Computational fluid dynamics for analysis of room air flow
#NO 11494 Detailed Experimental Data of Room Airflow with Displacement Ventilation
Chen Q, Yuan X, Hu Y, Glicksman L R, Yang X
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 133-140.
This paper presents a set of detailed experimental data of room airflow with displacement ventilation. These data were obtained from a new environmental test facility at the Massachusetts Institute of Technology (MIT). The measurements were conducted for three typical room configurations: a small office, a large office with partition, and a classroom. The experiment measured the distributions of air velocity, air velocity fluctuation, and air temperature by omni-directional hot-sphere anemometers and contaminant concentrations by tracer gas at 54 points in the room. Smoke was used to observe airflow. The data include the wall surface temperature distribution, air supply parameters, and the age of air in several locations in the room. Airflow using displacement ventilation is a kind of mixed convection and therefore, these data are especially suitable for validating Computational Fluid Dynamics (CFD) programs for prediction of indoor airflow.
#NO 11501 Study on Hybrid Air-Conditioning System Using Natural Ventilation in Office Space
Chikamoto T, Kato S, Murakami S, Kitamura N, Yue H W, Taeyeon K
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 181-188.
In Japan medium height and high rise office buildings have usually been designed with a fixed (permanently closed) window, in order to reduce the infiltration of outdoor air. In the current research, a semi-open indoor space of office design is proposed by the introduction of a hybrid air conditioning (cooling) system which utilises natural ventilation for controlling the indoor climate in spring and autumn. The hybrid system combines wind induced cross ventilation with a conventional mechanical air conditioning system. During spring and autumn, the outdoor air is at a thermally comfortable temperature and can be used for conditioning, thus saving air conditioning energy consumption. Based on CFD simulation results, the ventilation efficiency of the hybrid air conditioning system is analysed by investigating the age of air of the fresh outdoor air and the contribution ratio of supply opening of the natural ventilation. Then the improvement of the air quality at each point of the office room is examined, based on Fanger's perceived air quality concept. The research is intended to analyse the energy conservation effect, the effect on human perception of the air quality and the zone averaged heat and contaminant flow rate between task and ambient zones. Finally the efficiency and feasibility of the hybrid air conditioning system itself are analysed.
#NO 11508 Numerical Study of Personal Exposure to Contaminant and Draft Risk in a Workshop with Displacement Ventilation
Peng S H, Davidson L
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 233-240.
Contaminant dispersion and potential draft risk in a workshop with displacement ventilation were investigated with computational fluid dynamics (CFD) techniques. Three factors were considered: the location of the worker, the temperature of the supply air and the supply air flow rate. The capacity of CFD is demonstrated in optimizing the operation of a ventilation system by weighting two significant aspects, i.e., the indoor air quality and the worker's thermal sensation. On the basis of the numerical results, some suggestions are given for a better use of displacement ventilation systems.
#NO 11509 Measurements at and Simulations of the (improved) Desk Displacement Ventilation Concept
Loomans M G L C
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 241-248.
Steady state and transient Computational Fluid Dynamics (CFD)-simulations of a climate chamber configuration have been compared with similar full scale measurement results. The configuration comprises a task conditioning concept that applies the displacement ventilation principle. Earlier studies have indicated that this concept is not feasible for standard office configurations. CFD is applied for the investigation of an improved version of the concept. An example of such an improvement is given. For the steady state situation different boundary and cooling load conditions have been investigated. The presented results indicate the importance of a correct modelling of the wall heat transfer for this type of flow problem. Currently the applied CFD program does not allow a practical improvement of the results, e.g., via an imposed heat transfer coefficient. CFD-simulation result are compared. Given this comparison, an improved version is evaluated numerically.
#NO 11510 The Air Exchange Efficiency of the Desk Displacement Ventilation Concept - Theory, Measurements and Simulations
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 249-256.
The concept of air exchange efficiency of ventilation, a quantity entirely determined by the spatial distribution of the local mean age of air, is discussed. A divergence-type conservation equation for the local mean age of air is derived. This equation is solved numerically for a room ventilated by the desk displacement ventilation concept, using a CFD-routine. The CFD-calculated mean-age-of-air pattern is compared with mean age results from tracer experiments in a corresponding laboratory configuration. It is found that the air exchange efficiency of the air flow pattern induced by the desk displacement unit is only slightly above 0.5, the value for perfect mixing ventilation, for cooling situations.
#NO 11525 Vortex Air Distribution System for Boiler House
Livtchak A, Laurikainen J, Haapio J, Ahtila P
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 363-368.
This article describes a new and more efficient Vortex Air Distribution system for a soda recovery boiler house. Essentially the technology utilises directional air supply of up to 150 m/s to compensate for heat gains of up to 2000 kW. Issues addressed include all stages of the design process from the Computational Fluid Dynamic (CFD) experiment and scale mock-up tests in the laboratory conditions to the field measurements after the system had been installed. The supply air is distributed into the building through specially designed air terminals. It forms the vortex flow around the boiler surfaces displacing the contaminated warm air towards the exhaust at the top of the boiler house utilising buoyancy forces. Having uniform direction of the air movement inside the boiler house ensures efficient ventilation of the building, preventing stagnant ventilation zones from being formed. The warm air stratified at the top of the boiler house is used in the combustion process thus significantly improving the energy efficiency of the boiler. The air distribution system successfully operates in the soda recovery boiler plant in Rauma, Finland since 1996.
#NO 11534 Simulation of infiltration heat recovery.
Buchanan C R, Sherman M H
UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation Technologies in Urban Areas", 19th Annual Conference, held Oslo, Norway, 28-30 September 1998, pp 17-26.
Infiltration has traditionally been assumed to affect the energy load of a building by an amount equal to the product of the infiltration flow rate and the enthalpy difference between inside and outside. Results from detailed computational fluid dynamics simulations of five wall geometries over a range of infiltration rates show that heat transfer between the infiltrating air and walls can be substantial, reducing the impact of infiltration. The classical method for determining the infiltration energy load was found to over-predict the amount by as much as 95 percent and by at least 10 percent. However, in order to achieve significant heat recovery, flow paths which are unlikely in adventitious leakage are required.
#NO 11565 Measurement of heat and mass transfer through typical staircases.
Peppes A A, Santamouris M, Asimakopoulos D N
UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation Technologies in Urban Areas", 19th Annual Conference, held Oslo, Norway, 28-30 September 1998, pp 314-322.
This paper is concerned with heat and mass transfer through two typical staircases. The first staircase connects the two individual floors of a two-storey building, and the other connects the three individual floors of a three-storey building. A series of experiments have been performed in order to study the buoyancy driven flow between the floors. A single tracer gas decay technique was adopted. Temperatures at various points on each floor were constantly monitored and air velocity measurements were also provided at some specific locations. The heat and mass flow rates between the two floors, through the first staircase, were calculated from the tracer gas concentrations. The analysis of experimental data gives relations for the mass and heat flow rate as a function of temperature difference between the floors, and of the geometry of the particular staircase. Simulations of the same configurations have been carried out, using validated CFD algorithms. Airflow rates estimated by these simulations showed very good agreement with experimental values. The mass flow rates through the second staircase are estimated using the CFD method. In addition, the paper discusses the airflow patterns in the staircases.
#NO 11616 Deflection of wall-jets in ventilated enclosures described by pressure distribution.
Karimpanah M T
UK, Building and Environment, Vol 34, 1999, pp 329-333, 4 figs, 2 tabs, 9 refs.
The pressure field in fluid systems reflects the flow configuration. Measurements of the pressure along the perimeter of a slot ventilated room have been conducted for different room sizes. The momentum of the jet at the end of the room is decreased with increasing room length. The impingement region (region where the influence of the opposing wall is present) starts, independent of room size, when the distance from the supply device is about 70% of the room length. Corner flows could not be predicted by CFD using the linear eddy viscosity or standard stress models. However, these effects may be captured by using a second moment closure turbulence model with a new near wall approach now available in literature.
#NO 11625 A state-space representation of the dynamic model of air temperature distributions.
Ghiaus C, Peng X, van Paassen A H C
in: Netherlands, Apeldoorn, 1995, proceedings of the 19th International Congress of Refrigeration, Den Haag 20-25 Aug. 1995, pp 790-796.
Knowing the dynamic behaviour of the air temperature in air-conditioned rooms is important. The steady state flow field and temperature distribution can be calculated by computer fluid dynamics (CFD) programs. To study the dynamics (in order to control the temperature or to know the response with time in different places) is prohibitively time consuming if CFD programs are to be used. For certain ranges of inlet temperature, the flow field could be considered as fixed. The output of CFD (the static flow field) can be used to achieve a state space model of the dynamic response of the air temperatures at various places in the room. The dynamic calculations can then be carried out much faster. In fact, this idea is accomplished through combining two softwares, PHOENICS for the CFD and MATLAB for control. Moreover, a lot of programs (toolboxes) specially designed for system analysis and controller design are available in MATLAB.
#NO 11629 Calculation of convective heat transfer coefficients of room surfaces for natural convection.
Awbi H B
UK, Energy and Buildings, No 28, 1998, pp 219-227, 7 figs, 2 tabs, 15 refs.
Convective heat transfer from internal room surfaces has major effect on the thermal comfort, air movement and heating and cooling loads for the room. Recent studies have shown that the values of convective heat transfer coefficient used in building thermal models greatly influence the prediction of the thermal environment and energy consumption in buildings. In computational fluid dynamics (CFD) codes for room air movement prediction, accurate boundary conditions are also necessary for a reliable prediction of the air flow. However, most CFD codes use 'wall functions' derived from data relating to the flow in pipes and flat plates which may not be applicable to room surfaces. This paper presents results for natural convection heat transfer coefficients of a heated wall, a heated floor and a heated ceiling which have been calculated using CFD. Two turbulence models have been used to calculate these coefficients: a standard k-e model using 'wall functions' and a low Reynolds number k-e model. The computed results are compared with data obtained from two test chambers.
#NO 11632 A numerical study of solar chimney for natural ventilation of buildings with heat recovery.
Gan G, Riffat S B
Applied Thermal Engineering, No 18, 1998, pp 1171-1187, 7 figs, 2 tabs, 11 refs.
The performance of a glazed solar chimney for heat recovery in naturally-ventilated buildings was investigated using the CFD technique. The CFD program was validated against experimental data from the literature and good agreement between the prediction and measurement was achieved. The predicted ventilation rate increased with the chimney wall temperature. The effects of solar heat gain and glazing type were investigated. It was shown that in order to maximise the ventilation rate in a cold winter, double or even triple glazing should be used. Installing heat pipes in the chimney for heat recovery not only increased the flow resistance but also decreased the thermal buoyancy effect. To achieve the required air flow rates in naturally-ventilated buildings with heat recovery, use should be made of wind forces.
#NO 11722 A state space model of indoor temperature distributions.
Peng X, van Paassen A H C
in: proceedings of the 2nd International Symposium on Heating, Ventilating and Air Conditioning, Tsinghua-HVAC 95, 25-27 Sept 1995, Volume 2, pp 434-441.
To control the indoor thermal environment within the comfortable range, the dynamic temperature distributions and flows of room air must be correctly predicted. While the CFD (Computational Fluid Dynamics) technique can be used to carry out such a prediction task, its drawback is also obvious: too time-consuming. To solve this problems, the dynamic temperature distributions can be predicted with some fixed air flow fields calculated with CFD codes. That is, sacrifice the dynamics of indoor air flows and only preserve the dynamics of the temperature distributions. This paper discusses a state space model that can be used to predict the indoor dynamic temperature distributions. By dividing the room into several air zones and still using the fixed flow field, a much faster dynamic model of the indoor temperature distributions is constructed. This model can be easily used for designing and testing different indoor climate control systems.
#NO 11723 A type of dynamic calculation of indoor temperature distributions.
Peng X, van Paassen A H C
in: Belgium, University of Liege, Laboratory of Thermodynamics, 1995, proceedings of the 4th International Conference on System Simulation in Buildings, 5-7 December 1994, pp 57-68.
The requirements to know indoor thermal comfort ask for a more detailed study of room temperature responses. Although CFD (Computational Fluid Dynamics) techniques can be applied successfully to the prediction of indoor temperature distributions, using them for the dynamic calculation of temperatures and air flows is still a very expensive expenditure. For indoor climate control systems, it is necessary to make quick calculations of the dynamic temperature distributions in a room. To compromise, we are trying to use a limited number of fixed air flow patterns to perform the dynamic calculations,. Some of our initial study results are presented in this paper. For a typical heating situation, the dynamic indoor temperature distributions can be calculated satisfactorily with only one fixed air flow pattern. Further study indicates that when the heating power has changed, this flow pattern can be used once again for the dynamic calculations of air temperature responses.
#NO 11747 Numerical simulation of volatile organic compounds dispersion emitted from flooring materials in buildings.
Papakonstantinou K A, Kiranoudis C T, Markatos N C
Slovenia, Maribor, University of Maribor, 1998, proceedings of Third SITHOK-3 International Congress, May 9-11, 1998, Maribor, Slovenia, pp 181-187, 7 figs, 6 refs.
This paper deals with the simulation of VOCs concentration dispersion emitted from flooring material, with the purpose of understanding VOCs emission and dispersion mechanisms. A test chamber is examined, whose flooring material emits a number of VOCs. Given the area specific ventilation rate and considering as boundary conditions experimental data for the examined compounds concentration, the dispersion of the VOCs concentrations is examined, for two cases, steady state conditions and transient state conditions. The model developed is used in conjunction with a general-purpose CFD code, PHOENICS, that can provide detailed information on the flow field as well as pollutants concentrations fields. The results of the above two simulation cases are used as a guide for two other cases, where faster restoration of the air indoor quality was investigated by changing the rate of the ventilation system in the chamber. The simulation results could be used as a base for further analysis for other flooring materials, intending to a proper material selection as well as to a proper ventilation system for a more healthy and comfort environment in a building.
#NO 11783 Equations for a ventilation design derived from computational fluid dynamics.
Chow W K, Wong L T
Switzerland, Indoor and Built Environment, No 7, 1998, pp 276-288, 5 figs, 10 tabs, 23 refs.
Computational fluid dynamics (CFD) was used in a study of the air flow characteristics in the occupied building zone. Correlation equations between the mean air speeds and the percentage dissatisfied with the macroscopic flow numbers were derived. Ten macroscopic flow numbers including the total ventilation rate, the air change rate, ventilation rate, air diffusion performance index, modified jet momentum number, two new flow numbers and three expressions of jet momentum ratio were investigated. A total number of 25 numerical experiments under isothermal flow conditions with four different geometrical arrangements (labelled A-D) were performed. The correlation equations derived from CFD were compared with those obtained from experimental studies. It is found that the jet momentum ration RM2 gives the equation with the best correlation coefficient and so is recommended for ventilation design.
#NO 11831 Air flow simulations in a place dedicated to meditation. The Cistercian Cloister.
de la Foye A, Joanne P
UK, James & James Ltd, 1988, proceedings of "Environmentally friendly cities", PLEA 98 (Passive and Low Energy Architecture) conference, held Lisbon, Portugal, June 1998, pp 191-194, 9 figs, 5 refs.
Confronting the high density of town planning, architects and town planners are led to design small outdoor places which are inserted into the city but offer specified properties: serenity, calmness, unusual surrounding ... Within the framework of the CERMA laboratory, we are looking for reference architectural examples likely to meet such needs and transposable into a contemporary architectural project.
A research work in progress is dealing with Cistercian abbey cloisters, archetypes of a space sheltered from outer nuisances which was originally dedicated to meditation and self-communion. Our work consists of checking whether the tranquillity of this place lies on physical datas which are easily controllable by the designer.
In regard to our research, Cistercian cloisters present the following interests:
* it is a typical architectural figure from which several developments can derive: patios, squares, ...
* it is present in the whole of European countries and therefore has to suit to very different climatic and topographic compulsions;
* it was designed in a rational way and found upon a pattern which is easy to modelise.
A preliminary work has already been carried out which was focused on daylighting, acoustics, and air flow. The study of daylighting was based upon the modelisation of a sample of Cistercian abbey and its simulation with the software designed by the CERMA: Solene. The study of the soundscape rested on in situ measures made in the cloister of the Cistercian abbey of Noirlac (France) and theoretical estimations. We also undertook a preliminary approach of the cloister capacity for sheltering from the wind by setting up a 2D simulation with the finite element CFD code N3S. Our presentation will show this last point which supplied us quite interesting results and now form the subject of further research work.
#NO 11853 Simulation of the cooling effect of the night time natural ventilation: a 3D numerical application to the "Maison Ronde" of Mario Botta.
Marenne C, Groleau D, Raymond R
UK, James & James Ltd, 1988, proceedings of "Environmentally friendly cities", PLEA 98 (Passive and Low Energy Architecture) conference, held Lisbon, Portugal, June 1998, pp 495-498, 7 figs, 6 refs.
The present research applies the N3S 3D finite element CFD code to the air flow simulation on a well-known dwelling building located in South of Switzerland, the "Maison Ronde" of the architect Mario Botta. The summer night refreshing effect is examined when crossing ventilation due to the wind creates indoor air motion and for cooling walls and ceilings surfaces.
To be realistic, the simulation takes simultaneously into account the three main aspects of the problem.
#NO 11859 A comparison of predictive techniques for natural displacement ventilation of buildings.
Howell S A, Potts I
UK, Chartered Institution of Building Services Engineers (CIBSE), 1998, Proceedings of "Harnessing technology for sustainable development", CIBSE National Conference '98, held Bournemouth International Conference Centre, 18-20 October 1998, pp 156-164, figs, refs.
Previous work by Linden, Lane-Serff and Smeed (1990) has developed a simple mathematical model for natural displacement ventilation of an enclosure. The work also introduced the experimental salt-bath technique, which uses salt solutions and fresh water to generate buoyancy forces that are analogous to those found in naturally ventilated buildings. The work claims that a good correlation exists between the predictions of the simple mathematical model and the results obtained using the salt-bath technique.
The present paper reports further, independent experimental work using a test enclosure with air as the working fluid. A Computational Fluid Dynamics computer package is also used to predict the flow through the enclosure. The potential of each of the predictive techniques investigated is discussed. Although a simple mathematical model would be desirable, the conclusion of this paper is that such a model is not suitable for use in a design situation, and that alternative predictive techniques are preferred.
#NO 11866 Numerical simulation of three-dimensional airflow in unfurnished rooms.
Schulte T E, Bergstrom D J, Bugg J D
USA, ASHRAE, 1998, in: the ASHRAE Transactions CD, proceedings of the 1998 ASHRAE Annual Meeting, held Toronto, Canada, June 1998, 9pp, 12 figs, 1 tab, refs.
This paper considers the numerical modeling of room airflows and illustrates the usefulness of computational fluid dynamics as a design tool for ventilation systems. A computer code, which simulates steady, buoyant, turbulent, three-dimensional flows in Cartesian coordinates, was developed. The time-averaged equations for conservation of mass, momentum, and energy are solved. A low Reynolds number k-epsilon model is used to simulate the turbulent transport. The code was validated by comparing it to benchmark data for both lid-driven and buoyancy-driven cavity flows. The airflows in two unfurnished rooms were then simulated. Streamlines show that one room is poorly ventilated because of a large portion of the incoming air does not pass through the occupied region. The other room has uncomfortable regions because of excessive turbulent fluctuations. Use of computational fluid dynamics enables the velocity and temperature fields to be investigated in significantly greater detail than is possible with either analytical or experimental models.
#NO 11871 Numerical simulation of contaminant distribution around a modelled human body: CFD study on computational thermal manikin - Part II.
Murakami S, Kato S, Zeng J
USA, ASHRAE, 1998, in: the ASHRAE Transactions CD, proceedings of the 1998 ASHRAE Annual Meeting, held Toronto, Canada, June 1998, 8 pp, 7 figs, 4 tabs, refs.
The rising stream around a human body, attributable to metabolic heat can carry contaminants from the floor level to the human breathing system. Thus, the quality of the breathing air greatly depends on the concentration distribution in the lower part of the room and the characteristics of the local air motion around the body. In this paper, a modeled human body (computational thermal manikin) is placed in a room that is air-conditioned with a displacement ventilation system. Flow and temperature fields around the manikin are analysed by computational fluid dynamics (CFD) using a low-Reynolds-number type k-epsilon model. Based on the predicted flow field, the age of supply air and the residual lifetime of air in the room are also numerically calculated by CFD. Three cases of prediction of the concentration distribution are carried out with different locations of contaminant generation. The quality of the breathing air is assessed using the newly defined index, indicating the effective entrainment ratio of the lower region air to the breathing air. Results of the CFD analysis agree well with previous experimental data.
#NO 11880 Numerical simulation of laboratory fume hood airflow performance.
Kirkpatrick A T, Reither R
USA, ASHRAE, 1998, in: the ASHRAE Transactions CD, proceedings of the 1998 ASHRAE Annual Meeting, held Toronto, Canada, June 1998, 13 pp, 20 figs, 4 tabs, refs.
A three-dimensional computational fluid dynamics (CFD) analysis has been used to predict airflow patterns in laboratory fume hoods. The simulation includes bypass fume hood primary operational features including the top and bottom bypasses, front airfoils and rear-slotted baffles. All results were validated experimentally, and the simulation was found to adequately predict fume hood airflow patterns. The results indicate that fume hood flow patterns are highly dependent on inlet flow boundary conditions so that the computation must include the near field room airflow. Additionally, the study included the effects on the fume hood airflow of sash height changes, an operator positioned outside the fume hood, and equipment within the main fume hood chamber. It was shown that for conditions of a fully open sash height, a person in front of the fume hood, and an object inside the fume hood, the fume hood experiences a loss of containment of the flow.
