10:30am - 10:45am
Multivariate analysis of the influence between building design and energy performance, socio-demographic metrics, and the intra-urban environment
1UCLouvain, Belgium; 2Northeastern University, United States of America, Belgium
Through the advancements of direct and remote sensing technologies, we have recently learned that urban microclimate and air quality gradients within a city can often be more significant than city-rural or intercity gradients. Through the study of these urban environmental datasets, we are starting to understand the environmental inequality that characterize our cities. However, the urban parameters that are most critical to improve urban environmental conditions are yet to be identified through the understanding of the dependencies between intra-urban microclimate and air quality gradients, the urban fabric and the socio-demographic layers of the city, and the building usage metrics. This research makes use of high spatiotemporal urban air quality datasets collected through dense stationary urban sensing networks in New York City (NYC) as well as datasets on building usage metrics such as energy consumption and greenhouse emissions, urban design metrics describing the building and street characteristics, and socio-demographic datasets including population and health metrics. Finally, through a footprint-based regression analysis the correlation between the air quality, building usage and urban metrics has been studied. Highest correlations have been observed between air quality, urban design and socio-economic metrics. The results show that building usage metrics such as the energy use intensity, electricity purchase or greenhouse emissions are mainly affected by the building design characteristics. On the other hand, significant correlations have been observed between the urban design, socio-demographic and contaminant concentration gradients, addressing the critical role the planning and design of our cities plays in the environmental well-being of citizens. These findings emphasize the critical role urban planning and design parameters play in the environmental well-being of citizens, as well as in the building consumption patterns in cities.
10:45am - 11:00am
Importance of Microscale Climate Simulations in City Scale Overheating Assessments
1Concordia University, Canada; 2Construction Research Centre, National Research Council Canada
The goal of this study is to demonstrate the importance of high resolution (considered as 1 km in this study) climate simulations when conducting city-scale outdoor and indoor overheating assessments. This is to done by a) showing that urban climate is more accurate simulated at 1 km spatial resolution than lower resolutions (25 and 50 km resolutions at which regional climate models typically operate); and b) it allows for consideration of climate at urban locations which is typically higher than the rural locations. To this end, the urban climate around the cities of Ottawa and Montreal at 1 km, 25 km, and 50 km are used to assess outdoor and indoor overheating over the summer of 2018, which was unusually warm and encompassed an extreme heat event that caused around 100 deaths in these cities. Urban climate simulations are performed using Weather Research and Forecasting (WRF) model with three two-way nested domains centred at a location half-way between the two cities. The innermost domain has a grid resolution of 1 km, which allows for more accurate modelling of key microscale climate processes such as convection and urban heat islands. The WRF model is validated with reference to observational climate recorded by multiple weather stations located in this region. The weather conditions simulated in WRF are extracted for an airport location (which is typically considered when performing city-scale overheating assessments) and selected vulnerable locations around the cities and indoor conditions and used to perform EnergyPlus simulations of three different benchmarked residential building models, single house, row house and multi-unit residential buildings. The results from this study will highlight the importance of undertaking high resolution convection-permitting urban climate simulations when undertaking city-scale overheating assessment in cities across the globe.
11:00am - 11:15am
Mitigation measures for urban heat island and their impact on pedestrian thermal comfort
1ETH Zurich, Switzerland; 2Université de Sherbrooke, Canada
Recorded data show that heat waves are getting more frequent and intense with longer duration and at broader spatial scale. The resulting local conditions in urban areas can reach very strong heat stress levels, especially when compounded with situations that lead to local heat islands. Counter-measure strategies should involve careful planning with a combination of effective mitigation strategies, while keeping sustainability in mind. In the present study, the impacts of two different mitigation strategies, i.e. artificial wetting of pavements and vegetation, on pedestrian thermal comfort are evaluated.
A coupled approach is performed for a public square in the city of Zurich. Computational fluid dynamics (CFD) simulations are coupled with radiation models and unsteady heat and moisture transport (HAM) in porous urban materials. This allows for an accurate tracking of moisture content near surfaces available for evaporative cooling and for the calculation of drying rate. Trees are modeled as porous objects within the CFD domain including transpirative cooling. Lateral boundary conditions are obtained from mesoscale simulations with urban parameterization. Pedestrian thermal comfort is evaluated with the Universal Thermal Climate Index (UTCI).
