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R-Value of Sand

Brad White_141
Brad White_141 Member Posts: 21
in THE MAIN WALL
as used on Proton Therapy Centers turns out to be an excellent insulator for those cunning little protons....they go right through fiberglass in a hummingbird heartbeat.

When pouring the walls, it took weeks for the yards of concrete to cool, to release it's endothermic heat. Probably nothing compared to what you are dealing with, but for an HVAC guy, it was an interesting experience... Very stable indoor temperatures too, whether in Texas or Boston.

Comments

  • Joe Furfaro
    Joe Furfaro Member Posts: 30
    Insulating value of (beach) sand

    Working on a solar project and was thinking of insulating my solar storage pit with a good topping of beach sand instead of the styrofoam. I have used the foam for the sides and bottom but was curious on the r-value of sand.
    Moisture is not a problem in this case,
    Thanks
  • Cosmo_3
    Cosmo_3 Member Posts: 845
    Rain?

    I would think that once it would rain the r-value is lost. Will the sand be covered with something?


    Cosmo
  • Joe Furfaro
    Joe Furfaro Member Posts: 30
    Cosmo

    Cosmo, the pit is under the floor of my garage so water should not be a problem.
  • ALH_4
    ALH_4 Member Posts: 1,790
    not too good

    The R-Value might be somewhere between 0.3 and 0.4 per inch. So if you get around 5ft in there it should be decent. lol Why not just use a few inches of polyisocyanurate foam?

    -Andrew
  • Joe Furfaro
    Joe Furfaro Member Posts: 30
    Andrew

    thanks Andrew, just needed to hear that. Will look at the foam.
  • Brad White_141
    Brad White_141 Member Posts: 21
    Andrew is correct as usual

    and as noted elsewhere, if the sand is wet all bets are off...

    One question I used to give my students who thought that concrete was a good insulator because it is so thick... as in "I have foot-thick concrete walls"... I would ask them how much concrete at an R value of 0.08 would get you to the equivalent of an inch of R-5 extruded polystyrene? Answer is, 62.5 inches... there goes your zoning setback..
  • GMcD
    GMcD Member Posts: 477
    Yeah, but

    If you look at the thermal physics of that 12" of concrete, the time response is about 2 hours per inch of concrete. In a climate with warm days and cool nights, it will even out to the "average" daily/weekly day/night temperature. That being said, the more heating dominated your climate is, the less this thermal time resistance works for you, and the concrete tends to stabilize over the days during the climate swings to the average temperature, which can be quite low for those colder climates.

    The ideal envelope has to be climate adapted, and a general rule of thumb is to keep the mass on the inside, and apply insulation to the exterior of the mass for best performance. Basically, even in a cold climate, 6"-8" of concrete with a range of R-5 to R-10 exterior insulation will provide the "equivalent" of up to R-30 insulation in a conventional stick cavity wall.
  • GMcD
    GMcD Member Posts: 477
    Andrew has the right numbers

    I designed a heated sand volleyball bed design a couple years ago, and that is what the numbers came out to be, based on dry sand in a covered volleyball court. Was an interesting design with solar water panels supplementing the boiler due to good sunny climate conditions in wintertime at the particular location.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    We agree Geoff

    For simplicity, I discounted the thermal mass and just illustrated the insulative properties, R-value for R-value.

    Of course you are right. The best thing going would be thick concrete insulated on the outside as you suggest. Metering heat into that structure, properly controlled, would be a dream...

    Having performed site visits and punchlists in March or April within large concrete yet to be heated basements, that cold penetrates in ways that chill the bones. Even here in relatively tropical Boston, compared to your climate.
  • GMcD
    GMcD Member Posts: 477
    Ayup

    But I get a little spidey-sense tingling when the standard response to concrete and R-value is continually quoted. There is so little building thermal physics taught to building designers that they rely on the myth and legend method of education and on-the-job training. There are some good resources out there now, and hopefully through forums like this some of the education can get out there in the field. I like this site for thermal mass information:

    http://www.concretethinker.com/Papers.aspx?DocId=26

    Some good papers and tech info at the bottom of that page.
  • Perry_2
    Perry_2 Member Posts: 380
    Thick Concrete is a wonderfull insulator for the right things

    I did a rough heat loss calc on a nuclear plant's spent fuel pool - to see how much heat load was going out the concrete structure (this dealt with how much heat load the Spent Fuel Pool Heat Exchangers had to remove).

    Given how thick the walls and bottom was... Many many feet ("yards" would be a better unit of measurment), it turned out to be a good insulator - in that application. This was even after the fact that I cut the insulating value in half due to all the rebar in the structure....

    There was far more loss from the surface of the pool than through the walls and bottom.

    So, if you want to make the concrete people (and rebar people) happy in a big - big way.... Go for it.

    Personally, I'd insulate with some kind of foam system.

    Dry sand is also pretty lousey as well.

    Perry
This discussion has been closed.

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