PEDESTRIAN WIND COMFORT ASSESSMENT · MASSIVE SUPER-IMPRESSIVE & AWESOME IMAE White Collar Factory 2 Old Street ard London EC2 0AF T +11 7 47 94ff7 9999 F +11 7 47 94ff7 9ffffffinfo

Plot 12, Phase 1B (South)Reserved Matters Application

Brent Cross South Limited Partnership

October 2017

PEDESTRIAN WIND COMFORT ASSESSMENT

Contacts

Brent Cross South Limited Partnership 4 Stable Street London N1C 4AB www.brentcrosssouth.co.uk www.argentrelated.co.uk @argentrelated

AKT II

White Collar Factory, 1 Old Street, London EC1Y 8AF www.akt-uk.com

MASSIVE SUPER-IMPRESSIVE

&AWESOME

IMAGEWhite Collar Factory 1 Old Street Yard London EC1Y 8AF T +44 (0) 20 7250 7777 F +44 (0) 20 7250 7555 info @ akt-uk.com www.akt-uk.com

4109 Brent Cross South - Plot 12

PEDESTRIAN WIND COMFORT ASSESSMENTOCTOBER 2017

1.1 Introduction page 3

1.2 Executive Summary 3

2 Description of the Study 4

2.1 Site/ Building Details 4

2.2 Scope of Work 5

3 Results of the Study page 7

3.1 Macro Scale - Observations 7

Macro Views of Horizontal Planes at +1.50m 8

3.2 Micro Scale - Observations 13

Micro Views of Horizontal Planes at +1.50m 14

3.3 Comfort Assessment - Observations 18

Comfort Assessment at +1.50m and balconies 20

3.4 Comfort Assessment - Data Point Comparison 23

Tabulated Results 24

4 Conclusions page 25

4.1 Macro Scale Wind Effects 25

4.2 Micro Scale Wind Effects 25

4.3 Pedestrian Wind Comfort 25

Appendix A - Methodology 26

A.1 Wind Analysis 26

A.2 Wind Analysis 26

A.3 Digital Wind Tunnela an Model Details 26

A.4 Measurements and Analysis 26

A.5 Local Climate 26

A.6 Boundary Conditions 27

Appendix B - Analysis Criteria 28

B.1 Software and Toolkit Overview 28

B.2 Analysis Overview 28

B.3 Wind Comfort Assessment 29

B.4 Wind Comfort Criteria 29

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4109 - Brent Cross South - Plot 12

Contents

rev 0 24-10-2017Issued for Reserved Matters Application

Revision Date Status

Prepared by: Jeroen Janssen

Checked by: Jeroen Janssen

Approved by: Edoardo Tibuzzi

Figure 1.1 Aerial view of the area as it is currently, showing the approximate location of Plot 12, BXS

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This report has been prepared by AKT II on behalf of BXS Limited Partnership (BXS LP) to support a Reserved Matters Application for Plot 12, the adjacent streets and public realm and details an assessment which investigates the levels of pedestrian wind comfort at street level around the Plot 12 development and on terraces and balconies.

This reports supports the Reserved Matters Application (RMA) to conform to the conditions set out by the following documents:

•• Section 73 Permission Ref F/04687/13 dated on 23 July 2014, particularly Conditions 34.1 and 34.5. 34.Microclimate 34.1. Any Reserved Matters Application that includes a Building of more than 4 storeys in height, which abuts any Principal Open Space or Public Realm or any pedestrian route which is likely to be subject to use by pedestrians as a thoroughfare or to be used for recreation or relaxation, shall be accompanied by a wind tunnel or other assessment which demonstrates that appropriate levels of amenity, as set out in the Lawson Criteria for Distress and Comfort, which are summarised in Table 7 of the DSF, can be met. 34.2. Any Reserved Matters Application that includes a building of more than 4 storeys in height, where it is possible that the good practice standards in BRE 209 as set out in Table 6 of the DSF in relation to daylight and sunlight will not be achievable, shall be accompanied by a daylight and sunlight assessment undertaken in accordance with BRE 209 and BS8206.

•• Revised Development Specification and Framework dated from October 2013, particularly paragraph 2.80. 2.80 It will be a requirement at detailed design stage that all outdoor spaces are shown to accord with the appropriate wind effect standards for the relevant uses of the respective public and private open spaces and routes surrounding the various buildings in the development, derived from the Lawson Criteria for Distress and Comfort ("The evaluation of the windiness of a building complex before construction", TV Lawson, London Docklands Development Corporation). These provide a guide to the appropriate level of amenity that will be achieved, as set out in the Table 7. The objective will be to design to a minimum rating of C2 or better in significant parts of each of the main squares and higher where the proposed use requires.

