Emergy parameters for ensuring sustainable use of building materials

Highlights

• Emergy parameters can be effectively used for regulating the resource use.

• Combining emergy value with market cost of a material can assess its proceurement barrier.

• Large volume of low emergy materials often contribute to high building emergy.

Abstract

The transition towards a more resource efficient economy require suitable policies to regulate the resources needed to support development initiatives. Unregulated extraction of natural resources to support infrastructure expansion activities has led to resource constraints and environmental degradation. Hence an appropriate regulatory tool is necessary to ensure sustainability in resource use. The utility of emergy for resource use regulation in the construction industry has been demonstrated in this study. Emergy analysis has been identified as a comprehensive approach which is able to accommodate the work done by biosphere towards the formation of resources along with the energy used, until refined products are evolved out of them. An environmentally fragile area has been chosen as the study area and building data for the past 25 years has been analyzed using emergy approach to evaluate the environmental performance of buildings. Different parameters to assess sustainability of materials and processes connected with construction sector has been evolved in line with the thermodynamic principles. Further, the investigations undertaken have also established that a sustainable material use policy can be evolved across the required time periods to facilitate efficient utilization of natural resources and building materials. Emergy per unit cost, emergy per unit area of the building and percentage of emergy content in various building materials are identified as the key parameters that could be used to regulate the environmental sustainability of resource use in the construction sector. Also, establishing a time scale based resource use factor to ensure renewability of every natural resource would help not only to evolve strategies for optimum resource use but also to identify the potential options for recycling/reuse of construction materials.

Introduction

Buildings consume significant amount of natural resources as raw materials during its construction phase and often end its useful period of life by generating large quantities of waste (Bjorn, 2001). Over these years, this process has culminated in over-exploitation of environmental resources, global warming, damage to biotic and abiotic components and creation of higher environmental toxicity potentials (Wagner, 2002; Amoêda, 2015). Construction activity often consumes considerable quantity of inert natural materials towards the preparation of aggregates and building blocks such as clay block, granite, and natural stones. Uncontrolled extraction of raw materials from their places of origin to meet the rising demand, which initially might not be perceived as unsustainable, have resulted in severe environmental problems and damaged the local ecosystem by triggering regional instability (Brown and Ulgiati, 1997). These in turn raise significant challenges in ensuring sustainable use of construction materials that have very low replenishment rates (Bianchini et al., 2005). Several options are exercised to reduce this growing environmental degradation caused by the uncontrolled extraction and use of resources. Replacement of natural aggregates with recycled aggregates and development of new materials to ensure sustainable processes are found to have positive effect on reducing the emission of carbon dioxide-one of the most harmful greenhouse gas of anthropogenic origin (Burciaga et al., 2019; Reddy et al., 2019). Further, attempts are also made to configure the occupancy spaces in building units and to design the functional elements in order to reduce consumption of environmental resources and also the maintenance costs (Juan and Cheng, 2018).

The concept of material or product circularity is an emerging approach towards ensuring sustainability of construction materials. Demand to implement policies and regulations on material energy efficiency coupled with compelling need for certifications in environmental sustainability of building systems force the existing buildings too to renovate, repair or replace the redundant components or units (Andrić et al., 2017). The eventual demolition or modification of existing buildings to meet the aforementioned requirements in addition to the construction of new buildings, is expected to produce significant quantity of waste unless it is effectively reused (Khasreen et al., 2009). Thus, a transition is required from the linear understanding of consumption and production of construction materials towards a circular model where the products and materials continue to circulate instead of ending up as waste (Bundgaard et al., 2017; Tecchio et al., 2017; Ghisellini et al., 2016). Several works have been carried out for improving the material circularity through improving the supply chain management of materials (Gharaei et al., 2019a, 2019b; Hoseini Shekarabi et al., 2019). Further, research efforts are also undertaken for improving the quality control and green production policies of materials (Gharaei et al., 2019c, 2019d). Thus, in order to regulate the resource consumption in a sustainable manner, an appropriate yardstick for optimizing consumption is necessary.

Different parameters to assess sustainability in the selection of materials and construction processes are also widely reported. Thermodynamic principles are successfully used for defining environmental sustainability of building systems (Dincer and Rosen, 2012; Amantea et al., 2014). Buildings can be considered as thermodynamic engines that use energy to provide specific services and also maintain acceptable performance even under varying environmental conditions (Pulselli et al., 2007). A growing number of tools such as energy analysis, ecological footprint analysis, life cycle analysis, exergy analysis, emergy analysis, etc. are available for evaluating the material and energy requirements of these thermodynamic engines (Amponsah, 2011). However, except the emergy analysis tool, all the other available techniques are unable to provide a comprehensive environmental analysis as they exclude the environmental work provided by the biosphere in the formation of resources along with the energy used during extraction, manufacturing and maintenance of building elements (Srinivasan et al., 2011). Emergy is identified as a scientific method that can offer a more accurate and detailed picture of complex systems and their association with ecological elements (Niccolucci et al., 2007; Williamson et al., 2015). It accounts for services provided by the environment which are free and outside the economy established on the basis of monitory transactions (Brown and Ulgiati, 1999). Emergy analysis has been widely used to evaluate various types of systems, including geographical systems, food production, industrial processes, buildings, knowledge and human work (Amaral et al., 2016). It is also considered as a powerful tool for evaluating the housing and building industry and has demonstrated its utility in the development of environmental designs. Emergy based approach could successfully develop optimal insulation levels for a building envelope and to elevate its performance to meet maximum potential (Pulselli et al., 2007; Srinivasan et al., 2011). Emergy is also used to assess the optimum levels of recycling and is observed that materials whose refining costs are high have the greatest benefits when recycled (Amponsah et al., 2011, 2012; Brown and Buranakarn, 2003).

