Keywords

Building; retrofitting; cost-effective; optimal; sustainability

9.1 Introduction

The rational use of energy for sustainable development and a low-carbon future has been the concern of European directives. Aimed at attaining high-energy performance buildings for new and renovated structures, all the European Union (EU) member states made an effort to determine a common objective of reducing the energy and environmental impact of the building sector, putting forward the first version of the Energy Performance of Building Directive EPBD 2002/91/EC (European Commission and Parliament, 2002). The EPBD defines the common goals and guidelines and offers an ample range of procedure and computation methods for attaining significant improvement in the sustainability of buildings and cities. The EPBD Directives 2010/31/EU (European Commission and Parliament, 2010) have been revised to advance the energy performance and economic feasibility of building systems to nearly zero-energy buildings. Furthermore, there is the EU 20/20/20 program, which aims for 20% less primary energy use through energy-efficient retrofitting (Communication from the Commission to the European Parliament, 2008).

Thus, retrofitting entails the technical intervention in the energy system of a building for effective energy utilization. This can be done by replacement of inefficient appliances with efficient ones. Due to the variety of retrofitting options in buildings, it is challenging to develop typical rules, since every building has a unique pattern for energy consumption depending on inhabitant needs. Hence, researchers and scientists are pushing hard to optimally frame the retrofitting approaches in compliance with building standards and codes.

Cost-effective investments for energy-efficient buildings have continuously supported this hypothesis. Net benefits of individual retrofit technologies were proposed in earlier works by Pezzy (1984) and Hendeson and Harmelen (Henderson and Shorrock, 1989). In addition, macrolevel building energy retrofitting delivered comprehensive benefits (Clinch and Healy, 2003). The energy assessment models in these studies differ and vary in quality, reliability, and narrow economic considerations, which has resulted in challenging retrofitting measures. Since then, the trend has continued and has directed the interest of the scientific community towards performance of buildings, which accounts for 40% of energy demand in the world (Shaikh et al., 2014), with the aim of achieving net/nearly zero-energy buildings to alleviate energy consumption and wastage.

Building retrofitting is also a key strategy for attaining tangible outcomes in reducing world energy demand and environmental emissions. It generally involves replacements, modifications, and refurbishments of existing buildings to enhance energy efficiency, conservation, and savings. Besides, it also allows the utilization of distributed generation in the building for being energy-efficient.

Retrofitting is a challenging task that entails a holistic and integrated approach. Thus, multifaceted objectives are usually endured (Hopfe et al., 2013). The prime objectives are the minimization of energy consumption and maximization of economic benefits. Therefore, energy analysis of buildings is crucial to estimate the baseline energy demand and potential of energy savings for performance indications of cost-effective retrofit measures. Energy retrofits in buildings are valuable if the global life-cycle costs are minimized. This cost-optimal analysis is difficult due to their complexity, which includes climatic conditions, operation, functionality, and construction of the building. The cost-optimal analysis must be capable of offering effective packages for energy-retrofit measures (Corgnati et al., 2013; Kuusk et al., 2014).

The aim of the chapter is to identify the optimal cost-effective energy-retrofitting strategy. A holistic retrofitting scenario has been considered, which includes reduction of energy consumption, cost savings, capital investments, emissions, technology behavioral change, and comfort indexing, along with sustainability concerns. Besides, various uncertainty parameters and risk factors have been considered. Multifaceted optimal retrofitting strategies based on the optimized decisions are prioritized to address these challenges. In addition, some challenges for simulation toolkits have been discussed for the success of the building energy retrofit project.

This chapter includes challenges faced by building energy retrofitting, followed by optimization approaches for the design of retrofits considering the aforementioned challenges. Building energy retrofits and their sustainability have been discussed in detail. Finally, we present the conclusion and future directions.

9.2 Challenges in Building Energy Retrofitting

Identifying and quantifying the numerous benefits of building retrofits has become a new trend in the energy field, as energy efficiency is esteemed by building users (Kneifel, 2010). Building energy performance can be enhanced through various techniques including inculcating awareness, energy management, technical measures for energy conservation, and renewable energy (Wu et al., 2011). A systematic technical and management revolution is needed in practice for the attainment of greater energy and environmental goals for a sustainable future. Energy efficiency and the resulting savings can be attained from the interaction among the behavioral, technological, and organizational changes. These features and their interaction will facilitate in attaining holistic and optimized performance targets in buildings (Ruparathna et al., 2016). There are numerous factors to consider in building energy retrofitting, including current building stock, building practices local availability, labor and material accessibility, technology penetration, constraints of legal regulations.

