District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Researchers have made immense progress in understanding the urban-induced microclimate by numeric... more Researchers have made immense progress in understanding the urban-induced microclimate by numerical modelling. It has been around two decades since urban canopy models now commonly employed in mesoscale atmospheric models for operational and applied research purposes have emerged. To drive further advancement, it is timely to conduct a review of the state-of-the-art and lessons learnt from the relevant literature. In this paper, 102 urban climate real case modelling studies published in 2000-2019 are reviewed. Patterns and preferences in their study locations, periods, model choices, land cover databases, topics discussed, and scenarios investigated are holistically examined. There is an evident improvement in model complexity and urban surface data precision during the period reviewed. Most studies focus on the urban thermal climate and effects of urbanization. Based on the research gaps identified, more work is needed on the currently underrepresented but vulnerable cities in developing countries with tropical, arid, and cold climates. Collaborative field campaigns, initiatives to characterize cities in a consistent manner, and multi-scale modelling approaches have proven to benefit the progress in urban climate studies and should therefore be encouraged. More importantly, efforts should be invested in translating the science into information relevant to human well-being, urban planning, and policymaking.
The application of passive design strategies is crucial at the early architectural design stage f... more The application of passive design strategies is crucial at the early architectural design stage for building energy use minimization. However, the time-varying effectiveness of passive design strategies in responding to future climate change in hot and humid climates are rather limited in the literature. This paper aims to examine the dynamic effectiveness of passive design strategies for residential buildings in Hong Kong under the context of future climate change. Using the newly developed hourly weather data and adaptive comfort standard model, the dynamic effectiveness of viable passive design strategies for residential buildings are evaluated over time in the 21st century by plotting Givoni building bioclimatic charts (BBCC) and simulation-based sensitivity analyses in a validated EnergyPlus model. Results show that solar protection strategies are still the highly sensitive strategies for building energy performance and the effectiveness of external windows' airtightness is expected to increase up to 329% by the end of this century, whereas the cooling potential of ventilation utilization will significantly decrease over time. When the different combination of sensitive passive design parameters is implemented onto the baseline residential building model for different climate scenarios, the annual and peak cooling load can be reduced up to 56.7% and 64.5%, respectively.
Climate warming, rapid economic development, and urbanisation in (sub)tropical regions lead to in... more Climate warming, rapid economic development, and urbanisation in (sub)tropical regions lead to increasing electricity demand for building air-conditioning that could jeopardise the efforts of decarbonisation required to meet the climate change mitigation goals. This study investigates two strategies to reduce building energy consumption due to air-conditioning: 1) the bottom-up adoption of an Adaptive Thermal Comfort (ATC)-based cooling setpoint temperature and 2) the top-down implementation of efficient District Cooling Systems (DCS). The subtropical high-density city of Hong Kong is chosen for case study since detailed data on the city's current and realistic future urban form and function are available. Numerical simulations representing the feedback between urban climate and building energy consumption are conducted by employing a mesoscale atmospheric model coupled to an urban climate and building energy model for a scenario of future (mid-21st century) Hong Kong. A prolonged high temperature event representative of future extreme conditions is simulated, during which the ATC and DCS strategies reduce building cooling energy consumption by 9.7% and 5.9%, respectively. The ATC has almost no effect on the local meteorological conditions, whereas the DCS reduces daytime sensible heat flux by up to 600 W/m2 and near-surface air temperature by almost 1 °C in the districts where it is adopted. The DCS thus also contributes to lowering outdoor heat stress in these areas. The cost-free ATC strategy is easily applicable in residential buildings worldwide and can break the vicious cycle in overcooled buildings, where occupants are acclimatised to lower indoor temperature and thus require more air-conditioning than necessary. Apart from reducing energy consumption and near-surface air temperature, the DCS brings additional benefits in building space utilisation and rooftop design. Future policy orientations should therefore encourage a societal change towards the ATC lifestyle and incorporate DCS in the planning of new development areas.
