nZEB Performance Research Articles

A novel life cycle assessment methodology for transitioning from nZEB to ZEB. Case-study

This study analyzes the CO2 equivalent emissions of a LEED-certified nearly Zero Energy Building (nZEB) using a simplified Life Cycle Assessment (LCA) methodology, aligned with EN 15978. Focusing on the building's energy performance across its life cycle, the study demonstrates that in 2022, 95 % of the energy used for heating came from renewable sources, which decreases to 86 % by 2050 due to milder winters. However, the need for cooling increases by 9 % over the same period due to hotter summers. By 2050 and 2080, if the EU transitions to renewable electricity, the operational Global Warming Potential (GWP) could approach zero. The study highlights that embodied emissions (69 %) outweigh operational emissions (31 %) in 2022, emphasizing the need to reduce embodied GWP through material reuse and recycling. Notably, concrete and aluminum were found to contribute the most to embodied emissions. The research also shows that nZEBs can exceed the EU's 2030 energy targets, with renewable energy contributing 67 % of the building's total consumption. As climate change favors nZEB performance, the operational emissions will trend towards zero, but embodied emissions will become increasingly significant. To achieve the EU's zero-emission goals, it is crucial to prioritize reducing embodied GWP in future nZEBs. This study underscores the importance of nZEBs in mitigating climate change impacts, offering a pathway toward sustainable construction and energy efficiency.

Critical life cycle assessment of the innovative passive nZEB building concept ‘be 2226’ in view of net-zero carbon targets

Buildings constructed today need to be nearly-zero energy/emission buildings (nZEB) during operation. Amongst strategies to meet today's nZEB performance requirements are passive building concepts. However, it is unclear to which degree such concepts aid buildings to achieve net-zero carbon targets. To address this research gap, we conduct a life cycle assessment (LCA) of the passive nZEB concept '2226' based on its original prototype office building in Austria. We deploy a quantity takeoff and the measured end-energy demand to calculate the embodied and operational GHG emissions. In line with the recent draft of the building LCA standard EN15978, we split energy usage into building-integrated and non-integrated systems. Embodied GHG emissions make up about a third of the total life cycle GHG emissions (33%), and operational energy use accounts for two-thirds (67%) of the life cycle GHG emissions, considering the current Austrian energy grid mix. The contextualisation with the literature shows better performance in comparison to existing building standards, yet no reduction is achieved compared to buildings with similar nZEB ambitions. The measured end-energy analysis shows that two-thirds (68%) of the operational GHG emissions are allocated to building-integrated systems, i.e., those regulated by today's EU Energy Performance of Buildings Directive. Almost a third (30%) of the operational GHG emissions can be allocated to non-integrated systems, currently being reported as optional in the latest draft of the standard EN15978. We recommend extending the system boundary of building LCA including these end-energy uses by non-integrated systems in future building regulation and building LCA practice. • LCA of an innovative passive nZEB office building in Austria. • Embodied GHG emissions from BIM-based quantity take off; operational GHG emissions from measured data. • Allocation of operational GHG emissionsin distinct sub-modules B6.1, B6.2 and B6.3 • 30% of operational GHG emissions allocated to non-building integrated systems. • Reflections on other studies and critical discussion in relation to net-zero carbon targets.

Feasibility of net zero energy high rise apartment buildings in Australia

Net-Zero Energy (NZE) buildings are gaining popularity globally as a solution to reduce operational energy usage and limit greenhouse gas emissions in the building industry. Their deployment is occurring rapidly as many countries are planning to make it mandatory for new developments. Despite the advancements in research in the various aspects of NZE, significant barriers do exist to its successful adoption and implementation, particularly with respect to high-rise residential buildings which are becoming a major portion of the housing supply in Australia. One of the challenges attributed to the achievement of NZEB performance is the uncertainty involved in selecting appropriate solution strategies that could deliver quality performances. This paper investigated strategies that can deliver NZE performance for high-rise residential buildings in Australia. A calibrated model of 26 storey high-rise apartment building with 396 units was prepared for detailed analysis of NZE strategies using building simulation. The impact of various interventions was evaluated across cities in five climate zones in Australia and a guideline for solution sets that can deliver the goal for each climate zone is presented. The findings show that NZE performance for high-rise residential buildings can be realised in Australia, albeit with some limitations. While the tropical, subtropical and cold temperate climates appear to be more challenging, proper design and optimisation of the envelope proved to be effective in overcoming the challenges imposed by the more demanding climates. The impacts of shading from neighbouring buildings and objects presented the largest impediment to energy production through the façade.

