The containment vessel of nuclear power plants, concrete structures near the furnaces and roller lines, and chimneys, are exposed to high temperatures (120 °C to 350 °C) for long term. Research on ...the compressive properties of concrete after short-term high temperatures (usually within 3 h) has been widely conducted, while that of concrete after sustained high temperatures is scarce. In this research, the effects of temperature (120 °C to 350 °C), heating duration (3 h to 32 h) and initial stress level (0.2 to 0.6, ratio of initial applied stress to compressive strength at room temperature) on the failure mode, compressive strength, peak strain and stress-strain relationship of concrete after sustained high temperatures were studied. The results show that with increasing temperature and heating duration, concrete compressive strength gradually decreases, while concrete peak strain gradually increases. At heating duration of 24 h, the properties of concrete have basically stabilised. Preloading helps the concrete to resist the adverse effects of high temperatures by inhibiting the dehydration of cement matrix and the cracking of interfacial transition zone. For concrete with preload, transient thermal strain and short-term creep at high temperatures could not be recovered after cooling, which causes a significant increase in the peak strain of concrete. A compressive stress-strain model for concrete with preload after sustained high temperatures was developed, which consists of pre-creep ascending segment, creep segment, post-creep ascending segment and descending segment. Comparison of the prediction results with the test results proves that the model has high accuracy.
•Propose a model to predict transient cooling load of vehicles.•In the mild region, ambient air can handle 47.8 % of the total sensible cooling load.•Propose a novel ambient air-assisted cooling ...system and control strategies.•In the mild region, 83.7 % electric was saved, and COP was increased by up to 65.8 %.
Air conditioning system of electrical vehicles7 consumes much electricity for cooling. Using natural cooling source could effectively reduce energy consumption and extend mileage. In this paper, cooling load characteristics of electric vehicles were analyzed considering influences of climate conditions, and energy saving potential of using natural cooling sources were investigated to provide guidelines for the design of efficient air conditioning systems. First, a typical electrical vehicle was designed as the studying object, and a numerical model was established to calculate vehicle’s cooling load. Utilization ratio of natural cooling in severe cold regions, cold regions, and mild regions ranged from 36.7 % to 47.8 %, while the value was only 2.5 % in hot summer and warm winter areas. Then, a novel natural cooling assisted air conditioning system was proposed, and parametric studies were carried out to study energy-saving ratio and improvement of traveling hours. Average coefficient of performance of the novel system ranged from 4.47 to 6.08 with the air flow rate being 700 m3/h, and ranged from 5.78 to 7.71 with the air flow rate being 2000 m3/h. The values are 7.3 % to 65.8 % higher than the traditional air conditioning system. The electric consumption during cooling period could be reduced by up to 83.7 % in mild regions and by 24.9 % to 57.4 % in severe cold regions, cold regions, and hot summer and cold winter regions. Increasing setting temperature and enlarging air flow rate of the air conditioning system could effectively improve the energy-saving ratio. Traveling hours could be extended by 2.0 % to 15.8 %.
•The Indoor Overheating Hours (IOH) of dwellings are assessed at neighbourhood scale.•The mean of IOH during 2022 warm summer considering the microclimate is 10.9%•The microclimate effect increased ...IOH by 7.52% on average during 2022 warm summer.•Parameters that most influence IOH are floor level, window area and orientation.•Having more than one orientation in a dwelling reduced IOH by 9.7%
Indoor overheating is a current problem due to increasingly higher external temperatures and more frequent and extreme heatwaves which specially impact naturally ventilated dwellings. This paper presents a methodology at neighbourhood-scale to analyse indoor overheating hours (IOH) of residential typologies and to investigate building parameters that most influence IOH. This study is based on energy simulations for two climate scenarios: typical meteorological year and extreme warm summer with heatwaves (2022), and the effect of urban microclimate is considered by using the Urban Weather Generator tool. Results with the typical meteorological year show 0% IOH for all dwellings, while those derived from simulation with summer 2022 show a significant increase in IOH with values above 30% IOH in the most overheated ones. The effect of microclimate is especially relevant in the extreme warm summer and increases the IOH by 7,5% on average. Among the building parameters studied, the number of orientations (related to potential of natural ventilation), orientation and the floor level of the dwellings have the highest influence on IOH. These results could help policy-makers and technicians detect the risk of overheating in cities and buildings and prevent it by improving the adaptation of the residential stock to current warming.