Urban Canopy Models (UCMs) represent the exchange of momentum, heat, and moisture between cities ... more Urban Canopy Models (UCMs) represent the exchange of momentum, heat, and moisture between cities and the atmosphere. Single-layer UCMs interact with the lowest atmospheric model level and are suited for low-to mid-rise cities whereas multi-layer UCMs interact with multiple levels and can also be employed for high-rise cities. The present study describes the multi-layer coupling between the UCM Town Energy Balance (TEB) included in the land surface model SURFEX and the mesoscale atmospheric model Meso-NH. This is a step towards better high-resolution weather prediction for urban areas in the future and studies quantifying the impact of climate change adaptation measures in high-rise cities. The effect of the buildings on the wind is considered using a drag force and a production term in the prognostic equation for turbulent kinetic energy. The heat and moisture fluxes from the walls and the roofs to the atmosphere are released at the model levels intersecting these urban facets. No variety of building height at grid point scale is considered to remain the consistency between the modification of the Meso-NH equations and the geometric assumptions of TEB. The multi-layer coupling is evaluated for the heterogeneous high-rise high-density city of Hong Kong. It leads to a strong improvement of model results for near-surface air temperature and relative humidity, which is due to better consideration of the process of horizontal advection in the urban canopy layer. For wind speed, model results are improved on average by the multi-layer coupling, but not for all stations. Future developments of the multi-layer SURFEX-TEB will focus on improving the calculation of radiative exchanges, which will allow a variety of building heights at grid point scale to be taken into account.
To better understand the impacts of the warming caused by global climate change on building perfo... more To better understand the impacts of the warming caused by global climate change on building performance, future hourly weather data that account for climate change are crucial to building simulation studies. Downscaling from general circulation models (GCMs) by the morphing method has been adopted by researchers worldwide. Using this method, we developed six sets of future hourly weather data for Hong Kong, taking the typical meteorological year (TMY) as the baseline climate. The ensemble mean from 24 general circulation models (GCMs) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) has also been incorporated to take into account the uncertainties and biases between different models. These newly developed future weather data were then employed in the building energy simulation to evaluate the impacts of future climate change. Moreover, this study used the adaptive comfort standard (ACS) from ASHRAE Standard 55 in a mixed-mode residential building to consider the acclimatization effects of occupants in the changing climate. Results indicate that by the end of this century, the indoor discomfort percentage in the cooling seasons are expected to increase from 21.9% for TMY to 36.0% and 50.4% under RCP4.5 and RCP8.5 scenarios, respectively, while the annual cooling load is expected to increase up to 278.80%.
In face of the warming climate, proper building designs are necessary to combat the ever-increasi... more In face of the warming climate, proper building designs are necessary to combat the ever-increasing energy demands, especially in high-density built environments. Shading is a common practice in subtropical cities owing to its effectiveness and feasibility. However, window shading alone is insufficient for achieving a satisfying energy performance and may often be a compromise to the visual comfort of occupants. In contrast, shading opaque façades has a great potential for energy saving with more design flexibility. This study proposes the adoption of shading devices on opaque façades and evaluates their energy saving potentials under near-extreme summer conditions by conducting building energy simulations. The length, the number, and the angle of tilt of shading panels are varied to explore the effects of different shading panel configurations for typical public rental housing buildings in Hong Kong. Optimal configurations that give maximum energy savings with the smallest total area of shading panels are found for different angles of tilt. Results show an energy saving potential up to 8.0% when shading panels are applied to flats with westward-facing façades. The energy saving coefficients within the optimal zones are also provided to guide the design of façade shading features in different urban contexts.
Journal of Wind Engineering and Industrial Aerodynamics, Nov 1, 2018
In recent years, urban ventilation assessment and urban ventilation corridor plan have been condu... more In recent years, urban ventilation assessment and urban ventilation corridor plan have been conducted and adopted in the urban planning of Chinese cities in response to the national call from the Central Government of China as well as the public concern on the quality of living environment. Therefore, a national technical guide is needed to provide a state-of-the-art standard methodology and scientific technology on urban ventilation assessment, and to serve as an aid for decision-making in the initial stage of town planning and urban design. This paper first reviews the urban ventilation corridor plan related activities in Chinese cities since 2000 and points out the needs and problems. Secondly, it introduces the newly developed national technical guide 'Specifications for climatic feasibility demonstration-Urban Ventilation Corridor'. Thirdly, a case study of Chengdu Urban Ventilation Corridor Plan is presented to demonstrate the implementation of such considerations in local planning exercises. Lastly, it discusses the future trend of urban ventilation assessment and urban ventilation corridor plan in China.
