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Pressing problems in urban ventilation and thermal comfort affecting pedestrians related to current urban development and densification are increasingly dealt with from the perspective of climate change adaptation strategies. In recent research efforts, the prime objective is to accurately assess pedestrian-level wind (PLW) environments by using different simulation approaches that have reasonable computational time. This review aims to provide insights into the most recent PLW studies that use both established and data-driven simulation approaches during the last 5 years, covering 215 articles using computational fluid dynamics (CFD) and typical data-driven models. We observe that steady-state Reynolds-averaged Navier-Stokes (SRANS) simulations are still the most dominantly used approach. Due to the model uncertainty embedded in the SRANS approach, a sensitivity test is recommended as a remedial measure for using SRANS. Another noted thriving trend is conducting unsteady-state simulations using high-efficiency methods. Specifically, both the massively parallelized large-eddy simulation (LES) and hybrid LES-RANS offer high computational efficiency and accuracy. While data-driven models are in general believed to be more computationally efficient in predicting PLW dynamics, they in fact still call for substantial computational resources and efforts if the time for development, training and validation of a data-driven model is taken into account. The synthesized understanding of these modeling approaches is expected to facilitate the choosing of proper simulation approaches for PLW environment studies, to ultimately serving urban planning and building designs with respect to pedestrian comfort and urban ventilation assessment., Architectural Intelligence, 1 (1), ISSN:2731-6726

A CFD based procedure is described to identify the optimum inclination angle of a small-scale roof-top solar chimney for maximum ventilation performance. The absorber wall of the chimney under consideration is 500-mm long and the air gap width is 40 mm. Firstly, CFD simulations are performed on a two-dimensional solar chimney model with inclination angles varying from 30° to 90° relative to the horizontal plane under different heat fluxes. Subsequently, a mathematical procedure using the CFD data to estimate the ventilation performance of the solar chimney at different inclination angles under real climate conditions is described. The procedure accounts for the effect of the inclination angle on receivable solar irradiance and is applied to three Australian cities, corresponding to three different latitudes. It is found that the optimum inclination angle varies from 45° to 60°, depending on the latitude and season of operation.

A COVID-19 outbreak occurred in May 2020 in a public housing building in Hong Kong - Luk Chuen House, located in Lek Yuen Estate. The horizontal cluster linked to the index case' flat (flat 812) remains to be explained. Computational fluid dynamics simulations were conducted to obtain the wind-pressure coefficients of each external opening on the eighth floor of the building. The data were then used in a multi-zone airflow model to estimate the airflow rate and aerosol concentration in the flats and corridors on that floor. Apart from flat 812 and corridors, the virus-laden aerosol concentrations in flats 811, 813, 815, 817 and 819 (opposite to flat 812, across the corridor) were the highest on the eighth floor. When the doors of flats 813 and 817 were opened by 20%, the hourly-averaged aerosol concentrations in these two flats were at least four times as high as those in flats 811, 815 and 819 during the index case's home hours or the suspected exposure period of secondary cases. Thus, the flats across the corridor that were immediately downstream from flat 812 were at the highest exposure risk under a prevailing easterly wind, especially when their doors or windows that connected to the corridor were open. Given that the floorplan and dimension of Luk Chuen House are similar to those of many hotels, our findings provide a probable explanation for COVID-19 outbreaks in quarantine hotels. Positive pressure and sufficient ventilation in the corridor would help to minimise such cross-corridor infections.

Thermal energy storage (TES) is an important means for the conservation and efficient utilization of excessive and renewable energy. With a much higher thermal storage capacity, latent heat storage (LHS) may be more efficient than sensible heat storage. Phase change materials (PCMs) are the essential storage media for LHS. PCM emulsions have been developed for LHS in flow systems, which act as both heat transfer and thermal storage media with enhanced heat transfer, low pumping power, and high thermal storage capacity. However, two major barriers to the application of PCM emulsions are their instability and high degree of supercooling. To overcome these, various strategies have been attempted, such as the reduction of emulsion droplet size, addition of nucleating agents, and optimization of the formulation. To the best of our knowledge, however, there is still a lack of review articles on fabrication methods for PCM emulsions or their latest applications. This review was to provide an up-to-date and comprehensive summary on the effective strategies and the underlying mechanisms for the preparation of stable PCM emulsions and reduction of supercooling, especially with the organic PCMs of paraffin. It was also to share our insightful perspectives on further development and potential applications of PCM emulsions for efficient energy storage.

