For a typical office building, it is estimated that 45-50% of occupants will change their location or require an upgrading of their computer and/or telecommunications connections every year [1].

The advent of the Information Age resulted in the need for each and every workstation to be equipped with access to computer and telecommunications power sources and networks, often creating an unsightly abundance of cables, outlets and extension cords.

The role of any building’s cabling infrastructure is to provide occupants with voice, power and data connections capable of meeting not only present requirements but also the inevitable yet unpredictable future equipment upgrades, expansions and innovations. According to Moore’s Law the computing power of microprocessors doubles every 18 months. Consequently, it is difficult, if not impossible, to plan with any certainty the technological restructuring a company will undergo over a period of, say, 5 years. It is possible, however, to install a cabling distribution system whose inherent flexibility and routing options provide the potential for accommodating such unanticipated changes.

Facility Managers look for economical, practical and aesthetic means of routing cables throughout a building. Cable distribution options (see appendix) include loose cabling, surface raceways or baseboards, overhead cable trays, poke-through’s, and raised floors. Often a combination of methods may be utilized. In addition, facility managers must also accommodate the ducts, grilles and other air-distribution equipment related to a building’s HVAC system. When raised floors are employed solely for cable management, thereby necessitating the installation of a conventional ceiling-based air distribution system, floor to ceiling heights, space planning and future maintenance are restricted by the need to accommodate both an underfloor plenum and ceiling plenum within a typical office floor.

Alternatively, consider the use of an underfloor air distribution (UFAD) system. Integrating mechanical and electrical infrastructure within a single underfloor plenum, readily accessible and adjustable via the raised access floor system, offers advantages at all stages in a building’s life cycle, from planning to construction to occupancy - most notably in the area of flexibility.

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Versatility
Raised access floor systems consist of modular floor panels typically 600 mm (24 in.) square, mounted on pedestals secured to the structural slab. The height of the floor panels above the slab determines the plenum depth. Installations devoted only to cable distribution could be as low as 75 mm (3 in.); when incorporating air distribution systems, typical plenum depths range from 200 mm – 460 mm (8 in. – 18 in.).

Cables can be run in any direction within the plenum, either freely or contained within flexible conduits (according to fire code requirements). At various locations the cables are accessed via openings in the floor panels, floor mounted terminal boxes, or are integrated within modular office furniture. Raised access floor systems thus provide a multi-functional floor plane with access to the telecommunications and HVAC connections necessary to any workspace, without compromising the aesthetics of the finished-floor, enabling a building’s infrastructure to be both versatile and visually unobtrusive. 

With the prevalence of speculative office buildings, a problem facing many designers is how to ensure occupants’ needs are catered for when little or no information is known about the future tenants. When assessing which cabling system will best meet present and future tenant needs, facility managers/building owners typically try to determine:

• Current network requirements
• A realistic estimate of future upgrading/expansion tenants will undertake to incorporate new technology
• Changes in tenancy likely to occur in the foreseeable future, say 1-5 years, and
• the implications regarding tenants’ technological requirements.

The difficulty in resolutely answering any of the above highlights the need for a building services infrastructure that is as adaptable as currently possible.

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Cable Distribution
Traditional cabling systems consist of fixed outlets, connections and long cable runs for which changes usually involved contracting outside labor, and considerable disruption within the workplace. Contemporary systems are much more user friendly, such as the latest trend towards ‘modular cabling’ (also called universal, unified, or structured cabling) whereby all telecommunications functions –power, data and audio/video- are contained within a single wiring infrastructure. Vertical wiring runs from the main equipment room to satellite rooms or closets serving each floor/zone. Horizontal cabling handles transmissions between these closets and each individual workstation. 

Modular cabling, particularly when installed within a raised floor system, is popular for offering improvements in building operations efficiency, meeting tenants’ needs for advanced cabling and owners’ interests in reasonable costs. All telecommunications services are run within a modular cable unit and each outlet offers the option of access to any combination of power, data and audio/video. In terms of efficiency and low-cost operation or maintenance, when modular cabling is installed as part of a raised floor system in-house personnel using simple tools and standardized connector pieces can easily carry out reconfiguration. The process of removing/replacing carpet tiles and floor panels is a relatively ‘dry construction’ requiring no repair paintwork or plastering and can be carried out by in-house personnel, avoiding the need to hire professional labor. In addition, day-to-day business suffers minimum interruption as the process can be carried out quickly and cleanly. 