International Journal of Climatology, Jun 10, 2019
To build healthy, resilient, and climate-responsive cities, planners need ways to understand the ... more To build healthy, resilient, and climate-responsive cities, planners need ways to understand the local complexities of urban thermal climates. To assist in meeting this need, this study employs the simple classification of "local climate zones" (LCZs) to conduct a spatiotemporal thermal climatic analysis of the Toulouse Metropolitan Region (France) under warm and dry summer conditions. Simulations are performed using the mesoscale atmospheric model Méso-NH. These simulations provide a city-wide spatial coverage of 2-m air temperature (T2M), mean radiant temperature (MRT), and Universal Thermal Climate Index (UTCI). Model parameters describing the urban morphology are initialized based on administrative databases and independent of LCZ maps, which allows for an evaluation of whether the distributions of the modelled thermal climatic parameters will differ between LCZs. The results show that different LCZs possess significantly different distributions of T2M and MRT, confirming the suitability of the LCZ scheme for discerning the thermal environment of Toulouse. Compact urban settings (LCZ 1/2/3) show the highest T2M throughout the day and a nocturnal temperature difference of up to 2.8 K compared to rural settings. The MRT of LCZ 1/2/3 in the late afternoon (1700-2000 LST (UTC + 2)) can be as much as 6.3 K lower than it is for LCZs with open settings due to shading by dense urban structures. Additional analysis reveals that the intra-LCZ variabilities of T2M and MRT may be explained by the distance to the city centre. Finally, the thermal stress in different LCZs is assessed with the modelled UTCI. Among the built LCZs, the probability of strong heat stress is the highest for open high/mid-rise (LCZ 4/5) and lowest for sparsely built (LCZ 9) and open low-rise (LCZ 6) settings. For land cover type LCZs, dense trees (LCZ A) are the most favourable for daytime outdoor human thermal comfort. K E Y W O R D S heat stress, local climate zones, numerical model simulation, universal thermal climate index (UTCI), urban climate analysis, urban thermal environment
Anthropogenic modification of the natural environment has caused significant impacts on the local... more Anthropogenic modification of the natural environment has caused significant impacts on the local atmosphere and far-reaching changes to the global climate. Taking Hong Kong as a case study, high-resolution (250 m) mesoscale simulations are conducted using Meso-NH coupled with the multi-layer Town Energy Balance to investigate the effects of past (early 1960s), present (2018), and future (late 2040s) urban developments on the city's surface energy balance, heat island, boundary layer structure, and heat stress during a prolonged heatwave event. Overall, horizontal and vertical urban expansion has caused the urban areas to become warmer, drier, less ventilated, and more susceptible to hot nights. The dense built-up urban core in the Kowloon peninsula is also found to deepen the urban boundary layer and enhance the coastal urban heat island circulation. Reclaimed land exhibits the largest differences in 2-m air temperature relative to a no urban scenario due to the drastic change in surface thermal properties. Areas downwind of the planned artificial islands in East Lantau are expected to experience warmer and calmer conditions due to the altered wind field. Study findings raise awareness regarding the increasingly long durations of strong heat stress in urban areas and the need for heat stress mitigation.
