AnnaLea Kodiak wrote:
I may be misinformed about earthbags, I know they operate on the property of thermal mass as opposed to insulation, but I figured we wouldn't need insulation if the thermal was thick enough. I thought that if we were heating or cooling internally, the earthbags would retain that temperature and then radiate the heat or cool, reducing costs. Is this not true? Would it just go straight through and be lost to the outdoors? I may be misunderstanding how thermal mass works.
I don't know all the ins and outs because I'm still planning and learning myself. This is my understanding: Earthbags are no more insulative than, say, a thin sheet of metal would be. The difference is the thin sheet of metal exchanges that heat immediately whereas an earthbag retains heat and discharges it slowly. So slowly that if you live in a temperate climate, the sun has come up and recharged the heat before the wall has a chance to bleed off. But in general yes, the answer is the heat would go straight through and be lost to the outdoors, just in slow motion. So the question becomes how much temperature swing do you have, and how much do you want?
If you have winter and it gets cold sometimes, and the home is not insulated, you need to keep the heat going much, much more. Both because the outside cold will creep through the walls, and because the heat you generate will be lost through the walls. Heat seeks equilibrium. With insulation, the cold does not creep in, the walls hold your generated heat longer, and you use dramatically much less fuel to heat.
If you have summers that get hotter than 72 degrees, the sun will bake the walls and that heat will soon make its way through to start heating your interior. It might not snail its way through until 1AM or so, who knows, but at some point your interior will reach the temp it was when the sun was beating down, so you need to cool (if you have AC.) If you insulate, that sun heat is much less likely to penetrate to the walls, so you'll get "shade" temperature all day.
I'm currently investigating something I vaguely heard which is that if you dig down to the geothermal layer, you'll have a constant 55 degrees-ish base in your home, and if you have vents at the base of the walls and a vent at the top, convection will draw the cooler air in at the wall base and hot air out the top, pulling your geothermally cool air up as well, stabilizing the temperature of the whole interior. And in winter, you can close the bottom vents and run a fan down a duct from the top to the bottom, sending the warm air down to re-heat the bottom floor. This just something I'm trying to piece together from snippets I've heard and may not be accurate. But I know it works in teepees.