Conference 7.286::home_work

Sounds like it will use MEGAwatts and cost megaBUCKS to operate.  How can 
you keep from heating up the ground too?


...bill

    I would agree with .1.  I think the money would be better spent
    to fix the source of the water which is causing the ice.  Where's
    the water coming from?
    
    Phil

    	I heard of this guy that ran plumbing under his drive way and
    had it tied into a wood stove heater and circulated anti-freez through
    the system. It apparently help keep Ice and small amounts of snow
    from accumilating. It doesnt take much heat to keep stuff from frezzing
    Usually you dont get much frezzing rain below 30F and once you've
    cleared off the snow and warmed the drive way to melt the remaing
    thin film of snow you don't have to keep it warm.
    
    	I wouldn't try to do this with a fuel you have to pay a lot
    for though. It's still a lot of area to heat.
    
    			My 2 cents
                          
    					...Dave
    

    
    
    	Driveway and walkway heaters will not melt what is already there.
    You have to anticipate the storm and turn the heaters on before
    the snow starts falling. Most Digital facilities have heated walkways
    and the maint personal listen to the wheater reports and turn the
    heaters on when a storm is expected.
    
    	-Steve-
    

    I talked with a guy that used to install those heated units and
    he said that the 'anticipation routine' was a misconception.
    All one had to do was to look out the window and when it started
    falling, turn it on. Never would have a problem of too much snow/ice
    accumulating before the heating would occur.
    
    M
    

Considering the radiation area of driveway (the whole top AND the whole
bottom) and the difference in temperature you would need to create and maintain
(recall that the energy transfer goes as the square of the temperature
difference across the interface), I'd have to concur that you are looking
at significant energy costs for what's likely to be a marginal return in
deicing performance.

DIGITAL facilities with heated walks use the excess heat produced by the
heat exchangers in our computer rooms to heat the walks en route to evaporators
to dump the heat that's left. This is done with FLUIDS not with electrical
cables.

If you don't clear your driveway before you drive on it, or it gets heavily
rained on, you'll have ice. Salt and melting agents work fine on small patches.

Look at least twice. Better yet, ask someone who HAS the cables what it
costs and what it does.

Dennis

    I beg to differ. The quantity of heat exchanged by radiation is
    proportional to the difference to the fourth power of the absolute
    temperature of the radiating bodies. The rate at which energy is
    emitted, W, is given by the Stefan-Boltzmann law:
    
    W=e * o * T^4,
    e=emissivity
    o=constant
    T= absolute temperature, Rankine (Sp?) or Kelvin.
    
    George Dvorak
    297-5386
    

    FWIW_i used to date a girl whose parents owned a house at the top
    of a hill with 300 foot driveway with an 19% grade. They had to
    have heaters in their drive to get up to the house. I remember
    making a comment that it must cost a fortune to heat it.
    Her father told me $500 per winter. They shortly after broke out
    the 2 year old drive paved it with gravel and bought a 4 wheel drive.
    I think he said it was cheaper that way.
    
    
    -j
    

RE: .7

You *can* put insulation under the heated pavement to cut down on the amount
of heat wasted into the ground.

I doubt that all the DEC heated walks use waste computer heat.  Many of DEC
building did not start out as computer buildings, or are rented.  It sounds
quite likely that they would use some fluid for the heating, though...

RE: .8

:-) why'd they have to break up the old drive?  Wouldn't the 4x4 work on
pavement? :-)

Jim. 

    No the 4x4 dident work. If you saw the drive you would ask why the
    he(( would anyone build a house up there for. Getting up the drive
    wasent that hard it was getting down safely that was the trick.
    At the end of the drive is a 4 lane busy street also on a steep
    grade. I nearly met death backing out more than once on good days
    and to enter the street in a slide would insure death.
    This place is a good example of a house that shouldent have ever
    been built where it was. Nice view though, looks straight across
    garden of the gods into pikes peak. I was surprized they took
    the paved drive out myself but it really dident offer enough traction.
    
