Shedding Light on UFAD
Modern corporations restructure and reorganize at an increasing rate, and their offices must keep pace. Furthermore, such office areas demand more—and cleaner—power than ever before. Under these circumstances, many engineers are faced with the challenge of designing a power system that meets the ever changing electrical demands of technology, while still being flexible enough ...
Modern corporations restructure and reorganize at an increasing rate, and their offices must keep pace.
Furthermore, such office areas demand more—and cleaner—power than ever before. Under these circumstances, many engineers are faced with the challenge of designing a power system that meets the ever changing electrical demands of technology, while still being flexible enough to accommodate corporations with churn rates as high as 30%.
As explored in CSE’s last issue, one solution is to use an open office plan with an underfloor air-distribution system. But how, specifically, does UFAD affect the design of lighting, power, data and phone lines?
Distributing data and power
First, raised-floor installations allow for the possibility of a flush-mounted box in the floor of every cubicle, which can be easily relocated every time the office layout changes.
Each floor box should minimally be a five-slot box, utilizing at least two slots for power and the other three slots for voice, data and video (VDV) ports. Each power slot should include a duplex receptacle, with each outlet on a separate circuit. Flexibility for power connections can be provided by utilizing off-the-shelf components with prewired or preconfigured cables, connectors and underfloor power-distribution nodes. Power whips can plug into the floor box and the distribution node. This plug-and-play feature makes box relocation as simple as picking up the box—with its floor tile—unplugging it, moving it and plugging it back in. To accommodate this setup, whips and VDV cabling should be specified with up to 10 ft. of slack coiled at the floor box to provide for the relocation of each box within a 10-ft. radius. Power distribution nodes can then be hardwired through metallic conduit back to the respective panels for each area.
When a UFAD system is used, all underfloor boxes must be rated for “environmental air” per the National Electrical Code (NEC). All power conductors should similarly be contained in prewired, flexible metallic conduit/armored cable. The typical electrical load for a 10-ft. by 10-ft., VDV-connected office cubicle could be as high as 600 to 700 watts including: personal computers, computer monitors, task lights, auxiliaries such as a calculator or pencil sharpener and an ISDN/IP local-powered phone. Therefore, two 20-amp, 120-volt, AC single-phase circuits can feed up to five standard cubicles with one five-slot floor box each.
One of the duplex receptacle circuits should be considered as an isolated ground (IG) or as conditioned power dedicated for personal computer equipment. The other duplex receptacle circuit should be used for noncomputer equipment such as lights, calculators and other auxiliaries. The IG or conditioned power circuit can be color coded or labeled for computer use only. These recommendations, however, do not include high-density power areas of computer clusters or networked printer clusters, which require separate circuiting based upon their specific loads.
Beware of harmonics and transients
Additionally, the computer power and general-purpose power circuits should have separate paths back to the main distribution point. Any computer power risers should be sourced using K-factor-rated step-down transformers that compensate for the heating effects of power system harmonics, with a K-factor of 13 or better recommended for high-density VDV office areas. These transformers can also be specified with shielding as an added measure of protection. Consideration should be given to sizing all neutrals at 200% on the computer power risers and feeders to compensate for the additional harmonic currents generated by VDV and computer equipment.
Regardless of harmonics, all power systems should be specified with transient-voltage surge-suppression (TVSS) devices to protect against externally and internally generated transients. Suitable service entrance and distribution panel protection should be provided and consideration should be given to protection at the receptacle per application and owner requirements. TVSS devices that protect electronic components, such as personal computers, should be specified to clamp or clip the surge voltage to below 400 volts.
Grounding is also critically important in this environment, as the metallic raised floor needs to be bonded per the manufacturer’s requirements to the building grounding system. One strategy is to bond the raised-floor stringers to bare copper grounding conductors at the spacing intervals recommended by the manufacturer.
With power considerations out of the way, network and communications equipment can be connected. A typical individual office will have one phone and PC; in addition, there may be a networked printer, a modem, a small TV monitor and a video-conferencing connection. Most digital or analog phones are supported with one or two pair: IP phones will require two pair and ISDN phones will require three pair. Flexibility can be provided in two ways: a zone cabling approach or a slack loop approach.
A “zone” cabling approach works well where a fixed number of Category-5e cables are hardwired to various zone termination areas of the underfloor. From these areas, Category-5e cables are then run to the floor boxes and terminated. Any changes or future cable additions are made back only to the closest zone termination area. This reduces the cost of home-running new cable back to the horizontal cross-connect (HC) closet.