In comparison to conventional loose cabling the first costs of raised floors –in terms of cable management only- are likely to be higher. However, in the face of today’s high churn rates where the ability to rapidly upgrade technology and re-route cable networks is both necessary and expensive, investing in a higher-cost system which offers maximum flexibility and minimizes the frequency of required system upgrades can be the most cost-effective option in the long term. Beyond the basic wiring requirements, it is estimated that every $1 of additional expense, in the name of additional flexibility, will translate into a $5 savings over the building’s life cycle [2]. As an example, a case study carried out in 1999 by Carnegie Mellon University reported that although the first costs of an UFAD system (including raised floor) were $0.27/ft² greater than a ceiling based poke-through system, savings at first churn with the UFAD system were estimated as $4.66/ft², significantly overriding any initial expense [3].

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Integration
Cable management is not the only area in which facility managers seek to optimize financial investments. Many of the occupancy-related demands placed on, say, a lighting system are similar to those of the HVAC and security systems. In fact, maximizing overall building performance is the facility manager’s aim, and the driving force behind the increase in integrated building systems – a recent survey among members of the building industry showed 75% of building owners had impending projects incorporating systems integration [4].

Based on the premise that the ability to control and monitor building systems from any point within the overall network is the key to peak operation performance and efficiency, systems integration (see appendix) establishes a means of electronic communication between the numerous systems, and their control mechanisms, in a building. This involves an understanding of how information from one source can benefit the performance of another (security sensors activating the lighting network, for example) and the ability to recognize common parameters in the operation of the different systems.

Raised access floor systems offer the perfect opportunity for integration by providing, for the most part, an unrestricted plenum zone capable of accommodating a variety of building services and components. In a survey of the top ten systems building owners and managers generally integrate first, HVAC was the most popular, chosen by 91% of respondents, and electrical monitoring/management came in third, after fire safety, with a 50% scoring. These choices are logical considering the similarities in parameters for the flow of conditioned air and the flow of electronic information around a building. Both involve a distribution network, running from supply to user that needs to be as cost effective, efficient and versatile as possible. In the same way that each workspace is equipped with access to voice, power and data outlets, localized distribution of conditioned air –particularly when occupants are given individual control of the air supply to their own workspace- can be a highly valued component of modern office environments.

Underfloor air distribution (UFAD) systems make use of raised floors to provide an accessible and adjustable HVAC network that shares its distribution space with a cable management network, thus reducing the problems of accommodating both separately. There are many benefits associated with integrating occupant-controlled infrastructure within one accessible zone, potentially reducing the first costs of the air distribution systems, for example, as the floor plenum will already be required for cable management purposes and is thus not solely an HVAC expense. In terms of space planning such integration simplifies the job of the architect traditionally faced with reconciling the numerous grids of components in a typical office building, from HVAC grilles to desk units.

The most significant advantages of integration become apparent during a workplace’s first churn, when the high level of coordination and compatibility of various systems’ networks noticeably reduces costly downtime.

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Space Planning
Rather than surrendering interior design intentions to the parameters of a pre-determined building services layout, the flexibility of an integrated underfloor plenum allows the layout of floor diffusers and cable outlets to be determined once an office furniture configuration has been decided upon. Furthermore, in the same way as the location of present day furniture assemblies is rarely considered immovable or permanent, initial diffuser layouts can be easily altered in future reconfigurations.

The removal/insertion/relocation of a floor diffuser is a simple process involving the removal of carpet tiles and a floor panel –using a suction grip, or similar tools- and the laying down of an alternative panel and corresponding carpet tile (i.e. with or without a diffuser aperture). Since the majority of carpet manufacturers rely on adhesives to secure their tiles to the floor surface, some problems may be encountered if a tile is repeatedly pulled up and reaffixed.