This study aims to develop a fast-response sulfur hexafluoride (SF6 ) measuring system, and evaluate its performance in tracer gas measurements for studying transient airborne contaminant transport. The new system is based on a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor using a quantum cascade laser. Transient SF6 tracer gas measurements were carried out in an environmental chamber with an instantaneous source using both the QEPAS system and a traditional commercial instrument. Real-time SF6 concentrations, peak SF6 concentrations and average SF6 concentrations for one room time constant under two air change rates obtained by the two instruments were compared. The results show that the QEPAS system, which features a 0.4 s data acquisition interval, can provide detailed real-time SF6 concentrations even when the concentration is changing rapidly. The QEPAS system successfully captured the peak SF6 concentrations for all the studies cases, while commercial instrument failed in most studied cases. In most of the cases, the two instruments obtained similar average SF6 concentrations for one room time constant. However, when the concentration was in rapid change, the two systems would report significantly different results. The QEPAS system can be potentially applied in transient tracer gas measurements under complex scenarios.

In environments with similar physical parameters, thermal comfort and sensation feelings may differ indoors and outdoors. How indoor and outdoor thermal perception differ from each other remains unclear. This study compared and discussed 29,536 field survey data, including 19,191 sets of indoor data, and 10,345 sets of outdoor data, covering five Köppen climate zones during transitional seasons and summer. Indoor data points were collected from two databases: the ASHRAE Global Thermal Comfort II and the SCATs (Smart Controls and Thermal Comfort), while outdoor data points were collected from the RUROS database (Rediscovering the Urban Realm and Open Spaces) and five individual projects executed in Singapore, Hong Kong, Guangzhou, Changsha, and Tianjin. The concepts of neutral rate (NR) and comfort rate (CR) were developed to help categorize "neutral" and "comfort" across different studies. The results of this study show that people are less sensitive to changes in thermal environment outdoors than indoors. Moreover, thermal comfort cannot be simply treated as thermal neutral, particularly for outdoor spaces. Compared with MM (mixed-mode) and NV (naturally ventilated) spaces, outdoor space does not have the highest NR, but its CR is much higher, with a wide range of SET* (Standard Effective Temperature) corresponding to CR over 80 %, from 15.5 °C to 23.4 °C. In the Cfa (humid subtropical) climate zone, significantly higher CR are recorded for outdoor spaces, although the NR are similar or even lower than those of indoors. Natural thermal resources in the outdoor thermal environment may hold the key to extending indoor comfort ranges.

This study aims to develop a fast-response sulfur hexafluoride (SF

PTHs are massively deployed for disaster-relief after various natural disasters. Following a previous experimental study on applying PCMs to an experimental PTH, where only a very limited number of designs were experimentally examined, in this paper, different designs of applying PCMs to a disaster-relief PTH were numerically examined and the best one identified for guiding future practical applications. A numerical model for a full-scale PTH was established using EnergyPlus and experimentally validated. Using the validated model, a two-part numerical study was carried out. In the first part, a total of 16 different designs were defined and D10 identified as the most effective one, resulting in the highest number of acceptable hours at 90. In the second part, increasing PCM's thickness to beyond 20 mm would lead to negligible effects on further improving indoor thermal environment. Hence, 20 mm thickness was recommended as a reference value for future practical applications. Furthermore, the developed EnergyPlus based model for the experimental PTH may be adapted for other types of PTHs used in different climates. Hence, the outcomes of the numerical study may also guide the future applications of PCM to disaster-relief PTHs of various configurations, and located in different climates.

