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LL 21: Displacement Ventilation Strategies

AIVC, 2001
AIVC | LL
Bibliographic info: LL 21
Languages: English

Displacement Ventilation Strategies

#NO 2125 Ventilation systems in residential buildings: requirements to the design of systems and equipment.

AUTHOR Meyringer V

BIBINF Proceedings of the CLIMA 2000 World Congress on Heating, Ventilating and Air-Conditioning, Copenhagen, 25-30 August 1985. Edited by P O Fanger. Vol 6. Heating, ventilating and air-conditioning systems. p287-293. 6 figs, 7 refs. #DATE 00:08:1985 in English

ABSTRACT Evaluates results of the 'Ventilation in Residential Buildings' research programme of the German Federal Ministry for Research and Technology. It was found that conventional ventilation methods based on infiltration and window opening cannot secure proper air quality and at the same time provide energy conservation and user comfort, nor can intelligent ventilation habits be expected of the average user, for subjective and objective reasons. All ventilation systems evaluated had shortcomings. Soft displacement ventilation techniques taking advantage of natural buoyancy forces instead of contaminant dilution can be expected to provide major improvements in ventilation efficiency and user comfort in future.

KEYWORDS ventilation efficiency, air quality, ventilation strategy, occupancy effects

#NO 2181 Air exchange and ventilation efficiency.

Luftutbytes- och Ventilationseffektivetet.

AUTHOR Malmstrom T G, Sandberg M, Jarmyr R, et al.

BIBINF VVS & Energi, 1985, No 10, p23-51, figs, tabs, refs. #DATE 00:10:1985 in Swedish

ABSTRACT Several papers discussing ventilation efficiency, effective industrial ventilation, the positioning of ventilation inlets and outlets, displacement ventilation and other applications of the concept of ventilation efficiency.

KEYWORDS ventilation efficiency, industrial building, ventilation strategy

#NO 2213 Industrial ventilation - model tests and general development in Norway and Scandinavia.

AUTHOR Skaret E

BIBINF Ventilation '85. (Chemical Engineering Monographs 24). Amsterdam, Elsevier, 1986. Edited by Howard D Goodfellow. p19-31. 6 figs, 10 refs. #DATE 00:00:1986 in English AIVC bk

ABSTRACT Ventilation studies using small-scale water models have, especially in Norway gained new and important knowledge in industrial ventilation the last 15 years. The outcome has been twofold. First of all it has resulted inimportant experience in making small-scale model tests for ventilation studies. Secondly, it has increased the knowledge in where to apply and how to design efficient displacement ventilation systems. In most industries the displacement principle is outstanding compared to other principles for general ventilation. The displacement direction is generally vertical-up, providing for supply of fresh air directly to the workspace. In most cases thermal stratification can be utilized to optimize the effectiveness for the systems.Effective- ness is sensitive to the diffuser design for the supply air. It is also necessary to avoid using the ventilation system for space heating (covering the transmission losses). Research results and practical applications have developed hand in hand and have also resulted in new understanding andpractical definitions of the ventilation effectiveness as well as calculation methods, the two-zone model, and design guidelines for displacement ventilation systems.

KEYWORDS industrial building, modelling

#NO 2266 Displacement ventilation in theory and practice.

Deplacerande ventilation i teori och praktik.

AUTHOR Sandberg M, Blomqvist C

BIBINF VVS & Energi, May 1986. 5 figs, 2 refs. #DATE 00:05:1986 in Swedish

ABSTRACT Discusses two main methods of fan-assisted air supply to a room - mixing ventilation and displacement ventilation. Gives a detailed account of the effects which furniture and the opening of doors have on a room and discussses factors such as vertical temperature variations, air velocity at floor level. Illustrates these effects in diagram form. Notes difficulty in translating older comfort criteria for use in displacement ventilation.

KEYWORDS fan, door, displacement ventilation, door opening, mixing ventilation, air velocity

#NO 2649 Measurements of air exchange efficiency and ventilation effectiveness.

AUTHOR Helenius T, Seppanen O, Maranen A, et al

BIBINF Roomvent 87, proceedings, Stockholm 10-12 June 1987, 10p, 8 figs, 2 refs. #DATE 00:06:1987 in English

ABSTRACT Extensive measurements of ventilation effectiveness and air exchange efficiency were made in a test room of 53 m. According to the tests the most reliable method of measuring ventilation effectiveness is to compare the concentrations at various locations during steady state conditions. Both mixing and displacement flow patterns were used with three nominal timeconstants (2h, 0.91h, 0.45h) and temperature differences -3 K to +3 K between supply and room air. The measured average ventilation effectiveness varied between 0.8 and 1.3 with mixing flow pattern and between 1.1 and 1.9 with displacement flow. The average air exchange efficiency varied between 16% and 56% and between 46% and 72% respectively. The location of the human simulator affected the ventilation effectiveness much more than the nominal timeconstant and temperature difference. No reliable relation was found between the average ventilation effectiveness and the average air exchange efficiency. A relation between average and local efficiencies was found.

KEYWORDS ventilation efficiency, air change, mixing ventilation, displacement ventilation

#NO 2707 Comfort in the auditorium.

AUTHOR Todt W

BIBINF Sulz Tech Rev, 3/1987, p3-8, 14 figs, 1 tab. #DATE 00:00:1987 in English

ABSTRACT The special conditions in large rooms, such as theatre auditoriums and exhibition halls, impose particular requirements on the ventilation and air conditioning installations. Depending on the constructional characteristics of the building and on the requirements imposed by its utilization, there is a choice of several different methods of airflow distribution. Since the number of such large halls is relatively small and the constructional characteristics of the building as well as the mode of utilization vary significantly, only a slight degree of know-how transfer is possible. This therefore places greatly increased importance on design and airflow model testing by appropriate specialists, not to mention close cooperation between all concerned.

KEYWORDS auditorium, design, air flow, model, air conditioning, displacement ventilation, mixing

#NO 2832 Ventilation effectiveness - past and future.

AUTHOR Rodahl E

BIBINF in: Indoor Air '87, Proceedings of 4th International Conference on Indoor Air Quality and Climate, Berlin (West), 17-21 August 1987,Vol 4 Institute for Water, Soil and Air Hygiene, 1987, p57-68, 10 refs. #DATE 00:00:1987 in English

ABSTRACT During the last decade methods for evaluating the ventilation processes are being developed. The studies have for one thing unveiled the advantages of displacement ventilation. In fact displacement ventilation is not a new invention, and the results are in accordance with qualitatively based statements made a hundred years ago. People at that time came to the right conclusions mainly by observing that warmed air rises and cooled air sinks in the surrounding air. The developments during the last decade represent an important step forward. By increased use of computers in the future studies of ventilation processes additional improvements of ventilation systems are to be expected.

KEYWORDS ventilation effectiveness, displacement ventilation, ventilation system

#NO 2961 Ventilation by upward displacement.

Impulsarme Luftzufuhr durch Quelluftung.

AUTHOR Fitzner K

BIBINF Heizing, Luftung, Haustechnik, Vol 39, No 4, April 1988, 18 figs, 28 refs. #DATE 00:04:1988 in German

ABSTRACT Describes the method of ventilation by upward displacement.

KEYWORDS displacement ventilation

#NO 3392 Ventilating for comfort.

AUTHOR Martin H E

BIBINF Building Services, March 1989, pp36-37. #DATE 00:03:1989 in English

ABSTRACT Suggests displacement ventilation as a way of ensuring air quality in an occupied space and details three methods open to the designer.

KEYWORDS displacement ventilation, indoor air quality

#NO 3566 Ventilation by displacement: calculation of the flow in a three-dimensional room.

AUTHOR Davidson L, Olsson E

BIBINF in:UK, AIVC, 10th AIVC Conference, held at Espoo, Finland, 25-28 September 1989, Volume 1, February 1990, pp367-392, 13 figs, 1 tab, 15 refs. #DATE 00:02:1990 in English

ABSTRACT Displacement flow systems are becoming popular, especially in Scandinavia, for comfort ventilation. In these systems air is supplied near the floor at low velocity; the temperature of the supply air is a few degrees below that of the air in the room. The supply air is heated by persons and/or machinery in the room. Turbulent plumes are formed above these heat sources. Apart from the plumes, the flow in the room is divided into two zones: a lower zone (the occupied zone) to which clean cool air continuously is supplied, and an upper zone (above the occupied zone) where contaminated warm air is recirculating. In the present study, the flow in displacement flow systems (a water box model) has been calculated using finite difference methods; the results have been compared with experimental data, and the agreement is reasonably good.

KEYWORDS displacement ventilation, calculation techniques

#NO 3694 The air exchange efficiency of a lecture hall.

AUTHOR Breum N O

BIBINF Reprinted from: Ventilation '88, Proceedings of the Second International Symposium on Ventilation for Contaminant Control, 20-23 September 1988, London, UK, pp373-380, 3 figs, 1 tabs, 15 refs. #DATE 00:09:1988 in English

ABSTRACT The air flow pattern in a lecture hall (V=690m3) designed for displacement ventilation was characterised by age analysis in the case of a non-occupied hall as well as an occupied hall. The ventilation system was slightly (17%) unbalanced. For comparison the following three experimental signal-response tracer gas techniques were applied: "step-up", "decay" and pulse injection. The mean ages of air estimated by the "decay" technique were elevated (1-23%) compared to the results of the "step-up" method. Generally the pulse technique estimated the lowest mean ages. The estimated air exchange efficiency of the non-occupied hall was 50%, and for the occupied hall theefficiency was estimated to be 60%.

KEYWORDS air change rate, large building

#NO 3768 Ventilation by displacement in a three-dimensional room - a numerical study.

AUTHOR Davidson L

BIBINF UK, Building and Environment, Vol 24, No 4, pp363-372, 1989, 15 figs, 2 tabs, 19 refs. #DATE 00:00:1989 in English

ABSTRACT Displacement flow systems are becoming popular, especially in Scandinavia, for comfort ventilation. In these systems air is supplied near the floor at low velocity; the temperature of the supply air is a few degrees below that of the air in the room. The supply air is heated by persons and/or machinery in theroom. Turbulent plumes are formed above these heat sources. Apart from the plumes, the flow in the room is divided into two zones: a lower zone (the occupied zone) to which clean cool air continuously is supplied, and an upper zone (above the occupied zone) where contaminated warm air is recirculating. In the present study, the flow in displacement flow systems (a water box model) has been calculated using finite difference methods; the results have been compared with experimental data, and the agreement is reasonably good.

KEYWORDS displacement ventilation, numerical modelling

#NO 3782 Industrial ventilation design: supply air distribution. Teollisuusilmanvaihdon suunnittelu.

AUTHOR Tapola M, Uimonen J, Heinanen S, Hagner B

BIBINF Finland, Helsinki, KTM, Sarja D:145, 1987, 66pp, 38 figs, 14 refs. #DATE 00:00:1987 in Finnish

ABSTRACT In order to study the performance of general ventilation systems a series of empirical tests were carried out in various types of industrial environments. These field studies were carried out in eleven industrial premises. In some cases the studies were repeated under various load conditions. The empirical testing methods used were tracer gas technique, temperature field, air hygiene quality and air technique measurements. Tracer gas technique was used to monitor the movement of impurity emissions and the ventilation effectiveness as well as the air exchange rate. Moreover, the indoor air quality of the installations was monitored by temperature and concentration measurements. The systems were compared on the basis of the results obtained and the economical comparison reflected both equal air quality and ventilation effectiveness. This comparison model for displacing and mixing ventilation can be utilized for the preselection of ventilation systems. In support of this research the references of nine industrial ventilation installations have been included.

