Brad Caco Group M8X 2X9. Mr. Caco: Gradient. for mitigation

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1 December 16, 2015 Brad Caco Trinity Development Group Sun Life Financial Center, East Tower 3250 Bloor Street West, Suite 1000 Toronto, Ontario M8X 2X9 Mr. Caco: Re: Qualitative Pedestrian Wind Assessment Chapel Street, Ottawa, Ontario GWE File: DTPLW R1 1. INTRODUCTION Gradient Wind Engineering Inc. (GWE) was retained by Trinity Development Group to undertake microclimate studiess for the proposed mixed use development located at Chapel Street in Ottawa, Ontario. The complete scope of work within our mandate includes a qualitative assessment of pedestrian level winds and a roadway traffic noise study. This report provides a qualitative assessment of pedestrian wind comfort, while the noise component of our work wass submitted as a separate report on August 25 th, The current study is based on architectural drawings provided by B+H Architects in December of 2015, a review of existing surrounding context, statistical knowledge of the Ottawaa wind climate, and experience with similar past projects in Ottawa. Qualitative assessments, as compared to more elaborate wind tunnel or computational studies, serve to determine the suitability of anticipated wind conditions within various pedestrian areas, and to provide useful recommendations for mitigation that can bee introduced early in the design process. 127 Walgreen Road, Ottawa, Ontario K0A 1L0 T (613) F (613)

2 2. TERMS OF REFERENCE The focus of this qualitative pedestrian level wind assessment is a proposed mixed use development located at Chapel Street in Ottawa. The development comprises two 25 storey residential buildings linked by a large two storey podium as seen from Rideau Street. The proposed development is located on a sloping parcel of land bounded by Beausoleil Drive to the north, Chapel Street to the west, Rideau Street to the south, and adjoining properties to the east. For the purpose of this qualitative wind assessment, the north building nearest to Beausoleil Drive is identified as building A, while the south building nearest to Rideau Street is referred to as building B. Building A rises approximately 89 meters (m) above local grade (Beausoleil Drive) to the top of the roof parapet with a rectangular plan form. Building B rises approximately 93 m above local grade (Rideau Street) with an L shaped plan form at the southwest corner of the site. Ass a result of local topography, the Rideau Street ground floor is approximately 4.5 m higher than the Beausoleil Drive ground floor, which also means the 2 storey podium overlooking Rideau Street becomes 6 storeys on the Beausoleil elevation. The north half of the site, including building A, comprises 6 townhouse units facing northward and integrated with the building base. The remainder of the ground floor includes; the tower lobby accessed from Chapel Street, underground parking also accessed from Chapel Street, and a large enclosed double height loading dock accessed from Beausoleil Drive.. The south half of the site comprisess a large 2 storey retail podium and the 25 storey south building. The retail podium provides a number of small commercial retail units (CRUs) overlooking Chapel Street and a large double height contiguous CRU occupying the majority of the ground floor. Access to the residential tower lobby and underground parking also occurs from Chapel Street. Suitess begin on the 3 rd level of both buildings. The 3 rd floor of building B and 6 th floor of building A contain separatee indoor amenity spaces that overlook separate but connected outdoor amenity terraces between the two buildings. Regardingg wind exposure, the development is surrounded for all directions by low and medium rise residential and commercial developments. It is noted that two 22 storey buildings are located to the immediate west of the proposed development at 160 Chapel Street. As such, the existing massing creates generally suburban wind exposures for all wind directions. 2

