Air quality influenced by urban heat island coupled with synoptic weather patterns

Few studies have discussed the association between the urban heat island (UHI) phenomenon and air quality under synoptic weather patterns conducive to UHI. In this study, the authors used statistical analyses to study this association in the Taichung metropolis region. The air quality data obtained from government-owned observation stations and wind field profiles obtained from tethersonde monitoring (performed during 21-29 October 2004) were combined with the simulations of the horizontal wind fields at different heights by the air pollution model (TAPM).The results show that certain specific synoptic weather patterns worsen the air quality and induce the UHI phenomenon: Taichung's UHI appears clearly under the synoptic weather patterns featuring light air or breezes (0.56 m/s ≤ wind speed < 2.2 m/s) mainly from the north and west. Furthermore, under these weather patterns, the concentrations of air pollutants (NO₂, CO₂ and CO) increase significantly (P < 0.05) with the UHI intensity. The convergence usually associated with nocturnal UHI causes the accumulation of O₃ precursors, as well as other air pollutants, thereby worsening the air quality at that time and also during the following daytime period.     

Feasibility study of a novel dew point air conditioning system for China building application

The paper investigated the feasibility of a novel dew point evaporative cooling for air conditioning of buildings in China regions. The issues involved include analyses of China weather conditions, investigation of availability of water for dew point cooling, and assessment of cooling capacity of the system within various regions of China. It is concluded that the dew point system is suitable for most regions of China, particularly northern and west regions of China where the climate is hot and dry during the summer season. It is less suitable for Guangzhou and Shanghai where climates are hot and humid. However, an air pre-treatment process involving a silica-gel dehumidification will enable the technology to be used for these humid areas. Lower humidity results in a higher difference between the dry bulb and dew point of the air, which benefits the system in terms of enhancing its cooling performance. Tap water has adequate temperature to feed the system for cooling and its consumption rate is in the range 2.6–3 litres per kWh cooling output. The cooling output of the system ranges from 1.1 to 4.3 W per m³/h air flow rate in China, depending on the region where the system applies. For a unit with 2 kW of cooling output, the required air volume flow rate varies with its application location and is in the range 570–1800 m³/h. For a 50 m² building with 60 W/m² cooling load, if the system operates at working hours, i.e., 09:00 to 17:00 h, its daily water consumption would be in the range of 60–70 litres. Compared with mild or humid climates, the dry and hot climates need less air volume flow rate and less water.     

宁波轨交沿线不同深度土体温度变化规律观测

通过对宁波平原轨交沿线不同地段的7处土体地温观测点研究,得到宁波平原不同深度土体温度的变化规律及地层的恒温层位置,并初略确定气温对土体温度的影响下限深度。观测结果表明:宁波平原地表以下5 m范围内土体温度受气温影响很敏感,5~10 m影响不敏感,10~25 m影响很小,一般10 m以后趋于稳定,土体温度范围为18.3~19.7℃之间。观测研究结果,可为宁波轨交车站和区间隧道设计时结构温度应力、暖通设计等提供所需参数。     

A fieldwork study on the diurnal changes of urban microclimate in four types of ground cover and urban heat island of Nanjing,China

