Understanding resource consumption and sustainability in the built environment

Buildings and the infrastructure that supports them comprise the built environment. However, the human-constructed aspects of the built environment extend beyond formal buildings and centralized distribution infrastructure to also include informal and temporary housing settlements and distributed water, energy, and food systems. When considering sustainability holistically across its environmental, societal, and economic dimensions, these formal and informal built environments require place-based and fit-for-purpose solutions for the appropriate context.

Water, energy, and food are interconnected such that resource consumption in the built environment can exacerbate challenges with other resources. Food consumption requires water [1] and energy [2] for cultivation, with additional energy consumed for transportation, refrigeration in the cold chain [3], cooking, and food waste management. Energy consumption requires water [4] for hydrocarbon extraction and refining, thermoelectric and hydroelectric power generation, and biofuels feedstock cultivation. Water consumption requires energy [5] for source collection, treatment and disinfection, distribution (including bottled water and tanker truck deliveries [6]), end-use heating, and wastewater treatment. The connections between these resources can emerge in the built environment directly, or in the supporting infrastructure systems indirectly, introducing local and global considerations around resource sustainability.

Both quantitative and qualitative data support understanding of resource consumption in the built environment. Quantitative data include building-scale measurements from smart water and/or electricity meters, government databases, and exogenous parameters (e.g., weather, socioeconomic and demographic conditions) that affect resource consumption. Qualitative data include interviews and contextual observations to inform different analyses. Together, these data reflect the specific built environment context, and this context specificity motivates further data collection and sharing [7]. In collecting and sharing data, however, there are often tradeoffs between data spatiotemporal resolution (and its implications for privacy, data gathering, and management costs), monitoring locations, and study duration [8–12].

Data, both quantitative and qualitative, are useful to inform descriptive and predictive models of resource consumption in the built environment under different conditions. Different models have different applications, with many models supporting benchmarking and simulation of possible future scenarios. Various data gathering, handling (e.g., dimensionality reduction), and modeling approaches are represented in this focus issue, including regression [3] and other machine learning methods for classification [10, 11], principal component analysis [12, 13], participatory action research [8], differential equations representing underlying physical science [14], and other building-scale models [14–16]. Research models and analyses, combined with multi-scale digital applications [7], can translate impacts from large-scale infrastructure operations (e.g., CO₂ emissions from electricity generation) to the end-use scale [6, 16], though there are often overlapping spatial scales for resources and governance. Computational tradeoffs exist between model dimensionality and model skill [12]. Consequently, resource management and decision making with models requires consideration of tradeoffs and context.

The built environment includes many aspects of infrastructure to support humans and communities. At the large scale, numerous water/sanitation, power generation, and agricultural production facilities support water, energy, and food consumption inside buildings. These large-scale systems are linked by infrastructure networks, introducing both vulnerabilities and opportunities for sustainability measures. For example, truck transport of meat and prepared foodstuffs as part of the cold chain incurs additional energy and contributes CO₂ emissions [3]. Quantifying and benchmarking this energy for food, especially in the context of reducing food waste, presents useful data to inform sustainability actions that benefit both resources.

Similarly, centralized water systems in urban, peri-urban, and suburban areas depend on treatment plants, pumping stations, and pipeline infrastructure for water service provision. The energy dependence of water supplies, whether through centralized or decentralized infrastructure, causes energy constraints to become water constraints. Thus, water supply planning should extend beyond previous analyses focused on cities, piped access, and continuous supply systems to also include smaller towns with consideration of variability of access in time and space and gendered socioeconomic vulnerability [13]. For example, diesel generators for water supply in remote and isolated Australian Indigenous communities create water constraints when diesel supplies are disrupted [8]. Mixed quantitative and qualitative data advances the understanding of water security [8, 13], with many important considerations often neglected, especially in the context of clean drinking water [17]. Water from both formal (i.e., piped) and informal (i.e., bottled water, water deliveries by tanker truck) sources are important supplies in Beirut, Lebanon [6], reflective of many locations globally. The need for informal water sources also impedes sustainability because bottled water and water deliveries by tanker truck have higher energy and carbon emissions intensity than formal piped water distribution systems [6]. Consequently, consideration of context is necessary in evaluating resource sustainability.

