Effect of Attic Ventilation on the Performance of Radiant Barriers

The objective of the experiments was to quantify how attic ventilation would affect the performance of a radiant barrier. Ceiling heat flux and space cooling load were both measured. Results of side-by-side radiant barrier experiments using two identical 13.38 m² (nominal) test houses are presented. The test houses responded similarly to weather variations. Indoor temperatures of the test houses were controlled to within 0.2°C. Ceiling heat fluxes and space cooling load were within a 2.5 percent difference between both test houses. The results showed that a critical attic ventilation flow rate of 1.3 (l/sec)/m² of the attic floor existed after which the percentage reduction in ceiling heat fluxes produced by the radiant barriers did not change with increasing attic airflow rates. The ceiling heat flux reductions produced by the radiant barriers were between 25 and 35 percent, with 28 percent being the percent reduction observed most often in the presence of attic ventilation. The space-cooling load reductions observed were between two to four percent. All results compiled in this paper were for attics with unfaced fiberglass insulation with a resistance level of 3.35 m² K/W (nominal) and for a perforated radiant barrier with low emissivities (less than 0.05) on both sides.