Overheating in dwellings is a global concern that is increasing due to global warming and more frequent and extreme heatwaves. This study assesses the relationship between different building ...parameters (built period, floor level, orientation, window area and solar shading) and compares indoor overheating hours during summer in twelve apartments monitored in Pamplona (North of Spain). They were selected as samples from different Spanish built periods related to different energy regulations, without mechanical cooling and with some kind of exterior solar shading. Overheating hours were calculated using the UNE-EN 16798 standard, which establishes a maximum acceptable operative temperature. This limit is adaptive and it is defined as the exponentially weighted running mean of the daily outdoor temperature. Multilevel mixed-effects linear and logistic regressions were used to analyse and compare overheating hours. Floor level, window area and solar shading were the parameters that showed a significant relationship with indoor overheating hours (p < 0.01). Orientation and built period did not reach a statistically significant value (p > 0.01). It is particularly noteworthy that the apartments built under the current Spanish Energy Regulations (after 2006) do not show a significant reduction in indoor overheating hours compared to those built without any energy regulations. This assessment reveals that current building energy regulations may not be enough to avoid overheating or ensure adaptation to warmer conditions. Therefore, this study contributes to establishing the main building parameters to improve in order to adapt Spanish apartment buildings to warming conditions in temperate climates.
•Floor level, window area and shading have a significant influence on IOH.•CTE dwellings don't have a significant reduction of IOH comparing to PreCT79 period.•Windows >4m2 make dwellings 3 times more likely to experience IOH than windows <2m2.•Intermediate floors are 97% less likely to be affected by IOH than top floors.
•The damage degree of steel fiber reinforced concrete is significantly less than the plain concrete.•The strength reduction caused by high temperature thermal damage is greater than the strength ...recovery during cooling when the temperature is 600℃.•The dynamic performance of the concrete after high temperature cooling is significantly higher than that under high temperature conditions.•The influence of strain rate on the dynamic properties of steel fiber reinforced concrete is greater than the plain concrete.
The mechanical behaviors of structure concrete can degrade significantly at high temperatures from fire. The mechanical performance of structure concrete may recover to some extent during the subsequent cooling process after fire. A comparative study on the dynamic performance of concrete between at high temperature and after cooling down is necessary to predict dynamic response of structures subjected to fire or blast loads more precisely. In this paper, the dynamic characteristics of Steel Fiber Reinforced Concrete (SFRC) after high temperature cooling were examined with the use of Split Hopkinson Pressure Bar (SHPB) and compared with the test results at high temperature. The dynamic compressive strength, dynamic increase factor (DIF) of stress and peak strain of SFRC with different fiber volume (0%,1%,2%) after natural cooling from different target temperatures (200 ℃, 400 ℃, 600 ℃) to ambient temperature were obtained and compared. Experimental results show that the dynamic compressive strength and peak strain of the specimen first increases and then decreases with the increase of the strain rate cause the high temperature cooling process made the specimens prone to local failure at high strain rates. The mechanical properties of SFRC such as strength can be well recovered during the natural cooling process after high temperature. The deformation capacity and energy dissipation capacity of different types of concrete after high temperature cooling are greatly improved compared with that under high temperatures.
With the rapid process of urbanization and global warming, extreme heat events occur frequently, endangering urban dwellers' health. Urban parks could alleviate the severe urban heating climate. ...However, due to the scarcity of urban land, it is impractical to plan and design urban parks by increasing the blue-green space without restriction. Few studies have focused on optimization and the equity of the parks' cooling service. This study quantifies four cooling indicators of urban parks in Wuhan city, park's cooling intensity (PCI), park's cooling area (PCA), park's cooling gradient (PCG), and park's cooling efficiency (PCE), analyze the drivers for four indicators, discuss different cooling bundles (urban parks with similar specific cooling ability are grouped into bundles) for the specific heat mitigation demands, and map the spatial accessibility for residents to parks' PCA using spatial network analysis. We find that 54 of 60 urban parks have significant cooling effect, with average PCI of 3.5 ± 0.2 °C, PCA of 131.6 ± 29.6 ha, PCG of 17.9 ± 1.5 °C/km, PCE of 4.5 ± 0.8. Blue and green infrastructure inside parks and impervious surface ratio surrounding the parks play significant roles in cooling service. Larger urban parks usually have larger PCA, but lower PCG and PCE. Five cooling bundles clustered with specific dominant cooling indicators could be references for the specific demand considering tradeoffs in urban parks' design and planning. Taking one step further, we unmask the unequal accessibility of the urban parks cooling service in one extreme heat day: 83.6% of the residents in the central area can enjoy the urban parks' cooling service within 30-min walk, while most residents (74.4%) in suburbs are not able to access to the cooling service within 30-min walk. Our study should be valuable for the urban planning and practice to find heat mitigation solutions and improve residents' heat comfort, also helpful for local municipalities to consider the urban parks' service provision for marginal groups.