3 With respect to pedestrian winds, key areas under investigation include perimeter sidewalks along Rideau Street, Chapel Street and Beausoleil Drive, pedestrian walkways along the east side of the development, building ingress and egress for the full development, and the noted outdoor amenity space at the 3 rd level. A hybrid ground floor plan is provided in Figure 1, while a 3 rd floor plan is provided in Figure 2 for purposes of illustrating and discussing the various pedestrian sensitive locations. 3. METHODO LOGY The following section describes the analysis process, including a background discussion of pedestrian comfort. The essential aspects of a qualitative pedestrian wind analysis include: (i) consideration of the statistical properties of the local wind climate; (ii) consideration of the massing of the site (i.e., the shape, height and orientation of the buildings); and (iii) evaluation of anticipated pedestrian comfort measured against industry standardd guidelines based on in house experience. 3.1 Ottawa Wind Climate The statistical model of the Ottawa wind climate, which indicates the directional character of local winds on a seasonal basis, is illustrated on the following page. The plots illustrate seasonal distribution of measured wind speeds and directions in meters per second. Probabilities of occurrence of different wind speeds are represented as stacked polar bars in sixteen azimuth divisions. The radial direction represents the percentage of time for various wind speed ranges per wind direction during a 40 year measurement period. The preferred wind speeds and directions can be identified by the longer length of the bars. For Ottawa, the most common winds occur for westerly wind directions, followed by those from the east, while the most common wind speeds are below 10 meters per second ( m/s). The directional preference and relative magnitude of wind speed changes somewhat from season to season. Also, by convention in microclimate studies, wind direction refers to the wind origin (e.g., a north wind blows from north to south). 3

4 SEASONAL DISTRIBUTION OF WINDS FOR VARIOUS PROBABILITIES OTTAWA INTERNATIONALL AIRPORT NOTES: 1. Radial distances indicate percentage of time of wind events. 2. Wind speeds represent mean hourly wind speeds measured at 10 metres above the ground. 4

5 3.2 Pedestrian Wind Comfort Guidelines The pedestrian comfort guidelines used by GWE, which parallel industry standards, are based on the correlation between a variety of pedestrian activity types, and acceptable wind speed ranges for those activities. More specifically: (i) (ii) (iii) (iv) (v) Wind conditions are considered to be comfortable for sitting when gust wind speeds lesss than or equal to 14 kilometers per hour (km/h) occur att least 80% of the time. The corresponding mean wind speed is approximately 10 km/h. Wind conditions are considered to be comfortable for standing when gust wind speedss less than or equal to 20 km/h occur at least 80% of the time. The corresponding mean wind speed is approximately 14 km/h. Wind conditions are considered to be comfortable for strolling when gust wind speeds lesss than or equal to 25 km/h occur at least 80% of the time. The corresponding mean wind speed is approximately 17 km/h, respectively. Wind conditions are considered to be comfortable for walking when gust wind speeds lesss than or equal to 30 km/h occur at least 80% of the time. The corresponding mean wind speed is approximately 20 km/h. Dangerous wind conditions which affects pedestrian s ability to be stand or walk in a stable manner are defined to exist when a gust wind speedd greater than or equal to 90 km/h exists for more than 0.1% of the time (i.e., approximately 9 hours per year).. GWE s guidelines are based on gust wind speeds since people are most sensitive to wind gusts rather than to constant wind speeds, and are applied according to the intendedd use of the outdoor area. For example, a building entrance not served by a revolving doorr should be suitable for standing but need not be suitable for sitting, while a public sidewalk needd only be suitable for walking in most circumstances. 5

6 3.3 Considerati ion of Massing and Climate The physical features of a development site that are most influential to the local wind conditions include the massing and relative spacing of surrounding buildings, the geometry and orientation of the study building, and the alignment of the study building relative to prominent wind directions. Wind flow characteristics which combine to determinee how conditions will develop include phenomena known as downwash, channelling coupled withh acceleration, and shielding, as illustrated in the image below. Downwash 1 relates to the effect of winds against a tall building, whereby much of the impinging flow on the windward side of the building, nominally below two thirds of the total height, is directed to lower levels. Taller buildings with smooth façades and no podiums produce the strongest downwash effects at grade, while the presence of protruding balconies and a tower setback from the podium edge mitigates downwash effects at thee ground level. Channelling 2 refers to acceleration of wind through gaps, while acceleration of wind 3 occurs around building corners. Shielding 4 relates to calm zones on the leeward side of buildings, protected from prevailing winds. 6

