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Snow melt idea diagram

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Nealk
Nealk Member Posts: 5
Hello new here.
wondering if some can steer me in the rite direction and some pointers on a new heated driveway addition. 
Im renovating the driveway and front entrance of my house and wondering if I could add a snow melt to my system with heat exchanger on a combi boiler I’ve installed last year. I’ve attached a diagram I grew up plus my existing boiler I installed.
I plan to use

bell&gosset 225k btu heat exchangee
tekmar 654 thermostat outdoor temp sensor and slab sensor 
taco controller 

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  • Zman
    Zman Member Posts: 7,605
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    Your plan looks doable. I assume that you have just left out the air sep, ex tank, and other parts you need on the SM side for clarity.
    The issue you will run into is that the snowmelt will drag the boiler (and your house's heat) way down when it first fires up. It is also a good idea to limit how hot the slab can get.
    If you put a motorized 3-way mixing valve controlled by the 654 on the boiler side of the heat exchanger, you will be able to prevent the boiler temps from being pulled down using the boiler return temp protection setpoint and prevent overheating using the max slab temp setpoint
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    NealkCBRob
  • Nealk
    Nealk Member Posts: 5
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    Zmam thank you for your response. 
    I have an aqua stat tied in on the boiler side of the heat Ex set on priority on the taco box wouldnt that control that and prevent the boiler from dropping temperatures to low cutting the the pumps on radiant side until Ex catches up?
    CBRob
  • Zman
    Zman Member Posts: 7,605
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    The Tekmar has all the tools to give you precise control over the slab and solve the temp issue. I would install the 3-way and let it do it's job.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    CBRob
  • hot_rod
    hot_rod Member Posts: 22,468
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    700 sq ft of snowmelt could easily gobble up 100,000 btu/ hr

    so you need that capacity above the heat load if you will not get much melt. It could take an hour or more just to ramp up to melt temperature
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,605
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    hot_rod said:

    700 sq ft of snowmelt could easily gobble up 100,000 btu/ hr

    so you need that capacity above the heat load if you will not get much melt. It could take an hour or more just to ramp up to melt temperature

    It looks like he has 100 K/btu to spare. I think that the cold slab will draw it much more than that at startup. Tekmar used to make a controller that allowed you to set a delta T on the snowmelt side as well.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein