LOW-TECH MAGAZINE

Fruit Walls: Urban Farming in the 1600s

We are being told to eat local and seasonal food, either because other crops have been tranported over long distances, or because they are grown in energy-intensive greenhouses. But it wasn't always like that. From the sixteenth to the twentieth century, urban farmers grew Mediterranean fruits and vegetables as far north as England and the Netherlands, using only renewable energy.

These crops were grown surrounded by massive "fruit walls", which stored the heat from the sun and released it at night, creating a microclimate that could increase the temperature by more than 10°C (18°F). Later, greenhouses built against the fruit walls further improved yields from solar energy alone.

It was only at the very end of the nineteenth century that the greenhouse turned into a fully glazed and artificially heated building where heat is lost almost instantaneously -- the complete opposite of the technology it evolved from.

Reinventing the Greenhouse

The modern glass greenhouse requires massive inputs of energy to grow crops out of season. That's because each square metre of glass, even if it's triple glazed, loses ten times as much heat as a wall.

However, growing fruits and vegetables out of season can also happen in a sustainable way, using the energy from the sun. Contrary to its fully glazed counterpart, a passive solar greenhouse is designed to retain as much warmth as possible.

Research shows that it's possible to grow warmth-loving crops all year round with solar energy alone, even if it's freezing outside. The solar greenhouse is especially successful in China, where many thousands of these structures have been built during the last decades.

Burning the Bones of the Earth: Lime Kilns

This is a guest post by Brian Kaller, who blogs at Restoring Mayberry.

Explore the now-ruined estates of the Irish countryside and you occasionally find a stone cylinder, as much as several metres high and wide, open at the top and with a small door at the base.

Some resemble the medieval fortresses that still dot the landscape here -- but no one built fortresses so tiny, or half-buried in the side of a hill.

In fact, they are kilns for lime burning, a now-forgotten industry that sustained many agrarian communities before energy became cheap.

Rings of fire: Hoffmann kilns

About a year ago we presented a medieval building technique that could save large amounts of brick and thus embodied energy in construction: timbrel vaulting. Turns out that there is also a 19th century brick and tile production technique that is surprisingly energy efficient: the Hoffmann kiln, a giant version of the medieval oven stove.

Sunbathing in the living room: oven stoves and heat walls

Oven stoves are greener, more efficient, healthier, safer and cosier than all modern heating systems. Why are they gone and how do we get them back?

An oven stove is a very efficient and robust oven that radiates heat all day. In the US it was introduced only 20 years ago, but in Europe the technology is almost one thousand years old. Especially in Russia, Scandinavia and Central Europe the oven stove has a long and rich tradition.

In the 18th century, several European governments financed research to improve the technology, as a way to overcome an acute shortage of firewood: ecotech before the term existed. However, its further development and distribution was thwarted by the arrival of coal, gas and oil. Oven stoves are large, heavy and slow, but they offer so many advantages that they – again - deserve to be subsidized by the government.

Tiles as a substitute for steel: the art of the timbrel vault

The craftsmanship associated with timbrel vaulting has long vanished, but the achievements are still with us today.

Brick, stone and concrete are materials strong in compression (you can pile them up almost indefinitely), but weak in tension (if the structural breadth increases, the material has to be supported by many columns or it collapses).

Nowadays, this problem is solved by steel structures or the use of steel reinforced concrete - the tensile strength of steel is significantly more than that of bricks, stone or plain concrete. Pre World War II, the weak tensile strength of brick was compensated for by superior craftsmanship.

The "timbrel vault" allowed for structures that today no architect would dare to build without steel reinforcements. The technique was cheap, fast, ecological and durable.