Airflow In Buildings Research Articles

Real-time or faster-than-real-time simulation of airflow in buildings

Real-time flow simulation is crucial for emergency management in buildings, such as fire and accidental or intentional release of chemical/biological agents (contaminants). The simulation results can then be used to impose proper measures to minimize casualties. Computational fluid dynamics (CFD) is accurate, but too time-consuming. Nodal models are fast, but not informative. To obtain a quick and informative solution, this study proposes an intermediate approach between nodal models and CFD by introducing a fast fluid dynamics (FFD) method. This investigation used the FFD methods with and without turbulence treatments to study systematically four basic flows in buildings, and compared the numerical results with the corresponding CFD results and the data from the literature. The results show that, on one hand, the FFD can offer much richer flow information than nodal models, but less accurate results than CFD. On the other hand, the FFD is 50 times faster than the CFD. The results also show that the FFD with the laminar assumption has the best overall performance as regards both accuracy and speed. It is possible to conduct faster-than-real-time flow simulations with detailed flow information by using the FFD method. The paper introduces a fast fluid dynamics (FFD) method, which can simulate airflow and contaminant dispersion in buildings with real-time or faster-than-real-time speed and provide informative solutions. As an intermediate approach between nodal models and the computational fluid dynamics (CFD), the FFD can be a very useful tool for emergency management in case of fire and accidental or intentional release of chemical or biological agents in a building or around the buildings. The FFD can also be used as a preliminary test tool for quick assessment of indoor airflows before a detailed CFD analysis.

Quality Assured Measurements of Animal Building Emissions: Odor Concentrations

Standard protocols for sampling and measuring odor emissions from livestock buildings are needed to guide scientists, consultants, regulators, and policy-makers. A federally funded, multistate project has conducted field studies in six states to measure emissions of odor, coarse particulate matter (PM10), total suspended particulates, hydrogen sulfide, ammonia, and carbon dioxide from swine and poultry production buildings. The focus of this paper is on the intermittent measurement of odor concentrations at nearly identical pairs of buildings in each state and on protocols to minimize variations in these measurements. Air was collected from pig and poultry barns in small (10 L) Tedlar bags through a gas sampling system located in an instrument trailer housing gas and dust analyzers. The samples were analyzed within 30 hr by a dynamic dilution forced-choice olfactometer (a dilution apparatus). The olfactometers (AC’SCENT International Olfactometer, St. Croix Sensory, Inc.) used by all participating laboratories meet the olfactometry standards (American Society for Testing and Materials and European Committee for Standardization [CEN]) in the United States and Europe. Trained panelists (four to eight) at each laboratory measured odor concentrations (dilution to thresholds [DT]) from the bag samples. Odor emissions were calculated by multiplying odor concentration differences between inlet and outlet air by standardized (20 °C and 1 atm) building airflow rates.

Numerical Determination of Convection Coefficients for Internal Surfaces in Buildings Dominated by Thermally Stratified Flows

Convection coefficients for internal building surfaces, characterized by the air—surface temperature difference and local airflow, are crucial to a reliable building energy simulation and analysis based on the integrated modeling of heat and air flow in buildings, especially dominated by the thermally stratified flows, where the coefficients may vary significantly along each vertical wall. A turbulence model with a differential viscosity and dynamic turbulent Prandtl is proposed to predict the convective heat transfer for the case of thermally stratified flows in buildings. The local convection coefficients and then the bulk ones are numerically derived based on the law-of-the-wall method. Computational fluid dynamics (CFD) simulations are performed in an experimental enclosure and the results of air temperature profiles in the space are compared with the experimental data. Good agreements of thermally stratified pattern between the CFD and experiments are obtained. Although some discrepancies in the bulk convection coefficients are observed when natural convection is dominating, little differences in the temperature profiles give much confidence. As a whole, the CFD method using the turbulence model suggested in this study exhibits its good ability to effectively predict the convection coefficients.