An alternative is to use a “slack loop” approach, where a 10-ft. slack loop is placed at each floor box allowing the box to be moved within a 10-ft. radius without having to add cable. A benefit of this method is that it does not introduce another connection in the horizontal channel. The cable installed under the raised floor should be plenum-rated type CMP, and if cost permits, should be supported off the floor in wire-rod-type cable tray, as this helps define cable pathways and provides for easier moves or changes in the future.
Telecommunications cabling designs for high-density VDV office areas need to address bandwidth, flexibility and preparation for future applications. The typical five-slot floor box for raised-floor applications should be outfitted with a minimum of three four-pair Category-5e cables, with consideration given to an additional RG-6 coaxial drop and a one-pair fiber-optic multi-mode drop. All cables should be home-runned to the nearest telecommunications HC floor closet.
It is important to note that the Category-5e cable requirement is a minimum; consideration should be given to higher bandwidth Category-6 systems. But three Category-5e cables can support most data or voice applications, and can be cross-connected, as the application requires, in the HC floor closet. Category-5e cable will support up to 1,000 Base-T data applications including: digital or analog phones, ISDN phones, analog modems, IP phones and ISDN based video conferencing. The fiber, or coaxial drop, can support broadband video applications or very high bandwidth data applications. The voice, data and video ports, plus the additional high bandwidth port(s) will require two slots of the floor box and may require the plates to be specially punched, based upon the physical requirements of the jacks and the slot plates.
Quality lighting is another key in accommodating the design challenges of the modern, high-churn office.
The utilization of a task-ambient lighting system is one method of meeting the stringent lighting requirements set for these open-office spaces. Task-ambient schemes are so called because they typically only generate relatively low overall light levels—about 30 foot-candles—but are supplemented with specific task lighting as required. Ambient light produces a comfortable environment for working on computers or moving within the office, while the task lighting provides the higher light level required for specific jobs or individual needs.
Significant energy savings are not the only benefits achieved by not lighting the entire space at a high level. Task-ambient lighting is also well suited to environments with high churn rates. For example, linear, indirect pendants working off an 8-ft. modular design can be connected to create fixtures of various lengths that are easy to separate and rearrange. Aligning the pendants with the building structure—instead of furniture layout—allows the furniture plan to change frequently without affecting the lighting.
An additional benefit of an indirect scheme is that the light reflects off the ceiling, producing even, shadow-free illumination and limiting glare on computer screens. Calculations must be done to ensure that the ceiling uniformity ratio and the task plan-to-ceiling ratio complies with the Illuminating Engineering Society (IES) recommendations found in the IES handbook and its recommended practices 1 (RP-1).
In addition to indirect illumination schemes, those lighting VDV-intensive offices should also be aware of a relatively new lighting technology well suited to such environments. High Output T-5 lamps , or “HOT-5” lamps, for example, have dramatically impacted architectural lighting in the past few years.
HOT-5 lamps are 40% smaller than a standard 32-watt T-8 fluorescent lamp, yet produce nearly twice the amount of light. As a result, in many indirect ambient lighting systems, a single 55-watt HOT-5 lamp can replace two 32-watt T-8 lamps.
This switch, of course, allows an energy savings of 9 watts per T-8 eliminated, but the 50% reduction in the number of lamps purchased, stored, changed and disposed is the most significant factor in the long term.
The lamp’s size also allows for smaller, more efficient fixtures that can be more aesthetically pleasing. HOT-5 lamps also have the same life expectancy as standard T-8 lamps, along with improved color-rendering capabilities.
But as with all new technologies, there are complications. The design temperature for HOT-5 lamps is about 10°F higher (about 85°F) than that of other fluorescent lamps. In fact, Phillips Lighting notes that its T5 HO lamps produce 5,000 lumens at 35°C (95°F) and 4,450 lumens at 25°C (77°F)—the standard test temperature for lamps. As a result, a HOT-5 lamp can lose as much as 40% of its rated light output in low temperatures—for example, if an HVAC diffuser blows 55°F air across the lamp. Therefore, the technology might not make much sense with a standard HVAC system, as lamp lumens would have to be de-rated by at least 10% because the ambient air temperature would be too low. This is not a problem, however, if UFAD is employed. Typically such systems produce an outlet air temperature of 65°F at the floor and because the system allows air to stratify, the air near the ceiling and lamps is warm and uniform in temperature, allowing the lamps to operate at peak efficiency. It should be noted that 35°C is the optimum operating temperature of most fluorescent lamps, so even standard T8s would benefit from the warmer ambient ceiling temperatures of a UFAD system.
