Concept of net zero energy buildings (NZEB)

1. Introduction

The term net zero refers to the balance between the amount of produced greenhouse gas and the amount removed from the atmosphere. The term Net Zero Energy Building (NZEB) are characterized as zero net energy consumption buildings i.e. the total sum of energy used annually by the buildings is approximately equal to the total sum of the renewable energy produced on site. Recently, the idea of NZEBs, has changed from the study to practice. There are only a limited number of highly productive builders at present. The construction of NZEBs is becoming more and more feasible owing to advancements in building technology, renewable energy systems and academic research.

It is hard to locate a building that can be considered the first NZEB. One of the explanations may be that NZEBs might not be a new idea for a building, but just a modern term for houses. However few publications appeared in the late 70s and early 80s, in which phrases ‘A zero energy home or an autonomous energy house’ or an “energy-independent house” has been used. This was the moment when the oil crisis had its consequences, the problem of fossil fuel sources and energy usage has begun to be discussed.

Between 2014 and 2035, the global market for goods and services related to NZEB construction and renovation is expected to rise at a compound annual growth rate of 44.5%, surpassing $1.4 trillion last year. This is how the concept of NZEB is getting popular. Caulfield (2017) discussed about the exponential popularity growth of the NZEB for next two decades. The given Figure (1) shows the popularity and growth of NZEB revenue by products and services for next two decades.

Iqbal (2004) defined NZEB as the term used for the building that incorporates available renewable energy technologies commercially with energy efficiency construction methods where no fossil fuels are consumed. Kilkis (2007) defined NZEB as a building, which has a total annual amount of zero energy transfer through the building during all electric and other transfers that occur during a particular time span. Laustsen (2008) gave the general definition for ZEB: zero-energy buildings do not use fossil fuels and rely entirely on solar and other renewable energy sources to meet their energy needs. Noguchi et al. (2008)defined NZEB as the house that consume as much as energy it produces over a certain period of time.

Similarly, Berardi (2018) discussed their methodologies for design and evaluation of ZEB and NZEB. Their work was based on a literature review guidelines of the national action plans. While a broad global overview of the concepts of ZEB and NZEB is targeted and addressed topics such as the methodologies of energy balance, the limits of NZEB and NZEB type and energy. In the literature various NZEBs have been identified and evaluated over the decades, However the NZEBs was either defined differently or without an exact description in almost every article has been used. Quite frequently, the forms in which the zero energy target has been reached that affected the meaning of NZEBs.

The lack of common understanding of NZEBs became noticeable, as this concept of construction is thought to be an efficient ways to reduce the use of electricity and greenhouse gas emissions from the building energy sector. The analysis has shown that NZEBs are a complicated term that has been defined with the broad variety of words and terms.

1.1. Aim and methodology

The aim of the paper is to investigate the literature on the existing NZEB to make them self-sustaining and net zero in order to improve energy efficiency of the buildings. Because of the goal of reducing the use of non-renewable energy sources, the paper works on three key objectives with theoretical approaches which are listed below:

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Supply of energy from different sources of renewable energy.
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Increase the energy efficiency of building.
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Reduce dependency on fossil fuels.

In general terms, two design strategies are involved in NZEBs: reducing the need for energy in buildings by implementing EEMs (energy-efficient measures) and incorporating RETs (renewable energy (RE) and other technologies) to meet energy demands.

The initial stage is to gather research papers, abstracts, and unpublished material from Google Scholar, Elsevier, Science-Direct, IEEE, Springer, Taylor Francis, Wiley, Inderscience, and Emerald, among other sources. As part of state-of-the-art analysis, following a thorough examination of the concepts and iterative study process, this paper came up with some relevant keywords. Keywords like “net zero energy building,” “energy analysis of NZEB,” “energy integration to NZEB,” and “performance of NZEB under various climatic conditions” were used to find relevant documents in the database. A total of 2982 results were found during the search. There were 1563 academic journals, 165 conference materials, 296 magazines, 647 trade publications, and 59 books produced between 2002 and 2022. A second stage was developed to discover the most important material from widely circulated articles. The number of materials chosen had been reduced to 219 at the end of the second iteration phase. Only peer-reviewed publications and research papers were taken into consideration. Unpublished thesis and abstracts were not considered. Only 170 of the 219 items were deemed relevant. The year of publishing was used to minimize the number. Because they had the most up-to-date information, the most current papers were chosen for the investigation. We looked at publications over the previous 20 years, but we concentrated mostly on relevant papers published in the recent 10 years, with the last five years receiving the greatest attention.

