EFFECT OF FLOWING EXFILTRATED AIR BETWEEN ROOF AND FALSE CEILING ON AIR-CONDITIONING LOAD

Abstract

This dissertation work entitled "EFFECT OF FLOWING EXFILTRATED AIR BETWEEN ROOF AND FALSE CEILING ON AIR-CONDITIONING LOAD" is an attempt towards energy conservation. In the past, false ceilings have been purely decorative, being just a means of hiding the floor boards of the room above, but now they are taking on a functional task, viz, carrying air-conditioning ducts, providing fixtures for lighting, thermal insulation and sound damping. Some ceilings in fact combine two or more of these. By providing false ceiling, the temperatures in the occupied zone are reduced. If the space between roof and false ceiling is ventilated by outside air, a certain portion of the roof load may be carried away by this air due to the convective heat transfer between roof and air. This results in the reduction of cooling load requirements, thereby causing a saving in energy. By flowing outside air mixed with exfiltrated air, instead of outside air, as above, the cooling load is further reduced, since in this case the heat load carried •by the air is increased due to its temperature being lower than the outside ventilation.air. This dissertation work examine theoretically, the concept of providing a false ceiling panel beneath the roof to form a hollow, ventilated roof structure to reduce the cooling load requirements of the air-conditioning plant. The parameters taken into account and varied respectively are: (z) air velocity, (ii) angle of inclination of roof, (iii) length of roof, and (iv) time. A computer programme has been developed to calculate the saving in roof load for any combination of these parameters. The reduction has been found to range between 5 and 31 percent between 10 A.M. to 5 P.M. Also an attempt has been made to optimise these parameters. A combination of velocity of 3 m/s, roof length 10m, angle of inclination of roof as 00 gives maximum saving of 30.61% at 10 A.M. However, for overall energy saving during the day average percent saving has also been determined. It is found to be 2 4.428% at air velocity 3 m/s, roof length 10 m and angle of inclination of roof as 150. All the values of percent saving are with respect to roof heat load without flowing any air between the roof and false ceiling. 00000