Tall buildings

Tall buildings climate walk walking among giants Londons tall buildings are often designed in isolation, with no thought of how they will affect the surrounding environment. Julie Futcher and Gerald Mills have devised a walk that explains the impact on the citys climate O ur walk takes us through a part of London being transformed by the addition of very tall buildings to a familiar, urban landscape consisting mainly of buildings of 24 metres or less. While these new buildings in the City of London have energy management systems that are state of the art and are often treated as exemplars of modern design there is a debate going on about how these 2 3 4 pm 5 6 are tall an urban canyon. There is no vegetation along its length, and a great deal of pedestrian and vehicular traffic uses this route. The north-south orientation of the street, and its dimensions, mean that it is almost always in shadow, except around noon. All the buildings here have a commercial function, and are occupied during the daytime. The offices on the west side get morning sun and are warmed, while those on the east side are in shadow during the morning and vice versa in the afternoon. This street offers some shelter from the prevailing westerly winds, which also means that the pollutants from vehicles can accumulate near breathing level. We now proceed eastwards, to South Place. 1. Finsbury Square Gardens Finsbury Square. The first stop is an open, green square, just on the border between the borough of Islington and the City of London. The width of the square make out the balconies of an apartment block on the south-side faade that will rarely experience direct sunlight because of its aspect; one wonders if these balconies are much used. This building acts as a shading device for the glass-walled office across the street. Is there a case for the position of these building types to be reversed, so that the offices get the shade needed and the apartments receive sunshine? We turn left down Bloomfield Street towards London Wall. You may feel a sharp increase in wind as the prevailing westerly airflow is channelled along this thoroughfare. The buildings on this street are lower, and many are of pre-1960s construction; the differences may be best illustrated by the windows, which can be opened, allowing for natural ventilation, but also potentially introducing outside noise and polluted air. This street curves southwards toward Bishopsgate, and the cluster of tall buildings that are redefining the urban landscape of the City of London. The route of the walk from Finsbury Square to the River Thames 1 25m moisture. Moreover, the urban surface is faceted, and each facet sees only a portion of the sky; as a result, the city surface exchanges energy with itself and retains heat better than if it were flat (this is a major reason for the urban heat island effect). Finally, humans add heat and moisture plus a host of air pollutants to the urban atmosphere, mainly via buildings heating/cooling systems, and vehicles. As a result, urban areas have distinct climates, different in nearly every respect from that observed at standard weather stations such as those at Heathrow Airport. gusts, depending on the ambient wind velocity and on the dimensions and juxtaposition of building clusters. Third, the fabric and structure of a city affects the heating of the near-surface air. Urban surfaces are generally dry, with little vegetation, so available energy is used to warm the overlying air, rather than to add reflection) patterns that shade and may illuminate open spaces and other buildings Second, airflow near the surface of the Earth is greatly disturbed by the presence of buildings; in general, airflow near the ground is slowed in cities, but it is also more turbulent. A pedestrian will experience lulls and constructions fare when in situ; that is, when surrounded by other buildings. There appears to have been little consideration of the impact of these buildings, either on neighbouring structures or on the outdoor climate. Our field trip takes a path from Finsbury Square, through the eastern cluster of tall buildings, to the bank of the Thames. Walking this route exposes the pedestrian to a great range of microclimates created by the built landscape. Along the way, we observe the impacts of the changing landscape and speculate how the existing and planned buildings affect each other. At the outset, it is worth reminding ourselves of a few controls on the climate at the Earths surface, and how decisions on built form and function can affect these. First, the intensity of solar radiation is controlled mainly by the altitude of the sun, which is a function of time and latitude. London lies at 51.5N; New York, by comparison, lies at 40.7N. The effect of a building is to redistribute the available solar energy by intercepting the beam and generating a shadow at the rear. In cities, buildings vie for this resource, and create complex shadow (and is about 120m, and the surrounding buildings are all approximately the same height (25-30m), and are continuous along the length of the roads on each side. The squares dimensions allow it an expansive view of the sky so it receives sunlight for much of the day but provides little shelter from the wind. Much of the central square is covered with grass, which moderates the surface temperature. In addition, there are trees to offer shade, and to screen the area from traffic noise and pollutants. We would expect this square to warm and cool more quickly than other, more densely built, parts of the city. We walk south toward Moorgate, via a typical city