A thermal simulation model in a ventilated residential attic using a reflective coating

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20030602

Moujaes, S F; Alsaiegh, N T

A two-dimensional finite element model is developed to simulate the thermal performance of a residential attic. The attic is ventilated using an evaporative cooler for the occupied space which vents its exhaust air into the attic. The attic is also ventilated by outside air introduced at the perimeter (soffit) of the attic ceiling and is exhausted at the ridge of the roof. The thermal effects of an installed external reflective coating as well as the variation of evaporative cooler ventilation rates are investigated. The model is steady state using solar insulation flux and ambient temperature as driving functions. A k-turbulent model has been used to describe velocity and thermal distributions in the attic along with buoyancy effects on the different airstreams. As boundary conditions the inclined outer surfaces were assumed to have radiation and convection exchange with the ambient air and the effective sky temperature. The underside of the ceiling insulation is assumed to exchange heat with the air-conditioned room by convection. Visually several recirculation zones have been observed in the attic which seem to affect the surface temperature close by and seem to suggest the existences of convective cells. The application of the reflective coating on the outside of the roof surface seems to reduce the ceiling cooling load by about 25% over a dark shingle roof. Also increasing the ventilation rates by the evaporative cooler seem to have a detrimental effect on the reduction of the ceiling cooling load. It is also suggested that the more simple one dimensional assumption is only applicable on parts of the surface areas. Variations of temperatures have been shown to exist at the edges of the inclined surfaces and insulation especially at the locations of inlet and outlet vents of the attic.

• Research Organization: Univ. of Nevada, Las Vegas, NV (US)
• OSTI ID: 20030602
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
ATTICS
COOLING LOAD
MATHEMATICAL MODELS
REFLECTIVE COATINGS
RESIDENTIAL BUILDINGS
TEMPERATURE DISTRIBUTION
THERMAL ANALYSIS
VENTILATION