The selection of a single measure or combinations of cost-effective and cost-optimal energy retrofit measures in buildings is considered technically complex. The cost-optimal level can be defined as the energy performance level that leads to the lowest cost during the estimated economic life cycle of the building (Wittchen and Thomsen, 2012). This level of performance is considered as a range of costs that includes capital investments, equipment maintenance, operating costs, and energy savings. These can estimate the economic life cycle of a building. However, cost effectiveness has been defined as the relationship of monetary economics to the attainment of tangible outcomes. In other words, the money spent on retrofitting would have positive outcomes in terms of energy savings without the associated high costs (Wittchen and Thomsen, 2012).

The core challenges that can influence the selection of the retrofit program depends on the priorities of the various stakeholders, timing and methods of payback on investments, potential investors’ lack of access to risk analysis, uncertainty about benefit sharing, and the need for revisions in policies governing retrofits and energy contracts (Lu et al., 2014). These aforementioned challenges are quite relative in terms of policy measures and regulations. Furthermore, retrofits also claim social factors that need to be considered from the viewpoint of a building consumer.

The performance-effective and cost-effective complexity of retrofit interference states that each building varies and every consumer behaves differently, thus rendering the retrofitting task a multifaceted one. Generally, the tasks involved in building energy retrofitting are complex and heterogeneous. This requires special expertise for integration in extremely variable conditions. Thus, evaluating building retrofits is quite challenging due to the fact that the building and its environment involves complex systems such as technical, technological, ecological, social, comfort, esthetic, and other aspects (Asadi et al., 2014).

Some significant social challenges also include splitting incentives between the tenants and the landlord, technical expertise, unproven return on the investments, unease from the lender, lack of available capital, etc. These add more complexity in the building retrofit strategy. Some of these challenges are shown in Table 9.1.

The majority of building owners, managers, researchers, and scientists recognize that energy-efficient retrofits have the potential to yield ample savings on building operational costs and reduce environmental impact. However, substantial effort and time need to be spent by industry experts to identify various barriers to the large-scale adoption of building energy retrofitting.

9.2.8 Reliable Prediction of Building Energy Performance

To optimize the energy and cost savings in the building industry, retrofitting strategies are being promoted and accelerated. This improves energy efficiency and conservation within the buildings. However, building energy-performance assessment is challenging prior to having capital investment. In this case, building retrofit activities can be investigated and analyzed using simulation tools. Various simulation platforms (Lee et al., 2015) are available through which the analysis of a particular retrofit strategy can be observed prior to making any decisions.

The simulation-based retrofit strategy assists the consulting engineers, architects, and various other stakeholders that undertake retrofit projects. These platforms and toolkits are generally dependent on building energy computations as a major part of the process. These processes consist of energy raw data, simulation platform operation, core features, and the required output.

Simulation platforms offer an understanding of the behavior of complex systems that enables the simultaneous operation of various processes. Hence, building energy analysis platforms considering both complex dynamic or simplified energy computations in addition to input parameter data, scope, cost, user aptitude, and time all would completely influence the simulation speed and quality of output results (Perez-Lombard et al., 2009; Al-Homoud, 2001). So far, various simulation tools have been developed for building energy retrofitting and have been studied in detail by Lee et al. (2015). However, with these simulation tools and platforms a number of explorations can be observed; these are listed in Fig. 9.1.

Optimization: To resolve contradictory objectives in a retrofitting strategy. These are normally simulated with methodological techniques in order to get the best output.

Prediction: This will propose future scenarios for a particular retrofit technique, method, or technology in order to plan for the projected cost-effective resources and demands.

Proof: It declares the existence of possible retrofitting measures. The simulations can depict the possibility to develop certain behaviors for modeled processes.

Discovery: To discover unforeseen consequences with simple retrofitting process interactions, simulations are being performed.

Management: Simulation platforms help to understand the resource’s organization and operation.

Control: The control of any process for energy flow can be investigated with simulation platforms.

