In hot climate areas the roof plays a fundamental role in determining the environmental conditions being the most exposed surface to the solar radiation. Among the possible ways to reduce the heat load inside the building, the solution of creating air flows under or through the covering may be valid since capable of reducing the entering heat flow during the day and favouring the heat discharge during the night. Various experimental tests were carried out on different ventilated roofings installed on scale buildings. In a first phase the performances of three roof types positioned successively on a shed of 1 m x 8 m plan size and height varying from 1 to 3 m, were tested. One with a ventilated interspace 7 cm thick, realized under a fibreciment sheet insulated by a polystyrene layer 4 cm thick; one similar to the previous but with two longitudinal slots on the covering, 10 cm wide each; one without interspace but with a slotted covering and insulated. In a second phase the performances of six other roof types positioned two by two on two sheds of 1 m x 6 m plan size and height varying from 1m to 2 m were tested. Four coverings had a ventilated interspace of two different thickness (7 cm and 3.5 cm), and were provided with and without insulation. The other two coverings were slotted, with a longitudinal slot 2 cm wide, and also provided with and without insulation. In all cases to simulate the animals' heat production some lamps were disposed on the floor. The surface temperature values corresponding to the various layers were measured, as well as the speed and temperature values of the air in the interspace, the solar radiation, the internal and external temperature, the wind speed and direction. For a general comparison the following indexes were analysed: Ig = [100∙(Tint. – Text.)]/Text , being T the air temperature; Ir = [100∙(Tx – T1)]/Tx, being Tx the internal surface temperature of the inner layer and T1 the external surface temperature of the outer layer. The experiments confirmed the effectiveness of the addition of a ventilated interspace in improving the night thermal exchange of the insulated continuous coverings. But the slotted roofs without interspace revealed a higher efficiency in realizing a small gradient between the internal and external temperatures. The one without insulation was able to obtain the lowest inside temperature during the night, but the day temperature resulted excessive and an insulating layer revealed to be necessary in order to limit the solar load. Considering the performance during the whole day it was concluded that the covering slotted and insulated could realize the best compromise between the opposite day and night requirements. Future research must be carried on to determine the best slot design (size, shape and orientation).

Performance of ventilated roofs in hot climate

LIBERATI, PAOLO;ZAPPAVIGNA, PAOLO
2004

Abstract

In hot climate areas the roof plays a fundamental role in determining the environmental conditions being the most exposed surface to the solar radiation. Among the possible ways to reduce the heat load inside the building, the solution of creating air flows under or through the covering may be valid since capable of reducing the entering heat flow during the day and favouring the heat discharge during the night. Various experimental tests were carried out on different ventilated roofings installed on scale buildings. In a first phase the performances of three roof types positioned successively on a shed of 1 m x 8 m plan size and height varying from 1 to 3 m, were tested. One with a ventilated interspace 7 cm thick, realized under a fibreciment sheet insulated by a polystyrene layer 4 cm thick; one similar to the previous but with two longitudinal slots on the covering, 10 cm wide each; one without interspace but with a slotted covering and insulated. In a second phase the performances of six other roof types positioned two by two on two sheds of 1 m x 6 m plan size and height varying from 1m to 2 m were tested. Four coverings had a ventilated interspace of two different thickness (7 cm and 3.5 cm), and were provided with and without insulation. The other two coverings were slotted, with a longitudinal slot 2 cm wide, and also provided with and without insulation. In all cases to simulate the animals' heat production some lamps were disposed on the floor. The surface temperature values corresponding to the various layers were measured, as well as the speed and temperature values of the air in the interspace, the solar radiation, the internal and external temperature, the wind speed and direction. For a general comparison the following indexes were analysed: Ig = [100∙(Tint. – Text.)]/Text , being T the air temperature; Ir = [100∙(Tx – T1)]/Tx, being Tx the internal surface temperature of the inner layer and T1 the external surface temperature of the outer layer. The experiments confirmed the effectiveness of the addition of a ventilated interspace in improving the night thermal exchange of the insulated continuous coverings. But the slotted roofs without interspace revealed a higher efficiency in realizing a small gradient between the internal and external temperatures. The one without insulation was able to obtain the lowest inside temperature during the night, but the day temperature resulted excessive and an insulating layer revealed to be necessary in order to limit the solar load. Considering the performance during the whole day it was concluded that the covering slotted and insulated could realize the best compromise between the opposite day and night requirements. Future research must be carried on to determine the best slot design (size, shape and orientation).
International Symposium of the CIGR 2nd Technical Section
1
8
P.Liberati; P.Zappavigna
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/9809
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