Life Cycle Zero Energy Building (LC-ZEB)

Life Cycle Zero Energy Building (LC-ZEB): Comparison

Please note this is a comparison between Version 1 by Rui Castro and Version 2 by Camila Xu.

A life cycle zero energy building (LC-ZEB) is defined here as a building whose primary energy use in operation plus the energy embedded in materials and systems over the life of the building is equal or less than the energy produced by renewable energy systems within the building.

energy efficiency
energy retrofits
building life cycle

1. Introduction

Buildings currently consume 40% of the total primary energy in the United States (U.S.) and in the European Union (E.U.) [1] and are responsible for 55% of the greenhouse gas (GHG) emissions [2]. At least 30% of the built environment in the E.U. consists of historic buildings [3]. Therefore, there has been an increased interest in the definition of methodologies to improve the energy efficiency in existing buildings, especially the historic ones [3]. In fact, the Paris Agreement goals are to reduce global temperature rise below 2° Celsius above industrial levels this century and to reduce also CO₂ emissions by 80% in 2050 compared to 1990 [2]. By 2030, many countries, including Portugal, will have to reach at least 40% of the CO₂ emissions targeted by 2050 and improve energy efficiency by 20% compared to 1990 levels [4]. According to the Clean Energy for all Europeans package of proposals [5], around 75% of the buildings are energy inefficient, and the investment in this area is very short. The European Commission pointed out the several difficulties that are hindering the improvement of buildings’ energy efficiency: lack of skilled workers and capital as well as insufficient information about the process and possible benefits. Public policies and support programs such as The Amendment of the Energy Performance of Buildings Directive [5] have the goal of accelerating building renovation rates, focused on reducing GHG emissions not only by providing information to stakeholders but also incentive-based regulations. The retrofit of existing buildings is an increasing activity and a unique opportunity to refurbish adequately current building stock, because they will not be renovated again in the following decades.

There are various definitions of ‘zero energy’ building, or ZEB. This is a design concept that takes into account the energy used in the building, balanced with the production of energy, which combines green and renewable energy resources [1]. Other authors add a life cycle perspective to the definition of ZEB, taking also into account the embodied energy of the building and the energy related to construction works, proposing a definition of life cycle zero energy building (LC-ZEB). “A LC-ZEB is defined here as a building whose primary energy use in operation plus the energy embedded in materials and systems over the life of the building is equal or less than the energy produced by renewable energy systems within the building.” [6]. Under this perspective, the longer the life cycle of the building, the less carbon emissions will be released with efficient retrofits. In fact, it is estimated that an operational building in a 100-year period has 20% of its embodied energy [7]. On the other hand, the negative impact of the construction process of a new green building can take between 10 and 80 years to overcome [7]. When retrofitting historic buildings, it is important to conceal environmental variables to their intrinsic characteristics, including cultural values, as historic buildings were built to last for centuries and function independently of mechanic systems and technologies.

Therefore, this article will focus on the following research questions: Which criteria should be considered, from the point of view of the architect, when improving energy efficiency in building retrofits? What is the relative weight of buildings’ architectonic characteristics? What is the role of optimisation processes in adopting energy-efficiency measures in building retrofits?

Although the present research intends to be a starting point for further research within this subject, its novelty goes to the analysis of to which extent architectonic constraints influence the application of energy-efficiency measures in the building and how optimisation processes can help to assess multi-criteria frameworks from early design stages. This paper also correlates the building’s renovation process, from public policies to construction works, highlighting directions to its optimisation with the best architect tools and processes to understand the need for a retrofitting guide manual for the architecture profession.

2. Building Retrofits and Architectural Design

International and local policies, from regulation to practice approach [8], are essential to boost energy retrofits and guarantee efficient solutions, from design to construction and operation stages. By taking in account a building’s life cycle and existing conditions and defining methodologies to assess possible solutions, using multi-criteria frameworks [9], architectural practice plays an important role in this process, since it integrates technical solutions within existing building retrofits, balancing heritage and energy.

2.1. Energy Policies and Building Renovation

In the past decade, the EU has developed a significant number of resources for the use of renewable energy in the energy system and a proactive climate policy. However, a deeper energy transformation is necessary for the Paris Agreement to be fulfilled. This could be accepted socially and implemented with the right policies and incentives to mitigate and control the effects of deeper decarbonisation. To this end, countries must implement measures that incorporate the carbon emission limit [10].