Research by CBE [5] has shown that, given the uniformity of air flow delivered through floor outlets within any particular zone served by a pressurized UFAD system, when one or two floor panels are removed temporarily for repair/relocation work the reduction in air flow to other diffusers in the same zone is acceptable -providing the process of removing/replacing diffusers and floor panels takes a short amount of time, which is usually the case. In addition, the same amount of air is entering the overall zone, whether through the open floor panels, or diffusers within the same zone.

When properly coordinated, reconfiguration creates little waste. Carpet tiles and floor panels from a modular system, consisting of different unit types (with or without diffuser apertures) of a standard dimension, are easily interchangeable. A typical office may be equipped with a number of floor panels and carpet tiles, with diffuser-sized apertures, ready to be moved around and placed among the standard units where required.

As with many nascent technologies or systems there is also the risk of misuse that may override any potential benefits. Only when tenants and facility managers have awareness and understanding of the parameters of the modular floor system can scenarios be avoided such as holes being randomly cut in carpet tiles, or furniture being placed directly over a diffuser. Many disadvantages cited in relation to UFAD systems arise due to a lack of coordination between:

(i) Different components:
misalignment of the carpet tile and floor panel grids resulting in the need for oddly cut carpet pieces when diffusers are relocated. 

(ii) Tenants and facility managers:
office furniture moved haphazardly without consideration of diffuser locations.

Experiments carried out by CBE on the effects of varying plenum design configurations on the performance of pressurized plenums [5], have shown that while increasing the number of outlets in a single zone can be expected to improve the uniformity of air flow distribution, a 50% reduction in the number of outlets causes no significant degradation in performance. It should be stressed, however, that for optimal operation of any UFAD system, office reconfigurations must take into consideration the resulting overall pattern of diffuser locations, particularly when operating partitioned-plenum installations.

Integrating the distribution of conditioned air and voice/power/data within the underfloor plenum optimizes use of the floor area and minimizes the depth of plenum needed above the drop ceiling. In some cases ceiling plenums can be eliminated altogether when an alternative means of removing return air from the space is provided, such as return grilles located at a high level on internal walls. Architecturally, this provides a greater opportunity to utilize the ceiling plane for creative lighting (natural or artificial) effects and other space-enhancing devices. Architects and tenants also have more freedom in terms of planning the workplace without the restriction of ceiling grille locations. Consideration must still be given to other issues such as lighting layouts, and the proximity of return air grilles to high heat sources –yet with successful systems integration, a single design solution will address many problems simultaneously.

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Underfloor Plenum Layout
In addition to reducing the restrictions conventionally placed on office layouts, by allowing air to circulate freely through a plenum, whether over an entire floor area or within defined interior and perimeter zones, most UFAD systems offer a high degree of freedom in planning air distribution routes. Ceiling-based systems often require that ducts navigate around, or through, structural beams for example. Underfloor plenums are spatially structured, or divided, by the access floor pedestals and any necessary partitions. In systems with a supply duct running from the core to perimeter zones for example, linear ducting can easily run through the regular pedestal grid. In certain cases where ducts are larger than 600 mm (24 in.), and thus too broad to fit within the grid spacing, some pedestals can be removed and a horizontal bridge device installed in their place, freeing up more space and providing support to the access floor panels above. However, this expensive solution can generally be avoided with proper coordination of access floor- and UFAD-component sizes. Consideration of the pedestal grid dimensions at an early stage in planning and construction is a necessity.

As previously mentioned, the key to efficient, cost effective building services is integration -the ability for one system to accommodate another without impeding the performance of either. Trying to route a number of services to the same place, a workstation in this case, may result in solid obstructions within the plenum such as fan terminal units, or devices serving the cable management network. Experiments carried out by CBE [5] have found that pressurized plenums with at least 75 mm (3 in.) of clear space for air flow, in addition to the space required for other elements such as cable runs, are capable of maintaining a uniform distribution of airflow to diffusers, in a 300 m2 (3,200 ft2) zone. In situations where obstructions leave as little as 38 mm (1.5 in.) clear space above them, the risk of disrupting airflow is minimal providing the overall plenum depth is at least 180 mm (7 in.).

