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[Display omitted] • Quantify the effect of local flows on AC cooling demand in a hilly, coastal city. • Downstream UHI could accelerate mountain-induced channel flows by 50.26 % • Channel winds cause heat advection that soar downstream AC load by 2.62 W m−2. • UHI-induced local flows interact with mountains, stagnating the sea-breeze on leeside. • Stagnant sea breeze surges downstream 2-m temperature (AC load) by 0.9 °C (6.41 W m−2) Extreme heat aggravates thermal stress and electricity shortage in urban areas. This study investigates the (circulating) winds in Hong Kong during a heatwave. Unprecedentedly, the collective effect of coastal winds, complex terrain, and local flows on urban temperatures and air-conditioning load intensity (ACLI) is examined using the mesoscale Weather Research and Forecasting (WRF) model. Three representative wind patterns, including urban-accelerated channel wind, channel-wind-induced heat advection, and urban-mountain-stagnated sea-breeze, are analyzed. Our results show that the mountain blockage in foothill areas would increase 2-m temperatures (T 2) and ACLI by 1 °C to 2 °C and 5 W/m2, respectively. ACLI in compact high-rise areas (LCZ 1) is most sensitive to extreme heat. Moreover, the urban heat island (UHI) downstream is crucial that would accelerate channel flows by 1.66 m/sec (50.26 %). On the other hand, terrain-induced channel winds augment heat advection, increasing downstream T 2 (0.7 °C) and ACLI (2.62 W/m2). UHI-induced local flows interact with hilly slopes, stagnating the sea breeze on mountain leeward side. Subsequently, the winds would be slowed down by 0.81 m/sec while the temperature T 2 would be increased by 0.9 °C in downstream urban areas. Eventually, the daytime ACLI could be raised as much as 6.41 W/m2. [ABSTRACT FROM AUTHOR]

Heatwaves threaten human health and power systems. Urban climate is non-stationary and wide-spectrum, with high-frequency temperature and wind-speed variations that could overload power grids and expose people to extreme heat. In this study, Hilbert-Huang transform (HHT) was unprecedentedly used to decompose the urban-scale temperature (IMFθ 1 to IMFθ 6) and wind-speed (IMFW 1 to IMFW 6) signals during a 5-day heatwave event into 6 intrinsic mode functions (IMFs). The spatio-temporal characteristics, physical mechanism, and effective ranges of high-frequency components (IMF1 to IMF4) were unveiled. Temperature (wind speed) IMFθ 1 to IMFθ 4 (IMFW 1 to IMFW 4) had a temporal scale of 2.63 h (2.53 h), 5.88 h (5.78 h), 13.16 h (9.84 h), and 22.72 h (19.05 h); as well as a spatial scale of 2.31 km (0.99 km), 4.29 km (1.65 km), 5.94 km (2.64 km), and 6.6 km (2.97 km), respectively. The physical mechanisms of IMF1 to IMF4 were composed of turbulence and heat storage/release; disturbance induced by mountainous terrain and slope flows; land/sea breeze, together with anthropogenic heat. Besides, the peaked amplitudes of IMFθ 1 were most risky in compact/open high-rise urban (1.4 °C–1.6 °C) rather than rural (0.6 °C–1.0 °C) areas. The foothill areas within 8-km coverage were susceptible to IMFθ 2 (1 °C–2.1 °C). IMFθ 3 (0.6 °C–3.6 °C) was effective in urban areas within 10 km from coastline. IMFθ 4 (2.5 °C–3.5 °C) exhibited the most intense fluctuation in urban/suburban areas. The outcome provides references for policy makers to mitigate heat-related risks. [Display omitted] • HHT is applied to decompose short-term urban climate signals during a heatwave event. • Risky, high-frequency components of temperature and wind speed were extracted. • Spatio-temporal scales of high-frequency meteorological components were examined. • Implication from buildings, terrain, land/sea breeze, and anthropogenic heat to IMFs. • Revealed the effective ranges and susceptible urban areas for high-frequency components. [ABSTRACT FROM AUTHOR]

