Analyzing Embodied Energy and Embodied Water of Construction Materials for an Environmentally Sustainable Built Environment

Abstract

Buildings consume over 40% of global energy in their construction and operations contributing to over 39% of global carbon emission each year. This huge environmental footprint presents an excellent opportunity to reduce energy use and help deliver an environmentally sustainable built environment. Most of the energy is consumed by buildings as embodied energy (EE) and operational energy (OE). EE is used directly and indirectly during buildings' initial construction, maintenance and replacement, and demolition phases through construction products and services. OE is used in the processes of heating, cooling, water heating, lighting, and operating building equipment. Most environmental optimization research has been centered on energy and carbon emission overlooking another critical sustainability aspect, water use. Each building also consumes a significant amount of freshwater as embodied water (EW) or virtual water in its initial construction, maintenance and replacement, and demolition phases. Since each primary and secondary energy source depletes water in its extraction, refinement or production, there is also a water expense associated with EE and OE use that must also be included in total EW use. The total EW, therefore, includes both non-energy and energy related water use. Research suggests that there are tradeoffs between EE and EW that may complicate design decisions such as material selection for environmental sustainability. In other words, a material selected for its lower EE may have higher EW and selecting such a material may not help reach environmental sustainability goals since water scarcity is becoming a grave problem. In this paper, we created an input-output-based hybrid (IOH) model for calculating and comparing EE and EW of building materials frequently used in building construction. The main goal is to examine and highlight any tradeoffs that may exist when selecting one material over another. The results reveal that there is a weak correlation between EE and total EW that is the sum of energy and non-energy water use, which means that a design decision made solely based on EE may conflict with EW. The share of energy related water use in total EW of construction materials also varies significantly (2.5%-31.2%), indicating that reducing energy use alone may not be sufficient to reduce freshwater use; additional efforts may be needed to decrease the use of materials and processes that are water intensive. The results of this study are significant to achieving the goal of creating a truly sustainable built environment.