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3 Indoor Sand Volleyball Courts - Radiant In-Sand Heating (Electric!)

bman86
bman86 Member Posts: 6
Ive got 3 indoor beach sand volleyball courts in Connecticut. I'm looking to get a little heat into the sand to supplement the overhead propane radiant tube heaters. And I'd like to source some advice on the system

The 3 courts are 26ft x 52ft and side by side. I'm not too concerned with even distribution of heat around the area of each court. Just some decent heat for the toes about 8ft in from the sides where most of the time on court is spent.

The sand is about 11in deep, and sitting on 4in thick of rigid foam which is sitting on the dirt. So I have 4in of good insulation between the sand and the ground. I even have 2in going around the edges of the 112ft x 75ft building to keep heat from creeping out the sides! The building is just a fabric tension structure with literally zero insulation (think very large thick-fabric tent.

I can put the heating system - 3 zone panel, electric tankless heater, valves, etc - near the 26ft edge of the middle court. This puts the whole system right in the middle, as balanced as it can be. From this central location I'd like to (and this is where I need help) run a single loop out to each court. The loops would be ~180ft for the outer courts and ~120ft for the inside court. Each loop is just over-out-over-back-over ... no zig zagging or tight spacing.

If I just did the 1 loop out to each court, the out and back lines going the length of the courts would be 10ft apart if they are 8ft from each side line (seems crazy, but stick with me here). If I use 3/4in pex I could get some good flow through a relatively short loop, allowing me to transfer a good amount of heat to the sand.

So ... open fire ... let me know your thoughts and ideas here. If you've got some know how, let me know.

Right now I'm looking at buying, as examples ...

https://www.homedepot.com/p/Rheem-Performance-36-kw-Self-Modulating-7-03-GPM-Tankless-Electric-Water-Heater-RETEX-36/300800822#overlay

https://www.homedepot.com/p/Apollo-3-4-in-x-500-ft-Oxygen-Barrier-Radiant-Heating-PEX-Pipe-APPOB50034/302354347

https://www.homedepot.com/p/FloorHeat-3-Zone-Preassembled-Radiant-Heat-Distribution-Control-Panel-System-DP003/205675944?MERCH=REC-_-searchViewed-_-NA-_-205675944-_-N&

Thanks for the help

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,766
    If you really want electric heat, may I suggest looking at a purpose built electric boiler, rather than a water heater? Slant/Fin, for one, makes a good range with at least one model more or less in the size you mention. Couple with a thermostat in the sand somewhere typical it would be, in my opinion, a better choice than attempting to use a water heater which isn't meant to be used that way.

    Even if you are just going to keep the sand warm, in Connecticut... it's going to cost you.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    bman86
  • kcopp
    kcopp Member Posts: 3,890
    Sand is a terrible conductor of heat... and 11" of it would take forever to heat it up...if ever. I think it will cost a fortune to run.
    DerheatmeisterZmanSTEVEusaPAcross_skier
  • hot_rod
    hot_rod Member Posts: 15,392
    Just say no to heating sand :). Ever notice when you dig your toes into hot beach sand. A few inches down, it's not so hot.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    STEVEusaPA
  • Derheatmeister
    Derheatmeister Member Posts: 1,222
    As others have said:
    1. Due to the fact the sand has silica and tons of entrapped air is a terrible conductor of heat. In fact it acts as a thermal insulator..
    2. Using Electricity to heat a tent is going to cost a small fortune (Approx 3 to 4 times more than nat. gas)
    3. If you install the Resistance wires or tubing approx 12" below the surface it will have a serious lag. Probably days
  • bman86
    bman86 Member Posts: 6

    If you really want electric heat, may I suggest looking at a purpose built electric boiler, rather than a water heater? Slant/Fin, for one, makes a good range with at least one model more or less in the size you mention. Couple with a thermostat in the sand somewhere typical it would be, in my opinion, a better choice than attempting to use a water heater which isn't meant to be used that way.

    Thanks for that. I think you're right in that I really have an electric boiler application, and not a water heater or pool heater application

    And you're right that the Slant / Fin product offers a series of sizes. Here is an example of one available from Supply House

    https://www.supplyhouse.com/Slant-Fin-EH40-135-S2-EH40-135-S2-137000-BTU-Output-40KW-Single-Phase-Eight-Element-Electric-Boiler

    And yep, electric is going to cost me. But propane for the overhead radiant heaters is already costing me BIG TIME. Part of the business model for a few months out of the year. So it really wont hurt if my electric bill quadruples if it means my customers are happier, and I might save a little on the propane I'm using already to heat the sand.