Records of the past years showed that the climate of built-up regions differs significantly from rural regions and one of the most obvious and important modifying effects of urbanization on local climate is the urban heat island (UHI). In this paper, four types of land cover, namely urban bare concrete cover, urban woods or the shade of trees, urban water areas and urban lawn, were selected to study their microclimate, and the UHI was also analyzed using air temperature data measured at four fixed observation spots in Nanjing, China, during hot weather from July to September, 2005. Dry and wet bulb temperature data were obtained by whirling psychrometers, and wind speed data by cup anemometers. Our observed data focused on the detailed statistical analysis of the microclimate variation in the four types of land cover during the whole day. The results showed that: (1) the microclimate of these four types of land cover had significant differences among different observation sites. In general, the air temperature of these four types of land cover complied with the order during daytime: bare concrete cover>lawn>water areas>woods or the shade of trees, with reversed order during nighttime when the air temperature of the lawn became the lowest. Compared with the bare concrete cover, the other three types of land cover showed the effect of dropping air temperature ranging between 0.2 and 2.9 °C. There were some instant dynamic characteristics in detailed temporal series among these four types of cover in the different observation sites. (2) The UHI effect could be detected obviously by the air temperature difference between the urban center area and the rural area. The average UHI intensity during the monitoring period was between 0.5 and 3.5 °C; however, there were also significant day-to-day variations. A strong UHI effect usually occurred around midnight; while about 2–3 h after sunrise the UHI began to decrease till midday time; and during 13:00–15:00, the UHI effect had a sudden increase and then decreased again; after sunset, a peak UHI effect was frequently observed during 18:00–21:00. (3) Finally, by means of the standard deviation (SD), this paper provides a concise and comprehensive understanding for the temporal and spatial microclimatic dynamics of these four kinds of urban cover in the four observation sites. Air temperature at the height of 1.5 m in Nanjing showed that the nocturnally horizontal temperature gradient was somewhat different from that reported in other large cities, and a marked heterogeneity in a smaller ground cover scale could be detected from the microclimatic spatial pattern. There is no doubt that the analysis of these four types of land cover presents the insight into possible countermeasures to decrease the high air temperature in hot summers, and is relevant to the urban planning redevelopment.     

室外热环境评价指标湿球黑球温度简化计算方法

针对室外热环境评价指标湿球黑球温度在实测和数值计算中都比较难获得的问题,在湿热地区广州夏季收集了空气干球温度、湿球温度、黑球温度、相对湿度、风速、太阳辐射和湿球黑球温度等数据,对收集的数据进行相关性分析和回归分析,相关性分析结果表明：空气温度、相对湿度、太阳辐射与湿球黑球温度具有一定的线性相关度,可以采用上述三个气象因子作为湿球黑球温度的简化计算参数;回归分析结果表明：回归的关联式与实测湿球黑球温度的相关性较高,并且满足多元线性回归的各项检验,认为该回归方程具有较高的可信度,可以在城市热环境的实测评价和数值预测过程中,作为湿球黑球温度的简化计算方法应用。     

青藏直流输电工程粗粒冻土地基温度监测与分析

为分析青藏直流输电线路工程冻土地基的冻结情况及其对基础安全稳定性的影响,在青藏高原五道梁地区对装配式原型基础冻土地基进行1个冻融过程的地温监测,结合该地区气温资料,分析粗粒冻土地温随时间变化特点和沿深度分布情况。监测结果显示：地温呈周期性波动,振幅随深度增加而减小,原状和回填冻土地基上部均存在冻融状态交替的冻融活动层;监测期内基础底部冻土处于冻结状态,基础安全稳定;原状和回填冻土最大融化深度分别为3.0和3.2 m,通过建立地温估算公式,并利用地温变化幅值、均值等结果,得到原状多年冻土上限为3.1 m,与工程勘测和监测结果一致;建立冬季时高孔隙率回填冻土地基传热方程,分析地基传热性能和与孔隙率直接相关的地基中空气自然对流速度对地基回冻的影响。研究表明：冻土回填扰动加剧地温波动的振幅和增大冻土融化深度,但影响程度和范围有限;输电线路冻土装配式基础冬季施工,在冻融活动层深度内保持地基适当孔隙率,既可在冬季加速地基回冻,又可利用土体自然固结和融沉,提高压实度,从而在暖季减弱热量向地基深部扩散,有利于地基保持冻结。     

Modeling the thermal performance of an aquaculture pond heating with greenhouse

A transient analytical model is presented to study the effectiveness of an even shape greenhouse used for heating the aquaculture pond during extreme winters. The model was solved for the climatic conditions of Delhi (Latitude: 28°35′N), representing the northern India (comprising the states of Haryana, Punjab, Uttarakhand and Himachal Padesh) for the typical day (20th January) of winter. A simple trapezoidal design of aquaculture pond is proposed. Parametric studies involved the effects of length, breadth, depth, inclination of lining of fishpond, depth of water and air change in the greenhouse on the water heating in the fishpond. The performance of fishpond was assessed in terms of temperature gain, mean thermal efficiency and thermal load leveling. The optimum parameters for fishpond were 30 m length, 16 m breadth, 1.25 m depth, 1.0 m water depth, 75° lining inclination, and 8 air changes per hour for maximum temperature gain, maximum thermal efficiency and minimum thermal load leveling. A 20 °C rise in water temperature could be achieved during the day and 11 °C in the month of January. The maximum heat gain and loss are at around 16:00 and 7:00 h of the days, respectively.     

