CFD modelling and thermal performance analysis of a wooden ventilated roof structure

Thermal comfort and energy saving are objectives of key significance that building design must meet. Since a low energy building can be obtained as a result of the good realization of all its components, roofs call for particular attention as they represent a large part of a building’s total surface area. In this paper the benefit of using ventilated roofs for reducing summer cooling load is investigated. The investigation has been conducted comparing a ventilated roof assembly with different channel heights (3 cm, 5 cm, and 10 cm) to the same non ventilated structure, assuming buoyancy-driven airflow. Direct comparison between the open and the closed roof structures as a function of different cavity heights and outside environmental conditions is presented. To provide fundamental information about the thermal performance of these building envelope components, the computational fluid dynamics (CFD) model has been used to develop correlations for the characterization of the airflow and heat transfer phenomena in the ventilation cavity which have been implemented in a whole year energy simulation software. The present analysis shows a conflicting discrepancy among the indexes of performance describing the actual energy saving potential of a ventilated roof.

[1]  S. Lykoudis,et al.  Summer performance of a ventilated roof component , 2006 .

[2]  Jenq-Shing Chiou,et al.  Optimal spacing for double-skin roofs , 2008 .

[3]  Dirk Saelens,et al.  Energy Performance Assessment of Multiple-Skin Facades , 2003 .

[4]  Boštjan Černe,et al.  Determination of transient two-dimensional heat transfer in ventilated lightweight low sloped roof using Fourier series , 2007 .

[5]  J. Hirunlabh,et al.  Experimental investigation of free convection in roof solar collector , 2002 .

[6]  Mats Sandberg,et al.  Ventilated-solar roof air flow and heat transfer investigation , 1998 .

[7]  J. Hensen.  MODELLING COUPLED HEAT AND AIR FLOW: PING-PONG VS ONIONS , 1995 .

[8]  Qingyan Chen,et al.  On approaches to couple energy simulation and computational fluid dynamics programs , 2002 .

[9]  Zhiqiang Zhai,et al.  Numerical investigation on thermal performance and correlations of double skin façade with buoyancy-driven airflow , 2008 .

[10]  M. Santamouris,et al.  On the impact of urban climate on the energy consumption of buildings , 2001 .

[11]  Joseph Khedari,et al.  New configurations of a roof solar collector maximizing natural ventilation , 2001 .

[12]  Francesco Leccese,et al.  Energy analysis of ventilated and microventilated roofs , 2005 .

[13]  S. Lykoudis,et al.  Thermal performance of an innovative roof component , 2006 .

[14]  S. Antvorskov.  Introduction to integration of renewable energy in demand controlled hybrid ventilation systems for residential buildings , 2008 .

[15]  Ephraim M Sparrow,et al.  Natural Convection in Open-Ended Inclined Channels , 1985 .

[16]  Monika Woloszyn,et al.  Heat transfers in a double-skin roof ventilated by natural convection in summer time , 2008 .

[17]  Abdeen Mustafa Omer,et al.  Renewable building energy systems and passive human comfort solutions , 2008 .