7 4. ANTICIPATE ED PEDESTRIAN COMFORT Based on the massing of the study site, surrounding buildingg massing and the orientation to the local wind climate, the following statements summarize our experience of how these conditions affect pedestrian comfort in key areas around the site. Rideau Street Sidewalk; Galleria and Retail Entrances on South Façade (Figure 1, Tags A and B): The north sidewalk of Rideau Street, identified by Tag A in Figure 1, will be exposed to a combination of horizontal winds from easterly and westerly directions that are expected to create conditions suitable for sitting during the summer, standing during late spring and early autumn, strolling during early spring and late autumn, and walking during the remaining colder months. The noted wind conditions are considered acceptable for public sidewalks. The galleria and retail entrances (Tag B, Figure 1), both served by revolving doors, are protected within the setback area at the southwest corner of the site overlooking Rideau and Chapel Streets. Wind conditions close to the building façade are expected to be calmer than those reported for the Rideau Street sidewalk and exposed corner area. More specifically, winds affecting the patrons entering or leaving the building, as well as operation of the revolving doors, will be moderated by; (i) the corner setback of the building facades; and (ii) the setback of building B above the podium. The net influence of the building geometry will be to create wind conditions suitable for the intended uses throughout the year without the need for mitigation. Chapel Street Sidewalk; Building B Main Residential Entrance, Retail Entrances, Building and Stairwell Exits on West Façade (Figure 1, Tags C and D): Thee sidewalk along Chapel Street is identified by Tag C in Figure 1, while the building access points that front onto Chapel Street, ncluding the main residential entrance of building B, are identifiedd by Tag D. Pedestrian wind comfort along the Chapel Street sidewalk area will benefit from the existing building across the street at 160 Chapel Street to the immediate west. Building B setback above the podium will also limit any downwash that may occur along the building to grade level. As such, the site will largely be shielded from prominent westerly winds to create conditions suitable for sitting during the summer, standing during the shoulder months of spring and autumn, and suitable for walking during the remaining colder months. 7

8 Sidewalk Corner at the Intersection of Chapel Street and Beausoleil Drive (Figure 1, Tag E): Conditions at the noted corner, identified by Tag E in Figure 1, are expected to be windier than previous locations along Chapel Street due to the greater exposure to westerly winds. However, conditions will remain acceptable and suitable for walking, orr better, throughout the year. Main Lobby Entrance, Building A (Figure 1, Tag F): The main entrance of the north building A is setback and well protected by the building facades at the inside corner overlooking the intersection of Chapel Street and Beausoleil Drive. The narrow profile of the tower facing prominent westerly winds will also mitigate windy conditions at grade. As such, conditions at thiss location are expected to be calm and suitable for sitting during the summer and standing or better for the remainder of the year, which are acceptable for the intended use of the area. Beausoleil Drive Sidewalk; North Sidewalk and Townhousee Access (Figure 1, Tags G): The sidewalk along Beausoleil Drive will experience direct horizontal windss from prominent westerly, northwest and east directions. However, the tower setback above the podium will avoid significant downwash which often is the culprit of persistent uncomfortable conditions att grade. As such, wind conditions along the sidewalk are expected to be suitable for walking during thee winter and standing or better during the remainder of the year, which are acceptable for the area usage. Furthermore, conditions are expected to become calmer near to the townhouse entrances which also serve the intended purpose. Similar conditions are expected around the entrance to the loading dock and the exit stairs at the far eastern edge of the podium. 8