A description of the main elements and outcomes of the study is provided, including a technical appendix describing the boundary conditions and input parameters which defined the Computational Fluid Dynamics (CFD) study undertaken. Furthermore, a description of the pedestrian wind comfort levels is investigated in a comparative sense.

This study is targeted at a comparative assessment of pedestrian wind comfort around the site and the effects of the design proposal.

When assessing the pedestrian wind comfort for Brent Cross South Plot 12, large areas around the development fall in the most comfortable grade 'Pedestrian sitting', which means these areas are suitable for long term seating and leasure activities, such as a lunch, picnic or a play ground.

Some minor areas in the tertiary streets to the East and West, as well as the area along the High Street directly adjacent to the facade fall in the category 'Pedestrian Standing/Entrance Doors'. These areas are still very quiet considering wind comfort and are suitable for comfortably accessing the buildings and dwellings.

Other small areas in the tertiary streets, as well as most of the High Street, are falling in the category 'Pedestrian Walking Through'. These areas are still very much suitable for its use as streets and passageways, but less so as entrances or amenity spaces.

1.1 Introduction

1.2 Executive Summary

The effect of vegetation around the development is significant, specifically during the summer months when people are actually using the amenity spaces. The direct benefits are clearly visible in the image comparison of the direct simulation results. However, as soon as these results are statistically related back to the probabilites of the wind blowing from all direction related to the yearly windrose, these direct benefits become less visible. As can be seen in the images on these pages, the effect on the yearly comfort grades is minor, showing only slight improvements between the comfort values compared to the values found for the proposed development. This is mainly due to the fact that the development is already performing quite well in terms of pedestrian wind comfort and therefore the added benefit of the vegetation is rather small for the overall full-year comfort. Besides that, for the colder winter months the simulations without the trees are considered, while for the summer months the simulations with the vegetation is taken. These winter months are colder and windier, and therefore contribute to a larger extent to the worser months for the year-round comfort.

The study presented here clearly identifies trends of acceptable pedestrian wind comfort as a consequence of the proposed massing of the development, without a strong necessity of further mitigation measures.

2 Description of the Study

2.1 Site/ Building Details

2.1.1Location and surroundingsThe study site is located within the southern part of the Brent Cross Cricklewood regeneration area (BXC) located in the London Borough of Barnet. The site is located just South of the North Circular and the intersection with the M1 Motorway. It lies directly south of the existing Brent Cross South Shopping Centre. The study site covers Plot 12 within Brent Cross South (BXS), which will be the first buildings to be developed.

The National Grid reference for the site is 51.571591, -0.220805.

The proposed surrounding buildings for this study are a mix of new residential and mixed-use complexes, modelled according to the illustrative masterplan provided by Allies & Morrison.

2.1.2 Site BoundaryThe site of Plot 12 is bounded immediately to the North by the proposed new High Street through the centre of the BXC masterplan. To the North East corner, the plot connects to the proposed Market Square which in turn connects to the new bridge over the North Circular connecting to the Shopping Centre. To the South the plot connects to the already existing but to be enhanced Claremont Park.

2.1.3 Surrounding AreaThe Brent Cross South area is surrounded by large areas of low rise sub-urban residential neighbourhoods, a large park and playing field to the South, and the Brent Reservoir to the West. It is bounded on three sides by large scale transport infrastructure, the railway line on the West, the North Circular Road on the North and the A41 on the East. The regeneration area will be an area of relative medium to high-rise compared to its immediate surroundings.

2.1.4 Proposed DevelopmentThe proposed development for Plot 12 is modelled according to 3D models provided by Maccreanor Lavington Architects and is split in a North and South building mass.

The North mass, along the High Street is composed of a 13 storey block at the North East and a 9 storey block to the North West, where the top floor is set back from the High Street.

The South mass is built up from two parallel residential blocks of 8 storeys tall, with the top floor set back from the street, connected in the centre of the plot by a 6 storey building, including set back. The two parallel buildings are also connected by an elevated courtyard, which is privately accessible.

Between the North and South masses, there is a route through to the High Street on the North West corner and a public pocket park, both of which are pedestrianised areas.

Figure 2.1 Site in Brent Cross Cricklewood context Figure 2.2 Proposed Environment - Close-up of Geometric Model

0°

North Circular

High Street

Plot 12

Clarefield Park

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Site

2.2 Scope of WorkThe scope of work completed by AKT II Ltd. to conduct the Pedestrian Wind Comfort Assessment is broken down as follows:

2.2.1 Wind Analysis•• Specify the wind properties at the site, in terms of Mean Wind

Speed and Turbulence Intensity for the full spectrum of wind directions.

