• Energy Research

Abstract In several areas of the world, the population concentrates along the coastal regions, benefitting from the sea breeze, with warmer inland areas. However, increasing population is driving urban sprawl in traditionally low-density areas, enhancing the synergies between global and local climate change. Here we show that local climate mitigation can reduce the impacts of climate change, with the analysis of a new development area in Sydney, 50 km from the coast. With meso-scale climate modelling, we computed that by 2050 the peak summer temperature will increase by 0.8 °C and the daily average summer temperature by 1.6 °C. Mitigation with cool materials, greenery, and irrigation will lower the peak and average daily temperatures respectively by 2.2 °C and 1.6 °C with respect to the unmitigated future climate scenario. Mitigation techniques when applied in the whole Sydney area yield to cooling energy needs reductions by 6.7–8.6 kWh/m2 (13.4–19.3%) for typical residential, office, and school buildings, with a negligible heating penalty, compared to an unmitigated future scenario. Combined adaptation and mitigation can reduce the future cooling energy needs by 31.3 kWh/m2 (70%), 29.3 kWh/m2 (57.3%), and 20.9 kWh/m2 (59.4%) for typical residential, office, and school building, respectively. Our study indicates that the consolidated and widely available mitigation technologies alone cannot counteract the energy impact of both global and local climate change. A structured system of interventions at building and urban scale is necessary while developing novel and higher efficiency mitigation technologies.

Abstract Urban Heat Island (UHI) is a phenomenon resulting in the increase of ambient temperature in dense areas of cities in comparison with rural areas. UHI has been demonstrated to be relevant in the Sydney metropolitan area, with a peak intensity of up to 6 °C. This has the consequence of increasing of up to three times the cooling demand of buildings. With the general aim of mitigating the effects of UHI in Sydney, several strategies, involving the use of outdoor surfaces with high Solar Reflectance and the use of greenery on outdoor surfaces at ground level and on roofs have been implemented and tested. Moreover, the benefits due to the adoption of mitigation technologies, in terms of reducing both UHI intensity and building cooling demand have been predicted. Results have shown that solutions involving the increase of the global albedo of the city demonstrate the highest benefits, achieving a reduction of peak ambient temperature of up to 3 °C and of peak cooling demand of residential buildings of up to 20%.

AbstractOverheated outdoor environments adversely impact urban sustainability and livability. Urban areas are particularly affected by heat waves and global climate change, which is a serious threat due to increasing heat stress and thermal risk for residents. The tropical city of Darwin, Australia, for example, is especially susceptible to urban overheating that can kill inhabitants. Here, using a modeling platform supported by detailed measurements of meteorological data, we report the first quantified analysis of the urban microclimate and evaluate the impacts of heat mitigation technologies to decrease the ambient temperature in the city of Darwin. We present a holistic study that quantifies the benefits of city-scale heat mitigation to human health, energy consumption, and peak electricity demand. The best-performing mitigation scenario, which combines cool materials, shading, and greenery, reduces the peak ambient temperature by 2.7 °C and consequently decreases the peak electricity demand and the total annual cooling load by 2% and 7.2%, respectively. Further, the proposed heat mitigation approach can save 9.66 excess deaths per year per 100,000 people within the Darwin urban health district. Our results confirm the technological possibilities for urban heat mitigation, which serves as a strategy for mitigating the severity of cumulative threats to urban sustainability.

Employing a hybrid Genetic Algorithm (GA) and Monte Carlo (MC) simulation approach, energy consumption and renewable energy generation in a cluster of Net Zero Energy Buildings (NZEBs) was thoroughly investigated with hourly simulation. Moreover, the cumulative energy consumption and generation of the whole cluster and each individual building within the simulation space were accurately monitored and reported. The results indicate that the developed simulation algorithm is able to predict the total instantaneous and cumulative amount of energy taken from and supplied to the central energy grid over any time period. During the course of simulation, about 60–100% of total daily generated renewable energy was consumed by NZEBs and up to 40% of that was fed back into the central energy grid as surplus energy. The minimum grid dependency of the cluster was observed in June and July where 11.2% and 9.9% of the required electricity was supplied from the central energy grid, respectively. On the other hand, the NZEB cluster was strongly grid dependant in January and December by importing 70.7% and 76.1% of its required energy demand via the central energy grid, in the order given. Simulation results revealed that the cluster was 63.5% grid dependant on annual bases. In general, this stochastic algorithm is a self-learning one, i.e., at the end of each year, it utilizes the instantaneous energy consumption and generation data of each building to predict its energy balance in subsequent years. Hence, the accuracy and validity of the predictions increase over time. The simulation results are capable of modifying and readjusting the energy consumption patterns of buildings via appropriate predefined policies and well-designed monitoring systems.