The role of hybrid systems in the decarbonization of residential heritage buildings in mediterranean climate. A case study in Seville, Spain

Residential heritage buildings in the Mediterranean region face unexpected challenges in the field of energy efficiency and indoor environmental quality to ensure the sustainable conservation of historic town centres. This paper evaluates whether the conservation of their values can coexist with the current energy efficiency requirements and be included in urban decarbonization plans to prevent neglect and degradation. For this, a comprehensive decarbonization plan was drawn up based on the results of a previous energy audit on the case study selected, an 18th-century listed residential building in Seville, Spain. Envelope improvement was combined with mechanical ventilation and an integrated heat pump combining RESs and electricity from the public grid to cover all thermal needs in order to reach NZEB performance in the building. Despite the complexity of integrating demanding energy efficiency standards into heritage buildings, which requires case-by-case analysis and dynamic simulation, findings show a notable degree of approximation to NZEB performance. The main obstacles stem from the large amount of energy consumed by auxiliary systems and the relatively low presence of RESs in the national electricity mix.

A real-time diagnostic tool for evaluating the thermal performance of nearly zero energy buildings

The nearly zero-energy buildings (nZEB) presents a promising contribution to fulfill the EU sustainable future targets. However, the construction industry that leads the development of nZEB is facing challenges to guarantee its performance. In this context, this paper proposes a methodology framework based on Multizone Resistance–Capacitance Model to trace the nZEB performance challenges with quantifications for the time-dependent variables comprising occupant behaviors as well as the dynamic behavior of weather conditions and building operations. This approach incorporates Bayesian optimization for calibration purposes to minimize the required monitoring data. Moreover, the proposed framework integrates the uncertainty analysis (UA) with two-step global sensitivity analysis (GSA) in order to quantify and assess the uncertainty associate with the performance of the developed digital dwelling. The methodology application is demonstrated through a case study for a newly renovated two-story dwelling located in a district of Emmen at the Netherlands. The results confirm a high accuracy for the digital dwelling performance where the model offers a prediction accuracy of 2.2% and 7.03% for the thermal energy consumption and indoor zone temperature, respectively. On the other hand, the UA confirms a high uncertainty associate with the nZEB performance where the total thermal energy consumption can increase up to 100 kWh/m2/yr. This variation is driven by the infiltration rates followed by the building envelope characteristics. The proposed framework can serve a diagnostic tool to assist the construction and installation companies to maintain the performance of their products proactively.

Impact of Climate Change on the Energy and Comfort Performance of nZEB: A Case Study in Italy

Climate change is posing a variety of challenges in the built realm. Among them is the change in future energy consumption and the potential decay of current energy efficient paradigms. Indeed, today’s near-zero Energy buildings (nZEBs) may lose their virtuosity in the near future. The objective of this study is to propose a methodology to evaluate the change in yearly performance between the present situation and future scenarios. Hourly dynamic simulations are performed on a residential nZEB located in Rome, built in compliance with the Italian legislation. We compare the current energy consumption with that expected in 2050, according to the two future projections described in the Fifth Assessment Report (AR5) by the Intergovernmental Panel on Climate Change (IPCC). Implications for thermal comfort are further investigated by assuming no heating and cooling system, and by tracking the free-floating operative temperature. Compared to the current weather conditions, the results reveal an average temperature increase of 3.4 °C and 3.9 °C under RCP4.5 and RCP8.5 scenarios, estimated through ERA-Interim/UrbClim. This comes at the expense of a 47.8% and 50.3% increase in terms of cooling energy needs, and a 129.5% and 185.8% decrease in terms of heating needs. The annual power consumption experiences an 18% increase under both scenarios due to (i) protracted activation of the air conditioning system and (ii) enhanced peak power requirements. A 6.2% and 5.1% decrease in the hours of adaptive comfort is determined under the RCP4.5 and RCP8.5′s 2050 scenarios out of the concerted action of temperature and solar gains. The results for a newly proposed combined index for long-term comfort assessments reveal a milder future penalty, owing to less pronounced excursions and milder daily temperature swings.

