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Flow through Large Openings
#NO 1563 A computer algorithm for predicting infiltration and interroom airflows
AUTHOR Walton G N.
BIBINF ASHRAE Trans, 1984, Vol 90, Part 1B, p601-610, 5 fig, 12 ref. #DATE 00:00:1984 in English
ABSTRACT This report discusses the extension of an infiltration predicting technique to the prediction of interroom air movements. The airflow through openings is computed from the ASHRAE crack method together with a mass balance in each room. Simultaneous solution of the mass balances in all rooms having both large and small openings is accomplished by a slightly modified Newton method. A simple theory for two-way flow through large openings is developed from consideration of density differences caused by different temperatures in adjoining rooms. The technique is verified by comparison to published experimental results. The results indicate that the simple model provides reasonable results for complex two-way flows through openings. The model is as accurate as the available data, that is, about plus or minus 20%. The airflow algorithm allows infiltration and forced airflows to interact with the doorway flows to provide a more general simulation capability.
#NO 2980 A resistance approach to estimating airflow through buildings with large openings due to wind.
AUTHOR Aynsley R M
BIBINF Preprint: Ashrae transactions, Vol 94, Pt 2, 1988, 9 pp, 19 refs. #DATE 00:00:1988 in English
ABSTRACT Natural airflow due to wind has been utilized since antiquity to provide both fresh air and indoor summer thermal comfort in warm humid climates. Lack of suitable existing wind pressure data has resulted in the use of wind tunnel data from studies of solid models. This practice results in the elimination of the velocity pressure component at inlet openings and a corresponding source of error in estimates of flow. Another source of error is the effect of inclined wind incidence on discharge through inlet openings. Studies of these effects are cited. Current numerical methods for estimating the airflow rates through buildings with large openings are based on orifice flow theory. These methods do not account for internal flow losses due to obstruction of flow by furniture or surface friction. Friction losses can be significant in long corridors as local velocities often exceed 200 ft/min (1 m/s). Resistance-based flow theory, currently used for estimating mine ventilation, is suggested as a means of including losses due to orifices, obstruction by furniture, bends, and surface friction in a single simple flow equation. Flow conditions discussed include estimates of airflow through sequential orifices between inlet and outlet openings. Methods are provided for determining airway resistances from existing dynamic loss and discharge coefficient data. Calculaton of the equivalent resistance of combined parallel airway branches and resistance associated with friction losses along surfaces of airways are discussed. Many flows through buildings take the form of complex interconnected branching network flows. Application of the resistance approach to the iterative solution of complex network flows is described and areas in need of further research are identified.
#NO 3477 Some aspects of gravity driven air flow through large apertures in buildings.
AUTHOR Van der maas J, Roulet C A, Hertig J A
BIBINF ASHRAE Transactions, 1989, Vol.95, Pt.2, 11 figs, 26 refs. #DATE 00:00:1989 in English
ABSTRACT The authors compare the available algorithms for gravity driven air flows through large openings with the requirements for multi-zone air infiltration modelling. Two extreme situations are addressed by the literature : 1)providing a time-independent air flow formulated in terms of the constant temperature difference between a zone and the outside, 2) consideration of adiabatic walls providing a transient flow with the cold outside air filling the zone space completely so that the air flow comes to a halt.
#NO 3521 Some aspects of gravity driven air flow through large apertures in buildings.
AUTHOR Van der Maas J, Roulet C A, Hertig J A
BIBINF Preprint, ASHRAE Trans, Vol 95, Pt 2, 1989, 11pp, 11 figs, 26 refs. #DATE 00:00:1989 in English
ABSTRACT The authors compare the available algorithms for gravity-driven airflows through large openings with the requirements for multizone air infiltration modeling. It appears that two extreme situations are addressed in the literature. The first, providing a time-independent airflow, is formulated in terms of the constant temperature difference between a zone and the outside. The other, considering adiabatic walls, provides a transient flow, with the cold outside air filling the zone space completely so that the airflow comes to a halt. As an intermediate situation we present an algorithm that takes into account the heat transfer with the walls. The coupled equations for airflow and heat transfer are solved for the inside air temperature. The latter being lower than the wall temperature and always higher than the outside temperature, the proposed model predicts an air and heat flow rate, which is intermediate in magnitude with respect to the extreme situations addressed in the literature. For constant wall temperatures, the model predicts that the air flow rate is lower for zones with smaller heat exchanging wall surface area. Coupled to a thermal model for the wall surface temperature, the algorithm predicts the air flow to decrease with time. Experiments were performed on a full scale test room with a window to the outside. During cold windless nights, velocity profiles were measured in the window plane, and the temperatures of the inside air and the walls were recorded with time. Good agreement with the model is obtained, considering only the fraction of the wall surface area active in the heat transfer process, and measuring the inside air temperature in the outstreaming air. Effects which have been observed and should be included in the algorithm for detailed multizone air infiltration modeling are wind effects, the time development of temperature stratification, and the initial transient, whose time constant depends on furniture in the zone.
#NO 3587 The COMIS Infiltration Model.
AUTHOR Feustel H E, Grosso M, Phaff J C, Allard F, Herrlin M, Utsumi Y, Dorer V B, Liu Mingsheng, Yoshino H
BIBINF in:UK, AIVC, 10th AIVC Conference, held at Espoo, Finland, 25-28 September 1989, Volume 2, February 1990, pp233-251 16 refs. #DATE 00:02:1990 in English
ABSTRACT The COMIS workshop (Conjunction of Multizone Infiltration Specialists), using a multi-national team, is planning to develop a reliable, smooth running multizone infiltration model on a modular base. This model not only takes crack flow into account but also covers flow through large openings, single-sided ventilation, cross ventilation and HVAC-systems. The model contains a large number of modules which are peripheral to a steering program. COMIS can also be used as a basis for future expansion in order to increase the ability to simulate buildings. Small task groups were formed to work on particular problems in developing the modules. Each COMIS team member works on several task groups.
#NO 3921 Fundamentals of the multizone air flow model - COMIS.
AUTHOR Allard F, Dorer V B, Feustel H E, et al
BIBINF UK, AIVC Technical Note 29, May 1990, 115 pp, 38 figs, 8 tabs, 91 refs. #DATE 00:05:1990 in English
ABSTRACT The COMIS workshop (Conjunction of Multizone Infiltration Specialists) was a joint research effort to develop a multizone infiltration model. This workshop (October 1988 - September 1989) was hosted by the Energy Performance of Buildings Group at Lawrence Berkeley Laboratory's Applied Science Division. The task of the workshop was to develop a detailed multizone infiltration program taking crack flow, HVAC-systems, single-sided ventilation and transport mechanism through large openings into account. This work was accomplished not by investigating into numerical description of physical phenomena but by reviewing the literature for the best suitable algorithm. The numerical description of physical phenomena is clearly a task of IEA-Annex XX "Air Flow Patterns in Buildings", which will be finished in September 1991. Multigas tracer measurements and wind tunnel data will be used to check the model. The agenda integrated all participants' contributions into a single model containing a large library of modules. The user-friendly program is aimed at researchers and building professionals.
#NO 4638 A multi-tracer gas system with variable interval sampling.
AUTHOR Riffat S B
BIBINF UK, Loughborough University of Technology, [1990], 2pp, 1 fig, refs. #DATE 00:00:1990 in English
ABSTRACT The concentration decay technique is widely used for measurement of air flow in buildings. This technique involves the injection of a known amount of tracer gas into a building followed by a period of mixing toestablish a uniform tracer concentration. The decay of tracer gas is then measured. In the case of air flow measurements made between two zones, the variation of tracer gas concentration with time depends on the size of the doorway and on the temperature difference between the two zones. Recent work has indicated that the accuracy of air flow estimation is strongly influenced by the number of samples taken during the transient period. This is the first 2-10 minutes of the experiment when then the concentration of tracer gas is varying most rapidly. Tracer gas decay systems which are currently available do not have sufficient flexibility to provide accurate measurements of air movement through large openings as their sampling/analysis times are too long (typically 3-4 minutes) to allow a sufficient number of measurements to be taken during the transient period. Clearly there is a need to develop a new system which allows a large number of tracer gas samplesto be taken at intervals as short as 5 seconds during the transientperiod and a small number of samples at intervals greater than 5 seconds during the dominant period.
#NO 4697 Experimental study of heat and mass transfer across large vertical openings.
Etude experimentale des transferts de masse et de chaleur a travers les grandes ouvertures verticales.
AUTHOR Limam K, Inard C, Allard F
BIBINF "Ventilation et Renouvellement d'Air dans les Batiments", AIVC/AFME Workshop held 18-22 March, 1991, Lyon, France, 10pp, 12 figs, 7 refs. #DATE 00:03:1991 in French
ABSTRACT Large openings such as doorways or windows are privileged places through which a large amount of air, heat and pollutant species flows. In order to predict air flow rates through these systems, a physical model which can be integrated to multizone air flow models is proposed. This model is based on the empiric determination of discharge coefficients. Thedischarge coefficients may have different definition depending on thehypothesis of the selected model. In order to answer that indetermination we first present the experimental facility built in a thermally controlled environment set up in CETHIL, to discuss afterwards the first results obtained.
#NO 4998 A review of algorithms for airflow through large openings.
AUTHOR Riffat S B
BIBINF UK, Loughborough University of Technology, Department of Civil Engineering, 1991, 22pp, 55 refs. #DATE 00:00:1991 in English
ABSTRACT The present paper reviews results of research into airflow through large internal and external openings. A brief description of experimental work and algorithms developed by various researchers is presented. The paper also outlines requirements to improve existing airflow algorithms.
#NO 5167 Air flows through large openings: an overview of existing approaches.
AUTHOR Vandaele L, Wouters P
BIBINF Belgium, Belgian Building Research Institute, May 1989, (IEA Energy Conservation in Buildings and Community Systems, Annex XX: Air Flow Patterns within Buildings), 18pp, 11 figs, 45 refs. #DATE 00:05:1989 in English
ABSTRACT Air flow mechanisms are well known as far as these air flows are driven by steady wind pressure and by temperature difference. Most numerical models use of flow characterisation. Only few models take into account the special effects of air flow through large openings, for internal openings as well as - and even fewer - for external openings.
#NO 5246 Modelling of large openings.
AUTHOR Pelletret R, Liebecq G, Allard F, van der Maas J, Haghighat F
BIBINF UK, AIVC 12th Conference, "Air Movement and Ventilation Control within Buildings", held 24-27 September 1991, Ottawa, Canada, proceedings published September 1991, Volume 1, pp 99-110. #DATE 00:09:1991 in English
ABSTRACT The subtask 2 of Annex XX (Optimization of Air Flow Patterns Within Buildings) involved a research project called "Air Flows Through Large Openings In Buildings". The scope of this project was to test the range of validity of available algorithms, andwhere possible to develop new ones. This paper focuses on the new interzonal airflow studies which have been carried out inthis frame. The research was based on three test rooms (respectively at the University of Liege, at INSA Lyon and at CSTB Sophia Antipolis) and mainly focused on natural convection; the aim was to improve the knowledge and the numerical prediction of heat and mass transfer through doorways. This goal was achieved through a joint research effort which was based on the comparison of our experimental results. Moreover, these experimental results have been used to validate a C.F.D (Computational Fluid Dynamics) model developed at Concordia University.
#NO 5719 Air flow through large openings.
AUTHOR Allard F, Utsami Y
BIBINF COMIS: Rapport Final, Contrat INSA/AFME 88-04-0038, 1989, 31p. #DATE 00:00:1989 in French Energy and Buildings Vol 18 pp133-145 #DATE 00:11:1991 inEnglish.
ABSTRACT Study of air flow across large openings in a building. The different physical phenomena engendered by these air movements are described, and existing solutions for representing the behaviour of these openings in air flow models. A numerical model is presented aimed at describing the phenomenon for a large vertical opening based on the Bernoulli equation.
#NO 5720 Thermal and air flow between rooms through large openings.
Transferts thermo-aerauliques entre pieces a travers les grandes ouvertures.
AUTHOR Khodr-Mneimne H
BIBINF Universite; Nice, 1990 10, 122p (+ Annexes) These. #DATE 00:10: 1990 in French
ABSTRACT Development of a multizone thermal model incorporating air flow phenomena around large internal openings in a building. Experimental validation of the model in the DESYS test cell. Analysis of the results with natural convection and mixed convection. Analysis of its performance by comparison with another thermal and air flow model.
#NO 5721 Air flow through large openings: experimental study of the discharge coefficient.
AUTHOR Allard F, Bonnotte D, Liman K
BIBINF Intervention au IEA Annex 20 Expert Meeting, Oslo, 10-13 June 1990, 19p. #DATE 10:06:1990 in French
ABSTRACT Analysis of air transfer between different zones of a building through large openings. Presentation of a simulation conducted on the test cell MINIBAT, aimed at better understanding these phenomena.
#NO 5855 Simulation of airflow through large openings in buildings.
AUTHOR Schaelin A, Maas J van der, Moser A
BIBINF USA, Ashrae Transactions, Vol 98, No 2, 1992, 10pp, 12 figs, 1 tab, refs. #DATE 00:00:1992 in English
ABSTRACT The coupling of indoor airflow to the outdoor flow through large openings in buildings that allow bidirectional flow is of considerable interest for many applications. In this work, the airflow pattern has been calculated for situations in which warm air leaves a room through the upper part of the large opening and rises as a thermal plume, with and without interaction with wind. Both two- and three-dimensional CFD simulations of the velocity and temperature fields in a thermal plume agree well with the analytical models. These, in turn, are wellsupported by experiments. For single-sided ventilation without wind, the velocity profiles in the doorway predicted by CFD have features that are well known from experimental data but cannot be found in analytical models. With a normal incident steady wind on the opening, an increase of the convective flow is found in the three-dimensional case but not in the two-dimensional case. At the boundaries of the computation domain corresponding to the free atmosphere, a zero pressure gradient boundary condition was found to be sufficient to avoid unrealistic recirculation. By proper placement of these boundaries around a heated room, good numerical results can be achieved for a computation domain extended only a little to the outside of the room.
#NO 5963 A new method for linking results of detailed air flow pattern calculation with multizone models.
AUTHOR Schaelin A, Dorer V, Maas J van der, Moser A
BIBINF UK, Air Infiltration and Ventilation Centre, 13th AIVC Conference, proceedings, held Hotel Plaza Concorde, Nice, France, 15-18 September 1992. #DATE 15:09:1992 in English
ABSTRACT Multi-zone models are a common tool for calculating air and contaminant exchange within rooms of a building and between building and outdoors. Usually a whole room is then modelled by one calculation node with the assumption of homogeneously mixed conditions within this room whereas in real cases temperature and contaminant concentrations vary in space. The exchange to the neighbouring nodes via the flow paths is then a function of the local values of these variables. Detailed knowledge can be obtained from the solution of the transport equations for the airflow pattern within the room at the expense of far higher computation cost. This work shows a new approach called "method of detailed node values" to include results from detailed calculations in multi-zone models to give a better description of the real cases. Parameter transfer between a multi-zone program and a detailed air flow simulation program is discussed for different flow paths of practical importance. The method is demonstrated in an example case with air in/exfiltration, ventilation and contaminant propagation, and discussed in a second example with large openings. This new method promises to improve the multizone model predictions with few additional CFD computations.
#NO 5964 Modelling fluctuating airflow through large openings.
AUTHOR Haghighat F, Rao J, Riberon J
BIBINF UK, Air Infiltration and Ventilation Centre, 13th AIVC Conference, proceedings, held Hotel Plaza Concorde, Nice, France, 15-18 September 1992. #DATE 15:09:1992 in English
ABSTRACT Fluctuating airflow through buildings is caused by temporal and spatial variations of wind-induced pressures around building envelopes, and include pulsating airflow and eddy penetrations. Two approaches using a multi-zone pulsating airflow model are introduced in this paper to study the eddy penetration and multi-way airflow through large openings. In the first approach, the eddy flow is considered to be caused by imperfect correlations among pressures at different points of an opening. The concept of aerodynamic admittance functions is employed to modify the wind pressure spectra to represent the net effect of fluctuating pressures over the area of the opening. The other approach considers a large opening as composed of a number of smaller airflow paths, each permitting only pulsating airflow. Theoretical solutions are compared with field experimental results from the BOUIN test-house at CSTB, France.
#NO 6104 Air flow through large openings in buildings.
AUTHOR van der Maas J (editor)
BIBINF Switzerland, Ecole Polytechnique Federale de Lausanne, IEA Energy Conservation in Buildings and Community Systems Programme, Annex 20, Subtask 2 report, June 1992, 163pp. #DATE 00:06:1992 in English
ABSTRACT The work performed in this project was based on a literature review showing the necessary experimental work to improve the modelling of both airflow through doors and windows. New studies of interzonal airflow and single sided ventilation at seven laboratories in Europe and Canada, have been carried out in the project's framework and have led to improved models.
#NO 6271 Fluctuating airflow in buildings.
AUTHOR Rao J, Haghighat F, Bienfait D
BIBINF Indoor air quality, ventilation and energy conservation, 5th International Jacques Cartier Conference, Montreal, Canada, October 7-9, 1992, publisher: Center for Building Studies, Concordia University, Montreal, Canada, pp 484-489. #DATE 00:10:1992 in English
ABSTRACT Fluctuating airflow through buildings are caused by temporal and spatial variations of wind-induced pressures around building envelopes. An approach using the multi-zone pulsating airflow model is introduced inthis paper to study the fluctuating airflow through large openings. The approach employs the concept of aerodynamic admittance functions to modify the wind pressure spectra to represent the average fluctuating pressures over the area of opening. Theoretical solutions are compared with field experimental results from the BOUIN test-house of CSTB, France.
#NO 7053 Flow of aerosol particles through large openings.
AUTHOR Adam N M, Riffat S B
BIBINF UK, Air Infiltration and Ventilation Centre, 14th AIVC Conference, "Energy Impact of Ventilation and Air Infiltration", held Copenhagen, Denmark, 21-23 September 1993, proceedings, pp433-446. #DATE 21:09:1993 in English
ABSTRACT The first part of this paper describes a detailed study of the flow of aerosol particles through large openings and the second part describes deposition characteristics of aerosol particles in a single-zone chamber lined with different types of materials, e.g. aluminium foil and carpet. Tracer-gas and aerosol particles were injected into a naturally ventilated room and their concentrations with time were monitored. The room was fitted with a number of windows which allowed examination of single-sided ventilation. The behaviour of particles within the zone with respect to mixing, age-of-particles and particle effectiveness was also examined. The deposition rate of particles was found to be dependent on the type of lining material and size of particles used. Results indicated that particle exchange rates were higher than tracer-gas exchange rates.
#NO 7125 Preliminary results from laboratory measurements on vertical air flows in a large horizontal opening.
AUTHOR Klobut K
BIBINF Finland, Helsinki, Indoor Air '93, proceedings of the 6th International Conference on Indoor Air Quality and Climate, 1993, Vol 5, pp 545-550. #DATE 00:07:1993 in English
ABSTRACT The measuring stand was constructed in the lab-hall. The stand consisted of two vertically stacked zones separated by horizontal partition with a large opening. Air flows in the large opening between the zones were monitored by means of tracer gas technique. Variable parameters in the measurements were: direction and rate of net flow, temperature difference and dimensions of the large opening. The major findings from the measurements are: a) back flow (air flow in opposite direction to net flow) decreases when relative velocity of net flow (RVN) inthe opening increases; b) "up-down" net flow triggers stronger backflow than the "down-up" net flow; c) positive temperature difference (upper zone warmer) does not exclude the possibility for backflow to occur; d) backflow does not occur if the lower zone is not heated. The work is in progress on transforming the measurement results into the form of a mathematical model. The model will be validated and implemented in a computer program.
#NO 7172 Measurements of air change and energy loss with large open outer doors.
AUTHOR Nielsen A, Olsen E
BIBINF Proceedings of the 3rd Symposium on Building Physics in the Nordic Countries: Building Physics '93 (Bjarne Saxhof, editor), Thermal Insulation Laboratory, Lyngby, Denmark, 1993, vol 1, pp441-447, 2 figs, 3 tabs. #DATE 00:09:1993 in English
ABSTRACT In calculations of energy consumption for building is the air change important. The air change can be divided in two parts: ventilation and infiltration/exfiltration. The ventilation is controlled by the ventilation equipment. The infiltration (airstreaming from the outside to the inside) can only be estimated, if it is not measured, as it will depend on the air pressure difference and the leakage area. None of these is know to be very accurate. The infiltration can only be measured for a building. This measurement is normally done by measuring the air flow with a certain over or under pressure in the building. That is done with doors and windows closed. In a real case will opening of windows and doors give an extra infiltration heat loss. Our research had the purpose of finding the heat loss and air change when a large door is opened. Air flow through large openings in buildings.
#NO 7186 Air and heat flow through large vertical openings.
AUTHOR Hensen J L M, Maas J van der, Roos A
BIBINF Switzerland, LESO-EPFL, 1993, paper presented at the 3rd International Conference of the International Building Performance Simulation Association, Adelaide, Australia, 16-18 August 1993, 7 pp, 4 figs, refs. #DATE 00:08:1993 in English
ABSTRACT After a short description of the physical phenomena involved, unified expressions are worked out describing net airflow and net heat flow through large vertical openings between stratified zones. These formulae are based on those of Cockroft for bidirectional flow, but are more general in the sense that they apply to situations of unidirectional flow as well. The expressions are compatible with a pressure network description for multizone modelling of airflow in buildings. The technique has been incorporated in the flows solver of the ESP-r building and plant energy simulation environment. The relative importanceof the governing variables (pressure difference, temperature difference and vertical air temperature gradients) is demonstrated by parametric analysis of energy performance in a typical building context. It is concluded that vertical air temperature gradients have a major influence on the heat transferred through large openings in buildings and should be included in building energy simulation models.
#NO 7357 Velocity-pressure field of cross ventilation with open windows analysed by wind tunnel and numerical simulation.
AUTHOR Kato S, Murakami S, Mochida A, Akabayashi S, Tominaga Y.
BIBINF Journal of Wind Engineering and Industrial Aerodynamics, Vol 41-44, 1992, pp 2575-2586, 10 figs, 5 tabs, 11 refs. #DATE 00:00:1992 in English
ABSTRACT In order to investigate the mechanism of cross ventilation with open windows, velocity and pressure fields of airflows in an around building models are analyzed indetail by means of wind tunnel tests and numerical simulations. Large eddy simulation (LES) is used to 3Dturbulent flow analysis. The results of LES agree very well with those of the wind tunnel tests, and thus the accuracy of the numerical method used here is well validated. By means of LES, the spatial distributions of mean static pressure, turbulence energy, turbulence energy dissipation rate, etc. are examined with sufficient accuracy. The energy dissipating process (total pressure loss) along a cross flow through a building model is examined in relation to the conventional method for predicting the airflow rate of wind-induced ventilation, which uses static pressure drops and discharge coefficients of openings. However, in cross ventilation with large openings, the dynamic pressure which has a significantly large value in a room, conventional method based on static pressure drops. The airflow through large openings still preserves much of its mean kinetic energy when it remains inside the room and this is reflected in decreased values of the total pressure loss coefficients.
#NO 7481 Intermodel comparison of air flow through large openings.
AUTHOR Santamouris M J
BIBINF Newsletter of Annex 23 of IEA Energy Conservation in Buildings and Community Systems, 1994, No 4, pp 2-4, 5 tabs, 7 refs.#DATE 00:00:1994 in English
ABSTRACT In order to evaluate the accuracy of COMIS predictions for large openings,and to study its sensitivity, two tests have been performed. In the first test, COMIS is used together with four existing multizone air flow models to calculate natural ventilation in a building for various climatic and opening configurations. In the second test, COMIS predictions are compared with single-sided ventilation measurements taken in test cells. The results of the tests are reported.
#NO 7753 Experimental investigation of air flows through large openings in a horizontal partition.
AUTHOR Klobut K, Siren K
BIBINF Finland, Helsinki University of Technology, Laboratory of Heating, Ventilating and Air Conditioning, Report B35, 1994, 76 pp, 17 figs, 17 refs #DATE 00:00:1994 inEnglish
ABSTRACT In recent years, a computer simulation has gained considerable attention as a tool for predicting the air flows and an evolution of contaminant concentrations in buildings. Several computer programs, different in degree of sophistication and capabilities, have been developed for this purpose. However, what they all have in common is the lack of a suitable model for predicting the air flows through any large horizontal openings between vertically stacked building zones. Such flows may occur, eg., in a stairwell connecting two floors of a detached house. In order to satisfy an obvious need, the development of such a model has been a long term objective for a project initiated in the Laboratory of Heating, Ventilating and Air Conditioning at Helsinki University of Technology. In the first phase, the laboratory experiments were carried out to explore, for the first time, the influence of several parameters on combined forced and density-driven air flows through large openings in a horizontal partition. The two-way flows in the opening were monitored using a tracer gas technique. Variable parameters included the direction and rate of the net flow, the temperature difference between the zones, and the dimensions of the large opening.
#NO 7864 Energy and ventilation performance of double facade office buildings.
AUTHOR Raatschen
BIBINF UK, Building Research Establishment, BEPAC Conference, "Building Environmental Performance - Facing the Future" proceedings, 6-8 April 1994, University of York, UK, pps33-s42. #DATE 00:04:1994 in English
ABSTRACT A special double facade construction consisting of vertical shaft and vented box-window elements is introduced. During the last two years extensive tracer gas measurements have been carried out to quantify air movement, air exchange and air flow patterns between two facades and their influence on the building's ventilation and energy performance. New algorithms were developed to better and more reliably predict the air flows in the facade and through large openings. Measurement results collected from two low-rise buildings in Germany are compared against simulation results. The requirements for simulation codes are briefly summarized.
#NO 7883 Air and heat flow through large vertical openings.
AUTHOR Hensen, J L M, van der Maas J, Roos A.
BIBINF Belgium, International Building Performance Simulation Association, (IBPSA), 1993, proceedings of "Building Simulation '93", 3rd International IBPSA Conference, Edited by A E Delsante, J W Mitchell, R C van de Perre, held August 16-18, 1993, Adelaide, Australia, pp 479-485. #DATE 00:08:1993 in English
ABSTRACT After a short description of the physical phenomena involved, unified expressions are worked out describing net airflow and net heat flow through large vertical openings between stratified zones. These formulae are based on those of Cockroft for bidirectional flow, but are more general in the sense that they apply to situations of unidirectional flow as well. The expressions are compatible with a pressure network description for multizone modelling of airflow in buildings. The technique has been incorporated in the flows solver of the ESP-r building and plant energy simulation environment. The relative importance of the governing variables (pressure difference, temperature difference and vertical air temperature gradients) is demonstrated by parametric analysis of energy performance in a typical building context. It is concluded that vertical air temperature gradients have a major influence on the heat transferred through large openings in buildings and should be included in building energy simulation models.