    
    -j
    

    Well....let me clarify a few things.....my house is somewhat on
    a hill....probably a 20-25% grade.....the reason I had ice last
    year was we had a few small snowstorms that didnt require plowing..
    and of course, when Im going to work at 6:30am Im not going to
    shovel the driveway...its too big anyway....so when this occurred
    the snow got packed....then melting, freezing etc turned it into
    ice.....
    
    Additionally, twice when I came home from work I could only
    get half way up my driveway in my Trans Am.....in fact....wound
    up sliding off the driveway and stuck overnight.....this happened
    twice....so this year Im getting rid of the car in favor of
    something with front wheel drive.....then the wife said we should
    put in cables.....so thats what prompted my request....
    
    From the responses it sounds like I should just leave it alone
    and put up with the ice....
    
    Thanks for all the responses
    
    Rick

    re .3 (and anyone with an opinion)
    
>    	I heard of this guy that ran plumbing under his drive way and
>    had it tied into a wood stove heater and circulated anti-freez through
>    the system. It apparently help keep Ice and small amounts of snow
>    from accumilating. It doesnt take much heat to keep stuff from
>    frezzing
    What would you expect it would take to pull something like this
    off? My driveway will be somewhat long, and using a snowblower
    would take too long. I'm not crazy about plowing it myself, or
    having someone come by. This idea caught my interest, and I was
    wondering what the logistics would be to do this. It sounds like
    it would be set up like a FHW (or FWW?) system, run off a high
    output wood stove with a circulator, etc. I suppose the area
    underneath the pipes could be insulated with something that would
    reflect the heat up....
    It is (in any way) realistic, and perhaps even remotely economical?
    
    John

    I've seen underground walkway heaters both at school and at ZKO. 
    Neither system appears to be reliable.  It's rare for all of the zones
    to working all of the time.  I'd be concerned about digging up your
    driveway every couple of years just to repair a pipe.
    
    I suppose it's possible that neither of the systems I've seen used
    antifreeze to prevent pipes from breaking.  That could make a
    difference, but are you willing to gamble?
    
       Gary

    1.) you're talking lots of energy here. You rich?
    
    2.) you have to make sure you have plenty of heat available; otherwise
    you partially melt the snow, and then it freezes at night and you're
    worse off than before.
    
    I'd get a good snowblower.
    
    ...tom

    re .14
    
>    1.) you're talking lots of energy here. You rich?
    
    How much would it really be? It would have to run, I'd say, for
    the duration of every snow storm - ones requiring that the snow
    be removed, that it. It's not like it would be running all winter,
    24 hours a day. It's how efficient that heat can be transferred to
    the top of the driveway that would dictate the BTU's required
    I'd guess. If as much heat as possible could be forced up, instead
    of into the ground, it might not be too bad.
    
>    2.) you have to make sure you have plenty of heat available; otherwise
>    you partially melt the snow, and then it freezes at night and you're
>    worse off than before.
    That's the kicker. The BTU output has to be sufficient, otherwise
    it's useless.
    
    I look at this like some people look at garages. They justify the
    expense of one often for the sole reason of getting into a clean,
    somewhat warm car, as opposed to one that has to have its windshield
    scraped and snowed removed from and warmed up before they can
    drive away. That may not be an economical even trade, but convenience
    can carry a high price tag.
    Think of how nice it would be to get up after a snow storm and drive
    off instead of shovelling/plowing etc a driveway before you can leave?
    
    John

    I'm not sure how relevant it is, but for indoor FHW heat, you figure
    the required BTU output by multiplying the number of feet of baseboard
    by something like 580, or 590, or maybe its 600. That's of course after
    the heat losses have been calculated to determine how many feet of
    baseboard you need.
    
