Article

Modeling outdoor thermal comfort along cycling routes at varying levels of physical accuracy to predict bike ridership in Cambridge, MA

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The Universal Thermal Climate Index (UTCI) has been linked to outdoor activity patterns and used to evaluate the effectiveness of urban interventions to improve thermal comfort. This study investigates how simulating the urban environment at increasing levels of physical accuracy impacts UTCI values along three cycling routes in Cambridge, Massachusetts. Baseline UTCI values are estimated using a local weather file, and the following increments in physical accuracy are considered: wind-scaling, shading from buildings, shading and cooling from trees, computational fluid dynamics simulations for wind speeds, and simulated surface temperatures. With bike ridership data from Bluebikes, Boston's bike-sharing program, the relationship between bike ridership patterns and UTCI values along each route is studied. Supervised machine learning models are applied to predict bike ridership based on UTCI and other predictors. UTCI simulation results show that incorporating the various increments of accuracy influences hourly UTCI values at urban areas and exposed areas differently. Incorporating local wind speeds is especially impactful for urban areas. The statistical models trained to predict hourly bike trip counts based on UTCI and other demand and weather predictors achieved a root-mean-squared error of 1.06 trips. 47% of predictions were correct, and an additional 42% of predictions were off by 1 trip. This study demonstrates the importance of spatial refinement in simulating UTCI, and motivates future research into efficient simulation methods or rules-of-thumb for deriving spatial-temporal UTCI values. Future work into building a robust predictive model would motivate the design of thermally comfortable environments for human-powered transportation in cities.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Hence, the scope of this study was narrowed to assessing the data quality by low-speed sampling. We tested a thermal-biking campaign [6] in the Esposizione Universale Roma (EUR) district in Rome, Italy. The data quality was assessed by finding the time lag of sampling nuanced Ta and Rh variations below the driving speeds (< 6 m/s). ...
Conference Paper
Full-text available
Crowdsourced weather data has been increasingly used to provide the input data for the boundary conditions in the microclimate models as well as to validate the modelling outputs. MeteoTracker (MT) is an Internet of Things (IoT) application for domestic vehicles that can contribute to the intra-urban air temperature database for meteorology enthusiasts as well as research and design communities. To promote green and healthy mobility, we have validated the MT device on bicycles and evaluated its monitoring performance with 2 other Kestrel heat stress trackers (KT) at low travelling/wind speed. The pre-planned cycling route cuts through the EUR district in Rome, Italy in September 2021. The dual-sensor design and the radiation error correct system (RECS) in the MT devices demonstrate good abilities in probing air temperature and humidity nuances when passing through different urban areas, as the three devices remain highly synchronised (Pearson r > 0.86). However, the MT device may overshoot the response time (> 41 s) if the cycling speed is less than 3 m/s. We have suggested some strategies for improvement in reducing the response time of probing the ambience under nuanced thermal variability.
... The transient nature of thermal comfort has been widely discussed in indoor studies (Vellei et al. 2021). However, such understandings of outdoor environments are generally lacking (Young et al. 2022). ...