Nearly zero energy target and indoor comfort in Mediterranean climate: Discussion based on monitoring data for a real case study

The paper discusses the results of a monitoring campaign performed during the spring and autumn with the purpose to evaluate the operational energy performance of an existing nearly zero energy building (nZEB). It is located in Benevento, a middle-size city of South Italy with typical Mediterranean climate.A methodology for real-time nZEB performance analysis is proposed by taking into consideration the implications of the continuous interplay between external conditions and indoor occupant requirements as well as between on-site generation and the building loads with the resulting interaction with the energy grid. It takes into account the inertial properties of building envelope and the occupant perception in term of thermo-hygrometric and visual comfort as well as of indoor air quality. Compilation and assessment of appropriate quantitative indicators are proposed basing on data with hourly time step for finding the optimal management of the internal and external shades and the ventilation system. Moreover it is discussed how daily variations can influence the efficiency of the whole building-HVAC system with particular attention to the pre-handling system based on an earth-water heat exchanger.

A Novel Control Strategy for Improving the Performance of a Nearly Zero Energy Building

This paper deals with one of the most challenging problems in nearly zero energy buildings (nZEBs) of several multifaced and sometimes contradictory objectives that is the energy management. Specifically, aim of the paper is to propose an integrated control strategy (ICS) based on genetic algorithms that can provide an optimal balance between the objectives of energy saving, comfort of the building residents and maximum exploitation of the generated electric energy by the renewable energy sources through the proper utilization of a battery storage system (BSS). The above can be attained by optimizing a comprehensive cost function that considers the most important factors that may affect the performance of an nZEB, i.e., real-time electricity price, generated/consumed electric energy by each device, user preferences, state-of-charge, and energy price of the BSS, weather forecast and the nZEB's construction characteristics. The outcome of the ICS is the proper task scheduling and control of the electric loads as well as the regulation of the BSS operation so as the nZEB's performance is improved. The feasibility and effectiveness of the proposed ICS are verified in a hardware-in-the-loop system and selective experimental results are presented to demonstrate the operational improvements.

Hourly dynamic and monthly semi-stationary calculation methods applied to nZEBs: Impacts on energy and comfort

The EU Directive 2010/31 abstained from prescribing harmonized and strict requirements for nearly Zero Energy Buildings (nZEBs), to provide EU countries flexibility and room for maneuver in setting national targets, in view of the impact of local climatic conditions and specific territorial and socio-economical features on heating and cooling needs. Benchmarks are usually provided in terms of primary energy needs, however the definition of accurate calculation methodologies, notably as regards the cooling share, is a rather challenging task. Nonetheless, its accomplishment is cardinal to countries, like Mediterranean ones, were the building performance is mostly dictated by summertime sensitivities. This paper presents a cutting-edge approach to nZEB performance analysis: the monthly quasi steady-state (EN 13790 as implemented in Italian UNI/TS 11300) and hourly dynamic calculation methods (developed under the standard UNI EN ISO 52016-1:2018) are compared, with due attention to the cooling energy consumption, to spot pros and cons of a finer temporal discretization. Potential nZEB design alternatives in three different Italian climatic zones are contemplated and used to confront the effectiveness of the above procedures.