Validation of a Coupled Multizone-CFD Program for Building Airflow and Contaminant Transport Simulations

Current multizone airflow network models assume air momentum effects, contaminant concentrations, and air temperatures are uniformly and homogeneously distributed in a zone of a building. These assumptions can cause errors for zones where air and/or contaminant are not well mixed. A coupled multizone-CFD program has been developed to improve the multizone model by applying a CFD model to those poorly mixed zones and the multizone model to the remaining zones. This paper validates the coupled multizone-CFD program by using experimental data obtained in a four-zone facility with nonuniform distributions of air momentum effects, contaminant concentrations, and air temperatures. The calculated results by the coupled program generally agreed with the experimental data although discrepancies exist in some cases. The coupled multizone-CFD simulations used less computing time than the CFD simulations for the whole flow domain.

Experimental Evaluation of Airflow in a Low-Energy Building

This paper reports on tracer gas measurements of the ventilation flow within a low-energy building. Constant-concentration, decay and homogenous tracer gas emission methods were used. Low-energy buildings are airtight constructions; effective ventilation is thus very essential for the indoor climate. The results of this study show an airflow rate between 0.42 and 0.68 air exchanges per hour (ac/h), which should be compared to the minimum requirements in Sweden of 0.5 ac/h. It was found that the airflow changes with time and that the local mean age of air was different on different floors of the building and, to some extent, different at different heights.

Nonlinear Dynamic Analysis of Natural Ventilation in a Two-Zone Building: Part A—Theoretical Analysis

The nonlinear behavior and solution multiplicity of airflow and natural ventilation in multi-zone buildings are significant for building ventilation and smoke control design. A two-zone building with four openings is considered in this study. Nonlinear dynamic behaviors are analyzed, and we report on the fixed points (steady-state solutions) and their stability and provide a description of the bifurcation of the fixed points and an estimation of the separating curve between two stable fixed points. Different flow modes were identified with the same physical and boundary conditions. A multi-zone airflow and thermal coupled program was also used to evaluate the results. There was good agreement between the numerical and theoretical solutions, except that the unsteady-state solutions could not be predicted by the multi-zone program. These results may have significant implications for multi-zone modeling of natural ventilation and smoke or contaminant spread in buildings, as well as allow us to gain a good understanding of physical flow behavior and solution multiplicity.

06/00939 The effect of the use of openings on interzonal air flows in buildings: an experimental and simulation approach: Koinakis, C. J. Energy and Buildings, 2005, 37, (8), 813–823.

06/00939 The effect of the use of openings on interzonal air flows in buildings: an experimental and simulation approach: Koinakis, C. J. Energy and Buildings, 2005, 37, (8), 813–823.

06/00357 The effect of the use of openings on interzonal air flows in buildings: an experimental and simulation approach: Koinakis, C. J. Energy and Buildings, 2005, 37, (8), 813–823

06/00357 The effect of the use of openings on interzonal air flows in buildings: an experimental and simulation approach: Koinakis, C. J. Energy and Buildings, 2005, 37, (8), 813–823

CFD Reliability Issues in the Prediction of Airflows in a Naturally Ventilated Building

The potential for prediction error when using computational fluid dynamics (CFD) for investigating internal building airflows is assessed in the current paper. The ability of a proprietary CFD code, CFX, to simulate buoyant and forced airflow regimes, typical of a naturally ventilated building, are investigated using two experimental case studies from the literature. Comparisons are then made between simulated and measured airflows for a naturally ventilated building. Results from the two case studies indicate that structured meshes are less dependent on mesh density and yield consistent convergence and accuracy when coupled with the k-ϵ or k-ω turbulence models. Comparison of CFD predicted airflows with the full-scale building airflows was challenging due to scatter in the measured data. A structured mesh in conjunction with either the k-ϵ or k-ω turbulence models, showed reasonable correlation with the measured airflows, with both models performing equally.

POWBAM0 Mechanical Power Balances for Multi-zone Building Airflow Analysis

Conventional methods of multi-zone airflow analysis ignore mechanical energy conservation in forming the system equations governing building airflows. As a result, airflows computed using these methods generally violate this fundamental conservation principal and thereby falsely create or destroy kinetic energy within building zones. While the impact of this fundamental oversight has yet to be fully evaluated, it need not be tacitly accepted. This paper will present a rigorously detailed theoretical approach that imposes both mass and mechanical energy conservation to the problem of multi-zone airflow analysis and, through comparisons with results computed using computational fluid dynamics (CFD) and the conventional approach to multi-zone airflow analysis, will demonstrate that a power balance approach can predict building airflows that satisfy both of these fundamental conservation principles while offering greater capabilities than that of the conventional approach. Furthermore, it will be shown that the conventional approach is a special limited case of the practical application of the power balance approach. A computational prototype, POWBAM0, based on the theory will be introduced.

