The Wofati Greenhouse movie excerpt - intro

https://permies.com/greenhouse We wanted to install a greywater system so water from a kitchen sink could go to plants instead of a septic tank. Except those plants will be dormant in winter - so any funky sink stuff would just build up and be gross.

How about if we made a small greenhouse? Greenhouses are famous for needing more heat than homes - all that glass is a very poor insulator. Plus they can get too hot on a sunny day and kill
everything in the greenhouse.

Well, we have a lot of projects here doing amazing things to solve heating problems. So can we invent a greenhouse that never gets too cold or too hot? Maybe we can use some elements of Mike Oehler’s greenhouse design and some elements of our wofati design. And maybe a
few other ideas.

Our design starts with the general shape of Mike Oehler’s design from The Earth Sheltered Solar Greenhouse Book. He grew tomatoes in December, off-grid, with no heat of any kind, in Northern Idaho. The genius of his design includes 3 improvements over a traditional greenhouse.

(basic greenhouse)

Improvement #1: reduce the size of the air space with a trench

(a basic greenhouse with a trench)

Improvement #2: an earth berm on the north side (thus, some added
insulation and less glass)

(an earth berm greenhouse)

Improvement #3: most importantly, the 5 foot deep trench under the walkway.

(Oehler-style greenhouse)


I think that the trench adds a big dose of superpowers that most people overlook. If the deep ground temperature is a constant 50 degrees, then whenever the temperature in the greenhouse drops below 50, the 50 degree air from the trench will rise up & the colder air will sink down.

Before he died, I talked to Mike about another possible improvement:

Improvement #4: What if a copper pipe was blackened, shaped to follow the glass vertically and drop down to near the bottom of the trench. When the sun hits the greenhouse, the top of the pipe would heat up and act like a straw to pull cold air from the bottom of the trench. Eventually, the hot air at the top of the greenhouse would be pulled into the trench and warm it. I called it a destratification pipe. Mike agreed that this would probably help a lot!

(destratification greenhouse)

Improvement #5: A common farmer trick is to put 20 feet of well casing into the ground, then put a watering trough on top of that. When the outdoor temperature is negative 25 degrees (F), the water doesn't freeze. When the water gets cold, it cools the air at the top of the hole. So the 50 degree air from underground rises to the top & the colder air right below the trough sinks. There is so much air exchange that the water remains warm enough not to freeze. With this trick plus the previous improvements, maybe we can circulate enough heated air from the greenhouse through the pipe to get the temperature at the bottom of the hole closer to 70 degrees instead of 50!

(destratification greenhouse with well casing)

Improvement #6: Our wofati house design attempts to use heat from summer to heat a home through winter. We do this by berming dry earth against & on top of the structure and keep it dry with a membrane we call “the umbrella." We are still experimenting with these structures,
but so far they have had no freeze, even in our Montana winters. So let’s add dry dirt to the roof, the west side & the east side - and an umbrella to keep that thermal mass dry.

(wofati greenhouse)

Improvement #7: Our original mission was to design a year-round greywater system for a cold climate. In this case, “the problem is the solution”: greywater tends to be warm. If part of the greenhouse is dedicated to accepting greywater, then there is a constant stream of
warmth pouring into the greenhouse.

bernal brothers animation https://permies.com/bernal


Antonin Dvorak - Legends, Op.59 - 2. Molto moderato (G major) (Orchestral version, B.122) -Waterloo-Cedar Falls Symphony - Creative Commons

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