External factors beyond the local or regional context also affect sustainability in the built environment. Changes in climate lead to changes in building heating and cooling, such that rescaled global climate models can inform more efficient heating, ventilation, and air conditioning design and building configurations [18]. Climate change is likely to increase electricity demand in the built environment, particularly during summer peak periods, introducing demand management and possible budgeting challenges for communities, campuses, and campus-like operations [12]. At the individual building scale, global climate models linked with building climate design conditions project that heating degree days will likely decrease while cooling degree days might double for a case study building in Madison, Wisconsin, USA [18]. As a mitigation strategy, precooling at the residential scale can leverage distributed photovoltaic solar energy to shift electricity demand for air conditioning from peak to off-peak periods, with additional benefits of reduced CO₂ emissions, for a single-family home in Southern California, USA [16]. However, not all buildings are formal developments. In informal settlements in particular, natural ventilation is an important aspect of livability; however, outdoor air pollution can limit natural ventilation potential even when temperatures are suitable. Filtration combined with natural ventilation introduces energy tradeoffs, yet this energy consumption for filtration is still less than mechanical air conditioning [14].

Advancing toward sustainability goals requires a combination of design and operational factors for reducing resource consumption throughout the built environment, including residential-scale energy consumption [15]. Understanding community context is particularly important for creating community-driven resource sustainability approaches [8]. For example, in the context of the residential sector in Saudi Arabia, building insulation is a strong energy efficiency approach, motivating policy change regarding new building codes and existing building retrofit [15]. These built environment design conditions can advance toward sustainability through enhanced efficiency.

At the residential scale, consumption of water, energy, and food is closely linked with human activities and well-being, yet data are often limited at the scale of specific households [19]. Household-level data also introduce privacy concerns and economic implications of metering systems, such that data anonymization and modeling are common approaches to understanding the residential built environment. Residential resource consumption data are often recorded with time resolutions that make activity recognition tasks challenging. Combinations of methods expand understanding of water use at the residential scale, including fuzzy set analysis and principal component analysis [13], random forest classifiers [11], and other data-driven or physically-based approaches. Meter-level data can support modeling of the built environment to estimate specific end uses of water [11] and electricity [10]; however, temporal resolution can be a limiting factor in the quality of estimations [10, 11]. These analyses using household-scale meter, survey, and interview data can help fill a notable gap regarding sustainability related to water/energy consumption by residential users.

Beyond changes to the built environment itself, education and human behavior change play a substantial role in the type and amount of water, energy, and food consumption. For example, education and encouraging conservation/efficiency led to significant long-term sustainable water management outcomes in community-driven efforts with Australian Indigenous communities [8]. In a case study of northern Italy, coastal tourist areas showed little difference between water consumption on weekdays versus weekends, while residential areas had noticeably different hourly water consumption on weekends [9], demonstrating the changes in behavior associated with vacations compared to typical activities. At a larger scale, tourist activities change the spatial and temporal demand for water, with variability across seasons, weekdays/weekends, and weather conditions [9]. While human behavior and resource consumption change is complex [20], these results suggest that human engagement through education can play a notable role in advancing toward sustainability goals.

This focus issue presents diverse and valuable perspectives on resource consumption and sustainability in the built environment. Through combinations of quantitative and qualitative data, modeling methods, analyses, and decision support systems, the articles in this issue highlight sustainability aspects of water, energy, and food consumption ranging from the building-scale to supply chain infrastructure. The nexus of these resources presents substantial opportunities for technology transfer and synergies in sustainability actions, where positive outcomes for one resource might present additional positive conditions in other resources. Understanding the interconnectedness of current water, energy, and food consumption is an important first step in future research around sustainability in the built environment. Benchmarking of resource consumption presents notable opportunities for advancing sustainability within different community contexts [8]. Widespread use of models also enables simulation of many possible future conditions under uncertainty in comparison to baselines.

New knowledge is needed around complex challenges in urban areas [21], and such knowledge production and research directions should also extend throughout the built environment to inform solutions for various resources at a range of scales. Though most of the world's population lives in urban areas [22], sustainability is also important for rural, isolated, informal, and unique built environments, as they can often have disproportionately high tradeoffs in the water-energy-food nexus (e.g., greater reliance on energy for food and water security and vice versa). Education and human behavior change can advance sustainability solutions in practice, when combined with system-level and end-use efficiency. However, context is an important consideration around resource consumption and sustainability, motivating additional research around humans and their water, energy, and food consumption in diverse built environments. This context is especially important as we make the bold, global commitment to address the Sustainable Development Goals by 2030.