Chapter
Cities are composed of a multitude of interconnected interactive layers and systems. The contemporary urban discourse has seen the utilization of Open data in decoding and understanding complex urban patterns that have eluded researchers for decades. Different layers of raw data from historical city cores up to the atmospheric climate have become more accessible, opening new horizons for multidisciplinary research. The rising complexity of cities calls for emerging approaches that can address the relationship between different layers of data—existing or emerging. In this regard, the current chapter is introducing and applying a methodology to use historical, spatial, and temporal datasets from Open Street Map (OSM) processed by Space Syntax superimposed on simulated urban microclimate dataset to find correlating patterns on how urban morphology has shaped the cities and the microenvironments over time. The outcomes for the case of Munich, illustrate the typologies that can be utilized in planning and developing design strategies to address micro-climate and accessibility in cities.KeywordsUrban morphologyUrban climateSpace syntaxMicroclimateGIS
Article
Global warming and the urban heat island effect have led to the deterioration of the outdoor thermal environment and the rise of building cooling demand, calling for urban design with high environmental quality. However, little has been changed in the practice of urban street design. This paper bridges this gap by developing a framework of parametric simulation for design guidance of urban streets with an advanced urban canopy model that can simulate the interactive indoor-outdoor environment. Case studies are conducted at the neighborhood scale for six cities to improve outdoor thermal comfort and building energy efficiency in summer. The influence of street and building design parameters has been investigated based on 31104 simulations. Results reveal the conflict between optimizing outdoor thermal comfort and building energy efficiency. In the majority of the investigated cities, window-to-wall ratio, window type, and street orientation are the most influential parameters. Strategies by adjusting these parameters can significantly improve outdoor thermal comfort, as quantified by thermal stress hours, at a cost of increasing the building cooling load. Planting bigger and denser roadside trees always moderately reduces the thermal stress hours and building cooling load. These results demonstrate the potential of this framework to identify the design trade-offs between thermal comfort and building energy efficiency. The framework can be extended to help designers and policymakers at the early design stage for various cities.
Article
In recent decades, the pedestrian's outdoor thermal comfort has been critical for designing sustainable cities, which can be affected by wind flow in urban spaces. Urban forms influence wind speed, changing the urban air quality, and causing pedestrians' thermal comfort or discomfort. Therefore, it is required to design the urban spaces in such a way as to regulate the wind speed in order to provide thermal comfort situations for pedestrians based on their climate conditions. This study aimed to provide a framework for analysing the outdoor thermal comfort of various building layouts and their relation to wind speed in a site. This paper also proposed new indexes for improvements to the Physiological Equivalent Temperature (PET) index enabling the calculation of outdoor thermal comfort based on the likelihood of people being outside for a whole day. In-situ measurements were carried out in Tehran, Iran, to validate the presented framework. Simulations were conducted for 15 critical points in nine different building layouts for the windiest day on the site. ENVI-met was used to simulate the wind speed, outdoor air temperature, and mean radiant temperature, while PET was calculated by means of Leonardo and RayMan. The results demonstrated that pedestrians' outdoor thermal comfort for in-site and out-site points improved by 2.8% and 2.3%, respectively, compared to the current site situation. Also, the framework produced a suitable urban form to provide outdoor thermal comfort with evaluating different urban forms.
Conference Paper
Full-text available
Employing urban planning and design to promote active travel modes, such as walking and biking, are important for decarbonizing urban mobility. This paper proposes a modeling framework that investigates the interdependencies between the built environment and travel behaviors through the lens of urban microclimates. We combine travel data, built environment data, and Universal Thermal Climate Index (UTCI) calculations for New York City and train a predictive model for intra-city mobility patterns. Then, the impacts of UTCI features are studied through a sensitivity analysis and a spatial heterogeneity analysis. Results show that impacts of UTCI features can account for up to 4% change in the choice of active travel mode in dense urban areas. Also, impacts of microclimate vary across different travel contexts regarding season, time of day, activity, built environment, and traveler type. Our methodology and findings can inform future decision-making of microclimate-oriented spatial planning and design interventions.
Article
Full-text available
In the context of dense urban environments and climate change, pedestrians’ thermal experience plays an increasingly significant role in people’s health and well-being. In this research, the authors combine the fields of architecture, climate-responsive design, and robotic fabrication with the goal of investigating strategies to improve outdoor thermal comfort for pedestrians in cities with frequent extreme heat events. Based on a case study in the city of Munich, this paper presents findings into the technological approaches and methods for location-specific climate-resilient brick facades using robotic assembly. To achieve this goal, different bricklaying patterns were investigated to create a self-shading effect and thus reduce solar radiation and ultimately achieve an improved thermal condition for pedestrians moving along urban facades at street level. Using computer-aided microclimate simulation, generic self-shading brick pattern designs were tailored to highly location-specific microclimate requirements. Robotic assembly technology was used to produce such tailored, non-standard brickwork facades. The results of this research led to a data-informed design process with a demonstrator object being realized at 1:1 scale with a height of 2 m and a length of 3 m using a collaborative robot on site. Thermal measurements on the built demonstrator provided indications of reduced surface temperatures despite high solar radiation and thus validated the location-specific self-shading effects according to solar radiation simulation.
