1、BRITISH STANDARD BS 5925:1991 Incorporating Amendment No. 1 Code of practice for Ventilation principles and designing for natural ventilationBS 5925:1991 This British Standard, having been prepared under the directionof the Basic Data and Performance Criteria for Civil Engineering and Building Struc
2、tures Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 31May 1991 BSI 01-2000 First published September1980 Second edition May1991 The following BSI references relate to the work on this standard: Committee reference BDB/2 Draft for commen
3、t89/17211 DC ISBN 0 580 19285 7 Committees responsible for this BritishStandard The preparation of this British Standard was entrusted by the Basic Data and Performance Criteria for Civil Engineering and Building Structures Standards Policy Committee (BDB/-) to Technical Committee BDB/2, upon which
4、the following bodies were represented: The following bodies were also represented in the drafting of the standard, through subcommittees and panels: Aggregate Concrete Block Association Department of the Environment Association for the Conservation of Energy (Construction Industries Directorate) Ass
5、ociation of Building Component Department of the Environment for Northern Manufacturers Ireland Association of County Councils Electricity Supply Industry in United Association of District Councils Kingdom Association of Metropolitan Authorities Eurisol (UK Mineral Wool Association) Autoclaved Aerat
6、ed Concrete Products Flat Glass Manufacturers Association Association Gypsum Products Development Association Brick Development Association Hevac Association British Board of Agrment Institution of Civil Engineers British Cement Association Institution of Gas Engineers British Gas plc Institution of
7、 Structural Engineers British Precast Concrete Federation Ltd. Lighting Industry Federation Ltd. Building Employers Confederation Ministry of Defence Building Services Research and Information National House-building Council Association National Illumination Committee of Great Chartered Institute of
8、 Building Britain Chartered Institution of Building Services Royal Institute of British Architects Engineers Royal Institution of Chartered Surveyors Concrete Society Scottish Development Department Consumer Policy Committee of BSI Society of Chief Architects of Local Cranfield Institute of Technolo
9、gy Authorities Department of Education and Science Timber Research and Development Department of Energy (Energy Efficiency Association Office) Trades Union Congress Department of Health Watt Committee on Energy Ltd. Department of the Environment (Building Research Establishment) Association of Light
10、weight Aggregate Institution of Mechanical Engineers Manufacturers Medical Research Council British Coal Corporation National Council of Building Material British Concrete Masonry Association Producers Flat Roofing Contractors Advisory Board Phenolic Foam Manufacturers Association Amendments issued
11、since publication Amd. No. Date Comments 8930 December 1995 Indicated by a sideline in the marginBS 5925:1991 BSI 01-2000 i Contents Page Committees responsible Inside front cover Foreword ii Section 1. General 1 Scope 1 2 Definitions 1 3 Symbols 2 Section 2. General principles of ventilation 4 Basi
12、c data 3 5 Application 9 6 Provision for ventilation 9 7 Choice between natural and mechanical ventilation 13 Section 3. Natural ventilation 8 General 15 9 Flow characteristics of openings 15 10 Generation of pressure differences 16 11 Meteorological variables 18 12 Determination of natural ventilat
13、ion rates 19 13 Other mechanisms of natural ventilation 23 14 Fire ventilation 25 15 Air infiltration 25 16 Normal building practice for natural ventilation in dwellings 26 Appendix A Bibliography 28 Appendix B Calculation of contaminant concentration 29 Appendix C Calculation of ventilation rates t
14、o reduce the risk ofsurfacecondensation under steady state conditions 33 Appendix D Determination of ventilation requirements 34 Appendix E Calculation of reference wind speed u r 35 Appendix F Calculation of natural ventilation rates for a simple building 36 Index 39 Figure 1 Ventilation required t
15、o reduce the risk of surface condensationoccurring on the inner wall surface for various wall U-valuesandambient air conditions 6 Figure 2 Typical possibilities for inlets and outlets, for both natural andmechanical ventilation systems in dwellings 12 Figure 3 Correction to the dry resultant tempera
16、ture to take account ofairmovement 13 Figure 4 Pressure difference and flow created by temperature difference 18 Figure 5 Contours of u 50for the UK 20 Figure 6 Arrangement of openings in a simple building 23 Figure 7 Variation of J( ) with angle opening for (a) side-mounted casementwindows and (b)