KEYWORDS supply air, ventilation system, displacement ventilation, mixing ventilation, industrial building

#NO 4154 A methodology for indoor airflow computations and energy analysis for a displacement ventilation system.

AUTHOR Chen Q, Van der Kooi J

BIBINF Switzerland, Swiss Fed Inst of Technology, ETH Zurich, paper to be published in Energy and Buildings, 1990, 13 pp, 8 figs, 2tabs, 34 refs. #DATE 00:00:1990 in English

ABSTRACT This article presents a methodology for the computation of indoor airflow, air quality, space load and energy consumption of aroom with a displacement ventilation system. Since airflow andtransient heat transfer in the room are interrelated, the indoor airflow and the space load of the room must be predicted simultaneously. In order to reduce the computing costs, a simplified method has been introduced for the predictions. According to the present state of the art, the k-E turbulence model is suggested for the indoor airflow computations within a room. The air temperature distributions of the room are used in a cooling load program for space load calculations. This is very important for a room with a displacement ventilation system. An optimized algorithm is applied for the estimation of the energy consumption of the room. Finally, an application example is presented. The results indicate that, in a room with the displacement system, the indoor air quality is much better than with a well-mixed system, and the energy savings are significant.

KEYWORDS displacement ventilation, calculation techniques

#NO 4254 Thermal plumes in ventilated rooms - measurements in stratified surroundings and analysis by use of an extrapolation method.

AUTHOR Kofoed P, Nielsen P V

BIBINF Norway, Oslo, Norsk VVS, Roomvent 90 proceedings, 13-15 June 1990, paper 36, 20pp, 12 figs, 6 tabs, 18 refs. #DATE 00:06:1990 in English

ABSTRACT The design of a displacement ventilation system involves determination of the flow rate in the thermal plumes. The flow rate in the plumes and the vertical temperature gradient influence each other, and they are influenced by many factors. This paper shows some descriptions of these effects. Freeturbulent plumes from different heated bodies are investigated. The measurements have taken place in a full-scale test room where the vertical temperature gradients have been changed. The velocity and the temperature distribution in the plume are measured. Large scale plume axis wandering is taken into account and the temperature excess and the velocity distribution are calculated by use of an extrapolation method. In the case with a concentrated heat source and nearly uniform surroundings the model of a plume above a point heat source is verified. Itrepresents a borderline case with the smallest entrainment factor and the smallest angle of spread. Due to the measuring method and data processing the velocity and temperature excess profiles are observed more narrowly than those reported by previous authors. In the case with an extensive heat source the model of a plume above a point heat source cannot be used. This is caused either by the way of generating the plume including a long intermediate region or by the environmental conditions where vertical temperature gradients are present. The flow has a larger angle of spread and the entrainment factor is greater than for a point heat source. The exact knowledge of the vertical temperature gradient is essential to predict the flow of propagation due to its influence on the entrainment, e.g. in an integral method of plume calculation. Since the flow from different heated bodies in individual full-scale measurements seems to be the only possible approach to obtain the volume flow in: thermal plumes in ventilated rooms.

KEYWORDS thermal analysis, mathematical modelling

#NO 4255 Convection flows above common heat sources in rooms with displacement ventilation.

AUTHOR Mundt E

BIBINF Norway, Oslo, Norsk VVS, Roomvent 90 proceedings, 13-15 June 1990, paper 38, 12pp, 6 figs, 3 tabs, 17 refs. #DATE 00:06:1990 in English

ABSTRACT The convection flows from different heat sources in a room are the driving forces for the displacement ventilation. The volumes of these flows have to be known in order to see if the ventilation will behave as expected. Convection flows from different heat sources in surroundings with an even temperature has earlier been investigated. However the convection flows in surroundings with temperature gradients are not as well known.In rooms with displacement ventilation there is always a temperature gradient. The temperature gradients are dependent on the geometry of the room, the internal loads and the ventilation flow. This paper presents a method to calculate the gradients in the room, which have been experimentally proved. It also presents measurements of the air volume flows in plumes above common heat sources in rooms with different temperature gradients.

KEYWORDS convection, air flow, heating, displacement ventilation

#NO 4876 Displacement ventilation.

AUTHOR Jackman P J

BIBINF UK, Chartered Institution of Building Services Engineers, 1991, CIBSE National Conference 1991, held at University of Kent, Canterbury, 7-9 April 1991, pp 364-380, 17 figs, 9 refs. #DATE 00:00:1991 in English

ABSTRACT This paper presents information on the principles and application of displacement ventilation and discusses the most significant design parameters. Included are details of the performance characteristics of low velocity air terminal devices and of the resulting indoor environment based on experimental studies. Strategies for the design of displacement ventilation systems are also presented.

KEYWORDS displacement ventilation

#NO 5098 High versus low momentum ventilation in a machine workshop.

AUTHOR Breum N O

BIBINF Germany, Staub- Reinhaltung der Luft, No 51, 1991, pp 91-96, 5 figs, 19 refs. #DATE 00:00:1991 in English

ABSTRACT The common practice in industrial hygiene is to use high momentum (dilution) ventilation. Increasingly, low momentum (displacement) ventilation, which ideally supplies fresh air that displaces the contaminated air without mixing, is being introduced. By means of an intervention study the relative performance of the two principles of design was evaluated using signal-response tracer gas technique. In terms of supplying fresh air to the zone of occupancy low momentum ventilation was better than high momentum ventilation by a factor ranging from 1.0 to 4.0. This finding applies only if convective upcurrents are balanced by supply of incoming air and high level extract.

KEYWORDS workplace, ventilation strategy, displacement ventilation, dilution ventilation

#NO 5328 Thermal plumes in ventilated rooms - vertical volume flux influenced by enclosing walls.

AUTHOR Kofoed P, Nielsen P

BIBINF UK, AIVC 12th Conference, "Air Movement and Ventilation Control within Buildings", held 24-27 September 1991, Ottawa, Canada, proceedings published September 1991, Volume 3, pp 331-344. #DATE 00:09:1991 in English

ABSTRACT The flow rate in thermal plumes are influenced by many factors. Influence by enclosing walls is one of them. This article presents simple symmetry considerations to calculate the flow rate in such flows, and they are experimentally verified as regards wall plumes. When the flow takes place near to enclosing walls the entrainment is influenced and a reduction of the flow rate is observed. For displacement ventilation this means a reduction of the stipulated necessary ventilating air flow rate when an air quality based design method is used.

KEYWORDS air flow, thermal analysis

#NO 5556 Temperature gradients and convective air flows in displacement ventilation.

Temperaturgradienter och konvektionsfloden vid deplacerande ventilation.

AUTHOR Mundt E

BIBINF Sweden, Swedish Council for Building Research, unpublished report, [1991]. #DATE 00:00:1991 in Swedish

ABSTRACT For the design of displacement ventilation the amount of air transported in the convective air flows need to be known as they are responsible for the transport of the air in the room. These convective flows depend on the temperature and geometry of thesource as well as the surrounding conditions. The formulas presented so far are based on results obtained in rooms without temperature gradients, but the basis for displacement ventilation is a temperature gradient. An extended knowledge about the convective air flows at different conditions and the actual temperature gradients in displacement ventilation will form a better design basis for this ventilation principle. This report presents a simple method for the calculation of the temperature relations in rooms with displacement ventilation from which the temperature gradient can be obtained. The convective air flows from common heat sources in offices has been measured for different gradients. The results show that the convective air flows are influenced not only by the gradient but also by the ventilation air flow. This last-mentioned influence is for some cases greater than the influence of the gradient.

KEYWORDS displacement ventilation, air flow, convection, temperature

#NO 5605 Calculation method for airflow rate in displacement ventilation systems.

AUTHOR Laurikainen J

BIBINF USA, Ashrae, "IAQ 91 Healthy Buildings", proceedings of a conference held September 4-8, 1991, Washington, DC, pp 111-115, 1 fig, refs. #DATE 00:09:1991 in English

ABSTRACT The operation of displacement ventilation is based on the natural upward movement of air as it warms up. Different kinds of equipment warm the room air and cause an upward thermal current. The same heat sources might also produce impurities andcontaminants, which will rise with the convective flow.Temperature and concentration gradients are naturally formed in displacement ventilation. Contaminants and excess heat are exhausted at a high level. The aim is to keep the occupied zone as clean and comfortable as possible. At a certain level, the amount of convective flow is equal to the fresh airflow introduced to the space at floor level. This is the so-called shift zone. The main goal is to keep this shift zone above the occupied zone and achieve a clean and comfortable occupied zone. The design method for displacement ventilation is based on calculation of the total convective flow generated by the heat sources. Different kinds of heat loads cause different amounts of convection. This problem has been taken into account by selecting the most important heat-source parameters affecting the convective flow. These parameters were found in 140 tests conducted under both laboratory and field conditions. Correlations for the airflow rate calculations for displacement systems were developed by using these measurement results.

KEYWORDS air change rate, displacement ventilation

#NO 5630 Indoor airflow with cooling panel and radiative/convective heat source.

AUTHOR Jiang Z, Chen Q, Moser A

BIBINF USA, Ashrae, Transactions, Vol 98, Part 1, 1992, 10pp, 8 figs, 1 tab, refs. #DATE 00:00:1992 in English

ABSTRACT This paper numerically studies the effects of a radiative heat source and a cooling panel on indoor airflow, temperature stratification, and dispersion of contaminants in a furnished office with displacement ventilation. The air supply device simulated is a quarter-cylinder displacement diffuser. The percentage of radiative heat is considered to be 20% and 80%, respectively, and the ventilation rate changes from 2.1 ach to 4. 2 ach. Four cases, with and without a cooling panel, are examined. In order to determine the radiative heat transferbetween surfaces of the room, a simplified analytical method is proposed to estimate the temperature of an adiabatic wall so that computer time can be saved without a significant sacrifice inaccuracy. It has been found that a ceiling-mounted cooling panel can not only reduce the vertical temperature stratification but also strengthen the air movement. With the same total heat, the increase in the portion of radiative heat may enhance air movement and contaminant dispersion. Also, the air temperature in the central region becomes lower.

KEYWORDS airflow, displacement ventilation, office building, radiator, heat transfer, numerical modelling

#NO 5794 Field comparison of age of air measurement techniques.

AUTHOR Roulet C-A, Cretton P

BIBINF Switzerland, Lausanne, Ecole Polytechnique Federale, [1992], 15pp, 7 figs, 3 tabs, 7 refs. #DATE 00:00:1992 in English

ABSTRACT The measurement of the local mean age of air at various locations in a room is useful to verify the efficiency of the ventilation system and to assess the main air streams and the dead zones. Several methods, using tracer gas, can be used to measure the age of air. This paper presents a comparison of these methods, including a study of the possible advantages and inconveniences. Simultaneous measurements were performed with two tracers in an auditorium with balanced ventilation and complete mixing, using step-up, step-down and pulse techniques. Another experiment in a test office room with displacement ventilation brought some more experience. Practical consequences of these field experiments are also reported. Conclusions of this study are that a) good mixing of the tracer and the air to be marked is essential and is often a problem; b) step-up injection technique is best appropriate for rooms with pulsed air; c) pulse technique can also be used in these rooms but is more sensitive to concentration errors and d) step-down (or decay) technique should be reserved for rooms with significant infiltration. These conclusions are somewhat different than those published by other authors after similar studies.

KEYWORDS measurement technique, ageing, ventilation system, ventilation efficiency, auditorium, displacement ventilation

#NO 5845 9th AIVC Conference: Effective ventilation: Proceedings Volume 1.

AUTHOR Air Infiltration and Ventilation Centre

BIBINF UK, Air Infiltration and Ventilation Centre, 9th AIVC Conference proceedings Vol.1, held Novotel Hotel, Gent, Belgium, 12-15 September, 1988, 439pp. #DATE 00:09:1988 in English

ABSTRACT Twenty three papers form the ninth AIVC Conference, titles as follows: Keynote speech: Air Infiltration and Ventilation; Natural airflows between roof, subfloor and living spaces; Experimental analysis of air diffusion in large space; Determination of ventilation efficiency based upon short termtests; Ventilation strategies in the case of polluted outdoor air situations; Ventilation generated by a fluctuating pressure differential; Air motion in the vicinity of air-supply devices for displacement ventilation; Integral mass balances and pulse injection tracer-techniques; Commercial building ventilation measurements using multiple tracer gases; Constant concentration measurement with 2 tracers; Extended testing of a multifamily building using constant concentration and PFT methods; Analysis of errors for a fan-pressurization technique for measuring inter-zonal air leakage; The use of a guarded zone pressurization technique to measure air flow permeabilities of amulti-zone building; Air leakage between apartments; Air infiltration induced by heating appliances; Indoor formaldehyde levels in energy-efficient homes with mechanical ventilation systems; Recirculation of air in dwellings; Effective ventilation in offices - the occupant's perspective; Aventilation concept for future dwelling-houses; Natural ventilation for a Crown court: developing statistical assessment techniques at the design stage; Market analysis of sensors for the use in demand controlled ventilating systems; Ventilation design for a bus station; Ventilation and air quality in Belgian buildings: a state of the art.

KEYWORDS ventilation effectiveness, ventilation system

#NO 6065 Testing and modelling of thermal plumes in rooms.

AUTHOR Mierzwinski S

BIBINF Japan, Society of Heating, Air Conditioning and Sanitary Engineers of Japan, 1992, proceedings of the International Symposium on Room Air Convection and Ventilation Effectiveness - ISRACVE, held at the University of Tokyo, 22-24 July, 1992, pp 499-519. #DATE 22:07:1992 in English

ABSTRACT Thermal plumes, even weak ones, are essential factors causing air movement in rooms. Recently, convective flows have become of particular interest owing to displacement ventilation. Referring to ventilation processes predicting the paper discusses experimentally acquired knowledge of plumes characteristics as well as the experimentally improved integral method for calculation. The method makes it possible to simulate a plume over a heat source of any shape, also in theenvironment with stratification and to analyse and optimize numerically the measurement results in different conditions. Mutual relations between the plume model and buoyant ventilation modelling are mentioned. Attention is paid to the choice of methods for air flow pattern predicting in spaces with heat sources.

KEYWORDS modelling, air movement, convection, displacement ventilation

#NO 6121 Simulation of flow and heat transfer in ventilated rooms.

AUTHOR Yuguo Li

BIBINF Sweden, Royal Inst of Technology, Dept of Mechanics\Applied Computational Fluid Dynamics, 1992. #DATE 00:00:1992 in English

ABSTRACT The present thesis is a numerical/experimental study of air flows in rooms. The main emphasis is put on the numerical simulation and measurement of interactions between convection and radiation and the application of an efficient solver. Two radiation models are used: a Two-Band Radiation Model (TBRM) which allows two separate effects of short and long-wave radiation and the Discrete Transfer Model (DTM)which includes both gas and surface radiation effects. A simplified nodal approach is developed, which can predict the temperature profile,based on the flow and thermal characteristics with displacement ventilation. The simple four-node model predicts the mean vertical temperature gradient in the room well, when the heat loss is not significant compared to the heat load in the room (<10%). The results of multi-nodal model show quite good agreement with the experimental data, when the heat loss is larger (>10%). A numerical approach for predicting interactions between convection and radiation is developed in which the radiation exchange calculation is decoupled from the energy equation. Both a single-grid solver and a multi-grid method with local grid refinement are used to solve the discrete equations. The latter is shown to be considerably faster.

KEYWORDS simulation, air flow, heat transfer, displacement ventilation, indoor air quality, thermal comfort

#NO 6226 Control aspects of displacement ventilation with cooled ceiling.

AUTHOR Prochaska V, Kegel B, Kofoed P

BIBINF Roomvent '92, Third International Conference, Aalborg, Denmark, September 2-4 1992, Publisher: DANVAK, Lyngby, Denmark, Volume 3, pp 53-68. #DATE 02:09:1992 in English

ABSTRACT A test room with displacement ventilation and cooled ceiling was provided with a DDC (Direct Digital Control) System controlling the sequence between heating, air volume flow and cooling water flow for the ceiling. Air velocity and temperature profiles were measured at different locations in the room for various internal loads. The aim of the experiments was to analyse the system with regard to control and to compare various control strategies, which influence comfort conditions and energy consumption. Different control sequences were tested to optimize the system function. The test shows that unlike mixing ventilation the displacement ventilation system contains a dead timecomponent, above all with a small air change rate. To keep the total dead time as low as possible, it is preferable to use sensors with a small time constant. Sequences between cooling (VAV and ceiling) and heating as well as an energy free zone have to be considered to allow appropriate operation of the system. A system with displacement ventilation and cooled ceiling operates with numerous variables as room air temperature, supply air temperature, volume flow rate, humidity etc. The comfort at the work place as well as the energy consumption are influenced by the adjustment of these parameters. It is scarcely possible though to reach such an optimisation in a real building. For this purpose it is better to use simulation and laboratory tests to find the most favourable parameters and to apply them in the real equipment.A lot of work still remains to be done in order to optimise the control system. This will allow a further reduction of energy consumption as well as a lowering of the equipment peak performance without worsening of comfort.

KEYWORDS displacement ventilation, ceiling, air velocity, sensor

#NO 6263 Evaluation of air supply method in a classroom with a low ventilation rate.

AUTHOR Chen Q, Jiang Z

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 412-419. #DATE 00:10:1992 in English

ABSTRACT A numerical study has been carried out to predict the indoor air quality and thermal comfort in a classroom with a low ventilation rate. Four different air supply methods (displacement ventilation, well-mixed ventilation, and two low-wall-diffuser ventilation) are used. The airflow pattern, predicted percentage of dissatisfied (PPD), percentage dissatisfied people due to draught (PDd), CO2 concentration, and percentage dissatisfied people due to indoor air quality (PDa) are computed by a program with a k-e turbulence model. It has been found that the secondary flow generated by the buoyancy from the pupils is much stronger than the primary flow supplied from the diffusers. As a result, the overall ventilation effectiveness and thermal comfort are similar under the four air supply methods except in the region near the diffusers. Supplying fresh air in the lower level may cause draught.For an acceptable perceived indoor air quality, the ventilation rate should be increased to meet the requirement by the ASHRAE Standard 62-1989.

KEYWORDS school, ventilation rate, numerical modelling, thermal comfort, air flow

#NO 6329 Field comparison of age of air measurement techniques.

AUTHOR Roulet C-A, Cretton P

BIBINF Roomvent '92, Third International Conference, Aalborg, Denmark, September 2-4 1992, Publisher: DANVAK, Lyngby, Denmark, Volume 3, pp 213-230. #DATE 02:09:1992 in English

ABSTRACT The measurement of the local mean age of air at various locations in a room is useful to verify the efficiency of the ventilation system and to assess the main air streams and the dead zones. Several methods, using tracer gas, can be used to measure the age of air. This paper presents a comparison of these methods, including a study of the possible advantages and inconveniences. Simultaneous measurements were performed with two tracers in an auditorium with balanced ventilation and complete mixing, using step-up, step-down and pulse techniques. Another experiment in a test office room with displacement ventilation brought some more experience. Practical consequences of these field experiments are also reported. Conclusions of this study are that a) good mixing of the tracer and the air to be marked is essential and is often a problem; b) step-up injection technique is best appropriate for rooms with pulsed air; c) pulse technique can also be used in these rooms but is more sensitive to concentration errors and d) step-down (or decay) technique should be reserved for rooms with significant infiltration. These conclusions are somewhat different than those published by other authors after similar studies.

KEYWORDS ageing, measurement technique, ventilation system, tracer gas

#NO 6520 Evaluation of smoking lounge ventilation designs.

AUTHOR Straub H E, Nelson P R, Toft H R

BIBINF USA, ASHRAE Transactions, Vol 99, Pt 1, 1993, 10pp, 11 figs, 2 tabs, refs. #DATE 00:00:1993 in English

ABSTRACT Two displacement-type and two diffusion-type ventilation configurations were tested in a specially constructed smoking lounge. The four arrangements were tested under worst-case conditions of use to determine the most satisfactory method to ventilate a smoking lounge. Ventilation air was provided to the lounges at rates suggested by ASHRAE Standard 62-1989. Additional tests were performed at reduced ventilation rates.Concentrations of CO and CO2 were monitored in real time during the tests. Smokers were polled to determine their satisfaction with the air quality in each configuration. Air motion, velocities, and temperatures also were measured in the room. Ventilation at 60 cfm per person provided acceptable air quality in the lounge. Under the extreme conditions tested, ventilation at reduced volume resulted in unacceptable air quality. Results of this study indicate that smoking lounge air quality that is acceptable to the occupants can be attained by minor modification of existing convectional air distribution systems.

KEYWORDS tobacco smoke, ventilation system, displacement ventilation, diffusion

#NO 7104 Evaluation of a vertical displacement ventilation system.

AUTHOR Olesen B W, Koganei M, Holbrook G T, Seelen J, Woods J E

BIBINF Finland, Helsinki, Indoor Air '93, proceedings of the 6th International Conference on Indoor Air Quality and Climate, 1993, Vol 5, pp 265-270. #DATE 00:07:1993 in English

ABSTRACT The effectiveness of a vertical displacement ventilation system was evaluated when contaminants including tobacco smoke were present. The system tested supplied air through a perforated floor and carpet. The system performance was evaluated using ADPI, percentage dissatisfied due to draught, vertical temperature profile, air change effectiveness, and contaminant removal effectiveness. Gaseous contaminants were simulated with tracer gas. Also, particulates, CO and CO2 were generated by cigarettes and occupants. Several combinations of supply air flow rate and thermal loads in the occupied zone were evaluated. Because of the method of air supply, very uniform air temperature and velocity conditions were obtained. The risk of draught was found to be negligible. The air change effectiveness of the system varied from 130 to 200%, increasing with increasing supply air flow rate and decreasing with increasing thermal load in the space. Contaminant removal effectiveness and varied, depending on type of contaminant, from 80 to 580%.

