Tuesday, 21 February 2017

Five energy generations of tall buildings: an historical analysis of energy consumption in high-rise buildings

Here's an interesting look at energy consumption in high rise buildings by Philip Oldfield, in the Journal of Architecture: Vol 14, No 5.

A lot of sky scrapers today use less energy than the first ones built at the end of the 19th century, but it is difficult to say that there has been a trend towards less energy consumption over the years, and there is no evidence that it has been a prime concern of builders and designers.

A fundamental in the energy efficiency of a building is its form factor. This is the ratio of surface area to floor area. Buildings lose or gain heat through surface area, and are basically used by floor area, so other things being equal a lower form factor will mean less energy consumption, since the heat lost in winter needs heating to replace, and heat gained in summer needs cooling to remove. 

The form factor seems to have taken a couple of steps backwards. The first was in the zoning of buildings. As high rise buildings began to sprout up around New York, they grew not only upwards but also outwards, reaching for the sky and spreading out into whole blocks. This cast big shadows, stealing light and air from the surrounding neighbourhoods, leading to the 1916 Revised Zoning Regulations limiting the bulk of buildings at certain heights.

Although this inspired a lot of Art Deco, it increased the form factor since taller and pointier also has more surface area to less floor space.

The zoning represents the second generation of energy, and buildings of this period have higher form factor, higher U values and more energy use.

The next generations was heralded by the glazed curtain wall in 1951. These statements in steel and glass brought the form factor down, but the U values kept going up, and they were still heated by steam, so the energy use kept going up. Apparently buildings from the late 60s used more than twice the energy of buildings from the early 50s. Doubling in twenty years! 

The oil shock of 1973 stopped those energy bills from rising, bringing in the fourth generation. Form factors were down below the first generation, and those glass facades were doubled up and the U values also came down below the first generation of sky scrapers.

The fifth generation, since 1997, is marked by environmental consciousness. Interestingly the form factors of these buildings have gone up. The U values have gone down as they are using triple glazing, and energy generation is being incorporated, as well as natural ventilation techniques.

I can't help feeling that basic design considerations and simple thermodynamics are being overlooked in favour of adding green dressing and making bold statements. Building a windmill in the middle of your skyscraper looks cool, but couldn't you just clad it with solar panels?