Library Building Beyond the Books
Equipment installed here will operate and generate heat continuously. The air-conditioning system must be designed to operate whenever the technical equipment is operating, including during power outages. The space must maintain a controlled environment of 60 to 85 degrees Fahrenheit (15 to 29 degrees Centigrade) and a relative humidity in the range of 30 to 50 percent. Controls such as thermostats must be located within the space to be conditioned, and good airflow around the equipment must be maintained.
The technology infrastructure distribution facilities contain the equipment and cable terminations necessary to connect the network backbone systems to user locations. Rooms selected for use as distribution facilities must not be shared with other functions such as janitorial, electrical, or storage.
The main distribution facility (MDF) houses main termination patch panels and supports "core" technology equipment, such as the main data network router and switch. The main telephony and video distribution equipment is often colocated within the MDF. This is the origination point for central network connectivity via backbone cable routed to the other distribution facilities within the building.
Intermediate distribution facilities (IDFs) should be located in the center of the area to be served, because this will allow the maximum floor area to be serviced. The increasing use of high-speed network cabling and the associated length limitations restrict the distance between an IDF and the technology outlet being serviced from that center.
Industry standards governing performance of high-speed network cable require that the total distance (channel length) between distribution equipment (ethernet switches) in the IDF and the end users' networked equipment (usually personal computers) be no longer than 328 feet (100 meters).
In multistory buildings, IDFs should be "stacked" to facilitate routing vertical backbone cabling or riser cabling. It is recommended to have a room on each floor — even though distance and area served may not strictly require it — to support the maintenance effort and to ease operational difficulties.
Cable tray is widely used within modern communications cabling infrastructure, and is the preferred method of conveyance both outside and inside the distribution room. The type of cable tray selected depends on the area of application.
A less expensive alternative to cable tray is the use of "J"-shaped hangers known as J-hooks. To ensure that cable is properly supported without kinks or danger of cuts or snags, the J-hook should have wide bearing surfaces and rolled edges.
There are also several types of cable slings or "saddles" manufactured for communications cable conveyance. The saddles are made with a large metal plate that has rolled edges in the direction of cable flow. These devices can be attached to the building structure using various hanger-wire or rod support devices. The slings are similar in design to the saddles, but are treated with fire-retardant, plenum-rated cloth.
Floor duct systems are a network, or grid, of metal raceways with channels that can accommodate both electrical wiring and technology cable. The ducts are cast into and embedded in concrete floor, which allows horizontal distribution of the wiring and cables. The system allows a certain amount of flexibility for cable installation in open areas. Because of the construction technique, this distribution method can be considered only for new construction.
The advantages of using floor ducts are the mechanical protection they provide for cables, a certain amount of power and data outlet layout flexibility, and increased security. The major disadvantage of the floor duct system is its high initial cost of installation. The system does not support furniture layouts that are subject to frequent change.
Raised Access Floor System
Distribution of cables can also be accomplished through various types of raised access floor systems. The relatively expensive low-profile type is usually 3 to 4 inches (7.5 to 10 centimeters) high and is used for cable and electrical wiring distribution.
In recent years, there has been great success in providing the high flexibility of raised access floor systems at low or no additional cost compared to other systems, by using a high framing system, minimum 14 to 18 inches (35 to 45 centimeters), and supplying air through this plenum. The elimination of conventional overhead air ductwork, plus the high energy efficiency of this method of heating and cooling combine to produce a total system that is often less expensive than typical building infrastructure systems.
The high flexibility comes about through the ease of changing cabling and wiring under the raised floor to service new or changed locations, and also because of the integral outlet boxes and air diffusers built into the 24- by 24-inch (60- by 60-centimeter) floor panels. The architectural benefit of the raised-floor plenum system is that the ceiling area above can be clear of wires, conduit, and air ducts, eliminating the need for conventional ceilings and allowing the use of glare-free indirect lighting and higher spaces.
Coordination issues pertaining to library furniture and technology should be addressed from the beginning of a project. Furniture plans generated by the architect or interior designer during the design phases should ensure that all required elements fit the architectural plans as they develop and that the power and technology interface requirements are coordinated with furniture and workstations.
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This article was excerpted from "Technology Infrastructure Design for Libraries" with permission of the publisher, the Libris Design Project Portions of the material were originally created by Arup and recently updated by Randy Sparks, a principal with RLS, Inc. and Edward Dean, AIA, with 3D/I-San Francisco. Libris Design publications are supported by the U.S. Institute of Museum and Library Services under the provisions of the Library Services and Technology Act, administered in California by the State Librarian.