中美设计规范中场地分类和场地效应的比较

主要研究中美抗震设计中的场地分类和考虑场地效应的差异问题。首先,比较分析了一般场地、20 m深度范围内含软弱夹层场地、20 m深度以下含软弱土层场地的分类结果,发现FEMA450的场地分类对20m深度范围内软弱夹层厚度的反映比GB50011—2001更敏感,对20 m深度以下软弱土层厚度的考虑比GB50011—2001更细致。然后进行了不同场地、不同地震动水平下的反应谱比较,结果表明,FEMA450更合理地考虑了不同地震动特性下的场地效应。     

Predicting blood lead levels from current and past environmental data in Europe

The present case study on lead in Europe illustrates the use of the Integrated Monitoring Framework Strategy to assess the health outcome of environmental pollution by evaluating the associations between lead in various environmental compartments (air, soil, dust, drinking water and diet) and lead concentrations in blood (B-Pb) for various age-related sub-populations. The case study was aimed to investigate whether environmental, exposure and biomonitoring data at general population level, covering all EU member states, could be integrated. Although blood lead has been monitored extensively in Europe, consistent datasets are not yet available. Data diverge with regard to objectives, regional scale, sampling years, gender, age groups and sample size.Significant correlations were found between B-Pb and the concentrations of Pb in air and diet. The significant decrease of the Pb in air over time from 0.31 μg/m³ (P95: 0.94; n = 98) prior to 1990 to 0.045 μg/m³ (P95: 0.11; n = 256) in 2007 (latest observations included) (Δ = − 85%) corresponds to a decline in B-Pb by 48% and 57% in adult women and adult men, respectively. For pre-school children a more shallow decline in B-Pb of 16% was calculated over the same period. Similarly, the reduction in Pb-dietary intake from on average 68.7 μg/d (P95: 161.6; n = 19) in 1978 to 35.7 μg/d (P95: 82.3; n = 33) in the years post 2000 (Δ = − 48%) is paralleled by a decline in B-Pb of 32, 33 and 19% in adult women, primary- and pre-school children, respectively. Insufficient data exist for other age groups to calculate statistically significant correlations.Although regression models have been derived to predict B-Pb for different sub-populations in Europe based on Pb concentrations in air and soil as well as dietary intake, it is concluded that the available data are insufficient to accurately predict actual and future simultaneous exposure to Pb from various environmental compartments, and as a consequence the health impact of Pb for various target populations at EU scale. At least due to data availability, air Pb remains the best predictor of B-Pb in the population. However, lead emission sources have largely been reduced and inhalation of lead in air is not causal to B-Pb levels. Therefore, there is a need of adequate data for Pb in soil and house dust, and in diet and drinking water as these are causal exposure sources with a longer Pb half-life than air. An extended and more harmonized surveillance system monitoring B-Pb, especially in children, is urgently required in order to identify, quantify and reduce still remaining sources of Pb exposure.     

Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling

In this paper, numerical analyses of the thermal performance of an indirect evaporative air cooler incorporating a M-cycle cross-flow heat exchanger has been carried out. The numerical model was established from solving the coupled governing equations for heat and mass transfer between the product and working air, using the finite-element method. The model was developed using the EES (Engineering Equation Solver) environment and validated by published experimental data. Correlation between the cooling (wet-bulb) effectiveness, system COP and a number of air flow/exchanger parameters was developed. It is found that lower channel air velocity, lower inlet air relative humidity, and higher working-to-product air ratio yielded higher cooling effectiveness. The recommended average air velocities in dry and wet channels should not be greater than 1.77 m/s and 0.7 m/s, respectively. The optimum flow ratio of working-to-product air for this cooler is 50%. The channel geometric sizes, i.e. channel length and height, also impose significant impact to system performance. Longer channel length and smaller channel height contribute to increase of the system cooling effectiveness but lead to reduced system COP. The recommend channel height is 4 mm and the dimensionless channel length, i.e., ratio of the channel length to height, should be in the range 100 to 300. Numerical study results indicated that this new type of M-cycle heat and mass exchanger can achieve 16.7% higher cooling effectiveness compared with the conventional cross-flow heat and mass exchanger for the indirect evaporative cooler. The model of this kind is new and not yet reported in literatures. The results of the study help with design and performance analyses of such a new type of indirect evaporative air cooler, and in further, help increasing market rating of the technology within building air conditioning sector, which is currently dominated by the conventional compression refrigeration technology.     

Estimating the effects of ambient conditions on the performance of UVGI air cleaners

Ultraviolet germicidal irradiation (UVGI) uses UVC radiation produced by low pressure mercury vapor lamps to control biological air contaminants. Ambient air velocity and temperature have a strong effect on lamp output by influencing the lamp surface cold spot temperature. In-duct UVGI systems are particularly susceptible to ambient effects due to the range of velocity and temperature conditions they may experience. An analytical model of the effect of ambient conditions on lamp surface temperature was developed for three common lamp types in cross flow from a convective–radiative energy balance assuming constant surface temperature. For one lamp type, a single tube standard output lamp, UVC output and cold spot temperature data were obtained under typical in-duct operating conditions. Over an ambient temperature range of 10–32.2 °C and an air velocity range of 0–3.25 m/s, measured cold spot temperature varied from 12.7 to 41.9 °C and measured lamp output varied by 68% of maximum. Surface temperatures predicted by the heat transfer model were 6–17 °C higher than corresponding measured cold spot temperatures, but were found to correlate well with cold spot temperature via a two-variable linear regression. When corrected using this relationship, the simple model predicted the cold spot temperature within 1 °C and lamp UVC output within ±5%. To illustrate its practical use, the calibrated lamp model was employed in a simulation of the control of a contaminant in a single-zone ventilation system by an in-duct UVGI device. In this example, failure to account for the impact of ambient condition effects resulted in under-prediction of average space concentration by approximately 20% relative to a constant output system operating at maximum UVC output.     

PCB dry and wet weather concentration and load comparisons in Houston-area urban channels

All 209 PCB congeners are quantified in water in both dry and wet weather urban flows in Houston, Texas, USA. Total water PCBs ranged from 0.82 to 9.4 ng/L in wet weather and 0.46 to 9.0 ng/L in dry. Wet weather loads were 8.2 times higher (by median) than dry weather with some increases of over 100-fold. The majority of the PCB load was in the dissolved fraction in dry weather while it was in the suspended fraction in wet weather. Dissolved PCB loads were correlated with rain intensity and highly developed land area, and a multiple linear regression (MLR) equation was developed to quantify these correlations. PCA generated five PCB components with nearly all positive loadings. They were interpreted as DOC-associated A1248, wet weather primarily suspended fraction A1254/A1260 likely from building sealants, truly dissolved-associated wastewater dechlorination, watershed-sourced PCB 11, and monochlorinated PCBs (likely connected to a different state or source of dechlorination). The PCB 11 component was statistically higher in wet versus dry weather when no other component showed such clear distinctions. Hierarchical cluster analysis (HCA) did not always group dry and wet weather samples from the same location together illustrating the different congener composition that often exists between dry and wet conditions. Four wet weather samples from high percentage developed land (> 90%) watersheds had nearly the same fingerprint suggesting a generic “urban” signature in runoff, which in this case was caused by residual A1254/A1260 PCB stocks and currently produced PCB 11 in consumer goods.     