#NO 11897 CFD simulations of the effects of HVAC-induced flows on smoke detector response.
Klote J H
USA, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc (ASHRAE), 1999, in: the ASHRAE Transactions CD, proceedings of the 1999 ASHRAE Winter Meeting, held Chicago, USA, January 1999, 15 pp, 8 figs, 3 tabs, refs.
Rapid activation of fire protection systems in response to a growing fire is one of the important factors required to provide for life safety and property protection, Airflow due to the heating, ventilating, and air-conditioning (HVAC) system can significantly modify the flow of smoke along the ceiling and must be taken into consideration when a particular system is designed. At present, the standards used to guide the design of fire protection systems contain very little quantitative information concerning the impact of airflow produced by HVAC systems. This paper describes the results of a project that used computational fluid dynamics (CFD) to simulate smoke movement in response to HVAC-induced airflows. The HVAC simulations included ceiling-mounted slot diffusers, wall-mounted slot diffusers, high sidewall diffusers, and ceiling diffusers from which airflow drops to the floor, in combination with rectangular and slot returns. The CFD model was modified to calculate smoke detector activation times throughout the fire-driven flow field.
#NO 11901 Measurements and computations of room airflow with displacement ventilation.
Yuan X, Chen Q, Glicksman L R, et al
USA, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc (ASHRAE), 1999, in: the ASHRAE Transactions CD, proceedings of the 1999 ASHRAE Winter Meeting, held Chicago, USA, January 1999, 13 pp, 9 figs, 4 tabs, refs.
This paper presents a set of detailed experimental data of room airflow with displacement ventilation. These data were obtained form a new environmental test facility. The measurements were conducted for three typical room configurations: a small office, a large office with partitions, and a classroom.
The distributions of air velocity, air velocity fluctuation, and air temperature were measured by omnidirectional hot-sphere anemometers, and contaminant concentrations were measured by tracer gas at 54 points in the rooms. Smoke was used to observe airflow. The data also include the wall surface temperature distribution, air supply parameters, and the age of air at several locations in the rooms.
A computational fluid dynamics (CFD) program with the Re-Normalization Group (RNG) k-epsilon model was also used to predict the indoor airflow. The agreement between the computed results and measured data of air temperature and velocity is good. However, some discrepancies exist in the computed and measured concentrations and velocity fluctuation.
#NO 11904 Models for prediction of temperature difference and ventilation effectiveness with displacement ventilation.
Yuan X, Chen Q, Glicksman L R
USA, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc (ASHRAE), 1999, in: the ASHRAE Transactions CD, proceedings of the 1999 ASHRAE Winter Meeting, held Chicago, USA, January 1999, 14 pp, 12 figs, 1 tab, refs.
Displacement ventilation may provide better indoor air quality than mixing ventilation. Proper design of displacement ventilation requires information concerning the air temperature difference between the head and foot level of a sedentary person and the ventilation effectiveness at the breathing level.
This paper presents models to predict the air temperature difference and the ventilation effectiveness, based on a database of 56 cases with displacement ventilation. The database was generated by using a validated CFD program and covers four different types of U.S. buildings: small offices, large offices with partitions, classrooms, and industrial workshops under different thermal and flow boundary conditions.
Both the maximum cooling load that can be removed by displacement ventilation and the ventilation effectiveness are shown to depend on the heat source type and ventilation rate in a room.
#NO 11905 A CFD study for cold air distribution systems.
Hu S-C, Barber J M, Chuah Y K
USA, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc (ASHRAE), 1999, in: the ASHRAE Transactions CD, proceedings of the 1999 ASHRAE Winter Meeting, held Chicago, USA, January 1999, 15 pp, 15 figs, 4 tabs, refs.
This paper presents a computational fluid dynamics (CFD) study of the indoor environment provided by a cold air distribution system using three alternative types of diffusers, i.e., a square multi-cone type, a wall-mounted nozzle type, and a ceiling nozzle type. The surface condensation risk on the diffusers is also discussed using the CFD results and a simple condensation model. An innovative proposal to prevent surface condensation and cold air dumping when using multi-cone circular diffusers with cold air is presented. The results show no significant variation in temperature distribution, airflow patterns, mean age of air, and mean carbon dioxide concentration at the occupied zone using a conventional chilled air system compared with a cold air distribution system. The ceiling nozzle type diffusers are suitable for cold air distribution systems. The wall-mounted nozzle type diffusers lose their jet momentum very fast because of reversed flow, and, therefore, they have a very limited range of cooling areas. The risk of surface condensation on the diffuser increases as the supply flow rate increases. The influence of the multi-cone diffuser lips on airflow diffusion is very significant.
#NO 11992 A resistance approach to analysis of natural ventilation airflow networks.
Aynsley R M
Journal of Wind Engineering and Industrial Aerodynamics, Nos 67&68, 1997, pp 711-719, 17 refs.
Many buildings in warm humid climates, particularly in tropical regions, rely for much of the time on natural ventilation from prevailing breezes for indoor thermal comfort. Much effort in recent years has been directed toward the use of computational fluid dynamics in evaluating airflow through buildings based on the solution of Navier-Stokes equations incorporating a turbulence model. This approach requires extensive data preparation and a reasonably powerful computer to yield results within an acceptable computation time for both numerical solution and simulated flow visualisation. Quantitative evaluation of natural ventilation through many low budget buildings in tropical regions is not evaluated due to a lack of suitable simple computer programs. What is needed are programs that can run on modest personal computers and can be used quickly to compare the natural ventilation performance of alternative building layouts for prevailing breeze directions during the preliminary design stage. Smaller buildings are often designed for cross ventilation by prevailing breezes with flow entering a windward opening and exhausting through a leeward opening. Such flow through a limited number of openings in series can be calculated very quickly on a personal computer using an orifice flow approach based on estimates of pressure differences and discharge coefficients of openings. When buildings have external ventilating openings in a number of rooms and flow branches within the building it is no longer possible to calculate directly the airflow in the various branches of the airflow network. Flow in such networks can be analysed iteratively on a personal computer by repetitive solution of simultaneous equation for flow rates in branches at nodes and conservation of mass flow through the network. The procedure described in the paper uses the Hardy Cross method of balancing flows at network nodes until errors throughout the network are acceptably small. Sources of data on wind pressure distributions over building walls and shielding influence of nearby buildings are provided together with a detailed description of a procedure for solving network airflows sufficient for readers to write their own computer code.
#NO 12038 Turbulent force flow in an airblast storage room.
Li C, Li Y
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 451-458, 13 figs, refs.
Forced air circulation in a storage room either with freezing/cooling or controlled atmosphere is usually turbulent because a high air change rate is generally required. The interaction between the turbulent air flow and the product layers plays an important role in the performance of the storage room. In this paper, a homogenous model based on the Brinkman-Forchheimer-extended Darcy equation for both fluid and porous layer is described, in association with the standard k-ú turbulence model. Turbulent forced air circulation in a room containing porous layers is studied numerically by this model. A second order control volume technique is used for the discretisation of the governing equations. SIMPLEC is adopted for the treatment of the pressure-velocity coupling. The predicted results are compared with available experimental results in the literature. The effects of two different stored products on the flow field in the product layers are investigated, and useful information is provided for the optimised design of a storage room.
#NO 12039 An application study of a 3D CFD code "TASC" for predicting transient thermal problems of indoor environments.