    NOTEthat I'm really only looking to this system to raise the temperature of the sand by like 10F, maybe 20F on an extremely cold day or two. And even then, not completely or consistently. The sand gets moved around A LOT when players are running around, so that's my heat distribution concept. Even if I can use the system to keep the sand from getting cold overnight after it is already warmed up naturally or via my overhead heaters, then that's a win.

    Lots to think about. Thanks for your insight
  • bman86
    bman86 Member Posts: 6
    kcopp said:

    ... if ever.

    Indeed, that's the science part that I havent modeled or understood yet. Even if I do throw 30kw of energy down a 1in tube over 200ft, will that energy 10 or 11in down in the sand ever equate to making a toes-in-the-sand comfort difference a few inches down from the surface. Exactly what I need to prototype or model somehow. Or, get the "dont even bother" advice here on this forum - fully acceptable answer!

  • bman86
    bman86 Member Posts: 6


    1. Due to the fact the sand has silica and tons of entrapped air is a terrible conductor of heat. In fact it acts as a thermal insulator..

    Right, so it seems that if I can get the mass of sand heated to some baseline temperature (a big if), then the insulating ability of the sand would allow it to retain that heat for quite some time.


    2. Using Electricity to heat a tent is going to cost a small fortune (Approx 3 to 4 times more than nat. gas)

    I'm not trying to heat the air in the tent with this system, though I inevitably would a little bit. I'm just looking to heat the 11in deep volume / mass of sand such that it provides some level of comfort up in the top few inches to players' feet. Regardless, I agree that my electric bill will be seriously increased, which is tolerable.


    3. If you install the Resistance wires or tubing approx 12" below the surface it will have a serious lag. Probably days

    Right, exactly. If a cold spell comes through I can manually bypass the thermostat to tell the system to start heating ahead of the expected energy loss from the cold air. It will take days to heat up, but it will also take days to cool down which is the real meat on the bone here.
  • hot_rod
    hot_rod Member Posts: 15,392
    Bob Ramlow up in Wisconsin has been build sand bed radiant solar systems for years. Basically dump solar thermal into a large sand bed under the slab. It re-radiates to the space throughout the winter.
    So while being a poor conductor it can store and transfer heat energy.
    A 2' sandbed under 2000 sq ft would be around 400,000lbs of mass!

    Getting the warm sand to where it can be felt may be the issue.
    Make it wet or damp sand and conductivity goes way up :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • delcrossv
    delcrossv Member Posts: 326
    edited January 13
    I don't think just running a tube will do it. The heating is too localized (into an insulator). Now if the PEX was attached to some aluminum plates under the sand, then maybe you'd get some results as even though the thermal conductivity of the sand is low, you're applying heat to a much larger area than your tube.
    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
  • bman86
    bman86 Member Posts: 6
    hot_rod said:

    Bob Ramlow up in Wisconsin has been build sand bed radiant solar systems for years. Basically dump solar thermal into a large sand bed under the slab. It re-radiates to the space throughout the winter.

    I sent a message to him (hopefully) through the web site he is associated with. Fingers crossed that he will get back to me. I have VERY good southern exposure and plenty of area to put solar panels!! Thank you for that suggestion and referral.

  • bman86
    bman86 Member Posts: 6
    delcrossv said:

    Now if the PEX was attached to some aluminum plates under the sand, then maybe you'd get some results as even though the thermal conductivity of the sand is low, you're applying heat to a much larger area than your tube.

    Now that's an interesting idea. I wonder if some corrugated galvanized steel roofing panels would help. They are $30 each for a 2ft x 12ft section. Maybe cut them down to 1ft wide, or leave them 2ft. Interesting though, thank you!!
  • GroundUp
    GroundUp Member Posts: 1,311
    delcrossv said:

    I don't think just running a tube will do it. The heating is too localized (into an insulator). Now if the PEX was attached to some aluminum plates under the sand, then maybe you'd get some results as even though the thermal conductivity of the sand is low, you're applying heat to a much larger area than your tube.

    Until one of the players steps into a deep spot and lacerates their foot on a plate... Great idea, but the liability is not so great.