Urban canopy models (UCMs) represent the exchange of momentum, heat, and moisture between cities ... more Urban canopy models (UCMs) represent the exchange of momentum, heat, and moisture between cities and the atmosphere. Single-layer UCMs interact with the lowest atmospheric model level and are suited for low-to mid-rise cities, whereas multi-layer UCMs interact with multiple levels and can also be employed for high-rise cities. The present study describes the multi-layer coupling between the Town Energy Balance (TEB) UCM included in the Surface Externalisée (SURFEX) land surface model and the Meso-NH mesoscale atmospheric model. This is a step towards better high-resolution weather prediction for urban areas in the future and studies quantifying the impact of climate change adaptation measures in high-rise cities. The effect of the buildings on the wind is considered using a drag force and a production term in the prognostic equation for turbulent kinetic energy. The heat and moisture fluxes from the walls and the roofs to the atmosphere are released at the model levels intersecting these urban facets. No variety of building height at grid-point scale is considered to remain the consistency between the modification of the Meso-NH equations and the geometric assumptions of TEB. The multi-layer coupling is evaluated for the heterogeneous high-rise, high-density city of Hong Kong. It leads to a strong improvement of model results for near-surface air temperature and relative humidity, which is due to better consideration of the process of horizontal advection in the urban canopy layer. For wind speed, model results are improved on average by the multi-layer coupling but not for all stations. Future developments of the multi-layer SURFEX-TEB will focus on improving the calculation of radiative exchanges, which will allow a variety of building heights at grid-point scale to be taken into account.
Urban heat island (UHI) and cool island (UCI) effects are well-known and prevalent in cities worl... more Urban heat island (UHI) and cool island (UCI) effects are well-known and prevalent in cities worldwide. An increasing trend of extreme heat events has been observed over the last few decades and is expected to continue in the foreseeable future. In this study, warm periods (May to September) of 2000-2018 were examined to acquire a comprehensive understanding of the UHI and UCI characteristics for the case study of Hong Kong, China. 22 weather stations in Hong Kong were classified into four categories, namely urban, urban oasis, suburban, and rural, with reference to the local climate zone (LCZ) scheme, to analyze UHI and UCI phenomena during extreme heat and non-extreme heat situations. One representative type of extreme heat events was considered in this study: three consecutive hot nights with two very hot days in between (2D3N). Results show that both the UHI and UCI effects are exacerbated during extreme heat events. Using the concept of the UHI degree hours (UHIdh) and UCI degree hours (UCIdh), their spatial patterns in Hong Kong during extreme heat and non-extreme heat situations were mapped based on multiple linear regression models. It is found that the predictor variable-windward/leeward index is a significant influential factor of both UHIdh and UCIdh during extreme heat events. The resulting UHIdh and UCIdh maps not only enhance our understanding on the spatial pattern and characteristics of the UHI and UCI during extreme heat This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/joc.7222 This article is protected by copyright. All rights reserved. events, but could also serve as a useful reference in climate change adaptation, heat-health risk detection, cooling-energy estimation and policy making.
Skillful location-specific weather forecasts are invaluable for the public and concerned communit... more Skillful location-specific weather forecasts are invaluable for the public and concerned communities in planning daily activities and preparedness actions for weather-related impacts. Despite continuous enhancements in numerical weather prediction (NWP) models, it remains challenging to capture the intricate variations in meteorological conditions within a city with highly heterogeneous landscape and diverse urban environment such as Hong Kong. In support of regional weather forecasting services, the Hong Kong Observatory (HKO) has developed the Objective Consensus Forecast (OCF) system for various weather elements, including a 9-day automatic forecast in daily maximum and minimum air temperatures (Tmax, Tmin). OCF is a past performance-weighted multi-model consensus forecast which employs Kalman Filter (KF) as an adaptive post-processing method for NWP forecasts at different weather stations. Though the performance of OCF has been largely satisfactory in the past decade, recent tre...
The high-density building environment and complex, heterogeneous landscape in Hong Kong result in... more The high-density building environment and complex, heterogeneous landscape in Hong Kong result in significant spatial variability of local temperatures, winds and other weather elements down to the street level. To enhance meteorological observation and forecasting services, the Hong Kong Observatory (HKO) has been actively developing an urban-scale weather observing network in recent years through in-house efforts and collaboration with local communities. In this presentation, a novel real-time monitoring network, based on economical sensors deployed at various sites within the urban areas, providing basic temperature and relative humidity measurements will be introduced. They are found to provide useful data for analyses of daily temperature variations in urban areas under very hot or prolonged heat stress episodes. The new observations offer indispensable meteorological information and reference for studies of urban micro-climate and the impact of heat stress on public health...
