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Energies 2012, 5(7), 2178-2196; doi:10.3390/en5072178

The Impact of Roof Pitch and Ceiling Insulation on Cooling Load of Naturally-Ventilated Attics

1,*  and 2
1 Durham School of Architectural Engineering and Construction, University of Nebraska-Lincoln, Lincoln, NE 68588, USA 2 Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, NE 68588, Lincoln, USA
* Author to whom correspondence should be addressed.
Received: 29 May 2012 / Revised: 29 June 2012 / Accepted: 29 June 2012 / Published: 4 July 2012
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
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A 2D unsteady computational fluid dynamics (CFD) model is employed to simulate buoyancy-driven turbulent ventilation in attics with different pitch values and ceiling insulation levels under summer conditions. The impacts of roof pitch and ceiling insulation on the cooling load of gable-roof residential buildings are investigated based on the simulation of turbulent air flow and natural convection heat transfer in attic spaces with roof pitches from 3/12 to 18/12 combined with ceiling insulation levels from R-1.2 to R-40. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the investigated variations of roof pitch and ceiling insulation. Furthermore, it is predicted that the ceiling insulation plays a control role on the attic cooling load and that an increase of roof pitch from 3/12 to 8/12 results in a decrease in the cooling load by around 9% in the investigated cases. The results suggest that the increase of roof pitch alone, without changing other design parameters, has limited impact on attics cooling load and airflow pattern. The research results also suggest both the predicted ventilating mass flow rate and attic cooling load can be satisfactorily correlated by simple relationships in terms of appropriately defined Rayleigh and Nusselt numbers.
Keywords: attic; natural ventilation; roof pitch; insulation; cooling; turbulence; CFD attic; natural ventilation; roof pitch; insulation; cooling; turbulence; CFD
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Wang, S.; Shen, Z.; Gu, L. The Impact of Roof Pitch and Ceiling Insulation on Cooling Load of Naturally-Ventilated Attics. Energies 2012, 5, 2178-2196.

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