Advanced vertical air distribution systems for the 21st century

“Rastrelli”. A name, the name of a Russian architect of the 18th century, a ventilation genius, is chosen to illustrate the synthesis of old and new, and the importance of air distribution as an integral function of a building structure.

Advanced vertical air systems to enhance “natural ventilation” are being developed in several avant-garde institutions around the world. Historically, the development of vertical air shafts as an integrated part of a building was a major step forward for people’s health, and occurred at various times at various geographic locations.

For example, one of the major tasks being carried out by the Indian government today is introduction of simple chimneys from cooking stoves, which raises the life expectancy of the cooks considerably. At a next level, a serious problem in some crowded African townships is that smoke from chimneys creates the problem that fresh air inlets become “smoke inlets”, so that the need here is both for improved fuels to protect the micro-climate and advanced “Fortochka” windows to limit the entry of particles into rooms.

On the other hand, most buildings in the rich countries, particularly in the past 20–30 years, do not include chimneys or other building technology air shafts, because of the reliance on electrical/mechanical air movement devices. This is mainly a result of the architectural revolution of Bauhaus in the 1920s, which included admiration for complicated mechanical technology and a lack of respect for building technology knowledge acquired over the centuries.

It is ironic to note that modern building economists, when making analyses, even within popular concepts such as the fine sounding “Total Economic Analysis”, have no tools for coping with products that last more than 20–30 years, let alone 200–300 years, such as many “products” in The Winter Palace, such as chimneys/air-shafts. As with the international standards that omit tools that permit analysis of the thermal performance of “Fortochka”, these economic models omit tools that allow analysis of such air-shafts.

Progress is therefore hindered, in a way, by the conservative, or arrogant, or foolish, attitude of the people who developed these tools, but only for the products they knew exist. A more humble approach would have been to allow for the unknown, to accept that here at the end of the 20th century was not the end of the road of scientific development.

At the same time, however, the energy crises in the latter part of the 20th century, combined with the low durability of electro-mechanical devices and other disadvantages, such as noise, maintenance costs, lack of flexibility and particularly the health risk of equipment failure, led to a need for more sustainable technologies, and much recent ventilation research has concentrated on “natural ventilation” of various types.

But most current “natural ventilation” developments are either of a centralized type based on atriums or similar architectural features, or rely on complex engineering structures as additions to the building structure, whereas the Winter Palace architect Rastrelli designed an elegant method for individual control, by building multiple air shafts into the walls as a simple accompaniment to the chimneys.

The original ventilation 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.

Nowadays it would be termed a synthesis of architecture and engineering: then, in 1762, it was a natural, simple architectural feature, based on the newest scientific developments available, using knowledge that has not been lost, but that has not been applied for almost a century, since Bauhaus and Carrier et al created the unsustainable architecture of the 20th century.

The specific physical features of such systems are two or more parallel shafts leading from each room to a roof outlet, or chimney. The shafts are in the walls as part of the construction itself. One shaft is intended for air supply, the other for air removal, and it is possible to include heat recovery of various forms, natural or otherwise, when the warm outlet air and cool inlet air are adjacent to each other.

In the Winter Palace there are over 1000 shafts in total, so that the building is in fact as perforated as a Swiss Cheese, although it appears as a massive, solid construction. In a brick building this is a simple construction method, since the bricklayers simply omit bricks in these areas as they build upwards. In modern construction it is also simple to omit some insulation in the cavity in outside walls or cast shafts in concrete inner walls, but the design can, of course, be of many types.

Modern worries, such as condensation in cold air shafts, were not a concern for Rastrelli, because modern condensation is actually caused by the materials and systems used in modern construction. Rastrelli et al did not perhaps consciously know that they had produced buildings that were inherently condensation free (see “Palladio” section), but then again, perhaps their knowledge was more advanced than we think. It was after all their lifetime that gave us most of the great scientific advances we use (and rediscover) today.