KEYWORDS displacement ventilation, tobacco smoke, floor coverings

#NO 7117 Effect of cooled ceilings in rooms with displacement ventilation on the air quality.

AUTHOR Kruhne H

BIBINF Finland, Helsinki, Indoor Air '93, proceedings of the 6th International Conference on Indoor Air Quality and Climate, 1993, Vol 5, pp 395-400. #DATE 00:07:1993 in English

ABSTRACT The use of displacement ventilation systems combined with cooled ceilings for air-conditioning rooms has recently become more important. Reasons for this importance are the positive comfort effects of displacement flow with cooled ceilings and the better air quality compared with rooms with conventional HVAC systems. In order to achieve the best possible air quality in the breathing zone of a person it is necessary to investigate the influence of the cooled ceiling on the displacement flow and on the air quality. Measurements were conducted using a tracer gas method and infrared thermography. The investigations show that the cooled ceiling has effects on the air quality of the room because buoyant wall flows influence the displacement flow. This influence becomes measurable as it, while the ceiling temperatures decrease, increases the contamination in the fresh air layer.

KEYWORDS cooling, ceiling, thermal comfort, air movement

#NO 7224 Influence of buoyant wall-flow in rooms with displacement ventilation

AUTHOR Krhne H

BIBINF UK, CIBSE, proceedings of CLIMA 2000, 1-3 November 1993, Queen Elizabeth II Conference Centre, London, 1993, paper no. 210. German

ABSTRACT The use of displacement ventilation systems combined with cooled ceilings for air conditioning rooms has become more important lately. Reasons for this being important are the positive comfort criterias of displacement flow with cooled ceilings and the better air quality in relation to rooms with mixing ventilation. To achieve a maximum of air quality in the breathing zone of a person it is necessary to investigate the parameters which influence the displacement flow in the room and in the buoyant plume of a person. In order to determine the influence of the cooled ceiling on the displacement flow measurements were conducted with the tracergas method. Thermographic pictures of walls and the ceiling show the thermic conditionings of walls and ceiling. The investigations show that the cooled ceiling has effects on the air quality of the room. This is caused by buoyant wall flows influencing the fresh air layer. In this way thecontamination in the fresh air layer will increase.

KEYWORDS ventilation displacement_ventilation rooms air_flow walls buoyancy air_conditioning ceiling_cooling ceilings indoor air_quality tracers measuring thermophotography contaminants

#NO 7229 Plume in the process of ventilation by displacement

AUTHOR Mierzwinski S; Popiolek Z

BIBINF UK, CIBSE, proceedings of CLIMA 2000, 1-3 November 1993, Queen Elizabeth II Conference Centre, London, 1993, paper no. 341.

ABSTRACT In a displacement ventilation system a thermal plume which is formed over a heat source evokes circulation flows, thermal stratification of the room air and the air transport from the supply to the outlet openings. Theresults of experiments on plumes spreading in an enclosure with different inflow and outflow rates were analyzed by means of the improved integral method. The analysis proved that the entrainment factor of the plume could change and the volume flux of the plume could be limited by the supply air flux choking. The fact should be taken into consideration, particularly when controlling the position of the interface in the enclosure in displacement ventilation.

KEYWORDS ventilation displacement_ventilation air_flow jets experiment

#NO 7362 Numerical prediction of airflow and heat-radiation interaction in a room with displacement ventilation.

AUTHOR Li Y, Fuchs L, Sandberg M.

BIBINF UK, Energy and Buildings, No 20, 1993, pp 27-43, 16 figs, 38 refs. #DATE 00:00:1993 in English

ABSTRACT This paper presents a numerical method for predicting the surface radiation effects on the indoor thermal environment. The computational fluid dynamics simulations include the calculation of radiation between different surfaces and conduction through walls. The radiative effects on flow and temperature fields are studied in a room with displacement ventilation. The simulated results show good agreement with the measured data. By using different wall surface emissivities, the calculations show that the radiative effects are to heat the floor surface and to decrease the stratification seen with displacement ventilation.

KEYWORDS numerical modelling, air flow, displacement ventilation.

#NO 7880 Multi-grid prediction of conjugate heat transfer and air flow in buildings.

AUTHOR Li Y, Holmberg S, Fuchs L.

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 449-455. #DATE 00:08:1993 in English

ABSTRACT The heat conduction through the walls changes the heat load and its distribution in a room, and thus affects the air flow pattern in a buoyancy-controlled ventilated room. This paper presents a methodology of how conjugate heat transfer and air flow in a room can be handled in an efficient computational fluid dynamics (CFD) code. The wall and indoor air regions are simulated simultaneously. The standard k-e model is used for modelling the turbulence in rooms. The transport equations take thesame form in both fluid (air) and solid (wall) regions. The boundary conditions for the momentum and energy equations are specified at the outer surface of the walls. A multi-grid solver is applied to the problem of conjugate heat transfer and turbulent indoor air flow. The local grid-refinement technique is introduced to add local grid points in the regions where variable gradients are large. The multi-grid solver shows a much faster convergence rate than the single grid solver for the non-isothermal cases in this study. The developed approach is applied to a modelled 3D room and a room with displacement ventilation. This approach together with the previously developed general thermal boundary conditions, allows the study of interactions between indoor and outdoor environments.

KEYWORDS prediction, heat transfer, air flow

#NO 8134 Ventilation models.

AUTHOR Skaret E

BIBINF Belgium, Von Karman Inst. for Fluid Dynamics, Lecture Series 1993-07, "Advanced Design of Ventilation Systems", proceedings of conference held 7-9 June 1993, pp 1-25, 13 figs, 1 tab, refs.

ABSTRACT Ventilation for contaminant control involves, as a first step, the use of elimination technics, i.e. to apply any practical and economical method to prevent contaminant exposure, say: Using building materials that do not emit contaminants, close up processes and depressurize the enclosure, change the process, change to less toxicsolvents, apply hoods and other local exhaust methods, etc. When above are done there is still some residual contaminant emission to be handled by the ventilating system. In the design process of ventilating systems calculation models for analysing and dimensioning the systems should be utilized. This lecture presents calculation procedures especially suited for displacement ventilation in addition to linking it to mixing ventilation.

KEYWORDS (modelling, ventilation system, building material)

#NO 8311 Contaminant distribution around persons in rooms ventilated by displacement ventilation 

AUTHOR Brohus Henrik, Neilsen Peter V. 

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 293-312. 

ABSTRACT An optimal design of the ventilation system needs a proper prediction of the velocity, temperature and contaminant distribution in the room. Traditionally this is done either by the use of simplified models or by a somewhat more comprehensive CFD-simulation. Common to both methods is usually the lack of consideration for the persons present in the room. This paper deals with some of the effects of persons present in a displacement ventilated room, especially the effect on the contaminant distribution. It is demonstrated that although the contaminant distribution is affected the stratification in the flow is stable when people are moving around in the room. The exposure of a sitting and a standing person in proportion to the stratification height is examined. It is found that the flow in the boundary layer along a person to a great extent is able to entrain air from below the breathing zone. Measurements also show the possible disadvantage when contaminant sources are located in the lower part of the room. Two new quantities, applied in connection with personal exposure in ventilated rooms, are defined. 

KEYWORDS displacement ventilation, pollutant, occupancy effects

#NO 8327 Numerical prediction of the age of air in ventilated rooms 

AUTHOR Gan G, Awbi H B. 

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 2, pp 15-28. 

ABSTRACT This paper presents a method for predicting the local mean age of air in ventilated rooms using computational fluid dynamics. The airflow model consists of the continuity equation, momentum equation, thermal energy equation, concentration equation and equation for the age of air together with the k- turbulence model equations. The results concentration diffusion on the predicted age of air is investigated. The age of air is then used to evaluate the performance of different air distribution systems. It has been found that disregarding the diffusion term in the age equation increases the predicted age of air. It is shown that displacement ventilation is more effective than mixing ventilation in terms of a lower age of air. However, the age of air alone is not sufficient for assessing indoor air quality or the overall ventilation effectiveness for occupied spaces. 

KEYWORDS prediction, ageing, CFD

#NO 8521 Displacement ventilation performance - office space application 

AUTHOR Alamdari F, Bennett K M, Rose P M 

BIBINF UK, Building Services Research and Information Association. Technical Note TN 3/93, July 1993, 18 pp. 

ABSTRACT Displacement ventilation is a method that provides conditioned air to indoor environments with the view to improve air quality whilst reducing energy usage. These systems have been employed in industrial applications, notably in Scandinavia, for many years and have gained in popularity in office building spaces in recent years. Measurements of velocity and temperature fields have been performed in three modern office spaces to analyse the performance of the incorporated displacement ventilation system (1), based on thermal comfort and temperature gradient assessment (2). The measurements at one of the sites were used to verify the predicted data obtained by a microclimate computer model based on computational fluid dynamics (CFD) techniques. The model was subsequently used to study the effect of cold surfaces, infiltration, floor obstructions and supply air flow rates. Although the application of displacement ventilation is more difficult in office spaces with low ceiling heights, acceptable conditions were measured in two of the three sites considered in this study. However, both measurements and prediction indicated that secondary air flows resulting from infiltration and cold surfaces can adversely affect the ventilation performance and reduce thermal comfort. In the application of displacement ventilation care should be taken to minimise these extraneous effects. 

KEYWORDS displacement ventilation, office building, thermal comfort, numerical modelling.

#NO 8603 Performance of three air distribution systems in a ventilation duct factory 

AUTHOR Koskela H, Niemela R, Hautalampi T. 

BIBINF Sweden, Proceedings of the 4th International Symposium on Ventilation for Contaminant Control, Ventilation '94, held in Stockholm, September 5-9, 1994, Arbetsmiljoinstitutet, 1994:18, Part 1, pp 417-422. 

ABSTRACT The performance of ventilation and the air flow pattern in a factory hall with three different air distribution systems was studied using several methods. The supply air distribution was characterised by tracer gas experiments. A measurement carriage was used to measure the distribution of air velocity and air temperature in the hall. The contaminant concentration was measured by taking dust samples. A low contaminant concentration level was achieved with all ventilation systems. The low impulse units gave the highest local air change indexes in the occupied zone. They also created somewhat higher air velocities in the upper zone, than the perforated ducts. The mixing air distribution system produced a smaller vertical temperature difference and higher air velocities than the two displacement systems. 

KEYWORDS air distribution, factory, duct, tracer gas, air velocity. displacement ventilation

#NO 8923 Full scale measurements of indoor air flow (tests on two single rooms in an office building). 

AUTHOR Handa K 

BIBINF Sweden, Gothenburg, Chalmers University of Technology, Building Aerodynamics Research Group, December 1994, 59pp. 

ABSTRACT Full scale measurements of air flow velocities, temperature, intensity of turbulence and air exchange rate are carried out on two rooms with different type of ventilation located in the department of architecture at Chalmers University of Technology. The measurements have shown that mixed ventilation gives variable mean flow velocities with a high risk of draught as compared to the room provided with displacement ventilation. Air exchange rate for the room with displacement ventilation is obtained from tracer gas monitor and two different methods are employed in the measurements. The measurements have shown that both the decay and constant emission methods give similar results. 