#NO 7979 ventilation and energy flow through large vertical openings in buildings.
AUTHOR Maas J van der, Hensen J L M, Roos A
BIBINF UK, Air Infiltration and Ventilation Centre, 1994, "The Role of Ventilation", proceedings of 15th AIVC Conference, held Buxton, UK, 27-30 September 1994, Volume 1, pp289-302.
ABSTRACT After a short description of the physical phenomena involved, unified expressions are worked out describing net airflow and net heat flow through large vertical openings between stratified zones. These formulae are based on those of Cockcroft for bidirectional flow, but are more general in the sense that they apply to situations of unidirectional flow as well. The expressions are compatible with a pressure network description for multizone modelling of airflow in buildings. The technique has been incorporated in the flows solver of the ESP-r building and plant energy simulation environment. The relative importance of the governing variables (pressure difference, temperature difference and vertical air temperature gradients) is demonstrated by parametric analysis of energy performance in a typical building context and by comparison with experimental data in the literature. It is concludedthat vertical air temperature gradients have a major influence in the heat transferred through large openings in buildings and should be included in building energy simulation models. Finally, it is discussed how the air temperature gradient, an input parameter which depends strongly on the heating and cooling mode, could be predicted.
#NO 8208 A literature review of building related simulation models.
AUTHOR Tuomaala P.
BIBINF Finland, Helsinki University of Technology, Dept of Energy Engineering, Laboratory of Thermal Engineering, April 1992, 87 pp, 17 figs, 5 tabs, refs.
ABSTRACT Air infiltration and ventilation has a strong impact on both indoor air quality and energy consumption in buildings. Therefore it is important from both the epidemiological and energy conservation point of view, to be able to investigate and predict behaviour of buildings as effectively and reliably as possible. During the last decade, effective tools have been developed in computer technology, and also versatile mathematical solution libraries have been published. This gives new possibilities for numerical solution methods, because more interacting physical phenomena can be included in the very same simulation programs, for example, simulation of ventilation and infiltration together with thermal behaviour of a building. The development of single-zone models seems to be complete. The development of multizone infiltration and ventilation models shows a relatively slow evolution (Feustel 1989). Although the simple tests of the present air flow simulation programs look very promising, some important questions remain. The most important question concerns the reliability of the method for solving the air flow network equations. Solution of the non-linear equations has been demonstrated in several tests but has not been mathematically proven (Walton 1989). Predicting air flow through large openings is difficult. In the literature an agreement exists on the prediction of gravitational flow through vertical openings in steady state configurations using Bernoulli's equation. Nevertheless, a large uncertainty remains on the definition of the discharge coefficient. There is a lack of knowledge on the behaviour of horizontal openings in thermally driven flows, and the coupling with the flow patterns existing in each zone is not taken into account (Feustel et al. 1990) This literature review is made to get an overview of building-related simulation models. It is based on other reviews made earlier and some scientific articles about special topics, such as detailed description of some simulation programs, air flow through a large opening, modelling the thermal principles, and quantification of indoor air quality. Because of the numerous topics handled in this review, the results given by different authors have been represented quite briefly and without discussion. That is why this review is suitable mainly for introductory purposes.
#NO 8317 Predicting the thermal and airflow performance of large spaces
AUTHOR Awbi Hazim B, Baizhan Li.
BIBINF Poland, Silesian Technical University, 1994, proceedings of Roomvent '94: Air Distribution in Rooms, Fourth International Conference, held Krakow, Poland, June 15-17, 1994, Volume 1, pp 449-466.
ABSTRACT The ventilation of large glazed enclosures such as atria requires special attention due to the large solar gain in summer and large heat losses in winter. In these structures temperature stratification is unavoidable because of the large heights involved but the task of the designer is to achieve acceptable thermal environment at ground level. Furthermore, energy savings can b e achieved if passive ventilation is used by supplying outdoor air or air from internal openings leading to the atrium space. In this paper, the air movement in a parametric atrium building is investigated using computational fluid dynamics. The solar gain through the glazing is calculated using a building thermal analysis program for UK weather conditions covering all seasons. The thermal comfort within the enclosure is calculated using the PPD index. In addition to the airflow analysis the surface-to-surface radiation exchange is evaluated using a radiation model and the plane radiant temperature distribution in the atrium is used to determine the PPD for the occupied zone. The results show that acceptable thermal environment can be achieved in the summer if outdoor air is allowed to enter through large openings by the influence of buoyancy forces. In winter it is required to allow warm air from adjacent zones to enter the atrium space and rise by the effect of buoyancy, since supplying unheated outdoor air directly will not be acceptable for reasons of comfort and water condensation on the roof.
#NO 8358 Air flow pattern study through large openings.
AUTHOR Amara F, Litvak A, Guarracino G.
BIBINF France, Ecole Nationale des Travaux Publics de l'Etat, November 1994, proceedings of the European Conference on Energy Performance and Indoor Climate in Buildings, held Lyon, France, 24-26 November 1994, Vol 1, pp120-125.
ABSTRACT One of the main problems about air flow pattern study through large internal and external openings remains the choice of the discharge coefficients (Cd) used to compute the air flows. The range of Cd coefficient generally used in the literature is comprised between 0.6 and 1. For air flow prediction using a pressure network model such as PASSPORT-AIR, COMIS,ESP,..., no information is given to the user as regards the choice of Cd coefficients although predicted air flows strongly depend on this choice. This paper deals with the experimental determination of some correlations between the discharge coefficient and other parameters such as air temperature gradient through opening, wind speed and direction, size of opening,... To this end, a two-zone test using multiple tracer gas technique with decay mode is performed in a real scale cell (OPTIBAT) for various climatic conditions and for internal openings. A new algorithm adapted for tracer gas decay mode has been developed to compute the experimental air flows. The validation of this algorithm was successfully done using a two zone study performed in Japan by ENAI and SHAW [1]. On the other hand, experiments performed by Mr PELLETRET from CSTB are also used to define ventilation correlations for various sizes of opening.
#NO 8647 Improvement of multizone model predictions by detailed flow path values from CFD calculations.
AUTHOR Schaelin A, Dorer V, van der Maas J, Moser A
BIBINF USA, ASHRAE Transactions, Vol 100, Part 2, 1994, pp 709-720.