17、centre-pivoted windows 26 Figure 8 Variation of gas concentration c with t and ventilation rate Q forgasleakage rate q 30 Figure 9 Allowable reduction in minimum fresh air supply rate when thepollutant source is present for a limited period, t 1 , rather than continuously 31BS 5925:1991 BSI 01-2000
18、Page Figure 10 Allowable reduction in minimum fresh air supply rate whenthepollutant source is intermittent, being present for a length oftime,t 1 ,with a return period, t 2(r = t 1 /t 2 ) 31 Figure 11 Interconnecting spaces 32 Table 1 Fresh air requirement values for respiration 3 Table 2 Moisture
19、generation rates 5 Table 3 Flueless appliances: carbon dioxide production rates and airsupplyrates 8 Table 4 Recommended outdoor air supply rates 10 Table 5 Values of k for windows 15 Table 6 Equivalent area of ventilation openings 16 Table 7 Typical magnitudes of pressure created by wind and temper
20、aturedifference 17 Table 8 Factors for determining mean wind speed at different heights andfordifferent types of terrain from the Meteorological Office wind speed, u m ,measured at10m in open country 19 Table 9 Values of the ratio of mean wind speed exceeded for agivenpercentageof time to the50% mea
21、n wind speed u 50 19 Table 10 Mean daily air temperatures for 12 sites in the UK,1941 to1970 21 Table 11 Natural ventilation of a simple building 22 Table 12 Natural ventilation of spaces with openings on one wall only 24 Table 13 Mean surface pressure coefficients for vertical walls of rectangularb
22、uildings 38 Publication(s) referred to Inside back coverBS 5925:1991 BSI 01-2000 iii Foreword This British Standard has been prepared under the direction of the Basic Data and Performance Criteria for Civil Engineering and Building Structures Standards Policy Committee. It supersedes BS5925:1980, wh
23、ich is withdrawn. This revision takes into account research on ventilation and indoor air quality that has taken place since the publication of BS5925:1980. In particular, under section2, the ventilation requirements for the dilution and removal of airborne pollutants have been updated and account t
24、aken of the guidance given in BS5250. Under section3, a new clause dealing with air infiltration has been introduced. Recent increased awareness of the need for efficient use of energy in the design and management of buildings, as recommended in BS8207, has led to greater insulation levels and reduc
25、ed ventilation rates in both new and existing buildings. However, it is essential that a balance is struck between the needs for low ventilation rates commensurate with saving energy and the needs for higher ventilation rates required to ensure good indoor air quality and to reduce the risk of mould
26、 growth. Ventilation rates in different parts of a building may differ, depending on both the levels of occupancy and the occupants activities in those parts. It is important to remember the complex interrelationship of factors affecting condensation and to take particular care when designing new bu
27、ildings or considering changes or attempting to remedy problems in existing buildings. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of i
28、tself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to 40, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be i
29、ndicated in the amendment table on the inside front cover.iv blankBS 5925:1991 BSI 01-2000 1 Section 1. General 1 Scope This British Standard gives recommendations on the principles which should be observed when designing for the natural ventilation of buildings for human occupation. The standard is
30、 in three sections, as follows: Section 1. General Section 2 outlines the main reasons for the provision of ventilation and, where possible, recommends quantitative air flow rates. It is shown that these form the basis for air supply recommendations for different types of buildings and rooms charact
31、erized by usage. The basis for the choice between natural and mechanical ventilation is given. The design of mechanical ventilation systems is dealt with in BS5720. Section 3 gives recommendations on the design of natural ventilation systems and on the estimation of air infiltration rates in housing
32、. Appendix A is a bibliography and reference to publications listed in it are shown as: (see Appendix A15). Appendix B gives recommendations on evaluating contamination risks. Appendix C gives recommendations on calculating ventilation rates to reduce the risk of surface condensation under steady st
33、ate conditions. Appendix D gives recommendations on determining ventilation requirements. Appendix E gives recommendations on calculating reference wind speed. Appendix F gives recommendations on calculating natural ventilation rates for a simple building. This standard does not attempt to address t