KEYWORDS air velocity, turbulence, air change rate, ventilation system, mixing ventilation, displacement ventilation

#NO 8924 Numerical investigation of turbulent plumes in both ambient and stratified surroundings.

AUTHOR Shankar V, Davidson L, Olsson E 

BIBINF Indoor Air, No 5, 1995, pp 136-146, 15 figs, 2 tabs, refs. 

ABSTRACT Ventilation displacement systems have, during the last ten years, become more and more popular. In these systems cool air is supplied to the room, and the air is heated by heat sources. The rising air above these heat sources id of paramount importance to the behaviour of the ventilation displacement systems. In the present work the turbulent flow in plumes is studied numerically, using finite volume methods. The standard k-e model was found to under-predict the spreading of the plumes, and it was thus modified in two ways so as to predict spreading rates in agreement with experiments. We present a comprehensive comparison between predictions and experiments including spreading rates, velocity and temperature profiles, and turbulent shear stresses. The volume flow rate versus the vertical distance from the plume is also presented. Good agreement between predictions and experiments is obtained. 

KEYWORDS numerical modelling, turbulence, displacement ventilation

#NO 9171 About the meaning and the experimental assessment of some ventilation indices. Sul significato e la misura di alcuni indici di ventilazione. 

AUTHOR Fracastoro G V, Perino M 

BIBINF Italy, CDA, No 11, November 1995, pp 1142-1153, 3 figs, 4 tabs, 16 refs, in Italian. 

ABSTRACT In the last fifteen years, a number of experimental methods have been developed for the analysis of ventilation systems in the field. Among these, the tracer gas techniques, initially developed for the study of natural ventilation, are now widely applied also to mechanical ventilation systems, especially for evaluating the performance of innovative ventilation systems (e.g. displacement systems). The paper reviews the physical meaning and the main measurement methods of ventilation, air exchange, and air quality indices, with special attention to the techniques adopted to use them in the field. Examples of the application of these techniques are also given describing the protocols adopted by the authors. 

KEYWORDS tracer gas measurements, mechanical ventilation, displacement ventilation


#NO 9189 Buoyant plume in the process of ventilation - heat and momentum turbulent diffusion. 

AUTHOR Popiolek Z 

BIBINF paper presented at Annex 26 expert meeting in Poitiers, October 1993, 12pp, 7 figs, 5 tabs, 18 refs. 

ABSTRACT In a displacement ventilation system a thermal plume which is formed over a heat source evokes circulation flows, thermal stratification of the room air and air transport from the supply to the outlet opening. The results of experiments on plumes spreading in an enclosure with different inflow and outflow rates were analyzed by means of the improved integral method. The analysis proved that the entrainment factor of the plume could be changed and the volume flux of the plume could be limited by the supply air flux choking. They also proved that turbulent heat and momentum diffusion in the buoyant plume depended on the plume enthalpy and stratification in its surroundings. The fact should be taken into consideration, particularly when controlling the position of the interface in the enclosure in displacement ventilation. The paper presents analysis of volume flux increment in plumes. The analysis was carried out in order to find out how the accuracy of volume flux evaluation could be increased in practical engineer s calculations. Some information is given about the aim of the research on plumes presently carried out at the Department of Heating Ventilation and Dust Removal Technology, Silesian Technical University in Gliwice, Poland. 

KEYWORDS displacement ventilation, air flow

#NO 9722 CFD simulation of swirl jet displacement ventilation systems.

AUTHOR Tinker J A, Woolf D R S

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 1032-1037, 10 figs, 1 tab, 7 refs.

ABSTRACT An investigation was made into the methods of numerically simulating swirl jet displacement ventilation systems. Experimental data was obtained from a quarter-scale physical model that was ventilated using a swirl jet displacement type system. The data was compared with results obtained from a dynamic thermal model (DTM) and computational fluid dynamics (CFD) simulation under the same geometric configuration, flow rate and internal heat load. The CFD solution was developed from high to low resolution computational mesh with various solution techniques, the overall trade-off being between computing (cpu) time and accuracy of solution. The results showed that for any space under investigation the accuracy of the solution is mainly dependent on the degree of simplification and approximations involved within the solution. When the space under investigation involves a ventilation system that is highly complex in nature, as is the case of swirl jets, additional modelling difficulties may occur. The three-dimensionality of the solution may lead to misinterpretation of results if great care is not taken.

KEYWORDS computational fluid dynamics, displacement ventilation

#NO 9786 Simple design tools applied to an underground stadium and compared with indoor climate measurements.

AUTHOR van der Maas J, Kolsaker K

BIBINF Japan, proceedings of the 5th International Conference on Air Distribution in Rooms, Roomvent '96, held Yokohama, Japan, 17-19 July, 1996, Volume 2, pp 321-328.

ABSTRACT This paper presents results of the application of three different thermal analysis computer programs to Gjovik Olympic Mountain Hall. Gjovik Mountain Hall is an underground rock cavern used for ice-hockey, exhibitions, concerts, etc. which can accommodate 5800 spectators. Measurements in the hall are carried out, with the intention of using the results to verify design tools for the prediction of indoor climate and HVAC energy consumption. Continuous measurements have been taken of air flow rates and air temperatures, for one year. The data has been collected from Building Management System (BMS). The first computer program, Fres, was used for design energy calculations. Fres is a building simulation program for predicting heating, cooling and ventilation energy consumption. A building can contain one or several rooms with arbitrary number of walls and windows between them. The temperature profile of walls is solved with a one-dimensional Finite Difference method. The second program, LescoCool, is a simple zonal model. The model couples ventilation heat flow and the thermal response of the walls assuming i) displacement ventilation ii) a convective heat transfer coefficient iii) semi-finite wall thermal response iv) thermal equilibrium for radiative heat gain. The wall thermal response of the hall can be characterised with a single parameter, the mean thermal effusivity. The parameters determining these design parameters (including the wall surface area covered by acoustic panels) are discussed. Thirdly, measurements have been compared with the program RockHall, which is a 2 dimensional program for calculating conduction and heat fluxes through surfaces and heat exchange between surfaces. This program is developed specially for rock halls and is the most detailed of the three candidates.

KEYWORDS indoor climate, building design

#NO 9855 Full-scale measurements of indoor air flow.

Handa K, Pietrzyk K

UK, Air Infiltration and Ventilation Centre (AIVC), 1996, proceedings of 17th AIVC Conference, "Optimum Ventilation and Air Flow Control in Buildings", Volume 1, held 17-20 September 1996, Gothenburg, Sweden, pp 273-281.

Full scale measurements of air flow velocities, temperature, intensity of turbulence and air exchange rate are carried out on two rooms with different types of ventilation located in the department of architecture at Chalmers University of Technology. The measurements have shown that mixed ventilation gives variable mean flow velocities with a high risk of draught as compared to the room provided with displacement ventilation. Air exchange rate for the room with displacement ventilation is obtained from tracer gas monitor by employing decay and constant emission methods. The measurements give similar results for both the methods.

air flow, air change rate, draughts, displacement ventilation

#NO 9872 The effect on ventilation parameters of various ventilation strategies.

Simons M W, Waters J R

UK, Air Infiltration and Ventilation Centre, (AIVC), 1996, proceedings of 17th AIVC Conference, "Optimum Ventilation and Air Flow Control in Buildings", Volume 2, held 17-20 September 1996, Gothenburg, Sweden, pp 457-466.

The work described in this paper is aimed at predicting the local values of the ventilation effectiveness parameters of large industrial buildings by a technique which involves the use of computational fluid dynamics and multizonal modelling. A modelling technique is described and applied to a typical modern industrial building equipped with both, mixing and displacement ventilation systems. The results of modelling each of the above systems are presented and discussed. They provide an interesting insight into magnitude and spatial variations in local air change index that occur in the occupied space. The results also demonstrate how differences in ventilation strategy can result in distinctly different variations of ventilation effectiveness parameters. It is concluded that the modelling technique described may be used to provide important information about the air movement characteristics of buildings in terms of local air change index and also that it could prove to be a very useful design aid.

ventilation strategy, prediction, large building, industrial building, modelling

#NO 9878 A technique to improve the performance of displacement ventilation during cold climate conditions.

Hansson P, Stymne H

UK, Air Infiltration and Ventilation Centre, (AIVC), 1996, proceedings of 17th AIVC Conference, "Optimum Ventilation and Air Flow Control in Buildings", Volume 2, held 17-20 September 1996, Gothenburg, Sweden, pp 521-528.

Ventilation by displacement is a type of ventilation where the air flow is thermally driven. By this arrangement one obtains two zones in the room - a lower zone with supply air conditions and an upper recirculation zone with extract air conditions. Cold climate causes downdraught from windows and external walls and results in a mixing of air from the upper into the lower zone. To avoid this problem during cold climate a new principle for ventilation by displacement is tested. Excess heat from the upper zone of the room is used for heating cold surfaces. The principle involves creation of a narrow space in front of the exterior wall, separating the cold wall from direct contact with room air. Extract air from the ceiling level is forced down through this space by an extraction fan. This method can advantageously by applied in large buildings where an external wall mainly consists of glass panes. In this case it might be appropriate to utilise the space between the inner couple of glasses for extract air. Tracer gas and temperature measurements were carried out in a test-room. The result shows that the ventilation efficiency improves when using the new principle. The thermal climate also improves due to less down-draught and higher surface temperatures.

displacement ventilation, cold climate

#NO 9950 Displacement ventilation.

Jackman P J

UK, Building Services Research and Information Association (BSRIA), Technical Memorandum 2/90, 36pp, 27 figs, 5 tabs, 15 refs.

In buoyancy driven, displacement ventilation, the incoming "fresh" air is gently introduced near the floor and at a temperature just slightly lower than the design room air temperature. The cool air flows slowly over the floor and air that has become warmed rises above the cool layer. Any local heat sources in the lower part of the room create convection currents that also contribute to the general upward movement and the air is ultimately exhausted at high level. Although this type of system has been used in other countries, notably in Scandinavia, since 1970, there is little experience of its use in the UK. This report contains state of the art information on the application of this method of ventilation and data appropriate to the design and operation in this country.

displacement ventilation

#NO 10022 Effects of outdoor thermal environment in displacement ventilation - Part 2 Heat transfer analysis.

Li Y, Moller S, Symons J

Indoor Air '96, proceedings of the 7th International Conference on Indoor Air Quality and Climate, held July 21-26, 1996, Nagoya, Japan, Volume 1, pp 817-822.

A reliable prediction of heat transfer is very important in the analysis of displacement ventilation, not only to assess the system cooling load, but also to ensure that the system utilizes the thermal fluid flow principles to achieve the required vertical air displacement. Four different methods are used to extract the heat transfer data from the output of a computational fluid dynamics analysis. The total heat gain into the room from the outdoor environment can be more than 50% of the total cooling load. It is shown that the outdoor environment also affect their spatial distribution of the heat gain.

outdoor air, displacement ventilation, heat transfer

#NO 10298 Thermoeconomics applied to building services. 

Tozer R M, Missenden J F 

UK, CIBSE, 1996, proceedings of CIBSE/ASHRAE Joint National Conference Part Two, held Harrogate, 29 September - 1 October 1996, Volume 1, pp 131-137. 

