On 9 apr, 01:12, phoe...@[EMAIL PROTECTED]
(Damien Sullivan) wrote:
> Michael Ash <m...@[EMAIL PROTECTED]
> wrote:
> >I mentioned a roof because it should scale horizontally to a
> >basically infinite degree, and as a roof it doesn't have to be
> >particularly tall.
> >You'll need sup****ts at frequent intervals, of course, but that's
> >entirely doable. You may be able to piggyback on buildings and
> >utility poles to some extent if you want to make it cheaper, but
> >with enough money, roofing a city with glass ought to be entirely
> >feasible with current technology.
>
> "Enough money", but what *would* the cost be? As an advocate of roofed
> cities, I need to learn this.
>
> Going with the heater approach: I see estimates of $10-20/foot2 for
> heated driveways -- *not* including the cost of tearing up the ground
> and putting it back. Also, I hate these units.
>
> One square kilometer, 1e6 m2. 5000-25,000 people in urban
> environments.
> Energy budget of 50 to 250 megawatts, though most of that is
> thermal.
> Annual income of $150 to $750 million. (I picked $30,000/capita.)
> Maybe 1-5% available for wacky projects, over 30 years, which
> washes out.
>
<snip>
>
> Operation: 100 W/m2, 100 megawatts. Kind of high, especially if
> electric. Overkill? 8.8e8 kilowatt-hours, $88 million/year if
> electric. I don't how much good 10 W/m2 would do.
>
> Roofing: I see greenhouse cost estimates of $7.50/foot2, which I'll
> consider a lower bound -- much lower, given the height needed for an
> urban roof, though they may include equipment we don't need. 1/8 inch
> plexiglass, Lexan, or glass seem to be about $4/foot2 -- don't know if
1/8
> inch is thick enough! We need weather resistance. Anyway, we're
> probably talking at least $100 million construction, but hopefully much
> lower operation cost -- we're not aiming for some precise temperature,
> just "warmer". Of course there's maintenance, and dealing with summer.
>
Look at it this way: how much do you think the city itself cost?
Much of the city is roofed anyway. However, individual buildings are
much smaller than the whole city, because they are surrounded and
separated by unroofed streets.
The buildings have streets and multiple internal floors which have to
sup****t the contents. I suspect that roofing the streets would cost
less than building the houses with their roofs, floors and walls.
Now consider the heat flow.
In winter, the houses are heated anyway. What is the energy budget?
Some of that heat is lost through roofs, and will continue to be. But
a significant part of the heat is lost through sidewalls, windows and
doors - then carried away by convection and winds on streets.
Once the streets have been roofed over and enclosed, the heat escaping
by the sides of houses builds up there. As the streets warm up, either
a) the total fuel bill decreases or perhaps b) some of the energy
saved is used to heat the streets directly.
Since the streets are now roofed over, they are dry. Even if the air
is only heated to, say, +50 Fahrenheit and not to room temperature
inside houses, consider that a man exposed to wind and driving rain at
+60 F is likely feeling colder that someone in a dry and non-draughty
place at +40 F.
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