Typical plenum heights for UFAD applications are 200 mm – 460 mm (8 in. – 18 in.). This exceeds the required plenum height when raised floors are used solely for the purposes of cable management. However, as mentioned previously, by placing the air distribution system in the underfloor zone and reducing the need for deep ceiling ductwork associated with conventional ceiling-based systems, new build projects can achieve a 5-10% reduction in floor-to-floor heights, resulting in considerable savings in materials, construction costs and project time. Or, for the same overall floor-to-floor as conventional buildings, a greater floor-to-ceiling clear height can be achieved. Both options offer cost benefits related to the specific characteristics of a project, and highlight a significant feature of UFAD installations, namely versatility in application.

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Modular Components
Many of the advantages of both raised floors and, by extension, UFAD arise from the characteristics of the modular components involved. From pedestal spacing to carpet tile sizes, coordination between the various parameters is less complicated when design decisions are made with respect to the various modular dimensions involved, particularly when these dimensions are equal to, or multiples of, each other. In buildings with orthogonal floor plans this task is straightforward, non-orthogonal plans may require a number of custom sized panels or tiles at certain locations.

Modular systems have the greatest potential for facilitating quick modifications within an office environment. These modifications typically fall into the following categories:

1. Spatial Configuration
Changes in office hierarchy, layout or number of personnel may necessitate a rearrangement of workstations. Responding to new layouts of furniture simply requires substituting one type of floor panel (with floor diffuser/cable outlet) for another (without), as all panels will be of the same modular dimensions. Provisions should then be made for connecting into the nearest run of cables if the panel in question contains an information outlet. In plenums with fan terminal units the zoning layout should be consulted in order to maintain an even distribution of diffusers within that particular zone.

2. Load Distribution 
The addition of equipment or an increase in occupancy -both of which constitute heat sources- within any defined office zone will increase the demand for cooling in the proximity and may require additional floor diffusers. To increase the amount of air delivered to that zone standard floor panels could be replaced by diffuser-equipped panels placed in suitable locations (i.e. at an acceptable distance from occupants and unobstructed by furniture). UFAD systems employing fan terminal units may require minor adjustments to maintain a minimum airflow rate to all diffusers. Facility managers may wish to stock a surplus number of carpet tiles that are pre-cut with diffuser apertures for the purpose of meeting future reconfigurations involving an expansion in the total number of outlets required in the office space.

3. Occupant Preference
The ability to accommodate varying occupant preferences is a key characteristic of UFAD systems. In addition to the option of adjusting the airflow rate, a person may request that a diffuser be located closer to/farther from their workstation locale. As described above for spatial configuration changes, this procedure involves removing the carpet tiles and floor panel at the location in question, and replacing them with an alternative panel and tiles. For example, if an occupant requests that a diffuser be moved closer to their workstation, a standard panel is removed and replaced by a panel fitted with a diffuser aperture. Once the diffuser components are installed, a carpet tile, cut according to the location of the diffuser, is placed as the finished floor surface and surrounding tiles are reaffixed. Consideration may need to be given to the location of plenum partitions, VAV boxes and the overall distribution of diffusers within a particular zone.

When carpet tiles form the finished floor surface of a raised access floor system the issue of coordinating the modular sizes and grid dimensions of floor panels and carpet tiles must be addressed. Some manufacturers provide a composite unit of floor panel-plus-carpet tile so architects need only work with one modular dimension, as pedestal spacing is a function of the floor panel size. As components can be ordered on a supply-on-demand basis this potentially reduces material waste. When additional diffusers need to be installed, floor-and-panel composites can be ordered instead of necessitating the cutting of holes in existing carpet tiles that may later become redundant when, say, following a future reconfiguration new diffuser locations do not match those of the present.

However, the majority of UFAD installations comprise floor panel and carpet components from separate manufacturers. As floor panels are typically 600 mm (24 in.) and carpet tiles 450 mm (18 in.) or 900 mm (36 in.), this raises the question of whether carpet joints and floor panel joints should align where possible, or be consistently staggered. Differences in opinion exist, yet many UFAD system installers recommend staggering joints between the two surfaces to avoid problems with uplift.

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Summary
In summary, raised floors offer a cost-effective means of addressing the key factors characterizing 21st century workplaces, namely the need for an infrastructure flexible enough to meet high churn rates in our multi-tenant, multi-technology environments where the pace of future expansion is guaranteed, yet the nature of the expansion unpredictable. When properly coordinated and factored into decisions at the design, construction and occupancy stages, integrating cable management and air distribution services within the plenum of a raised access floor can increase the potential versatility of a workplace; and the ability to quickly meet occupant preferences contributes to a more dynamic work environment at all levels. 

