Achille Knapen – Belgian Engineer and Innovator

Achille Knapen was a Belgian civil engineer whose dehumidifying inventions helped preserve several important historical buildings.

Firstly, a thank you to Discovering Belgium reader Mansur Sultani who suggested this addition to the list of Famous Belgians covered here.

Marie-Frédéric Knapen, known throughout his life as Achille Knapen, was born on September 29, 1860, in Mons, Belgium, and passed away on July 26, 1941, in Trans-en-Provence, France. A civil engineer and inventor, he was renowned for his dehumidification inventions and for constructing an “air well” designed to harvest atmospheric moisture.

A hygiene engineer

Knapen considered himself to be a “hygiene engineer” as he wanted to “heal buildings of their original defects to safeguard the health of their occupants”. Many of his inventions were aimed at the removal of moisture from buildings by using an artificial cooling device.

For example, he patented a process for drying out buildings to prevent their decay due to moisture and molds. His invention, “the single-branch atmospheric siphon process with automatic priming” brought a major evolution in the treatment of humidity on walls, and earned him the title of médecin des pierres or “the stone doctor”.

The principle was to use evaporation channels or single-branch siphons arranged in the walls. Drying occurred through the circulation of air through the channels. Knapen contributed to the preservation of several important historical monuments such as the frescos of La Chaise-Dieu, the Château de Versailles, the Trianon, the Louvre Palace, and the Académie Française in Paris.

Air well construction

Knapen also came up with an idea to bring water to desert areas. As a trial or pilot project for his ideas, between 1930 and 1931 he built a 14-meter-high puits aérien (air well) atop a 600-foot hill in Trans-en-Provence, south-eastern France. Resembling a giant beehive, this structure aimed to condense atmospheric moisture into usable water.

Its massive three-meter thick walls are made from porphyry granules and cement mortar, coated with a cement mortar coating. They are designed to keep the inside temperature cool. The walls are punctured by a number of holes that let in warm, moisture-laden air during the day.

At night, when the temperature drops, the water vapor in the air condenses against a huge concrete column built inside the structure, and drips down to a collecting basin at the bottom of the structure.

This experimental structure was envisaged for use in desert regions or drought-effected areas. However, despite initial public excitement, the air well’s water yield was disappointing. Knapen had hoped for a daily yield of 30,000 liters per day. In practice it produced only a few liters daily. The project was abandoned, although the construction still remains and can be visited. Here is a short walk around the area, taking in Achille’s construction.

Photographs © Trans-en-Provence Office de Tourisme and Michel Royon/Wikimedia

Honors and recognitions

Despite this setback, Knapen continued his work on dehumidification systems and processes, and received multiple accolades for his engineering innovations and his work in preserving ancient buildings and monuments:

• Laureate of the Royal Academy of Sciences of Belgium
• Recipient of the triennial Couvreux Prize from the Société des Ingénieurs Civils de France
• Gold Medal from the annual Engineers of France competition
• Highest award in the Inter-Allied Competition of the City of Paris for superior construction methods
• Knight of the Legion of Honour (France)
• Officer of the Order of the Crown (Belgium)

In Brussels he has a street named after him: La rue Knapen.

Discover other Famous Belgians in the fields of science, engineering and technology. And if you want to see someone featured in this series, which now numbers 31, just drop me a line and I’ll see what I can do.

Denzil Walton

I created Discovering Belgium in 2011 to share the country’s hidden stories, fascinating places, and remarkable people. Through articles, photography, and audio walks, I share discoveries that reveal Belgium beyond the obvious. Hope you enjoy this site.