Results show that the cooling provided by trees is large enough to reduce the thermal stress during day time, in some cases until moderate levels with a reduction in UTCI by up to 7 °C. During night time, trees reduce the sky view factor and lead to slightly worsened thermal comfort. Without any additional shadowing, cooling provided by artificial wetting is more limited, with a maximum reduction of 2.5 °C in UTCI. This is similar to the cooling amount observed in the case of a street canyon based on an optimized wetting strategy. However, the effective duration of cooling is found to be much shorter in the case of public square due to much higher exposure to solar radiation.
11:15am - 11:30am
The impact of the spatio-temporal morphology of urban green infrastructure on urban building energy consumption: A case study in the hot-summer-cold-winter climate
1School of Architecture, Southeast University, Nanjing, China; 2Key Laboratory of Urban and Architectural Heritage Conservation, Ministry of Education, Nanjing, China; 3College of Architecture and Urban Planning, Tongji University, Shanghai, China; 4Key Laboratory of Ecology and Energy-saving Study of Dense Habitat (Tongji University), Ministry of Education, China
Studies have confirmed that urban green infrastructure (UGI) has a profound impact on urban building energy consumption through regulating urban microclimate, providing shading to buildings, and other mechanisms. This impact is largely dependent on the morphology of UGI. Although this conclusion is widely accepted, there lacks a systematic approach to quantify the impact and thus the knowledge regarding its magnitude. This paper discusses the mechanisms of UGI on urban building energy consumption. The city of Nanjing, a Chinese city in the hot-summer-cold-winter climate, is morphologically analyzed to extract prototypes of UGI forms. These prototypes are simulated for their microclimate and urban building energy consumptions using a co-simulation technique, which links ENVI-met to EnergyPlus. The simulation results are statistically analyzed to quantify the impact of UGI morphology on urban building energy consumption. The energy consumption of different morphological groups in summer and winter is compared to determine the impact of UGI morphological features on urban building energy consumption.
11:30am - 11:45am
Development of Integrated Urban Greenery Cover for Enhancing Microclimate Thermal Performance
Ryerson University, Canada
Green spaces and vegetation cover offer various environmental benefits, including building energy-saving and mitigation of the urban heat island (UHI). The influence of enriching the urban vegetation is fundamental in UHI mitigation policies promoted over the last years in the Greater Toronto Area (GTA). Increasing the urban greenery cover is introduced promoting the intensification of the urban tree canopy and the incorporation of vegetated façades and green roofs. In this paper, a modelling approach is developed and validated including microclimate simulations to investigate the effect of the increased horizontal and vertical green infrastructure on the microclimatic thermal performance of the typical urban typologies of the GTA. The validation ensures the model ability to predict the cooling effect of the green infrastructure within different urban typologies. The proposed enhancements confirm a maximum reduction in peak air temperature of 3.7 ˚C and daily average building energy savings of 0.16 kWh/m2. Moreover, the maximum value of the heat stress, the temperature-humidity index, during the heat wave period is reduced from 41.2 to 37.6 avoiding the heat warning conditions and reducing the moderate heat stress duration by 60% of the daytime.
11:45am - 12:00pm
An automated workflow for urban greening based on photosynthetic radiation modeling.
1University of Houston, United States of America; 2Technische Universität Kaiserslautern, Kaiserslautern, Germany
The presence of vegetation - besides supporting the biophilia hypothesis - is known to improve outdoor thermal comfort and mitigate the effects of Urban Heat Island in cities. Urban greening can be applied on ground level or elevated parks, roof tops, and building facades. The main parameters that affect plant growth are moisture, soil nutrients and light. Of these parameters, the first two can be supplemented through irrigation and fertilization, while the lighting requirements need to be met exclusively through daylight.
The goal of this research is to develop an automated workflow that facilitates design decisions on vegetation growth potential and vegetation species selection within their climatic and geometrical context. This workflow builds on a previous study done by the authors on the use of radiation-based modeling using Radiance to calculate Daily Light Integral (DLI) values. The methodology developed by the authors so far allows the incorporation of context – geometries and material properties – while calculating DLI. It uses daylight simulations in order to calculate hourly DLI values, taking advantage of the overlap between visible (wavelength range) and photosynthetically active (wavelength range) parts of the solar spectrum.
Presently, to evaluate context-based vegetation species suitability, a series of manual time-consuming and error-prone observations are required. These include vegetation selection and monthly or seasonal DLI requirements of species. This novel workflow uses hourly light results to extract monthly or seasonal average DLI values using a Grasshopper-based prototype. It then seamlessly compares them against light requirements of listed cultivars to evaluate their suitability. A basic cultivar dataset is created that is open to expansion based on cultivars growth data availability. The study offers an automated workflow for vegetation selection to agriculturalists, urban planners and landscape designers - especially in applications of vertical farms or density sensitive contexts, or any plant growth exercise.