1、Architecture in a Climate of Change Page52-Page62 Low energy techniques for housing It would appear that,for the industrialised countries,the best chance of rescue lies with the built environment because buildings in use or in the course of erection are the biggest single indirect source of carbon e
2、missions generated by burning fossil fuels,accounting for over 50 per cent of total emissions.If you add the transport costs generated by buildings the UK government estimate is 75 per cent.It is the built environment which is the sector that can most easily accommodate fairly rapid change without p
3、ain.In fact,upgrading buildings, especially the lower end of the housing stock,creates a cluster of interlocking virtuous circles. Construction systems Having considered the challenge presented by global warming and the opportunities to generate fossil-free energy,it is now time to consider how the
4、demand side of the energy equation can respond to that challenge.The built environment is the greatest sectoral consumer of energy and,within that sector,housing is in pole position accounting for 28 per cent of all UK carbon dioxide (CO2) emissions. In the UK housing has traditionally been of mason
5、ry and since the early 1920s this has largely been of cavity construction.The purpose was to ensure that a saturated external leaf would have no physical contact with the inner leaf apart from wall ties and that water would be discharged through weep holes at the damp-proof course level.Since the in
6、troduction of thermal regulations,initially deemed necessary to conserve energy rather than the planet,it has been common practice to introduce insulation into the cavity.For a long time it was mandatory to preserve a space within the cavity and a long rearguard battle was fought by the traditionali
7、sts to preserve thissacred space.Defeat was finally conceded when some extensive research by the Building Research Establishment found that there was no greater risk of damp penetration with filled cavities and in fact damp through condensation was reduced. Solid masonry walls with external insulati
8、on are common practice in continental Europe and are beginning to make an appearance in the UK.In Cornwall the Penwith Housing Association has built apartments of this construction on the sea front, perhaps the most challenging of situations. The advantages of masonry construction are: It is a tried
9、 and tested technology familiar to house building companies of all sizes. It is durable and generally risk free as regards catastrophic failurethough not entirely.A few years ago the entire outer leaf of a university building in Plymouth collapsed due to the fact that the wall ties had corroded. Exp
10、osed brickwork is a low maintenance system； maintenance demands rise considerably if it receives a rendered finish. From the energy efficiency point of view,masonry homes have a relatively high thermal mass which is considerably improved if there are high density masonry internal walls and concrete
11、floors. Framed construction Volume house builders are increasingly resorting to timber-framed construction with a brick outer skin,making them appear identical to full masonry construction.The attraction is the speed of erection especially when elements are fabricated off site. However,there is an u
12、nfortunate history behind this system due to shortcomings in quality control.This can apply to timber which has not been adequately cured or seasoned.Framed buildings need to have a vapour barrier to walls as well as roofs. With timber framing it is difficult to avoid piercing the barrier.There can
13、also be problems achieving internal fixings.For the purist,the ultimate criticism is that it is illogical to have a framed building clad in masonry when it cries out for a panel,boarded,slate or tile hung external finish. Pressed steel frames for homes are now being vigorously promoted by the steel
14、industry.The selling point is again speed of erection but with the added benefit of a guaranteed quality in terms of strength and durability of the material. From the energy point of view,framed buildings can accommodate high levels of insulation but have relatively poor thermal mass unless this is
15、provided by floors and internal walls. Innovative techniques Permanent Insulation Formwork Systems (PIFS) are beginning to make an appearance in Britain.The principle behind PIFS is the use of precision moulded interlocking hollow blocks made from an insulation material,usually expanded polystyrene.
16、They can be rapidly assembled on site and then filled with pump grade concrete.When the concrete has set the result is a highly insulated wall ready for the installation of services and internal and exterior finishes.They can achieve a U-value as low as 0.11 W/m2K.Above three storeys the addition of
17、 steel reinforcement is necessary. The advantages of this system are: Design flexibility； almost any plan shape is possible. Ease and speed of erection；skill requirements are modest which is why it has proved popular with the self-build sector.Experienced erectors can achieve 5 m2 per man hour for e
18、rection and placement of concrete. The finished product has high structural strength together with considerable thermal mass and high insulation value. Solar design Passive solar design Since the sun drives every aspect of the climate it is logical to describe the techniques adopted in buildings to
19、take advantage of this fact assolar design. The most basic response is referred to aspassive solar design.In this case buildings are designed to take full advantage of solar gain without any intermediate operations. Access to solar radiation is determined by a number of conditions: the suns position
20、 relative to the principal facades of the building(solar altitude and azimuth)； site orientation and slope； existing obstructions on the site； potential for overshadowing from obstructions outside the site boundary. One of the methods by which solar access can be evaluated is the use of some form of
21、 sun chart.Most often used is the stereographic sun chart in which a series of radiating lines and concentric circles allow the position of nearby obstructions to insolation,such as other buildings,to be plotted.On the same chart a series of sun path trajectories are also drawn(usually one arc for t
22、he 21st day of each month)； also marked are the times of the day.The intersection of the obstructionsoutlines and the solar trajectories indicate times of transition between sunlight and shade. Normally a different chart is constructed for use at different latitudes (at about two degree intervals).
23、Sunlight and shade patterns cast by the proposed building itself should also be considered.Graphical and computer prediction techniques may be employed as well as techniques such as the testing of physical models with a heliodon. Computer modelling of shadows cast by the sun from any position is off
24、ered by Integrated Environmental Solutions (IES) with itsSuncastprogram.This is a user-friendly program which should be well within normal undergraduate competence. The spacing between buildings is important if overshading is to be avoided during winter months when the benefit of solar heat gain rea
25、ches its peak.On sloping sites there is a critical relationship between the angle of slope and the level of overshading.For example, if overshading is to be avoided at a latitude of 50 N,rows of houses on a 10 north-facing slope must be more than twice as far apart than on 10 south-facing slope. Tre
26、es can obviously obstruct sunlight.However,if they are deciduous,they perform the dual function of permitting solar penetration during the winter whilst providing a degree of shading in the summer. Again spacing between trees and buildings is critical. Passive solar design can be divided into three
27、broad categories: direct gain； indirect gain； attached sunspace or conservatory. Each of the three categories relies in a different way on thegreenhouse effect as a means of absorbing and retaining heat.The greenhouse effect in buildings is that process which is mimicked by global environmental warm
28、ing.In buildings,the incident solar radiation is transmitted by facade glazing to the interior where it is absorbed by the internal surfaces causing warming.However,re-emission of heat back through the glazing is blocked by the fact that the radiation is of a much longer wavelength than the incoming
29、 radiation.This is because the re-emission is from surfaces at a much lower temperature and the glazing reflects back such radiation to the interior. Direct gain Direct gain is the design technique in which one attempts to concentrate the majority of the buildings glazing on the sun-facing facade.Solar radiation is admitted directly into the space concerned.Two examples 30 years apart are the authors house in