Paving the Way to NZEB on two Historical Blocks in Lisbon Pombaline Quarter

The 1758 Lisbon Pombaline Quarter reconstruction plan is made of compact rectangular shaped residential blocks, built with a system that complies solid mass construction elements with a light wooden structure. If we take into consideration both constructive and architectural inherent features of the original Pombaline block, it shows the potential to achieve NZEB level if an energy retrofit strategy at a block scale is implemented, instead of the usual single building or fraction approach. The retrofit of historic buildings has raised questions regarding interventions depth and efficiency, as the impact on the built heritage value has to be residual or null while energy-related improvements must be noticeable. With this in mind, this paper intends to analyse and compare the result on energy demand and primary energy consumption of passive, active and BIST/PV systems packages implementation on two original blocks, with the challenge of minimizing the impact on case studies appearance. A Building Energy Simulation methodology is applied using the whole-of-building dynamic simulation software EnergyPlus. The results show that exterior envelope improvements can reduce up to 50% heating and cooling energy demands increasing thermal comfort at the same time. Finally, a combined VRF/Biomass heating solution display the best results on primary energy consumption while photovoltaic and solar thermal systems proved to have an essential role to achieve NZEB performance.

Assessing evidence-based single-step and staged deep retrofit towards nearly zero-energy buildings (nZEB) using multi-objective optimisation

There is a dearth of data and evidence in the literature to assist the industry in determining the most appropriate strategies for large-scale deep retrofitting of non-domestic buildings to achieve healthy low-energy buildings. Support to decision-making and enabling deep retrofit of these buildings requires approaches such as long-term renovation strategies and building renovation passports. This paper compares the impact of single-step and staged retrofit approaches to improve the building energy performance of an existing building to a nearly zero-energy building (nZEB) level with improved comfort and optimal life-cycle costs. The novel developed methodological framework is applied to a university building built in 1975 (partially retrofit in 2005) that is expected to be completely retrofitted in 2020. A set of scenarios are analysed for the case study building using a combination of retrofit measures towards achieving the cost-optimal non-dominated solutions (Pareto front) based on multiple-objective optimisation for the decision-maker. The results highlight that a single-step retrofit can achieve a reduction of up to 60% in primary energy consumption and reduction of 38% in discomfort hours. The findings also indicate that nZEB performance with the primary energy consumption in the range of ~ 75–90 kWh m−2 year−1 (with plug loads) can be achieved cost-effectively through single-step deep retrofit for a university building. Results also highlighted the inability to achieve higher energy performance or improved comfort in two stages relative to completing a deep retrofit in a single stage. The results aim to contribute to the existing debate on the economic and environmental feasibility in realising long-term renovation strategies for existing non-domestic buildings, especially university buildings.

A clustering based grouping method of nearly zero energy buildings for performance improvements

Collaborations among nearly zero energy buildings (nZEBs) (e.g. renewable energy sharing) can improve nZEBs’ performance at the community level. To enable such collaborations, the nZEBs need to be properly grouped. Grouping nZEBs with similar energy characteristics merely brings limited benefits due to limited collaboration existed, while grouping nZEBs with diverse energy characteristics can bring more benefits. In the planning of nZEB communities, due to the large diversity of energy characteristics and computation complexity, proper grouping that maximizes the collaboration benefits is difficult, and such a grouping method is still lacking. Therefore, this paper proposes a clustering based grouping method to improve nZEB performance. Using the field data, the grouping method first identifies the representative energy characteristics by advanced clustering algorithms. Then, it searches the optimal grouping alternative of these representative profiles that has the optimal performance. For validation, the proposed grouping method is compared with two cases (the nZEBs are either not grouped or randomly grouped) in aspects of economic costs and grid interaction. The study results demonstrate that the proposed method can effectively improve nZEBs’ performances at the community level. The propose method can provide the decision makers a means to group nZEBs, which maximize the collaboration benefits and thus assists the planning of nZEB communities.

