Advanced inside surface materials for buildings for climatic control in the 21st century

“Palladio”. The name of an Italian architect of the 16th century, a genius of cool-building design, is chosen to illustrate the synthesis of old and new, and the importance of inside surface materials as an integral part of a building’s climatic control system.

It is becoming clear to many scientists, especially in the Northern climates, that the unnoticed change from traditional building surface materials that are hygroscopic (predominantly organic materials such as timber, clay, paper, chalk-based paints and renderings etc.), to modern surface materials that are inert to moisture (glass, steel, concrete, plastic paints etc.), has not been studied sufficiently.

Researchers at several avant-garde institutes are currently investigating the indoor climate effects of, for example, timber houses compared to concrete houses, and there are certainly many indoor climatic advantages available by the use of advanced surface material systems to enhance “natural cooling/warming, natural humidification/dehumidification”. This research effort, especially in the Northern countries, is increasing.

Many current developments are however popularly understood to be of a primitive type, based on low technological grass-roots activities, whereas the Winter Palace architect Rastrelli continued the traditions of Palladio by designing elegant “Renaissance air-conditioning systems”.

Such systems, if they can be called that, allow a synthesis of artistic decoration, architecture, and engineering, by using room surfaces, both in content (choice of materials) and form (“corrugations” such as columns, balustrades etc. increasing the surface area 2–3 times the plane area) to interact with outside air moisture and thus regulate the indoor climate.

The original cooling system in the Winter Palace is thus not a separate engineering system, or even a system integrated with the architecture: it is a part of the building itself.

It would not have been possible if the building was made of stone, as in “classical” construction, or of concrete, as in “modern” construction. But brick, stucco, and frescoes, or modern equivalents, are ideal.

Historically, it was the stonemason turned architect Palladio who created the revolutionary change from expensive stone to cheaper imitations, and some sources suggest that even frescoes by artists such as Paulo Veronese were just a cheap way of creating the impression of a tapestry, which was a necessary thermal insulator against cold stone surfaces.

There are 3 specific physical features of such “renaissance air-conditioning” systems:

  1. The hygroscopic quality of the surface material.
  2. The quantity of this material.
  3. The interaction of the inside air (moisture) with the outside air (moisture).

Climatic stability is maximized by using high performance materials, corrugations (or other increased surface area methods, such as statues, furnishings, etc.), and adequate openings to the outside air, where it should be noted that the “Fortochka” and “Rastrelli” systems are ideally suited for the purpose.

The key scientific features are diffusion and evaporation and condensation of moisture from or to the outside air from or to the surface materials. This mass transfer of moisture, as it is called, is regulated by the partial pressures of moisture in the outside air in relation to the partial pressure in the indoor air.

Evaporation from the inside surfaces (during the day) produces cool surfaces as well as cooler air and limits the natural decrease of humidity levels. Condensation on the surfaces (during the night) causes warmer surfaces as well as warmer air and limits the natural increase in humidity.

The scientist John Dalton discovered the basic laws of gaseous diffusion in 1801, but the method had already been used for centuries. It is still valid in vernacular architecture many places in the world, but was lost to modernism in the 20th century.

It is well known that dew “falls” at night and disappears a few hours after the sun’s appearance. The relative humidity of the outside air is highest during the early hours of the day and lowest in the early afternoon. Unless of course there is rain or fog, but in this case cooling is unlikely to be so necessary. These natural outside air fluctuations can interact with inside surfaces through diffusion of moisture through openings in windows or air shafts.

The beauty of the system is that it is self-regulating: the higher the air temperature rises during the day, the lower the relative humidity will be, and the more evaporation will occur from surface materials, so that inside temperatures will always be lower than outside.

My mother, as a child in the 1930s, worked in the library of Cornedo, Vicenza, a 16th century building of the Palladio type, although of unknown architectural origin. She remembered the summer siesta periods, when villagers would come to the cool library building.

There are of course numerous preconditions for this system to function, and it is important to note the interdependency of all the items in “The Hermitage Climatic Regulation Method”.

It is futile to use this “Palladio” feature without adequate solar shading (see “Matisse” feature), without removal of thermal pollutants (see “Texas” feature), or without air (moisture) transparency (see “Fortochka” and “Rastrelli”).

In Rastrelli’s time, and Dalton’s, there were limited materials available to allow experiment and optimization of this process. Now, numerous experts are developing materials, or composites, and producers of materials with hygroscopic properties market this feature.

For example, the special clay “Bentonite” combined with wood fibres is an example of a high efficiency hygroscopic material currently being tested, but the traditional Hermitage materials are adequate—unless they are covered with a plastic film of inert paint instead of the traditional chalk based paints.

The Winter Palace still (mostly) contains the original materials, and if The Hermitage is true to these original materials, and refrain from the temptation of modern plastic based paints, this property can be enhanced and utilized anew.

In 1997 it was only by applying moisture exchange factors to the calculations of heat and moisture balance that the climatic measurements taken in the rooms could be explained. Paradoxically, all modern calculation methods do not include such algorithms, but the simple explanation is that such algorithms are deemed unnecessary, because most 20th century surface materials have no hygroscopic properties to model or calculate.

Indoor surface materials with hygroscopic properties have many advantages for buildings, but are inadequately studied.

For housing, for example, hygroscopic materials can effectively limit high levels of room relative humidity (a property named “buffering”) thus eliminating surface condensation, thus eliminating the mould growth that causes many health problems.

At the same time, by limiting high humidity levels, excessive ventilation is not needed, and a low background ventilation level is adequate, thus saving energy.

I believe there is a need to develop a 21st century identity of indoor surface materials for buildings and create a (new) renaissance.

This is therefore the explanation for the choice of name to describe these types of advanced surface materials, using the name of the Great Italian renaissance architect who changed from construction using stone to always using brick and plaster, from inert materials to “living” materials: Palladio.

Sergio Fox