1.2Definition of NZEBs

For zero energy solar homes, Charron (2008) also offers a definition: “Homes using solar thermal and solar PV technologies to generate as much energy as their annual load are referred to as net-Zero Energy Solar Homes (ZESH)." As per ASHRAE (Kilkis, 2007): “ZEB is a building, uses no more energy than is provided by the building on-site renewable energy sources on annual basis”. Although studies describe ZEB projects in which biomass, wind energy are seen as potential RESs, these sources of renewable energy are not as common as solar energy.

Before creating a NZEB specification, the following are the most important issues to consider: (1) the balance metric, (2) the balancing time, (3) the type of energy usage used in the balance, (4) the type of energy balance, (5) the agreed renewable energy supply options, and (6) the link to the energy infrastructure and (7) the requirements for the energy efficiency and the indoor climate.

The literature on zero energy is becoming popular with the NZEBs definition. Most of the papers focus on the demonstration of various zero energy buildings; however there are a range of documents which have been substantially recorded. It helped to explore the interpretation and definition of the NZEBs idea. The general ideas for NZEB is shown in Figure (2); the total energy requirement of the building can be met through the on-site energy generated by the renewable energy sources and if that is not sufficient then the energy from the local electrical grid can be utilized. Whenever the energy generation by the onsite renewable energy sources are more than the requirement of the building, then the excess amount of energy can be fed to the local grid.

Torcellini et al. (2006) furnished the zero energy building design and indicated that the four well-documented concepts were explored: net zero energy locations, net zero energy source energy, net zero energy cost, and net zero emissions. Noguchi et al. (2008) work was aimed at bringing together the public and private sectors to develop homes that combine resources and energy-saving systems to reduce their environmental effects. In order to minimize the negative effect on the climate, the Eco Terra housing prototype described.

As part of the Energy Efficiency in Building Project, Brahme, et al. (2009)Brahme et al. (2009) discussed the modelling of single-family residence as a case-in point to demonstrate the most common strategies considered during NZEB design process, the ease of using various instruments to model these strategies, and issues of quality control of input/output. Hernandez and Kenny (2010)explained fields such as renewable energy evaluation and the idea of ‘net energy’ as used in ecological economics, which takes into account the energy used during the manufacturing phase of a commodity, is commonly applicable. In order to describe a life cycle zero energy construction, it provided a model and specification of a simplified approach to account for embodied energy along with usage of energy in action and reclaims the original principle of ‘net energy.’ The LC-ZEB (Low Cost Zero Energy Building) is defined as a structure whose primary energy consumption in service is equal to or less than the energy produced by renewable energy systems plus the energy embedded in materials and systems over the building's lifetime.

The study of Marszal et al. (2011) focused on the different approaches to potential methodologies for Zero Energy Building (ZEB) calculation. The paper addressed a coherent ZEB definition and a rigorous methodology to measure electricity. Zhivov et al. (2010) had shown the optimization process of net zero energy and its illustration for a cluster of buildings in Fort Bliss. The optimized cluster would reduce the amount of renewable energy needed to make the building cluster net zero. Kaneda et al. (2010) discussed about the use of plug in loads as building are being more energy efficient along with the reduction in the energy consumption. Novotny (2011) discussed the connection between water conservation, reclamation; reuse and energy use to the objective of achieving a net zero carbon footprint in sustainable cities in the future. Nielsen, et al. (2011) calculated the size of NZEBs to be constructed inside DH areas and studied how the heat mismatch of NZEBs have an effect on various forms of danish DH systems. Voss et al. (2010) studied about the zero-energy home and focused on the context and different effects affecting the energy balance method.

Hamdy et al. (2012) tested the performance of the optimization algorithms to find the cost optimal solutions for nearly zero energy buildings, which has high energy performance whereas Kneifel (2012) aimed to construct a full simulation of building energy that replicate the design of the NZERTF (Net Zero Energy Residential Test Facility) to estimate its energy efficiency, both in aggregate terms and at the level of individual occupants and equipment.