•• Run a steady state CFD1 simulation for each of the 12 main wind directions for the design proposal.

1 Computational Fluid Dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyse problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of gases (such as air) with surfaces defined by boundary conditions (such as ground and buildings).

2.2.2 Site Model•• Generate a 3D CAD model for the design proposal, including the

direct surroundings, for the purpose of conducting a digital wind environment study.

2.2.3 Measurements and Analysis•• Conduct an atmospheric boundary layer2 CFD simulation for the

full spectrum of wind directions.

•• Measure the pedestrian level wind speeds around the development at ground level and other relevant heights where accessible spaces, balconies and roof terraces exist

2 In meteorology the atmospheric boundary layer (ABL), is the lowest part of the atmosphere. Its behavior is directly influenced by its contact with a planetary surface. On Earth it usually responds to changes in surface radiative forcing in an hour or less. In this layer physical quantities such as flow velocity, temperature, moisture, etc., display rapid fluctuations (turbulence) and vertical mixing is strong.

in the proposed developments, for the full spectrum of wind directions.

•• Analyse the measured wind speeds in conjunction with the wind frequency statistics at the site to provide an assessment of the wind environment in terms of pedestrian comfort according to the Lawson Comfort Criteria.

2.2.4 Report•• Provide a technical report summarising the main findings of the

study.

•• Following the results of the analysis, potential areas for mitigation measures are proposed in order to improve pedestrian level wind comfort.

Figure 2.3 Proposed Environment - Overview of Computational Geometry Figure 2.4 Proposed Environment - Overview of Computational Geometry with vegetation included

Various headings to whichthe CFD simulations are run

Various headings to whichthe CFD simulations are run

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3.1Macro Scale - Observations on Horizontal Planes Comparing the results for the proposed environment at the macro scale shows a variety of wind speed-up and slow-down in a few specific areas. See the image sequence of the Macro Analysis on the following pages, that accompany this discussion.

Along the new High Street some areas of minor wind speed up can be noticed, specifically for the directions 0°-30°, 90°-120° and 270°-330° (NNE, East and West respectively). This is mainly caused by the long linear character of the street in combination with locating the taller buildings along the High Street.

These tall buildings generate some turbulent wind effects around the corners, resulting in wind speed-up effects in the tertiary streets as well, to the West and East of Plot 12. Additionaly, the South facade of the masterplan creates a frontal area facing the wind, with these tertiary streets funtioning as openings in this closed front. This has the effect of local wind speed-up in these tertiary streets, most notably in the directions 90°-210°.

Following convergence of the simulations for all the wind headings for the proposed environment, the results of the full computational domain can be examined and visualised. This is done by generating a set of vertical and horizontal sampling planes, finding a velocity vector for each cell that is intersected by the plane. The velocity is then reported as a colour gradient on the plane. This process is carried out for each wind heading.

In order to meaningfully compare images, all the colour plots use an identical colour scale from blue to red, where blue represents low wind speeds and red the highest wind speeds (these top wind speeds generally only occur at the top of the domain, far above the buildings and accessible terraces.

Wind is a natural force that responds to large scale phenomena first and only in a second order to the micro scale directly around the proposed development. For this reason section 3.1 will first establish the Macro scale observations of effects occuring around the development, caused by its surrounding masterplan. Following to that, section 3.2 will then zoom in to the Micro scale of the direct spaces in and around the Plot 12 boundary and the effects of the wind within these spaces. These simulation results will then be converted to a year-round pedestrian wind comfort and assessed according to the Lawson comfort criteria.

3 Results of the Study

The images on the bottom row of the next few pages show the results for the simulations with vegetation and landscaping included. This set of results investigate the effect of trees and landscaping in slowing down the wind and therefore increasing the levels of comfort. As can be seen in the colour images, many of the areas where wind speed-up was originally occurring, now are slowed down significantly, meaning that this improves the wind microclimate around the development considerably.

0 m/s

Colour plots showing wind speed with input V: 10 m/s equivalent at 10m height

7.5 m/s 15 m/s

Figure 3.1 Proposed Environment Heading 120° Horizontal Plane at 1.50m. Colour gradient showing resulting wind velocities

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0 m/s


7.5 m/s 15 m/s

0°30°

60°

Proposed Environment

Proposed Environment with Landscaping included

Minor wind speed up along the High Street due to its linear character.The effect of vegetation is a direct slow down of wind speed along the High Street.

Wind speed up along the High Street and in the wider N-S street due to its (resp.) linear and open character.The effect of vegetation is a direct slow down of wind speed along the High Street.

