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Slab on-grade radiant floor and solar heat gain

sajufe
sajufe Member Posts: 1
Hi,

This is a (as far as heating is concerned) gut renovation of an early 19th century farm house. The house itself will be heated by panel radiators; a modern addition by a slab-on grade radiant floor.

The system is based on a mod/con gas boiler (Lochinvar), with a fairly straightforward distribution system (constant pressure circulators and home-fun manifolds with actuators). 7 zones in total, mostly bedrooms.

The issue is that the load calculations show significant solar heat gain in the addition (west-facing glass). I am looking for a way to control the supply temperature for the addition in part based on outdoor sunlight intensity. Basic outdoor reset won’t be sufficient due to the sheer amount of glass and solar heat gain, even with low e windows.

There are mixing controllers available in Europe that support sunlight senso, but I’m concerned about servicing an imported component. What are other options that are available to manage this situation? (Ideally the system would gradually decrease the supply temp towards the afternoon, then completely shut off until the night as long as the concrete is warm.) I suppose one could always run the AC (but then the homeowner would probably wonder why not just install a forced air or ductless system in the first place..)

Comments

  • DZoro
    DZoro Member Posts: 1,048
    A combination floor and air sensing thermostat will help. Keep water temps as low as possible with the outdoor reset. There's a good chance that even the designed water temps will be higher than necessary.

    D
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2019
    Another thought is window coverings that use solar controllers.

    I really can’t believe a strategically placed slab sensor will not work though.

    Constant circulation will help plane out warm areas. It’s to bad there wasn’t a zone that has no solar influence you could utilize that gain to your advantage.
  • hot_rod
    hot_rod Member Posts: 21,868
    Having dealt with a lot of the early passive designs in cold sunny SW climate, I've found the key to be controlling the solar gain.

    There are automated window shadings available to run off temperature sensors, mounted high in the room to read stratification sensors, timers, photocells or a combination of.

    We also installed temperature responsive exhaust fans in tall stratified rooms, not the best solution.

    Ideally that solar gain in the slab could be directed to the cooler north facing rooms or a garage slab, if you want to spend that much $$ and engineering.

    I guess it will come down to how much gain and how much of a problem it is for you.

    I have also seen large homes in Colorado running heat in the back rooms, cooling in the large solar gain areas, at the same time. Seems a bit counterproductive.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,546
    It’s a shame to not use that passive gain to your advantage. Even a well insulated storage tank with a HX.
  • hot_rod
    hot_rod Member Posts: 21,868
    It would be some low grade energy, probably under 90F. But shove it into an indirect to pre-heat DHW. An indoor solar thermal collector of sorts.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GordyJean-David Beyer