Marique et al. (2013) investigated “Definition of Zero Energy Neighborhood”. Authors proposed a method of calculation considering three key topics: the consumption of energy in buildings, the effect of the place on energy consumption for everyday mobility and the use of energy in buildings from renewable energy sources. Sharma (2013) reviewed the developments on zero energy building envelope with respective to the benefit in the building designers and constructors. The paper discussed the state of the art on different components of the construction envelope such as materials for insulation, potential insulation, materials, walls, roofs, doors and windows glazing off the energy efficiency possibilities. Integration of photovoltaic with the house envelope for on-site power was also addressed.

Attia et al. (2013) investigated the use of output modelling techniques for construction. Attia et al. (2013b) investigated the use of simulation results of construction as a means of NZEBs’ design decisions. For Solar Deng et al., 2012, Kazanci et al. (2013) addressed the heating, cooling and ventilation concerns of the house. Various innovative approaches were examined, namely the use of soil, photovoltaic/thermal panels (PV/T panels) and phase change material(PCM). The U.S. Army enacted a policy in January 2014 directing all facilities to introduce net-zero energy policies by reducing energy consumption and rising renewable energy output. Gibson (2014) compared and ended with persistence and successful anchoring of change in the culture of the Army toward net zero energy strategies. Perlova et al. (2014) discussed the reduction in CO2 emission due to transition towards low energy consumption buildings construction. Saberbari and Saboori (2014) simulated a grid-connected NZEB in order to obtain the optimized configuration of the construction in terms of availability and expenses of system.

Zhivov et al. (2010) demonstrated the Energy Master Planning (EMP) concept and automated Net Zero Planner (NZP) tool. Jadhav (2015) integrated energy-efficient technology into the design, development and operation of both new and existing buildings by reducing its environmental impact.

Kotireddy et al. (2015) carried out optimization results of different net zero energy building plans, with different net zero energy designs under uncertainties related to potential energy demand and onsite energy balance. Banerjee (2015) discussed the idea of zero energy construction for the low-energy building designs. Hu (2016) had practiced net zero energy building art. The paper explained the significance of promoting net-positive institution building and addressed the differences between net-zero and net-positive buildings, buildings that produce more energy than they consume and their similarities. International Journal of Scientific Research in Science, Engineering and technology. (n.d.).concentrated on India's net zero energy building campaign. As per their study the main objective of green construction is to allow effective use of resources and reduce the negative effects on the environment.

Vora et al., 2017a, Vora et al., 2017b focused on the construction sectors that can play a crucial part in dominant energy use. To mitigate the environmental impression by buildings, NZEBs and solar buildings are emerging as a promising explanation. He proposed buildings that minimize energy consumption and optimally use solar energy both passively and actively. Study by Rezaei and Kamelnia (2017) showed that there are five general techniques for achieving zero energy construction. Through case study, they tried to discover zero energy building design solutions. As per the study six active cases were chosen and their design solutions were grouped into five categories, including the following: conservation of electricity; passive solar solutions; active solar solutions; efficient energy systems; and other renewables. Their findings indicated that ‘passive solar solutions' are more evolved and provide flexible solutions. As NZEB should have balance between energy produces and consumed in a building and usage of renewable energy, which is shown in Figure (3).

AbuGrain and Alibaba (2017) looked at how an existing multi-story building in the Mediterranean could be made more energy efficient. In Denmark, most buildings are connected to electricity grids and about half are to district heating (DH) Systems. Connecting buildings to larger networks of energy allows them to send or receive energy from these systems. NZEB typically have very low energy costs. . Khan et al. (2017) aimed to build a sports gymnasium with almost zero electricity in Calolziocorte building, Italy. In the first instance, the base case was constructed with conventional buildings materials and the overall demand for energy is estimated. Greco et al. (2017) described the economic variables that can improve investment in cantered with public and local authorities, private businesses, energy-neutral refurbishments, Institutes and end-users of science. Energy efficiency research has recently been proposed to minimize buildings' energy use by planning the energy consumption structural parameters.