Conference Paper
Full-text available
PANDO is a numerical process-based simulation tool that enables the user to model individual trees and canopies in Rhino Grasshopper interface. This plugin simulates radiation fluxes in three different wavebands of photosynthetic (PAR), near infrared (NIR) and thermal. It also counts for photosynthesis and transpiration by tree canopies. PANDO can be used also to estimate root water uptake, drainage, canopy interception and cooling potential of trees by coupling with outdoor thermal comfort models. The tool enables the user to plan and design urban greenery more efficiently in cities considering the benefits and future paybacks.
Article
Full-text available
Urban areas are characterized by a plurality of microclimates given by the diversity of morphologies, optical and radiative properties, solar access and air circulation in different street canyons. For these reasons, beyond strategies at urban scale, mitigation needs to be addressed at district or even at urban canyon scale, just like the design of buildings. Among different options, canopy shading has been proposed in several urban contexts, and to assess the impact of this mitigation technique on air temperature and outdoor thermal comfort conditions we performed numerical simulations for a north-south oriented urban canyon with high solar access (height to width ratio equal to 0.18) in the climate context of Milano (Italy).
Article
Full-text available
The Universal Thermal Climate Index (UTCI) aimed for a one-dimensional quantity adequately reflecting the human physiological reaction to the multi-dimensionally defined actual outdoor thermal environment. The human reaction was simulated by the UTCI-Fiala multi-node model of human thermoregulation, which was integrated with an adaptive clothing model. Following the concept of an equivalent temperature, UTCI for a given combination of wind speed, radiation, humidity and air temperature was defined as the air temperature of the reference environment, which according to the model produces an equivalent dynamic physiological response. Operationalising this concept involved (1) the definition of a reference environment with 50% relative humidity (but vapour pressure capped at 20 hPa), with calm air and radiant temperature equalling air temperature and (2) the development of a one-dimensional representation of the multivariate model output at different exposure times. The latter was achieved by principal component analyses showing that the linear combination of 7 parameters of thermophysiological strain (core, mean and facial skin temperatures, sweat production, skin wettedness, skin blood flow, shivering) after 30 and 120 min exposure time accounted for two-thirds of the total variation in the multi-dimensional dynamic physiological response. The operational procedure was completed by a scale categorising UTCI equivalent temperature values in terms of thermal stress, and by providing simplified routines for fast but sufficiently accurate calculation, which included look-up tables of pre-calculated UTCI values for a grid of all relevant combinations of climate parameters and polynomial regression equations predicting UTCI over the same grid. The analyses of the sensitivity of UTCI to humidity, radiation and wind speed showed plausible reactions in the heat as well as in the cold, and indicate that UTCI may in this regard be universally useable in the major areas of research and application in human biometeorology.
Article
Full-text available
Over the past century more than 100 indices have been developed and used to assess bioclimatic conditions for human beings. The majority of these indices are used sporadically or for specific purposes. Some are based on generalized results of measurements (wind chill, cooling power, wet bulb temperature) and some on the empirically observed reactions of the human body to thermal stress (physiological strain, effective temperature). Those indices that are based on human heat balance considerations are referred to as "rational indices". Several simple human heat balance models are known and are used in research and practice. This paper presents a comparative analysis of the newly developed Universal Thermal Climate Index (UTCI), and some of the more prevalent thermal indices. The analysis is based on three groups of data: global data-set, synoptic datasets from Europe, and local scale data from special measurement campaigns of COST Action 730. We found the present indices to express bioclimatic conditions reasonably only under specific meteorological situations, while the UTCI represents specific climates, weather, and locations much better. Furthermore, similar to the human body, the UTCI is very sensitive to changes in ambient stimuli: temperature, solar radiation, wind and humidity. UTCI depicts temporal variability of thermal conditions better than other indices. The UTCI scale is able to express even slight differences in the intensity of meteorological stimuli.