    In a 10 foot driveway, I'd take a WAG and say you needed at least 5
    rows of tubes times the number of feet of driveway.  That's just going
    straight down.  If it was mine, I'd probably consider a shape like
    this all the way down (taking even more feet of pipe)
    
    		---------|
                ---------
    		|
    		---------
    		        |
    		---------
    Well, a squared off S shape anyway.  My guess is you'd need quite a
    heat generating source, might be possible from a big stove, and if
    it works, an excellent addition.
    

    It can be done and it is done.  Two blocks from my house, is a funeral
    home, with a heated parking lot.  That's right.  The whole parking
    lot.  Plus, the walks from the lot.
    
    When the snow starts to fall, you can see the heat pipe pattern.
    Must be nice, to have money.

    re .17
    
>    It can be done and it is done.  Two blocks from my house, is a funeral
>    home, with a heated parking lot.  That's right.  The whole parking
>    lot.  Plus, the walks from the lot.
    Interesting. Where exactly is this? Maybe they could give me some
    numbers.
    
>    Must be nice, to have money.
    I'm not convinced doing this is so outrageously expensive. For one,
    the temperature does not need to get that high. Secondly, it does
    not have to run that long or often. Thirdly, if the stove can provide
    additional heat to the house as part of this, your overall fuel
    bill will be less.
    
    John
    

    I'd be curious to know what kind of pump you'd need in order to
    circulate the water....
    
    Edd

    
    	What are you going to do about the very top part of the driveway if
    your local snowplow-driver takes bets on how high he can pile the snow
    where your driveway meets the road?  If you only plan on enough heating
    capacity to melt the snow as its falling, how will it handle a sudden
    two foot "snow fall"?
    
    	If you crown the driveway so the water runs off, will it try to run
    off into the grass that is presumably covered with several inches of
    snow and puddle/freeze?  Seems to me that you'll need to slope the
    driveway into a drain.  (Also heated?)
    
    	Yes, this sounds like a wonderful convenience.  Yes, it also sounds
    like a complex and expensive convenience.  Would it be cheaper to move
    to Florida for the winter?  ;-)
    
    								-craig

    
>    	What are you going to do about the very top part of the driveway if
>    your local snowplow-driver takes bets on how high he can pile the snow
>    where your driveway meets the road?
    Build up speed on my clear driveway and blast thru.
    Really, there isn't much anyone can do in that situation. 
>      If you only plan on enough heating
>    capacity to melt the snow as its falling, how will it handle a sudden
>    two foot "snow fall"?
    I've never seen snow fall in 2 foot increments. Snow always falls
    "as it falls". However it would be foolish to do this and not put
    out enough BTUs to handle anything above a flurry.
    
>    	If you crown the driveway so the water runs off, will it try to run
>    off into the grass that is presumably covered with several inches of
>    snow and puddle/freeze?  Seems to me that you'll need to slope the
>    driveway into a drain.  (Also heated?)
    As long as the drive and land around it is graded properly so rain
    is not a problem, I don't suspect melted snow should be. A drain
    at the end would probably be a good idea.
    
    On the surface, this idea does sound expensive. Without a physics
    background, I can't say exactly how expensive for sure. Maybe it's
    not that outrageous? That's why I'd like to find someone who's
    done it.
    
    John

    Out of  curiosity,  I  asked  one of the electricians here in MR01 what
    system  is used  to  heat  the  sidewalks.    He  said  it's  called  a
    "Snowmelt", and that it  is  electric  resistance  mat that is put down
    before the concrete sidewalk is  poured.  He thought that the ones here
    in MR01 run on 480 V,  but that other voltages are available.  I looked
    in the yellow pages for a manufacturer and came up with zip.
    
    I agree with you that the power  levels  are not that high, because you
    only need to get the temp.  above  freezing.  I'm too lazy to calculate
    a  probable value because I don't know where to  look  up  the  thermal
    conductivity of dirt.  IMO the easiest way to figure  it out is to call
    the funeral home and find out who installed theirs.  Money?   they have
    lots (all those gold fillings they recycle *8^O ).
    