Adoption and implementation of NZEBs on a wide scale will potentially greatly contribute to the greening of the construction industry. However, is still in the early stages. Jain et al. (2017) tried to determine the governance background for the introduction and adoption of NZEBs by niche development. Harkouss (2018)outlined the methodology of cost-effectiveness ability to maximize net-zero energy building design and were evaluated by an energy simulation and optimization program coupled with a ranking decision-making technique. Singh (2018) emphasized the function and significance of the building envelope and related construction facilities in achieving the NZEB goal and addressed the different phenomena and certain materials used in the building envelope.

Gupta et al. (2019) assessed the new buildings and included an over view of an existing building to make it a perfect NZEB. Al- Yoklic et al. (2010) conducted a survey on more than 60 residential buildings in Al-Amarah region, Iraq to investigate the existence of the most common building materials used in building envelopes. For each combination of elements, the findings were tabulated and compared. The results showed that the best alternative for exterior windows is reflective glass. Alsilani (2018) research studied three main objectives:

(1)
To analyse the efficiency of house energy
(2)
To evaluate the effect on energy consumption of the actions of the occupants
(3)
To evaluate the energy performance of indirect evaporative cooling system use compared to conventional cooling systems.

Whereas Galleghar (2019) showed one way of home energy performance measurement, that is through a Home Energy rating system (HERS) rating. Alhalabi (2020) focused on the redesigning of the buildings with the means of the converting them into zero buildings through active and passive measures. Bordbari et al. (2019) proposed a multi-objective probabilistic prognosis method of optimization on the basis of statistical techniques, i.e. the method of the empirical rule and two-point method of calculation for the study of energy efficiency in buildings. Gallardo and Berardi (2019) assessed the energy and thermal efficiency of a radiant cooling panel system with integration of phase change materials (PCMs) for use in retrofit projects for construction. Cucuzzella and Goubran (2019) examined infrastructure projects that present a deliberate merging through sustainable design between urban change, community growth, culture and technology. Piderit et al. (2019) identified a structure for the new norm to reach NZEB and this study recognized the need for advanced public policies to achieve the implementation of buildings with an energy neutral concept to provide a standard structure for the NZEB.

Fabrizi (2020) found out two key terms: optimization and holistic plan to describe the ZEBs. Vidal et al. (2020) discussed the possible causes and health-related effects of excess heat in NZEB housing in the Northern Climate. Khakia et al. (2020) aimed to evaluate the energy efficiency of two-story residential buildings located mountainous village and to determine the influence of many parameters, namely construction orientation, window-to-wall ratio (WWR), type of glazing, devices for shading, and insulation, depending on the energy quality.

The power in future buildings is created in the construction itself from harvested RES. In this sort of Buildings; the NZEB, known as the building's annual net energy is zero, meaning the building generates precise energy or even more energy as it absorbs during a year. Assembling the Net-Zero Energy Building's Energy System calls for significant fundamental investment and rigorous analysis, arrangement of atmospheric weather conditions and forecasting.

2. Performance analysis

This paper also presents the performance analysis of NZEB. Mertz et al. (2007)defined the method of conducting and comparing lifecycle costs for normal, CO2-neutral and net zero energy buildings and identified the lowest-cost energy net-zero house, the lowest-priced CO2-neutral house, and the whole house at the least-cost. Wittkopf et al., 735. (2008) introduced the concept of Integrated Photovoltaic Construction at the first zero-energy building in Singapore. The work presented introduced the design of the BIPV growth, requirements for final designs, and tender evaluations. Noguchi et al. (2008) put public and private sectors working together to build homes that incorporate wealth and resources energy saving systems with a view to reduce their production effect on the climate.