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Researchers have made immense progress in understanding the urban-induced microclimate by numeric... more Researchers have made immense progress in understanding the urban-induced microclimate by numerical modelling. It has been around two decades since urban canopy models now commonly employed in mesoscale atmospheric models for operational and applied research purposes have emerged. To drive further advancement, it is timely to conduct a review of the state-of-the-art and lessons learnt from the relevant literature. In this paper, 102 urban climate real case modelling studies published in 2000-2019 are reviewed. Patterns and preferences in their study locations, periods, model choices, land cover databases, topics discussed, and scenarios investigated are holistically examined. There is an evident improvement in model complexity and urban surface data precision during the period reviewed. Most studies focus on the urban thermal climate and effects of urbanization. Based on the research gaps identified, more work is needed on the currently underrepresented but vulnerable cities in developing countries with tropical, arid, and cold climates. Collaborative field campaigns, initiatives to characterize cities in a consistent manner, and multi-scale modelling approaches have proven to benefit the progress in urban climate studies and should therefore be encouraged. More importantly, efforts should be invested in translating the science into information relevant to human well-being, urban planning, and policymaking.
The application of passive design strategies is crucial at the early architectural design stage f... more The application of passive design strategies is crucial at the early architectural design stage for building energy use minimization. However, the time-varying effectiveness of passive design strategies in responding to future climate change in hot and humid climates are rather limited in the literature. This paper aims to examine the dynamic effectiveness of passive design strategies for residential buildings in Hong Kong under the context of future climate change. Using the newly developed hourly weather data and adaptive comfort standard model, the dynamic effectiveness of viable passive design strategies for residential buildings are evaluated over time in the 21st century by plotting Givoni building bioclimatic charts (BBCC) and simulation-based sensitivity analyses in a validated EnergyPlus model. Results show that solar protection strategies are still the highly sensitive strategies for building energy performance and the effectiveness of external windows' airtightness is expected to increase up to 329% by the end of this century, whereas the cooling potential of ventilation utilization will significantly decrease over time. When the different combination of sensitive passive design parameters is implemented onto the baseline residential building model for different climate scenarios, the annual and peak cooling load can be reduced up to 56.7% and 64.5%, respectively.
Climate warming, rapid economic development, and urbanisation in (sub)tropical regions lead to in... more Climate warming, rapid economic development, and urbanisation in (sub)tropical regions lead to increasing electricity demand for building air-conditioning that could jeopardise the efforts of decarbonisation required to meet the climate change mitigation goals. This study investigates two strategies to reduce building energy consumption due to air-conditioning: 1) the bottom-up adoption of an Adaptive Thermal Comfort (ATC)-based cooling setpoint temperature and 2) the top-down implementation of efficient District Cooling Systems (DCS). The subtropical high-density city of Hong Kong is chosen for case study since detailed data on the city's current and realistic future urban form and function are available. Numerical simulations representing the feedback between urban climate and building energy consumption are conducted by employing a mesoscale atmospheric model coupled to an urban climate and building energy model for a scenario of future (mid-21st century) Hong Kong. A prolonged high temperature event representative of future extreme conditions is simulated, during which the ATC and DCS strategies reduce building cooling energy consumption by 9.7% and 5.9%, respectively. The ATC has almost no effect on the local meteorological conditions, whereas the DCS reduces daytime sensible heat flux by up to 600 W/m2 and near-surface air temperature by almost 1 °C in the districts where it is adopted. The DCS thus also contributes to lowering outdoor heat stress in these areas. The cost-free ATC strategy is easily applicable in residential buildings worldwide and can break the vicious cycle in overcooled buildings, where occupants are acclimatised to lower indoor temperature and thus require more air-conditioning than necessary. Apart from reducing energy consumption and near-surface air temperature, the DCS brings additional benefits in building space utilisation and rooftop design. Future policy orientations should therefore encourage a societal change towards the ATC lifestyle and incorporate DCS in the planning of new development areas.