Yakeya N, Kitagawa K, Onishi J
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 459-466, 8 figs, 1 tab, refs.
In Japan, room air-conditioners with inverter equipment are widely used to create thermally more comfortable environments by using smaller amount of energy consumption. Recently new housings have been designed to reduce thermal heat load by improving insulation and ventilation performances. In order to design better
air-conditioners, we need to evaluate indoor thermal environments more correctly by considering not only air-conditioner controllability but also housing thermal performances.
This paper describes the applicability of our 3D transient CFD code "TASC" (Total Air-conditioning system simulation Code) to predict indoor thermal environments. TASC is designed to solve coupled heat transfer between airflow and indoor materials (wall envelopes and furniture), including convective heat transfer, radiation exchange among indoor materials, heat conduction through walls and heat source/sink like radiation panels. This code will be a powerful tool for many recent design problems as described above.
Some numerical examples are shown on the transient indoor thermal environments when a room is heated up by heat-pump type room air-conditioners. Effects of a computation time step on accuracy and computational efforts are investigated through numerical experiments. We confirmed TASC could compute stably at the time step of 30 seconds, that was approximately equal to the control interval computation time step are examined under the conditions where the inputs from air-conditioners (e.g. volume flow or jet temperature) change quickly. We also show that TASC is successfully applied to compare the heating-up ability of different types of heat-pumps.
#NO 12040 Non-passive particle dispersion in a displacement ventilated room - a numerical study.
Holmberg S, Li Y
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 467-473, 6 figs, 1 tab, refs.
Health effects caused by aerosol air pollutants in the breathing air is a main target for occupational health investigations. The effects of aerosol particles on health usually depend on the dose of particulate matter (PM) retained at various locations of the respiratory tract. Displacement ventilation has been proved to be an effective ventilation system for the removal of passive pollutants in many buildings. The question is often asked about the performance of non-passive particle removal in a room ventilated by displacement ventilation
In the present paper, non-passive particle dispersion behaviour in a room ventilated by displacement ventilation is investigated numerically. The dispersion of particles is predicted by a drift-flux model where a settling term is added to the concentration equation, and the body force term in the momentum equation is treated using the principle of a Boussinesq approximation, similar to that in a thermal-buoyancy-driven flow. Turbulence effects in the air stream are modelled with a standard k-e turbulence model. Some preliminary model validation work has been done by comparing numerically calculated results with those measured in an aerosol chamber. The main purpose of this study is to find out how particles of different sizes behave in a displacement ventilated room, and how different ventilation conditions change the exposure levels in the breathing zone.
#NO 12042 Influence of various factors on the predictions furnished by CFD in cross-ventilation simulations.
Freskos G O
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 483-490, 14 figs, refs.
The results of various numerical simulations of wind induced flows through large openings in a room are presented. The study is parametric on the sizes and relative positions of the openings and the wind direction. Various grid densities have been used. Grid independency for the presented results is demonstrated. Validation of the numerical approach is performed using measurements on a test cell with a single opening. The influence of the inflow wind profile is studied. It is shown that different flow patterns are induced within the dwelling when different profiles are assumed. In a two-zone room the main flow is deviated, due to the presence of the partition. The partition increases the obstruction of the flow entering the room. On the other hand better distribution of the flow within the room is obtained.
#NO 12043 CFD simulation of airflow and temperature field in room with convective heat source.
Lu W, Howarth A T, Tam C M, Jeary A P
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 491-498, 8 figs.
CFD simulation of airflow and temperature field in a heated room has been described in the paper. The tracking of pollutant particle movement is also presented here. The comparisons between computation and experiment show good and acceptable agreement. It can be concluded that CFD prediction can capture the main features of convective flow and provide satisfactory results. It can be seen that the thermal wall jet created by radiator greatly influences airflow pattern, temperature and pollutant particle distribution in the heated room. It can also be seen that the area close to the heat source takes high risk of air-borne contamination and imposes harmful effect to the occupant.
#NO 12044 Experiments on evaporative emissions in ventilated rooms.
Topp C, Nielsen P V, Heiselberg P, Sparks L E, Howard E M, Mason M
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 1, pp 499-505, 7 figs, 2 tabs, refs.
In many new buildings the indoor air quality is affected by emissions of volatile organic compounds (VOCs) from building materials. The emission process may be controlled either by diffusion inside the material or evaporation from the surface but it always involves mass transfer across the boundary layer at the surface-air-interface.
Experiments at different velocity levels were performed in a full-scale ventilated chamber to investigate the influence of local airflow on the evaporative emission from a surface. The experiments included velocity measurements in the flow over the surface and measurements of chamber air concentrations.
The results show that the emission, expressed in terms of the mass transfer coefficient, increases with velocity for fixed temperature, relative humidity and air exchange rate. This emphasises the importance of testing materials at the correct velocity and turbulence level in order to obtain the actual emission rate for a given product.
#NO 12054 Forecast of the properties of a cold vertical wall jet coming from a fan coil.
Marchal D, Vialle P J
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 49-54, 7 figs, 2 tabs, 2 refs.
The study of the flow in a room cooled by a fan-coil pointed out how the form of air flow and comfort could be influenced by the characteristics of the cold jet blowing out. It is based both on practical experiment and on numerical simulation using CFD code. Combining these methods allowed a large number of configurations to be studied, in association with different conditions for the appliance.
Using the results in combination enabled a relation to be established between the problem data, the device characteristics and the comfort conditions obtained. A simple rule was derived from this, which can be used in air-conditioning premises, in order to make the right choice or scaling of the air-conditioning appliance depending on its conditions of use.
#NO 12056 Spectral analysis of a turbulent warm plane air jet (using hot wire anemometry).
Amiri S, Sandberg M, Moshfegh B
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 63-70, 5 figs, 2 tabs, refs.
The thermal comfort of occupants is directly related to a number of parameters such as velocity of airflow, turbulence intensity and temperature distribution of room air. Thus the knowledge of the characteristics of the above-mentioned parameters is crucial for design engineers and knowledge of the turbulent properties is also important for improving the CFD codes. The present paper describes the experimental investigation of the flow field in a warm plane air jet under the influence of a heat sink in an insulated room. The purpose of this work is to establish how the turbulent fluctuations are distributed over different frequencies as a function of the Archimedes number. In addition to the local maximum velocity, the turbulence intensity and the turbulence length scale, the properties of velocity fluctuations in terms of autocorrelation function and the spectral density are investigated experimentally. The measurements are made at different distances from the supply for Reynolds numbers varying from 1514 to 8689 and for the corresponding Archimedes numbers between 2.69 104 and 4.22 1.
#NO 12058 A CFD simulation of the air flow pattern created by an Aaberg slot exhaust hood.
Ingham D B, Wen X, Foumeny E A
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 83-88, 4 figs, refs.
A Computational Fluid Dynamics technique is employed to predict the two dimensional turbulent air flow which is created by an Aaberg slot exhaust hood reinforced by a two-dimensional wall jet flow. The standard turbulent k-e model, control volume method and SIMPLE algorithm are used to simulate the airflow.
The numerical results for the effect of the Aaberg slot exhaust hood on the airflow pattern, shape of the capture region and the velocity distribution of the capture region in the system are presented.
#NO 12066 Combined simulation of airflow, radiation and moisture transport for heat release from human body.
Murakami S, Kato S, Zeng J
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 141-150, 11 figs, refs.
