Numerical simulation of buoyancy-driven turbulent ventilation in attic space under winter conditions

Wang, Shimin; Shen, Zhigang; Gu, Linxia

doi:10.1016/j.enbuild.2011.12.012

Cited by 26 publications

(39 citation statements)

References 29 publications

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“…The roof-top temperature of T rt = 345.15 K specified in this study is corresponding to a typical peak roof temperature in summer days at several geographical regions in the United States, as evident in field measurements [4,30,31] and modeling predictions [21]. More discussions on the bases for the parameters chosen in the simulation can be found in [22], while the impacts of roof pitch and ceiling insulation on attic cooling load were reported in [29].…”

Section: Numerical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

Wang

Shen

2012

Energies

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Abstract:The impacts of ventilation ratio and vent balance on cooling load and air flow of naturally ventilated attics are studied in this paper using an unsteady computational fluid dynamics (CFD) model. Buoyancy-driven turbulent ventilations in attics of gable-roof residential buildings are simulated for typical summer conditions. Ventilation ratios from 1/400 to 1/25 combined with both balanced and unbalanced vent configurations are investigated. 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 variations in ventilation ratio and vent configuration. The predicted temperature fields are characterized by thermal stratification, except for the soffit regions. It is demonstrated that an increase in ventilation ratio will reduce attic cooling load. Compared with unbalanced vent configurations, balanced attic ventilation is shown to be the optimal solution in both maximizing ventilating flow rate and minimizing cooling load for attics with ventilation ratio lower than 1/100. For attics with ventilation ratios greater than 1/67, a configuration of large ridge vent with small soffit vent favors ventilating air flow enhancement, while a configuration of small ridge vent with large soffit vent results in the lowest cooling energy consumption.

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Section: Numerical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

Wang

Shen

2012

Energies

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“…For each roof pitch value, both a sealed attic case and a vented attic case are modeled. Similar to [22], the turbulent air flow and natural convection heat transfer inside the attics are modeled in terms of the v2f model [23][24][25], which has been shown by previous studies (e.g., [26][27][28]) to be the best Reynolds-averaged Navier-Stokes (RANS) model for indoor air flow simulation. A major difference from [22] is that an unsteady numerical formulation is adopted in this study, because the steady model could not produce convergent solutions for some cases with roof pitches higher than 8/12, even after carefully adjusting the various under-relaxation factors.…”

Section: Introductionmentioning

confidence: 99%

“…The impacts of ambient air temperature, vent size, and ceiling insulation on heating load and ventilating air flow rate suggested that both sufficient ventilation and insulation are needed to ensure the proper functions of the attic and its energy efficiency. The attic studied in [22], however, was assumed to have a fixed roof pitch of 5/12.…”

Section: Introductionmentioning

confidence: 99%

“…For example, Medina et al [19,20] proposed a correlation-based mathematical model for vented residential attics and compared model predictions with experimental data, and Moujaes and Alsaiegh [21] employed a finite element model to simulate the thermal effects of placing a radiant barrier system inside a vented residential attic for a case study under summer weather conditions. In a recent study [22], we employed a two-dimensional steady-state computational fluid dynamic (CFD) model to simulate the buoyancy-driven turbulent ventilation and heat transfer in a triangular attic space of a gable-roof residential building under winter conditions. The impacts of ambient air temperature, vent size, and ceiling insulation on heating load and ventilating air flow rate suggested that both sufficient ventilation and insulation are needed to ensure the proper functions of the attic and its energy efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Roof Pitch on Air Flow and Heating Load of Sealed and Vented Attics for Gable-Roof Residential Buildings

Wang¹,

Shen²

2012

Sustainability

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Pitch value is an important consideration in residential gable roof design and construction. However, how roof pitch, coupled with air flows in attic space, affects the energy performance of building attics has been barely investigated. In this paper, a 2D unsteady computational fluid dynamics (CFD) model is employed to investigate the effects of roof pitch on air flow and heating load of both sealed and vented attics for gable-roof residential buildings. The simulation results show that air flow in the sealed attics is steady and asymmetric, while that in the vented attics is a combination of an essentially symmetric base flow and a periodically oscillating flow. For both the sealed and vented attic cases, the heating load is found to increase with the roof pitch, and the heat transfer of turbulent air flow in attic space can be satisfactorily correlated by a simple relationship between appropriately defined Nusselt number and Rayleigh number.

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Numerical simulation of airflow in naturally ventilated attics for different attic geometries

Jyothiprakash

et al. 2022

Heat Trans

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Attic geometry and ventilation in a different attic geometry play a very important role in residential building energy performance. To evaluate the effect of ventilation ratio and vent balance on attic performance, a two-dimensional finite volume model is employed to simulate the buoyancy-driven turbulent ventilation and heat transfer in an attic space of different geometries like gable, gambrel, and saltbox roofs of residential buildings under winter conditions. The impact of ventilation ratio on ventilating airflow rate, heating load rate, and rate of heat gained is investigated for all three types of roof geometries.The model under consideration consists of a passive ventilation system with a ridge and soffit vent. Meshing is done by using ANSYS Workbench and numerical simulations are carried out by using ANSYS FLUENT 19 analysis software. The effect of passive ventilation on ridge-vent attic performance is evaluated in this study. Ventilation ratios for soffit vents ranging from 1/400 to 1/25 are investigated.Convection boundary conditions are used for the attic walls to account for thermal resistances of ceilings and roofs. In addition, the performance of these vented attics is compared to the heat transfer in a sealed attic. The results show that the symmetrical

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Numerical simulation of buoyancy-driven turbulent ventilation in attic space under winter conditions

Cited by 26 publications

References 29 publications

Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

Effects of Roof Pitch on Air Flow and Heating Load of Sealed and Vented Attics for Gable-Roof Residential Buildings

Numerical simulation of airflow in naturally ventilated attics for different attic geometries

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