Thermoeconomics is a blend of thermodynamics with economics. The thermodynamic analysis uses the second law and the concept of exergy, the measure of usefulness of energy. Economics involves costing exergy flows in life costing techniques. The objective of thermoeconomics is to minimise a cost function, taking into account capital, maintenance and running costs. Most of these are expressed in terms of thermodynamic variables of the system. This will establish the most cost effective design parameters. This paper presents methods for applying a thermoeconomic analysis to a building services system, consisting of displacement ventilation air conditioning. The specific cost of indoor environment cooling is optimised in terms of system variables, such as water and air temperatures and mass flow rates. Firstly, certain system parameters are optimised, providing detailed exergy costing related to the plant capital and operating costs. Secondly, by analysing these, the most appropriate design modifications are implemented, and the system is again optimised. From the work presented, an improved thermal and economic design results, with a reduction in Life Cycle Cost of 21%. 

displacement ventilation, thermal performance


#NO 10586 Air distribution in an office building as measured with a passive tracer gas technique.

Stymne H, Boman C A

UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation and Cooling", 18th Annual Conference, held Athens, Greece, 23-26 September 1997, Volume 1, pp 379-388.

A passive tracer gas technique, the homogenous emission technique was utilised for measuring the air distribution in a part of an office building with displacement ventilation. Measurements were made during one winter period and one summer period. During the winter period the ventilation was run continuously, while on/off regulation was used during the summer period. The result from the winter measurement shows that the displacement effect was satisfactory but less pronounced close to the window-side of the office. The paper discusses the effect of on/off ventilation strategy on the requirement of the measurement technique and the implications of such strategy on air quality. It is shown that the homogeneous emission tracer gas technique yields the true average mean age of air, also during transient conditions, but that special precautions must be taken when using intermittent sampling of the air.

air distribution, tracer gas

#NO 10771 Comparing turbulence models for buoyant plume and displacement ventilation simulation.

Chen Q, Chao N T

Indoor Built Environ., No 6, 1997, pp 140-149, 5 figs, 17 refs.

Computational fluid dynamics may be used to predict the details of airflow in rooms served by displacement ventilation systems, provided a suitable turbulence model can be found. Since buoyant plumes are central to the displacement ventilation strategy, four turbulence models - three eddy-viscosity models (the 'standard' K-E model, and an RNG K-E model) and th Reynolds stress model - were applied to simulate airflow in a turbulent buoyant plume. Corresponding experimental data from the literature were used for validation, although for a plume stronger than expected in rooms as no reliable plume data for room air flow were found. The Reynolds stress model predicted velocity, temperature, and turbulence quantities satisfactorily while the eddy-viscosity models performed poorly. The eddy-viscosity models were then applied to predict airflow in a furnished room with displacement ventilation. The computer airflow patterns, mean velocities, temperature, and contaminant concentrations agree reasonably well with the experimental data obtained from a full-scale test chamber, but the discrepancies in some locations were large. 

turbulence, displacement ventilation

#NO 10923 Simplified method for indoor airflow simulation.

Chen Q, Xu W

Belgium, Proceedings of Clima 2000 Conference, held Brussels, August 30th to September 2nd 1997, paper 47, 18pp, 10 figs, 1 tab, refs.

At present, numerical simulation of room airflows is mainly conducted by either the Computational-Fluid-Dynamics (CFD) method or various zonal/network models. The CFD approach needs a large capacity of computer and a skillful expert. The results obtained with zonal/network models have great uncertainties. This paper proposes a new simplified method to simulate three-dimensional distribution of air velocity, temperature, and contaminant concentrations in rooms. The method assumes turbulent viscosity to be a function of length-scale and local mean velocity. The new model has been used to predict natural convection, forced convection, mixed convection, and displacement ventilation in a room. The results agree reasonably with experimental data and the CF1) computations. The simplified method uses much less computer memory and the computing speed is at least 10 times faster, compared with the CFD method. The grid number can often be reduced so that the computing time needed for a three-dimensional case can be a few minutes in a PC. 

air flow, simulation

#NO 11014 The advantage classroom; sustainable design for achieving indoor air quality, comfort, and an improved learning environment.

Belida L M, Turner W A, Martel S M, Johnson W

USA, Washington DC, Healthy Buildings/IAQ '97, 1997, proceedings of a conference held Bethesda MD, USA, September 27 - October 2, 1997, Volume 1, pp 123-128, 1 tab, 7 refs.

In March of 1996, a new Elementary School was occupied which is the first in the United States to utilise the concept of displacement ventilation as the primary means of providing both good indoor air quality and thermal comfort. In addition, the integrated "sustainable" design concepts of the facility also address other important factors including: sitting, programming, lighting, acoustics, energy efficiency, classroom computer usage and access for planned HVAC preventive maintenance. Ventilation and thermal comfort objectives are achieved through the use of a combination of 100% outdoor air delivered low in the classroom, and the use of demand controlled ventilation. This paper presents a brief explanation of the basic advantages of non-mixing, ventilation systems and discusses the HVAC costs, operational savings and environmental benefits of implementing this concept. Because of the success of the design in this initial facility, we have pursued this design strategy in several more schools that are currently under construction and are now utilising this approach for all school designs.

school, indoor air quality, thermal comfort, displacement ventilation

#NO 11091 A critical review of displacement ventilation.

Yuan X, Chen Q, Glicksman L R

USA, Ashrae Transactions, Vol 104, Pt 1, 1998, 13pp, 11 figs, 1 tab, refs.

This paper reviews several aspects of the performance of displacement ventilation: temperature distribution, flow distribution, contaminant distribution, comfort, energy and cost analysis, and design guidelines. Ventilation rate, cooling load, heat source, wall characteristics, space height, and diffuser type have major impacts on the performance of displacement ventilation. Some of the impacts can be estimated by simple equations, but many are still unknown. Based on current findings, displacement ventilation systems without cooled ceiling panels can be used for space with a cooling load up to 13 Btu/(h.ft2) (40 W/m2). Energy consumed by HVAC systems depends on control strategies. The first costs of the displacement ventilation system are similar to those of a mixing ventilation system. The displacement system with cooled ceiling panels can remove a higher cooling load, but the first costs are higher as well. The design guidelines of displacement ventilation developed in Scandinavian countries need to be clarified and extended to that they can be used for US buildings. This paper outlines the research needed to develop design guidelines for US buildings.

displacement ventilation, ventilation rate, cooling

#NO 11277 Ventilation and thermal performance of design options for stadium Australia.

Lomas K J, Eppel H, Cook M, Mardaljevic J

International Building Performance Simulation Association (IBSPA), 1997, proceedings of "Building Simulation '97", the Fifth International IBSPA Conference, held September 8-10, 1997, in Prague, Czech Republic, Volume I, pp 135-142, 12 figs, 2 tabs, refs.

For Stadium Australia, the planned centrepiece of the year 2000 Sydney Olympics, the architects aimed to minimise energy consumption by incorporating passive design measures which would provide ventilation, natural cooling and warming and daylight. This paper describes the simulations undertaken to guide the design of one space in the stadium - a banquet hall. Lighting simulations demonstrated that a facade design incorporating external fixed, horizontal shading and a light shelf can provide satisfactory daylighting levels and permit winter solar gains to offset heating demands, whilst excluding the summer sun. Thermal analyses illustrated that natural stack driven displacement ventilation can deliver conditions which might be considered comfortable despite the hot, sunny summertime conditions. The strategy employed ground cooling during the day, and night venting to cool insulated thermal mass at night. Summer comfort cooling could easily be incorporated to guarantee satisfactory internal temperatures. This hybrid solution had much lower energy demands, plant loads and operating periods than a conventional air conditioned solution. CFD analyses demonstrated that sufficient fresh air could be well distributed throughout the hall and that night venting would occur.

thermal performance, large building, passive design

#NO 11297 Application of CFD in investigation of ventilation strategies for improvement of working environment in a waste incineration plant.

Heiselberg P, Svidt K, Kragh H

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 155-163, 5 figs, 1 tab.

In this study CFD was applied to investigate the ability of different ventilation systems and strategies to improve the working conditions in a waste incineration plant. The plant, I/S Amagerforbraending, had expanded to be able to supply both district heating and power. This caused too high temperatures in the working zones and measures to reduce these levels had to be taken. Different solutions were suggested. CFD calculations of the indoor environment were included in the decision-making. This resulted in valuable new information which was very useful in the decision process. Especially in evaluation of the effects of combined solutions the calculations proved to be valuable and contributed to ensure reliable solutions to complicated ventilation problems. The investigation showed that displacement ventilation with an increased supply air flow rate at floor level was not the best solution in this case because of work stations distributed in the whole hall and not only close to the floor. A solution with low momentum air supply at ceiling level proved to give a more even temperature distribution in the hall. The solution was also much more effective since lower supply air temperatures were possible without causing draught problems.

computational fluid dynamics, ventilation strategies, industrial building

#NO 11317 Displacement ventilation design.

Zhivov A M, Shilkrot E O, Nielsen P V, Riskowski G L

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 427-438, 5 figs, refs.

Presents new design guidelines for displacement ventilation systems which it is hoped will help designers to avoid using displacement ventilation where it may be inappropriate. States that the new guidelines have the following superior features compared with existing design procedures: They are easy to understand and to use; Temperature gradient and heat removal efficiency are computed considering turbulent and radiant heat exchange between the upper and the lower zones; Contaminant removal efficiency computation method introduced in the design procedure allows one to predict contaminant concentration in the occupied zone air and in the exhausted air; Concept of inhalation efficiency coupled with a contaminant removal efficiency utilised in the design procedure allows one to predict contaminant concentration in the breathing zone; Contaminant stratification level is computed based on the data for airflow rates in thermal plumes above typical heat sources in spaces with a temperature gradient. It was shown that temperature gradient has a significant impact on the thermal plume rise and the airflow rate in its horizontal cross-sections.

displacement ventilation, guidelines

#NO 11483 Natural Displacement Ventilation of an Enclosure with a Distributed Buoyancy Source Applied to One Vertical Wall

Cooper P, Mayo G A, Sorensen 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 45-52.

This paper describes fundamental research into the behaviour of a naturally displacement ventilated space with one vertical heated wall. The experimental methodology involved the use of a water-filled scale model of a naturally ventilated room where salt solution was uniformly injected through one porous vertical wall to simulate uniform heating of the latter at full-scale. A computer-based image capture and analysis system was used to determine the resulting salt concentration profile within the enclosure as a function of time from video film of the experiments. Salt concentration was then used to infer temperature profiles at full-scale. Experimental results are presented including the depth of the ambient air layer in a natural displacement ventilated room as a function of the non-dimensional vent size. Details of the transient development of the stratification profile are also given. The non-dimensional steady state stratification profile is found to be approximately linear and varies relatively little with respect to the magnitude of the buoyancy flux applied at the vertical wall.

displacement ventilation, natural ventilation, scale model

#NO 11485 Convective Flows and Vertical Temperature Gradient with the Active Displacement Air Distribution

Sandberg E, Koskela H, Hautalampi 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 1, pp 61-68.