Article
Outdoor thermal comfort simulation simulations rely on the mean radiant temperature (MRT) seen by pedestrians as an important input that remains difficult to compute. Especially for large urban models, computing relevant surface temperatures and radiation fluxes that make up the MRT is a daunting task in terms of simulation setup and the computational overhead. We propose a new algorithm to estimate exterior surface temperatures of building facades, roofs, and ground surfaces in an arbitrary urban 3D model. The algorithm discretizes all model surfaces and clusters them by material properties and sky and sun exposure to reduce computational complexity. The model setup is fully automated, and the algorithm is implemented in the popular Rhino3d CAD environment. We demonstrate the accuracy of the algorithm by comparing both the resulting external surface temperatures against a high-fidelity simulation and the final MRT against real-world measurements. We report an RMSE of 1.8 °C and 2.0 °C, respectively, while reducing simulation times by a factor of ∼80. Envisioned applications of the algorithm range from rapid microclimate simulations in fast-paced urban design processes to large scale urban comfort evaluation of existing cities.
Article
For urban CFD simulations, it is considered a best practice to use a box-shaped simulation domain. Box-shaped domains, however, show drawbacks for airflow from several wind directions as remeshing and additional preprocessing steps become necessary. We introduce a routine to create a cylindrical mesh that expedites the simulation of arbitrary wind directions using OpenFOAM. Results computed with the cylindrical domain are validated against wind tunnel data. We report that the cylindrical method yields comparable results in terms of accuracy and convergence behaviour. Further, run time comparisons in a real-world scenario are conducted to discuss its advantages and limitations. Based on the findings, we recommend using the cylindrical approach if at least eight wind directions are analyzed for which we report 18% run time savings. The cylindrical domain along with automated best practice boundary conditions has been implemented in Eddy3D – a plugin for Rhinoceros.
Article
There has been no study on the impacts of street tree interval on the street-level radiant environment, although it has been a key factor in the design of thermally comfortable streets. In this study, the variation in pedestrian mean radiant temperature (MRT) is investigated as a function of the tree interval using a newly developed multilayer MRT model. Tree size and street size are considered in the model experiments. The results show that MRT was most effectively reduced by large trees, indicating that they may be planted at wider intervals compared to smaller trees to achieve comparable MRT reductions. Furthermore, as the tree interval decreases, MRT reduction was increased exponentially by small trees, while MRT reduction was increased linearly by large trees. Therefore, urban planners can reduce pedestrian exposure to radiation by planting either larger trees or closely spaced smaller trees. These results provide insight into optimal configurations of street trees for maximum reduction of MRT in a variety of urban canyon configurations.
Article
This study presents a novel approach to validate the capability of biometeorological indices to predict the likelihood of urban dwellers to be outside during midday. Over a period of ten months three Wi-Fi scanners were used in a public courtyard in Cambridge, MA, to record outside dwelling patterns. Based on encrypted MacIDs courtyard attendees could be divided into 16,000 regulars and 676,000 visitors. Universal Thermal Climate Index (UTCI) predictions based on a combination of measured microclimatic conditions and mean radiant temperature simulations using ENVI-met were shown to strongly correlate with the number of regulars present during lunchtime with coefficients of determination (R2) of 92% during spring and 70% during summer/fall, respectively. Lunchtime attendance peaked for UTCI values in the thermal comfort and moderate heat stress ranges. In parallel, the probability for regulars to have lunch outside more than doubled during those UTCI conditions and the median lunchbreak length increased from 8 min to 12 min. These findings suggest that UTCI can be used as a reliable environmental performance metric to support the design and preservation of comfortable outdoor spaces. The reported use of public Wi-Fi data can help city governments to better understand – and potentially improve – the use of outdoor spaces while maintaining the privacy of their constituents.