•The cooling effect of parks within Wuhan was 3.5 ± 0.2 °C in an extreme heat event.•Blue and green infrastructure inside parks play vital roles in cooling service.•Small comprehensive parks have efficient cooling effect with high land scarcity.•Urban parks' service provision should be considered for marginal groups.
Coupon test specimens with the gauge length part of Q460D high-strength steel or ER55-G weld respectively were heated up to high temperature of 900 °C and then cooled in water. Uniaxial tensile tests ...were conducted on those cooled specimens. The engineering stress-engineering strain curves were obtained. Meanwhile, twelve smooth round bar specimens made of Q460D high-strength steel and ER55-G welds were heated up to high temperature of 900 °C and then cooled naturally or cooled in water. Cyclic loading tests with two different loading protocols, namely constant amplitude and variable amplitude, were conducted on these specimens at different strain levels. The engineering stress-engineering strain curves of each specimen were obtained, enabling to compare and analyze the differences of the results in cyclic mechanical properties of each specimen in terms of damage morphology, hysteresis performance, and ductility characteristics. The test results show that the different cooling methods after the high temperature of 900 °C have a significant impact on the ultimate strength and elongation of Q460D high-strength steel and ER55-G welds. The ultimate strength of the specimens after water cooling was significantly higher than that of the specimens after natural cooling, while the elongation result was opposite. It was obvious from the test results that water cooling and natural cooling after high temperature led to a decrease in ductility and energy absorption capacity of the base metal and welds to various degrees, while their energy dissipation capacity was significantly improved at low strain level.
•Coupon tests were conducted on specimens after high temperature and water cooling.•Mechanical properties of Q460D steel after 900 °C and water cooling were obtained.•Cyclic tests were conducted on smooth round bars after high temperature and cooling.•Cyclic engineering stress-engineering strain curves of Q460D steel were obtained.•Cyclic mechanical properties of specimens after high temperature were analyzed.
► A brief overview of PCM solutions for buildings is provided. ► Some weaknesses of existing PCM solutions for buildings were identified. ► New solutions for PCM integration in buildings are ...proposed. ► Proposed solutions overcome identified weaknesses of existing solutions.
The use of night cooling ventilation in addition of phase change materials (PCMs) is a very powerful strategy for reducing the cooling demand of buildings. Nevertheless, there are inherent drawbacks in the way things have been doing so far: (a) The limited area of contact between PCM and the air; (b) the very low convective heat transfer coefficients which prevents the use of significant amounts of PCM and (c) the very low utilization factor of the cool stored due to the large phase shift between the time when cool is stored and time when it is required by the building. In this paper, we present innovative solutions using PCM to overcome the above situation. Compared with existing solutions, innovative solutions proposed, increase the contact area between PCM and air by a factor of approximately 3.6, increase the convective heat transfer coefficient significantly, and improve the utilization factor due to the inclusion of active control systems which allow the cold stored be actually used when required.
•Urban parks averagely cool down 2.34 ± 0.07 °C, 151.43 ± 4.39 m.•Urban parks’ cooling effect accumulates to 108.55 °C • m.•Suburb residents have more difficulty accessing parks’ cooling services.
...The rapid urbanization process has given rise to urban heating problem and social stratification, prompting calls to evaluate and improve the quality and equity of parks’ cooling service. Our study quantified cooling effect of 1,337 parks from both maximum and accumulation perspectives and investigated cooling accessibility through network analysis in 26 cities of Yangtze River Economic Belt (YREB), China's largest sustainability experiment. 1,189 (88.93%) parks showed significant cooling effect. On average, per park cooled down 2.34 ± 0.07 °C and 40.34 ± 1.17 ha, which was more than four times park area. The accumulative cooling intensity and gradient averaged at 108.55 ± 3.15 °C • m and 0.64 ± 0.02 °C, respectively. Our study also uncovered inequity in cooling accessibility in hot summers, as about 40.3% residents could not access to parks’ cooling service within 30-min walk. Suburban residents had more difficulty accessing to parks’ cooling services. This study can guide greater planning and design of parks to move toward a more equitable and livable direction across different urbanization hierarchy cities.
