Everything Solar Forum


 View Only
  • 1.  Hot Air Heat Storage

    Posted 01-25-2022 05:37 PM
    My house was built in 1978 with a very efficient, south-facing, 600 SF hot air collector, inclined 60 degrees from horizontal. A gravel heat storage bin was linked to it. The bin was not, however, able to store heat hot enough to be of benefit on a following cloudy day. A persistent odor from the collector's insulation prevents blowing the air directly into the house. I now blow the hot air directly into my crawl space. A significant amount of heat appears to be lost to the ground in the crawl space.

    The house has extensive, high, south-facing windows and an attached greenhouse which add significant passive solar heat. The house is also heated by a gas, hot-air furnace.

    I am considering constructing a "room" in the crawl space, approximately 15' x 15' x 3' high, into which the collector's hot air would be exclusively circulated. This "room" would be insulated at the ground and sides and filled with large, sealed containers of water. The intent is that the collector's heat would be stored and pass up through the wood framed floor to a central room in the house.

    I'd appreciate comments and suggestions.

    Thank you,

    George Mattson, retired architect
    Bozeman, Montana


  • 2.  RE: Hot Air Heat Storage

    Posted 01-26-2022 02:51 PM
    That heating strategy faded out many years ago and for good reason....it didn't work very well.
    I would spend your time and money on additional building envelope insulation and a PV array.

    Steve Kawell
    Durango Solar Homes
    Durango CO

  • 3.  RE: Hot Air Heat Storage

    ASES Award Winner
    Posted 01-27-2022 10:51 AM

    I would consider utilizing a small geothermal system to "up the heat". You have some good
    geothermal heat pump companies in Maine.

    While rock-bin storage works, so can hybrid approsches with trombe walls

    Stay warm ! - Scott

    Scott Sklar


    The Stella Group, Ltd.

    706 North Ivy Street, Arlington, VA 22201

    VA Phone:  703-522-1195 (3049 direct)

    E-mail:   solarsklar@aol.com

    Website:  www.TheStellaGroupLtd.com


    The Stella Group, Ltd.. is a global strategic technology optimization owner's rep firm for 

    clean energy users and companies, with a focus on system standardization, 

    modularity and web-enabled diagnostics.  Scott Sklar is an Adjunct Professor at 

    The George Washington University teaching three unique interdisciplinary 

    sustainable energy courses, and an Affiliated Professor with CATIE, an 

    international graduate university in Costa Rica offering graduate degrees

    on sustainability. Sklar is the Sustainable Energy Director at GWU's Environment 

    and Energy Management Institute (EEMI).

    Scott Sklar
    President & Adj Professor
    The Stella Group, Ltd, GWU EEMI
    Arlington, VA

  • 4.  RE: Hot Air Heat Storage

    Posted 01-26-2022 03:02 PM
      |   view attached
    Water is a good choice to store thermal energy.  Water can store at least four times as much energy as the same amount of stone.  If you want to increase the energy going into your water tanks, evacuated solar hot water collectors can be used.  At my home today, the tank (about 1,000 gallons) was heated when the outdoor temperature was under 15°F all day.  The photo shows the pump controller displaying the tank temperature of 177°F, at the end of the day.

    Stu Besnoff
    Alpine Solar Heat and Hot Water, LLC

  • 5.  RE: Hot Air Heat Storage

    Posted 01-27-2022 11:28 AM
    Wow. You have me time tripping here. Heat storage mediums are usually "stinky" whether air, water or whatever. You almost always have to use exchangers of one form or another. 600 SF is a large amount of BTU's over the course of a day. My 200 SF direct feed hot air panel dumps over 100,000 Btus on a PSD and its vertical. You have to hit an easy 300,000 in a day, which is allot. Rocks, concrete, masonry, etc. only have an Specific heat of around .2, so it takes a huge amount of mass to hold that much heat. Water is of course 1, but only about 40% as dense. Allot of the in ground spaces for thermal storage were under insulated in practice. As you suspected, allot of unwanted heat loss.
    If I had a house from scratch, I would do geothermal horizontal ground loop with a normally constructed loop for Summer ac, but a separate Winter loop in the form of a dug out square hole lined with xps, pond liner inside the insulation, filled with packed sand then soaked to the top with water. xps on top then ground covered. Outside would be a medium sized flat plate liquid collector array going to a GEO-grade PEX loop inside the sand storage. The solar collection loop would run year round. A second PEX loop would feed the HP in Winter. I do something similar with my actual current house, but its done in a non insulated trench for both heat and cool. I cannot get the extreme feed temps that I could get with dedicated hot and cold areas. This segregated arrangement would allow decent temps for Summer AC and super good COP's for Winter mode at the HP top allowed input temp.. You could if you want just manually switch the loops twice a year, or make it auto.. If you wanted to get even more radical, put a freezing loop in for the AC ground "area", designed to run to above ground exposed piping at night in winter, freezing the ground way down. You would need a certain amount of top and side insulation for that, but not the bottom or anything else special. That would boost your AC COP as well, like the heating mode...
    The luxury of a clean slate....

    william fitch