Reliable energy models are required to predict urban-scale air-conditioning (AC) load under extreme outdoor temperatures which is crucial to power security. In this study, we proposed a new landuse/landcover (LULC) scheme for these models by combining the local climate zones (LCZs) from World Urban Database Access Portal Tools (WUDAPT) and building category (BC) map. Apart from evaluating against the conventional LULC of Moderate-resolution Imaging Spectrometer (MODIS) and WUDAPT, the impact of urban canopy parameters and BC on the simulated meteorological conditions and AC load during the 2016 heatwave in Hong Kong was examined by the Weather Research and Forecasting (WRF) model. Incorporating LCZs (BC) reduced the bias of 2-m temperature (T 2), 2-m relative humidity (RH 2), and AC load intensity by 0.4 °C (2.0 °C), 1.98% (0.68%) and 6.78 W m−2 (13.09 W m−2), respectively. It captured the heterogeneous, intra-urban T 2 and turbulence kinetic energy (TKE). Further sub-classifying the BC in LCZs led to WUDAPT/BC which performed even better and significantly improved WRF output. It simulated well the daytime wind speed, mitigated the overprediction (underprediction) of T 2 (RH 2), and rectified the underpredicted AC load in WUDAPT. Its benefit was prominent in daytime as well as in compact high-rise/mid-rise and open high-rise areas. (200 words). • A new LULC scheme is proposed by combining WUDAPT and building category (BC) data. • WUDAPT/BC is unprecedentedly used to improve WRF reliability. • WUDAPT/BC outperforms WUDAPT and MODIS in urban-climate simulation. • WUDAPT/BC outperforms WUDAPT and MODIS representing intra-urban heterogeneity. • Including BC data reduces the bias of urban-scale air-conditioning load by 54.23%. [ABSTRACT FROM AUTHOR]

The urban moisture island (UMI) can aggravate the thermal stress due to the urban heat island (UHI) in subtropical and tropical cities. In this study, we investigated the spatiotemporal variation patterns of UMI in Hong Kong, a subtropical coastal city, using the fine-resolution mesoscale Weather Research and Forecasting (WRF) model by integrating local climate zone (LCZ) maps based on the World Urban Database and Access Portal Tools (WUDAPT). Our results show that at regional scale, the UMI phenomenon tends to occur in coastal areas, possibly owing to rich moisture sources from sea breeze and inhibited moisture penetration due to barrier effects of mountains. Specifically, an all-day UMI effect was found in coastal low-density low-rise areas (LCZ5&8&10), while a nocturnal UMI effect and a daytime urban dry island (UDI) effect were found in coastal high-density high-rise areas (LCZ1&2). The UDI effect at daytime can be attributed to strong vertical moisture convection associated with intensive surface sensible heat fluxes in a strongly mixed urban boundary layer (UBL). The UMI effect at night can be attributed to blocked ventilation aisle, inhibited dewfall due to UHI, and weakened upward motion in a stable UBL. On the other hand, UMI can increase regional heat risks with additional 37.5% neighbourhoods in Extreme caution level and additional 6.1% neighbourhoods in Danger level. In addition, the impact of UMI on human thermal stress was found to be dominant at daytime in coastal low-density low-rise areas (LCZ5&8&10) and at nighttime in coastal high-density high-rise areas (LCZ1&2). • Coastal low-density low-rise areas witnessed an all-day UMI phenomenon. • Coastal compact high-rise areas witnessed a nocturnal UMI and a daytime UDI. • Weakened ventilation and UHI-induced dewfall are possible reasons of UMI. • The synergistic UMI and UHI effects can aggravate urban thermal stress. [ABSTRACT FROM AUTHOR]

During the COVID-19 pandemic, wearing protective facemasks (PFMs) can effectively reduce infection risk, but the use of PFMs can amplify heat-related health risks. We studied the amplified PFM-induced human thermal stress via both field measurements and model simulations over a typical subtropical mountainous city, Hong Kong. First, a hot and humid PFM microenvironment has been observed with high temperature (34–35 °C) and high humidity (80–95%), resulting in an aggravated facial thermal stress with a maximal PFM-covered facial heat flux of 500 W/m2 under high-intensity activities. Second, to predict the overall PFM-inclusive human thermal stress, we developed a new facial thermal load model, S PFM and a new human-environment adaptive thermal stress (HEATS) model by coupling S PFM with an enhanced thermal comfort model to resolve modified human-environment interactions with the intervention of PFM under realistic climatic and topographical conditions. The model was then applied to predict spatiotemporal variations of PFM-inclusive physiological subjective temperature (PST) and corresponding heat stress levels during a typical heat wave event. It was found wearing PFM can significantly aggravate human thermal stress over Hong Kong with a spatially averaged PST increment of 5.0 °C and an additional spatial area of 158.4% exposed to the severest heat risks. Besides, PFM-inclusive PST was found to increase nonlinearly with terrain slopes at a rate of 1.3–3.9 °C/10°(slope), owing to elevated metabolic heat production. Furthermore, urban residents were found to have higher PFM-aggravated heat risks than rural residents, especially at night due to synergistic urban heat and moisture island effects. ● We studied PFM-induced human thermo-physiological responses via experiments. ● We proposed a new PFM-inclusive human thermal stress model. ● Wearing PFMs can lead to additional 158.4% of residents exposed to 'sweltering' heat risk. ● Urban residents tend to suffer more PFM-aggravated heat risks than rural residents at nights. ● PFM-aggravated thermal stress increases nonlinearly with terrain slopes. [ABSTRACT FROM AUTHOR]