As the thermal sensation of humans depends directly on heat transfer characteristics between the body surface and the surrounding environment, it is very important to clarify the heat transfer characteristics of a human body surface in detail. This paper describes a combined numerical (NOTE I ) simulation system of airflow, thermal radiation and moisture transport based on a human thermos-physiological model used to examine the total (sensible + latent) heat transfer characteristics of a body surface. The human body is assumed to be naked (NOTE 2). flow, temperature and moisture fields are investigated with 3-dimensional Computational Fluid Dynamics (CFD). The CFD uses a low-Reynolds-number type k- e turbulence model, with the generalised curvilinear coordinate system (Boundary Fitted Coordinates) to represent the complicated shape of a human body. Thermal radiation is calculated by means of Gebhart's absorption factor method, and the view factors are obtained by the Monte Carlo method. Gagge's two-node model is included to simulate the metabolic heat production and the thermoregulatory control processes of a human body. However, heat loss due to respiration is specified in advance and is not included in the simulation directly. The prediction results agree well with those of an actual human body in a similar situation.
#NO 12069 A study on numerical prediction method of indoor thermal environment including human body.
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 167-172, 6 figs, 10 refs.
In the evaluation of thermal environment in a living quarter, thermal sensation index can be obtained from heat balance in occupants. In particular, however, in personal air-conditioning or in task-ambient air conditioning, it is necessary to perform more detailed prediction and evaluation of air flow and air temperature distribution around human bodies. For this purpose, indoor environment including bodies of the occupants must be estimated and evaluated, and experiments using thermal mannequin or human subjects and numerical prediction such as CFD are useful.
The primary aim of the present study was to establish a method to obtain air flow and air temperature distribution by numerical prediction method. Major features of the prediction method are as follows:
ò Air flow and air temperature distribution around bodies of the occupants is obtained by CFD. The k-epsilon two equation turbulence model commonly used as turbulence model is adopted. To cope with the complicated configuration of human bodies, generalised curvilinear coordinate system is used. As the calculation method, SIMPLE method and SIMPLER method are adopted. On continuity equation residual, calculation time, calculation stability, etc., the two methods are compared with each other.
Complicated configuration of human body in seated position is approximated by measurement of coordinates of a subject. The surface is approximated using triangles.
Calculation relating to giving and receiving of radiation heat and to heat balance inside the human body is not performed. To facilitate the calculation of heat radiation condition of the surrounding walls and human bodies, it is assumed that surface temperature is already known.
As a case study, thermal and air environment around occupants in a room is estimated when floor panel heating is installed in a small experimental room.
#NO 12076 Computer analysis of the air pollution in the Myceane Hall of the Archaeological Museum of Athens.
Papakonstantinou K A, Kiranoudis C T, Patrikiou F K, Markatos N C
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 219-226, 30 figs, 2 tabs, refs.
The paper presents a mathematical model, implemented in a general computer code, that can provide detailed information on velocity and temperature fields as well as pollutants concentrations prevailing in three-dimensional buildings of any geometrical complexity, for given external meteorological conditions. The model involves the partial differential equations governing flow and heat transfer in large enclosures containing heat sources. Turbulent flow is simulated and buoyancy effects are taken into account. The model allows for such practical aspects of the problems under consideration as blockages, internal heat and contaminant loads, external weather conditions, the presence of people, etc. The model is used to assess the environmental conditions inside the main Hall of the National Archaeological Museum of Athens (Myceane Hall) with external conditions corresponding to Ministry of Environment spring-autumn, summer and winter days.
#NO 12083 Assessment of the systemic approach using radioactive tracers and CFD.
Berne P, Blet V
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 275-280, 9 figs, 1 tab, refs.
An application of the systemic approach is presented for the study of the ventilation of a room in an industrial facility. First, a series of tracer gas experiments was made with a radioactive tracer. Analysis of the Residence Time Distribution (RTD) curves, supported by some CFD, then enabled to build a simple zonal model for the description and quantification of the observed air flow patterns. This model was able to reproduce the experimental RTDs inside the room as well as at the exhaust.
#NO 12084 The influence of furniture on air velocity in a room - an isothermal case.
Nielsen J R, Nielsen P V, Svidt K
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 281-286, 5 figs, refs.
Using isothermal full-scale experiments and 3-dimensional CFD simulations it is investigated how normal office furniture influences the air movements in a mixing ventilated room.
Two different types of inlets are used in the experiments and a set-up with normal office furniture is made. The set-up is simulated with one of the inlets where a volume resistance represents the furniture.
The jet under the ceiling is investigated and it is found that the normal office furniture does not influence the air movements in the upper part of the room. In the lower part of the room the maximum velocity in the occupied zone is studied. This velocity is reduced in the furnished room compared to the empty room and the reduction increases as the total length of the furniture volume in the main flow direction increases.
#NO 12088 Study on airflow characteristics in and around building induced by cross ventilation using wind tunnel experiment and CFD simulation.
Iino Y, Kurabuchi T, Kobayashi N, Arashiguchi A
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 307-314, 14 figs, 3 tabs, 2 refs.
In the present study, airflow were evaluated in and around S types of building models induced by cross ventilation in case opening conditions and approaching flow angles were different. Both techniques of wind tunnel experiment and numerical simulation was employed, and the problems and advantages of these methods were discussed The airflow characteristics were discussed from the following 4 viewpoints: wind pressure coefficient distribution, air velocity distribution, ventilation rate, and main airflow path. As a result, X was found as follows: I) When opening was positioned approximately at the centre of windward or leeward walls and approaching flow angle was 0_, the difference of wind pressure coefficients on the walls was within 0.2 even when the opening conditions were different. Thus, overall flow around the building was not changed within the range of the opening conditions under the present study, and the airflow passing through the windward opening ran downward. 2) In case approaching flow angle was different, wind pressure coefficient was decreased with the increase of the approaching flow angle. The airflow passing along wall surface was changed in transverse direction. Air velocity was also increased, and ventilation rate was decreased. When the approaching flow angle exceeded 45_, flow resistance at the windward opening increased. In case the airflow entered without running perpendicularly to windward wall, the airflow ran straight after entering the windward opening.
#NO 12092 Comfort problems and energy losses at shop entrances - field investigations and numerical simulations.
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 335-342, 13 figs, 2 tabs, 5 refs.
In order to give some guidance for the optimisation of shop entrances regarding comfort and energy savings, a project was launched by the City of Zurich. The project covers field investigations in 12 shops with different entrance types, and analytical and numerical investigations (CFD) for complementary results.
The emphasis of this work was on the interaction between the situation at the entrance for different technical local solutions with other factors of importance like building ventilation, building tightness and combination with other entrances. As a main result for the practitioner, a lot of recommendations can be drawn from these investigations and will also serve as the basis for governmental guidelines.
#NO 12103 Comparison of zonal and CFD modelling of natural ventilation in a thermally stratified building.
Li Y, Delsante A, Symons J G, Chen L
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 415-422, 8 figs, 1 tab, refs.
This paper compares two well-known modelling approaches for natural ventilation in a multi-zone building with thermal stratification and large openings. The zonal approach in this paper assumes a fully mixed condition in each zone, and considers the bi-directional flows through all large openings. The zonal model is integrated into a thermal analysis code to provide simultaneous prediction of both ventilation flow rates and air temperatures in each zone. The CFD approach uses a finite-volume method for turbulent flows. A simple pressure boundary condition is used at all external openings in CFD.