For example, there is a great deal of analysis in avant-garde institutions of the mechanism of interstitial condensation, and it appears that hygroscopic materials have two natural defences against condensation: first they absorb moisture, limiting the vapour pressure available for transfer of moisture through the structure, and secondly, they, combat condensation that may occur through capillary action backwards into the structure, and redistribution of moisture, preventing actual water production.

After the fire in 1834 in the Winter Palace almost all the 1000 original shafts were closed, although some were reused in the modernization after World War II, so that there are now approximately 200 shafts in operation. It is clear that fire protection is important, and fire dampers built into the shafts can automatically isolate areas of the building into manageable “fire compartments”—a necessary feature for all buildings, but especially relevant for the Hermitage. Emphasis should be on fire management to ensure smoke removal for visitor escape, and vertical shafts with high level openings are essential for this.

The key scientific feature of the “Rastrelli” advanced air system is that the openings from each shaft into the room are offset: one opening, or grille, is placed at a low level near the floor; the other is placed at a high level, near the ceiling.

Natural thermal forces in any heated room result in higher temperatures near the ceiling than at floor level. Warmed, used, air rises and fills the shaft nearer the ceiling. The result is one shaft with warmer air, and one with cooler air. The air density in the two shafts is different, producing a pressure difference according to the Bernoulli equation δΡ = (ρ1−ρ2).g.h. In larger rooms, the temperature difference is greater, so that this natural air circulation is enhanced, although the proportions are, quite naturally and harmoniously, the same.

With this natural driving force there is air circulation in the room, controlled by the room occupants who can regulate air quantity by adjusting grilles on the lower level shaft.

The above system was also elegantly used by Rastrelli to provide air for combustion in the open fireplaces of the original heating system in most of the rooms. A fireplace naturally draws air from the room as part of the combustion process, and if this air has to come from the windows it often results in uncomfortable draughts. By constructing a second shaft parallel to the smoke chimney with an outlet adjacent to the fireplace discomfort and wastage of warm air is avoided. After the fire of 1834 the system was again reused in a different way, because the open fireplaces were considered a fire danger (despite the fact that the cause of the fire was actually a construction mistake during rebuilding of some rooms). Be that as it may, the open fires were replaced by stoves in the basement, with double shafts: one for the smoke, another for the warmed air to the rooms. The ingenious “doubleness” of Rastrelli’s design continued, even then.

Although it may not seem relevant to discuss fireplaces in modern buildings there are in fact many institutions studying and developing high efficiency bio-fuel stoves as a natural, future, alternative to pumping warm water several kilometers from centralized boiler plants. Such centralized hot water production is obviously an effective way of using “waste” heat from electricity production from coal or oil fired power stations. But if the trend towards a solar future continues, and electrical generation from wind and sun dominate in the future, then other forms of heating will become more practical.

In conjunction with the advanced windows named “Fortochka” (described in a separate section) the “Rastrelli” double offset shaft system provides a multitude of ventilation possibilities, so that individual people can have the air quantity and quality they desire.

In a building such as the Hermitage with numerous visitors it is of course the custodians who would be able to adjust indoor conditions to match changeable outside conditions, as required. The visitors require an average climatic condition acceptable to them all, but the possibility for personal ventilation to optimize the experience of comfort is described in the section “Individuals”.

A variant of the simple double air shaft system is the “intelligent” type, where the shafts can be fitted with small hidden motors, sensors, fire alarms, and communication devices, so that the shafts can interact with the windows and respond to telephone requests or to pre-set requirements to automatically adjust the climatic conditions in a room.

The basic scientific principles of such “advanced” offset air shafts are found in The State Hermitage Museum (The Winter Palace), which may be a surprise, except that it was after all here in Russia in 1726–1732 that the mathematician Daniel Bernoulli discovered the above equations of nature, and it is likely, is it not, that Bernoulli talked to his contemporary, the Winter Palace architect, Bartolomeo Francesco Rastrelli (1700–1771)?

Perhaps we will never know, but Rastrelli certainly utilized these basic forces of nature, of air movement, for the first time, to my knowledge, in a building. This is therefore the explanation for the choice of name to describe these types of advanced air shafts, using the name of a Great Russian architect of Italian descent: Rastrelli.

Sergio Fox