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I've noticed that most thermally efficient constructions limit the use of windows due to glass' low R-value. According to this, one is forced to choose between well-lit spaces or thermally efficient ones.

Earthships, contrary to this, use plenty of windows facing the sun. Is this because the double panel glass corridor (used as a greenhouse) provides more thermal resistance than a glass wall alone? Since enclosed air cavities have higher R-values, I assume this to be the case.

Earthship greenhouse

Under which conditions will this hold? What should be the dimensions of this corridor? Is the temperature inside the double panel wall bearable or is it too high to be used as a living space? Can window shades or deciduous trees be used to regulate temperature in these cases?

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    It's unclear what you mean by "internal greenhouse" and "double panel glass corridor." Is this simply insulated glazing, where a window has multiple glass panes with a gap between them? Or something more complicated?
    – LShaver
    Sep 25 '18 at 21:52
  • @LShaver I've included an image of an earthships' greenhouse situated between two rows of glass panel walls.
    – Federico
    Sep 25 '18 at 22:37
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    Confusing. What is the internal greenhouse? What is the double panel wall?
    – paparazzo
    Oct 28 '18 at 4:47
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    @paparazzo I agree. Its confusing. The greenhouse is flanked by two walls of glass panels. I was asking about the thermal efficiency of this corridor and its possible applications in other constructions.
    – Federico
    Oct 29 '18 at 23:12
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    @paparazzo The question could be rephrased as: "Is the earthship's green house an effective pasive solar building design?". In asking the question I was thinking in Trombe Walls, which are an effective way of regulating temperature inside a building.
    – Federico
    Oct 30 '18 at 0:59
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Earthships are one very romantic notion of what a house should be, but the massive amount of glazing usually leads to thermal problems. This is particularly true of the earlier designs (1970s through the 1990s).

https://www.greenbuildingadvisor.com/article/earthship-hype-and-earthship-reality

There is a long, long, long history of failed earthships that you really should study before trying to fix what is inherently a broken design.

All visible light ultimately ends up as low-grade thermal heat. There is no way around that — it's basic physics. You can't let the light in without letting the heat in. Just. Not. Possible.

Even if you filter out the UV and the infrared, you end up with ~42% of total solar energy as visible. That's as much as ~315W of heat per m² of glazing.

Unless you can solve the problem of what to do with the heat that builds up once visible light degrades in the living space — in the order of GlazingArea*cos(latitude)*315W — there's no point worrying about what's happening in the corridor/greenhouse outside.

Earth coupling is usually the first (and best) option to consider to store/sink heat and moderate internal temperatures, but that depends entirely on your local climate (which you haven't described). It might not even be a viable option. If it isn't, then things get complicated really quickly, with alternatives introducing new problems of their own that then need to be resolved by adding/doing other things. Bandaids on top of bandaids on top of bandaids.

The "least broken" designs I've seen don't try to move light into the living space, they instead break up the living space and then move the fraction of the living space that genuinely needs it into the light. A fundamentally different approach, which seems to work well in the right climate.

All that said, when I went through this process recently for my own home (in a warm temperate climate), I ended up with a well-insulated lightweight frame, an appropriate amount of double-glazed/thermally-broken/argon-filled/low-e/high-SHGC windows primarily on the equator-facing wall, a 2.4m deep verandah around the whole house with translucent sheeting towards the equator, and an exposed/earth-coupled/polished concrete slab insulated only around the edges. Less complexity, much easier to build, much less active management required, and very thermally self-regulating.

Real-world performance » romantic ideals (at least in my book).

PS: In an earthship with a greenhouse/corridor out front, incoming light gets absorbed by plants and paths, converted to low-grade heat, and re-emitted as long-wave IR. The glazing between the greenhouse and the living space is (now) usually double-glazed. Since glass is opaque to long-wave IR, the outer pane of the IGU absorbs the radiation from the greenhouse, heats up, and then re-emits it in both directions. Even in the absence of a low-e coating, half of the heat goes back into the greenhouse. So it's not really "the enclosed air gap" that increases the R value, it's primarily radiation dynamics and how different parts of the spectrum interact with the glazing between the greenhouse and the living space. The physics wasn't well understood in the 1970s when the first earthships were built. Now the physics is understood, but most folk can't seem to grasp/apply it.

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    There is a lot of useful information in this post but it does not appear to be an answer to the question that was asked. The question seems to be legitimate (though it might benefit from some further detail) and seems like it merits a real answer. Sep 26 '18 at 14:13
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Dual pane window with a narrow difference is a different dynamic. You basically just double each widow. A large room still just doubles each window pane. Air free to move is low R value.

Glass has low thermal capacitance and is translucent. Opposite of Trombe wall.

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