The active displacement air distribution method is a combination of displacing and mixing. It is a low impulse system based on special nozzle ducts, which are usually placed above the occupied zone. Depending on nozzle spacing in the duct and duct position related with heat sources, it is possible to get a more displacing or more mixing system. A study called Convective Flows and Vertical Temperature Gradient with the Active Displacement Air Distribution was started in September 1996 and it will end in December 1998. The main aim of the study is to determine the guidelines for air flow rate dimensioning of the system. The focus is in cases where thermal loads and need of cooling are dominating and dimensioning is possible by using vertical temperature gradient. The performance of supply air flow patterns together with convective air flows is studied experimentally by carrying out measurements in a test room and in field plants. This paper presents the aim of the study and the two-zone calculation method developed for modelling the temperature stratification in the test room. Some experimental results of the test room measurements are compared with the results of the calculation model. The results show that with uniform heat load / floor area and with high air velocities through the nozzles the air distribution behaves near fully mixing. When the heat sources create relatively strong plumes, they are able to control the room achieved. Thus dimensioning with lower airflow rates is possible. Two other papers named Behaviour of Convective Plumes with the Active Displacement Air Flow Patterns and Test room and Measurement system for Active Displacement Air Distribution regarding this study are also submitted to be presented at this conference.

displacement ventilation, mixing ventilation, duct, temperature gradient

#NO 11487 Cooled Ceilings / Displacement Ventilation Hybrid Air conditioning System - Design Criteria

Tan H, Murata T, Aoki K, Kurabuchi 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 1, pp 77-84.

For realizing comfort and ventilation efficiency simultaneously using a cooled ceiling (CC)/ displacement ventilation (DV) hybrid air conditioning system (CC/DV), Vertical distribution of temperature, local ventilation efficiency, and thermal comfort were studied by conducting a series of experiments to determine the design conditions. The characteristics of the thermal environment were measured in a laboratory, which was set up to simulate an office room in summer. The local air change efficiency was measured by tracer gases method and a subjective experiment was also carried out. The interaction between the major system parameters of room cooling load (P), CC cooling output ratio (h), ventilation airflow rate (Q), temperature gradient (dt) and the relevant constraints were studied. The results of these experiments showed the temperature gradient in the occupied zone, an important factor of DV, adversely affects thermal comfort. As a result, the temperature gradient in the occupied zone should be in a range of 2-2.5 deg. C to realize comfort and ventilation efficiency simultaneously. A diagram for the system design was developed using the relationship among the above factors, which provides a useful and practical design tool.

chilled ceilings, displacement ventilation, hybrid air conditioning

#NO 11488 A Semi Empirical Flow Model for Low-Velocity Air Supply in Displacement Ventilation

Skaaret E

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 85-92.

Similar to supply air jets in mixing ventilation this paper describes a comprehensive flow model for displacement ventilation derived from the integrated Navier-Stokes differential equations for boundary layers. A new test method for low velocity diffusers in displacement ventilation is developed based on this new flow model. Contrary to jet flow, it is shown that the only independent variable in the new model is the buoyancy flux. In addition to this variable the calculations need a single empirical constant which is determined from a limited number of full scale tests of a limited number of similar shaped diffusers of different size. There are made a number of tests to try out the new model. The results are promising. For plane (two dimensional) flow the velocity accelerates to a constant value. For radial flow there is also an acceleration zone, after which the velocity decays. Both theoretical and empirical data predicts that for similar shaped diffusers the width of the near zone (distance from the centre of the diffuser to a chosen velocity depends only on the buoyancy flux, not the dimensions of the diffuser (radius and height). One consequence of this is, among others, that the width of near zone cannot, for a certain air flow rate, be shortened by choosing a larger radius and a lower height of the diffuser. The diffuser constant K for radial diffusers has, however, turned out to be more or less dependent on the difference in temperature between the supply air and the room air, probably due to that the outflow is not ideally radial and the effect of flow become more radial. The new model also enables the designer to calculate the near zone for arbitrary air flow rate, supply air temperature and arbitrary supply diffuser size of similar shaped diffusers. Practical benefits are, among other things, improved test standards and design methods for displacement ventilation.

displacement ventilation, modelling, testing

#NO 11503 Displacement Ventilation and Cooled Ceilings

Alamdari F

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 197-204.

The performance and effectiveness of any ventilation and cooling strategy depends largely on the method of air distribution and heat removal system. The consequences of poor air distribution and cooling systems are draughts, air stagnation, large temperature gradients and radiation asymmetry. These factors are the chief cause of the occupants' dissatisfaction with their thermal environment, and are major contributors to the so-called 'sick building syndrome'. Cooled ceilings combined with displacement ventilation, sometimes known as 'comfort cooling', has gained popularity in recent years. In the UK, the traditional cooling strategies such as fan coil and vav is now being challenged with static cooling systems in majority of the new and refurbishment projects. The increasing trend towards the use of these systems has led to a number of research programmes to study the air movement, thermal environment and condensation risk of these systems (Alamdari, et al 1993, 1996; Martin et al 1997, Butler 1997). The room air distribution and thermal environment of the combined displacement ventilation and cooled ceiling systems are presented in this paper.

displacement ventilation, chilled ceiling

#NO 11532 A semi empirical flow model for low velocity air supply in displacement ventilation. 

Skaaret E

UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation Technologies in Urban Areas", 19th Annual Conference, held Oslo, Norway, 28-30 September 1998, pp 1-9.

Similar to supply air jets in mixing ventilation this paper describes a comprehensive flow model for displacement ventilation derived from the integrated Navier-Stokes differential equations for boundary layers. A new test method for low velocity diffusers in displacement ventilation is developed based on this new flow model. Contrary to jet flow, it is shown that the only independent variable in the new model is the buoyancy flux. In addition to this variable the calculations need a single empirical constant, which is determined from a limited number of full-scale tests of a limited number of similar shaped diffusers of different size. There are made a number of tests to try out the new model.

The results are promising. For plane (two-dimensional) flow the velocity accelerates to a constant value. For radial flow there is also an acceleration zone, after which the velocity decays. Both theoretical and empirical data predicts that for similar shaped diffusers the width of the near zone (distance from the centre of the diffuser to a chosen velocity depends only on the buoyancy flux, not the dimensions of the diffuser (radius and height)). One consequence of this is, among others, that the width of near zone cannot, for a certain air flow rate, be shortened by choosing a larger radius and a lower height of the diffuser. The diffuser constant K for radial diffusers has, however, turned out to be more or less dependent on the difference in temperature between the supply air and the room air, probably due to that the outflow is not ideally radial and the effect of the temperature difference is to make the flow become more radial. The new model also enables the designer to calculate the near zone for arbitrary airflow rate, supply air temperature and arbitrary supply diffuser size of similar shaped diffusers. Practical benefits are, among other things, improved test standards and design methods for displacement ventilation.

modelling, air flow

#NO 11553 Top-down natural ventilation of multi-storey buildings.

Hunt G R, Holford J M

UK, Air Infiltration and Ventilation Centre, proceedings of "Ventilation Technologies in Urban Areas", 19th Annual Conference, held Oslo, Norway, 28-30 September 1998, pp 197-205.

We examine natural ventilation in buildings with multiple storeys, each storey linked to a common chimney or atrium and ventilated using 'top-down chimneys' to draw in relatively unpolluted air from openings located high above street level. Two significant issues relating to ventilation design and management are addressed. First, the common stack provides connections between every storey and, consequently, the ventilation of each storey cannot be calculated in isolation, but must be calculated simultaneously for all storeys. Second, the introduction of the top-down chimney results in frictional losses whose magnitude depends, in part, on the chimney length and cross-sectional area. We develop a simple theoretical model to quantify the effect each storey has on others, and to predict how ventilation openings should be resized in order to overcome the pressure losses associated with the top-down chimney. The model describes the thermal stratification and ventilation flow rate in each storey, and leads to design curves for the sizing of vents to achieve the required ventilation. We focus on steady-state displacement ventilation and compare our theoretical predictions with paradigm small-scale laboratory experiments in a model two-storey building. Our study indicates that, with careful design, top-down ventilation of multi-storey buildings is a realistic strategy in urban environments.

multi storey building

#NO 11624 A zero-equation turbulence model for indoor airflow simulation.

Chen Q, Xu W

UK, Energy and Buildings, No 28, 1998, pp 137-144, 10 figs, 1 tab, 23 refs.

At present, Computational-Fluid-Dynamics (CFD) with the 'standard' k-e model is a popular method for numerical simulation of room airflow. The k-e model needs a lot of computing time and a large computer. This paper proposes a new zero-equation model to simulate three-dimensional distribution of air velocity, temperature, and contaminant concentrations in rooms. The method assumes turbulent viscosity to be a function of length-scale and local mean velocity. The new model has been used to predict natural convection, forced convection, mixed convection, and displacement ventilation in a room. The results agree reasonably with experimental data and the results obtained by the standard k-e model. The zero-equation model uses much less computer memory and the computing speed is at least 10 times faster, compared with the k-e model. The grid size can often be reduced so that the computing time needed for a three-dimensional case can be a few minutes on a PC.

modelling, displacement ventilation

#NO 11826 Displacement ventilation - theory and design.

Nielsen P V

Denmark, Aalborg University, Department of Building Technology and Structural Engineering, August 1993, 132 pp.

Displacement ventilation is a type of air distribution principle which should be considered in connection with design of comfort ventilation in both small and large spaces. Research activities on displacement ventilation are large all over the world and new knowledge of design methods appears continuously. This book gives an easy introduction to the basis of displacement ventilation and the chapters are written in the order which shows some of the new research activities taking place at Aalborg University. It is written for students as well as engineers.

displacement ventilation

#NO 11875 Comparison of heating and cooling energy consumption by HVAC system with mixing and displacement air distribution for a restaurant dining area in different climates.

Zhivov A M, Rymkevich A A

USA, ASHRAE, 1998, in: the ASHRAE Transactions CD, proceedings of the 1998 ASHRAE Annual Meeting, held Toronto, Canada, June 1998, 12 pp, 12 figs, 4 tabs, refs.

Different ventilation strategies to improve indoor air quality and to reduce HVAC system operating costs in a restaurant with nonsmoking and smoking areas and a bar are discussed in this paper: A generic sitting-type restaurant is used for the analysis. Prototype designs for the restaurant chain with more that 200 restaurants in different U.S. climates were analyzed to collect the information on building envelope, dining area size, heat and contaminant sources and loads, occupancy rates, and current design practices.

Four constant air volume HVAC systems with a constant and variable (demand-based) outdoor airflow rate, with a mixing and displacement air distribution, were compared in five representative U.S. climates: cold (Minneapolis, Minn.); maritime (Seattle, Wash.); moderate (Albuquerque, N.Mex.); hot-dry (Phoenix, Ariz.); and hot-humid (Miami, Fla.).

For all four compared cases and climatic conditions, heating and cooling consumption by the HVAC system throughout year-round operation was calculated and operation costs were compared. The analysis shows:

energy consumption, mixing ventilation, displacement ventilation, public building

#NO 12034 Improvement of a plume volume flux calculation method.

Popiolek Z, Trzeciakiewicz Z, Mierzwinski S

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 423-430, 7 figs, 3 tabs, 16 refs.

The paper presents the results of the research on application of the equation describing the increase in the air volume flux in buoyant plume above a point heat source to calculate plumes in rooms with displacement ventilation.