Biophysical properties and thermal performance of an intensive green roof

Green roofs have been increasingly enlisted to alleviate urban environmental problems associated with urban heat island effect and stormwater quantity and quality. Most studies focus on extensive green roofs, with inadequate assessment of the complex intensive type, subtropical region, and thermal insulation effect. This study examines the physical properties, biological processes, and thermal insulation performance of an intensive green roof through four seasons. An experimental woodland installed on a Hong Kong building rooftop was equipped with environmental sensors to monitor microclimatic and soil parameters. The excellent thermal performance of the intensive green roof is verified. Even though our site has a 100 cm thick soil to support tree growth, we found that a thin soil layer of 10 cm is sufficient to reduce heat penetration into building. Seasonal weather variations notably control transpiration and associated cooling effect. The tree canopy reduces solar radiation reaching the soil surface, but the trapped air increases air temperature near the soil surface. The substrate operates an effective heat sink to dampen temperature fluctuations. In winter, the subtropical green roof triggers notable heat loss from the substrate into the ambient air, and draws heat upwards from warmer indoor air to increase energy consumption to warm indoor air. This finding deviates from temperate latitude studies. The results offer hints to optimize the design and thermal performance of intensive green roofs.     

Thermal comfort for naturally ventilated residential buildings in Harbin

This field study was conducted during summer 2009 in Harbin, northeast of China in order to investigate human responses to the thermal conditions in naturally ventilated residential buildings in cold climate. We visited 257 families in six residential communities and collected 423 sets of physical data and subjective questionnaires. The neutral temperature is 23.7 °C, with the clothing insulation of 0.54 clo. The neutral temperature in Harbin is lower than neutral temperatures in warm climates by others, which is in accordance with the thermal adaptive model. 80% of the occupants can accept the air temperature range of 21.5-31.0 °C, which is wider than the summer comfort temperature limits by the adaptive model. The preferred temperature range fell between 24.0 °C and 28.0 °C. About 57.9% of the subjects voted “no change” with the humid range of 40% and 70%. 61.5% of the occupants voted “no change” with the air velocity within the range of 0.05-0.30 m/s. In summer, occupants preferred air velocity of lower than 0.25 m/s even at higher indoor temperature, which is different from the other field studies. The Harbin occupants in naturally ventilated dwellings can achieve thermal comfort by operable windows instead of running air-conditioners.     

The effects of climate change on energy consumption of cooling systems in Tehran

Energy consumption in buildings is heavily affected by climate change. It causes significant variations of the outdoor design conditions, cooling and heating loads. In this paper, a total of 40 years (1967-2006) of hourly temperature data were considered in four decades and outdoor design conditions for each decade were calculated. It was found that wet-bulb temperature (WBT) has increased by 3.28 °C during the mentioned period, which impacts on design and selection of the cooling equipment. The results show that cooling hours is projected to increase around 15% over the whole 1967-2006 period. The most important result found in this study is the inability of direct evaporative cooling (DEC) systems in preparing comfort condition after 1997, whereas these systems provided thermal comfort in Tehran's buildings from 1967 to 1996. The prediction of climate change impacts on the outdoor design conditions and cooling systems performance until 2020 demonstrates dry bulb temperature (DBT) and WBT increase 1.05 °C and 2.42 °C respectively. Hence, indirect-direct evaporative cooling systems (IDEC) may not be responsible for the years after 2016. Besides, the additional energy for absorption and vapor compression (VC) cooling systems will grow quickly in the future.     

Selection of typical weather data (test reference years) for Subang,Malaysia

The paper discusses methods of selecting typical weather data and describes the selection of test reference years (TRYs) for Subang, Malaysia. The TRYs were selected using the Finkelstein–Schafer statistic, from 19 years of meteorological data recorded during the period 1980-98. Changing the weighting of the various meteorological variables (dry bulb temperature, solar radiation, relative humidity and wind speed) in the range appropriate for building performance studies had little effect on the selection, so it is recommended that equal weightings should be used unless there are particular reasons for using some other weighting. The replacement of relative humidity by moisture content had little effect on the selection.     

