The focus of the designers and conservationists of these facilities is to design and maintain a stable environmental condition, within the setpoints, throughout the year, to meet the preservation criteria. Storage of other valuable media such as magnetic tapes, films, computer disks, and photographs present a similar situation, but they require different environmental consideration for their storage facilities.
As early as the 1960s, preservationists, conservation scientists, and archivists began to recommend cooler spaces with lower humidity for storing books and other paper-based materials. The intent of lowering the temperature, humidity, and pollutant levels was not to prevent the ultimate decay of the books, but to slow the process of deterioration.
The recommendations were to maintain the book storage environment at 68 degrees F and 50% rh, although no set of worldwide standards was established. Experiments with artificial aging tests indicated that there is a direct relationship between the rise in the environmental temperature and the chemical reaction of the ink in the paper even in the absence of pollutants, light, and other factors.
Building Design ConsiderationsArchitectural Elements.Architectural design of record and book archival facilities has changed and varies from one country to another. Many of these variations are due to the local environmental climate and the date of the design, while others are due to social and economical factors. The climate effect is easy to understand when we compare cooler climate construction, for instance, in higher elevations, in Europe.
Another variation in the architectural aspects of these storage facilities is underground construction. Although these facilities were built to take advantage of cool climates or natural underground insulation, they do not have a set temperature or humidity control. The environmental controls are allowed to vary seasonably as the outside conditions change.
In the United States, major institutions, primarily universities, have constructed state-of-the-art archival facilities for their rare books, and in some cases for their artifacts. These storage facilities are operating at temperatures as low as 50 degrees and 35% rh. Table 1 lists the temperature and humidity setpoint and allowable range of some of these facilities.
These archival facilities are built in modules, with approximately 30-ft high bay areas for book shelving, and have no windows. The building envelopes have a tight structure with vapor barriers to prevent moisture, outside air, and pollutants from migrating to the inside of the building. The insulation rating of R20 to R30 with galvanized facing installed on all exterior surfaces provides low heat transfer to the outside.
High-resistance insulation reduces the cooling and heating equipment size and operational cost as well as maintaining a uniform controlled temperature at the building envelope and in the core of the building. In addition to the high bay modules for shelving, a separate area for book preparation and office areas is added to the facilities.
Mechanical Systems. It is highly important that the mechanical engineer, the architect, and the facility operator discuss the project through all aspects of the process, from design to commissioning and start-up of the systems.
Special attention should be given to walls, ceiling, and the floor to keep the surface temperature close to the desired room temperature. The HVAC system for a facility goes beyond maintaining the comfort level and it must be capable of maintaining a constant low temperature and humidity in the facility. Even the most sophisticated data center HVAC systems are not adequate to maintain the relatively steady state condition of these environments with a high degree of sensitivity and accuracy.
These storage facilities usually have a higher ceiling height than other facilities. The air distribution is constant volume with sufficient flow to prevent stagnant air pockets that will create temperature fluctuation. The air supply distribution is from the ceiling level and return air from the lower level. The cooling coil performs the first stage of dehumidification, and the second stage is by a nondusting desiccant dehumidification unit. The steam used in the humidifier system is a clean steam to prevent adding chemicals to the airstream.
The mechanical system must operate on a 24/7 schedule, and it must have redundancy in the equipment to allow for maintenance shutdown without affecting the operation of the HVAC system. The internal load is low due to infrequent human activity and low demand for lighting. Also, the infrequent opening and closing of doors can change the environmental conditions. Airlocks are provided to minimize the room pressurization effect and outside air infiltration.
The economical analysis should consider the cost of the building as well as the operation of the climate control equipment. Figure 2 shows a typical schematic drawing for the mechanical system.
For mechanical system performance, two site criteria should be considered during the construction site selection process. One is available utilities, and the other is best available outdoor air quality. Adding on-site emergency power generators will compensate for interruption to the main electric service. The mechanical systems also rely on water.