A collaborative control optimization of grid-connected net zero energy buildings for performance improvements at building group level

Due to inherent differences in building usage and system configuration, NZEBs frequently show different sufficiency of renewable energy at same moments, thereby providing chances of renewable-energy-sharing among NZEBs. Conventional controls are developed for NZEB performance improvements at single building level while potential collaborations (renewable energy sharing) between NZEBs are rarely considered. For this reason, they are unable to achieve optimized results at building group level. This study thus proposes a new collaborative control in which renewable energy sharing are realized among NZEBs. Adopting different objective functions, case studies have been conducted to compare the proposed control with a conventional one in two aspects, i.e. operation cost and grid friendliness. The study results have shown that the proposed collaborative control is able to achieve performance improvements through renewable energy sharing among NZEBs. The proposed collaborative control can be implemented in practice to realize renewable energy sharing among NZEBs and thus improve the cost effectiveness and grid friendliness at building group level.

The effect of glazing on nZEB performance

In the last decades, European countries have provided for stringent energy requirements for new buildings. In improving the energy performance of buildings, windows play a significant role as they largely influence the energy need. The windows design should base on the balanced trade-off between the solar heat gains and the heat transfer by transmission.In the paper, for some Italian climatic zones, the relation between the optimal window-to-wall ratio (WWR) and the energy need in residential nearly zero-energy buildings (nZEBs) is investigated. In the case studies, the envelope thermo-physical properties are consistent with the nZEB requirements established at national level. The energy performance assessment is carried out by means of a detailed dynamic simulation tool (EnergyPlus). The influence of different orientations and sizes of windows on the energy performance and the peak power are studied. The paper analyses the effect of WWR in the design of nZEBs.

Simulation of Dynamic Thermal Behaviour for Housing in Warm Climate: The Case of Thermal Mass in Lightweight Envelopes

Comparison between simulation results and measured performances is usually an open scientific problem, crucial to achieving the goal of NZEB performance. This paper addresses this issue in relation to residential buildings, using as a case study "RhOME for denCity", the housing prototype developed by Roma TRE University and winner of Solar Decathlon Europe 2014. In a Mediterranean climate, the use of the mass combined with natural cross ventilation to control the indoor microclimate can be very effective in reducing HVAC use. Therefore, a "massive layer" was introduced in the inner surface of the envelope to not only contribute to the envelope transmittance value and the shifting phase of the thermal waves, but also as a thermal shock absorber to adjust the internal temperature, in both summer and winter. This experimental envelope was tested over two weeks during the competition in Versailles. Although prototype thermal behaviour was monitored only during the competition, and not over an extended period, initial results provide information on how to size the thermal mass contribution for indoor comfort. In-depth simulation through TRNSYS was run prior to the construction phase. This paper presents the comparison between monitored performance and simulations in order to measure the amount of mass needed to obtain a numerical improvement in indoor comfort performance.

Energy and exergy analysis of prosumers in hybrid energy grids

ABSTRACTSurplus energy can be a recurrent phenomenon in zero-energy buildings (ZEBs) with onsite generation systems, usually resulting in the export of excess electricity. Yet, converting electricity into heat and exporting it could improve the overall energy balance. This study analyses the energy and exergy performance of a Finnish nearly zero-energy building (nZEB) as a heat and electricity prosumer, and proposes alternative energy topologies to improve energy and exergy levels, primary energy demand and CO2 emissions. The results show that increasing the installed capacity of the photovoltaic systems would lead to zero energy, exergy, emissions and a balance of primary energy. However, by instead using the surplus electricity to drive a heat pump and export heat, the currently installed capacity would lead to a net energy export of over 4000 kWh/a. Thus, energy conversion could significantly enhance the contribution from heat and electricity prosumers to smart energy grids, though not without affecting other criteria. Two management strategies arise: favouring heat export improves the net energy and CO2 emissions reduction but lessens the net exergy, while favouring electricity export improves the net exergy and primary energy reduction. The findings highlight that energy conversion can enhance nZEB performance and its exchange with hybrid grids.

