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Open Slab Heatloss??

Guys...please help me out!

a Customer and friend of mine is going to install some slab warming in an open Starting Pit of a Race Track. The Pit itself is 20x60Ft and must be maintained at a surface temperature of 70°F, while 50°F outside would be the worst scenario (or Design).

Unfortunately, I do not know exactly whether or not there will be a wind guard.

How would one calculate a heatloss of a slab as such that is open? I know for snowmelt, we all have a number, whether it is 100, 125 or 150 BTUhs/sqft. But this one should be a lot less, shouldn't it? HELP!!




  • Boilergeek
    Boilergeek Member Posts: 42

    how thick is the slab?
  • hydronicsmike
    hydronicsmike Member Posts: 855
    according to the customer...

    ...it should be roughly 10" thick. Raceway is going to be in Quebec and will not be covered from the wind.....Thanks for helping.

  • Dan Peel
    Dan Peel Member Posts: 431
    surface area

    You should be able to treat the slab surface the same as you would a swimming pool surface and only need to input to satisfy the mass from the tubing to the surface. Interesting application. Dan

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  • I'd have to

    make a wild guess. A 50° design temperature is very warm and you're only looking to raise the temperature 20° at most, right? And you're not trying to raise the air temperature, only the slab temperature.

    I'd say design it for 50 BTU's/[], space the tubing at 6" o.c., 140° water temperature. Use your 511 stat with slab sensor.

    1,200 [] x 50 BTU/[] = 60,000 BTU at design temperature.

    That 10" thick slab will give you some flywheeling, but no one will notice.

    BTW, I've reserved a table for 3 for the 24th; looking forward to it.


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  • Jon_2
    Jon_2 Member Posts: 109
    Another Factor

    Quebec in the winter gets colder than where I live on the St. Lawrence River. You will have to protect those circuits with anti-freeze for those nice -20 to -40 days during the winter when it is idle.
  • hydronicsmike
    hydronicsmike Member Posts: 855
    Sounds close enough...

    ...and will most likely work. But I was wondering how one would actually figure it out without using a rule of thumb, more for my own knowledge than anything else. We normally don't get into the heatloss calcs anyways, but it's just one of those things again that I would like to know about...

    Was thinking of using a Mixing Control with maybe 9 Slab Sensors averaged to maintain that pit at the 70°F they want. The Mixing Control with Slab Sensors, for this single zone system, will give me continuous circulation and steady water temperature adjustment and should eliminate any flywheel effect.
    This is a pretty interesting job. I never knew that the surface temperature of those Pits was that important. But was told that it is part of some regulation that wants to ensure that all cars have the same starting condition....IE tire tracktion on a warmer vs. milder slab surface.

    Am looking forward to seeing you in Oakland in a couple of weeks. It will be nice to see you again.

    I won't be in Boston (ISH in October) after all. This trip has been axed for me.

    Talk to you soon.

  • hydronicsmike
    hydronicsmike Member Posts: 855
    Yes Sir...

    ...you bet there will be 50/50% Glycol in the tubes. I guess they dont plan on racing anymore once it gets much cooler than 50°F outside.

    But I do wonder what the BTUh/sqFt would be if I had to maintain this same slab at 70°F when it is -20°F outside......
    Thanks for the hlp...Mike
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