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No technological innovation of the past 10 years has had a bigger effect on engineering services than the increased use of IT. Advances in IT and the use of e-mail and the Internet mean that, in many organisations, every member of staff now has a PC on their desk.

The blanket use of IT not only has implications on the IT cabling infrastructure, but also on the number of power outlets needed to serve computers, printers, scanners and other devices. Add to this the flexibility needed to facilitate changes to the initial space planning layout, and the issue of power and data infrastructure becomes a critical factor in a building鈥檚 life-cycle performance.

The building chosen to illustrate some of the power and data servicing options available is a new 17 000 m² academic facility for a major higher education establishment in the south of England. At the heart of the new facility are six floors of academic space with a total area of 9894 m². The brief states that this space must facilitate change of use during the life of the building, and be flexible enough to accommodate a complete range of lecture facilities, from open-plan areas to individual lecture rooms or workshops, with room sizes ranging from 10 to 80 people. A further stipulation is that adequate IT and power infrastructure must be available throughout the flexible teaching space to ensure that a combination of fully serviced lecture facilities can be created.

This article reviews the performance of three power and data installations over 25 years. Although they all fulfil the basic criteria for flexibility and adaptability, it should be noted that the options chosen are not exhaustive, and a range of other methods for servicing flexible space do exist.

The options covered in the article are:

• Option 1 Solid floor and skirting trunking

• Option 2 Raised access floor and floor outlet boxes

• Option 3 Raised access floor and floor grommet.

The decision between the options will depend on a number of factors, including the building鈥檚 form and shape and the degree of 鈥渇uture proofing鈥� and flexibility required. However, an end user responsible for maintaining, modifying and upgrading the installation should not ignore whole-life costs. This article demonstrates that, despite a significantly lower capital cost outlay, skirting trunking (option 1) is more than 8% more expensive over the life-cycle than raised floor and floor grommet (option 3).

The cost model is based on four data or voice communications outlets and four power outlets for every 10 m2 of flexible teaching space. To maximise flexibility, each option combines data and voice communications on a structured wiring system. Using Category 5 enhanced specification cabling, this integrated approach allows any RJ45 outlet on the network to be used for either IT or telecommunications. This means that rather than having to wire in a new point every time a telephone is added or moved, another RJ45 point can be re-addressed as a voice communications outlet.

Capital costs for the three data and power systems

The capital cost calculations include flooring, power and data and voice installations. The options also include an allowance to cover builder鈥檚 work in connection, main contractor鈥檚 preliminaries, overheads, profit and attendance, and an apportionment of professional fees. Choosing option 1 results in a reduction of 150 mm in height for each floor, which (based on a consistent floor-to-ceiling height for each option) makes the building height for this option 900 mm lower than for the other two. Therefore, the capital cost for option 1 includes a 拢135 000 reduction to take account of the lower costs for cladding, structure and so on.

Whole-life costs

WThe whole-life cost for each option, expressed as a net present value, has been calculated over a 25-year period. A discount rate of about 4% has been used over the life-cycle. The table below identifies the life expectancy of the elements.

Of all the variables within a whole-life cost model, the effect of technology, and in particular IT, is perhaps the most difficult to assess. In this instance, the life expectancy of the structured wiring installation has a major influence on the whole-life cost. Knowing the life expectancy of the data cable installation is irrelevant; the key is to understand when new technology will make the installation redundant.

As a result of continued improvements in PC chip performance and the need to carry more information at greater speeds, IT network cabling has a relatively short lifespan compared with its guaranteed life expectancy (which is typically 20 years). Anecdotal evidence suggests that, in businesses that use cutting-edge IT, it is not uncommon for cabling to be replaced every five to seven years. In less demanding environments, this rises to 10-12 years. However, regardless of the guaranteed life expectancy of the cabling, many IT networks will need to be upgraded before the end of their warranty periods because they are unable to cope with the additional traffic generated by faster PC chips, and associated software developments such as video and multimedia.

Therefore, although the cable system used for the capital cost model has a 20-year guarantee, the whole-life cost model allows for complete replacement after 12 years, which is deemed to be the maximum likely lifespan for cabling in this type of environment.

Many of the power components within the three options have life spans of 10-15 years. In reality, these would also be replaced at the same time as the IT wiring to ensure that all power and data replacement works are undertaken together in a co-ordinated and cost effective manner, and this is reflected in the whole-life cost model.

The whole-life cost calculation for each option consists of three primary elements:

• Major replacements Major items such as replacing carpet, skirting trunking, floor boxes and power tap-off, and the data/voice structured wiring installation

• Maintenance, testing and sundry replacements Periodic testing of the power and IT installation; allowance for replacement of components damaged or requiring replacement before the end of their planned life expectancy

• Annual modification Annual modification or 鈥渃hurn鈥� is the amount of reconfiguration necessary to accommodate annual changes to space planning layouts. These changes are a consequence of increased student numbers or changes in course structure or content, and invariably mean modifying room sizes, and adding or removing rooms. This has a significant effect on partitioning and lighting layouts, and also on the power and data infrastructure. The cost model excludes any costs associated with moving or dismantling furniture or desks.

Cost analysis

The capital cost of option 1 (skirting trunking and solid floor) is about 16% lower than the cost of option 2 (raised floor and floor boxes) and option 3 (raised floor and floor grommets). This is mainly thanks to the saving achieved by not installing a raised floor and losing 150 mm per storey. However, option 1 does not perform as well over the life-cycle.

For all options, major replacements are the largest element of whole-life expenditure. Although carpet renewal (which is common to all elements) is a large proportion of the replacement cost, option 1 performs worse than the others because the skirting trunking (which provides the containment for both the power and data/voice wiring) needs to be replaced at the same time as the structured wiring installation.

Sundry replacements for options 2 and 3 are slightly higher than for option one because of the greater possibility of damage to the floor boxes or, for the floor grommet option, the power and data outlet arrangements. Conversely, options 2 and 3 perform better than option one on the annual churn costs.

The skirting trunking option, although flexible if outlets need to be added in existing trunking runs, is not easy to modify if partitions or room layouts change. This is particularly evident in rooms that are more than 3 m deep and need trunking around the whole perimeter to provide the density of power and data infrastructure required. Changes in room layout can have major consequences on the skirting trunking installation, and this is reflected in the comparative costs for annual modifications.

The underfloor power options perform well in this category thanks to the inherent flexibility of the systems, and the ease with which floor box or grommet positions can be changed. If power and data outlets need to be moved, it is simply a case of unplugging the power lead from the underfloor busbar, unplugging the data fly leads from the sub-floor boxes, and then plugging the connections back in at the new location. Even with the point-to-point retesting of the data cables, the operation is relatively simple and takes less than an hour to reposition four data/voice and four power outlets.

Overall, the floor grommet option is the best performer, albeit by a very small margin over the floor box option. This is mainly because of slightly cheaper components and a greater degree of flexibility when moving power and data outlets.