ACR Journal

CMYK / .ai CMYK / .ai CMYK / .ai acrjournal.uk 27 VENTILATION impact on energy consumption. By contrast, when supplying air via floor grilles, the air velocities are lower, as there is no need to achieve coanda effect. This in turn can offer improved acoustics. In addition, the air supplied to the occupied zone does not have to be reduced to the lower temperatures necessary for mixed air distribution. In fact, for commercial premises, the temperature would typically be in the region of 19°C, just slightly cooler than the design temperature of the occupied zone. In addition, it may be possible to reduce cooling loads as only the occupied zone needs to be supplied with conditioned air. This can be particularly beneficial in rooms with high ceilings. These lower cooling loads reduce the demand placed on chillers and other energy- consuming components across the HVAC system. Plus, there is no longer a need for fans/motors within secondary terminal units such as fan coil units. There may also be increased opportunities for “free cooling” (using fresh air) for a large proportion of the year. An academic study in 2002 quantified potential energy savings of underfloor air distribution as being between 5% and 35%. Reduced duct work: Depending on the building design, a raised floor can allow the floor void to be pressurised and act like a plenum, with the air being balanced at each diffuser. This can mean that the requirement for ductwork is reduced. Easier installation: As the equipment is installed into the floor and floor void, the requirement to work at height is removed, reducing health and safety risk for contractors and service engineers. Increased flexibility for building owners/occupants: As floor grilles are typically installed into floor tiles (or designed as replacement 600 x 600 tiles, in the case of the TROX AFG), reconfiguration of spaces is made easier. Since there is little or no ductwork involved, the floor tiles can be easily rearranged, and the tiles incorporating diffusers can simply be moved to different locations to suit each new configuration. Given the frequency and cost of ‘churn’, this increased flexibility is extremely valuable to building owners and occupiers throughout the lifecycle of the equipment. Q. Are there applications in which it is inadvisable to use underfloor ventilation/ displacement air management? Displacement ventilation requires the supply air to be cooler than the room air. So, this approach is only suitable for cooling with a supply temperature range of -2K to -4K. As a general rule, heating is not recommended using displacement ventilation. The TROX FBA floor diffuser, however, incorporates a swirl unit, this causes high induction and allows for heating, as long as the temperature differential is kept to a minimum. In order to maximise the effectiveness of this heating, the FBAs should be evenly spread throughout the floor plate. The height of the room is an important factor as there can be a considerable amount of mixing in the region below the ceiling, due to the interaction between upward and downward moving buoyant air flows. Generally, buoyancy-driven ventilation is less effective where ceiling heights are low, for example less than 2.5 m. With regard to air quality, displacement air management is less preferable where the contaminants are colder/ denser than the ambient air. Laboratories/science campuses, of course, will require specialist air management systems. TROX’s LabControl systems are purpose-designed for these applications. Q. Which floor grille/diffuser models are best suited to the application? TROX UK manufactures three types of floor grille/diffuser: the AF (linear bar grille), the AFG (600 x 600 tile replacement grille), and the FBA (floor-mount swirl diffuser). As a general rule the AFG is the best option for data centres and other applications involving high cooling loads. It is designed for the supply of large volumes of air and is available with zinc- whisker free construction for added peace of mind in data centres. It is suitable for stringer widths of up to 40mm and pedestals of up to 90mm in diameter. The AF and FBA are ideal for sites such as offices, auditoria, airport concourses, theatres, cinemas, conference rooms, hotels, sports halls, fitness rooms, restaurants, shops and factories. The AF model is typically installed around the perimeter of the occupied space, to discharge cold air up the glazing to mitigate any solar gains. For further information on floor grilles/diffuser based applications, or displacement ventilation strategies more generally, contact TROX on 01842 754545 or email: sales@troxuk.co.uk www.troxuk.co.uk AF linear bar grille AFG tile replacement grille FBA floor-mount swirl diffuser