This is reasonable agreement between the overall ventilation flow rates and average zonal air temperatures predicted by the two modelling approaches. It is found that the multi-zone approach predicts a lower neutral level for the building than predicted by CFD. This might be mainly due to the fact that thermal stratification is neglected in the present multi-zone model. It is explained by a new emptying air-filling box model for natural ventilation of single-zone buildings.
#NO 12113 CFD simulation of air velocity distribution in occupied livestock buildings.
Svidt K, Zhang G, Bjerg B
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 491-496, 8 figs, 1 tab, refs.
In modern livestock buildings the design of the ventilation systems is important in order to obtain good air distribution. The use of Computational Fluid Dynamics for predicting the air flow and air quality makes it possible the include the effect of room geometry, equipment and occupants in the design of ventilation systems. However, it is not appropriate to include the detailed geometry of a large group of lying or standing animals affecting the air flow in the building. It is necessary to have relatively simple models of the animals, which are easier to implement in the computer models. In this study, laboratory measurements in a ventilated test room with 'pig simulators' are compared with CFD-simulations.
#NO 12115 Contamination control by unidirectional flow ventilation in a refuse disposal facility.
Nishioka T, Moteki M, Miyagi H, et al
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 503-510, 15 figs, 6 tabs, 6 refs.
A series of CFD and model experiments were carried out in order to find the most effective ventilation system in a separated refuse disposal facility. The ventilation system needed in the facility protects the working space from dust and odours generated by handling refuse. The desired ventilation system is to introduce the outdoor air from one side of the working area and to exhaust the contaminated air through the opposite side of the refuse stock yard, so-called the unidirectional airflow ventilation.
Both of these experiments indicated that an air curtain system and a wind shield screen which were added to the basic system could improve the ventilation efficiency. System performance was measured at a newly built facility. The measurements proved that this system needs only an additional 3% of total flow rate to effectively protect the working space from contamination.
#NO 12121 CFD modelling and experimental validation of air flow between spaces.
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 547-554, 24 figs, 4 tabs, refs.
Studies of airflow between two adjacent spaces of building were carried out using CFD simulation. The results of CFD simulation were validated against test data set obtained from full-scale experimental tests. The agreement and discrepancy between the prediction and measurement results were discussed. Further numerical exercises were carried out to study under the conditions that were difficult to achieve by experiments and the results obtained were supplemented to the understanding of convective heat transfer between adjacent rooms.
#NO 12123 Numerical simulation of natural ventilation of a bedroom in a warm climate.
Chiang C M, Chou P C, Lai C M, Wang W A, Chao N T
Sweden, Stockholm, KTH Building Services Engineering, 1998, proceedings of Roomvent 98: 6th International Conference on Air Distribution in Rooms, held June 14-17 1998 in Stockholm, Sweden, edited by Elisabeth Mundt and Tor-Goran Malmstrom, Volume 2, pp 563-567, 3 figs, 1 tab, 14 refs.
This study utilizes the two-chamber model to simulate naturally ventilated airflow through a window opening in a common-type bedroom in Taiwan. Standard k-epsilon turbulence model is implemented to account for such a natural convection flow pattern. The driving force in this space is mainly the heat flux generated by occupant's skin. The result shows that under normal operation indoor, carbon dioxide (indoor air contaminant for IAQ) is less than 1000 ppm. ASHRAE Standard recommended.
#NO 12141 Indoor air quality and infection problems in operating theatres.
Tinker J A, Roberts D
EPIC '98, Volume 1, pp 285-290, 7 figs, 1 tab, refs.
There is a risk that patients can catch a range of infections during any stay in a hospital. A recent UK Office of Health Economics report highlighted that 10% of in-patients contract a hospital acquired infection from one source or another. There are many sources of infection but one specific route is via the surgical wound during an operation. Bacteria can be carried from the source to the wound site by currents of air causing post-operative infection at a later date. Even though clean air is delivered from the theatre ventilation system it is often contaminated with microorganisms such as those originating from the skin of the operating staff and the patient themselves. At the start of the project, a physical model of a typical theatre with a laminar-flow air inlet in the ceiling was built and used to collect air velocity and temperature data. The experimental data was then compared to results simulated by a Computational Fluid Dynamics (CFD) model. Once confidence had been gained in the simulation process, an actual theatre was computationally modelled. The aim of the research was to test various ventilation scenarios to observe how room parameters affect the air-flow paths in theatres. Once this had been completed, ways to re-direct contaminated air away from the operating table and other critical areas of the theatre to reduce post-operative infection rates were examined. The research showed that CFD is a suitable tool for visualising air-flow patterns in operating theatres and the results highlighted improvements that could be made to the design of new theatres and modifications which could be made to existing ones.
#NO 12157 Greenhouse natural ventilation by buoyancy forces.
Haxaire R, Roy J C, Boulard T, Lamrani M A, Jaffrin A
EPIC '98, Volume 2, pp 522-527, 10 figs, refs.
Convective transfers mainly determine the energy and mass balances which regulate the micro-climate inside a greenhouse. Air flow and temperature patterns induced by natural ventilation through greenhouse roof openings are only considered here. Flow visualisations were performed on a half scale test cell simulating the absorption of solar radiation at the floor surface of a single-span greenhouse. Temperature and air flow patterns were observed in a steady regime i) with a single sided roof vent and ii) with two symmetrical ones. An air inflow always take place at the lower part of the openings and feed a single convective loop which follows the walls of the greenhouse before escaping through the upper part of the vents. These natural convective patterns were numerically simulated by models of a Computational Fluid Dynamic code (CFD 2000T""). It was found that the convective cell, velocity values and the temperature profiles were generally in good agreement with the experimental results.
#NO 12158 Measurement and CFD modelling of airflow through stairwells.
Peppes A A, Santamouris M, Asimakopoulos D N
EPIC '98, Volume 2, pp 528-533, 3 figs, 1 tab, 10 refs.
The present paper deals with one of the most important mechanisms of inter-zone mass and energy transfer, namely the buoyancy-driven flows through stairwells that connect the floors of buildings. To further investigate these phenomena, experimental as well as theoretical studies have been carried out. A series of experiments have been performed in order to study the airflow through a typical stairwell that connects the two individual zones of a two-storey house. Airflow rates between the two zones were measured using a single tracer gas decay technique. The analysis of results provided relations which can predict the volumetric flow rate as a function of the interzonal average temperature difference between the two floors. Simulations of these experiments were carried out, using validated CFD algorithms. Airflow rates estimated by these simulations showed good agreement with experimental values despite the difficulties related to the applicability of CFD to model the buoyancy driven flows. Finally the paper discusses the airflow patterns through the stairwell.
#NO 12173 Numerical simulation of the air cooling by natural ventilation inside the "Maison ronde" of Botta.
Raymond F, Marenne C, Groleau D
EPIC '98, Volume 3, pp 807-812, 6 figs, refs.
The present study applies the N3S CFD code to the air cooling simulation on an "architectural reference object", namely the "Maison Ronde" of Mario Botta. The summer night situation is examined when natural ventilation creates indoor air motion and cools the building structure. The transient behaviour of the walls is represented by a thermal model coupled with the CFD code. The simulation evaluates the unsteady temperatures of the outdoor and indoor air flow together with those of the wall surfaces. Obtained results are analysed according to the architectural specificities of the building in order to identify the key components that play a major role in the efficiency of the passive cooling process.