The tests carried out in test room have given information about practical defining of the distance from the origin, assuming entrainment coefficient values and possibilities of assuming equal widths of temperature and velocity profiles in order to determine the origin distance. They have also informed whether it is possible to use the model of plume above a point heat source in an enclosure where displacement ventilation is applied. The tests were preceded by an analysis of buoyant plumes, on the basis of available literature data.

calculation techniques, modelling, displacement ventilation, air distribution

#NO 12037 A method for prediction of room temperature distribution.

Hong-zuo Zhao, An-gui Li

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 445-449, 2 figs, 1 tab, refs.

The heat sources in a room with upward air supply, can be ideally decomposed into some basic models. Based on searching of the solution of the basic models, then solving the varieties of practical problems, a simplified method for predicting vertical temperature distribution of room air is submitted in this paper. Calculated values of some practical examples agree satisfactorily with experiment results.

temperature distribution, prediction, displacement ventilation, mixing ventilation

#NO 12230 The influence of air supply and exhaust locations on ventilation efficiency and contaminant exposures in rooms.

Holmberg S, Hokkanen J, Jarmyr R, Danielsson P O, Bartec L, Holmer I, Nilsson H

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 18-23.

An efficient ventilation system is characterised by an well-organised and turbulence-controlled air stream that rapidly corrects disturbances in air quality and thermal comfort in the ventilated space. Air supply and exhaust conditions are investigated here in order to find stable flow conditions and an efficient elimination of both gas and solid phase contaminants. Heat and thermal comfort requirements are also included. Existing displacement ventilation installations cannot always meet the current requirements of good indoor air quality, thermal comfort and energy use, and improved solutions are therefore needed. It is shown here that the conditions of both air supply and exhaust are critical to the overall ventilation effectiveness in a room. Personal exposures have been studied by computer simulations. A new numerical method has enabled assessments of exposures to particle contaminants, which are extremely difficult to measure in practice.

numerical modelling, particle

#NO 12754 The performance of building ventilation systems in practice: findings from the Probe project.

Cohen R

in: UK, The Institution of Mechanical Engineers, 1999, "Building Ventilation Design", proceedings of a seminar held at IMechE HQ, 28th October 1999.

The Probe project has undertaken post-occupancy evaluations of sixteen buildings. The studies reviewed the buildings' services, energy performance, management and occupant satisfaction. Ventilation strategy ws a key factor for all these aspects and this paper reviews and compares the success of the many approaches found, ranging from simple and advanced natural ventilation through mechanical displacement ventilation to traditional full air conditioning systems.

building design

#NO 12762 Comparison of energy consumption between displacement and mixing ventilation systems for different US buildings and climates.

Hu S, Chen Q, Glicksman L R

USA, ASHRAE Transactions, Annual Meeting 1999, Seattle, 12 pp, 7 figs, 3 tabs, refs.

A detailed computer simulation method was used to compare the energy consumption of a displacement ventilation system with that of a mixing ventilation system for three types of U.S. buildings: a small office, a classroom, and an industrial workshop. The study examined five typical climatic regions as well as different building zones. It was found that a displacement ventilation system may use more fan energy and less chiller and boiler energy than a mixing ventilation system. The total energy consumption is slightly less using a displacement ventilation system. Both systems can use a similarly sized boiler. However, a displacement ventilation system requires a larger airhandling unit and a smaller chiller than the mixing ventilation system. The overall first costs are lower for the displacement ventilation if the system is applied for the core region of a building. 

displacement ventilation, mixing ventilation

#NO 12899 Air distribution and air quality in a large open space.

Waters J R, Simons M W, Grazebrook J

UK, Building Serv Eng Res Technol, Vol 20, No 4, 1999, pp 195-200, 12 figs, 7 refs.

A case study of the ventilation characteristics of office accommodation forming part of a recently refurbished building is presented. A mechanical system ahs been installed to ventilate and cool two floors that are interconnected by a series of atria, with a novel application of displacement ventilation applied where there is a very low ceiling height. The air distribution and air quality within the space have been studied by the application of computational fluid dynamics (CFD) to allow the computation of air change effectiveness in terms of local mean age. Variations in ventilation strategy have been explored and the results have been verified by perceived occupier satisfaction. 

refurbishment, office building, cooling, atrium, air distribution

#NO 12901 Displacement ventilation for industrial applications. Types, applications and design strategy.

Zhivov A M, Nielsen P V, Riskowksi G, Shilkrot E

USA, HPAC Heating/Piping/AirConditioning Engineering, March 2000, pp 41-50, 6 figs, 16 refs.

Describes types, applications and design strategy for displacement ventilation for industrial applications. Almost all US ventilation and air conditioning systems are of the mixing (dilution) type. Fresh, outdoor air is mixed with room air, resulting in fairly uniform temperatures, humidities, and contaminant concentrations throughout all areas and levels of the room; displacement ventilation differs in that it creates stratified levels of temperatures and contaminant concentrations within a room.

displacement ventilation, design

#NO 13049 Selective ventilation in large enclosures.

Calay R K, Borresen B A, Holdo A E

Energy and Buildings, NO 32, 2000, pp 281-289, 7 figs, 18 refs.

A new method for providing ventilaton in large enclosures, which utilises the principle of 'selective withdrawal' of contaminants while ensuring energy efficiency and allowing a better use of space, is presented in this study. The concept is based on dividing the enclosed space ventilation-wise into separate zones using a combination of horizontal partitions by stratification and vertical partitions by temporary walls. This gives a high degree of flexibility in the use of available space. The relative influence of all the parameters on the flow patterns inside an enclosure is discussed in order to identify the design parameters that should be controlled to apply the technique successfully. An experimental study in a scale model was conducted, which provided a better understanding of the physical processes that occur in such enclosures. The influence of exhaust location on the flow field was studied in particular. It was found that by controlling the position of exhaust the stratification effects are enhanced and maintained at a desired level in order to achieve a successful utilisation of the selective ventilaton system.

displacement ventilation, large building, air flow pattern, stratification

#NO 13069 The use of heat pumps to induce airflow on hot days in otherwise passive 

ventilation systems.

Gage S A, Ayres P, Axon J

UK, Air Infiltration and Ventilation Centre, proceedings of "Innovations in Ventilation Technology", 21st AIVC Annual Conference, held The Hague, Netherlands, 26-29 September 2000, paper 20.

The paper presents results from a wider study into providing displacement ventilation in urban areas by taking air into buildings from the top without the use of fans. Results from large scale experimental work are given. These results indicate that ventilation airflows can be induced using gravity chillers and heaters in conditions where this type of installation would otherwise fail. The paper also describes initial experiments undertaken to see how far the same equipment can be used in heat recovery.


One test installation is modeled using a proprietary zonal model. Experimental results are also compared to the results which could be inferred from CIBSE data. The authors argue that both the zonal model and the CIBSE data are very conservative tools for predicting low speed gravity driven airflows and suggest that more accurate methods of modeling airflows would enhance the take-up of this type of technology.

heat pump, air flow, displacement ventilation

#NO 13314 Temperature and velocity measurements on a diffuser for displacement ventilation with whole field methods.

Linden E, Cehlin M, Sandberg M

UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 1, pp 491-496, 4 figs, refs.

In this study the instantaneous temperatures and velocities close to a diffuser for displacement ventilation have been recorded using whole-fed measuring techniques. The air temperatures were measured indirectly by the use of a low thermal mass screen in conjunction with infrared thermography. The measuring screen was mounted parallel to the airflow, acting as a target screen. By using the thermal images the size of the near zone was also calculated. To determine air movements a whole field method called particle streak velocimetry (PSV) was used. Images of tracks created by small, low-density particles, suspended in the air, were analyzed using computerized image processing to obtain the velocities. The experiment took place in a climate chamber in which the wall and air temperatures were controlled. The diffuser was located in the centre of one of the walls. The tests were conducted for a supply flow of 15 l/s and a temperature difference between the inlet air and the room air of 4oC and of 6oC. This paper deals with the results obtained from the two whole-field measurement methods. The results show that the two whole-field measurement methods can be good tools for visualizing and measuring air velocities and temperatures in rooms. These techniques could be used in the work of improving the indoor climate. 

Indoor climate, whole field measurement methods, air velocity, air temperature, digital infrared camera, temperatures, diffuser, displacement ventilation, infrared thermography, 2D particle streak velocimetry (PSV), digital pictures, particle tracking.

#NO 13329 Implementation of displacement ventilation system by using a wall mounted air conditioner.

Hsu H C, Chiang H, Shih Y C, Shyu R J

UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 2, pp 731-736, 9 figs, 1 tab, refs.

Wall-mounted air conditioning systems including window-type and split-type air conditioners are widely used in Asian countries. However, these systems blow cold air directly into the working space perpendicular to the mounted wall and may make people affected by these air conditioners experience discomforts such as draught and uneven temperature distribution. Now a wall-mounted air conditioning system is expected to effectively implement the displacement ventilation system for space cooling and cold draught avoiding. Computer simulation method and experimental measurement were used to justify this new system design. Thermal comfort indices (PMV and PPD) as well as temperature and velocity patterns were reported in this paper. The results show that the displacement ventilation system, which was designed for a centralised air conditioning system in the past, can now be implemented in a rather small-scaled residential air conditioning system.

Displacement ventilation system, wall-mounted air conditioning system, thermal manikin, thermal comfort, draught, CFD

#NO 13365 A comparative study of different air distribution systems in a classroom.

Karimpanah T, Sandberg M, Awbi H B

UK, Oxford, Elsevier, 2000, proceedings of Roomvent 2000, "Air Distribution in Rooms: Ventilation for Health and Sustainable Environment", held 9-12 July 2000, Reading, UK, Volume 2, pp 1013-1018, 4 figs, 3 tabs, refs.

This study involves comprehensive experimental measurements and CFD simulations in a mock-up of a full-size classroom with realistic loads. Four different air distribution systems have been tested: (1) Mixing ventilation produced from a high velocity ceiling supply device; (2) Bag-supply (textile) device located in the ceiling; (3) Displacement ventilation using a standard low velocity air supply device; (4) A down-to-floor impinging jet air supply device. The measured wall temperatures have been used as boundary conditions for the CFD simulations. Predicted and measured quantities are: air velocity, air temperature, ventilation effectiveness and local mean age of air. The down-to-floor impinging jet was also tested in a field trial.

Air distribution methods, school ventilation, full-scale measurements, CFD, impinging jet

#NO 13555 Temperature and contaminant stratifications in the active displacement air distribution method.

Sandberg E, Koskela H, Hautalampi T

in: "Progress in Modern Ventilation", Proceedings of Ventilation 2000, Volume 1, proceedings of the 6th International Symposium on Ventilation for Contaminant Control, held Helsinki, Finland, 4-7 June 2000, Finnish Institute of Occupational Health, Helsinki, Finland, 2000, pp 100-103, 2 figs, 7 refs.

The main objective of this study was to determine a calculation model and a computing program for the calculation of the dimensioning air flow rate in the active displacement air distribution method. The model was to be developed especially for practical cases and based on the temperature and contaminant stratifications. The study consisted of six tasks: flow models, test room measurements, calculation for the test room, field measurements, calculation model for field cases, and computing program.

temperature stratification, displacement ventilation


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