    Grins,
    
    gjd
    
    

    
    Re: .20
    
    	Sorry, but you missed my perhaps-too-subtle joke about the "two foot
    snowfall" -- I was referring to the quick pile of snow dumped onto the top
    of the driveway as the snowplow comes by.  You might want to consider
    *not* heating the very top section where this dumping occurs.  If you
    heat it, but only enough to handle a regular snowfall, you might end up
    melting only part of the snowpack and form a big block of ice.
    
    	The drainage, though, is a more serious problem and it is not the
    same as draining the driveway during a rain.  During a rain, you have
    this:
                  crowned driveway           dirt and/or grass
             ============================--------------------------
    
    and the dirt, being porous, will absorb the water coming off the
    driveway.  After a few snows, however, this is what you'll have:
    
                                           ________________________
                                          /
               crowned heated driveway   /  snow piled on top of the dirt
             ============================--------------------------
    
    Since snow doesn't absorb water well (especially after the top crust
    gets icy after one wet/freeze), the water can't roll off the driveway
    like it could when it rains in the summer.  You'd then either need a
    heated drain or else keep running the heat long enough -- and with
    sufficient capacity to keep the water from freezing -- to evaporate
    it.  (Do you have a garage?  Be careful about this puddle getting big
    enough to come into it.)
    
    								-craig

    
    	Oh yeah, forgot one thing in my last reply.  There is one more $$$
    effect that has to be weighed when looking at MRO or the funeral home
    and saying that it must be economically feasible.  These places, being
    public places, have much higher legal liabilities if they don't keep
    the access paths clear.  With a heated sidewalk, I bet they get a good
    break on their insurance that would help defray the cost of running the
    system.
    
    								-c

    re several previous. 
    
    I'm still confused as to how one is going to provide enough heat to any 
    uninsulated, outdoor surface to melt any significant snowfall.  When we 
    get a snow storm where the average accumulation exceeds 1 inch/hour
    (that's an arbitrary metric), I don't think it's going to matter 
    whether the temperature of the walkway is slightly above freezing 
    -- snow is going to pile up.  Once this happens, the temperature of the 
    walkway surface becomes a moot point  -- because the snow is piling up
    on more snow (already below freezing).  Of course the snow will
    eventually melt, but are you going to be willing to wait until, say
    6-inches to a foot of snow is melted by a driveway that's maybe 35
    degrees?  It sounds to me like this approach will not be very 
    effective in any heavy snowstorm.  So what's the benefit?  If it only
    works in light snowfall, it has a minimal benefit in this area.  It's
    not the light snowfalls that cause problems -- you can either just 
    ignore them and wait for the sun to melt it (asphalt and concrete heat 
    up real fast when thesun comes out) or brush it away.  It's the
    big/heavy snow that causes a problem.  I say spend the money on a good 
    snowbower.  
    
      

Re: .25

> When we get a snow storm where the average accumulation exceeds 1 inch/hour
> (that's an arbitrary metric), I don't think it's going to matter whether the
> temperature of the walkway is slightly above freezing -- snow is going to
> pile up.

This statement fails to convince me.  Perhaps some physicist out there can 
provide some hard facts?

Here is my feeble attempt at being a physicist:

1 foot of snow = one inch of ice or water.  (I'm fairly sure about this)
1 inch snow / hour = 1/12 inch of water(ice) / hour

ice to water is 560 calories per cc (this I definately do not remember for sure)

to raise water one degree is 1 calorie per cc. (I'm certain about this)

So about 570 calories per cc of ice. (hopefully)

Let's base our calcualtions on one square foot of driveway or sidewalk.

1/12 inch of ice per hour over 1 square foot is 12 cubic inches of ice.

12 cubic inches of ice per hour per square foot.

