International News
Shimizu and six colleagues at UCL Energy Institute in London analysed the electricity and gas bills for 611 office buildings in England and Wales . They found that high-rises of 10 storeys and higher used 76 % more electricity per square foot than low-rises of five storeys and under .
“ The results show that height is a significant predictor of energy use , even accounting for other variables ,” the researchers wrote in a paper published in the journal Building Research and Information . In fact , each additional storey in a building is associated with a 2.4 % increase in electricity use and 2.9 % increase in fossil fuel use , more than doubling the average emissions per square foot for the tallest buildings in their survey .
LIFTING PEOPLE , AIR AND WATER , AND WINDOWS THAT LEAK HEAT AND COLD One big reason for this is that tall buildings have elevators . In the tallest buildings , elevators account for as much as 10 % of energy use , AS + GG found . Tall buildings also rely on fans to push and pull air through heating , cooling and ventilation systems , and pumps to lift water very long distances .
At the opposite end , single-family homes are , as expected , more carbon-intensive . Beyond their dispersed heating and cooling infrastructure , they are exposed to the weather on all sides , whereas four-storey courtyard apartment units share one to two walls each .
Elevators , fans and pumps aren ’ t the only culprits . Windows also reduce efficiency compared to solid walls , and tall buildings tend to have a lot of windows .
“ The best-performing glass is , with almost with no exceptions , worse than the worst-performing solid opaque wall ,” said Ann Edminster , a zero-energy and zero-carbon consultant who wrote a chapter on height in the book The New Carbon Architecture .
The reasons for this are fairly obvious . Windows allow unwanted heat into buildings in summer and allow it to escape in winter , forcing mechanical systems to run harder during more hours of the day , which increases carbon emissions . Typical glass windows insulate only one-fifth as well as the worst wall material , Edminster said .
A predilection for tall , glass-fronted buildings makes solving this problem a challenge for architects . Glass windows and facades can be equipped with shading devices that cut unwanted rays , but building owners “ want to preserve that glass facade look , and that is a real problem ,” said Charlie Curcija , a mechanical engineer at Lawrence Berkeley National Laboratory who works on energy performance and windows .
IMPLICATIONS FOR THE NEXT GENERATION OF BUILDINGS As electricity gets cleaner and building codes are updated , newer tall buildings will become more energy-efficient .
Wikipedia / S . Nitzold
The Jeddah Tower in Saudi Arabia will be the world ’ s tallest building , reaching a height of 1 000m , and is currently still under construction .
The team at AS + GG explored these possibilities in their analysis of nine types of new-build structures , taking into account land use , new utility service , and the carbon emitted to make the concrete , steel and other building materials involved . According to this analysis , the four-storey courtyard still had the lowest overall emissions after 40 years of operations . Small triplex units were the next lowest , while a 65-storey high-rise took third place . But buildings higher than 100 storeys compared poorly , largely due to the steel and concrete needed to keep them standing .
Other research shows that large buildings account for more emissions than their smaller counterparts .
Research done by the Zero Cities Project shows that in Seattle , for example , just 3 % of buildings are larger than 20 000 square feet , but these are responsible for 45 % of all buildingrelated emissions , with similar ratios in other American cities . Similarly , in Cambridge , 4 % of buildings were responsible for 74 % of building emissions .
But for architect and educator Ed Mazria , this concentration of the emissions offers a focus for efficiency efforts . If there are
Continued on page 21
www . hvacronline . co . za RACA Journal I January 2021 19