Explanation: Sometimes behavior of the process is unclear and plausible explanations can be postulated.

Operation: The scientific process flow can be proved and verified through the operation of the proposed system.

Reliability: The system reliability for process operation can be observed through the energy retrofit simulations.

Critique: Theoretical descriptions are also used to observe the phenomena through the simulations proposed by scientists and researchers.

Prescription: The suitable mode of operation or method of organizing the workflow can be accelerated with the help of simulation platforms.

Hence, various tools offer different types of functionality but can still be easily accessible. These tools can have different levels of complexity, need for data input, and long run time (Lee et al., 2015). However almost every simulation platform provides a variety of building energy retrofitting parameters, but a few of them, such as water savings, indoor air quality, greenhouse gas emissions, and consumer preferences, are limited. This is suggested to expand and enhance platform capability for the evaluation of a wide range of environmental parameters. In addition, building energy simulation platforms include the assessment of risk factors, consumer preferences, interoperability, and expansion of output parameters for a broader vision of cost-effective retrofitting strategies.

9.3 Optimization Approaches for the Design of Building Energy Retrofit

Energy reduction for the purposes of energy conservation and efficiency through optimal retrofitting in the built environment is a strategic research challenge (Al-Homoud, 2001). Since energy retrofit tasks are heterogeneous and complex, this involves integration of numerous variable working domains. Thus, a thorough evaluation of building retrofit is challenging due to complex systems regarding technical, technological, social, esthetic, ecological, comfort, and other facets (Asadi et al., 2014), as every subsystem affects the total performance efficiency. Along with this, the interdependency of these subsystems plays a critical role (Kaklauskas et al., 2005). In that context, there is an international report comprising of three working groups dealing with the scientific basis of global warming (Working Group I), its consequences (Working Group II), and options for slowing the trend (Working Group III) (Tobias et al., 2009). This latter section specifically deals with the global potential of building energy efficiency for mitigating global warming.

Building energy retrofitting with development of efficient technologies supports energy conservation measures (ECMs) to enhance the energy performance. The selection of appropriate measures needs to satisfy various demands within the buildings. Therefore, in order to propose energy retrofitting, decision makers should consider primarily the socioeconomic energy-related factors as key performance indicators. Whereas, the other technoeconomic factors can be taken into account for attaining the best balance between the stakeholders’ and occupants’ requirements (Wang et al., 2014). The orientation of solutions or end results obtained would be the ultimate tradeoff of the selected parameters. These tradeoff solutions must be benchmarked through the cost-optimal or cost-effective approach. The cost-optimal levels have been defined as the energy performance level that leads to the lowest cost during the estimated economic life cycle of the building. This level of performance is considered as a range of costs that includes capital investments, equipment maintenance, operating costs, and energy savings. These can estimate the economic life cycle of a building. Whereas, the cost effectiveness has been defined as the relationship of monetary economics with the attainment of tangible outcomes. This means that they money spent on retrofitting would have positive outcomes in terms of energy savings without large associated costs.

The multicriteria or multiobjective (MO) model has been the growing trend in evaluating building energy retrofitting projects. The selection criteria mainly focuses on capital cost, energy efficiency, and other comfort factors such as occupants, space utilization, and other subjective factors such as visual, air quality, and thermal comfort (Shaikh et al., 2016) as can be seen in Fig. 9.2. The criterion of decision-maker’s priority in energy retrofits leads to sustainable practices within the buildings. The MO approach is proposed for the planning, evaluation, and design phase of retrofitting projects (Wang et al., 2014), as within these criteria, necessities are often contradictare and subject to various constraints for satisfying the specific requirements of the energy retrofit plan.

Moreover, the performance measures can be categorized into three objectives that can be taken into account: energy, economic, and environmental challenges (De Boeck et al., 2015). This also includes energy savings and societal impact as performance measures. Besides, the actions for improving building energy efficiency involve manifold, inadequate, and contradicting evaluation of actions. These significant challenges can be dealt with using the multiobjective optimization models. In this regard, the set of potential alternatives can be implicitly determined in terms of constraints stating feasible trade-off. Thus, optimizing multiple contradictory objectives, potential alternatives must be known prior to explicitly assessment through quantitative or qualitative criteria. The logical course to be followed for the toolkit analysis of a multiobjective retrofit is shown in Fig. 9.3.

