• Energy Research

Abstract This study aims to analyze and optimize the photovoltaic-battery energy storage (PV-BES) system installed in a low-energy building in China. A novel energy management strategy considering the battery cycling aging, grid relief and local time-of-use pricing is proposed based on TRNSYS. Both single-criterion and multi-criterion optimizations are conducted by comprehensively considering technical, economic and environmental performances of the system based on decision-making strategies including the weighted sum and minimum distance to the utopia point methods. The single-criterion optimizations achieve superior performances in the energy supply, battery storage, utility grid and whole system aspect respectively over the existing scenario of the target building. The multi-criterion optimization considering all performance indicators shows that the PV self-consumption and PV efficiency can be increased by 15.0% and 48.6% while the standard deviation of net grid power, battery cycling aging and CO2 emission can be reduced by 3.4%, 78.5% and 34.7% respectively. The significance and impact of design parameters are further quantified by both local and global sensitivity analyses. This study can provide references for the optimum energy management of PV-BES systems in low-energy buildings and guide the renewable energy and energy storage system design to achieve higher penetration of renewable applications into urban areas.

Abstract This paper focuses on the application of sensitivity analysis (SA) to typical passively designed high-rise residential buildings in hot and humid climates by considering multiple indoor environmental indices and impact factors. The sampling based Monte Carlo Analysis (MCA) is adopted to carry out multiple regression analyses between selected input parameters and output indices. Input parameters including the building layout, envelope thermophysics, building geometry and infiltration & air-tightness extensively cover each aspect of passive design strategies to improve the sustainability of buildings, while miscellaneous output indices represent major indoor environment factors such as lighting, ventilation and thermal comfort conditions addressed by the local green building guidance. A dynamic simulation program generates all required outputs based on input parameters by constructing a generic building model with different assumptions of internal loads, ventilation control methods, running periods and weather conditions. The calculated sensitivity indices on different output indices chances with simulation control variables, whereas the window solar heat gain coefficient and window to ground ratio are consistently among the most influential design factors. In addition, ASHRAE Adaptive Comfort Standard with 90% Acceptability is determined to be the most adequate assessment method of the building thermal comfort in hot and humid climates similar to Hong Kong. This proposed SA approach accounts for most identified impact factors in a passively designed building and can therefore help conceive potential sustainable solutions in early architectural design stages.

Buildings are the major consumers of energy in Hong Kong and most urban areas in the world. Building environmental assessment schemes, and green building rating tools (GBRTs) have been adopted by architects, engineers and researchers for more than 20 years to help promote more sustainable construction activities. Each rating tool highlights energy use as a significant portion of the assessment and provides guidance on more energy efficient strategies. Building energy efficiency can usually be improved by both passive and active technologies. Active design involves making more energy efficient heating, ventilation, air-conditioning (HVAC) systems, hot water production, lighting and any other building services application, whereas passive design focuses more on building envelope related aspects determined by the architectural design so as to reduce the demand of the building for energy. Recently, there has been renewed interest in passive strategies because of the low extra investment and the potential benefits in energy saving. The passive design approach has also been recognized in the latest versions of green building rating tools. Five representative rating systems, which all developed their own passive design criteria leading to the award of credits, are subject to comparative examinations in respect of the comprehensiveness, effectiveness and accuracy of each criterion in this paper. Passive design criteria including the building layout, envelope thermophysics, building geometry, air-tightness and infiltration performance and their effects on building energy consumption are also comprehensively reviewed. The results show that a holistic design approach based on passive energy saving strategies proves to be an effective way to reduce building energy budgets. However, more consolidated weighting systems to enable comparison of different passive strategies should be incorporated in green building rating tools based on further sensitivity and parametric studies.