ABSTRACT Multizone models are a common tool for calculating air and contaminant exchange within the rooms of a building and between a building and the outdoors. Usually a whole room is modeled by one calculation node with the assumption of homogeneously mixed conditions within this room, but in real cases, temperature and contaminant concentrations vary in space. The exchange to neighboring nodes via flow paths is a function of the local values of these variables. Detailed knowledge can be obtained from the solution of the transport equations for the airflow pattern (computational fluid dynamics, CFD) within the room at the expense of far higher computation cost. This work shows how results from CFD calculations can enhance the accuracy of multizone model predictions to give a better description of real cases. Parameter transfer between a multizone program and a detailed airflow simulation program is discussed. The method is then applied to example cases with air in/exfiltration, ventilation, and contaminant propagation and flow through large openings and shows its ability for a more accurate prediction of the contaminant spread. In the cases shown, concentration values differ by up to a factor of 2.5 from the purely multizonal approach. In the case with open windows, the multizonal prediction is 0.12 ppm for the concentrations in a neighboring room, whereas the corresponding values of the new method vary between 0.05 and 0.23 ppm for different source positions.
#NO 9051 Application of air flow models to aircraft hangars with very large openings.
AUTHOR van der Maas J, Schaelin A
BIBINF UK, Air Infiltration and Ventilation Centre, 16th AIVC Conference Implementing the results of ventilation research , held Palm Springs, USA, 18 - 22 September, 1995, Proceedings Volume 1, pp 127-142.
ABSTRACT In lime maintenance hangars, air planes stay about 2 hours, usually at night-time. The cooling down of the inside air during the opening time of the hangar gates (up to 5 times per night, lasting 1.5 to 30 minutes each) has a considerable impact on the comfort conditions for the workers, and on the energy required for reheating. The time-dependent air flow rates and associated heat loss rates during the door opening and closing cycles is assessed by simple transient thermal models and CFD (Computational Fluid Dynamics) calculations. The results obtained by these models agree well with the experimental data of the transient temperature response during the opening and closing of the door of a real full scale hangar. The effect of using huge air curtains (up to a height of 20m, a width of 80m, and moving air volumes at rates of 400 m3/s) to prevent heat loss was studied numerically by CFD in two- and three- dimensional models for time-dependent conditions. The study covers also transient effects when an aircraft is actually crossing the air curtain, and shows the feasibility of assessing the energy saving potential of such air curtains using CFD.
#NO 9181 Heat and mass transfer through large openings by natural convection.
AUTHOR Santamouris M, Argiriou A, Asimakopoulos D, Klitsikas N, Dounis A
BIBINF UK, Energy and Buildings, No 23, 1995, pp 1-8, 2 figs, 1 tab, 35 refs.
ABSTRACT Convective heat and mass transfer through large openings play an important role in the thermal behaviour of buildings. These phenomena become even more determinant in the case of naturally ventilated buildings. This paper reviews the models describing the involved phenomena due to gravitational and boundary layer pumping flows proposed up to 1992. A sensitivity analysis is also presented, aimed at a comparison of these models and a determination of the points requiring further research.
#NO 9182 Suitable algorithms for calculating air renewal rate by pulsating air flow through a single large opening.
AUTHOR Fuerbringer J-M, Van der Maas J
BIBINF UK, Building and Environment, Vol 30, No 4, 1995, pp 493-503, 14 figs, 6 tabs, 21 refs.
ABSTRACT Building ventilation of an enclosure with a single opening is affected not only by the steady mean effect of air pressures and temperatures around and within the building, but also by the turbulent nature of the wind. To improve understanding of the physical phenomena causing air exchange through a single opening, models to simulate the indoor pressure resulting from fluctuations of the wind-induced outdoor pressure are analysed and experimental requirements for model validation are discussed. The influence of the dimensions of the opening and the volume of the room on the time constant are discussed and the numerical constraints of the non-linear low-pass filter modelling for infiltration are highlighted. In particular the frequency limits for data logging or simulations are dependent on this time constant. A method is proposed to avoid the oscillation of the simulated indoor pressure for the case of under-sampling which frequently occurs because of the limitation of data acquisition rates. The need for further work on this problem is discussed.
#NO 9710 The use of the PASSYS test cell for the measurement of single sided ventilation.
AUTHOR Ducarme D, Vandaele L, Wouters P
BIBINF France, Ecole Nationale des Travaux Publics de l'Etat, November 1994, proceedings of the European Conference on Energy Performance and Indoor Climate in Buildings, held Lyon, France, 24-26 November 1994, Vol 3, pp 886-890, 4 figs, 4 tabs.
ABSTRACT In the frame of the European PASCOOL project, several experiments regarding single sided ventilation were carried out at BBRI in the outdoor PASSYS test cell. The test room of 30 m3 has a vertical window of about 1 m2. During a first measurement period an open cold box, which allows one to control the vertical wind speed, was placed in front of this window. During a second measurement period, the window was directly exposed to `real wind'. The air flow rates through the large opening is derived from the energy balance of the test room. This approach is possible because the heat flow through the cell envelope can be accurately determined thanks to the Pseudo-Adiabatic-Shell. Tracer gas measurements were carried out in parallel. They are made difficult because a clear air flow pattern appears and accordingly, the concentration in the room is not homgenous. An error analysis has been applied on both methods. The agreement between both methods is very good and the heat balance approach proved to be more accurate than the tracer gas technique. a correlation model was derived from the first measurement period.
#NO 10069 Two dimensional numerical study of airflow through large openings.
Li K, Teh S L
Indoor Air '96, proceedings of the 7th International Conference on Indoor Air Quality and Climate, held July 21-26, 1996, Nagoya, Japan, Volume 2, pp 1027-1032.
Natural ventilation is important to indoor air quality because its rate is usually low and cannot be easily adjusted. The results of a numerical study on the airflow within a single-sided naturally ventilated room with a large opening is presented here. Lam-Bremhorst low-Reynolds-number k-e model together with a self-developed two-dimensional flow simulation code based on SIMPLE algorithm was used. External temperatures in equatorial climate similar to those of Singapore were selected. Two room set-ups were examined. The firs is with a heat source and the second a split unit air-conditioner. Air exchange rates were predicted. It is found that the presence of the circulation fan in the split unit air-conditioner will decrease vertical temperature gradient in the opening region and hence the ventilation rate is lowered.
#NO 10110 Airflow through horizontal openings.
Kohal J S
UK, University of Nottingham, Institute of Building Technology, 1995, PhD Thesis, 169pp.
Describes measurement of airflow through large horizontal and vertical openings using tracer gas techniques. First the accuracy of different types of tracer gases was examined before measurements were conducted in a two zone chamber to determine airflow through small horizontal openings. Experiments were also conducted to determine airflow through large horizontal openings between two rooms in a building. Similar measurements were carried out between two zones in a small scale chamber. Results from these measurements were used to establish empirical equations for heat and mass transfer through large openings. The work also involved CFD prediction of airflow through horizontal openings. Results were compared with those obtained using tracer gas techniques. Finally, field tests were carried out involving measurement of airflow through large openings in a two storey house.