Macro Scale -Horizontal Planes at +1.50m above ground level

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The images on the following pages compare the Macro results of the CFD simulations for the different wind headings for the proposed environment.

These colour plots represent a horizontal sampling plane, coloured according to velocities when the simulation reached convergence.

A blue to cyan colour (0-3.5 m/s) in these images represents a calm and to be expected wind velocity, where light green (3.5-5 m/s) show a minor wind speed up which most likely are not a reason of concern regarding the year-round comfort (see page 18-24). A yellow colour (~7.5 m/s) represents a major speed up, starting to become a concern regarding pedestrian comfort, with the orange colours (8-9 m/s) becoming more critical.

The colour gradients on these pages show the results of a single incident velocity, which will be combined to a year-round pedestrian wind comfort in section 3.3 (page 18).

0 m/s


7.5 m/s 15 m/s


150°

120°

90°

Wind speed up along the West street due to openings between the South facing masses. The effect of vegetation is a direct slow down of wind speed along the side streets.

Wind speed up along the East street due to openings between the South facing masses. The effect of vegetation is a direct slow down of wind speed along the side streets.


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Continuation of previous series.

0 m/s


7.5 m/s 15 m/s


180° 210°

240°




10



0 m/s


7.5 m/s 15 m/s


330°

300°

270°


Wind speed up along the High Street and in the wider N-S street due to its (resp.) linear and open character.The effect of vegetation is a direct slow down of wind speed along the High Street.

Minor wind speed up along the High Street due to its linear character.The effect of vegetation is a direct slow down of wind speed along the High Street.


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3.2Micro Scale - Observations on Horizontal PlanesLooking at the local micro scale wind climate around the site, it is possible to extract more fine-grained differences between the different wind directions around the design proposal. See the images below and sequences on the following pages.

From the horizontal plots on the next few pages it becomes clear how calm the wind climate in the courtyards is for most of the wind directions. This is a positive contribution to the pedestrian comfort for these locations. The only directions that cause a minor speed-up for the Pocket Park on the north are 0°, 90° and 210°, however these effects are very minor and will not cause any concern at all.

The side streets show some wind speed-up in a few specific directions, most notably in the directions 90°-210°. This is mainly caused by the long linear character of the street in combination with locating the taller buildings along the High Street, as well as the exposure of the tertiary streets to wind from the South, as the tertiary streets funtion as isolated openings in a further closed wind-facing frontage.

The simulation results with the vegetation and landscaping included show similar results as the observations on the macro scale. The trees and landscaping are helping the wind microclimate around the development significantly by slowing down the wind from all directions, specifically in the side streets and the area directly South to the Plot 12 site boundary.

0 m/s


7.5 m/s 15 m/s

Figure 3.4 Proposed Environment Heading 150° Visualisation of Streamlines Colour gradient showing resulting wind velocities

Figure 3.3 Proposed Environment Heading 180° Horizontal Place at +1.50m Colour gradient showing resulting wind velocities

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0 m/s


7.5 m/s 15 m/s

Micro Scale -Horizontal Planes at +1.50m above ground level


0°30° 60°


Minor wind speed up in the pocket park to be expected for wind from the North.The effect of vegetation is a direct slow down of wind speed within the space.

Minor wind speed up in the pocket park to be expected for wind from the North.The effect of vegetation is a direct slow down of wind speed within the space.

Minor wind speed up in area directly South to the Plot 12 boundary.The effect of vegetation is a direct slow down of wind speed within this area.

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The images on the following pages compare the Micro results of the CFD simulations for the different wind headings for the proposed environment.

These colour plots represent a horizontal sampling plane, coloured according to velocities when the simulation reached convergence.

A blue to cyan colour (0-3.5 m/s) in these images represents a calm and to be expected wind velocity, where light green (3.5-5 m/s) show a minor wind speed up which most likely are not a reason of concern regarding the year-round comfort (see page 18-24). A yellow colour (~7.5 m/s) represents a major speed up, starting to become a concern regarding pedestrian comfort, with the orange colours (8-9 m/s) becoming more critical.

The colour gradients on these pages show the results of a single incident velocity, which will be combined to a year-round pedestrian wind comfort in section 3.3 (page 18).

0 m/s


7.5 m/s 15 m/s90°

120°

150°




Wind speed up along the East and West streets due to openings between the South facing masses. The effect of vegetation is a direct slow down of wind speed along the side streets.

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Documents

PEDESTRIAN WIND COMFORT ASSESSMENT · MASSIVE SUPER-IMPRESSIVE & AWESOME IMAE White Collar Factory 2 Old Street ard London EC2 0AF T +11 7 47 94ff7 9999 F +11 7 47 94ff7 9ffffffinfo