We assessed whether increasing airflow with an electric fan is similarly effective as decreasing air temperature with air cooling (AC) in preventing heat-related reductions in productivity, and elevations in body temperatures and discomfort in a warm/humid indoor environment. In 48 experimental trials, we compared the reduction in the human heat stress response of sixteen participants during 135 min of intermittent arm ergometry at a fixed heart rate of 110 beats min−1, from a simulated tropical environment (HOT; 30 °C, 70%RH; wind °C, 70%RH, wind °C, 70%RH, wind = 4.2 m s−1). Cumulative work was similarly improved (+11%) by FAN compared to AC. Likewise, reductions in rectal temperature, thermal sensation, and thermal discomfort were similar with the two different cooling strategies. Sweat losses in the FAN trial were higher compared to AC but lower than HOT without fanning. In conclusion, fanning offers an effective method for alleviating thermal stress and preventing productivity losses for workers exposed to environmental heat. Moving air instead of chilling it may require a little more sweating, but it can save electricity and hence lower greenhouse gas emissions compared to AC.

An architectural feature, ‘lift-up’ (or elevated) design, has been reported as an effective design to improve weak pedestrian-level wind (PLW) conditions in a subtropical high-density city. This design provides a semi-outdoor space under the elevated building which allows wind to penetrate through, but the influence of surrounding buildings on its performance has been rarely reported. This study aims to assess the influence of surrounding buildings on the PLW around an elevated building. LES (large eddy simulation) approach is applied after validation against the previous wind tunnel tests. Validation studies have confirmed and proven the accuracy of LES for the simulations, with the correlation coefficients R above 0.89 between the predictions and the experiments. Furthermore, the differences of flow fields are assessed around a single elevated building and a building array with an open space, a building and an elevated building respectively in the centre. Results indicate that wind amplification exists within the semi-outdoor space under the elevated building in all conditions although this effect is partially lowered by the surrounding buildings. The fields of turbulence intensity and gust wind speed around the surrounded elevated building are investigated by LES. These findings can be helpful for using the ‘lift-up’ design to improve wind and thermal comfort at pedestrian level.

Warm and hot days account for most of the time in Hong Kong. Outdoor thermal comfort studies in Hong Kong should give its first consideration to warm and hot days. This study presents investigations about thermal comfort through 1600 human subject responses from the onsite survey with concurrent meteorological parameter measurements. Probit analysis was used for searching the thermal neutral range of Hong Kong residents in a year span. Logistic regression was used for locating the meteorological parameter ranges for thermal neutral and comfort conditions. It is shown that people had difficulties defining their actual thermal feelings near the thermal neutral status when being asked to use the nine-point thermal sensation scale. Obvious thermal adaptation effect for thermal neutral conditions were observed among Hong Kong residents over the seasons in a year. The transitional seasons had a wider thermal neutral range than that of winter and summer. Summer had the narrowest thermal neutral range. Wind and solar radiation had an interaction effect with air temperature in determining thermal sensation and thermal comfort. Wind can effectively offset the negative effect of solar radiation in summer when the air temperature was lower than 31 °C. The thermal comfort condition allowed a higher limit of solar radiation than the thermal neutral condition when the air temperature was lower than 31 °C. The investigations in this study provide some unique insights into the way to assess urban thermal comfort in the building design stage.

The appropriate selection of a turbulence model directly affects the prediction of pedestrian-level wind (PLW) around buildings. Delayed detached eddy simulation (DDES) model, has been reported to be able to predict airflow around a building as good as large eddy simulation (LES) does, but with a lower mesh requirement and much less computing time. This study aims to see if DDES model can perform similarly when simulating the wind flow around a building array. This hypothesis is tested by comparing wind velocities of DDES, LES, and a benchmark wind tunnel experiment. Sensitivity assessments of DDES model are conducted, including the mesh resolution and the choice of an unsteady Reynolds Averaged Navier-Stokes (URANS) model used in conjunction. The normalized minimal grid sizes (0.005 for the building array's windward side and 0.0025 for the lateral and leeward sides) and the unsteady k − ω shear stress transport (SST) model are the most economical and effective. Simulated results are further quantified using four validation indices. Specifically, the correlation coefficient R between the predicted mean velocities using DDES and LES is 0.90, which basically proves our hypothesis in the mean flow field; but DDES only takes 80.3% of the computing time using LES. The time histories and spectrums of instantaneous velocities are also analyzed, indicating that DDES performs the similar predictions as LES of the unsteady flow fluctuations, while it has the potential to save computing time and mesh numbers.

