Displacement Ventilation Risto Kosonen (ed.) Arsen Melikov Elisabeth Mundt Panu Mustakallio Peter V. Nielsen rehva Federation of European Heating, Ventilation and Air Conditioning Associations GUIDEBOOK NO 23 Single user license only, copying and networking prohibited. All rights reserved by REHVA. Single user license only, copying and networking prohibited. All rights reserved by REHVA. REHVA Displacement Ventilation Risto Kosonen (ed.) Arsen Melikov Elisabeth Mundt Panu Mustakallio Peter V. Nielsen Single user license only, copying and networking prohibited. All rights reserved by REHVA. DISCLAIMER This Guidebook is the result of the efforts of REHVA volunteers. It has been written with care, using the best available information and the soundest judgment possible. 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List of contents 1 DISPLACEMENT VENTILATION IN A NUTSHELL........................................... 1 2 TERMINOLOGY, SYMBOLS AND UNITS ............................................................ 4 2.1 Terms and definitions ................................................................................... 4 2.2 Symbols ........................................................................................................ 5 3 ROOM AIR DISTRIBUTION .................................................................................... 8 3.1 Need for Ventilation ..................................................................................... 8 3.2 Ventilation and room air distribution principles .......................................... 8 3.3 Displacement ventilation and thermal comfort .......................................... 11 3.4 Displacement ventilation and air quality .................................................... 12 4 PERFORMANCE OF DISPLACEMENT VENTILATION .................................. 15 4.1 Displacement Ventilation Method ............................................................. 15 4.2 Air flow pattern .......................................................................................... 15 4.3 Temperature distribution ............................................................................ 16 4.4 Convection flows – the engines of displacement ventilation ..................... 20 4.5 Contamination distribution ......................................................................... 28 4.6 Ventilation effectiveness ............................................................................ 29 5 CALCULATION OF SUPPLY AIRFLOW RATE ................................................ 34 5.1 Temperature based design methods ........................................................... 34 5.2 Calculation of vertical room air temperature distribution .......................... 35 5.3 Vertical position of the heat source ............................................................ 39 5.4 Calculation examples when using temperature based design models ........ 39 6 AIR DIFFUSERS FOR DISPLACEMENT VENTILATION ................................ 42 6.1 Commonly used diffusers .......................................................................... 42 6.2 Radial air flow or plane air flow from low-velocity diffusers ................... 44 6.3 Air flow from low –velocity diffusers ....................................................... 44 6.4 Air distribution from a low-velocity diffuser giving a radial flow in the occupied zone ............................................................................................. 45 6.5 Air distribution from wall-mounted diffusers giving plane flow in the occupied zone ............................................................................................. 53 6.6 Air distribution from floor-mounted diffusers ........................................... 54 iii Single user license only, copying and networking prohibited. All rights reserved by REHVA. 7 DESIGN OF DISPLACEMENT VENTILATION .................................................. 56 7.1 Design criteria ............................................................................................ 56 7.2 Design of air distribution ........................................................................... 56 7.3 Integration with separate heating and cooling systems .............................. 60 7.4 Control of indoor conditions ...................................................................... 64 8 CASE STUDIES ......................................................................................................... 67 8.1 Air distribution with four typical air supply methods in a classroom ........ 67 8.2 Comparison of calculated and measured vertical temperature gradients for displacement air distribution ...................................................................... 70 8.3 Field measurements for a multipurpose arena ........................................... 72 9 RESEARCH FINDINGS ........................................................................................... 74 9.1 A CFD Benchmark test for manikins in displacement flow ...................... 74 9.2 Full-scale tests and CFD- simulations of indoor climate conditions ......... 74 9.3 Test on the performance of displacement ventilation– proper simulation of occupants .................................................................................................... 77 9.4 Airborne cross infection risk in a room with displacement ventilation ..... 80 9.5 Displacement ventilation design based on occupants’ response ................ 83 9.6 Convective boundary layer around human body ....................................... 87 10 REFERENCES ........................................................................................................... 91 iv Single user license only, copying and networking prohibited. All rights reserved by REHVA. Preface Displacement ventilation is primarily a This guide discusses methods of total vol- means of obtaining good air quality in oc- ume ventilation by mixing ventilation and cupied spaces that have a cooling demand. displacement ventilation and the guide It has proved to be a good solution for book gives insight of the performance of spaces where large supply air flows are re- the displacement ventilation. It also takes quired. into account different items, which are cor- related, to well-known key words: free con- Some advantages of displacement ventila- vection flow; stratification of height and tion: concentration distribution; temperature dis- tribution and velocity distribution in the oc- • Less cooling needed for a given tempera- cupied zone and occupant comfort. ture in the occupied space; • Longer periods with free cooling; The guide book discusses two principal • Potential to have better air quality in the methods which can be used when the sup- occupied spaces; ply air flow rate of displacement ventilation • The system performance is stable with all system is calculated: 1) temperature based cooling load conditions. design, where the design criterion is the air temperature in the occupied zone of the Displacement ventilation has been origi- room and 2) air quality based design where nally developed in Scandinavian countries the design criterion is the air quality in the over 30 years ago and now it is also a well- occupied zone. Some practical examples of known technology in different countries the air flow rate calculations are presented. and climates. Historically, displacement ventilation was first used for industrial ap- The air flow diffusers are the critical factor: plications but nowadays it is also widely most draught problems reported in rooms used in commercial premises. with displacement ventilation are due to high velocity in the zone adjacent to the dif- However, displacement ventilation has not fuser. This guide explains the principle for been used in spaces where it could give the selection of diffuser. added values. For that there are two main reasons: firstly, there is still lack of This guide also shows practical case studies knowledge of the suitable applications of in some typical applications and the latest displacement ventilation and secondly, research findings to create good micro cli- consulters do not know how to design the mate close to persons is discussed. system. These and some other aspects are discussed REHVA