Robust optimal design of renewable energy system in nearly/net zero energy buildings under uncertainties

It is acknowledged that the conventional design methods can easily lead to oversized system or unsatisfactory performance for different design conditions. Most existing studies on design optimization of net zero energy building (nZEB) are conducted based on deterministic data/information. However, the question is: How is the actual performance of a design nZEB in different years considering uncertainties? This study, therefore, proposed a robust design method for sizing renewable energy systems in nZEB concerning uncertainties in renewable resources and demand load. The proposed robust design method is applied to the planning of renewable energy system for the Hong Kong Zero Carbon Building. The annual performance of nZEB under the optimal design options are systematically investigated and compared using the proposed robust design method and the deterministic method. It is meaningful to obtain a fitting formula to identify the relationship between the probability of achieving annual zero energy balance and the design mismatch ratio. On the basis of Monte Carlo uncertainty propagation methods, the uncertainty of nZEB performance is quantified which provides flexibility for designers in selecting appropriate design options according to the required probability of achieving nZEB during the design stage.

Match Performance Analysis for a Solar-driven Energy System in Net Zero Energy Building

Match performance is a critical consideration on the design of energy system for zero energy building/community. A case study regarding an residential building of net zero energy (NZEB) is presented in this article. In addition to the passive design of energy efficient, indoor terminal units and renewable energy power system, an emphasis is placed on solar-driven energy system which employed LiBr and CO2 as working fluids for a hybrid cycle of vapor compression and absorption. The performance of NZEB was evaluated in terms of the indoor comfort, energy balance and match.

Impacts of renewable energy system design inputs on the performance robustness of net zero energy buildings

Due to the intermittent and uncontrollable nature of renewable energy resources, the performance of nZEB (net zero energy buildings) may suffer a great degree of uncertainties. In this study, a GA (genetic algorithm) optimization approach is employed to search optimal sizes of four design options for a net zero energy building. Then, sensitivity analysis is conducted on an optimized system (photovoltaic/wind turbine/bio-diesel generator) to investigate the impacts of the design input variations on the building performance (i.e. operation cost, CO2 emission, impact on grid). The results show that, with 20% variations in the four variables, the maximum change of the combined objective is 26.2%. In addition, wind velocity is the key factor concerning mismatch ratio, the cost and CDE (CO2 emissions), while the building loads should be considered with high priority concerning the comprehensive performance (combined objective) of the building. The performance of the energy system, integrating photovoltaic and bio-diesel generator, is not the best. But, compared with the other three design options, the variations of operation variables have least effects on its performance (i.e. most robust performance). The results also provide the quantitative assessment on the impact of active energy generation systems on enhancing the performance robustness of net zero energy buildings.

Cost optimal and nearly zero energy performance requirements for buildings in Estonia

Estonian cost optimal and nearly zero energy building (nZEB) energy performance levels were determined for the reference detached house, apartment and office building. Cost optimal energy performance levels, i.e. the energy performance leading to the lowest life cycle cost according to defined methodology, are implemented into new Estonian energy performance regulation as minimum requirements for new buildings. The regulation that came into force since 9 January 2013 includes requirements for nZEB buildings, but they are not mandatory. Compared to previous requirements, cost optimal requirements improve energy performance by 20%-40% depending on the building type and energy sources used. The results of the reference office and apartment building are reported. The results of the reference detached house, being previously reported, have been recalculated with new energy carrier factor for electricity, which was one major change in the regulation in addition to new requirements. When the detached house showed global cost curves with well-established cost optimal points, global cost curves were much more flat for the apartment and office building. This indicates that the results are sensitive to input data and relatively small changes in input data can significantly shift the cost optimal points. As uncertainties related to nZEB performance level and cost calculation are generally much higher due to high performance technical solutions not commonly used and costs not well established, it is recommended to repeat nZEB calculations with possibly refined input data before setting mandatory nZEB requirements.