34、hermal comfort aspects of ventilation such as indoor air movement, temperature stratification, exact position of ventilation openings etc. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard the
35、definitions given in BS5643 and BS6100 apply, together with the following. 2.1 absolute temperature temperature measured with respect to absolute zero 2.2 discharge coefficient coefficient which relates the volume flow rate through an orifice to its area and the applied pressure difference 2.3 equiv
36、alent area area of a sharp-edged orifice through which air would pass at the same volume flow rate, under an identical applied pressure difference, as the opening under consideration 2.4 input rating heat available for liberation by combustion within an appliance, based upon the gross calorific valu
37、e of the fuel 2.5 kerosine petroleum oil fuel suitable for appliances with small vaporizing and atomizing burners; classified as class C in BS 2869 2.6 open-flued appliance appliance designed to be connected to an open flue system; its combustion air being drawn from the room or internal space withi
38、n which it is installed 2.7 premium grade kerosine kerosine suitable for flueless space heaters, complying with the requirements of the specification for class C1 petroleum oil fuels in BS2869 NOTEThe non-preferred term is paraffin. 2.8 reference static pressure static pressure in the free wind, awa
39、y from any interference with the flow 2.9 static pressure pressure which would be recorded by a pressure gauge moving with the flow, i.e. static relative to the fluid 2.10 wake region of disturbed flow which persists some distance downstream of a building or similar structure exposed to the windBS 5
40、925:1991 2 BSI 01-2000 3 Symbols For the purposes of this British Standard the following notation applies. Commonly used abbreviations for units of measurement are not listed. A Equivalent area of an opening A 1 , A 2 Equivalent area of specific openings denoted in the text A 3 , A 4 A b A w a Expon
41、ent relating wind speed to height C d Discharge coefficient for an opening C p Surface pressure coefficient Mean surface pressure coefficient c Concentration of contaminant in air by volume c e Concentration of contaminant in outside air c o Concentration of contaminant at time t = 0 c E Equilibrium
42、 value of contaminant concentration g Acceleration due to gravity H 1 Vertical distance between the centres of two openings in a wall H 2 Vertical distance between top and bottom edges of a rectangular opening in a wall h Vertical distance between ground and the eaves or parapet J Function relating
43、ventilation rate through an open window to the angle of opening, K Factor relating wind speed to height k Window leakage factor L Length of a crack l Length of a building M Metabolic rate n Exponent relating flow rate through crack to applied pressure difference C p p Surface pressure Mean surface p
44、ressure p o Static pressure in undisturbed wind Q Volume flow rate of air Q b Volume flow rate of air due to the effect of temperature only Q w Volume flow rate of air due to the effect of wind only Q r Reduced air flow rate for intermittent contaminant emission q Input volume flow rate of contamina
45、nt R Ventilation rate r Return period of an intermittent pollutant source t Time U Thermal transmittance u Wind speed u m Wind speed at10m, exceeded for a given proportion of time u r Reference wind speed V Room volume w Width of building z Height Angle made by wind relative to building % Difference
46、 between two values of the same quantity, e.g. Area ratio Absolute temperature e Absolute temperature of outside air i Absolute temperature of inside air Average of inside and outside air temperatures Air density Angle made by an open window with the plane containing the wall of a building. p %C p B
47、S 5925:1991 BSI 01-2000 3 Section 2. General principles of ventilation 4 Basic data 4.1 General A supply of fresh air is required for one or more of the following: a) provision for human respiration; b) dilution and removal of airborne pollutants, including odours and tobacco smoke; c) control of hu
48、midity; d) provision of air for fuel-burning appliances; e) control of thermal comfort; f) clearance of smoke resulting from an accidental fire. In4.3 to4.8 each of these is discussed and guidance given on quantitative requirements. 4.2 Composition of outside air In ordinary engineering practice fre
49、sh air means air from outside. The usually accepted composition of dry air by volume is: The carbon dioxide content is variable and may be lower than0.035% in country areas and higher in built-up areas, due primarily to fuel combustion for transport, heating and industrial purposes. Outside air may also contain particulate matter and other combustion products such as sulphur dioxide and nitrogen oxides. These are currently limited by European Council Directives (seeAppendix A1). The main var