Brahme et al. (2009) described the single-family residence modelling to demonstrate the most common strategies considered during the design process of NZEB. Sartori et al. (2010) provided a harmonized structure for defining characteristics of Net ZEBs by evaluating the parameters and selecting the relevant options thorough elaboration of sound Net ZEB concepts. Omar et al. (2010) used the results of the study to define and fix the issue within the review of building design. The objective was to shift the building of the faculty from an energy user to an energy producer in order to achieve NZEB for education. Musall et al. (2010) summarized the status of two phases of research within the context of IEA Task 40/Annex 52 towards solar buildings with net zero capacity’. Lund et al. (2011) used an overall approach to the energy system to examine the mismatch dilemma of net zero energy and zero emission buildings and the results suggest that such compensation factors are slightly below one for photovoltaic (PV) buildings and a little above one for wind turbine buildings. Whereas Kolokotsa (2011) did analysis of the technical advances in each of the critical ingredients that can enable the potential integration of effective NZEB, i.e. precise simulation models, sensors and actuators, and control of the construction. Khandelwal et al. (2011) explored the ability to minimize a central air-conditioned building's annual energy consumption by advanced evaporative cooling systems. Hemsath et al. (2011) described the first phase of a residential study program to reduce the effect of new development on the atmosphere by using a zero net energy test house as a basis through research and education. Salom et al. (2011) presented Load Matching and Grid Interaction (LMGI) indicators and that can be used to calculate the versatility of the architecture of a building to adapt to variable generation conditions, loads and grid conditions and Voss et al. (2011) reported on the background and the various effects affecting the energy balance approach.

Musall (2012) talked about the building-integrated co-generation and concluded that it is suitable especially for (future) biomass systems. Scognamiglio, et al. (2012) envisioned potential formal outcomes, possibilities and problems for the usage of PV in ZEBs and new study problems for potential architectural partnerships between PV and ZEBs. Todorovic (2012) reviewed the critical position of Building Performance Simulation (BPS)-dynamic analysis of the inextricable link between building energy demand for HVAC and other building technical systems to achieve zero energy status for sustainable energy supply and renewable energy sources (RES) availability. Gardzelewski et al. (2012) focused on residential design and construction in which solar design and construction was used. Strategies for Passive house are used to achieve Net-Zero use-Energy focus on illustrating optimal architectural and mechanical system design strategies for the construction of three places along the Rocky Mountain Front Range.

Deng et al. (2012) introduced a case study for a NZEB in Shanghai where energy-efficient passive architecture, solar collector system, Heating, Ventilation and Air-Conditioning (HVAC) system, indoor terminal units and the building's renewable energy power system was integrated briefly, particularly the concept of the energy system. Aelenei and Gonçalves (2013) unveiled a sustainable system for the exchange of insights into the NZEB approach used in an office building and had shown that the combination of traditional and creative energy efficiency interventions with renewable systems is capable of achieving zero-energy performance without considerable effort. Bourrelle et al. (2013) proposed a new NZEB energy balance strategy that takes into account the actual sum of energy needed by NZEBs and emphasized the increase in demand for grid electricity, as well as the importance of ensuring that no net non-renewable energy is needed for a house. Kurnitski (2013) made several calls to adopt lower performing for heating and cooling energy needs. Kneifel (2014) compared the NZERTF's life-cycle cost performance design to a comparable building design consistent with the Maryland code using the outcomes of Energy Plus (E+) energy simulations for the entire house, electricity rate for local utilities Schedules, and a report from the contractor estimating the relevant construction costs.

Dama et al. (2014) proposed a case study of Milan, where the result indicated that natural night ventilation and ventilation optimized solar control with daylight integration might have a big effect on reducing cooling, lighting and lots of systems without raising demand for heating. Marique et al. (2013)explored the possibility of applying the idea of ‘zero-energy construction’ to the neighborhood scale by taking into account two key points: (1) the effect of the urban type on energy needs and the renewable energy development on site and (2) the impact of the position on energy use in transport. BAU University architecture building was selected as a case study to test the energy efficiency in comparable buildings in comparison with methods for zero energy architecture. Evola and Margani (2014) proposed a versatile technological solution to improve the energy efficiency of Italian residential real estate built between 1950 and 1990, i.e. before strict energy consumption reduction regulations were implemented. Stefanović et al. (2014) dealt with NZEB type defined for its cost.

DeKay (2014) used the concept of a Bundle-Up! Game to build climate design learning strategies and their complicated approaches whereas Ubinasa et al. (2014) overviewed the passive strategies used in Net plus Energy Houses and reflected the effects of passive design strategies on comfort and convenience of houses. Kanters, et al. (2014) investigated the consequences of major design decisions on the renewable energy efficiency of solar buildings with net zero energy. Mellawi, et al. (2015) presented net zero energy single family two-storey housing prototype, which is assessed using energy efficiency modelling tools to determine the environmental impacts during the early design phase to help develop a design that is capable of meeting our climate-related economic, environmental and social challenges.