street terraced buildings of uniform height, separated by a street about as wide as the buildings South Place, looking towards Ropemaker Place Looking west along Chiswell Street, the urban landscape has changed significantly; very tall buildings, many clad in glass, form a narrow canyon. At ground level, there is little solar access as the buildings on the south side shade the faade of those on the north side for much of the year. You can Limited sunlight penetrates the canyon of buildings on Chiswell Street view of the Heron Tower, which is remarkable only for its size, standing more than 180m tall. On its south faade, embedded in its glass wall, are photovoltaic cells that allow it to gather nearly 2.5% of its energy via onsite renewables. However, there is no right to solar energy, and the building planned for 100 Bishopsgate will shade this energy-generating faade, instantly neutralising a significant part of its green credentials. The route continues south along The Heron tower At the corner of Wormwood Street and Bishopsgate, we have a good Wormwood Street, then right into St Mary Axe, which brings us past Norman Fosters building 30 St Mary Axe (the Gherkin), with its unusual, aerodynamic shape. Its tapered form ensures that, despite its height, the view of the sky vault at ground level is relatively expansive. On the few occasions when rain falls on calm days, the shape of the building creates a halo effect on the ground, as the slight bulge in its envelope shelters the surrounding ground. 300m of the Cheesegrater, and shelters the ground from fast-moving air streaming down its face. There is a small square at the intersection here, which has seating, but one wonders how much it is used because it offers little protection from the elements. A new tower planned for this area (52-54 Lime Street), will change the climate dynamics of this area yet again. The route continues onto Fenchurch Street, which takes us to another recent addition to the tall buildings of London. Changing lines of the city Existing buildings Planned building 180m 25m Willis Building (behind) Llyods Building Overlooking the Thames and The Shard The final stop is on the Thames embankment. On the far side of the river, the 300m-tall, glass-sheathed Shard rises impressively above the 40 Leadenhall St (behind & planned) September 2013, the solar beam on the curved, south-facing faade was concentrated and reflected downward, onto the pavement and buildings of adjacent Eastcheap. The intensity of the solar energy was sufficient to melt parts of a Jaguar car, to singe carpet in a barbers shop and even to cook eggs. Some have blamed global warming for the event, but the cause was immutable solar geometry and a lacuna in design thinking; along with the Heron Building, it demonstrates the relationship between buildings in an urban setting. It has taken a major investment to fix the problem. We continue along Eastcheap, turning onto St Marys Lane, crossing over Lower Thames street, and down to the Thames, shown in a north to south cross-section of the Thames extending from 20 Fenchurch Street to The Shard below. The arrow depicts the altitude angle of the sun at noon, at the time of the summer equinox. 52-54 Lime St (behind & planned) The corner of St Mary Axe and Leadenhall Street This is the heart of the Citys eastern cluster, with an assortment of very tall buildings, including two of Richard Rogers designs the Leadenhall Building (the Cheesegrater Rogers Stirk Harbour + Partners) and the Lloyds Building (the inside-out building) which opened in 1986. 122 Leadenhall St Aka the Cheese Grater St Helens (behind) Aviva Tower 30 St Mary Axe (behind) Aka the Gherkin 100 Bishopsgate (planned) The Herron Tower Herron Plaza (planned) BISHOPSGATE The juxtaposition of tall buildings here creates a great variety of conditions on the ground, depending on the direction of the wind and the position of the sun. In some places, the wind is squeezed between buildings, creating a Venturi effect and unpleasant gusty conditions at the ground. One should note the glass canopy that extends from the faade Philpot Lane At 20 Fenchurch Street is a remarkable building by Rafael Violy; clad in glass, its floorspace increases with height to maximise the value of office space thereby creating its distinctive shape and moniker, the Walkie-Talkie. Atop its 37 storeys is a restaurant and garden that are open to the public. To ensure its completion, the City of London became a partner to acquire the right to light of affected buildings. However, it was not its shading effects that gained international attention quite the reverse; during a sunny ec oD 40 20FC Eastcheap River Thames The Shard How the curved facade of 20 Fenchurch Street reflects solar beam, and the Shards long shadow eor Rmade See For YourSeLF surrounding landscape. Its shape belies its immensity; its shadow at noon will extend more than 350m for half of the year. Further east along the Embankment, you can see the Strata building to the South. It has three turbines at roof level, which can access the much-faster winds that gust above the rooftops of buildings. If the heights of the surrounding buildings increase, of course, this renewable resource will become diminished. In any case, since its completion, the blades have barely turned! CJ See For YourSeLF The authors will be organising a walk through the City at 1pm on Saturday 21st February. Email julie@climate22.com for details Julie Futcher is an architect at Urban Generation and Gerald Mills is an urban climatologist and lecturer at University College Dublin Wind speeds increase in gaps between buildings