Development of new and validation of existing convection correlations for rooms with displacement ventilation systems

Building airflow, thermal, and contaminant simulation programs need accurate models for the surface convective boundary conditions. This is, especially, the case for displacement ventilation (DV) systems, where convective buoyancy forces at room surfaces significantly affect the airflow pattern and temperature and contaminant distributions. Nevertheless, for DV, as a relatively new ventilation system, the convective correlations are adopted from more traditional mixing ventilation correlations, or non-existent. In this study, the existing recommended correlations are validated in a full-scale experimental facility representing an office space. In addition, new correlations are developed for floor surfaces because the current literature does not provide necessary correlations, even though, the floor surface is responsible for >50% of the total convective heat transfer at the envelope. The convective correlations are typically functions of a surface-air temperature difference, airflow parameters, and characteristic room dimensions. Validation results show that the floor convection correlations expressed as a function of volume flow rate are much stronger than the correlations expressed as a function of a temperature difference between the surface and local air. Consequently, the new convection correlation for floor surfaces is a function of the number of hourly room air changes (ACH). This correlation also takes into account buoyant effects from local floor heat patches. Experimental data show that the existing correlation can be successfully applied to vertical and ceiling surfaces in spaces with DV diffuser(s). Overall, the new and the existing convection correlations are tabulated for use in building simulation programs, such as annual energy analyses or computational fluid dynamics.

Development of an integrated model for airflow in building spaces

In building energy simulation, an integrated modelling of airflow in the building needed. Therefore, in this paper two approaches are used for building energy simulation: zonal network for modelling of the building segments and Computational Fluid Dynamics (CFD) for modelling of the airflow. It is noted that a synchronize solution process is needed for the building and the CFD equation-sets. For this purpose an iterative procedure is used to corresponding solution of these equations.

The effect of the use of openings on interzonal air flows in buildings: an experimental and simulation approach

Internal air flows due to ventilation through large openings is an integral part of the ventilation and energy design of buildings and should be taken into account among other thinks in the simulation of occupants’ behavior. In this paper, the effect of the arrangement and use of the internal openings in a two-storey house on the interzonal flows inside the building's rooms is examined, with the aid of nodal ventilation modeling. Validation experiments are also performed for a series of arrangements of internal and external openings, by conducting tracer gas measurements. A parametrical investigation is carried out for selected parameters, including the effect of the percentages of the windward and leeward openings on the interzonal flows, monitoring magnitude and direction changes, for specific climatic conditions. Conclusions about interzonal flows and ventilation design are drawn.

Wind pressure distribution influence on natural ventilation for different incidences and environment densities

Natural ventilation is of increasing interest in building industry because of recent focus on environmental concern, considered with both comfort and economical criteria. The aim of this study is to investigate how wind may induce natural ventilation, with focus on wind incidence and large scale environment density influences. These parameters modify flows inside and outside buildings. Numerical dynamic simulations are achieved for a standard office building using pressure coefficients obtained from a parametrical model. Simulations allow to describe inside building air flow for three incidences: 0°, 45°, 90° and three theoretical environments: open, suburban and urban. Originality of this study is to work with both vertical and horizontal pressure coefficient gradients. Results show how important horizontal gradients are in air flow comprehension. Urban wind driven ventilation potential is also discussed. Some words are said on existing tools limitations. The need for further studies is illustrated in order to obtain handy pressure coefficients prediction tools and to optimize openings mechanical regulation. The all study falls under the step of sustainable architecture.

The development of an accurate tool to determine convective heat transfer coefficients in real buildings

This paper reports on a project to construct and test an instrument that, for the first time, enables the accurate measurement of convective heat transfer coefficients (chtcs) in real buildings. Computer simulation models for the prediction of heat and airflow in buildings commonly rely on such empirically derived values. However, there are large uncertainties associated with their evaluation and use.The instrument described in this paper has been tested by measuring the chtcs on a heated plate mounted in a test room. The experimental work reported here was made up of two parts:(1) A 'proof of concept' with both platinum resistance (PRT) and thermocouple temperature sensors mounted on a moveable 'tracker'.(2) Measurements made on a reference surface with a final 'fixed' instrument.The results are encouraging. Comparisons of the chtcs determined by the new instrument and the chtcs determined by the 'traditional' heated plate method have shown close agreement. It seems that the new instrument has great potential for use in real buildings. (C) 2004 Elsevier B.V. All rights reserved.