#NO 10181 Interzonal airflow from garages to occupied zones as one reason for building related illness: three case studies using tracer gas measurements.
Tappler P, Damberger B
Indoor Air '96, proceedings of the 7th International Conference on Indoor Air Quality and Climate, held July 21-26, 1996, Nagoya, Japan, Volume 4, pp 119-124.
Tracer distribution measurements were performed to assess pollutant transport from basement garages situated in a commercial building and in two residential buildings, in which the occupants had reported typical garage odors and complained about bad indoor air and typical SBS symptoms. A tracer gas technique (tracer gas SF6. infrared detection) was used in all three buildings to study the contaminant distribution in the buildings. In the commercial building, a leaky HVAC system distributed contaminated air from the garage to other zones of the building. A second reason was a large opening in the encasing wall of the exhaust shaft of the garage. In the residential buildings exhaust fans as well as tightly sealed windows and doors led to interzonal airflow from the garage. The results indicate that faulty construction and insufficient sealing between the garage and the occupied floors can most certainly be a reason for building-related illness. The tracer gas technique applied has proved a good tool for detecting leaks and faulty construction in buildings.
#NO 10607 Experimental approach of air flow through a door connecting rooms with different temperature.
Papamanolis N, Santamouris M, Dascalaki E, Argiriou A, Asimakopoulos D N
UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation and Cooling", 18th Annual Conference, held Athens, Greece, 23-26 September 1997, Volume 2, pp 591-600.
Air flow through doors, windows and other large openings constitutes a major factor in building ventilation. However, due to the complexity of the physical process involved, relevant physical phenomena are not yet fully understood. The paper presents data obtained from five consecutive experiments concerning air flow through a large opening (door) connecting two rooms (volumes 28.3 m3 and 38.1 m3 respectively) with different air temperatures. The experiments were conducted within the two chambers (Service and Test Room) of a PASSYS Test Cell, a full equipped outdoor facility for thermal and solar monitoring. The experiments involved the heating of one room (Test Room) until there was a significant temperature difference between the rooms. After that, the door was opened, and the mass heat exchanges between the two rooms were measures using the available equipment. More specifically, the experimental data, corresponding to 30 sec step records, concerns the measurement of tracer gas (N20) concentrations, indoor temperatures, air speed and direction in the middle of the door opening, outdoor temperature and wind speed and direction. This paper attempts a qualitative analysis of the experimental results as a first step towards a more comprehensive study of the physical processes in operation in relevant phenomena.
#NO 11210 Simulation tools for analysing natural ventilation of large enclosures with large openings.
Li Y, Delsante A E, Symons J G
Australia, AIRAH Journal, Vol 51, No 11, November 1997, pp 21-28, 11 figs, 1 tab, refs.
Two simulation tools for natural ventilation with large openings are briefly discussed in this paper. The first program, SIX integrated with CHEETAH, is able to predict air change rates for natural ventilation with large openings. The second program, Ventair, is capable of predicting both air change rate and airflow pattern. The air change rates predicted by SIX and Ventair for an example large enclosure agree well. Although this agreement provides some confidence in these predictions, it does not necessarily indicate that the simulation tools presented here are ideal. Reliable experimental techniques are needed, not only as possible design tools, but also to provide experimental validation to analytical models such as those developed here. Such an experimental tool is not available at present, especially for large enclosures with large ventilation openings. work currently undertaken includes consideration of vertical temperature gradients, vertical wind velocity profile and integration of a multi-cell version of SIX into CHEETAH. An example application is presented for Sydney's Flemington Market, in which both models have been applied.
#NO 11309 A field study of cold air flows through doorways of industrial buildings.
Hejazi-Hashemi M G, Siren K E
The Canadian Environment Industry Association (CEIA), 1997, "Ventilation '97: Global Developments in Industrial Ventilation", proceedings of the 5th International Symposium on Ventilation for Contaminant Control, held in Ottawa, Ontario, Canada, September 14-17, 1997, Volume I, pp 299-306, 6 figs, 1 ref.
A problem, which appears in many industrial buildings is spreading of the outdoor cold air coming in through the doorways and other large openings, causing draught and pollution at the work places, disturbing the proper functioning of the ventilation as well as disturbing some production processes and increasing the maintenance and energy costs. The goal of this study was to achieve quantitative, measured information of the effects of cold air flows in the industrial environment. The method used was field measurements, which were carried out during the wintertime 1996 in industrial buildings located in the northern part of Finland. Totally 12 industrial buildings, representing a wide variety of different situations were monitored. The results show remarkably high cold air flow rates through doorways. Air flow velocities up to 7 m/s and air flow rates up to 60 m3/s were measured. High flow rates occurred especially in tall buildings, where the stack effect is high. As a consequence adverse effects on thermal conditions, ventilation, processes and the energy consumption were observed. The results serve as a base for an analysis, where simple tools are developed for the planning stage of industrial ventilation and especially for the prevention of cold air flows in arctic and sub arctic climates.
#NO 11550 Experimental impact valuation of fouling on extract air terminal devices performances: an accelerated artificial fouling approach.
Spennato B
UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation Technologies in Urban Areas", 19th Annual Conference, held Oslo, Norway, 28-30 September 1998, pp 171-178.
A humidity controlled airflow terminal device works as a humidity sensor: its opening surface varies according to relative humidity inside a room in order to match air flow rate to pollution. These components are fouling up when used during several months.
In a laboratory, an air flow with a high rate of particles is fouling up five identical air devices in a few hours. Considering a constant relative humidity, the impacts on two devices are similar: it seems that artificial fouling tests can be reproduced. These first tests show a high sensitivity to fouling at low relative humidities (small openings devices) and nearly no sensitivity at high relative humidities (large openings devices).
The characteristic curve of a humidity controlled air flow device represents the air flow rate in function of the relative humidity at a set pressure loss. The curves of four devices are compared before and after the accelerated fouling: the most important absolute air flow reduction is about 3.1 1/s. This maximum is always reached near the point of RH=60%. The corresponding relative reduction varies from 14% to 23%. The nearly same relative reductions are measured at the point of RH=60% with two years old fouled up devices from real dwellings although the fouling is visually very different. Thus, the accelerated artificial fouling experiments seem to be representative of real cases.
#NO 11639 Kylmien ilmavirtausten torjunta teollisuushalleissa. Suunnitteluohje.