A phase change material (PCM) emulsion was prepared by dispersing the PCM in water with the aid of emulsifiers, which had higher fluidity, higher thermal conductivity, and more flexible volume change than the solid-liquid PCMs. However, a critical issue for their large-scale applications is phase instability due to aggregation and precipitation of the PCM droplets. This work was to develop stable PCM emulsions prepared with n-hexadecane by manipulating the key factors and analyzing the emulsion properties including emulsifier combinations and process conditions, interfacial film properties, droplet size distribution, and rheology characteristics. The stability was further improved with the addition of SiO2 nano-particles. The SiO2 nano-particles also acted as an effective nucleating agent to reduce the degree of supercooling. The thermal performance for potential application in thermal energy storage systems was also examined. Eventually, a novel and highly stable PCM-in-water nano-emulsions with droplets on a scale of tens of nanometers and a transparent appearance was developed for potential application in active thermal energy storage systems.

In disaster relief reconstructions, the severe indoor thermal environment of the prefabricated temporary house (PTH) limits its massive utilization. Here, the application of phase change material energy storage system (PESS) has been proposed in the full-scale experimental PTH. In the experimental investigations, a movable PESS was designed aiming at regulating the indoor environment of the PTH during the daytime in hot summer, by charging the cool energy during the nighttime. The movable PESS revealed positive impacts on the indoor environment regulation in the experimental PTH. In addition, the distance between the PESS and the west wall also had influences on the cool energy discharging of the PESS and the indoor thermal environment of the experimental PTH.

Vertical transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) along a vertical column of flats has been documented in several outbreaks of coronavirus disease 2019 (COVID-19) in Guangdong and Hong Kong. We describe an outbreak in Luk Chuen House, involving two vertical columns of flats associated with an unusually connected two-stack drainage system, in which nine individuals from seven households were infected. The index case resided in Flat 812 (8th floor, Unit 12), two flats (813, 817) on its opposite side reported one case each (i.e., a horizontal sub-cluster). All other flats with infected residents were vertically associated, forming a vertical sub-cluster. We injected tracer gas (SF

Large eddy simulation (LES) is increasingly recognized as an important approach in the assessment of pedestrian level wind (PLW) conditions, while its numerical performance is sensitive to a few key parameter settings. This study aims to further identify the sensitivities to these main influencing parameters in modeling wind flow around a building array using LES. This is achieved by quantitatively comparing mean wind velocities from the LES predictions and those from a benchmark wind tunnel experiment. The parameters investigated are the mesh resolution, discretization time step and sampling period, vortices’ number of the inlet flow, the upstream distance of the computational domain, and the sub-grid scale (SGS) models. Results are quantified using four validation indices. Specifically, the correlation coefficient R between the predicted results using SGS model with the dynamic Smagorinsky-Lilly method and the experimental results is 0.89, which is higher than those between the experiment results and other three SGS models. Based on the sensitivity tests, it is recommended that the normalized discretization time step be set below 0.09, and that the normalized sampling period and vortices’ number be above 219 and 190, respectively, in the LES simulation of PLW flows around a building array.

Latent heat thermal energy storage (LHTES) using phase change material (PCM) has many application potentials, in view of the fact that it has higher thermal energy storage capacity than the sensible heat thermal energy storage such as stratified water storage (SWS). However, the stored thermal energy in an LHTES system is not all effective in discharging due to the additional heat transfer resistance between PCM and heat transfer fluid (HTF). An LHTES system could have a higher effective storage capacity than an SWS system only if it is well designed. The optimal design of an LHTES system could be realized only after the effective energy storage ratio, Est, is analyzed in the design stage. In comparison to the laborious computational analysis method, in this work, we developed an analytical technique from the effectiveness-NTU theory to calculate the required heat transfer length and predict Est of the basic unit in any tube-in-tank LHTES system. The technique was first compared with the numerical simulation method we reported earlier, and then used to find the optimal design under various constraints. It was shown that heat transfer enhancement in PCM could effectively improve the effective storage capacity of an optimal design. However, the maximum Est was limited by the thermal resistance in HTF when the enhancement in PCM was over a certain threshold. It was demonstrated that the use of HTF in a low-Re turbulent region could enhance heat transfer in HTF and achieve an Est as high as that in a laminar region while obtaining a higher discharging rate if heat transfer in PCM was well enhanced. This analysis provided quantitative guidelines on designing optimal tube-in-tank LHTES systems.