ZAER: A Zonal Model for Heat Transfer and Air Flow in Unconditioned Buildings. - An Experimental Validation

This paper presents a three-dimensional zonal model, ZAER, for heat transfer and air flow calculations. It is based on an intermediate approach between single-air-node and CFD models. The indoor air volume is divided into macroscopic homogeneous zones. Heat and mass balance equations are written for each zone, while the mass flow rates across the interfaces are calculated by power pressure laws. The simulation tool ZAER allows the determination of temperature fields and air flow distributions inside unconditioned buildings, taking into account external boundary conditions. We also present an experimental validation of the model by comparing its predictions with experimental data obtained from measurements on the experimental cell Minibat (CETHIL, INSA Lyon Laboratory), for different configurations. The results obtained are in good agreement with experimental data, and suggest that the ZAER model is an appropriate tool to assess satisfactorily temperature heterogeneity and air movement within a room.

Automatically generated zonal models for building air flow simulation: principles and applications

In our formulation of zonal models for calculating room air temperature and flow distributions, the behavior of a room is represented by the connection of SPARK calculation modules. Modules to describe the building walls and various systems have been created. They form the models library. By assembling the appropriate modules, a zonal model of an entire building can be constructed. A model-generating tool called GenSPARK automates this process. SPARK solves the set of equations resulting from this construction to obtain the air flow and temperature distribution in the building. We describe our formulation of zonal models, show how GenSPARK works and give examples of configurations we are able to analyze.

Evaluating the Air Pressure Response of Multizonal Buildings

Air flow in buildings is a complex flow and pressure distribution problem that makes quantification difficult. However, certain parameters have recently become easy to quantify – specifically the air pressure relationships within buildings. The measured building air pressure field can be used with network analysis to solve the building flow and leakage regime creating an analytical macro model of the building flow and leakage regime. The response of the analytical model can be further tuned by perturbing both the building air pressure field and the analytical model. Building analysis typically focuses on flows and requires that all flow paths into and out of a control volume be defined. The flow path resistances need to be characterized. Determining all air flow paths and determining the flow path resistances directly is difficult. As such, estimates of these flow path resistances are commonly used. These estimates are based on limited field data and laboratory measurements. The literature provides some component values that vary by orders of magnitude and their application is often unable to predict building flow fields (ASHRAE, 1997). Standard building analysis develops the building pressure field from the flow field. This paper argues that developing the flow field from the building pressure field is more powerful. Determining the characteristics of the building pressure field directly is considerably easier than determining flow path resistances. It allows closing of the gap between the mathematical sophistication of available multi-cell air flow models and the necessary input information defining the building boundary conditions. This approach allows the pressure response of the building to be used to ‘‘tune’’ the models extending the range of their applicability and accuracy.

The threat of chemical and biological terrorism: preparing a response

When a deadly contaminant is released in a city, the window of time for meaningful response is brief. High-performance computing can play a major role in preparing an effective response. This article describes one such effort, which exploits detailed 3D computational fluid dynamics simulations of the airflow in buildings and cities.

Study of natural ventilation in buildings by large eddy simulation

Natural ventilation in buildings can create a comfortable and healthy indoor environment, and can save energy used in the mechanical ventilation systems. Two subgrid-scale models of large eddy simulation (LES), a Smagorinsky subgrid-scale (SS) model and a Filtered dynamic subgrid-scale (FDS) model, have been used to study airflow in buildings with natural ventilation. It was found that, for fully developed turbulence flow with a high Reynolds number, both the SS and FDS models provide good results. However, if the flow has both turbulent and laminar characteristics, or the wall effect is significant, the SS model performs poorly due to its constant model coefficient. The FDS model can still predict this flow correctly because its model coefficient varies over space and time according to flow types. Furthermore, for a single-sided ventilation, it is important to obtain instantaneous flow information in order to correctly predict ventilation rate and air change effectiveness. Reynolds Averaged Navier Stokes (RANS) modeling cannot correctly calculate the ventilation rate in this case.