Ensuring pedestrian comfort in a large-scale, open-air retail environment.
Brickell City Center is a 5.4-million-square-foot complex in downtown Miami comprising office, retail, hotel, and residential spaces. With a footprint that will span three city blocks when completed, the billion-dollar project incorporates many sustainable design elements—notably a strong emphasis on pedestrian access via multiple walkways connecting to an open-air shopping mall.
Miami’s tropical climate makes it difficult to create environments that are pedestrian-friendly. During the summer, temperatures often exceed 90˚F (32˚C) and the hot, humid days typically include heavy afternoon thundershowers. On the Brickell City Center site, cooling breezes off Biscayne Bay mitigate the heat somewhat, but wind and rain remain a challenge.
The project’s centerpiece is a raised platform on which people can walk above street level between the shopping areas and adjacent condo and office buildings. Sheltering this platform is a “climate ribbon” – an undulating strip of steel and glass that offers protection from the sun and rain while redirecting breezes to provide natural air conditioning. Project architects Arquitectonica of Miami and designers Hugh Dutton & Associés of Paris knew this innovative passive design element had to be executed perfectly to achieve the vision of an urban “lifestyle development” where pedestrians move comfortably throughout the complex. So they turned to the wind engineering and microclimate experts at RWDI.
Embarking on a rigorous technical analysis of the challenge, we identified two fundamental issues:
1.How do we define acceptable comfort?
Perceptions of thermal comfort vary from person to person. People experience conditions such as air temperature, humidity and wind velocity differently depending on personal factors such as activity level, duration of exposure and clothing. Expectations also matter: we expect to be more comfortable inside a restaurant than at a bus stop. The design of a public space must recognize this complex interplay of variables in arriving at a metric of comfort that reasonably accommodates the largest number of people. For Brickell City Center we adopted a survey-based measurement technique called the standard predicted mean vote, which yields an index showing where 80% of respondents are aligned in their perception of thermal conditions. A key observation, confirmed by past experience, was that people were willing to accept a wider range of conditions in an outdoor setting – and given Miami’s climate, would even tolerate some measure of discomfort.
2. How can we accurately model the microclimate?
To replicate as closely as possible the effect of the climate ribbon, the RWDI team combined in-depth statistical analysis of local climate data with advanced computational modeling. Examining many years of records compiled at Miami International Airport, we assessed the full spectrum of weather scenarios. Next, we explored potential wind impacts through simulations and gauged sun effects using proprietary insolation modeling techniques. After testing against a rich matrix of variables, including the influence of nearby high-rise towers and other structures that had yet to be built, we were able to predict airflow and solar radiation beneath the climate ribbon with a high degree of accuracy – at every hour of the day, and through the changing seasons.
Based on our detailed microclimate modeling, we assigned a thermal comfort score at regular intervals along the entire climate ribbon. We then collaborated with the design team to explore various configuration and construction options. Once that investigation was complete, the designers were ready to optimize their specifications and move forward, confident that the hundreds of thousands of people who will soon be walking through Brickell City Center will find its retail spaces and open walkways attractive and comfortable all year round.