Residential Net-zero Energy Building Research Articles

Building retrofitting towards net zero energy under climate change

Abstract The challenge in Net-Zero Energy Building (NZEB) retrofitting is to identify the most effective measures to address energy performance issues. This paper presents a machine learning model for optimizing retrofit measures to achieve NZEB under the influence of climate change. Specifically, the non-dominated sorting genetic algorithm (NSGA-III) minimizes energy consumption and the predicted percentage of dissatisfaction (PPD) while achieving a NZE balance, thereby obtaining the Pareto front. The Order of Preference by Similarity to Ideal Solution (TOPSIS) ranking technique is then applied to the Pareto front to obtain an optimal solution. Various passive energy retrofit measures are investigated, and renewable retrofit measures are employed to cover the required energy. This process is repeated for different time frames to consider the impact of climate change on selecting retrofit measures. The results clearly indicate that, for retrofitting a residential NZEB, higher insulation values are needed for future scenarios compared to the present scenario due to the effects of climate change. Using the future scenarios defined by the Shared Socioeconomic Pathways framework, a higher level of envelope insulation and renewable retrofit measures are required to achieve NZEB in the Sustainable Future scenario compared to the Fossil Fuel-dependent Future scenario, with increases of 35% and 50%, respectively.

Envelope design optimisation for residential net zero energy buildings within cold and semi-arid climate: A case study of Shiraz

Selection of the optimum values for net zero energy buildings (NZEB) is a complex task, due to the existence of multiple objectives. In the current study, cold and semi-arid climate was considered for investigation, and DesignBuilder was used for simulating a residential NZEB in Shiraz, Iran, as a case study. First, optimum solutions for minimising the cooling and heating demands were obtained by obtaining a Pareto front including 21 points. Then, phase changing materials (PCMs) were integrated to the envelope to further optimise energy consumption. The obtained results illustrated that using PCMs on both sides of the envelope can significantly reduce the energy consumption. Findings of this study are beneficial for the future plans of Iran, particularly with regards to improving sustainability within the building sector.

Design and transient analysis of renewable energy-based residential net-zero energy buildings with energy storage

In this research, by the installation of solar collectors and photovoltaic panels, a building with almost zero energy emissions is designed in TRNSYS software, and with a parameter study on a residential building located in a typical city, the optimal design conditions to provide suitable conditions for thermal comfort, and the electrical power required by the building is suggested. Also, to improve the investigated system, in addition to the two-dimensional design, the three-dimensional design of the building is examined. After the design of the building, it is observed that Bushehr is suitable for designing a building with almost zero energy emissions through the installation of solar collectors and photovoltaic panels due to having the appropriate intensity of sunlight. Also, due to the suitable radiation conditions, it is suitable to use a battery to store electrical energy, and also because the cooling load required to provide thermal comfort in the summer season is high, therefore, the use of a diesel engine is suitable for use in emergency situations. Among the different fuels for starting a diesel engine, diesel fuel has the lowest consumption, and hydrogen fuel has the highest consumption.

An integrated energy simulation and life cycle assessment to measure the operational and embodied energy of a Mediterranean net zero energy building

Net Zero Energy Buildings can play a key role in reducing the energy use, greenhouse gas emissions and the use of natural resources associated to the built environment. It is widely recognized that in low energy building a shift in relevance may occur from the operational to the embodied impacts. However, building performance assessment focus mostly on the operational phase and on primary energy consumption. This study aims to assess the energy and environmental impacts of a residential net zero energy building expanding the analysis to the full life cycle and to a wide range of environmental impact categories. The methodological approach integrates a non-steady state building energy simulation and the life cycle assessment methodology. The analysis is performed by considering four different design scenarios using alternatively two thermal insulation materials (extruded expanded polystyrene (XPS) and cellulose fibres (CF)) combined with two configurations for a building integrated photovoltaic system (with and without a battery storage system). The main results highlight that the CF/battery storage system scenario has the lowest impact in almost all the energy and environmental categories investigated, while the configuration with XPS and without battery storage system has the worst performances. In detail, the indicators “global energy requirement” and “climate change” are 18% and 34% lower than the XPS/no battery scenario. However, the impact increases in terms of resource depletion (4%). This outcome confirms the importance of a life cycle perspective to orient the low energy buildings design process towards more sustainable solutions. Moreover, very different results can be achieved if the credits beyond the building system boundaries are included or not in the balance. In detail, if system boundaries are expanded to include the net environmental credits, the configuration with CF and without battery storage system is the best, while the XPS/battery storage system one is the worst. “Global energy requirement” and “climate change” decrease, respectively, by 37% and 29% from XPS/battery configuration to CF/no battery storage configuration. Therefore, the management of the credits beyond the building system boundaries is an aspect not to be overlooked in similar approaches while defining a clear and unambiguous procedure to manage it in the perspective of a wide diffusion of low energy buildings.