Abstract In this study, a novel high-efficient energy-saving vacuum BIPV (building integrated photovoltaic) curtain wall, which combines photovoltaic curtain wall and vacuum glazing technologies, was developed and investigated. This vacuum BIPV curtain wall can not only perform on-site power generation, but also significantly reduce the heat transfer through the building envelope with improved thermal insulation. The thermal and power performance of the vacuum PV glazing were investigated by experiments and numerical simulations. A prototype of the vacuum BIPV curtain wall was set up for a short-term outdoor testing to consolidate its thermal and power performance under typical weather conditions of Hong Kong. A comprehensive energy model was then developed to predict the dynamic power and thermal performance of the vacuum BIPV curtain wall to evaluate its annual energy saving potential compared to other advanced window technologies used in buildings in Hong Kong. Based on the simulation model, an optimum design of the vacuum BIPV curtain wall was proposed. In addition, the annual energy-saving potential for a typical high-rise commercial building with the application of miscellaneous BIPV products was estimated using the typical meteorological data. BIPV characteristics were jointly optimized with other passive architectural design parameters and the net building energy demand can be decreased by up to 60% compared with a benchmark office building in Hong Kong. The target of near-zero energy high-rise building can therefore be further approached by this integrated design optimization process.

Abstract This study aims to explore the techno-economic feasibility of renewable energy systems for power supply to high-rise residential buildings within urban contexts. Experiments on a photovoltaic (PV) and battery storage system under maximizing self-consumption and time-of-use strategies are conducted to study the system performance and validate energy balance based battery and energy management models. Four renewable application scenarios are investigated for a typical high-rise building in Hong Kong through coupled modelling and optimizations with TRNSYS and jEPlus + EA. A comprehensive technical optimization criterion integrating the energy supply, battery storage, building demand and grid relief indicators is developed, and the levelized cost of energy (LCOE) considering detailed renewables benefits including the feed-in tariff, transmission loss saving, network expansion saving and carbon reduction benefit is formulated. Experimental results show that root mean square deviations between the tested and simulated battery state of charge for the two strategies are 1.49% and 0.94% respectively. It is indicated that the PV system covers 16.02% of the annual load at a LCOE of 0.5252 US$/kWh and the PV-wind system covers 53.65% of the annual load at the lowest LCOE of 0.1251 $/kWh. The added battery improves the annual average load cover ratio and self-consumption ratio by 14.08% and 16.56% respectively, while the optimum PV-wind-battery system covers 81.29% of the annual load at an affordable LCOE of 0.2230 $/kWh. Techno-economic analyses of different typical scenarios can provide valuable references to related stakeholders for a promotion of renewable applications in high-rise buildings and further reduction of urban carbon footprint.

Reducing the lifecycle energy use of buildings with renewable energy applications has become critical given the urgent need to decarbonize the building sector. Multi-objective optimizations have been widely applied to reduce the operational energy use of buildings, but limited studies concern the embodied or whole lifecycle energy use. Consequently, there are issues such as sub-optimal design solutions and unclear correlation between embodied and operational energy in the current building energy assessment. To address these gaps, this study integrates a multi-objective optimization method with building energy simulation and lifecycle assessment (LCA) to explore the optimal configuration of different building envelopes from a lifecycle perspective. Major contributions of the study include the integrated optimization which reflects the dynamics of the whole lifecycle energy use. Insights from the study reveal the optimal configuration of PV and composite building façades for different regions in sub-Saharan Africa. The lifecycle energy use for the optimized building design resulted in 24.59, 33.33, and 36.93% energy savings in Ghana, Burkina Faso, and Nigeria, respectively. Additionally, PV power generation can efficiently cover over 90% of the total building energy demand. This study provides valuable insights for building designers in sub-Saharan Africa and similar areas that minimize lifecycle energy demand.

Abstract Although semi-transparent photovoltaic windows can generate electricity in situ, they also increase the cooling load of buildings significantly due to the waste heat as a byproduct. However, vacuum glazing, which has excellent thermal insulation, can effectively solve the above issues for PV windows. In order to take advantage of excellent thermal insulation performance of vacuum glazing, a novel vacuum photovoltaic insulated glass unit (VPV IGU) was presented. The electrical characteristics of the PV laminated glass were tested in laboratory under standard test conditions. Then power generation and thermal performances of the VPV IGU were evaluated through experiments. Results have indicated that the VPV IGU can not only generate electricity, but also help reduce the cooling load as well as improve the indoor thermal comfort.