EFFECT OF OUTDOOR PRESSURE FLUCTUATIONS ON NATURAL VENTILATION IN A ROOM WITH TWO OPENINGS

2012 ◽  
Vol 20 (02) ◽  
pp. 1250003 ◽  
Author(s):  
HWATAIK HAN ◽  
JUNG KYUNG KIM ◽  
CHANG-HO HAN
Keyword(s):  
Natural Ventilation ◽  
Pressure Fluctuations ◽  
The Other ◽  
Wind Pressure ◽  
Airflow Rate ◽  
Governing Equations ◽  
Dimensionless Parameters ◽  
Runge Kutta Method ◽  
Room Volume ◽  
Synchronized Region

We investigated the effects of outdoor pressure fluctuations on natural ventilation in a room with two openings. One opening is exposed to an oscillating outdoor pressure and the other is exposed to a fixed neutral pressure. The ventilation airflow rate depends on the amplitude and period of the outdoor pressure fluctuations, the room volume, and the sizes of the openings. Dimensionless parameters are derived from the governing equations that determine indoor pressure responses due to outdoor pressure fluctuations. The pressure responses and the airflow rates through the openings are obtained using a fourth-order Runge–Kutta method. The flow regions are categorized into a synchronized region, an opening resistance region, and a transition region, depending on the dimensionless parameters. Applications are considered using an example building space to investigate the effective air change rates depending on the size of the openings and the period of wind pressure fluctuations.

Estimation model for natural ventilation by wind force considering wind direction and building orientation for low-rise building in China

2020 ◽  
pp. 1420326X2094498
Author(s):  
Tian-Wen Wang ◽  
Wei Yin ◽  
Lin-Li Fu ◽  
Zhi-Yi Zhang
Keyword(s):  
Architectural Design ◽  
Natural Ventilation ◽  
Cooling Capacity ◽  
Ventilation Rate ◽  
Wind Pressure ◽  
Dynamics Simulation ◽  
Airflow Rate ◽  
Climate Data ◽  
Estimation Model ◽  
Wind Force

Building natural ventilation can effectively prevent the building from overheating and eliminate indoor pollutants, including viral aerosols and volatile organic compounds, without consuming energy. Natural ventilation by wind force is influenced by many factors, making it difficult to calculate accurately. This increases the complexity of designing natural ventilation systems. In this study, we use a computational fluid dynamics simulation and wind tunnel verification to determine the wind pressure coefficients of each facade of a cube-shaped building and draw their corresponding curves. Subsequently, we input the climate data of 31 major cities in China to analyse their potential for natural ventilation. The results show that although some cities have long ventilation hours, the wind-forced ventilation rate is relatively low. For example, cities such as Guangzhou and Nanning that were previously considered suitable for natural ventilation have relatively small ventilation rates that may reduce the cooling capacity of natural ventilation. The ratio, 0.12, of the average airflow rate to the local average wind velocity should be used to estimate the wind-ventilation rate during the early stages of architectural design to determine the total windows area in every facade.

A modified Runge-Kutta method

SIMULATION ◽  
1968 ◽  
Vol 10 (5) ◽  
pp. 221-223 ◽  
Author(s):  
A.S. Chai
Keyword(s):  
Error Estimate ◽  
Linear Combination ◽  
Experimental Results ◽  
The Other ◽  
New Method ◽  
Kutta Method ◽  
Starting Values ◽  
Runge Kutta Method ◽  
Runge Kutta ◽  
A Minor

It is possible to replace k2 in a 4th-order Runge-Kutta for mula (also Nth-order 3 ≤ N ≤ 5) by a linear combination of k1 and the ki's in the last step, using the same procedure for computing the other ki's and y as in the standard R-K method. The advantages of the new method are: It re quires one less derivative evaluation, provides an error estimate at each step, gives more accurate results, and needs a minor change to switch to the RK to obtain the starting values. Experimental results are shown in verification of the for mula.

CFD Modeling of Pressure Coefficients for a Natural Ventilation Study in an Experimental Low Rise Building

2013 ◽  
Author(s):  
Robel Kiflemariam ◽  
Cheng-Xian Lin
Keyword(s):  
Natural Ventilation ◽  
Pressure Coefficient ◽  
Wind Pressure ◽  
Analytical Models ◽  
Cfd Modeling ◽  
Engineering Practice ◽  
Pressure Coefficients ◽  
Wind Pressure Coefficient ◽  
Detailed Assessment ◽  
Ventilation Rates

Mean wind pressure coefficient (Cp) is one of the major input data for natural ventilation study using building energy simulation approach. Due to their importance, they need to be accurately determined. In current engineering practice, tables and analytical Cp models only give mostly averaged results for simpler models and configurations. Considering the limitation of tables and analytical models, Computational Fluid Dynamics (CFD) could provide a means for an accurate and detailed assessment of Cp. In this paper, we make use of a relatively high resolution, detailed experiments done at Florida Intentional University to validate a CFD modeling of the pressure coefficients Cp. The results show that existing CFD model has a good agreement with experimental results and gives important information of distribution of Cp values over the surface. The local values of the Cp are investigated. In addition, the CFD derived Cp and discharge coefficient (Cd) values are utilized in semi-analytical ventilation models in order to get a more accurate value of ventilation rates.