Comfortable and healthy outdoor microclimates are beneficial to sustainable urban development. Based on a comprehensive comparison of some currently frequently used thermal comfort indices, including PMV, WBGT, PET, SET*, and UTCI, the differences among these indices are significant in dealing with the fundamental energy balance model, descriptive equations, and application boundary conditions. In order to validate these indices, a subjective questionnaire survey with field measurements was carried out on a university campus in Guangzhou in southern China. Results revealed strong linear relationships between operative temperature and mean radiant temperature (Tmrt), WBGT, PET, SET*, UTCI, as well as PMV. However, the relationships between these thermal comfort indices and the mean thermal sensation vote (MTSV) are not clear for a hot outdoor environment, especially when the operative temperature was above 34 °C. The ranges of the heat stress category and PMV need to be modified for the evaluation of hot outdoor environments.

Cooling load is difficult to predict for a radiant system, because the interaction between a building’s thermal mass and radiation heat gain has not been well defined in a zone with a cooling surface. This study aims to reveal the effect of thermal mass in an external wall on the transmission load in a space with an active cooling surface. We investigated the thermal performances in a typical office building under various weather conditions by dynamic simulation with Energy-Plus. It was found that the thermal mass in the inside concrete layer had positives in terms of indoor temperature performance and energy conservation. The peak cooling load of the hydronic system decreases 28% in the proper operating state, taking into account the effect of the thermal mass in an external wall. Compared to the performances in zones with equivalent convective air systems (CASs), the peak cooling load and the accumulated load of the combined system (radiant system coupled by fresh air system) are higher by 9%–11% and 3%–4%, respectively. The effect of thermal mass is evident in a transient season with mild weather, when the relative effects are about 45% and 60%, respectively, for a building with radiant systems and a building with equivalent CASs.

During disaster relief reconstructions, prefabricated temporary houses (PTHs) have been extensively used for resettling disaster victims. However, due to the nature of disaster relief, PTHs are normally light-weighted, without an electrical thermal environmental control systems installed. Hence, the thermal environments inside these PTHs can become intolerably hot in summer. Therefore, simple and low cost measures should be applied to disaster-relief PTHs for improving their indoor thermal environments. In this paper, an experimental study on applying PCMs to disaster-relief PTHs is reported. Two different designs of applying PCMs were examined. In Design 1, PCMs were fixed to the internal surfaces of a model PTH and the related experimental results demonstrated that both indoor air temperature and internal surface temperature of the model PTH can be reduced at daytime. However, in Design 2, a movable PCM based energy storage system (PESS) was used and the related experimental results suggested the use of the mobile PESS with a total charge of 148.8 kg PCM helped reduce the average indoor air temperature by 3.2–3.6 °C. The experimental results from both Designs suggested that, due to the nature of disaster relief and since outdoor air at a lower temperature may be the only cooling energy source for charging the PCM, a movable PESS system was preferred, so that it can be moved to outdoor at nighttime for being charged with more cooling energy using lower temperature outdoor air not adversely increasing the air temperature inside PTHs.

Lift-up buildings are advantageous in improving the wind circulation in a congested and compact city. However, the wind conditions in the void underneath a lift-up building, also known as the lift-up area, are vital for wind comfort of occupants of lift-up buildings. This study tested 28 lift-up buildings in a boundary layer wind tunnel to assess the influence of key design parameters; height and width of the main structure, and height, width, depth, and the shape of the central core on the wind conditions in the lift-up area. The results of the analyses show a significant influence of building height on the magnitude of wind speeds in the lift-up area while the width of the central core controls the area with low wind speeds. Tall buildings with short lift-up cores have small areas with acceptable pedestrian wind comfort, which can be increased by adopting corner modifications for the central core. The area of acceptable pedestrian wind comfort increases in oblique wind directions as the areas of high (>3.5 m s−1) and low (, Highlights • This study evaluated the influence of design of lift-up buildings on pedestrian wind comfort. • A total number of 28 lift-up buildings were tested in a boundary layer wind tunnel. • Dimensions of the building and the central core differently influenced pedestrian wind comfort. • A second-order, non-linear multivariable regression model was developed to predict pedestrian wind comfort.