Alajmi et al. (2016) showed the possibility of transforming a public building from an inefficient consumer of energy into NZEB and was accomplished by cost - effective energy efficiency initiatives (EEMs) and solar energy systems integration. Wongwuttanasatian et al. (2015) demonstrated the NZEB concept in Thailand as a self-energy provider and was updated in part to minimize its energy consumption by using a number of energy-efficient technologies. Whereas Vergini and Groumpos (2015) defined a new approach to NZEB modelling by Fuzzy Cognitive Maps (FCM). The European Economic Community (EEC) is a pioneer in setting goals for all EU member states to install Net-Zero Energy Buildings (NZEB), with the first relevant date set for 2020. Attia (2015)defined the performance target for Nearly Zero Energy Buildings (nZEB) in EU members. Energy performance target specified in building codes for non-residential buildings of some EU member countries are shown in Table 1:

Table 1. Performance Target for nZEB in some EU members (Attia (2015); D'Agostino et al. (2017); Hamburg et al. (2020)).

Country	Non Residential Buildings (kWh/m2/Year)		Notes
Country	New	Existing	Notes
Sweden	30–105	ND	Depend on type of building and Climate
Spain	45–60	120	Proposed indicators defines the net PE use and maximum total PE use
Romania	50–102	120–140	Depend on type of building and climate
France	70–110	ND	Depend on climate
Denmark	25	25	Include: Heating, Cooling, DHW and Lighting
Bulgaria	30–50	40–60	–
Austria	170	220
Cyprus	125	125
Hungary	60–115	ND	Depend on type of building
Latvia	95	95
Malta	60	ND
Netherlands	0	ND
Poland	45–70–190	ND	Depend on type of building
Slovenia	70	100
Slovakia	60–96 (offices) 34 (schools)	ND	Depend on type of building

Irulegi et al. (2017) suggested some important measures in the retrofitting process of the building envelope including upgradation of HVAC, Electrical Lighting, and renewable energy. Their analysis showed the proposed retrofitting strategies reduces the energy consumption as indicated in Table (2).

Table 2. Retrofit strategies with energy reduction.

Retrofit Strategies of Design	Reduction in Energy (in %)
1. Upgrading HVAC	23
2. Electrical Lighting	5
3. Renewable Energy	44

Latief et al. (2016) identified the NZEB architecture variables that fit the state of the tropical climate, where design variable analysis are orientation of structure, and passive design. Greco et al. (2016) identified the factors affecting zero energy viability renovation of existing commercial buildings. The majority of building consumption is connected to the use of active systems to preserve the comfort of the interior of NZEB.

Harkouss et al. (2016) adopted the thermal comfort criterion as main optimization constraint and showed that the exclusion of cost parameters can lead to unfeasible solutions. D'Agostino et al. (2016) presented an evaluation of the present situation with respect to NZEB implementation in the Member States in Europe whereas Chandanachulaka and Khan-ngern (2016) introduced the zero energy design for consumption for a small device on a stand-alone photovoltaic (PV) system dwelling house. Ferrari and Beccali (2017) evaluated the energy retrofit of a building representative in public tertiary stock, in order to boost energy efficiency towards the requirements of almost NZEB. The results showed that by implementing market-available and well-proven retrofit technical solutions, it is possible to reduce primary energy demand and related emissions by up to 40% from current values.

An analysis was carried out on photovoltaic solar systems to determine the best system configuration from a financial and environmental perspective.

The review on performance analysis is tabulated below in Table (3):

Table 3. Performance analysis with representative references.

