Boland, 1997). Expanding climate variability is also making it increasingly difficult to predict future patterns based on historical records or stationarity (Dessai and Hulme, 2007; Salas et al.,

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2012). In addition, unforeseen failures in the system including pipe breaks, fixture malfunctions, power interruptions, and treatment deficiencies instantly exclude the associated source from the water cycle for the duration of the failure.

Another major source of uncertainty is a result of socio-economic factors (Huang et al., 2013). The interactions undertaken by building occupants with the fixtures serving the building demands directly impact consumption and wastewater generation resulting in unique patterns over time used for demand forecasting (Alvisi et al., 2007). The behavior and resulting water consumption of an occupant varies based on the building in which they currently reside (Pieterse-Quirijns et al., 2013; Stoker and Rothfeder, 2014). For example, it is likely an occupant will exert a higher hygienic demand at home rather than in a commercial setting due to social purpose of each structure. Specific variables controlled by occupants include the number of use events for a demand fixture and the duration of the use event (Blokker et al., 2010; Wong and Mui, 2007). The variability among occupant groups should be acknowledged when predicting water consumption and generation for net-zero analysis.