Thermal effect of temperature gradient in a field environment chamber served by displacement ventilation system in the tropics

The effect of vertical air temperature gradient on overall and local thermal comfort at different overall thermal sensations and room air temperatures (at 0.6 m height) was investigated in a room served by displacement ventilation system. Sixty tropically acclimatized subjects performed sedentary office work for a period of 3 h during each session of the experiment. Nominal vertical air temperature gradients between 0.1 and 1.1 m heights were 1, 3 and 5 K/m while nominal room air temperatures at 0.6 m height were 20, 23 and 26 °C. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative humidity at 0.6 m height was maintained at 50%. It was found that temperature gradient had different influences on thermal comfort at different overall thermal sensations. At overall thermal sensation close to neutral, only when room air temperature was substantially low, such as 20 °C, percentage dissatisfied of overall body increased with the increase of temperature gradient. At overall cold and slightly warm sensations, percentage dissatisfied of overall body was non-significantly affected by temperature gradient. Overall thermal sensation had significant impact on overall thermal comfort. Local thermal comfort of body segment was affected by both overall and local thermal sensations.     

Profile storage of organic/inorganic carbon in soil: From forest to desert

Understanding the distribution of organic/inorganic carbon storage in soil profile is crucial for assessing regional, continental and global soil C stores and predicting the consequences of global change. However, little is known about the organic/inorganic carbon storages in deep soil layers at various landscapes. This study was conducted to determine the soil organic/inorganic carbon storage in soil profile of 0-3 m at 5 sites of natural landscape from forest to desert. Landscapes are temperate forest, temperate grassland, temperate shrub-grassland, temperate shrub desert, and temperate desert. Root mass density and carbon contents at the profile were determined for each site. The results showed that considerable decrease in root biomass and soil organic carbon content at the soil profile of 0-3 m when landscape varied from forest to desert along a precipitation gradient, while soil inorganic carbon content increased significantly along the precipitation gradient. Namely, for density of soil organic carbon: forest > grassland > shrub-grassland > shrub desert > desert; for density of soil inorganic carbon: forest, grassland < shrub-grassland < shrub desert < desert (P < 0.05 in all cases). In landscapes other than forest, more than 50% soil carbon storage was found in 1-3 m depth. For grassland and shrub-grassland, the contribution from 1-3 m was mainly in the form of organic carbon, while for shrub desert and desert the contribution from this depth was mainly in the form of inorganic carbon. The comparison of soil C storage between top 0-1 m and 1-3 m showed that the using top 1 m of soil profile to estimate soil carbon storages would considerably underestimate soil carbon storage. This is especially true for organic soil carbon at grassland region, and for soil inorganic carbon at desert region.     

Prediction of room temperature and relative humidity by autoregressive linear and nonlinear neural network models for an open office

In this study, a linear parametric autoregressive model with external inputs (ARX) and a neural network-based nonlinear autoregressive model with external inputs (NNARX) are developed to predict the thermal behaviour of an open office in a modern building. External and internal climate data recorded over three months were used to build and validate models for predicting dry bulb temperature and relative humidity for different time-scales (30 min to 3 h ahead). In order to compare the accuracy for different step-ahead predictions, different performance measures, such as goodness of fit, mean squared error, mean absolute error and coefficient of determination between predicted model output and real measurements, were calculated. For the NNARX model, the optimal network structure after training, is subsequently determined by pruning the fully connected network using the optimal brain surgeon strategy. The results demonstrate that both models provide reasonably good predictions but the nonlinear NNARX model outperforms the linear ARX model. These models can both potentially be used for improving indoor air quality by focusing on building intelligence into the controller in HVAC plants, in particular, adaptive control systems.     

蒸发冷却在我国不同区域地下工程中的适用性分析

以送风状态点的干球温度、湿球温度及含湿量为基准,建立了蒸发冷却适用区域的6区模型,并以室内状态点的上限值作为送风状态点,分别以夏季空调室外设计参数、地下工程夏季空调设计参数、夏季空调干球温度及不满足200 h含湿量作为室外状态设计参数,计算并分析了各种形式的蒸发冷却系统在我国不同区域地下工程中的适用性,为蒸发冷却在地下工程中的应用提供基本设计依据。