Book - School of Science and Technology

Zone units (air handling units)Traditional systems 381An alternative approach to the problem of providing local control to a variety of buildingzones having differing demands involves the provision of a recirculating air handling unit,having a booster reheater or recooler, within each zone. Outside air, in a quantity suitableto provide for occupancy, is conditioned as to temperature dependent upon outsideconditions and corrected for moisture content by means of what is, in effect, a conventionalcentral plant. This supply is delivered to the local zone plant where it is heated orcooled as may be required to suit the zone conditions. Figure 14.5 shows two alternativelocal plant arrangements, incorporating cooling only, suitable in this case to provide forconditions within the apparatus area of a major telephone switching centre. Note howintegration of the air-conditioning system within the structure has been arranged.For a more conventional application to an office building, Figure 14.6 shows plantsarranged in floor service rooms. In case (a), air recirculation from the individual roomspasses through louvres above the doors into the corridor and thence back to the zoneplant. While such an arrangement has the great merit of simplicity, coupled with relativelylowcost, current thinking and fire regulations disapprove of the use of a corridor means ofInsulated perimeter ductHeatingChilledwaterCable gridReturn grilleFan coil unitSupply linear diffusersFresh air ductChilled waterCondenseAir supplydistributionFan coil unitApparatusFigure 14.5 Fan-coil unit with ducted outside air