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steam snowmelt?

i think the only bug to iron out would be how to separately zone the building heating from the snowmelt HX if there is no DHW system already. (i have yet to pay a site visit to determine this) are there steam specific zone valves that would be required? any other foreseeable problems in doing this?

Comments

  • is it possible?

    a customer who owns an old hotel with a steam boiler asked me if they could do a snowmelt system off of it. my boss who used to work on steam in the 70's inquired with his old retired steam buddies who said no way. building is set up as one thermostat controlled zone with no TRV's. is it possible, and if so what would your approach be? (i am no steam guy)
  • Chris_82
    Chris_82 Member Posts: 321
    Not all that silly,

    It's just that snowmelt systems are on for a long time, what would you do about the heat being constantly on? There are a number of Hx units to heat water, but again what about the rest of the building? By the way for a good steam heat exchanger, which still needs another exchanger to pass water thru, plan on about $3,000.00 +++ min. for that, considering what a dedicated sidewalk warmer is going to cost, why would you entertain the thought? What makes the hot water in that building? Tap off of that with a dedicated storage tank I would start at about 200 gallons, and double wall hot water/ glycol HX unit for a suggestion. Digging is gererally more of a problem than anything else. We installed a number of hot water/steam systems in the Boston Symphony Hall as an example but never steam heating outside units, they simply freeze the second the steam shuts off. I have lots of suggestions if anyone is serious about this.
  • Al Corelli_2
    Al Corelli_2 Member Posts: 395
    Gotta ask Grandpa about this one.

    He once told me, a long time ago, that he did snowmelt with steam condensate for the USPS. If I remember right, he said most Post Offices had this, as the government would be less likely sued if someone slipped.

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  • ttekushan_3
    ttekushan_3 Member Posts: 958
    My understanding

    is snowmelt in the old old days was done with steam. Specifically where district steam was used. If I'm not mistaken, some of the Downtown Cleveland sidewalks are steam snowmelt run from City Steam.

    Its not hard to imagine since steam is good at quickly heating a LOT of thermal mass. So what if the boiler is off for awhile? The walks wouldn't be able to cool that quickly.

    But the big question: Do you have enough boiler to pull it off? If the snowmelt demand reaches the steam's stall point, you probably won't have any heat in the house.

    -Terry
    terry
  • to clarify

    it would probably be a closed loop glycol snowmelt system coming off of a heat exchanger. i don't imagine steam sidewalks would be too practical in our case. i'm not sure how the DHW is generated but i will look into it. that may be the way to go, installing a storage tank on a setpoint.
  • Dr Pepper
    Dr Pepper Member Posts: 38
    Snowmelt

    Yes, you use a steam to water heat exchanger, closed loop of propylene glycol. I'm in Northern Illinois and I designed several, one for a parking ramp, it's installed for almost 10 years. Low pressure steam, I used a brazed plate heat exchanger, get the system sized by people that know what they are doing and know how your controls will work. I used tekmar with the automatic sensor in the tire track. Go to their web site, they used to have good controls info. Also, make sure there is sufficient boiler capacity to heat the building AND melt the snow. Those two duties tend to come at the same time.
  • Dr Pepper
    Dr Pepper Member Posts: 38
    Snowmelt...rethink

    Reread what I said and it worked for me in my application. Reread what you said and I'm not so sure. Find out if it is a one or two pipe system. One pipe needs to shut down and start up to work. Two pipe can just run, but you will need controls for the rooms. But 1st, figure how much sq.ft he wants to snowmelt then X 125 btuh/sq.ft. to get a ballpark load for snowmelt. Bottom line is he may be much better off to put in a nice little condensing boiler that will run at 110F, condense like crazy, melt snow like mad, save him a ton of gas money, and not screw up his building heating system. I've spec'd Triangle Tube boilers for a few bank jobs, 250,000 btu/h, hangs on the wall and a stainless steel HX. Food for thought.
  • i like that idea

    and it would probably work out cheaper too. something to think about for sure, thanks.
  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
    Steam to anything heat exchangers are \"it\"

    Steam pipes used for heating outdoor slabs used to be done all the time in railroad applications, to keep the switches clear from snow. The trick, because condensate can freeze, was to design pipings that would not ever accumulate puddles of condensed steam. This was often done by using no traps at all, by just letting the open end of the pipe barf into the landscape. Foolproof. But live steam travels around the floor.

    This solution is not applicable to a closed system such as yours.

    Obviously, you'll use an antifreeze solution in your driveway slab. Cool, that part won't ever freeze and burst. Fine. But... it will get really cold though, freezing cold... freezing cold enough to freeze whatever water you have in a water to glycol heat exchanger upstream. I agree, in normal winter conditions, you shouldn't ever risk freezing the water side of your boiler loop, but imagine a burner failure while the loop pumps keep circulating and now, the cold glycol will soon burst your plate heat exchanger. :(

    There are only two safe ways to get heat for your glycol loop.

    A

    Use glycol system wide, all the way to the boiler. Never count on a water to glycol heat exchanger to stop the freeze. Thus using heat (for snow melting) from below the water line of a steam boiler is not foolproof safe.

    B

    The magically safe method is to use a steam to water heat exchanger, or in this case a steam to glycol exchanger. The glycol can freeze all it wants, it'll never begin to pester the steam system in any way. Turn the steam on, the glycol will soon cook. Turn the steam off and the glycol will be thermally isolated from the home heating system, without risk of freezing the exchanger and without risk of sucking away valuable BTU on a snowless day.

    Steam coils are brilliant. They operate one way only, they're like thermal heat checks and foolproof to boot. Hot water coils need much piping sophistication and much pumping and much valving to prevent these pesky backwards heat flow.

    C There is a more appropriate scheme

    Install a dedicated low temperature boiler just for the snowmelt. In view of the cost of everything else, an extra appliance is not outrageous.

    Look at your numbers. A new and improved combined domestic water and snow melt might be attractive. Pulling year-round domestic water production from the steam heating boiler would also be very attractive. Perhaps your hotel has a swimming pool with a pool heater to tap into.

    Others here in this post, already came up with the solutions, I just wanted to jump in. Thanks for reading along.
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