[Greenbuilding] Insulation Under Snow Melt Slab for sidewalk

[RT]

On Fri, 23 Sep 2011 15:17:14 -0400, nick pine <nick at early.com> wrote:

> "Michael Zyla" <mzyla at verizon.net> says:
>
> See  <http://www.concretenetwork.com/concrete/snow_melting_systems/>
>
>> ... The fluid is warmed to temperatures of 140 to 180 F to provide  
>> sufficient heat for snow melting.
>
> Wow. Why not flow 50-60 F groundwater over the driveway, with a  
> plastic-film-lined trench full of stones and water on each side to  
> rewarm the water?



The interesting thing about wintertime in places where it gets cold enough
to have snow accumulations o nthe ground is that air temperatures and  
ground near-or-at-surface
temperatures are typically cold enough for water to change from liquid
state to solid state ... or to use the highly technical term "freeze".

If one "flowed 50 -60 degF water over the (snow & ice-covered) driveway" ,
that may be an OK way to create a skating rink for the kids  but
it would be a lousy way to create a driveway surface with enough friction
to stop moving vehicles (ie to prevent them from crashing into something
(ie houses, people, shrubbery) or simply just sliding off the driveway and
into a snow-filled ditch if sloped sufficiently).

So that would be one reason "Why not".

And in order to "flow that water over the driveway" one would need a  
system of conduit + valves to deliver it and control the flow ... and  
unless the water was being spilled over the driveway 24/7 (which of course  
is a stupid idea of the first order) the conduit and control valves would  
be subject to freezing.

An interesting thing about water when it freezes is that it expands
volumetrically by about 9% and that expansion is powerful enough to cause  
frost-affected earth to
lift massive buildings up and/or crack concrete and masonry, pop fence  
posts and boulders out of the ground ...
and burst plumbing that is trying to contain/control the water, and that  
bursting usually happens at an inopportune time (usually when people are  
in bed asleep) so that the resultant flooding makes a pretty good mess  
(frequently in the basement).

But to cut a long story* short, suffice it to say that it's just a BAD  
idea from the get-go.


But perhaps more relevant to this "Green" building List is that the
idea of using auxiliary heating to melt snow on a driveway (or sidewalk)
would require a very BIG stretch to be considered Green.

There are these nifty items that the ancients (ie
pre-push-button-everything era) devised, called "snow shovels and snow
scoops" .... and they were ingeniously designed to enable humans to move
great volumes of snow with minimal effort and even that minimal effort can
provide some health benefits (ie "exercise").

I would venture that the use of such devices to remove snow and ice from
driveways and walkways would be the preferred "Green" solution.

But in response to the below grade insulation strength question:

The eXtruded PolyStyrene (XPS) insulation that is typically available at
retail building outlets (ie Home Despot et al) usually has a minimum
compression resistance of something like 30 pounds per square inch @
maximum 10% deformation.

(There are higher strength XPS foams available ( ie 40 and 60 psi) but  
they aren't typically stocked in consumer retail building supply outlets.)

And if one does the arithmetic (no BASIC routines necessary), one sees  
that for a slab of concrete
sidewalk say, 3 feet wide by 5 ft long (between control joints) the
bearing capacity provided by the XPS would be in the neighbourhood of (15
sq ft x 144 sq inches per sq ft x 30 pounds per sq inch = 64,800 lbs) ~25  
tons (allowing for usual factors of safety) without any expectation of  
even minimal crushing of the foam (ie no
deformation).

Even white beadboard (aka Expanded PolyStyrene (EPS)) typically has a
minimum compression resistance of 10 psi @max 10% deformation) and when
placed under the same sidewalk slab, the bearing capacity would be over 8
tons/tonnes. (but EPS is not recommended for use in wet service conditions)

I doubt that even the Governator with his urban assault vehicle personal
transport could exceed that bearing capacity.

===========================
* Longer story (you may want to skip this part if you're in a hurry):

Years ago when I was a student at Univ of Waterloo and living on a farm  
just past Philipsburg (on the way to Stratford) I was returning home after  
making a trip into town that morning to write an exam.

There was a pretty good blizzard blowing and the road that was my usual  
route from the highway to my concession road was drifted over so badly  
that it was impassable so I kept going to try the next sideroad. It was  
filled in too but being a bit more open to the wind, hadn't drifted over  
as badly.

With enough speed to build up sufficient momentum, I was able to crash  
through the deepening snow ... until I reached a dip in the road where it  
crossed over a creek and my truck simply floated up on top of the  
accumulated snow so that the spinning wheels were nowhere near the ground  
anymore.

Wrapping a spare pair of jeans around my head so that I could breathe  
without being choked by the blowing snow, I started digging out the wheels  
but the holes were filling up faster than I could dig so I decided to  
leave the truck and hoof it the rest of the way, feeling my way along  
using the wire fences by the roadside as a guide because visibility was  
pretty much zero.

At one point the fence disappeared too and I was lost and going blind  
until I bumped into a building which I eventually determined was the stone  
church which was across the road from my farmhouse.

To cut the longer story short, the township snowplough pulled my truck out  
of the drifted-in sideroad about a week or two later and left it at the  
church for me. The engine compartment was packed solid with snow. I dug  
the engine out using various impromptu "tools" and got it running again  
without incident.

One of my housemates had also driven in to write an exam and he had to  
abandon his vehicle back at the first sideroad and it had to be hauled out  
and dragged home using a tractor, his engine compartment being packed  
solid with snow too.

He thought he'd be smart and save himself a lot of time and labour by pour  
boiling water over the snow-packed engine compartment. BAD idea. It froze  
into a solid chunk of ice that did not thaw out until Spring (a month or  
more later (I have "2 months" in my mind but this happened decades ago and  
the old memory may be inaccurate).


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  C A >
(manually winnow the chaff from my edress if you hit REPLY)