Predictive permanent magnet synchronous generator based small-scale wind energy system at dynamic wind speed analysis for residential net-zero energy building

Integration of small-scale wind energy system to residential buildings for a target to achieve net-zero CO2 emissions is a revolutionary step to reduce the dependency on the national grid. In this paper, a predictive 20 kVA permanent magnet synchronous generator (PMSG) based small scale wind turbine is investigated at dynamic wind speed with a sensing control system to manage and monitor the power flow for a supply to a typical residential building. A control system is applied that regulates the power from the wind turbine. Results indicate that the proposed control system maximizes the power efficiency within the system. The maximum power generation capacity of the wind turbine is 20 kWh with 415 VAC and 50 Hz frequency. A storage system of 19.2 kWh that supplies the energy to the load side. The applied control unit improves the energy management and protects the power equipment during the faults. The research is conducted using MATLAB/SIMULINK and mathematical formulations.

Energetic and economic evaluation of hybrid solar energy systems in a residential net-zero energy building

Net-zero energy buildings are playing a critical role in the decarbonization of future cities since the buildings are responsible for 30–40% of total energy consumption. A residential net-zero energy building with a prospect of commercialization was introduced, which adopts solar energy systems and heat insulation solar glass that simultaneously generates electric power and minimizes heat loss. Dynamic and parametric simulation models were developed based on the TRNSYS platform and were validated by experimental data or standard test reports. A multi-criteria decision-making framework based on the energetic and economic criteria was developed to evaluate system performance and to find the favorable layout of the energy system in the residential net-zero energy building. Twelve system scenarios, covering the individual heat insulation solar glass system, the hybrid systems integrated with solar PV, solar thermal and heat insulation solar glass, and the hybrid systems combined solar thermal and heat insulation solar glass, were comparatively assessed. Among the system scenarios inclusive of solar thermal technology, a combination of the compound parabolic concentrated solar collector and variable-effect absorption chiller is highly recommended. However, the system scenario, which consists of a specific PV area of 8.4 m2/kW and employs heat insulation solar glass, is most favorable due to a highest primary energy saving ratio of 1.05 and a lowest levelized total cost of 5920 US$/year. All system scenarios proposed herein are not economically feasible at the current economic parameters in Singapore’s climate. However, the optimized hybrid system (integrated with solar PV, solar thermal and heat insulation solar glass) is sufficient to reach the net-zero energy target while the optimized solar PV system combined heat insulation solar glass is a solution of the positive energy building.

A holistic design approach for residential net-zero energy buildings: A case study in Singapore

The concept of net-zero energy buildings is an important element and dimension of the sustainable built environment. This paper introduces a holistic design approach for residential net-zero energy building (NZEB) by adopting the Triple Bottom Line (TBL) principles: social, environmental, and financial. The social need is mapped to human comfort and nature contact (i.e. thermal comfort achieved by natural cooling, and visual comfort achieved by daylighting); the environmental need is mapped to energy efficiency; and the financial need is mapped to life cycle cost (LCC). Multi-objective optimizations are conducted in two phases: the first phase optimizes the utilization rate of natural cooling and daylighting, and the second phase optimizes energy efficiency and LCC. Sensitivity analysis is conducted to identify the most influential variables in the optimization process. The approach is applied to the design of residential NZEBs in a tropical country, Singapore. The potential of building residential NZEBs in Singapore is evaluated with two typical residential building types: a landed house and apartment building. The required capacity of a renewable energy system (RES) is calculated. Results show that while it is achievable to build a net-zero energy landed house with only rooftop solar panels, it is much more difficult to achieve net-zero energy for apartment buildings. Further design considerations and analysis show that for a 25-floor H-shaped residential building with a solar panel integrated facade, the produced electricity is able to meet the energy demand of up to 19 floors. Findings and derived insights from the case study show that although some variables need to be carefully selected to balance daylighting and natural cooling, the two objectives do not always contradict each other regarding certain variables. Similarly, environmental aims and economic aims do not always contradict each other on certain variables. Also, the social aims do not contradict environmental and economic aims, as the findings show that designing for daylighting and natural cooling contributes to the improvement of energy efficiency and cost effectiveness. These results provide a framework and modeled cases for design insights, parametric design, and trade-off analysis toward sustainable and livable built structures.