Emergy can be defined as the sum of all inputs of energy needed directly or indirectly to produce products or deliver services (Odum, 1996; Brown and Ulgiati, 2004). It is the memory of all energy values that was degraded in a transformation process before reaching the current state of any matter (Brown and Ulgiati, 1999). Different forms of energy are involved in the emergy estimation of materials and the emergy value of each of the streams and systems in the network of energy flow is determined in emergy analysis (Hau and Bakshi, 2004). In this, the energy value of all materials are converted into a common unit of solar energy called solar emergy joules or in short, solar emjoules (sej). This enables the direct comparison of various materials, energies, and processes which could not have been done otherwise (Brown and Ulgiati, 2004). Emergy estimation incorporates the rate of natural resource consumption and exploitation, carrying capacity of the environment, and the production of wastes and pollutants across the lifecycle (Giannetti et al., 2006). Sustainability of materials used in the building systems could also be effectively assessed using emergy analysis. Environmental assessment of buildings using emergy is gaining momentum among the research community as it unifies different kinds of energy used for the material production and services into a common unit (Roudebush and BrownM T, 2015).

The baseline reference for all emergy calculations includes three sources of earth energy: the available energy from solar radiation, geothermal sources, and dissipation of tidal momentum (Brown et al., 2016). The solar emergy of a resource or commodity is calculated by expressing all the resources and energy inputs used for its production in terms of their corresponding inputs of solar energy equivalent (Odum, 1996). Thus, the concept of emergy helps to overcome the obstacles faced in using varied types of energy obtained from different materials or sources that are traditionally used (Amponsah, 2011). The Unit Emergy Value (UEV) of an item can then be derived, which is the emergy required to generate one unit of a product or service, either directly or indirectly. In some cases, it is convenient to express emergy as per unit basis of volume, mass, etc. to transform the accounted quantities in the emergy expression (Giannetti et al., 2006). Higher UEV of a service or product is an indicator of a higher amount of energy utilized in the production of 1 unit of that service or product and vice versa. Thus, the total solar emergy of a product, can be estimated using Eqn. 1,

$$U=\sum _{i=1}^n{E}_i\times T_i$$

where U is the total emergy calculated over all the independent input flows, E$\text{i}$ is the exergy, i.e., the energy available to be used, and T$\text{i}$ is the solar transformity of the i$\text{th}$ input flow of a product or service. The same item can have varying values of transformity depending upon the system pathways used for its production. In order to avoid the repetitive process of calculating the transformities each time, UEVs reported in the earlier studies are used here (Amponsah and Le Corre, 2011). Though emergy is increasingly being used as a tool for environmental system evaluations, it is still in its early stages with many issues yet to be resolved, especially in the evaluation of building construction sector. These issues include variability in UEVs of the same material depending on the place of origin, method of production and baseline revisions occurring from time to time. Subsequently, it is also suggested that emergy investigation results could be appropriately used by public policymakers in the planning of sustainable pathways for resource use, as well as for careful management of natural resources (Ulgiati et al., 1994).

The resource use pattern is observed to vary across different time periods and hence intervention at appropriate instant need to be initiated judiciously. Investigating the time scale effect on the ecosystem services, when appropriately represented in the emergy values, would provide utility information for policy framing and regulatory intervention on natural resource use. Emergy per unit cost is an appropriate indicator of environmental degradation issues emerging from extraction/procurement of natural resources. It could be used to identify the cost escalation occurring due to sudden variation in material supply. Building emergy to building cost ratio has been used earlier to assess the emergy flow involved in a building maintenance activity (Pulselli et al., 2007). Emdollars which are considered as the economic equivalent of emergy is obtained by dividing emergy by the ratio of emergy to money in the economy and they reflect emergy contributions to an economy (Odum, 2002). Another parameter called emprice, which is the emergy received for money spent, is appropriate to assess the life cycle emergy cost of materials like concrete and clay brick (Brown and Buranakarn, 2003). Environmental barriers in the procurement of materials that result in the cost escalation and environmental degradation could be forecasted well in advance by correlating with the available market cost information on materials. Thus, when the focus is given on any particular sector or production process such as building industry, emergy based parameters are capable of providing insights into the thermodynamic efficiency and quality of the process and its output, and its interaction with the surrounding environment (Brown and Ulgiati, 1997). This makes it necessary to demonstrate the utility of emergy parameters for real time environmental assessment of resource use pattern prevailing in a region. Suitability in selecting emergy as a parameter for the resource use regulation in the construction industry is evaluated based on the data obtained from randomly selected houses constructed in the chosen study area during a period of 25 years from 1994 to 2018. The specific objectives of the research are to understand (i) the implication of material use based on the variation of building emergy values across a time span of 25 years (ii) the impact of various material choices that emerged during the chosen period (iii) identification of appropriate emergy parameters that could act as a tool to regulate the resource use and (iv) to establish the utility of emergy parameters for understanding the interaction of construction process with the surrounding environment.

Organization of this paper consists of the following sections. Section 1 included introduction, review of literature and objectives of this research. Section 2 describes the methodology of work undertaken and illustrates the study area and its environmental significance. This section also contains the system boundary and systems diagram which is the basic element of emergy analysis. Section 3 discusses the results of analysis carried out on the variation of material emergy, key contributors of emergy and parameters of emergy to assess resource availability. Section 4 presents the conclusion, future impact and limitations of the current study.