There are various developed methods and approaches available for the assessment of conditions and support decisions pertaining to building energy retrofitting (Asadi et al., 2014). The optimization methodologies have been broadly categorized into two main approaches:

The weighted summation method is the most common approach, in which the decision maker assigns weight to each objective function, thus making it possible to find the ultimate design solution that optimizes the weighted sum of the objectives. The first ever multicriteria analysis was proposed by Gero et al. (1983) for attaining the tradeoffs between thermal performance and capital cost and usable area within the building. Energy performance of indoor air quality for multicriteria decision-making has been observed in Jaggs and Palmer (2000). Elaboration of retrofit scenarios (Flourentzou and Roulet, 2002) and the retrofitting strategies using the multicriteria approach has been discussed in Rey (2004). The multivariant design criteria has been proposed in Kaklauskas et al. (2005), defining the priorities, needs and degree of utility for building retrofit alternatives, thus offering the most recommended variant. These aforementioned studies allow building retrofits with preevaluated and predefined substitute variants of retrofit options. A small number of solutions does not guarantee that the best solution has been attained, whereas, with a large number of solutions, the selection and evaluation process turned too complex to handle. The multicriteria analysis method does not even offer the sensitivity analysis criterion variations with other criteria.

The other approach is based on multiobjective optimization (MOO), which facilitates a huge set of building retrofit options. These options would implicitly be defined by the constraints defining the search space, thus trying to grasp the tradeoff between the objective functions and attain a feasible compromise of solutions. Hestnes and Kofoed (2002) discuss the retrofit scenarios within office buildings for improving energy performance and indoor working conditions, i.e., the comfort index, through the use of passive low-energy technologies. Poel et al. (2007) offer cost-effective measures for energy performance assessment of existing buildings. Genetic algorithm-based decision support for housing assessment and refurbishment strategies of existing building has been proposed in Juan et al. (2009). The life-cycle primary energy implications of retrofitting with improved thermal, ventilation, heat recovery, and efficient hot water tap models have been developed by Dodoo et al. (2010). The prediction of annual energy for space heating has been compared for long-term measurements (Hens, 2010), in addition to the benefits of solar boiler and PV panel that have been utilized for net zero-energy building. Environmental and cost-assessment improvement options have been modeled based on LCCA (Nemry et al., 2010). Pre- and postretrofit analyses for airtightness for ventilation and energy use have been observed in Nabinger and Persily (2011). The hierarchical pathway for zero-carbon building refurbishment is to minimize energy demand and match with the local renewable energy supply. Policy analysis and relevant stakeholders’ involvement offers a clear vision and choices of refurbishment techniques (Xing et al., 2011). The energy retrofit at the municipal level has been considered for energy modeling of barriers to overcome (Caputo and Pasetti, 2015). Cost-optimal energy performance and thermal comfort have also been tackled using multiobjective optimization (Ascione et al., 2015).

9.4 Building Energy Retrofit and Sustainability

The energy retrofit of buildings is turning into a gigantic challenge for researchers and scientists to attain economic, environmental, and social benefits for their community and countries. Several global organizations have come into the arena and have devoted their significant resources to crafting sustainable built environments (Hartkopf and Loftness, 1999). In this context, building refurbishment and renovation has attained significant attention as a feasible alternative for alleviating the cost, abatement of environmental impacts, and maintaining social viability globally (Juan et al., 2010). These organizations consider holistic approaches to rate building performance metrics within their countries. To that end, the Building Research Establishment Environmental Assessment Method (BREEAM), based in the United Kingdom, is primarily focusing on environmental assessments and technological research in the building sector. In the United States, the Leadership in Energy and Environmental Design (LEED) program offers certification for buildings that perform in an environmentally friendly manner in both indoor and outdoor climates of the building envelope. The design and construction of buildings to attain sustainability is offered by both the Green Star (GS) and Green Mark (GM) programs based in Australia and Singapore, respectively. However, the National Australian Built Environment Rating System (NABERS), also based in Australia, focuses on the operation performance targets that measure and rate building energy utilization. Built Green Canada (BuiltGreenCan) is a voluntary program for supporting green practices in the building sector for attaining a green future. Whereas, China’s 3-star rating tool encourages the stakeholders to invest in green developments of envelopes and attain sustainability. The development and promotion of energy, environment, and ecological sustainable techniques and policies are offered by the Comprehensive Assessment System for Built Environment Efficiency (CASBEE) in Japan. The Hong Kong Building Environmental Assessment Method (HKBEAM) offers eco-efficiency and sustainability measures for building practices to utilize fewer energy resources. Korea Green Building Council (KGBC) focuses on the facilitation of transforming best practices in building sustainability. Relatively, Green Building Index (GBI) looks for the design and operation of the buildings for overall impact analysis of the built environment. It proposes measures of energy efficiency, sustainable site management, indoor environmental quality, water efficiency, materials and resources and innovation (Shaikh et al., under review).