Investigation of the flexibility of a residential net-zero energy building (NZEB) integrated with an electric vehicle in Hong Kong

The flexibility of a net zero energy/emission building (NZEB) in the cooling dominated area is quantitatively investigated in this research. Flexibility sources include the renewable energy, i.e. building integrated photovoltaics (BIPVs) and wind turbine, and thermal energy storages, i.e. air handling unit cooling storage tank (ACST) and domestic hot water tank (DHWT). Parametric analysis has been conducted based on all proposed flexibility indicators with respect to the renewable energy capacity, the volume of both the ACST and the DHWT, and the set point temperature for recharging the DHWT. From our results, to meet the annual energy balance, this NZEB should be equipped with BIPVs and an 8 kW wind turbine, while these BIPVs should be installed on four walls and the roof (totally 306 m2 BIPVs). Considering the grid feed-in tariff in Hong Kong, the NZEB will get the net annual operational income at 646.3 HK$/m2.a. Flexibility factors indicate the flexibility of the energy storage systems for storing the surplus renewable energy (REe) and fulfilling the building demand. During the charging process, the increase of the REe capacity shows positive impact on flexibility factors of both the ACST and the DHWT. In the case when BIPVs are on four walls, with respect to the increase of the rated wind turbine capacity from 0 to 8 kW, the flexibility factor of the ACST increases from 0.49 to 0.58 during the charging process, whereas it decreases from -0.51 to -0.59 during the discharging process. Meanwhile, the flexibility factor of the DHWT increases from 0.32 to 0.57. Moreover, with respect to the increase of the ACST volume from 0.5 m3 to 2.5 m3, the flexibility factor increases from -0.23 to 0.17 considering both the charging and the discharging processes. With respect to the increase of the DHWT volume from 1 m3 to 3 m3, the flexibility factor increases from 0.32 to 0.74. With respect to the increase of the set point temperature for recharging the DHWT from 65 ºC to 100 ºC, the flexibility factor increases from 0.32 to 0.82. Moreover, in comparison with the nighttime interaction between the building and the vehicle, the daytime interaction will reduce the reliance on the grid for charging the EV. Moreover, the energy interaction between the building and the vehicle will be enhanced.

Net-zero Nation: HVAC and PV Systems for Residential Net-Zero Energy Buildings across the United States

This study compared the energy performance and initial cost of photovoltaic (PV) and heating, ventilating, and air-conditioning (HVAC) equipment for a residential net-zero energy building (NZEB) in different climate zones across the United States. We used an experimentally validated building simulation model to evaluate various electrically-powered and commercially-available HVAC technologies. The HVAC accounted for 23.8 % to 72.9 % of the total building energy depending on the HVAC option and climate zone. Each HVAC configuration was paired with a PV system sized to exactly reach the net-zero energy target, so the economics were compared based on the initial PV + HVAC cost. Mechanical ventilation was considered with and without heat recovery; the heat recovery ventilator (HRV) saved a significant amount of energy in cold winter months and hot summer months, and the energy recovery ventilator (ERV) provided additional benefit for humid zones. The HRV was cost-effective in the cold northern latitudes of Chicago, Minneapolis, Helena, and Duluth, where energy savings reached 17.3 % to 19.7 %. In other climates, ventilation without recovery was more cost effective, by 1 % to 9 %, and sometimes even more energy efficient. The ERV was never the lowest cost option. A ground-source heat pump (GSHP) and an air-source heat pump (ASHP) were compared, with the GSHP providing significant energy savings, 24.3 % to 39.2 %, in heating-dominated climates (Chicago through Duluth). In warmer climates, the GSHP saved little energy or used more energy than the ASHP. The PV + HVAC cost was lower everywhere with the ASHP, though it is possible for colder climates that a carefully sized GSHP and ground loop could be cost-competitive. The energy and cost data as well as the required PV capacity could guide HVAC and PV designs for residential NZEBs in different climate zones.

