Book - School of Science and Technology

404 Air-conditioningChilled water Perforated ceiling Cooling finsChilled waterRadiant panelConvective panelsFinned coilFinned pipesChilled beamsFigure 14.30 Chilled ceiling systems: radiant (Trox); convective (Krantz); chilled beams (Stifab Farex)underside flush therewith or be partly below the ceiling surface to form a dropped beameffect. A minimum depth of ceiling void of about 300 mm is required for installation inthis instance. Some later models are suitable for suspension belowthe ceiling. Othersincorporate the facility to introduce ventilation air via nozzles within the unit to increase,by induction, the air flowacross the coil and thus extend the sensible cooling capability.One of the advantages of a chilled ceiling system is that it has capacity to offset highcooling loads without producing an unacceptable air movement within the space, a resultwhich is often difficult to achieve with air-based cooling systems. With all types of chilledceiling, temperature control is via a simple control valve acting in response to a thermostat,with chosen sections being controlled independently to provide zone control. Thissame control principle may be applied also to areas of perimeter radiant heating whichmay be integrated with the chilled ceiling panels to provide for winter weather.Although convective systems have a higher sensible cooling capacity compared withradiant panels, 160 W/m 2 and 120 W/m 2 respectively, it is important to recognise thatradiant systems reduce the mean radiant temperature in the space and, in consequence,reduce also the resultant temperature sensed by occupants by as much as 2 K.Recent solutions incorporating chilled beams also integrate other service outlets andlighting within a common prefabricated casing.Alternative methods of coolingReference was made in the preamble of this chapter to the need for avoidance, wherepossible, of methods for dealing with over-heating in occupied spaces which rely upon the