Urban Canopy Models (UCMs) represent the exchange of momentum, heat, and moisture between cities ... more Urban Canopy Models (UCMs) represent the exchange of momentum, heat, and moisture between cities and the atmosphere. Single-layer UCMs interact with the lowest atmospheric model level and are suited for low-to mid-rise cities whereas multi-layer UCMs interact with multiple levels and can also be employed for high-rise cities. The present study describes the multi-layer coupling between the UCM Town Energy Balance (TEB) included in the land surface model SURFEX and the mesoscale atmospheric model Meso-NH. This is a step towards better high-resolution weather prediction for urban areas in the future and studies quantifying the impact of climate change adaptation measures in high-rise cities. The effect of the buildings on the wind is considered using a drag force and a production term in the prognostic equation for turbulent kinetic energy. The heat and moisture fluxes from the walls and the roofs to the atmosphere are released at the model levels intersecting these urban facets. No variety of building height at grid point scale is considered to remain the consistency between the modification of the Meso-NH equations and the geometric assumptions of TEB. The multi-layer coupling is evaluated for the heterogeneous high-rise high-density city of Hong Kong. It leads to a strong improvement of model results for near-surface air temperature and relative humidity, which is due to better consideration of the process of horizontal advection in the urban canopy layer. For wind speed, model results are improved on average by the multi-layer coupling, but not for all stations. Future developments of the multi-layer SURFEX-TEB will focus on improving the calculation of radiative exchanges, which will allow a variety of building heights at grid point scale to be taken into account.
To better understand the impacts of the warming caused by global climate change on building perfo... more To better understand the impacts of the warming caused by global climate change on building performance, future hourly weather data that account for climate change are crucial to building simulation studies. Downscaling from general circulation models (GCMs) by the morphing method has been adopted by researchers worldwide. Using this method, we developed six sets of future hourly weather data for Hong Kong, taking the typical meteorological year (TMY) as the baseline climate. The ensemble mean from 24 general circulation models (GCMs) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) has also been incorporated to take into account the uncertainties and biases between different models. These newly developed future weather data were then employed in the building energy simulation to evaluate the impacts of future climate change. Moreover, this study used the adaptive comfort standard (ACS) from ASHRAE Standard 55 in a mixed-mode residential building to consider the acclimatization effects of occupants in the changing climate. Results indicate that by the end of this century, the indoor discomfort percentage in the cooling seasons are expected to increase from 21.9% for TMY to 36.0% and 50.4% under RCP4.5 and RCP8.5 scenarios, respectively, while the annual cooling load is expected to increase up to 278.80%.
In face of the warming climate, proper building designs are necessary to combat the ever-increasi... more In face of the warming climate, proper building designs are necessary to combat the ever-increasing energy demands, especially in high-density built environments. Shading is a common practice in subtropical cities owing to its effectiveness and feasibility. However, window shading alone is insufficient for achieving a satisfying energy performance and may often be a compromise to the visual comfort of occupants. In contrast, shading opaque façades has a great potential for energy saving with more design flexibility. This study proposes the adoption of shading devices on opaque façades and evaluates their energy saving potentials under near-extreme summer conditions by conducting building energy simulations. The length, the number, and the angle of tilt of shading panels are varied to explore the effects of different shading panel configurations for typical public rental housing buildings in Hong Kong. Optimal configurations that give maximum energy savings with the smallest total area of shading panels are found for different angles of tilt. Results show an energy saving potential up to 8.0% when shading panels are applied to flats with westward-facing façades. The energy saving coefficients within the optimal zones are also provided to guide the design of façade shading features in different urban contexts.
Journal of Wind Engineering and Industrial Aerodynamics, Nov 1, 2018
In recent years, urban ventilation assessment and urban ventilation corridor plan have been condu... more In recent years, urban ventilation assessment and urban ventilation corridor plan have been conducted and adopted in the urban planning of Chinese cities in response to the national call from the Central Government of China as well as the public concern on the quality of living environment. Therefore, a national technical guide is needed to provide a state-of-the-art standard methodology and scientific technology on urban ventilation assessment, and to serve as an aid for decision-making in the initial stage of town planning and urban design. This paper first reviews the urban ventilation corridor plan related activities in Chinese cities since 2000 and points out the needs and problems. Secondly, it introduces the newly developed national technical guide 'Specifications for climatic feasibility demonstration-Urban Ventilation Corridor'. Thirdly, a case study of Chengdu Urban Ventilation Corridor Plan is presented to demonstrate the implementation of such considerations in local planning exercises. Lastly, it discusses the future trend of urban ventilation assessment and urban ventilation corridor plan in China.
