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Old Posted May 22, 2012, 10:08 PM
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Might High-Rises Become Uninhabitable?

Uninhabitable High-Rises


May 15th, 2012

By Steve Mouzon

Read More: http://www.originalgreen.org/blog/un...igh-rises.html

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Sustainability may be defined as "keeping things going in a healthy way, long into an uncertain future." That uncertain future is very unlikely to include cheap energy at levels we know today. At unaffordable energy price levels, what fails to work in high rises?

1. Wind speed increases with distance from the ground. A gentle breeze on the ground translates to something closer to a gale higher up. Open two windows for cross-ventilation on the forty-second floor, and all your papers may get blown out into the street. That increased wind speed, when combined with rain, plays havoc with weatherstripping in operable windows. Operable windows in high-rise offices therefore have serious issues. But on a hot day without cheap fossil fuel, inoperable curtain walls have an even bigger problem: without the ability to cross-ventilate, the building may literally be uninhabitable because without a way to dump excess heat, interior temperatures would soon become even hotter than outdoors.

2. Our great-grandchildren will ask "what were they thinking?" about many of our building techniques. Chief amongst them will be glass curtain walls. The best possible curtain wall today is not as good an insulator as a 2x4 wood stud wall, R-11 fiberglass batts, and the cheapest possible finishes. Yet we wrap all four sides of buildings (including east and west sides, facing the hot, low sun) with the stuff, acting as if the laws of thermodynamics don't exist. But as energy costs climb towards the unaffordable, glass-clad high-rises will move closer towards being uninhabitable.

3. We sun-screen our curtain walls to a high percentage because if you're sitting near the curtain wall, the glare through clear glass would be far too strong to work comfortably. But the sun-screening cuts down on the light that's able to reach deeper into the space, so only those workstations right on the window have good daylighting. Interestingly, the screening percentage often allows close to the amount of light you would get if you put traditional windows in the wall because they only occupy 15-25% of the wall.

4. In most moderate climates, passively-conditioned buildings benefit from exterior walls with thermal mass, a property almost completely missing from glass curtain walls. Unfortunately, high-rise buildings cannot be retrofit with massive walls because the building structure would not support the many tons of additional weight. This, combined with the issues above, mean that glass-clad buildings that cannot be retrofit will be uninhabitable in a period of unaffordable energy costs.

5. The towers of large buildings built before air conditioning were shaped like letters so that no wing was more than 30 to 40 feet wide. They daylit beautifully. With transoms over doors to the hallway, they cross-ventilated nicely as well. Most high-rises have floor plates far in excess of 40 feet in their narrowest dimension, meaning that only the corner offices cross-ventilate and only the outer offices daylight. The bulk of the floorplate would be uninhabitable in a period of unaffordable energy costs.

6. Elevator motors consume more energy than any other single piece of equipment in a high-rise building. In a period of unaffordable energy costs, people would only be able to occupy floors as high as they could physically climb. For most people, that limit is a climb of 4 or maybe 5 flights of stairs, resulting in a city that looks much more like historic London, Paris, or Rome than Manhattan or Vancouver.

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Old Posted May 23, 2012, 12:57 AM
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1. There are building products which cover this. They're fixed windows with a strip on the side that is basically a vent that can be opened or closed. They let air in and could protect against sudden gusts. Of course later on they praise "traditional" skyscrapers even though they had normal operable windows, and also a lot of paper weights. You can find old cartoons about office workers dealing with the heat and then the wind when they open a window. But they survived ok!

2. There are definitely a lot of buildings that did not properly consider their orientations... and a lot of them are lowrises. Bad orientation is just as detrimental to a 5 story building as it is to a skyscraper.

3. Most decent sun screening devices not only reduce glare, but they diffuse the light and get it deeper into the building. I can only speak generally, but if the architect cares enough to put in sun devices, they probably care about the quality of the natural lighting and have considered how deep the lights goes and the quality of the light.

4. Curtain walls are just wall assemblies hung from the floor slabs. They don't have to be glass. And I don't see why if you were removing a curtain wall you couldn't replace it with a stone/concrete veneer or insulation or anything else. I don't see why the floor slabs wouldn't be able to hold it.

5. I think that's an unfortunate trend, but really, artificial lighting will always be cheap. If energy is so expensive that you can't afford some LED lighting, then civilization has probably already collapsed and there is no longer a need for cubicle farms.

6. Is the cost of operating elevators vertically any less than the cost of transporting people horizontally? In the scenario where elevators are too expensive to operate because of energy costs, so will just about every other energy-dependent form of transportation.


I do prefer the low-midrise urbanism of London and Paris over the skyscrapers of Manhattan, but only in some extreme scenario would they be uninhabitable because of energy costs. Like I said before, at that point civilization would have already collapsed anyway.
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Old Posted May 23, 2012, 3:42 AM
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175 W Jackson - Chicago, was a fine example of the older more "green" building, openening windows, transoms, lots of light, skylights above each stairwell. Now the old wooden sash windows have been replaced with sealed modern stuff.

But for ventilation - been in high rise apartments many times, a strong wind means you don't need cross ventilation, anything but a penthouse and it is a moot point as you only have 1 - maybe 2 walls w windows. A small vent window, or a sliding door partially opened, is more than sufficient.

Yes dumping heat is a problem, look at the 9th (?) floor S side of the UNITRIN building and you will see the vents we had to put in for our little server room back in the dot com boom.
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Old Posted May 23, 2012, 3:45 AM
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As usual the writer focuses on HVAC without considering transportation. And they consider heat gain without talking about heat loss, which is easier with thicker buildings...

Some people just don't like highrises, and they create arguements to support that idea. (I'm fine with a midrise vernacular but there's a place for highrises.)
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Old Posted May 23, 2012, 8:50 PM
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Only number 1 and number 6 are exlusive for highrises as far as I can tell. And tell Werner Sobek about number 2 - the inner glass panes in the curtain wall of his R128 house are warm to the touch when the outer ones are below freezing.

R-128 house on Google images
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Old Posted May 24, 2012, 4:04 AM
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Quote:
Originally Posted by Jasoncw View Post

4. Curtain walls are just wall assemblies hung from the floor slabs. They don't have to be glass. And I don't see why if you were removing a curtain wall you couldn't replace it with a stone/concrete veneer or insulation or anything else. I don't see why the floor slabs wouldn't be able to hold it.
I think the author was trying to deceptively focusing on walls that achieve a large thermal mass through having a large mass. Massive amounts of insulation don't stop heat transfer, they just slow it down. Walls with high thermal mass phase shift it, absorbing heat during the day and releasing it at night. New phase change materials are in the works that can effectively do this while being much lighter than a thick concrete or masonry wall.

Quote:

6. Is the cost of operating elevators vertically any less than the cost of transporting people horizontally? In the scenario where elevators are too expensive to operate because of energy costs, so will just about every other energy-dependent form of transportation.
As far as I was aware, elevators are just about the most energy efficient
manner of transporting people. Thanks to the counterweights, the motors are mostly just accelerating the cabs, not actually having to supply the extra force to lift them.
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