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Appendix
Summarized below are a number of options for power and communications distribution in both new-build and retrofit projects. Often a combination of methods forms the overall cable management system in order to overcome the particular limitations of each.

Raised Floor Systems
The most flexible and versatile option in terms of unrestricted routing, potential for reconfiguration and ease of accessibility. Cables are run freely through the plenum created between a structural slab and raised access floor installation. Each workstation can connect into the cable network either via outlet boxes flush-mounted into floor panels, or openings provided in selected floor panels that enable cables to extend up to outlets integrated within modular furniture systems. Raised access floor systems accommodating modular cabling networks are the best example of a cabling innovation with the ability to support the multi-vendor, multi-technology infrastructure demanded by present day workplace environments. See modular cabling for more information.

Consideration should be given to the structural, spatial, and visual impact of any cable distribution option. Factors influencing one of these parameters will undoubtedly have consequences for the others.

Loose Cabling
Cables (copper/fiber optic) are routed to workstations through wall and ceiling cavities. Although the least expensive option on a first cost basis, changing cable routes, increasing the number of cables, or carrying out maintenance work is disruptive both to the building’s structure and occupants. In the event of a faulty connection or cable breakage, tracing cables along their route can be difficult due to their concealment within the building’s cavities. This problem is compounded by the high risk of physical damage to the unsupported cables that must run around structural members and sharp corners, resulting in poor data transmission performance.

In retrofit projects where there is a lack of space for accommodating the components of ceiling- or floor-based ducting, loose cabling may be a feasible option, providing the structural intrusion of routing through cavities can be minimized.

Cable Trays
A commonly used system whereby cable trays installed in the ceiling plenum are used to distribute cabling from telecommunications closets to workstations throughout an office floor or zone. At required locations a vertical conduit brings cables from the trays down to workstation outlet boxes. When properly designed, in terms of routing and sizing, cable trays can accommodate potential re-routing and upgrading, and their location above a removable-tile drop ceiling system facilitates access for maintenance. Disadvantages include the need to accommodate vertical conduits at workstations, and the need for a clear space of 200-300 mm (8-12 in.) above the ceiling plane.

Surface Raceways
As an alternative to concealing cabling in the ceiling/underfloor plenum, surface raceways are conduits installed around the perimeter of defined workspaces; affixed to a building’s external or internal walls for example. Although the cabling, and associated components, within raceways are accessible, and relatively inexpensive to install, routing options are limited to the location of walls. Workstations at a distance from the perimeter zone must rely on an alternative means of distribution to be connected to the cable network. Some modular furniture systems incorporate provisions for integrating cables within their partitions or desk units for example. Consideration should also be given to minimizing the visual and spatial impact of the raceways.

Poke-Through
In this system, cabling serving a particular floor runs within the ceiling plenum of the floor below. Where required, penetrations are made through the structural slab enabling the cables to enter the workspace for connections. Due to the significant structural implications associated with drilling through the floor slab, and the disruption caused to occupants of the floor below when accessing the cabling (implying this system is not so feasible for multi-tenant buildings), reconfiguration can be costly and complicated. When locating points of penetration, consideration must also be given to maintaining the structural integrity of the slab.

Modular Cabling
Described as a multi-vendor, multi-technology infrastructure, modular cabling installations can accommodate multiple cable systems comprising different media –voice, power and data- and originating from different manufacturers. The result is, effectively, a platform, or framework, upon which the building’s technological infrastructure is formed.

Typical installations comprise three basic cabling components: riser cabling, workstation cabling, and, in a campus environment, outside plant cabling; and are subject to industry standards regulating performance- and physical-characteristics. For example, distinguishing between these three cable routes, and types, enables the infrastructure system to comply with standard ANSI/EIA/TIA-568-A Commercial Building Telecommunications Wiring Standard, which restricts the distance between active equipment (PCs and network equipment, for example) to a maximum of 90 m (295 ft) for copper cabling [6].