For cooling equipment, it is recommended that air cooled systems be specified to eliminate the need for cooling towers. However, water used for humidification and boiler operation should also be stored adequately on-site in case of interruptions to the main supply water. Added precautionary measures to be considered are diesel and natural gas the for heating system. The issue of air quality is of great importance and is explained below.
Air Quality. Two types of pollutants, gasses and particulates, affect the deterioration of paper and other library archive materials. Particulates such as dust and soot disfigure materials and accelerate the aging process. Installing high-efficiency mechanical filters in the AHUs removes particulates to an acceptable level.
The pollutants in the form of gasses, generated in urban areas, especially sulfur dioxide, nitrogen oxide, peroxide, and ozone react with material through chemical reactions. This process damages paper and leather with the result of paper becoming discolored and brittle and the leather becoming powdery.
Although researchers have not determined the exact level of gasses that cause deterioration of archival materials, acceptable levels of gas concentrations have been adopted by preservationists. Along with the installation of gas phase filtration in the mechanical system, the facility should be equipped with gas monitoring and control systems. The monitoring is performed by air sampling, real-time, or reactive monitoring methods. The important part of monitoring selection system is the accuracy of detecting gasses at low-level concentrations. Table 2 lists the most common gaseous pollutant and the levels of which they must be controlled.
The sensitivity and accuracy of the instruments have the outmost importance in providing the required environmental condition. The building control system should have adequate sensors and control devices to allow for accurate system performance and monitoring. Multiple sensors should be installed where the rooms are large, to get broader readings for diagnosis and control of any possible microclimates created within the storage facility.
Lighting Considerations. Exposure of the library materials to light, both artificial and natural, also accelerates the deterioration process through chemical reactions, and it causes materials to fade and change color, making the prints, photographs, and bindings less legible. Molecules within objects accelerate the chemical reactions by absorbing the energy emitted from light. Over time the effect of the lighting is accumulative and irreversible.
Although all light waves are damaging to paper, UV rays are more damaging to the library materials. UV waves have higher frequency; consequently they have higher energy than other wavelengths in the spectrum. Increases in energy levels can break down the molecules or create oxidation, which is the transfer of energy to oxygen molecules within the objects. This unstable, charged oxygen then reacts with other molecules that initiate a chemical reaction. Sunlight as well as many manmade light sources contain a high level of UV radiation.
Book archival areas are built without windows or skylights to prevent the collection's exposure to natural light. However, the use of artificial lighting sources cannot be eliminated. Artificial lighting sources also generate UV as well as visible light waves.
One lighting design is to install indirect fluorescents lamps with UV protection covers. The UV protection shield must be regularly monitored and replaced to ensure its effectiveness. The installation of motion sensors eliminates material exposed to lighting when people are not around. Another lighting application is the use of high-pressure sodium lamps, which emit low levels of UV and generate less heat.
Visible light waves must also be kept to a minimum to protect storage materials. Light waves visible to human eyes are measured in lux (lumans per square meter) or footcandles (ftc). The recommended level of light to sensitive materials, including paper, is debated by researchers, but the current practice is to limit the light exposure for paper to 55 lux (15 ftc). CCI has published guidelines and standards based on International Standards Organization (ISO) for estimating rate of light fading and the recommended light level.
ConclusionLibrary archival facilities were evolved to preserve paper-based materials by providing a cool, dry, and dust-, pollutant-, and radiation-free environment for materials that are not directly accessible to the public. The purpose of these facilities is to prolong the life of the collections and to eventually reproduce the material. Tighter environmental conditions result in an extended life for the materials.
However, the stringent environmental control setpoints require added cost to the construction and the operation of the facility. An in-depth cost-benefit analysis that includes the capital cost as well as the operating cost, especially in regions with hot and humid summers, has to be performed to justify the construction project.
To achieve this, preservationists must first determine the required life expectancy of the preserved materials, thereby providing the basis for establishing the environmental conditions. Then the design team can provide the building and the operating costs. ES
EDITOR'S NOTE:The images associated with this article do not transfer to the Internet. To review the figures, please refer to the print version of this issue.