tCool materials are characterized by high solar reflectance and high thermal emittance; when applied tothe external surface of a roof, they make it possible to limit the amount of solar irradiance absorbed bythe roof, and to increase the rate of heat flux emitted by irradiation to the environment, especially duringnighttime.However, a roof also releases heat by convection on its external surface; this mechanism is not negligi-ble, and an incorrect evaluation of its entity might introduce significant inaccuracy in the assessment ofthe thermal performance of a cool roof, in terms of surface temperature and rate of heat flux transferredto the indoors. This issue is particularly relevant in numerical simulations, which are essential in thedesign stage, therefore it deserves adequate attention.In the present paper, a review of the most common algorithms used for the calculation of the con-vective heat transfer coefficient due to wind on horizontal building surfaces is presented. Then, withreference to a case study in Italy, the simulated results are compared to the outcomes of a measurementcampaign. Hence, the most appropriate algorithms for the convective coefficient are identified, and theerrors deriving by an incorrect selection of this coefficient are discussed.
|Titolo:||Proper evaluation of the external convective heat transfer for the thermal analysis of cool roofs|
|Data di pubblicazione:||2014|
|Appare nelle tipologie:||1.1 Articolo in rivista|