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SWA in U/F floor slab

whjohnson
Got a job where a new submain - approx 25 metre run in 16mm 3 core SWA. Embedded directly into a new concrete floor where wet U/F heating will be installed. Am trying to work out the best order of installation - that is, should the cable go in first, then the insulation, followed by the U/F pipework,and finally followed by the slab. Am not sure what order the u/f heating side will be installed and am also thinking about how if any correction factors may need to be applied for the current carrying capacity. I have sized the cable with a little overhead in mind in terms of actual final demand, but am still a little concerned about final slab operating temperature

Comments welcome.

PS - Am not liking this new format - it is like writing inside a letterbox when compiling posts!
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    When you say 40', is that the actual temp of the slab?

    On my system that's the water temperature (from the blending valve) - as it's below a timber floor there's no concrete slab as such (pipes just clipped to the sides of the joists). With a concrete slab it's not uncommon to run it at a higher temperature to get a better heat output - the limit being not so hot that the surface is uncomfortable to walk on in bare feet. Either way there'll be a temperature gradient between the surface and the pipes, but close-ish to the pipes it won't be much less than the water temperature.

     
    SWA in below the insulation. If there is any significant heat transfer downwards, it's not doing its job!

    But similarly where does the heat from the cable go? It can't go upwards or a little sideways and upwards like it can with a conventional buried cable. Going downwards there maybe a large thermal capacity initially, but also a large thermal resistance (like an old house with very think masonry walls - take ages to warm up but once they're warm they stay warm...)


       - Andy.
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  • 0
    When you say 40', is that the actual temp of the slab?

    On my system that's the water temperature (from the blending valve) - as it's below a timber floor there's no concrete slab as such (pipes just clipped to the sides of the joists). With a concrete slab it's not uncommon to run it at a higher temperature to get a better heat output - the limit being not so hot that the surface is uncomfortable to walk on in bare feet. Either way there'll be a temperature gradient between the surface and the pipes, but close-ish to the pipes it won't be much less than the water temperature.

     
    SWA in below the insulation. If there is any significant heat transfer downwards, it's not doing its job!

    But similarly where does the heat from the cable go? It can't go upwards or a little sideways and upwards like it can with a conventional buried cable. Going downwards there maybe a large thermal capacity initially, but also a large thermal resistance (like an old house with very think masonry walls - take ages to warm up but once they're warm they stay warm...)


       - Andy.
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