Construction materials are responsible for a large consumption of primary materials, as well as for large energy consumption. In view of this, for sustainable construction, it is necessary to take into account the characteristics and environmental impact of the materials to be used. Therefore, it will be important to analyse each material separately. The determination of the environmental impact of the materials can be evaluated based on several methodologies [11], such as Life Cycle Analysis (LCA), Carbon Footprint Analysis, Embodied Carbon, and Cradle-to-Cradle, among others. All these tools have the main objective of reducing the environmental impact of the production of construction materials, and consequently reducing the use of raw materials. Furthermore, the use of efficient energy is targeted, favouring the use of recycled and/or renewable materials of low environmental impact.

Carbon emissions from building materials have a short-term climate impact. The Incorporated Carbon Review reports that even by de-energizing energy networks, buildings can continue to be a major generator of emissions in the long term due to the carbon incorporated in the materials used [10]. Research conducted by Bionova Ltd. Helsinki, Finland (One-Click LCA) and sponsored by Saint-Gobain shows that the energy efficiency has increased as well as the use of renewables; however, the proportion share of incorporated carbon also increased [12].

To determine the environmental impact of a single material, a Life Cycle Assessment (LCA) is to be performed. The analysis of the life cycle of materials is usually carried out in buildings that seek sustainability certifications, and therefore that seek low-energy consumption. However, there are few studies on the applicability of this analysis to traditional buildings, which are mostly found in built environments [13].

According to Barbiero and Grillenzoni (2019) [8], there are three approaches to raise efficient renovation buildings rates: the law regulation approach, financial incentives approach, and practice approach. The E.U. Clean Energy for all Citizens package (COM(2016) 860) [5], which was delivered in 2016 after the Energy Performance of Buildings Directive (EPBD 2010/31/UE) [14], intended to accelerate building renovations not only by providing financial incentives to energy-efficient retrofits in buildings and the use of renewable energy resources but also by providing technical information regarding energy performance to stakeholders of industrial and public buildings. By using this framework, the E.U. develops long-term strategies, involves the financial and construction sectors, and improves environmental and living conditions while generating a skilled workforce and jobs. In fact, the incorporation of non-energy benefits for building energy efficiency is introduced as an important feature of the energy productivity by some researchers [15].

The Work Programme 2018–2020 for “Secure, clean and efficient energy” [16] intends to support the priorities in the Energy Union Strategy: renewable energy; smart energy systems; energy efficiency; and, as an additional priority, Carbon Capture Utilisation and Storage (CCUS) with several calls for projects [16]. From the actions included in each call, we can highlight the development of materials and technologies for energy efficiency in retrofits, optimisation processes in deep renovations, innovations in technology and in design, integration of various disciplines and stakeholders along the process, creation of replicable solutions, and smart buildings operation.

Regarding national projects on energy-efficient buildings, we can highlight the Swedish research project ‘Potential and Policies for Energy Efficiency in Swedish Historic Buildings’ [9], with a top–down approach, evaluating the implementation of national energy policies in historic buildings and conflicting situations between efficiency solutions and preserving buildings’ characteristics. Those challenging situations were also studied by the Royal Swedish Academy of Engineering Sciences. Both entities highlight methodological interdisciplinary approaches in the decision-making process to assess and choose the most appropriate construction and performance measures [9].

Italian case studies also demonstrate the need to invest and improve energy efficiency in historic buildings, which represent a large portion of Italian building stock and energy consumption. Some difficulties were also analysed in the Italian case [17]: the best construction measures for passive and active energy systems in buildings are many times conflicting with the conservation of buildings’ historic character and heritage protection regulations; energy-efficiency actions must be evaluated case by case, because each building is unique; regulations and external conditions vary from one area to another.

The best solution in terms of energy is not always the best solution in terms of heritage. Some authors ^[18][19][18,19] have suggested the development of guidelines to professionals, owners, and tenants to help them adopt the best technical and cost–benefit solutions to their buildings. Guidelines and support mechanisms need to be included in the incentives and energy policies, so that passive solutions packages can be associated to different discount rates.

Several methodologies were presented in the literature about retrofitting processes. A generic transversal method with five phases [20] was selected: (1) project setup and pre-retrofit survey; (2) diagnosis; (3) identification of retrofit options; (4) site implementation and commissioning; (5) validation and verification of results. In stage (3), a model-based approach or model-free approach can be used. In model-based approaches, options must match the maximum targeted goals [20]. Several goals were identified in 40 different systems for buildings retrofits [21]: “reducing energy consumption and CO₂ emissions, improving indoor living conditions/comfort, assessing refurbishment needs, estimating costs, other environmental impacts”.

2.2. Assessment Tools

The selection of a multi-criteria board to assess the decision-making process is essential to define the type of approach to energy retrofits for buildings. We attempted to categorise the articles analysed, regarding the criteria used in the definition of frameworks for retrofit processes. Four different categories were identified alongside their corresponding efficiency measures: (1) energy performance assessment; (2) pathological and typological; (3) cost-efficiency energy assessment throughout the life cycle of a building; (4) fleet-based life cycle assessment applied to building stock.

The most basic approach is energy performance-based, which addresses all the main factors affecting energy efficiency: the building envelope, active systems, and renewable energy resources. This approach usually uses algorithms and model-based simulations [22].

Piderit, Agurto, and Marín-Restrepo (2019) [3] suggest a pathological diagnosis combined with a different analysis of energy and heritage issues. The authors support that buildings’ refurbishment must occur to correct pathologies, which should be ranked by severity and used as a tool to select the most appropriate energy-efficiency measures. This is a multidisciplinary case-by-case method.

Some intervention plans may include building envelope insulation, airtightness, and moisture protection, shading, heat recovery ventilation, and lighting optimisation through passive architectural design and the incorporation of renewable energy sources. In addition, [23] approach retrofit strategies by type of renovation: whole house, fabric first, room-by-room, step-by-step, and measure-by-measure. Another bottom–up approach using typology criteria was applied to Italian building stock. Ref [24] identified 120 building types, which were classified into six construction ages, four building sizes, and five climatic zones, and they also defined energy efficiency measures, conducted cost–benefit analyses, and scaled up the results.

In order to accomplish the goals set out in the EPBD Directive, the third approach, which integrates also a building’s life cycle when determining the most cost-efficient package of solutions, is applied by [19] to a reference building representative of the Portuguese residential building stock. Ref [25] also incorporated the embodied energy of buildings in their analyses, from the construction phase to operation phase, to reduce GHG emissions, respectively, in Australian, Chinese, and Portuguese buildings. Ref [26] also added the building’s end-of-life stage to a framework to assess the best retrofit options in Portuguese historic buildings, concealing energy efficiency and heritage.

The last one is a variation of the previously described life cycle approach, as it presents a fleet-based life cycle assessment applied to building stock, as it identified a gap in the connection between direct emissions in the operation stage and indirect emissions in the production, construction, and waste management phases [2].

2.3. Deep Retrofits versus Non-Invasive Retrofits

A deep retrofit of existing building stock is the strategy indicated by some authors to achieve long-term energy efficiency [18].

Deep retrofits include not only improving a building’s envelope but also optimising their basic infrastructures, such as heating, ventilation, and air-conditioning (HVAC) systems or domestic hot water (DHW) heating sources. However, energy efficiency is not an isolated criterion. If taking into account architectural and heritage constraints and the embodied energy of the buildings, other scenarios must be considered. If the goal is to improve existing conditions, life cycle assessment gains importance not only in a cost-effectiveness solution but also in CO₂ emissions. In replacement scenarios, 52.4% energy savings are achieved compared to light retrofitted (21.5%), but according to Barbiero and Grillenzoni (2019) [8], 48.8% of light retrofits costs would be recovered in 30 years, whereas only 21.8% of costs would be recovered in deep renovations. Adaptive thermal comfort models (18–27 °C) are compatible with light refurbishment of traditional buildings in Portugal [26].

According to [24], depending on the size of the building and its location, isolating the building’s opaque envelope can be a more expensive measure for the total renovation budget than glazing. This happens not because of the cost of the material itself but because of the installation costs that must be added, such as scaffolding and labour, as well as the extent of the material use. However, the most satisfactory results, in terms of energy savings, have been associated with the refurbishment measures of the building envelope.

In the reviewed literature, some researchers recommend non-invasive retrofits rather than whole building deep renovations [18]. The implementation of packages of energy-efficiency measures, without interfering with the building’s intrinsic characteristics, as a result of a multi-criteria approaches, should be complemented with changes in behaviour and the building’s operation, namely temperature setpoints and lighting.