Net-zero Nation: HVAC and PV Systems for Residential Net-Zero Energy Buildings across the United States

Abstract This study compared the energy performance and initial cost of photovoltaic (PV) and heating, ventilating, and air-conditioning (HVAC) equipment for a residential net-zero energy building (NZEB) in different climate zones across the United States. We used an experimentally validated building simulation model to evaluate various electrically-powered and commercially-available HVAC technologies. The HVAC accounted for 23.8% to 72.9% of the total building energy depending on the HVAC option and climate zone. Each HVAC configuration was paired with a PV system sized to exactly reach the net-zero energy target, so the economics were compared based on the initial PV + HVAC cost. Mechanical ventilation was considered with and without heat recovery; the heat recovery ventilator (HRV) saved a significant amount of energy in cold winter months and hot summer months, and the energy recovery ventilator (ERV) provided additional benefit for humid zones. The HRV was cost-effective in the cold northern latitudes of Chicago, Minneapolis, Helena, and Duluth, where energy savings reached 17.3% to 19.7%. In other climates, ventilation without recovery was more cost effective, by 1% to 9%, and sometimes even more energy efficient. The ERV was never the lowest cost option. A ground-source heat pump (GSHP) and an air-source heat pump (ASHP) were compared, with the GSHP providing significant energy savings, 24.3% to 39.2%, in heating-dominated climates (Chicago through Duluth). In warmer climates, the GSHP saved little energy or used more energy than the ASHP. The PV + HVAC cost was lower everywhere with the ASHP, though it is possible for colder climates that a carefully sized GSHP and ground loop could be cost-competitive. The energy and cost data as well as the required PV capacity could guide HVAC and PV designs for residential NZEBs in different climate zones.

Net-zero nation: HVAC and PV systems for residential net-zero energy buildings across the United States

This study compared the energy performance and initial cost of photovoltaic (PV) and heating, ventilating, and air-conditioning (HVAC) equipment for a residential net-zero energy building (NZEB) in different climate zones across the United States. We used an experimentally validated building simulation model to evaluate various electrically-powered and commercially-available HVAC technologies. The HVAC accounted for 23.8% to 72.9% of the total building energy depending on the HVAC option and climate zone. Each HVAC configuration was paired with a PV system sized to exactly reach the net-zero energy target, so the economics were compared based on the initial PV + HVAC cost. Mechanical ventilation was considered with and without heat recovery; the heat recovery ventilator (HRV) saved a significant amount of energy in cold winter months and hot summer months, and the energy recovery ventilator (ERV) provided additional benefit for humid zones. The HRV was cost-effective in the cold northern latitudes of Chicago, Minneapolis, Helena, and Duluth, where energy savings reached 17.3% to 19.7%. In other climates, ventilation without recovery was more cost effective, by 1% to 9%, and sometimes even more energy efficient. The ERV was never the lowest cost option. A ground-source heat pump (GSHP) and an air-source heat pump (ASHP) were compared, with the GSHP providing significant energy savings, 24.3% to 39.2%, in heating-dominated climates (Chicago through Duluth). In warmer climates, the GSHP saved little energy or used more energy than the ASHP. The PV + HVAC cost was lower everywhere with the ASHP, though it is possible for colder climates that a carefully sized GSHP and ground loop could be cost-competitive. The energy and cost data as well as the required PV capacity could guide HVAC and PV designs for residential NZEBs in different climate zones.

