point cover jan 13 - Boston Redevelopment Authority

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Expanded_PNF\04_Environmental_FINAL.do
c
Vanasse Hangen Brustlin, Inc.
The Point, Boston
No-Build Conditions – includes existing buildings on and around the Project Site as well as planned
buildings within the study locus; and
Build Conditions – includes the proposed building design within the existing site surroundings and any
planned buildings within the project area.
The scale model was equipped with specifically designed wind speed sensors that were connected to the
wind tunnel’s data acquisition system to record the mean and fluctuating components of wind speed at a fullscale
height of about five feet above grade in pedestrian areas throughout the study area. Study locations
were selected by RWDI based on their extensive experience in modeling pedestrian level wind conditions in
Boston. These locations were reviewed by the BRA and updated per their comments prior to testing. Specific
study locations were selected to adequately model conditions at along the public pedestrian ways around the
site, adjacent abutting properties and at key building roof locations. The horizontal extent of the study area
was selected to capture any locations likely to be affected by the Project. This methodology was confirmed by
comparing the modeled conditions at the perimeter of the study area under the No-Build and Build
Conditions. See Appendix C for further information.
Wind speeds were measured for 36 wind directions, in 10 degree increments, starting from true north. The
measurements at each sensor location were recorded in the form of ratios of local mean and gust speeds to
the reference wind speed in the free stream above the model. The results were then combined with long-term
meteorological data, recorded during the years 1973 to 2011 at Boston’s Logan International Airport, in order
to predict full scale wind conditions. The analysis was performed separately for each of the four seasons and
for the entire year. The results of the wind tunnel study were compared to the BRA recommended criteria for
evaluating pedestrian level winds.
This study involved state-of-the-art measurements and analysis techniques to predict wind conditions at the
study site. However, some uncertainty remains in predicting wind comfort, and this must be kept in mind.
For example, the sensation of comfort among individuals can be quite variable. The comfort limits used in
this report represent an average for the total population. Also, unforeseen changes in the project area, such as
the construction or removal of buildings, can affect the conditions experiences at the Project Site. Finally, the
predictions of wind speeds are necessarily a statistical procedure. The wind speeds reported are for the
frequency or occurrence stated (on percent of the time). Higher wind speeds may occur but on a less frequent
basis.
Pedestrian Wind Comfort Criteria
The BRA has adopted two standards for assessing the relative wind comfort of pedestrians. First, the BRA
wind design guidance criterion states that an effective gust velocity (hourly mean wind speed +1.5 times the
root-mean-square wind speed) of 31 miles per hour (mph) should not be exceeded more than one percent of
the time. The second set of criteria used by the BRA to determine the acceptability of specific location is based
on the work of Melbourne. This set of criteria is used to determine the relative level of pedestrian wind
comfort for activities such as sitting, standing or walking. The criteria are expressed in terms of benchmarks
for the 1-hour mean wind speed exceeded one percent of the time (i.e., the 99 th percentile mean wind speed).
They are as follows in Table 4-1.
4-4 Environmental Protection