Valkeapaa A, Hejazi-Hashemi S, Siren K
Finland, Helsinki University of Technology, Faculty of Mechanical Engineering, Laboratory of Heating, Ventilating and Air Conditioning, 1998, report B55, 94 pp + app., in Finnish
Cold outdoor air inside industrial buildings causes draught problems and increases energy consumption of the building. Also cold outdoor air has a harmful effect on the processes and ventilation system and the floor area near the door opening cannot be used in productive activity. Furthermore, cold outdoor air is warmed slowly and causes a long duration temperature stratification, which removing is very difficult.
Prevention for cold air flows depends on many contemporaneous factors, such as the climate conditions, the building layout and height, the near terrain, the places of door openings, the number of door openings and the building structures. The most important thing in prevention of cold air flows is to recognise these factors and to understand the interaction between the climate conditions, the near terrain and the building itself. If the building structure disadvantages are not solved by heating and ventilation means, HVAC-engineers have to interface in these structure disadvantages.
The aim of this new planning rule for the prevention of cold air flow is to instruct HVAC-engineers to find the decisions for the prevention cold air flows in the large openings and on the cover of industrial buildings. The planning rule can be used also in the negotiations with customers. Because of that the planning rule includes many photos and pictures of preventing solutions.
The planning rule is developed together with the experts of industrial ventilation and the manufacturers. The planning rule includes the form of risk index, three main decision trees and some auxiliary decision trees. Preventing solutions are introduced among other things the air curtains, the shelter structures of loading docks and the service entrances. The planning rule is complete with the simulation programme CAFCAM, which can calculate air flows through the door openings, the pressure distribution of industrial building and the position of neutral pressure level.
#NO 11782 Building ventilation: a pressure airflow model computer generation and elements of validation.
Boyer H, Lauret A P, Adelard L, Mara T A
UK, Energy and Buildings, No 29, 1999, pp 283-292, 13 figs, 45 refs.
The calculation of airflows is of great importance for detailed building thermal simulation computer codes, these airflows most frequently constituting an important thermal coupling between the building and the outside on one hand, and the different thermal zones on the other. The driving effects of air movement, which are the wind and the thermal buoyancy, are briefly outlined and we look closely at their coupling in the case of buildings, by exploring the difficulties associated with large openings. Some numerical problems tied to the resolving of the non-linear system established are also covered. Part of a detailed simulation software (CODYRUN), the numerical implementation of this airflow model is explained, insisting on data organization and processing allowing the calculation of the airflows. Comparisons are then made between the model results and in one hand analytical expressions and in another and experimental measurements in case of a collective dwelling.
#NO 11988 Modelling large openings with COMIS.
Dascalaki E, Santamouris M, Bruant M, et al
UK, Energy and Buildings, No 30, 1999, pp 105-115, 8 figs, 4 tabs, 32 refs.
Conjunction of Multizone Infiltration Specialists (COMIS) is a model that can be used to simulate air flow and pollutant patterns in a multizone structure. Experimental data from air flow measurements in single sided naturally ventilated spaces, common in urban environments, and from cross-ventilated spaces, are compared against predictions from COMIS. The single sided ventilation experiments were performed in two zones of a full scale building. Results from both experimental and calculated data using COMIS were in good agreement.
#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 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 12105 Upward flows in a multi zone building with subfloor plenums and solar chimneys.
Li Y, Delsante A, Symons J G
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 429-436, 8 figs, refs.
Solar chimneys are often used to extract air from a building by thermal stacks, while subfloor plenums are used to passively cool air before it is supplied to a building. This paper examines the overall flow pattern in buildings with both solar chimneys and subfloor plenums. For a multi-zone flow system in which each zone has only two effective openings, an analytical solution is derived. A sufficient condition for upward flows to occur is derived from the analytical solution.
A two-room building with two solar chimneys and two subfloor plenums at two different heights, and an internal large opening is also considered. No analytical solutions exist for this configuration. A multi-zone natural ventilation program considering bi-directional flows is used to solve the problem numerically. Much more complex flow patterns are identified and analysed.
#NO 12587 Effective depth of fresh air distribution in rooms with single-sided natural ventilation.
Gan G
UK, Energy and Buildings, No 31, 2000, pp 65-73, 5 figs, 1 tab, 17 refs.
This paper introduces the effective depth of fresh air distribution in rooms with single-sided natural ventilation. A numerical method for the determination of the effective depth is described. Ths numerical method is based on the CFD technique involving the governing equations for air flow and the transport equation for the local mean age of air. The renormalisation group k - e model of turbulence is used with equations for the conservation of mass, momentum and energy to predict turbulent buoyancy-induced room air movement. The air flow through a large opening is derived from the Bernouli theory. The predicted air flow pattern, air temperature and local mean age of air are used to determine the effective depth of fresh air distribution in a naturally ventilated room with a window opening for summer cooling. It is shown that the effective depth for thermal comfort may not coincide with that for air quality and in summer, the requirement for thermal comfort is the limiting factor to the effective room depth. The effects of window opening levels and room heat gains on the air flow rate and effective depth are investigated.
#NO 12589 Experimental and theoretical case study on cross ventilation - designing a mathematical model.
Schmidt D, Maas A, Hauser G
Nordic Journal of Building Physics, Vol 2, 1999, 14 figs, 3 tabs, refs.
Natural ventilation through windows and other openings in the building envelope is still the most common way to ensure the necessary fresh air supply in buildings. To date, there are few validated models for the calculation of ventilation rates through large openings. In particular, there is a lack of information about natural cross-ventilation. On the basis of an empirical study a mathematical model for the calculation of cross-ventilation in buildings is presented in this paper.
In order to investigate the different influences on the airflow through large openings in the building envelope, measurements of air change rates under natural conditions are carried out for certain types and configurations of openings. By using the collected data, the influences of the buoyancy and wind driven airflow are analysed. The influences of the two phenomena on each other are determined in detail. Based on published numerical models for single-sided ventilation and knowledge about airflow patterns through windows, a new model for cross ventilation is derived. Again, this model is validated with the measured data. By using this new model, convection heat loss and thermal loads of buildings can be calculated more specifically.
#NO 12946 Characterisation of natural convection in a room communicating with the outside environment through a door.
Carvalho M G, Ramos J E, Pitarma R A
in: PLEA '99 "Sustaining the Future - Energy, Ecology, Architecture", proceedings of a conference held Brisbane, Australia, September 22-24, 1999, edited by Steven V Szokolay, published by PLEA International, in conjunction with the Department of Architecture, The University of Queensland, Brisbane, Volume 1, pp 477-482, 4 figs, 1 tab, refs.
The present paper describes a numerical method for analysing three dimensional natural convection in rooms connected to the outside through large openings. The calculations made use of a Computational Fluid Dynamics (CDF) procedure which solves the three-dimensional equations for the conservation of mass, momentum and thermal transfer and air flow turbulence.
The CFD predictions agree with the experimentally observed features of the flow field, including the vertical air temperature stratification, with a reasonable degree of accuracy.