In summary, office buildings with power densities of 1.5 watts per sq. ft. are a thing of the past. Distracting overhead lighting reflections on computer screens should also be a thing of the past. Modern offices require flexible power and lighting systems that respond to the increasing use of computers as well as high churn rates and energy/environmental concerns.
UFAD systems easily accommodate changes to cabling and wiring. Indirect lighting, combined with task-ambient lighting, eliminates glare and simultaneously reduces waste and hazardous disposal costs (mercury) by 50%. Additionally, UFAD systems allow new technology, like HOT-5 lamps, to thrive, generating real maintenance and energy savings—below 1 watt per sq. ft. But more importantly, these technologies often create more comfortable environments, ultimately improving employee satisfaction.
‘Eyes’ Have it for Indirect Lighting
According to a recent study conducted by Cornell University, indirect lighting has had notable effects on employees. The study took place in an office housing 200 Xerox employees who regularly work with computers. During a scheduled renovation, the facility was equipped with a pair of lighting systems: a ceiling-recessed parabolic downlighting system (PBL) and a lensed indirect uplighting system (LIL). A benchmark survey was taken before the renovation. Participants were then surveyed one year after the renovation and again a year later. Both groups significantly preferred the LIL system.
Specifically, 80% in the LIL group preferred the LIL, while only 3% preferred the PBL. In the PBL group, 50% preferred LIL vs. 25% for PBL.
Furthermore, only 23% of the study’s participants reported eye-focusing problems in the LIL groups, whereas 40% reported such problems in the PBL group.
Similarly, only 25% of the LIL group reported tired eyes vs. 55% in the PBL group.
Award-Winning VDV and Lighting
The Keystone Building, located on the State Capitol Complex in Harrisburg, is a 940,000-sq.-ft. structure housing a variety of government agencies. Integrating the lighting and communication systems into the architecture to provide the flexibility this modern office required, while blending into the historic fabric of the Pennsylvania State Capitol Complex, was challenging enough. But, hometown consultant Brinjac Engineering desired to make the building not only functional and flexible, but also highly energy efficient, environmentally friendly and maintenance conscientious. Their labor was recognized by the Consulting Engineering Council of Pennsylvania, who awarded Brinjac Engineering its Diamond Honor for excellence in engineering in the building systems category for the voice, data and video system design. The project also received a Diamond Honor for excellence in engineering in the category of energy, for the lighting system.
To accommodate the building’s power/voice-data-video needs, redundancy was built into the floor closets, main closets and routing paths of fiber and copper. Floor and main closets were tied together; redundant outside plant services were included; and underfloor Category-6 drops were installed to raised-floor boxes, UPS systems and network/cable-management systems.
Essentially, the data network was designed as a “building network utility,” using layer-three switching technology, virtual networking, security firewalls and redundant switches for automatic fail over. This approach was fairly unique, in that it is “unified” and “homogenous” among the multiple agencies using it. It is also centrally maintained, and flexible to accommodate changes.
For illumination, a linear, indirect pendant with an 8-ft. modular design was utilized in the open office space. The modules are connected to create fixtures of various lengths that can be separated and easily rearranged. Due to a 9.5-ft. ceiling height, spacing the fixtures at 15 ft. on center in order to align with the building structure was unrealistic using means of the day.
“HOT-5” or High Output T-5 lamps, which were just introduced at the time, were used prominently. Compared to a space designed to meet the ASHRAE 90.1 standard, the following advantages were accrued:
60% reduction in lamps.
80% reduction in mercury content.
50% reduction in replacement stock and costs.
50% reduction in the heat load of lighting system.
45% reduction in total energy usage.
Similar energy-saving efforts were implemented in the building’s nine-story atrium, case hearing rooms and even the parking garage.
Compared to a space designed to ASHRAE 90.1, the Keystone Building achieved the following results:
At 3,000 hours per year, the building’s atrium and open office spaces have an annual energy savings of 658,130 kilowatt-hours. At $0.07 per kilowatt-hour, this translates to $46,000 per year—not including the savings associated with the reduced cooling load.
The quantity of lamps required for the open office space was reduced by nearly 8,000 lamps, thus reducing material and labor maintenance cost.
The smaller quantity of lamps, combined with the reduced lamp size of the HOT-5 lamp meant a storage space reduction of 80%.
Large quantities of fluorescent lamps must be disposed of as hazardous waste due to their mercury content. The lower mercury HOT-5 lamps, in conjunction with 60% fewer lamps, resulted in significant waste disposal savings.