International Journal of Climatology, Jun 10, 2019
To build healthy, resilient, and climate-responsive cities, planners need ways to understand the ... more To build healthy, resilient, and climate-responsive cities, planners need ways to understand the local complexities of urban thermal climates. To assist in meeting this need, this study employs the simple classification of "local climate zones" (LCZs) to conduct a spatiotemporal thermal climatic analysis of the Toulouse Metropolitan Region (France) under warm and dry summer conditions. Simulations are performed using the mesoscale atmospheric model Méso-NH. These simulations provide a city-wide spatial coverage of 2-m air temperature (T2M), mean radiant temperature (MRT), and Universal Thermal Climate Index (UTCI). Model parameters describing the urban morphology are initialized based on administrative databases and independent of LCZ maps, which allows for an evaluation of whether the distributions of the modelled thermal climatic parameters will differ between LCZs. The results show that different LCZs possess significantly different distributions of T2M and MRT, confirming the suitability of the LCZ scheme for discerning the thermal environment of Toulouse. Compact urban settings (LCZ 1/2/3) show the highest T2M throughout the day and a nocturnal temperature difference of up to 2.8 K compared to rural settings. The MRT of LCZ 1/2/3 in the late afternoon (1700-2000 LST (UTC + 2)) can be as much as 6.3 K lower than it is for LCZs with open settings due to shading by dense urban structures. Additional analysis reveals that the intra-LCZ variabilities of T2M and MRT may be explained by the distance to the city centre. Finally, the thermal stress in different LCZs is assessed with the modelled UTCI. Among the built LCZs, the probability of strong heat stress is the highest for open high/mid-rise (LCZ 4/5) and lowest for sparsely built (LCZ 9) and open low-rise (LCZ 6) settings. For land cover type LCZs, dense trees (LCZ A) are the most favourable for daytime outdoor human thermal comfort. K E Y W O R D S heat stress, local climate zones, numerical model simulation, universal thermal climate index (UTCI), urban climate analysis, urban thermal environment
Anthropogenic modification of the natural environment has caused significant impacts on the local... more Anthropogenic modification of the natural environment has caused significant impacts on the local atmosphere and far-reaching changes to the global climate. Taking Hong Kong as a case study, high-resolution (250 m) mesoscale simulations are conducted using Meso-NH coupled with the multi-layer Town Energy Balance to investigate the effects of past (early 1960s), present (2018), and future (late 2040s) urban developments on the city's surface energy balance, heat island, boundary layer structure, and heat stress during a prolonged heatwave event. Overall, horizontal and vertical urban expansion has caused the urban areas to become warmer, drier, less ventilated, and more susceptible to hot nights. The dense built-up urban core in the Kowloon peninsula is also found to deepen the urban boundary layer and enhance the coastal urban heat island circulation. Reclaimed land exhibits the largest differences in 2-m air temperature relative to a no urban scenario due to the drastic change in surface thermal properties. Areas downwind of the planned artificial islands in East Lantau are expected to experience warmer and calmer conditions due to the altered wind field. Study findings raise awareness regarding the increasingly long durations of strong heat stress in urban areas and the need for heat stress mitigation.
