Snowmelt: worked good until

Wethead7

We installed a snowmelting sustem for a customer in 92. The system worked great until this year,still melts snow, but the local city staff is covering it with ice,snow, other stuff. The City changed the strret to a emregantcy snow route last summer.We have change the controls so, that the call for melt overrides the outdoor reset. The system is part of the main house heating system. Two boiler, indirect hot water, baseboard, radiant floor, Taco-tekmar control system this thing worked very good. How do we change the snowmelting system in to a melting slab? As a note we changed the honeywell reset to taco zone panels and Taco(tekmar) two stage outdoor reset last year. The customer was having problems overheating parts of the house, with nine zones plus hot water and the melting controls the system was diffacult to trouble shoot. The overheating problem was found to be rubber parts in B&G zoone valves.

Thanks

Mike

Paul Mitchell

No radiant wizard by

far. In fact I am a Rookie...when it comes to radiant, compared to some of these guys. But if you changed controls last year...all was fine prior to that? Gotta be something with that? I find most problems are simple but sometimes a complicated system makes us think complicated.

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hr

It's all about horsepower!

if you need to melt it faster you may need more boiler. Of course pipe and pump sizes generally go along with it. You may be able to up the boiler and shove some more heat out there.

A snowmelt calc and design would be in order, that would spell out the potentia; of what you currently have.

Watts Radiant has designed melt pads for airport use, check with them. I'll bet 200 btu's per square foot or more may be need if they are heaping it, (snow) on your pad, above what it was designed for.

Melting large amounts of snow (mostly air) takes time and lots of fuel. Not for the weak of pocketbook1 Will the city share the expense of operating this beast?

hot rod

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flange

if you think about it you sized the system to be able to melt x amount of snow on a given surface area. the system will operate on cruise control within those parameters. now you have a situation where you are heaping multiples of that amount onto your slab. as stated you need more capacity. if you were simply able to bump up your supply temp this would help, but how much? just like with making steam, you use more btu's for actually changing state than for raising the temp, so basically each time you cover that slab with 2 times x amount of snow you need twice as much capacity, and raising brine temps alone wont do it. can you raise the supply temp and also your delta t? why would tyour customer do this for the city anyway is he filthy rich?

scrook_2

or...

is the customer the city too? If no, I'd suggest they have the city refrain from depositing snow on his/her property, otherwise look at a dedicated snowmelt boiler or staging a second boiler to the first, assuming you cannot increase the firing rate of the boiler and the GPM's to the slab

Wethead7

The details

Controls replaced October 02 system melted fine. The street was changed into snow route in the summer of 03. We installed additional relay so snow melt takes both boilers onto operating controls(190f) bypassing outdoor reset. House to street 13 feet,curb cut 65 feet. Tube layout is leingh wise. 3/4 pex on 9 inch centers. Four circuts, manifold in the flower bed. Tubing is three inches froom the top of the concrete. Concrete is 12 inches thick, 5500 psi striegh. The water temps after spool up 120f out, 80f return. We think the heat exchanger is about maxed out. The boilers cycle. The snow melts in two to three days.

The customer was required to install the drive way by the city. The city wanted to widen the street in the mid 90's did not happen. We do not think anybody wanted to rip out the drive. The customer spec'd the mesh four inches from the bottom and top. That's right two layers of mesh. The center contains rebar that is over one inch in dia, on one foot centers. Tearout and redue is not really an option.

Is there anything we left out? The customer does not care about fuel cost. I was thinking of upping the heat exchange.
Any small detail that I missed would be helpful. The real problem in the place overheats when the rest is overriden.

Thanks for the help

Mike

Radiant Wizard

Go Back

to the drawing board. Start as if you have nothing installed. New heat loss, new radiant design, new snow melt design. Take those figures and you current system configuration and melt the two (no pun intended)together.

If you try to do this any other way you are going to be wasting your time and time is money.

I would turn this into 2 seperate systems. You already have stated that you have two boilers. The first system would be dedicated to the house only. The second stricly for the snow melt. If you do this you should have no more problems with overheating the house and you can basically just run a supply & return with the second boiler for the snow melt and run 180 degree water through it. I would probably remote a simple light switch somewhere upstairs so that the homeowner can flip the switch on when snows approaching and off when he doesn't need it. I know it sounds primative but keep it simple.

Best of Luck.

hr

If the boiler

is cycling off, then your distribution HX and or piping is not up to the same capacity! You may be able to up some pumps to move more gpm. The boiler should run non stop at design.

Divide the total of square footage your melting by the boiler output and you will determine the BTU/sq. ft. you can deliver to the slabs.

Distribution piping loss figures in also, depending where the boiler is located in relation to the slabs, insulation around distribution piping, etc of course.

ASHRAE has snowmelt classifications for amount of snowmelt for various class of design. It used to ba a simple BTU/ sq. ft formula. it has been changed and upgraded to amount of melt also, I believe. The RPA should have that info for you, if needed.

You need both the boiler power and the distribution to, and into, the slab to make it all happen. Sounds like you have a bottleneck somewhere. It may or may not put you over the edge, however to widen the restriction, however

The HX manufacture can run the capacity info for you if you give them the component size info. Flat Plate in PA is real good, and helpful at sizing, as is Tony Conner, at this.

hot rod

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dennisD

I'm just a homeowner with interest in radiant and enjoy getting information from the wall.

This post so far hasn't said if city trucks are going slowly and rolling snow 2-3 feet high for a distance of 3-4 foot width at the end of the driveway or going fast on a snow route and throwing snow a depth of several inches for most of the depth of the 13 foot driveway.
Wouldn't each require a different approach? If the latter, it does seem more heat to the entire slab would be necessary.
But if the first example, would a separate zone of tightly space tubing embedded in a concrete or asphalt "speed bump" of the width necessary to melt the mound of snow work? (I say "speed bump" for lack of a better definition. I just mean a new layer of concrete of the width and depth designed, to melt whatever amount of snow that is being pushed onto the drive from the street. Don't know much about concrete but assume today's technology has something that could be poured within a depth of a couple inches.)
If the plows are throwing snow for a wide distance, could the homeowner ask that they slow down to roll most of the snow onto a specially design "melting slab".
I hope my intrusion into your excellent forum doesn't offend anyone.

Dennis

An afterthought: Could existing driveway be routed out to install more tubes at tighter spacing closer to surface.

Wethead7

After

Some review we have discovered the following. The reset control has lowered the water temp. The flow thru the driveway could be increased. The big one is bridging. The stuff from the street not in contact with the concrete. Does anybody have away to resolve bridging??

Thanks Hot Rod your view point was helpful

Thak you all

Mike