Selecting HVAC systems to achieve comfortable and cost-effective residential net-zero energy buildings

HVAC is responsible for the largest share of energy use in residential buildings and plays an important role in broader implementation of net-zero energy building (NZEB). This study investigated the energy, comfort and economic performance of commercially-available HVAC technologies for a residential NZEB. An experimentally-validated model was used to evaluate ventilation, dehumidification, and heat pump options for the NZEB in the mixed-humid climate zone. Ventilation options were compared to mechanical ventilation without recovery; a heat recovery ventilator (HRV) and energy recovery ventilator (ERV) respectively reduced the HVAC energy by 13.5% and 17.4% and reduced the building energy by 7.5% and 9.7%. There was no significant difference in thermal comfort between the ventilation options. Dehumidification options were compared to an air-source heat pump (ASHP) with a separate dehumidifier; the ASHP with dedicated dehumidification reduced the HVAC energy by 7.3% and the building energy by 3.9%. The ASHP-only option (without dedicated dehumidification) reduced the initial investment but provided the worst comfort due to high humidity levels. Finally, ground-source heat pump (GSHP) alternatives were compared to the ASHP; the GSHP with two and three boreholes reduced the HVAC energy by 26.0% and 29.2% and the building energy by 13.1% and 14.7%. The economics of each HVAC configuration was analyzed using installation cost data and two electricity price structures. The GSHPs with the ERV and dedicated dehumidification provided the highest energy savings and good comfort, but were the most expensive. The ASHP with dedicated dehumidification and the ERV (or HRV) provided reasonable payback periods.

A methodology for economic efficient design of Net Zero Energy Buildings

This work developed a methodology and an associated calculation platform in order to identify the economic efficient design solutions for residential Net Zero Energy Building (NZEB) design considering the influence of the local climate, the endogenous energy resources and the local economic conditions. One case study of a detached house for 3 climates was analyzed with the tool developed in order to gain insights on the economic space of NZEB solutions and the influence of the climatic context. A methodology for assisting the choice of economically efficient NZEB solutions from the early design stage is now available. Its use in practice may be of great relevance as the results showed that the differences between an economically efficient and economically inefficient NZEB can be over three times both in terms of initial and life cycle cost.

Assessing electrical bottlenecks at feeder level for residential net zero-energy buildings by integrated system simulation

Recent European communications focus on the enforcement that by 2020 all new buildings are nearly Zero-Energy Buildings (ZEBs) and on the deployment of a European Smart Grid. The presented work focuses on assessing the electrical challenges at neighborhood level of an building stock evolving towards ZEBs, and identifying the resulting challenge in multidisciplinary dynamic simulation models required to perform this assessment.A tool for Integrated District Energy Assessment by Simulation (IDEAS) is developed. This IDEAS tool allows simultaneous transient simulation of thermal and electrical systems at both building and feeder level.Residential ZEBs show a self-consumption of locally generated photovoltaic (PV) electricity of 26±4% at building level. Resulting feeder voltage fluctuations and possible transformer overload are quantified as bottlenecks. When all dwellings are intended to achieve a ZEB status, (i) a fraction of 14–47% of local PV supply is wasted by inverter curtailing depending on the feeder strength, while (ii) the peak transformer load is found to be 3.3kVA per dwelling which may affect power security in existing feeder designs.

Life cycle cost analysis of a multi-storey residential Net Zero Energy Building in Denmark

It is well recognized that in the long run, the implementation of energy efficiency measures is a more cost-optimal solution in contrast to taking no action. However, the Net ZEB concept raises a new issue: how far should we go with energy efficiency measures and when should we start to apply renewable energy technologies? This analysis adopts the LCC methodology and uses a multi-family Net ZEB to find the answer to this question. Moreover, it looks at the issue from the building owner’s perspective, hence it should be seen as a private economy analysis. The study includes three levels of energy demand and three alternatives of energy supply systems: (1) photovoltaic installation with photovoltaic/solar thermal collectors and an ambient air/solar source heat pump; (2) photovoltaic installation with a ground-source heat pump; (3) photovoltaic installation with district heating grid. The results indicate that in order to build a cost-effective Net ZEB, the energy use should be reduced to a minimum leaving just a small amount of left energy use to be covered by renewable energy generation. Moreover, from the user perspective in the Danish context, the district heating grid is a more expensive source of heat than a heat pump for the Net ZEB.