These countries have embraced sustainable development trends in green buildings. Each of the countries, specifically the organization, considers specific target characteristics in the building industry. Thus, transforming their building envelopes is either regulated entirely, or there is a voluntary adoption of building codes, guidelines, and standards, or there is a mix of all of those factors. Moreover, they have opted for green building practices for the cutting-edge benefits of energy savings and reduction in greenhouse gas target attainments. The widespread adoption of green building practices could lead to security of energy supplies, enhanced competitiveness among stakeholders, and success in green developments.

Sustainable building practices are encouraged across the globe. Green programs for transforming building practices in new building construction is worthwhile for huge evolving economies, thus emphasizing the significance of sustainable retrofit practices for existing building stock across the board. The current awareness of green and sustainable buildings is high among the construction industry, designers, real estate, etc. New sustainable construction, no matter how energy-efficient and environmentally sensitive, may not by themselves transform the environmental impact of the built environment.

In the Industrialized countries, more than 98% of envelopes consist of existing building stock, whereas new construction only accounts for 1–1.5% of total buildings (Tobias et al., 2009). In addition, the percentage of new building construction in dense urban landscapes would be even less. Besides, occupants, their energy profiles (i.e., electricity, water, and gas, and other raw energy) will be required for long terms. Hence, green property retrofits are critical for energy conservation globally, and green building construction and design will entirely realize their suitability in existing building envelopes only.

Thus, in order to enhance the rate of building refurbishments and retrofitting, it is necessary to develop appropriate methods for building energy audits aimed at energy retrofits (Ma et al., 2012). The cost-effective retrofitting of existing office building stock is a key target for both energy and environmental sustainability. However, energy efficiency measures pose diverse and contradictory requirements. Therefore, it is generally proposed to devise a multicriteria method to support design strategy in decision-making for energy-efficient solutions. For the development of sustainable retrofit projects, the following criteria need to be taken into account:

9.5 Conclusions

The cost-effective optimization of retrofitting within building envelopes has been extensively discussed in the chapter. It provides in-depth details for retrofitting scenarios, which helps in developing a holistic approach for multiobjective optimization. The barriers and challenges to energy retrofitting, keeping in mind energy efficiency, cost effectiveness, capital investment, greenhouse gas emissions, and comfort index, have been discussed. In addition to that, simulation tools and their specific requirements have been discussed in detail for preretrofit analysis of buildings prior to decisions being made regarding the retrofit plan. It is believed that the positive winds have blown in catalyzing long-term retrofitting in buildings. Penetration of latest certified efficient technologies helps in assessing energy use both at the micro- and macrolevels.

Traditional legal relations between tenants, owners, and their lenders for cost–benefit incentive-based commitments will help to attain energy efficiency. Along with government subsidies, this will help push energy-efficient retrofitting to a higher level.

Furthermore, various studies need to be conducted to investigate the energy-saving profile of building energy retrofitting for detailed benefit attainment, influence on occupant behavior, broader vision for the comfort requirements for optimized models, the development of policy mechanisms for technology penetration and subsidies, etc. In addition, detailed optimization tools need to be developed so that building owners can easily recognize optimal cost-effective benefits. Appropriate strategies for adoption of renewable energy resources in retrofitted buildings need to be studied to attain more energy efficiency within existing structures. Investment uncertainty and risk factors need to be studied for retrofitting analysis. Thus, there are many potential open research areas in the field of building energy efficiency and sustainability.

Acknowledgment

The authors are grateful to Mehran University of Engineering and Technology and the Department of Electrical Engineering for the motivation to conduct this research.