#NO 12184 Wind driven and thermal air flow patterns at courtyards.
Alvarez S, Sanchez F, Zambonino F J, Coronal J F, Perez-Lombard L
EPIC '98, Volume 3, pp 997-1002, 7 figs, 4 refs.
Air flow patterns and temperature distribution within courtyard have been studied. Wind and thermally driven flow have been thoroughly analysed as a function of the depth to width ratio (Aspect ratio) as main parameter. CFD results show a quite similar behaviour regarding to velocity profiles for all the cases, though temperature profiles are highly affected by dimensions of the courtyard. The whole study can be extrapolated to urban canyons, where air flow patterns are quite similar as a result of having the same geometry.
#NO 12212 An intermediate model to predict thermal comfort and air quality in a building.
Musy M, Wurtz E, Nataf J-M
UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 1, pp 685-690.
In this paper, a zonal model used to predict the air movement, temperature distribution and air quality in a room is presented. It is based on a rough partitioning of the room: it is an intermediate approach between one-node models (that consider an homogeneous temperature in each room, and, for that reason, do not permit to restrict the thermal comfort in a room) and CFD models (that require great amount of simulation time). Where plumes, jets or thermal layers occur, air flow is described by empirical laws. In low velocity domains, flow rates are calculated in respect to the pressure distribution. This air flow model is coupled with a building envelope model including the calculation of radiant and conductive exchanges. The complete model is implemented in an object oriented environment, SPARK, in which modelling a room consists in connecting the different pre-design elementary models. Hence, the way of modelling is very modular, so that the zonal model can now be applied to a very large field of configurations. The strict syntax of SPARK permits having the simulation automatically generated. Now, imagining the creation of a very flexible tool that allows to represent a whole building is realistic. Results of simulations in a 3D-room will be given and it will show that this model yields rather accurate results even with a rough partitioning.
#NO 12234 Experimental and numerical investigation on temperature and air velocity distribution in a room equipped with split-system air conditioner.
De Carli M, Peron F, Zecchin R
UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 2, pp 42-47.
Spilt-system air conditioning is increasingly used both for residential and commercial applications, owing to its low cost and installation ease. The indoor split-system unit is commonly of the wall-mounted type and, due to its dimensions and position, very often it gives rise to appreciable air velocities and temperature gradients in the occupied zone of the room. This work reports and discusses some experimental data collected in a test room with wall-mounted indoor unit, under different operating conditions. A CFD numerical model has been developed and assessed on the basis of the experimental data; the model can be applied to investigate the influence of different parameters such as air flow and velocity, inlet air temperature, position of the unit, direction of air flow etc. From the results of parametric analyses some conclusions can be drawn, with reference to comfort conditions, useful to improve the design and construction of this type of air conditioning equipment and to develop more efficient installation criteria.
#NO 12256 Hybrid air conditioning based on natural and mechanical ventilation in office buildings.
Kato S, Murakami S, Chang H, Chikamoto T, Kim T
UK, Garston, BRE, 1999, proceedings of Indoor Air 99, the 8th International Conference on Indoor Air Quality and Climate, and the Air Infiltration and Ventilation Centre (AIVC) 20th Annual Conference, held Edinburgh, Scotland, 8-13 August 1999, Volume 2, pp 404-409.
The performance of a hybrid air-conditioning system which utilises wind-induced cross ventilation is investigated. The characteristics of flow and temperature fields are examined using CFD simulation under various conditions of inflowing outdoor air i.e. air temperature, air exchange rate and width of the opening for cross ventilation. In this simulation, the room air controlling system (VAV system) which is used to keep the task zone at a target temperature is reproduced through changing the supply airflow rate of the air-conditioning system. Cooling load of the mechanical air-conditioning system is analysed based on the results of these simulations. When the inflaming outdoor air flows in the lower part of the room, it does not mix with the room air and cools the task zone well.
#NO 12325 Modelling of air flow through a slatted floor by CFD.
Svidt K, Bjerg B, Morsing S, Zhang G
Denmark, Aalborg University, Dept of Building Technology and Structural Engineering, Indoor Environmental Engineering, Paper No 89, December 1998, 7 pp, 8 figs,
In this paper two different CFD-approaches are investigated to model the airflow through a slatted floor. Experiments are carried out in a full-scale test room. The computer simulations are carried out with the CFD-code FLOVENT, which solves the time-averaged Navier-Stokes equations by use of the k-epsilon turbulence model. The simulations are two-dimensional and the slatted floor has been modelled in two different ways: A resistance volume and a resistance plane. The resistance volume has been defined as a volume covering the outer dimensions of the slatted floor i.e. 1.17m wide, 5.00m long and 0.02m thick. The resistance plane is defined in the same way except that it has no thickness. In both cases two parameters are used to specify the characteristics of the slatted floor: a free area ratio and a resistance coefficient. At an opening area of 39% the predicted airflow rate is in the range of 6 to 12% less than measured. At lower opening area ratios there is an increasing difference between the two models. The differences are due to different airflow patterns resulting from the models.
#NO 12383 Room airflow studies using sonic anemometry.
Wasiolek P T, Whicker J J, Gong H, Rodgers J C
Denmark, Indoor Air, No 9, 1999, pp 125-133, 9 figs, refs.
To ensure prompt response by real-time air monitors to an accidental release of toxic aerosols in a workplace, safety professionals should understand airflow patterns. This under standing can be achieved with validated computational fluid dynamics (CFD) computer simulations, or with experimental techniques, such as measurements with smoke, neutrally buoyant markers, trace gases, or trace aerosols particles. As a supplementary technique to quantify airflows, the use of a state of the art, three dimensional sonic anemometer was explored. This instrument allows for the precise measurements of the air velocity vector components in the range of a few centimetres per second, which is common in many indoor work environments. Measurements of air velocities and directions at selected locations were made for the purpose of providing data for characterising fundamental aspects of indoor air movement in two ventilated rooms and for comparison to CFD model predictions. One room was a mock-up of a plutonium workroom, and the other was an actual functioning plutonium workroom. In the mock-up room, air velocity vector components were measured at 19 locations at three heights (60, 120 and 180cm) with average velocities varying from 1.4cm s -1 to 9.7 cm s-1. there were complex flow patterns observed with turbulence intensities from 39% up to 108%. In the plutonium workroom, measurements were made at the breathing zone height, recording average velocities ranging from 9.9 cm s -1, to 35.5 cm s-1 with turbulence intensities from 33% to 108%.
#NO 12406 Roomvent '98 6th international conference on air distribution in rooms. Volume 1.
Mundt E, Malmstroem T-G (eds.)
Sweden, Stockholm, KTH, 1998, proceedings of a conference held Stockholm, Sweden, June 14-17, 1998, 536 pp.
Volume 1 of the conference contains papers from the following sessions: applications, residences; flow systems, displacement ventilation; calculations and measurements, CFD and related topics; IAQ and comfort, air quality; applications, offices and hospitals; flow systems, displacement and local ventilation; calculations and measurements, scale and computer models; IAQ and comfort, particles and cleanrooms; applications, industries; flow systems, plumes; calculations and measurements, CFD, applications; IAQ and comfort, emission and sorption.
LL 20: Computational fluid dynamics for analysis of room air flow
Computational fluid dynamics for analysis of room air flow