Influence of environmental boundary conditions on convective heat transfer coefficients of wall internal surface

Dario Ambrosini,Luca Evangelisti,Roberto De Lieto Vollaro,Francesco Asdrubali,Claudia Guattari,Domenica Paoletti,Tullio De Rubeis

doi:10.1051/e3sconf/202131202012

Dario Ambrosini, Luca Evangelisti + Show 5 more

Open Access

https://doi.org/10.1051/e3sconf/202131202012

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Abstract

In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box (GHB) apparatus. An experimental setup characterized by air and surface temperature probes, and a hot-wire anemometer was used. Five small fans were installed in the metering chamber to generate a forced air flow characterized by different velocity values. So, the GHB was used for investigating the influence of different air speed values on internal convective coefficients. Considering horizontal heat fluxes, an internal convective coefficient values of 2.5 W/m2K is reported in the Standard ISO 6946. However, no exhaustive description about this value is provided. The aim of this work is to experimentally determine the internal thermal surface resistance, quantifying how the convective heat transfer coefficient varies as air velocity changes.

Highlights

The building energy balance is strongly influenced by heat transmission losses through the opaque and transparent envelope
Convective heat transfer phenomena were investigated by means of a Guarded Hot Box (GHB) apparatus
Thermal performance is measured in terms of heat loss and it is generally expressed in the construction industry as thermal resistance (R-value) or thermal transmittance (U-value) [1]

Summary

Introduction

The building energy balance is strongly influenced by heat transmission losses through the opaque and transparent envelope. Walls U-value is the most important thermophysical properties influencing the energy performance of a building [2,4]. The standard provides conventional surface resistances which can be applied for plane surfaces without detailed information on the boundary conditions. These values, that include convective and radiative thermal contributions, are obtained considering specific operating conditions. The convective heat transfer coefficients are given with different heat flux directions, but no detailed information on their determination are supplied

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