System Layout and Components
Network equipment is housed in telecommunications closets (TCs), which are distributed around a building according to the particular zoning or organization of the cable management system. A central TC is designated as the main distribution point, and is connected to all other secondary TCs by copper/fiber optic backbone cabling, also known as riser, or vertical, cabling. This results in a star-shaped, or ‘star-wired’, network with the central TC forming a nucleus from which backbone cabling radiates outwards.

From each secondary TC, horizontal cabling transmits information to and from information outlets, the points of communication for cabling in the proximity of each workstation. Patch cable assemblies –cables with connectors attaching equipment at workstations to information outlets- facilitate easy technological reconfigurations or equipment additions at a later stage. By linking each workstation back to a main distribution TC, all equipment located within the system is effectively interconnected, improving both communication between devices, and overall system management.

In addition, each information outlet can be separately reconfigured from a central location, in terms of the media connections offered, without disrupting other outlets within the entire system. This reduces the downtime (time during which office functions may need to be suspended) typically experienced in offices at great expense.

The key to an effective modular cabling system is the implementation of a good cable management strategy. At this stage, once the cable wiring structure has been defined –location of main distribution points, TCs and cable routes- the specific requirements tenants will place on the user systems should be identified. All cables are categorized relative to their cable bandwidth per distance, a measure of how much information a particular cable can carry. For example category 3, sufficient for voice-grade applications, has the capacity of a bandwidth up to 16 MHz; category 5 is the most common (bandwidths up to 100 MHz) or 5E, a non-standard category, is used for bandwidths up to 200 MHz and distances over 100 m (328 ft).

To maintain the level of communications performance specified by the cables, cable connections and terminating devices should have an equivalent rating. ANSI/EIA/TIA (the bodies regulating commercial building telecommunications) require that each workstation be supplied with at least two telecommunications cables, whose specific categories are also regulated by standards. In this way every workstation will support the most fundamental and commonly used telecommunications applications -such as voice and data for example.

Systems Integration
Integration is a means of optimizing overall building performance by monitoring and controlling a range of building systems and functions that effectively communicate with each other to ensure a high level of operational quality and efficiency. For example, a security system may be linked to: 

a time-of-day schedule, to allow entry at specific times 
the building maintenance system (BMS), to turn on the HVAC once occupants have arrived 
electronic building usage records, for monitoring tenancy/occupancy. 
There are many different modes of systems integration, the fundamental requirement being the ability to establish communications between the different devices and controls comprising a building’s services. This communication can be set up in a number of ways, for example: 

Control devices transmitting data electronically within their system.
Control devices transmitting data electronically to other systems within the building.
Hard-wired connections, a very common method of linking data from different building systems within a central BMS.
Building systems operating independently but communicating electronically with a common BMS. This is a popular option in today’s buildings following the introduction of BMS-software packages.
Building systems electronically communicating information to the entire controls network, exemplifying the highest level of ‘integration’. This option developed following networking innovations in the building industry, and offers the greatest potential for future expansion.

Benefits
One of the key components of an effective BMS is that of building operation monitoring. The benefits of implementing an integrated building system are immediately quantifiable:

Single, user-friendly interface. Any number of systems within the BMS network can be accessed via a single interface. Simplifying the time and level of expertise needed to operate the network can result in increased productivity and reduced training costs.

Centralized monitoring. Centralizing the controls and operational information of the many systems comprising the BMS enables comprehensive monitoring, and analysis at the general level of energy usage and/or, more specifically, parameters such as operational temperatures, for example.

Lower maintenance and repair costs. System-wide monitoring enables breakdowns and operational faults to be quickly identified, and diagnosed, reducing office downtime due to failure of any particular system.

A recent survey among members of the building industry showed 75% of building owners had impending projects incorporating systems integration [4].

In addition, an integrated BMS brings many qualitative benefits to the workplace, such as:

• Improved BMS monitoring.
• Reducing both major system breakdowns and periods during which the workplace experiences sub-standard operation of various building services. 
• Centralized and coordinated programming.
• Synchronizing the operation and control of different systems for maximum effect with minimum effort -for example, time of day-based lighting and HVAC schedules. 
• All of the above, both qualitative and quantitative, contribute to improving the satisfaction and comfort of both occupants and owners.