9 Public Pathway along East Side of Development (Figure 1, Tag H): A public pathway, which is identified as Tag J in Figure 1, extends from Rideau Streett to Beausoleil Drive and is flanked by the proposed development to the west and the existing 2 storey EconoLodge to the east. Given that the pathway is narrow and protected from prominent winds, conditions along the pathway and within the vicinity of the noted building access points are expected to be calm and suitable for the intended uses throughout the year. The widenedd area on the north side will remain suitable for walking or better year round. Outdoor Protected Amenity Areas on Podium Roof (Figure 2, Tags I and J): Wind conditions over the podium amenity roof are expected to vary considerably. Thee calmest areas are expected to be located around the access doors (Tags I) for both buildings. As such, these areas will be suitable for sitting during the 3 warmerr seasons and suitable for standing during the winter, whichh are acceptable conditions for the areas. The remaining area between buildings A and B, identified by Tags J, are expected to experience moderately windy conditions. While west and southwest winds willl be shielded by the existing tall buildings across Chapel Street, prominent northwest winds will funnel through and over the podium to create moderately strong winds. The adverse influence of easterly winds will likely be limited during the winter period which is not of significant concern. As such, mitigation measures will be required over open areas that are planned forr sitting and lounging. Mitigation measures will include perimeter wind screens comprising 1.8 m tall solid glass barriers ( e.g., glazed wind guards) or the equivalent landscape elements (i.e., dense coniferous plantings) arranged to provide continuous protection. Given the large extendd of the middle podium area, mitigation measuress can be limited to those areas reserved for sedentary uses (patio, sitting, eating) according to the landscape plans. Mitigation is not required for active use areas such as walking / running tracks, playgrounds, or non accessible landscape areas. The implementation of the noted mitigation measures is expected to result in conditions suitable and acceptable for sitting during the summer months, and shoulder seasons of late spring to early autumn. 9

10 Existing vs Future Wind Conditions: The introduction of the proposed development is not expected to adversely influence existing neighbouring buildings. Although modest changes to wind speeds may occur beyond the site property, pedestrian comfort over areas outside the immediatee influence of the study site is expected to remain similar to existing conditions. Additionally, within the context of typical weather patterns,, excluding anomalous local storm events, such as thunderstorms, tornadoes and downbursts, no dangerous or consistently strong wind conditions are expected anywhere over the subject site on an annual basis. Of particular interest, no areas over the study site are likely to experience conditions that would be considered unsafe, or troublesome for elderly persons. 10

11 5. SUMMARY AND RECOMMENDATIONS Based on the qualitative analysis of site plans, the proposedd building forms and the wind statisticss for Ottawa, grade level wind conditions over the proposed development site at Chapel Street, including building access points, are expected to be suitable for the intended uses throughout the year without mitigation. The exception to this statement is the joint 3 rd and 6 th level podium roof where wind conditions are expected to vary from relatively calm in some areas to windy in others. The calmest areas are expected to be located around the access doors for both buildings. As such, these areas willl be suitable for sitting during the 3 warmer seasons and suitable for standing during the winter, which are acceptable conditions for the areas. The remaining area between the buildings is expected to experience moderately windy conditions. While west and southwest winds willl be shielded by the existing tall buildings across Chapel Street, prominent northwest winds will funnel through and over the podium to create moderately strong winds. The adverse influence of easterly winds will likely be limited during the winter period which is not of significant concern. As such, mitigation measures will be required over open areas that are planned forr sitting and lounging. Mitigation measures will include perimeter wind screens comprising 1.8 m tall solid glass barriers ( e.g., glazed wind guards) or the equivalent landscape elements (i.e., dense coniferous plantings) arranged to provide continuous protection. Given the large extendd of the middle podium area, mitigation measuress can be limited to those areas reserved for sedentary uses (patio, sitting, eating) according to the landscape plans. Mitigation is not required for active use areas such as walking / running tracks, playgrounds, or non accessible landscape areas. The foregoing analysiss and statements are based on experience and knowledge of wind flow patterns in suburban settings. Hence, this assessment is intended to assure adequate pedestrian safety relating to wind while providing general guidance relating to pedestrian comfort around the subject site. 11

12 This concludes our pedestrian level wind assessment and report. We thank you for the opportunity to be of service. Sincerely, Gradient Wind Engineeringg Inc. Justin Ferraro, B.Eng., EIT Project Manager Vincent Ferraro, M.Eng., P.Eng. Managingg Principal GWE DTPLW R1 12

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