Book - School of Science and Technology

Other systems 397allowed to be slightly greater with this type of system than with one relying on conditioningof the general space. It is claimed that such systems have inherent flexibility to providefor changing the location of terminal devices to suit variations in an office layout. Specialair terminal devices have been developed for floor and desk distribution, as described inChapter 15.A development of the upward air distribution principle is an arrangement where boththe supply and the extract positions are at floor level, with the floor void divided into asupply plenum and a return air space. With this arrangement, no false ceiling is necessarysince all servicing may be from lowlevel, including up-lighting. This system uses fanassistedconditioning modules to filter, cool, heat and humidify recirculated air, the unitsbeing either free-standing in the space served or incorporated into service zones. In mostcases, they will be supplied with heating, chilled and mains water piping and with a powersupply. A typical arrangement of such a system is illustrated in Figure 14.24.The conditioned air is discharged into the supply plenum to which are connected fanassistedterminal units, which may be either wall mounted or of an underfloor type, thelatter being connected to supply grilles integrated into a standard 600 mm square floorpanel. Return air is collected through similar panel mounted grilles into the return airsection of the floor void from which it is drawn into the conditioning module. Outside airfor ventilation purposes is introduced into the return air section of the floor void andtemperature control in the space is achieved by varying the ratio of conditioned andrecirculated room air introduced; alternatively, electric trim heaters may be used.A clear underfloor depth of 200 mm will be required and, typically, up to 300 m 2 may beserved from a single module. As will be appreciated, air-tightness around the perimeterand at baffles between the supply plenums and the return air zones is critical to maintainperformance. These systems provide good flexibility for changes in furniture layout andall components, including the conditioning modules, terminal units, false floor panels andvoid baffles are available as a proprietary system. Individual desk-top controls areavailable, as a proprietary package, to allowthe occupant to set the conditions to suithis or her preferred working temperature: some systems also incorporate a presenceFloor mountedsupply terminalsUnderfloorsupply plenumReturn air floorgrillesUnderfloorreturn air spaceAir-conditioningmoduleFloor voidbaffleUnderfloorsupply terminalsFigure 14.24 Upward air-flow system with floor distribution (Liebert Hiross)