scholarly journals A review of airflow rate estimation techniques for natural ventilation in buildings

2021 ◽  
Author(s):  
Miguel Chen Austin ◽  
Dafni Mora ◽  
Denis Bruneau ◽  
Alain Sempey
Keyword(s):  
Thermal Behavior ◽  
Pressure Difference ◽  
Natural Ventilation ◽  
Airflow Rate ◽  
Empirical Equations ◽  
Friction Characteristics ◽  
Estimation Techniques ◽  
Thermal Buoyancy ◽  
Modeling Techniques

As natural ventilation involves local and global interactions, the estimation of these interactions can be performed by many approaches. Such approaches, rather more experimental and numerical than analytical, often require a great deal of instrumentation and equipment, which results in higher demands on project budget and funding.  The present work is devoted to comprehending the natural ventilation concept, and to assess the existing experimental techniques already implemented for past researchers in the estimation of the ventilation airflow rate due to the wind and thermal buoyancy effects. A brief review of modeling techniques is also presented. This will provide a strong theoretical grasp of the natural ventilation process as part of the main elements in the thermal behavior of buildings. Ultimately, these bases are intended to help choose the most suitable techniques to estimate the natural ventilation airflow rate. The adequate benefit-to-budget technique appears to be the airtightness tests (blower door tests), since empirical Equations relating the airflow directly to the pressure difference in the building for both cases: infiltrations (openings closed) and openings opened, can be obtained.  Also, the location of the leakages can be identified without complications, and this technique has the potential to estimate in situ the airflow capacity and friction characteristics of the openings.

Computational Study of Streamfunction-Vorticity Formulation of Incompressible Flow and Heat Transfer Problems

2011 ◽  
Vol 52-54 ◽  
pp. 511-516 ◽  
Author(s):  
Arup Kumar Borah
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Boundary Conditions ◽  
Incompressible Flow ◽  
Computational Study ◽  
The Other ◽  
Governing Equations ◽  
Flow And Heat Transfer ◽  
Continuity Constraint ◽  
Transfer Problems

In this paper we have studied the streamfunction-vorticity formulation can be advantageously used to analyse steady as well as unsteady incompressible flow and heat transfer problems, since it allows the elimination of pressure from the governing equations and automatically satisfies the continuity constraint. On the other hand, the specification of boundary conditions for the streamfunction-vorticity is not easy and a poor evaluation of these conditions may lead to serious difficulties in obtaining a converged solution. The main issue addressed in this paper is the specification in the boundary conditions in the context of finite element of discretization, but approach utilized can be easily extended to finite volume computations.

Fundamental Differences Between Newtonian and Non-Newtonian Micro-EHL Results

1995 ◽  
Vol 117 (1) ◽  
pp. 29-35 ◽  
Author(s):  
L. Chang ◽  
W. Zhao
Keyword(s):  
Surface Roughness ◽  
Numerical Methods ◽  
Practical Interest ◽  
Operating Conditions ◽  
Convergence Criteria ◽  
Governing Equations ◽  
Rheological Models ◽  
Dimensionless Parameters ◽  
Machine Elements ◽  
Thinning Effect

Numerical analyses of micro-EHL problems have shown remarkably different results with Newtonian and non-Newtonian rheological models. However, no consensus has been reached whether a Newtonian model can be used in micro-EHL analysis. It is difficult to prove the point numerically as researchers use different numerical methods, grid sizes, time steps, and convergence criteria. This paper analytically studies the fundamental differences between Newtonian and non-Newtonian micro-EHL results. Algebraic governing equations are derived in terms of dimensionless parameters of the problem. Results are obtained for a range of key dimensionless parameters of practical interest. These results suggest that Newtonian and non-Newtonian micro-EHL results would be qualitatively different and the differences would be most pronounced with surface roughness of short wavelengths. Since surface roughness of machine elements contains substantial short-wavelength contents, a Newtonian rheological model is likely to generate misleading micro-EHL results under all operating conditions under which the shear-thinning effect of the lubricant is significant.

Implementation of the Wideband Autoparametric Vibration Absorber on a Flexible Structure

2003 ◽  
Author(s):  
Ashwin Vyas ◽  
Anil K. Bajaj ◽  
Arvind Raman
Keyword(s):  
Slow Rate ◽  
Excitation Frequency ◽  
Response Amplitude ◽  
Control Signal ◽  
Experimental Results ◽  
The Other ◽  
Flexible Structure ◽  
Vibration Absorber ◽  
Governing Equations ◽  
Near Resonance

The dynamics of a resonantly excited thin cantilever with an active controller are investigated experimentally. The controller mimics a passive wideband absorber discussed in [1]. PZT patches are bonded to both sides of the beam to actuate it, while an electromagnetic shaker drives the beam near resonance. An active controller consisting of an array of uncoupled controllers is developed, such that the governing equations for the controller are quadratically coupled to the resonating system. The control signal, in terms of the motion of the controllers, is quadratically nonlinear. The controller is implemented using a modelling software and a controller hardware board. Two sets of experiments are performed: one with a constant excitation frequency and the other with a linearly varying excitation frequency at a slow rate (non-stationary excitation). The experimental results verify the analysis presented for the passive wideband autoparametric vibration absorber. They also demonstrate the effectiveness of the absorber in reducing the response amplitude of structures, and its robustness to frequency mistuning.

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