Urban canopy models (UCMs) represent the exchange of momentum, heat, and moisture between cities ... more Urban canopy models (UCMs) represent the exchange of momentum, heat, and moisture between cities and the atmosphere. Single-layer UCMs interact with the lowest atmospheric model level and are suited for low-to mid-rise cities, whereas multi-layer UCMs interact with multiple levels and can also be employed for high-rise cities. The present study describes the multi-layer coupling between the Town Energy Balance (TEB) UCM included in the Surface Externalisée (SURFEX) land surface model and the Meso-NH mesoscale atmospheric model. This is a step towards better high-resolution weather prediction for urban areas in the future and studies quantifying the impact of climate change adaptation measures in high-rise cities. The effect of the buildings on the wind is considered using a drag force and a production term in the prognostic equation for turbulent kinetic energy. The heat and moisture fluxes from the walls and the roofs to the atmosphere are released at the model levels intersecting these urban facets. No variety of building height at grid-point scale is considered to remain the consistency between the modification of the Meso-NH equations and the geometric assumptions of TEB. The multi-layer coupling is evaluated for the heterogeneous high-rise, high-density city of Hong Kong. It leads to a strong improvement of model results for near-surface air temperature and relative humidity, which is due to better consideration of the process of horizontal advection in the urban canopy layer. For wind speed, model results are improved on average by the multi-layer coupling but not for all stations. Future developments of the multi-layer SURFEX-TEB will focus on improving the calculation of radiative exchanges, which will allow a variety of building heights at grid-point scale to be taken into account.
Urban heat island (UHI) and cool island (UCI) effects are well-known and prevalent in cities worl... more Urban heat island (UHI) and cool island (UCI) effects are well-known and prevalent in cities worldwide. An increasing trend of extreme heat events has been observed over the last few decades and is expected to continue in the foreseeable future. In this study, warm periods (May to September) of 2000-2018 were examined to acquire a comprehensive understanding of the UHI and UCI characteristics for the case study of Hong Kong, China. 22 weather stations in Hong Kong were classified into four categories, namely urban, urban oasis, suburban, and rural, with reference to the local climate zone (LCZ) scheme, to analyze UHI and UCI phenomena during extreme heat and non-extreme heat situations. One representative type of extreme heat events was considered in this study: three consecutive hot nights with two very hot days in between (2D3N). Results show that both the UHI and UCI effects are exacerbated during extreme heat events. Using the concept of the UHI degree hours (UHIdh) and UCI degree hours (UCIdh), their spatial patterns in Hong Kong during extreme heat and non-extreme heat situations were mapped based on multiple linear regression models. It is found that the predictor variable-windward/leeward index is a significant influential factor of both UHIdh and UCIdh during extreme heat events. The resulting UHIdh and UCIdh maps not only enhance our understanding on the spatial pattern and characteristics of the UHI and UCI during extreme heat This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/joc.7222 This article is protected by copyright. All rights reserved. events, but could also serve as a useful reference in climate change adaptation, heat-health risk detection, cooling-energy estimation and policy making.
Skillful location-specific weather forecasts are invaluable for the public and concerned communit... more Skillful location-specific weather forecasts are invaluable for the public and concerned communities in planning daily activities and preparedness actions for weather-related impacts. Despite continuous enhancements in numerical weather prediction (NWP) models, it remains challenging to capture the intricate variations in meteorological conditions within a city with highly heterogeneous landscape and diverse urban environment such as Hong Kong. In support of regional weather forecasting services, the Hong Kong Observatory (HKO) has developed the Objective Consensus Forecast (OCF) system for various weather elements, including a 9-day automatic forecast in daily maximum and minimum air temperatures (Tmax, Tmin). OCF is a past performance-weighted multi-model consensus forecast which employs Kalman Filter (KF) as an adaptive post-processing method for NWP forecasts at different weather stations. Though the performance of OCF has been largely satisfactory in the past decade, recent tre...
The high-density building environment and complex, heterogeneous landscape in Hong Kong result in... more The high-density building environment and complex, heterogeneous landscape in Hong Kong result in significant spatial variability of local temperatures, winds and other weather elements down to the street level. To enhance meteorological observation and forecasting services, the Hong Kong Observatory (HKO) has been actively developing an urban-scale weather observing network in recent years through in-house efforts and collaboration with local communities. In this presentation, a novel real-time monitoring network, based on economical sensors deployed at various sites within the urban areas, providing basic temperature and relative humidity measurements will be introduced. They are found to provide useful data for analyses of daily temperature variations in urban areas under very hot or prolonged heat stress episodes. The new observations offer indispensable meteorological information and reference for studies of urban micro-climate and the impact of heat stress on public health...
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