VDV Expo Preview
Voice, data and video (VDV) systems have quickly become an “essential” part of most buildings, especially offices and institutional facilities. And as quickly as these systems are being adopted into facility planning and expenditures, VDV standards and configurations are changing as well.
In fact, one sure sign of the importance of these systems in buildings can be found in the ongoing debate over whether CSI’s Masterformat should include a separate division for computer and communications equipment (see “Task Team Recommends Addition of Division 17,” p. 39).
Another indicator of VDV’s prominence in the industry is the emergence of a number of relatively new trade shows focused exclusively on this market. Take the third annual Voice-Data-Video Expo set for March 11-13 at the Las Vegas Hilton. Highlighting the latest in VDV technology, the exhibit, sponsored primarily by the National Electrical Contractors’ Association, features a trade floor with a variety of data cabling, cable-management system and design software vendors. In addition, the show schedule includes educational sessions on VDV design and installation procedures. Visit
Following is a sampling of the products that will be on display at the show:
Category-6 cable connectors offer the first standards-compliant system on the market. This ETL-verified system includes modular 110 jacks, patch panels and patch cords, as well as 110 blocks and 110 cords. Additional features include a higher signal-to-noise ratio and backward compatibility. (Clarity by Ortronics)
Cable support for air-handling spaces keeps wiring off the floor and provides support independent of raised-floor pedestals. Consisting of a block of polyethylene foam that absorbs vibrations and shock, the support meets the UL-2043 requirements for air-handling spaces. (Plenum Pier by Erico)
Aerial fiber cabling system is the only multi-fiber, bundled air-blown system for LAN applications available in North America. Additionally, the system performs under extreme temperature variations, simplifying its direct, point-to-point installation. (FutureFlex by Sumitomo Electric Lightwave)
Surface raceway provides data and electrical distribution for flexibility in office environments. This full line of products offers either steel, PVC or aluminum construction. Removable covers facilitate easy wiring access. (Thomas & Betts)
Floor-mount rack enclosure pivots open to allow unrestricted rear-equipment access in unusually small spaces. Featuring multiple cooling options, the units are available with solid, vented or plexiglass front doors, and can safely accommodate up to 350 pounds of equipment. (SR-40-22 by Middle Atlantic/DataTel)
Adapter accommodates SC fiber-optic connectors and workstation patch cords, featuring a unique shutter on the front that protects against dust and contamination when the SC port is not in use. A dust cap is provided on the rear of the adapter as well. (QuickPort by Leviton)
Fiber-optic power meter measures power, loss and optical-return loss in field, computer or laboratory environments. Featuring a fully-customizable interface, this hand-held device offers a microprocessor-based operating system and can store test results for later readout on a PC. (DM3000 by Fotec)
Underfloor cable-management system is a 6-in.-deep tray that fits nicely in access-floor systems. Available in 10-ft. lengths, this wire-mesh cable tray comes in a variety of finishes and 18- and 20-in. widths. This system will adapt to almost any configuration, handling 90-degree turns, twisting around obstructions and making multiple-level changes. (CF 150 by Cablofil)
Activation cover for infloor wire- and cable-management systems is designed to exceed new UL requirements for scrub water exclusion. Available to install in carpet, tile and wood floors, this line of covers prevents not only water from entering electrical and communication compartments, but dirt and dust as well. (FloorPort by Wiremold)
Task Team Recommends Addition of Div. 17
After evaluating proposals for changes to Construction Specifications Institute’s (CSI) 2002 MasterFormat—including the possible addition of a separate Division 17 for low-voltage wiring—the MasterFormat Expansion Task Team has made its final recommendations to the CSI executive committee.
The task team proposes that CSI expand the MasterFormat to include divisions for computer and communications systems, mechanical, electrical and plumbing, heavy civil construction and process engineering. If approved, the new MasterFormat will have more than 40 division numbers, but only about 20 would be in use.
“We’ve concluded that adding divisions is better than trying to fit it all in the existing 16 divisions,” says Dennis Hall, chairman of CSI’s Expansion Task Team. “The task team’s plan is to leave Divisions 3 through 14 pretty much alone. What it all means is that those now using MasterFormat would be able to keep using it much as they do now, and many types of projects that could not use MasterFormat will be able to use it in the future.”
The details of how many divisions and their content remain to be worked out, Hall says. He notes some new divisions are proposed to be created but left blank to provide room for revising MasterFormat in future years as construction products and technology evolve.
As of press time, the executive committee of CSI was meeting to review the recommendation and make a decision.