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close this book Prevention and treatment of mold in library collections with an emphasis on tropical climates: A RAMP study
close this folder 4. Prevention
close this folder 4.1 Building design and modification
View the document 4.1.1 Location
View the document 4.1.2 Structural considerations in environmental modification

4.1 Building design and modification

If one is fortunate enough to be involved in the design of a new building with state of the art environmental controls, there is ample coverage in the library and museum literature, beginning with Garry Thomson's excellent volume, "The Museum Environment"1 which should be an invaluable aid to librarians. No attempt will be made here to retrace this ground. Instead, attention will be focused on the modification of existing buildings and the design of new buildings which will not incorporate environmental control.

It should be noted that a building constructed with the idea that environmental controls will be added at some future date is not a viable option. A building designed in such a way that environmental controls can be effectively installed and economically operated in the future, will most probably be insufferable for both users and collections in the meantime. The low ceilings and closed interiors that make environmental control possible create the worst possible environment in the tropics. By the same token, a building designed to take advantage of natural ventilation makes the installation of a complete environmental control system virtually impossible, or at the very least, astronomically expensive. Decisions regarding the environment must be made early in the planning.

Even without environnmental control, good design can do much to reduce the negative impact of the locale's prevailing climate. There is surprisingly little literature available on building design in the tropics. Vance's bibliography2 lists a scant fifteen pages of references, many 20 to 30 years old. Though the literature is not extensive, working together the librarian and the architect can design a building that will safely house the collection. In building design, it is important that the area's particular type of tropical climate be taken into consideration since the requirements will be different for each of them, though some common denominators do exist.

 

4.1.1 Location

The various climatic zones discussed in the introduction are important in determining the requirements of a new building, or the best methods for modifying the enviroment in existing structures. Fry and Drew3 provide additional information on the particular variations between continental and island locations which will be helpful in modifying the environment. Only general guidelines can be included here.

In the tropical rainforest climate (Af) where conditions are relatively uniform year round, temperatures are seldom extremely high (usually less than 90 F), and winds are light or non-existent, the major effort should be concentrated on improving circulation and lowering the relative humidity.

In the monsoon climate (Am) the stronger prevailing winds may be used to advantage for improved ventilation and circulation and more resources can be devoted to lowering the relative humidity, especially during the rainy months.

In the tropical savanna (As or Aw), with three distinct climatic seasons, more elaborate systems may be required. During the dry, hot seasons, dust and dirt will be a particular problem. The building must be capable of being closed against dust during this period, while maintaining adequate ventilation in order to prevent the build up of heat in the interior of the building. The problems associated with extremely high temperatures, dust and desiccation may make air conditioning the most important factor in maintaining collections in these conditions. Because there are two dry seasons and a relatively short wet season, mold may be a problem for only a small portion of the year, or not at all. Every effort should be made to prevent extreme fluctuations in RH between seasons. The utilization of natural ventilation in savanna climates varies from that in the Af and Am climates. Okley4 provides several useful diagrams suggesting possibilities for natural ventilation in As and Aw climates.

 

4.1.2 Structural considerations in environmental modification

Temperature and circulation can be modified directly through building structures. Relative humidity can be modified only indirectly through the effective use of natural ventilation or through technological control which will be discussed later.

Temperature

East and west walls, which receive the brunt of the morning and afternoon sun should be protected and insulated so that the sun's heat is not transmitted to the interior of the building. The roof, which has a high level of exposure to the mid-day sun, should reflect heat and there should be an attic or ventilation space directly below the roof to provide insulation for the interior of the building.

Double wall construction is an excellent way of insulating buildings in the tropics. Air is an effective insulator, and prevents heat from passing through the outer wall to the inside of the building. In many places in the tropics, the hollow cement block is a staple of the building trade. It provides an economical, though not always aesthetic, building material, and provides adequate insulation for the interior of the building. A true double wall construction is more effective, but considerably more costly. This construction is also used effectively in temperate climates where extremes of cold and heat make long term operating costs for environmental control a primary consideration.

The brise soleil is a variation on the double wall. It may be designed as part of the building, or attached to the facade of existing buildings. Though not as effective as a double wall, it provides protection by absorbing the sun's primary radiation. It also reduces the light levels inside by shading the windows, and allows windows to remain open even in the rainy season. It may cover the entire wall, part of the wall, or in some cases, only windows though this latter construction is considerably less effective in reducing the transmission of solar radiation.

Shading of exposed walls can take a number of other forms, including exterior landscaping with trees and shrubs, the extension of over ranging roofs, and the installation of exterior canopies. The use of interior blinds, curtains or louvres can also reduce the transmission of heat through window glass. Kukreja5 provides a table evaluating the effectiveness of various shading devices based on their reduction of total heat gain, efficiency in ensuring cross ventilation, and the percentage of natural light resulting from that particular form of control.

Glass both transmits and intensifies heat. Large windows in tropical climates can significantly increase interior temperatures, yet are incorporated into many buildings for aesthetic reasons. Ultra violet and heat absorbing films are effective in reducing heat and UV light without obscuring views or lowering the light levels too greatly.

High ceilings are a common feature of older buildings in the tropics and are an effective means of diffusing interior heat. As the warm air rises, it can be pulled out of the building with ceiling or attic fans or through windows placed directly beneath the roof overhang.

Ventilation

In general, buildings in tropical climates should be oriented in such a way as to take advantage of any prevailing winds and designed so that cross ventilation is possible in all areas of the building.

Even buildings designed to utilize natural ventilation will require back-up systems of mechanical ventilation for those times when prevailing winds fail or shift.

Placement of windows is a principle means of assuring adequate air circulation, once the orientation of the building has been determined. Kukreja6 provides excellent diagrams of interior air movement for various window placements. These are useful not only in the design and modification of buildings, but in anticipating problems and determining stack arrangements. He notes that a single window serves no purpose as far as interior ventilation is concerned, and that if modifications are to be made, the best results are obtained by placing windows on opposite walls to insure cross ventilation. Enlarging the outlet window opening results in a definate increase in interior air movement, even when the inlet window remains unchanged. Circulation is also increased significantly by increasing the height of narrow inlet and outlet openings. He also compares the circulation figures for various window areas in relation to floor area, demonstrating that air movement peaks when window openings are equal to 25% of the area's floor space.

Louvred windows can provide excellent ventilation, and are common in the tropics, but are difficult to seal against rain and insects, and their use is best combined with other window treatments. All open windows should be screened with well fitted, fine mesh, fiberglass screens. Placement of the screens on the inside of the windows will facilitate their removal for cleaning, particularly if there is a brise soleil on the outer wall.

If the existing building has high ceilings, the installation of ceiling fans is an excellent investment. Used in conjunction with standing floor fans, or window fans adequate air circulation can be maintained at a relatively modest cost even in Af climates where there is very little natural air movement.