Article
The study encompasses the validation of the dynamic, RADIANCE-based daylight simulation method DAYSIM, which uses the concept of daylight coefficients and the Perez sky model to predict the short-time-step development of indoor illuminances. Measured and simulated illuminances have been compared under 10,097 sky conditions in a full-scale test office with a double glazing and external venetian blinds. The additional planning effort for the designer compared to a conventional daylight simulation is addressed. It has been found that the treatment of direct sunlight strongly influences the accuracy of the daylight coefficient method. Three different simulation modes for the direct sunlight are investigated. The simulation results prove that indoor illuminances can be modeled with comparable accuracy for various blind settings under arbitrary sky conditions. Daylight autonomies are predicted with an accuracy below 2% points, where simulation errors stem with roughly equal parts from the raytracing and the sky model.
Article
A numerical simulation method is developed for predicting the effective radiation area and the projected area of a human body for any posture. This method is based on the solar heat gain simulation for buildings. To confirm the validity of the present method, predicted effective radiation area factors and projected area factors for both standing and seated persons are compared with those by the measurements. It was found that predicted values agree quite well with those by the subjective experiments within 10% accuracy. The effective radiation area and the diagrams of the projected area factors for a person sitting on the floor are illustrated. Moreover, the angle factors between a standing person and rectangular planes are calculated and compared with the results by Fanger.
Article
The relative humidity (RH) and the dewpoint temperature (td) are two widely used indicators of the amount of moisture in air. The exact conversion from RH to td, as well as highly accurate approximations, are too complex to be done easily without the help of a calculator or computer. However, there is a very simple rule of thumb that can be very useful for approximating the conversion for moist air (RH > 50%) which does not appear to be widely known by the meteorological community: td decreases by about 1°C for every 5% decrease in RH (starting at td = t, the dry bulb temperature, when RH = 100%). This article examines the mathematical basis and accuracy of this and other relationships between the dewpoint and relative humidity. Several useful applications of the simple conversion are presented, in particular the computation of the cumulus cloud-base level (or lifting condensation level) as zLCL (20 + t/5) (100 - RH), where zLCL is in meters when t is in degrees Celcius and RH in percent. Finally, a historical perspective is given with anecdotes about some of the early work in this field.
2018 revision of world urbanization prospects
United Nations, 2018 revision of world urbanization prospects [Online]. Available: https://www.un.org/development/desa/publications/2018-revision-of-world -urbanization-prospects.html, 2018.
Living Streets : Strategies for Crafting Public Space
  • L Bain
  • B Gray
  • D Rodgers
L. Bain, B. Gray, D. Rodgers, Living Streets : Strategies for Crafting Public Space, John Wiley & Sons, 2012.
Local Actions to Support Walking and Cycling during Social Distancing Dataset
  • T Combs
T. Combs, Local Actions to Support Walking and Cycling during Social Distancing Dataset, 2020.
Bluebikes System data
Bluebikes Boston, Bluebikes System data, Apr. 28, https://www.bluebikes.com/sy stem-data.
Development of global typical meteorological years (TMYx)
  • L K Lawrie
  • D B Crawley
L.K. Lawrie, D.B. Crawley, Development of global typical meteorological years (TMYx). http://climate.onebuilding.org/contact/default.html, 2019. (Accessed 11 May 2021).
The Human Bio-Meteorological Chart A Design Tool for Outdoor Thermal Comfort
  • W Kessling
  • M Engelhardt
  • D Kiehlmann
W. Kessling, M. Engelhardt, D. Kiehlmann, The Human Bio-Meteorological Chart A Design Tool for Outdoor Thermal Comfort, 2013.