Representative references	Research work/Investigation
Shuai Deng et al. (2012)	Integration of energy system
Dama et al. (2014)	Big effect on reducing cooling due to ventilation.
Evola and Margani (2014)	Versatile technological solution to improve the energy efficiency
Vergini and Groumpos (2015)	NZEB modelling by FCM
Harkouss et al. (2016)	Thermal comfort criterion as main optimization constraint
Ferrari and Beccali (2017)	Energy retrofit evaluation of a building
Attia (2018)	Comfort requirements, technology, climate sensitivity, quality of construction, and evidence-based design
Ballarini et al (2019)	For the thermal and visual performance assessments, dynamic simulation was used to calculate energy and comfort using Energy Plus and DIVA, respectively. According to the findings, energy retrofit operations on the building exterior would result in considerable improvements in thermal performance, both in terms of energy savings (37% of yearly primary energy for heating) and thermal comfort.
Carpino et al (2020)	They looked at six months of monitoring data from a Danish nZEB. The impact of three different occupancy profiles on final energy use is investigated using a simulation model: the ‘Compliance profile,’ which is based on regulations, the ‘Standard profile,’ which is based on average data from surveys, and the ‘Actual profile,’ which is based on measured data from the actual building case. The three distinct occupancy profiles, as well as the results obtained by employing the three occupancy models in performance prediction, show significant disparities.
Marszal et al. (2010)	Energy measurement methodologies
Magrini et al. (2020)	A case study (single-family residential nZEB) is shown to demonstrate how careful and integrated design of the building exterior and systems not only allows for nearly entire renewable energy coverage, but also generates an energy surplus that can be shared with metropolitan grids.
Moran et al. (2020)	This research evaluates the best retrofit packages for gas-heated semi-detached and end-terraced houses in Ireland in terms of building material thermal efficiency and energy demand.
Rey-Hernández et al. (2020)	The performance of a hybrid ventilation system called LUCIA, which combines Earth-to-Air Heat eXchangers (EAHX), free cooling, and evaporative cooling Air Handling Unit Heat eXchanger (AHU-HX), all controlled by a Building Management System (BMS) in a net Zero Energy Building (nZEB), is examined in this research paper. LUCIA nZEB, located in Valladolid, Spain, is the world's first safe-building against Covid-19, approved by the international organisation WOSHIE.
Bienvenido-Huertas et al. (2021)	The findings looked at heating and cooling needs, cluster analyses, and population effect, indicating that improving thermal attributes might provide buildings with higher energy performance for a larger number of people.

Attia (2018) proposed a book that focused on lessons learned from the design, planning, operation and integration of the most important subjects of the NZEB, such as multidisciplinarity, carbon footprint, comfort requirements, technology, climate sensitivity, quality of construction, and evidence-based design. Abdullah, et a. (2017) proposed an integration of photovoltaic as sensitive shading devices for an energy efficient office building. Gardea et al. (2014)overviewed the NZEBs undertaken with a passive design approach. Attia et al. (2017) offered suggestions for how to transform the gaps found into future growth opportunities of High-performance climate sensitive houses. Vora et al. (2017) analysed on the detection of factors affecting the construction of net zero energy buildings (NZEB) in the Indian sector industry. Irulegi et al. (2017)proposed a framework for analysing student comfort in real-world situations to identify and test strategies for achieving NZEB in university buildings and discussed the critical issue of addressing with energy and comfort in a specific building.

Karlessi et al. (2017) illustrated the concepts of the integrated design process and tied smart construction technology to the process. In order to accelerate the three key aspects of smart buildings' interdisciplinary nature, it introduced phase towards the design and implementation of zero energy:

1.
Smart buildings' design phase concepts and its integration
2.
Smart buildings with smart technologies
3.
NZEB and its integration in smart grids

Oh et al. (2017) carried out state-of-the-art analysis of the recent research on nZEB implementation strategies as a consequence, it is possible to classify previous studies relating to NZEB into two groups based on two perspectives: i) passive strategies; (ii) active strategies. Review of these studies had shown that the use of passive building strategies is efficient in terms of energy savings, but not adequate in terms of the implementation of NZEB. The active strategies focusing on the RE and its back-up system. Skye and Wu (2018) compared the energy efficiency and initial costs of PV and HVAC installations for residential NZEB in various climate zones. Latief et al. (2019) used experiments and a case study to verify the design variables for an ideal Near Zero Energy House (nZEH) design, including building orientation, PV panels, fenestration, and passive design. Ramos et al. (2019) studied the combination of traditional recovery methods and the cooling capacity of the building's thermal mass for night ventilation and quantified using CFD simulations. Marszal et al. (2010)presented a summary of the energy measurement methodologies of NZEBs suggested by organizations representing eight separate countries: Germany, Austria, Canada, Denmark, Italy, Norway, the USA and Switzerland. A few studies had been conducted prior to this date on the thermal satisfaction of NZEB; one of the aims of the study was to draw a distinction between the thermal parameters for the thermal comfort assessment of a net-zero energy building occupant.