London scoping - ukcip

Final Report
112
with some arguing that it should be relaxed or scrapped in favour of individual client/designer
arrangements.
These results are in line with other work which has shown that in order to meet the comfort
criterion even outside the centre of London for a present-day ‘hot’ summer, several features
have to be included in the building design to lower indoor temperatures. Examples are high
thermal mass, solar shading and natural (windows open) or mechanical (fans) night-time
ventilation. Most of these features are lacking in existing buildings, and are expensive, difficult
or impossible to retrofit. Night ventilation is one measure which is very effective outside
London and often feasible to retrofit (though window opening must be designed to avoid a
security risk). But since the urban heat island effect is at its greatest at night in summer, already
raising the city temperature by about 3°C overnight and slightly more in the future, the
effectiveness of night ventilation will be considerably reduced compared to non-urban areas.
Also, summer cooling relies on high ventilation rates largely or totally provided by open
windows. With high noise levels from traffic and pedestrians in much of London, this may not
be a practical option.
The inevitable conclusion is that much of the existing commercial building stock is likely to be
often uncomfortably warm later this century. This includes many existing buildings currently
without air conditioning, and new buildings which have not been designed for summer
conditions. Many clients and designers are therefore likely to go down the higher energy air
conditioning route with more predictable internal conditions. One compromise approach which
can result in a low-energy but comfortable building is the use of ‘mixed-mode’ operation. Here,
the building is designed to be cool in summer with natural ventilation most of the time, but a
limited amount of cooling is provided during the hottest periods to limit internal temperatures to
(say) 25ºC, thus automatically satisfying the comfort criterion. The mixed-mode approach has
been used successfully in many recent buildings, but is not standard practice. Buildings could
be designed to minimise internal gains and take full advantage of natural ventilation, whilst
leaving open the possibility of incorporating AC at a later stage should this prove to be
necessary. One could, for example, put in high ceilings to leave space for chilled beams or
ductwork, though there would be a higher initial construction cost. Such inherently flexible
approaches could be a useful response to the uncertainty inherent in climate change because
under a low climate change scenario, natural ventilation may be sufficient. Use of natural
ventilation wherever possible within a mixed-mode operation reduces the AC load, thereby
limiting the energy use and running costs.
There is also the possibility for significant innovation into more sustainable forms of cooling
buildings. For example, chilled water could be provided by district Combined Heat and Power,
perhaps powered with fuel cells (as adopted by Woking Borough Council). Borehole water
could be utilised for cooling, with fuel-cell driven pumps, where it can be abstracted
sustainably. Photovoltaics could be used in place of expensive cladding on prestigious
buildings to provide electricity for air conditioning: the supply of PV electricity coinciding with
high cooling demand.
Building specifications in the commercial sector in the UK, and London in particular, have
frequently been driven by the perceived need on the part of property developers to provide a
high quality development, thereby increasing the range of potential occupants, but not really
taking full account of the client’s energy costs (Guy & Shove 2000). Changing current
practices, such that a sustainable response to climate change is feasible, may therefore involve a
different approach to how building specifications are made.