The energy efficiency of geothermal heat exchanger (GHE) systems can be significantly impacted by the thermal performance of heat transfer fluid inside. In the present study, nanofluid (CuO/water) was experimentally used in the GHE to investigate its thermal performance as circuit fluid. The main part of experimental system consisted of a 0.8 m × 0.5 m × 0.58 m box, two double U-tubes, thermocouples and thermal resistors. A three-dimensional discrete phase model was built to simulate the flow process. By using nanofluid, the heat transfer rate and pumping power consumption of the GHE system increased by 39.84% and 16.75%. Moreover, the heat load-to-pumping power ratio had an enhancement of 20.2%. Furthermore, the previous literature showed that the nanofluids, which had a significant effect on the heat transfer of other types of heat exchangers, had an insignificant effect (less than 5%) on the energy efficiency of GHEs. The simulation result showed that the special structure of traditional GHEs may be the main reason for the lower possibility of collision between nanoparticles and the insignificant effect of nanofluid on its heat transfer enhancement. Therefore, the length of every straight tube segment should be restricted to achieve the better thermal performance of GHEs using nanofluids as heat transfer fluid. [ABSTRACT FROM AUTHOR]

Highlights • Heat load effect was investigated experimentally through a validated testing box. • Various ground thermal distributions during the operation and recovery periods. • Thermal interference and increasing load can enhance layered thermal distributions. • Ground stratification cannot be ignored for multi-GHE with considerable heat loads. Abstract To experimentally investigate the effect of heat loads on the thermal performance of vertical ground heat exchangers (GHEs) in a layered subsurface, a series of experiments were conducted using a testing box filled with sand and clay. Temperature distributions during the operation and recovery periods were different in the layered subsurface, where materials with high thermal diffusivities (e.g. sand) excel in both heat transfer and recovery. With more heat transferred from tubes, the sand and clay located close to the tubes showed drastic temperature variations along the length of tubes, especially around the interface between layers. The thermal interference could enhance the layered thermal distribution in the stratified underground, especially in materials with low thermal diffusivities. Moreover, if the applied power increased by four times, the proportion of the temperature difference between sand and clay to the sand temperature increased from 12.9% to 32.7%, which indicated a more severe thermal stratification. Therefore, it is recommended to consider the effect of ground stratification for multi-GHEs with considerable thermal injection and severe thermal interference, especially in materials with low thermal diffusivities. [ABSTRACT FROM AUTHOR]

Thermal performance predictions of ground heat exchangers (GHEs) can be largely affected by the ground stratification and the heat distributions. Based on a validated laboratory device, predictions from numerical models with variable (Q v) and constant (Q c) heat transfer rates along the depth of GHEs were compared against the experimental data. The model with Q v gave a more accurate prediction on the ground temperature, while the Q c model weakened the ground stratification effect and overpredicted the clay temperature by up to 76.6%, especially at the late stage. These models predicted different ground temperature distributions at various locations and time. Specifically, for a two-layered structure in this study, the sand temperature predicted by the model with Q v was higher than the clay one, while the Q c model witnessed an opposite trend and more severe thermal interference in both layers at the end of the 24 h operating period. Furthermore, a comparison of the models with layered and equivalent material reveals that the effect of axial heat load distribution could be more significant on the heat transfer of a stratified subsurface. Therefore, it is recommended to apply the variable axial thermal exchange distributions for heat transfer predictions of GHEs in a layered ground. • Effect of axial heat load distribution on performance prediction was investigated. • The assumption of uniform heat exchange may lead to unacceptable predictions. • Thermal distributions at different time and locations were compared. • Predictions for a layered subsurface should apply variable axial heat load profile. [ABSTRACT FROM AUTHOR]

As the first line of defence in the lung, alveolar macrophage contributes to maintaining lung immune homoeostasis. Characterized by the heterogeneity and plasticity, macrophages polarize into two pro-inflammatory and anti-inflammatory phenotypes regarding the biological and pathological environment. In the past decade, numerous studies have revolutionized the relationship between cellular metabolism and macrophage functions. Mitochondria dysfunctions, which results in altered cellular metabolic profile, were observed in the alveolar macrophages during chronic lung diseases. In addition, alveolar macrophages adapt metabolic reprogramming to produce an immune response against the pathogens. Here, we outline the role of mitochondria in the development of macrophage phenotypes and functions and highlight the mitochondrial dysfunction in the setting of chronic lung diseases. Lastly, we emphasize the therapeutic relevance of targeting metabolic pathways in alveolar macrophages, which may shed light on developing novel strategies against chronic lung diseases. [ABSTRACT FROM AUTHOR]