OPINION
THE SELFISH GIANTS
Modelling must look at the impact of buildings on the performance of nearby structures – otherwise energy strategies will be compromised and lawyers hired, says Julie Futcher and Gerald Mills
Grandiose new city towers don’t make great neighbours. The
skyhigh interlopers muscle their way in to prime sites and proceed to steal energy, shade and sightlines from nearby buildings, while dumping unwanted waste on the surrounding streets in the form of blistering heat, blinding glare and turbulent winds. Too many buildings are being designed without due consideration of their impact on the wider built environment. Minds have been concentrated on the issue by the impact of 20 Fenchurch Street – aka the Walkie Scorchie – on its neighbours when light refl ected by its concave glass façade scorched buildings and objects. It exposed some of the gaps in the methodologies that assess building energy performance1
. Among these
is the failure to account for the interdependent energy relationships between buildings and to evaluate the energy performance of the built environment as a whole, rather than on individual buildings. Assessment is currently based on
the reduction of regulated energy demand through a fabric-fi rst approach, alongside the supply of energy from renewable sources. This means that the potential for the building form to reduce energy demand at the outset is overlooked, and energy effi ciency
measures are applied generically, regardless of the external environment. We evaluate the energy performance
of buildings as though they were divorced from the surrounding urban landscape. The effect of neighbouring buildings on the energy load is ignored and vice versa. The ‘Walkie Scorchie’ is one of
two recent examples on the London skyline. Its energy management strategy is expected to exceed current target reductions by about 24%2
At noon at the time of the
However, this design presumes that owing
to its optimisation ratio of fabric and technologies. Unfortunately, its ability to refl ect and focus solar energy onto nearby Eastcheap has become a defi ning attribute that will necessitate a costly modifi cation to the façade. This exceptional event highlights a
more general point; 20 Fenchurch Street affects the thermal performances of all the surrounding buildings to a greater or lesser degree – through refl ection, shading and modifi cation of airfl ow patterns – yet there is no standard means of assessing these impacts. The second example – Heron Tower – is a 230m glass-clad tube3
. About
2.5% of its energy needs are supplied by building-integrated photovoltaics, consisting of 3,000m2
of PV cells
embedded in the glazing on the south façade, which will generate 92,000kWh of electricity a year4
. Shard
Heron Tower
100 Bishopsgate
20 Fenchurch Street
equinox, 100 Bishopsgate will cast a 145m shadow up the south- facing facade of PVs on Heron Tower
the façade will continue to have a nearly unobstructed access to the solar beam and this depends entirely on what is built on the plot 30m to the south (100 Bishopsgate). The site has planning permission for a 172m offi ce tower, and if construction goes ahead, the energy management strategy of Heron Tower will be compromised – for example, at noon at the time of the equinox, 100 Bishopsgate will cast a 145m shadow up the south-facing façade of PVs on Heron Tower. Both examples highlight the urban
energy management issue because of their size viz-à-viz the adjacent buildings. Each protrudes well above the height of the surrounding urban landscape and is treated as an isolated entity (from an energy perspective). As a result, the energy effects are inequitable. While the buildings along Eastcheap will not have a signifi cant effect on the performance of 20 Fenchurch Street, the reverse is not the case. Similarly, Heron Tower achieves much of its green credentials by capturing the solar beam over a large area while casting
a long shadow. The irony is that if 100 Bishopsgate is built as planned, Heron Tower will fi nd itself in the same situation as its lowly neighbours – deprived of solar resource. It is time to take an integrated approach to the energy exchanges of buildings in urban areas and to integrate this into traditional building impact assessments, which include concerns about protected views, sky light, glare and dangerous winds.
References 1 ‘Industry urged to learn lessons from the Walkie- Scorchie’
portfolio.cpl.co.uk/CIBSE/201310/ news/
2
www.20fenchurchstreet.co.uk/technical.html 3
www.arup.com/Projects/Heron_Tower.aspx
4
www.construction-manager.co.uk//features/put- it-panel/
Section showing positioning of 100 Bishopsgate next to Heron Tower, and the fi ctional repositioning of The Shard. It clearly demonstrates the interdependent energy relationships between buildings – 100 Bishopsgate will put Heron Tower’s PVs in the shade
● DR JULIE FUTCHER AND DR GERALD MILLS are undertaking a study with De Montfort University to look at the effects of interdependent relationships on building performance. Contact
julie@climate22.com
26
CIBSE Journal Febuary 2014
www.cibsejournal.com
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