Abstract Application of highly absorptive construction materials is proved to be one of leading causes of urban overheating in big cities. To avoid the excessive heat by the conventional construction materials, several advanced heat-rejecting coating technologies were developed during the last decades. The main idea behind heat-rejecting coatings is to have colder coatings with the same appearance and colour of conventional coatings. One of the existing technologies for heat-rejecting coatings are advanced coatings with high solar reflection in the infrared range or so-called cool coatings. Recently, re-emission of the visible-range light by nano-scale semiconductors, known as Quantum Dots (QDs), were introduced as another effective heat-rejecting technology. In this paper, we showed that QDs also demonstrate a very high solar transmission in the near-infrared range, and therefore, a highly near-infrared reflective base layer can significantly improve their cooling potential. The high transmission value in the near-infrared range is due to the low absorption coefficient in the wavelengths longer than absorption edge wavelength (i.e. the wavelength corresponding to the bandgap energy) in semiconductors. We show that surface temperature reduction potential of CdSe/ZnS QDs film through fluorescent cooling is about 2.5 °C, which could be increased by another 8.1 °C with a highly near-infrared reflective base layer in a typical sunny day.

Abstract The building envelope incorporates significant amount of construction materials and is a key determinant of the embodied energy and environmental impacts in buildings. It is also a mediator between indoor and outdoor environmental conditions and has significant impacts on operational energy use in many types of buildings. The present article utilizes a multi-objective optimization algorithm to explore optimum building envelope design with respect to energy use and life cycle contribution to the impacts on the environment in a low-rise office building in Seattle, Washington. Design inputs of interest include insulation material, window type, window frame material, wall thermal resistance, and south and north window-to-wall ratios (WWR). The simulation tool eQuest 3.65 is used to assess the operational energy use, while Life Cycle Assessment (LCA) methodology and Athena IE are used to estimate the environmental impacts. Also, a hybrid artificial neural network and genetic algorithm approach is used as the optimization technique. The environmental impact categories of interest within the LCA include: global warming, acidification, eutrophication, smog formation, and ozone depletion. The results reveal that the optimum design scenario incorporates fiberglass-framed triple-glazed window, about 60% south WWR, 10% north WWR, and R-17 insulation.

Abstract Climate change is one of the most significant environmental issues facing communities, while poor construction and absence of effective air-conditioning (AC) predominantly cause indoor overheating. Although AC may help meeting indoor comfort, it increases the vulnerability of low-income residents, triggers large energy consumption, and generates anthropogenic heat, which worsens heat stress outdoor. The capacity of buildings to maintain comfortable thermal conditions without mechanical cooling is the key factor protecting occupants against the rising temperature. Residents of Darwin, Australia, will be largely affected by increasing temperature where the annual peak ambient temperature may increase by 7.4 °C in 2060, while the number of hours above 30 °C will rise by 70%. Based on regional climate modelling for the Australian area and using a building energy simulation platform, we computed that by 2060 the indoor air temperature in a typical residential building may exceed 30 °C for over 4000 h under free-floating condition, with a peak daytime and night-time temperatures of 39 °C and 36.5 °C, respectively. The sensible thermal energy need for cooling per unit area under thermostatically controlled condition will increase from the current level of 110.7 kWh/m2 to 196.8 kWh/m2 in 2060. Different adaptation techniques when applied to the typical residential building yield to the peak indoor air temperature drop by 3.3–12 °C, and cooling energy needs reductions by 23.5–195.3 kWh/m2 (12–99.7%) for low, medium, and high retrofit buildings compared to the typical residential building in 2060. Our study indicates that improved building quality is necessary to enhance survivability and energy efficiency in Darwin considering the role of building adaptation measures to counterbalance the impacts of global warming.