In Jordan, optimising the building envelope by the external walls and roof can save 72% of the energy spent on the heating and cooling loads [27]. In 363 residential buildings in the region of Calabria, divided into two different groups (apartments and single houses), the retrofit strategy was to improve exterior walls and replace windows for more efficient ones, with an overall saving of 770,392 tCO₂/year [28]. In Bernardas’ Convent retrofit, in Lisbon, Martins and Carlos (2014) [29] adopted an integrated conservation approach by assessing the impact of changing the form, function, and materials in the interior and preserving the authenticity of the exterior of the building. The attic was insulated, and exterior windows were replaced by others with identical design. In a brick building from 1902 at Vassar College in Poughkeepsie, New York, the authors decided to refurbish historic wood windows and install storm protection in order to respect the character of the building and adopt the best economic solution [18]. In the retrofit of the historic Zrenjanin brewery in Serbia, the external envelope was upgraded by insulating the inner face of external walls, eliminating thermal bridges, and introducing double glazing and external window protection. This intervention was limited to the external envelope in order to preserve the building’s authenticity [7]. Another study was developed in a typical 1920s Swedish building [9]: a 1.5 storey, single-family house with wooden structure. Three degrees of intervention can be highlighted: reducing CO₂ emissions by 20% (by implementing a package of measures: heat pump, weather stripping, attic insulation, and adding a pane of glass to some of the windows); reducing 50% of CO₂ emissions (with the installation of a wood-pellet boiler, weather stripping, attic insulation, and external wall insulation) and saving 74% of energy, when taking in account life-cycle techno-economic optimisation (with the installation of a wood-pellet boiler, attic floor, wall, and crawl space insulation, and window replacement). The author concluded that to reduce 50% or more CO₂ emissions, the appearance of the building would be affected. On the other hand, with the package of measures to save 74% of energy, the attic and crawl space would need regular monitoring because of risk of mould growth. In a case study office building located in Carbonia, Sardinia, a PV system was installed with some retrofit actions to reduce the payback time. The authors identified the most appropriate retrofit solutions, which were in line with governmental financing incentives. Although the retrofitting of the building envelope can be a good energy-efficiency solution, it has a very large payback time. Cost–benefit analyses determine that this is ineffective when considered isolated [17].

Table 1 provides an overview of the above-mentioned case studies, highlighting the criteria subjacent to the corresponding energy retrofit.

Table 1.

Building energy retrofits and retrofits: multi-criteria decision.

Case Study	Country	Goal	Passive System	Active System	Results	Criteria
Amman building stock [27]	Jordan	improve energy efficiency	building envelope optimised by external walls and roof		reduced 72% energy saving on the heating and cooling loads	energy efficiency; architectonic authenticity
363 residential buildings in the region of Calabria [28]	Italy	improve energy efficiency	exterior walls improved; window replacement		saved 770,392 tCO	₂	/year	energy efficiency; architectonic authenticity
Bernardas’ Convent retrofit, Lisbon [29]	Portugal	improve energy efficiency	attic insulation; window replacement by others with identical design			energy efficiency; architectonic authenticity; change of function
1902 building in Vassar College [18]	USA	improve energy efficiency	refurbish historic wood windows refurbished; storm protection installed			energy efficiency; architectonic authenticity; best economic solution
Zrenjanin brewery [7]	Serbia	improve energy efficiency	inner face of external walls insulation; thermal bridges elimination; new double glazing and external window protection			energy efficiency; architectonic authenticity
Typical 1920s Swedish building [9]	Sweden	reduce CO	₂	emissions by 20%	package of measures: weather stripping; attic insulation; adding a pane of glass to some of the windows	installation of a heat pump	reduced 20% of CO	₂	emissions	energy efficiency; architectonic authenticity; reducing CO	₂	emissions
		reduce 50% of CO	₂	emissions	package of measures: weather stripping; attic insulation; external wall insulation	installation of a wood-pellet boiler	reduced 50% of CO	₂	emissions; appearance of the building affected
		save 74% of energy, when taking in account life-cycle techno-economic optimisation	attic floor, wall, and crawl space insulation; window replacement	installation of a wood-pellet boiler	saved 74% of energy; risk of mould growth in the attic and crawl space (regular monitoring needed)
Office building located in Carbonia, Sardinia [17]	Italy	improve energy efficiency	package of retrofit actions to reduce the payback time	installation of a PV system		energy efficiency; architectonic authenticity; best economic solution regarding governmental financing incentives