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Walking on air

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technical & practice

A new type of floor duct integrates an easily variable, underfloor air-conditioning system with the finished floor layer

What would you say if I told you that the type of floor you specify could qualify as tax-deductable expenditure?

Not just the materials or the services underneath it but the substrate, the support layers and even, possibly, the floor finish. What's more, all of this could be depreciated and set off against general income at the year end, all legal and above board in accordance with Capital Allowances rules and regulations. Imagine mentioning it in an early design meeting with the quantity surveyor, and picture how the client would sit up and listen. Well, have I got your attention?

The new floor system manufactured by Stockholm-based company Protek and marketed in this country through its London offices offers such a benefit. The system comprises a raised floor deck supported off the structural floor slab by a variableheight steel substructure. Effectively, it is a similar system to most service duct floors, raising the floor to provide a serviceable space below in which to locate services.

The floor decking layer comprises square panels of high-density chipboard or fibre-reinforced calcium silicate board, faced with a wide choice of finishes - from marble and oak laminate to slate. These panels are set on top of the support grid rather than inset into a channel, meaning there is scope for the flooring to be laid with no gaps. The support steel grid provides a edge bearing for the decking of about 20-30mm (depending on the loading requirements) and a rubberised cover strip over the top of the support framework ensures a tight seal and impact sound deadening. The seal with the steel supports and the fine tolerances between each floor square are important in preventing air leakage draughts from the void below into the habitable spaces above.

Raised service floors are the reflected plan of suspended ceilings, performing many of the functions that the traditional ceiling void enables. By locating the service void at floor level, however, access is more manageable; electricity feeds can rise conveniently to floor terminals rather than in drops or busbars; pipework risers to radiators are easily accommodated and, if the soffit is suitably well-finished, the suspended ceiling can be eliminated.

At a show office in Clerkenwell, London, the oak veneer flooring and matt white walls were illuminated by beautifully designed floor-mounted uplighters and task lighting only, eliminating the need for soffit cabling and ceiling-mounted fluorescents.

As an aside, when I first visited Tate Modern before it opened, one of the many unattractive finishing treatments - apart from the architraves, the inappropriate door ironmongery, the non-flushness of wall surfaces and the Heath Robinson light boxes - was the allegedly minimalist shadow gap between floor and walls, which proved elusively difficult for hamfisted workmen to achieve with panache. With the best will in the world, any movement in the floor level was bound to show up as discrepancies in this tolerance gap.With a raised floor, plaster finishes can be taken down to floor level (beyond the line of the floor finish) without the need for skirtings, making a very neat line with the floor finish.

Carpet tax

The key aspect of Protek's flooring is that it is classified not as a floor but as a ventilation system, whereby its underfloor void acts as the air-conditioning duct space. Instead of air being brought into the room by purpose-made ducts, the floor is the 'ductwork' - the depth between structural floor and the underside of the flooring (usually 280mm) over the full surface area of the open floor plan. Therefore, the floor void is used entirely for the distribution of clean, conditioned air, which has been recirculated by decentralised zone units.

The fact that the system can honestly be described as an air-conditioning plenum qualifies it as tax-deductable PMFF (plant, machinery, fixture and fittings). Depending on the surface veneer adding weight for acoustic deadening, even the finish could be classified as an essential element in the service provision requirements.

Outside air is drawn in and mixed with return air from the room, which is then filtered, cooled (or heated) and introduced into the raised plenum floor. As the air circulates under the floor, it is drawn up through fan-based units, which, at different controllable speeds, push the conditioned air into the room through floor-mounted grilles. These units have up to five speeds but are fitted with low-noise fan assemblies. The high density of the calcium sulphate flooring squares (1.45kg/m 3- so that the 600mm x 600mm x 36mm panels weigh about 53kg/m2) ensures that the floor makes a satisfactory bond with the support framework and deadens the faint noise of the fans (about 46dBA with loose laid tiles).

Comfort zones

Dedicated space must be provided for the zone handling air conditioning unit, which controls the filtration of air, ventilation, cooling and heating needs and distributes conditioned air under the floor. The air is chilled or heated, as determined by the BMS, by water-serviced cooling.

Heating coils in the service core and the zoned air con unit (ZA) continuously monitor and control the air temperature in the floor plenum and in the room for each assigned zone.

To maintain a particular controlled zone, internal partitions should either not be taken down to the structural slab beneath the floor or, if this is unavoidable, fitted with ventilation grilles to allow the free passage of air through the partition. Care should be taken to ensure that fire barriers are not breached, although intumescent grilles are available.

One feature of the access floor is the underfloor baffle, which creates and separates the underfloor areas, as required, into paths for supply and return air. The baffle can be repositioned to suit user needs for different airflow patterns and directions. Supply and return flows are integrated into one RAG unit (a Swedish abbreviation that apparently translates as Intelligent Underfloor Air Terminal) at the floor grille. These floor grilles are built into special tiles and are visible at floor level.

The RAG units are controlled locally - to give a maximum microclimate differential - by lifting the floor square and manually setting onboard temperature sensors and fan speeds. The modular dampers then adjust automatically during the cooling/heating or recycling mode and fresh air is ensured throughout (even during recycling).

Mains electricity cables are laid in underfloor power tracks that can be plugged into at locations to suit spursto-floor sockets or RAG units. Since the RAG units have no pipework connections or duct fixings, they are effectively free-standing, wired in only to the mains below ground and easily connected. To access the underfloor area, floor tiles can be lifted with the aid of the suction handle, gripping the tile to be hoisted out of place. Such is the ease of manoeuvrability of the individual components (although floor tiles are sometimes heavy) that a grille, and hence RAGs and air outlet points, can be relocated quickly and easily, meaning that changes to workstation layouts need not be a slave to the M&E layout, it being possible for air ducts to follow the needs of the occupant.

One other interesting feature of the raised floor system is that plant pots can be sunk beneath the surface and so appear to be growing out of the floor level, like genuinely planted foliage. Personally, I prefer allowing the soil/pebbles to appear flush with the surface rather than the proprietary containers with visible 50mm steel trim kickers used to contain the soil, but generally they provide a visually intriguing spectacle.

Step change

While there are tremendous benefits to the Protek system, care must be taken when installing it to weigh up the pros and cons and the implications of raised floor heights on the rest of the building. New build can easily accommodate this floor buildup, but in refurbishments there will be knock-on effects on door threshes (and hence lintol heights); lift lobby heights (although air-con may not be needed in lift lobbies, steps will be needed to achieve the 300mm or so changes in height - check DDA requirements for ramped access); and the Health & Safety in the Workplace regulations on sill heights (erstwhile sill heights of 1m, for example, will become approximately 720mm after installation, requiring lower panes to be in toughened glass).

In general, though, this floor system is a rival to chilled beams, freeing up internal spaces and doing away with the need for suspended ceilings and their consequent time, effort and cost of step-ladder maintenance. As usual, the best ideas tend to be the simplest.

Protek, tel 020 7730 5221, www. wmprotek. com; Lyktan Lighting, tel 020 7409 3454, www. atelje-lyktan. se; Sadi flooring panels, tel 0039 0444 390555

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