12 cubic inches = 2.54 x 2.54 x 2.54 x 12 cubic centimeters.

1966 cc ice per hour per square foot.

1,120,620 calories per hour per square foot.

Of course there will be losses to the ground and air.  As a worst case senario,
lets allow for 45% heat loss to the ground and 20% to the air.  35% of the heat
will actually be transferred to the snow...

3.3 Million calories per hour per square foot.

Anyone care to finish this by supplying a formula to convert calories to BTUs or
WATTS?  Corrections welcome seeing as I'm recalling this stuff from high school.

    .26 has the right idea, except he used heat of vaporization (liquid to
    gas) instead of heat of fusion which is a lot lower.  
    
I did some rough calculations on how much energy it would take to melt a
given amount of snow, plus heat up the driveway material, plus heat loss 
to the surrounding air.

The assumptions I used were: 

10" of snow = 1 inch of water
6" of gravel and asphalt
Heat of fusion of water = 80 cal/gram
  (Heat of fusion is the energy required to convert ice at 32 degrees 
   to water at 32 degrees)
25% of heat is lost below and to the sides of the driveway (SWAG)
25% of heat is lost through conduction and radiation from the surface

I won't bore you with the math, but for a 12 ft by 50 ft driveway and a 10" 
snowfall, it would take about 225 kilowatt-hours of energy to melt the snow.

That's 100 amps for 10 hours at 220 volts, or

768,000 BTU's which is the total output of my gas furnace for 7 hours.

That's a lot of energy for a modest snowfall and a small driveway.

Bob   
                                                          

    In Windham, New Hampshire, an acquaintance of mine has a heated
    driveway. He pays to have it plowed and the slight snowy remainder,
    which turns to ice for the rest of us, just melts away for him. 
    His house sits at the top of a long and very steep driveway and
    this was his solution a number of years ago to the icy driveway 
    syndrome.  

    Even with my slight incline, I have occasionally had to leave my 
    car at the bottom of the driveway -- couldn't get a grip on the 
    ice.
    			-- Julie

    Most of the time I've been able to talk the sun into melting the
    "snowy remainder" for me..
    
    Typical weather pattern around here (mass.) is that after any decent
    snowfall the weather turns bright and sunny; as long as you've got
    the driveway mostly cleared, the sun will handle the rest even if
    it's below freezing..
    
    ...tom

    re: coils
    It sounds as though this person's system is not adequate. I can't
    see investing in this and still having to plow. However, if his
    drive slopes downhill to the north, icing could be quite a problem,
    and one that's best solved by coils.
    
    John

    Howcum people don't use snowshovels anymore?  Non polluting, cheap,
    energy efficient, good exercise.
    
    

    
    re .29
    
    That's what I do. Just get the snow off the driveway and the Sun
    does the rest. I found that the winter after I resealed it the snow
    would melt better, mainly due to the fact it was blacker/darker.
    
    re .31
    
    Because I have 2 90' driveways. The light snow I'll do by hand,
    but the 5" or more I bring out the blower.
    
    Mike

    RE .31
    
    and a signifigant cause of the increase in first-time and fatal
    heart attacks in the winter.  
    
    erercise is not by itself good; proper exercise is.  Shoveling snow
    while possibly PART of a proper exercise program, is NOT a proper
    exercise program.
    
    -Joe
    

    In Windham, New Hampshire we are proud of our forests -- no one
    has sunshine on their driveways.  We have trees that drop sap on
    car windshields.  And we get mildew on the decking.  We hear
    trees scream with pain when someone approaches with a saw .... 

    Anyway, the sun never melted any ice from my driveway.  I do have
    to admit that it is only a couple times a winter that the plowed
    driveway turns to ice, but when it does, bummer. 

    I am such a gadget freak that if I were wealthy and if I were not
    so concerned about the environment, I would have heated driveways
    in a minute! 

		-- Julie, we're going to be building & running scared