People's outdoor thermal sensation varies from that indoors. The highly asymmetric solar radiation and transient wind environment are the main causes. The University of California-Berkeley developed a multi-nodal human body thermal regulation model (the UCB model) to predict human thermal sensation and comfort in asymmetric and transient indoor environments. However, few studies compared its predictions with the survey responses outdoors. In this study, subjects' thermal sensations outdoors were surveyed and compared with the UCB model predictions. Meteorological parameters were monitored using a microclimate station, and over a thousand human subjects were surveyed. Results point out that subjects were highly sensitive to the changes in wind speed, especially under low-radiation conditions. However, the UCB model failed to predict such a high sensitivity. Besides, subjects had a higher tolerance to high air temperatures in outdoor environments when the solar radiation was acceptable, but the UCB model over-predicted the TSV (thermal sensation vote) in such conditions. Both the on-site results and the predictions by UCB model showed that subjects were more sensitive to wind speed in hotter environments while they were least sensitive to solar radiation in neutral thermal conditions. This study helps to reveal the potential of a multi-nodal thermal regulation model to address the asymmetric and transient features of outdoor environments and indicates the need to further refine the model for better quantitative prediction of outdoor thermal sensations.

Stratified water storage (SWS) is of high energy efficiency, but of low energy density as it relies on the sensible heat of water. Latent heat thermal energy storage (LHTES) system using phase change material (PCM) is of higher energy density, and might be an alternative to the bulky SWS system. However, the utilization of latent heat in PCM has been hindered by the low thermal conductivity of PCM. Previous research has demonstrated that high thermal conductivity components, such as metal foam, can be used to enhance the effective thermal conductivity of PCM, keff. In this work, we proposed an index of effective energy storage ratio, Est, to characterize the effective energy storage capacity of an LHTES system with reference to an ideal SWS system of the same volume. A conjugate numerical fluid flow and heat transfer method was first validated and then used to characterize the Est of a tube-in-tank design. The effect of keff on Est was demonstrated. It is shown that there is an optimum compactness factor (CF) for PCM at any finite keff, and that the optimum CF and the corresponding maximum Est are higher for PCM at a higher keff. It is also shown that, even at the optimal CF for PCM at any keff, quite a percentage of the theoretical energy storage capacity is not utilized, indicating that heat transfer enhancement in the fluid side may further improve the Est. This analysis provides implications on an optimal design of LHTES systems.

So far, the research on the convective heat transfer coefficient (hc) in outdoor thermal comfort has mainly employed CFD simulation and wind tunnel experiments, which are difficult to fully restore the complex microclimate wind environment. In the traditional thermal comfort model, the influence of turbulence intensity (TI) on the hc might be underestimated. This study aims to measure the hc of the human body surface in the outdoor environment. A thermal manikin was placed in a lift-up building. The ambient wind speed ranged from 0.5m/s to 4m/s, with the TI ranging from 4% to 55%. The experimental results show that under the same wind speed, the difference in hc between high and low TI can be up to 15%. Based on that, the regression formula for predicting hc related to wind speed and TI was proposed. This experimental study supplements the lack of field measurement of hc in outdoor thermal comfort research, which is helpful to improve the accuracy of the outdoor thermal comfort model.

One of the factors that limit the cooling capacities and application potentials of radiant cooling panels is the condensation risk. The self-condensate-repellency tendency of superhydrophobic surface materials provides a possibility to mitigate the condensation risk. This paper studied the size ranges of condensate drops formed on a superhydrophobic aluminum sheet of the size 25 mm × 25 mm attached to a cooled ceiling panel in a climate chamber in the humidity range between 50% and 80% and at the temperature of 25 °C and air change rates from 0 ACH to 9 ACH. Using an optical magnifier, large drops up to the size 802.5 µm were observed in certain fixed positions in the large view area of 4.08 mm × 3.06 mm under different experimental conditions; whereas in a smaller focused view area of 0.96 mm × 0.72 mm the diameters of the largest drops were found to first increase over time and then reached around 80 µm with occasional size of 152 µm. All these were in contrast with the continuously growing drops simultaneously observed on the ordinary aluminum sheet, which reached 4 mm. The largest size of the droplets in the small focused area increased from 54.1 µm to 151.7 µm as humidity increases from 50% to 80%, but did not change much as the air change rate changed from 0 ACH to 9 ACH. This series of experiments confirm our hypothesis that condensate drop sizes can be limited within the un-perceivable range, namely below the sensory and visual thresholds, in typical indoor conditions because of the droplet jumping mechanism that occurs on the nano-engineered superhydrophobic surface, but it remains to be ascertained whether the large condensate drops formed at certain fixed points in the other parts of the tested nanostructured surface were associated with some defects in the nano-scale, and whether this can be eliminated on a larger area of practical application scale.

With the development of the urban city, increasing attention has been paid to outdoor thermal comfort. In this paper, an analysis of the sensitivities of different factors, including the personal factors and physical parameters of the thermal environment was conducted. The results showed that there was a strong linear relationship between the Physiological Equivalent Temperature (PET) and operation temperature. When the operation temperature was lower than 32 °C, the effect of air velocity on the PET was positive. However, the effects of other factors, including relative humidity, clothing insulation, and metabolic rate, on the PET were insignificant. An exponential relationship was found between the UTCI and the operation temperature. The effect of air velocity change on the UTCI became weaker and weaker with the increase of operation temperature. Compared with the PET, the linear relationship between the UTCI and relative humidity was clearer. A field survey of thermal comfort carried out in Guangzhou University was used for the validation of the thermal comfort models. It was observed that the clothing insulation requirement increased with the decrease of air temperature in autumn. The variations in metabolic rate were also obvious, from 1met to 3.8 met. More than 70% of the people had been walking before they arrived at the survey locations. In addition, there were some differences in the neutral PET and UTCI temperature between the metabolic rates of 1.0–2.0 met and of 2.6 met. Meanwhile, models of MTSV against the PET and UTCI under different metabolic rates were established.

The dual temperature air-source heat pump reduces energy consumption and has wide application potential. A novel dual temperature air-source heat pump (NDAHP) system based on ejector-vapor compression cycle is proposed in this study. The system produces two types of heat sources (high- and low-temperature hot water). A theoretical model describing the performance of the system is established and validated, and the performance indices of the system, including the heating coefficient of performance (COPh), heating capacity per volume (qv), and the second law efficiency (ƞII) are obtained. The above-mentioned indices of the conventional dual temperature air-source heat pump (CDAHP) system and the NDAHP system using various refrigerants (R717, R1234yf, R134a, and R290) are compared. Results show that the NDAHP outperforms the CDAHP under various operating conditions. Compared with the CDAHP, the NDAHP improves the COPh, qv, and ƞII by 20.0% to 48.9% under a typical operating condition. The R290 shows the best performance among the various refrigerants. The performance of the NDAHP system is more sensitive to the evaporating temperature than the condensing temperature. Additionally, the ƞII of the NADHP system is significantly affected by the high-temperature heating load ratio (LR) and increases with the increase of the LR. This study hopes to provide a foundation for further research on the NDAHP systems.

Ongoing urbanization has led to complexities in the urban terrain, increasing roughness length within the atmospheric surface layer, and introduced highly turbulent wind flow at pedestrian height. This research aims to explicitly examine the effect of wind flow turbulence on thermal perception under outdoor conditions. A wind tunnel with passive grid was used to introduce turbulence into simulated wind conditions. Thermal physiological (skin temperature) and perceptual (questionnaire) responses were collected from 20 college-age subjects during the exposures to various simulated urban wind conditions. Results confirm that increased turbulence intensity enhances perceived coolness by reducing the skin temperature. We updated the convective heat transfer coefficient in a numerical skin thermoreceptor model and also Gagge's two-node thermophysiological model so that they both reflect more accurately the effects of turbulence intensity on skin temperature. Skin temperatures simulated with the modified models were in good agreement with experimental observations, and corrected the un-modified model's 30% and 50% underestimation of mean skin temperature decrement for standing and cycling conditions respectively. These findings contribute to the broader goal of a thermal comfort model for application to urban microclimate.