Title AS 1668.2 Supp 1-1991 The use of mechanical ventilation and air-conditioning in buildings - Mechanical ventilation for acceptable indoor-air quality - Commentary (Supplement to AS 1668.2-1991) Licensee Licensed to LUU MINH LUAN on 25 Feb 2002 Conditions of use This is a licensed electronic copy of a document where copyright is owned or managed by Standards Australia International Your licence is a single user licence and the document may not be stored, transferred or otherwise distributed on a network You may also make one paper copy of this document if required Web Check-up AS 1668.2 Supp1—1991 Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited Australian StandardR The use of mechanical ventilation and air–conditioning in buildings Part 2: Mechanical ventilation for acceptable indoor–air quality— Commentary (Supplement to AS 1668.2 – 1991) This Supplement was prepared by Committee ME/62, Mechanical Ventilation and Air Conditioning It was approved on behalf of the Council of Standards Australia on 20 May 1991 and published on July 1991 The following interests are reprsented on Committee ME/62: Association of Consulting Engineers, Australia Australian Assembly of Fire Authorities Department of Administrative Services Australian Construction Services Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited Australian Institute of Environment Health Australian Institute of Refrigeration Air Conditioning and Heating Australian Uniform Building Regulations Coordinating Council Building Owners and Managers Association of Australia Council of Air Conditioning and Mechanical Contractors Associations of Australia Council of the City of Sydney Confederation of Australian Industry Fire Protection Industry Associations of Australia Insurance Council of Australia Metal Trades Industry Association of Australia Public Works Department, N.S.W Review of Australian Standards To keep abreast of progress in industry, Australian Standards are subject to periodic review and are kept up to date by the issue of amendments or new editions as necessary It is important therefore that Standards users ensure that they are in possession of the latest edition, and any amendments thereto Full details of all Australian Standards and related publications will be found in the Standards Australia Catalogue of Publications; this information is supplemented each month by the magazine ‘The Australian Standard’, which subscribing members receive, and which gives details of new publications, new editions and amendments, and of withdrawn Standards Suggestions for improvements to Australian Standards, addressed to the head office of Standards Australia, are welcomed Notification of any inaccuracy or ambiguity found in an Australian Standard should be made without delay in order that the matter may be investigated and appropriate action taken AS 1668.2 Supp1—1991 Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited Australian StandardR The use of mechanical ventilation and air–conditioning in buildings Part 2: Mechanical ventilation for acceptable indoor–air quality— Commentary (Supplement to AS 1668.2 – 1991) First published as SAA MP47.C2–1980 Revised and redesignated AS 1668.2 Supp1–1991 PUBLISHED BY STANDARDS AUSTRALIA (STANDARDS ASSOCIATION OF AUSTRALIA) THE CRESCENT, HOMEBUSH, NSW 2140 ISBN 7262 6981 PREFACE Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited This Commentary on AS 1668, The use of mechanical ventilation and air–conditioning in buildings, Part 2: Mechanical ventilation for acceptable indoor–air quality, was prepared by the Standards Australia Committee on Mechanical Ventilation and Air Conditioning to provide guidance on the application of the Code by explaining the intent of those clauses which could be the subject of requests for interpretation This publication supersedes SAA MP 47, Part C2: Commentary on AS 1668, SAA Mechanical Ventilation and Airconditioning Code, Part C2: Ventilation requirements The contents have been revised to incorporate all alterations included in AS 1668, Part 2–1991 The clause references in the Commentary are those for the corresponding clauses in AS 1668, Part 2–1991, prefixed by the letter ‘C’ E Copyright — STANDARDS AUSTRALIA Users of Standards are reminded that copyright subsists in all Standards Australia publications and software Except where the Copyright Act allows and except where provided for below no publications or software produced by Standards Australia may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing from Standards Australia Permission may be conditional on an appropriate royalty payment Requests for permission and information on commercial software royalties should be directed to the head office of Standards Australia Standards Australia will permit up to 10 percent of the technical content pages of a Standard to be copied for use exclusively in–house by purchasers of the Standard without payment of a royalty or advice to Standards Australia Standards Australia will also permit the inclusion of its copyright material in computer software programs for no royalty payment provided such programs are used exclusively in–house by the creators of the programs Care should be taken to ensure that material used is from the current edition of the Standard and that it is updated whenever the Standard is amended or revised The number and date of the Standard should therefore be clearly identified The use of material in print form or in computer software programs to be used commercially, with or without payment, or in commercial contracts is subject to the payment of a royalty This policy may be varied by Standards Australia at any time CONTENTS Page SECTION C1 C1.1 C1.2 SCOPE APPLICATION SECTION C2 C2.1 C2.2 C2.3 C2.5 C2.6 Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited C3.5 C3.6 C3.7 C4.2 C4.3 C4.4 C4.5 C4.6 C4.8 C4.10 C4.11 C4.13 5 EXHAUST DILUTION PROCEDURES SCOPE OF SECTION GENERAL EXHAUST VENTILATION LOCAL EXHAUST AIR FROM ENCLOSURES HAVING EXHAUST AIR REQUIREMENTS REPLENISHMENT OF EXHAUST AIR COMBINATION OF EXHAUST SYSTEMS AIR DISCHARGES SECTION C4 4 SUPPLY AIR DILUTION PROCEDURE SCOPE OF SECTION OUTDOOR AIR INTAKES OUTDOOR AIR FLOW RATES OUTDOOR AIR MIXING AND DISTRIBUTION OUTDOOR AIR FLOW SECTION C3 C3.1 C3.2 C3.3 C3.4 SCOPE AND GENERAL 8 8 9 VENTILATION OF ENCLOSURES USED BY VEHICLES WITH INTERNAL COMBUSTION ENGINES APPLICATION OF SECTION GENERAL CASE CARPARKS ENCLOSURES OTHER THAN CARPARKS QUEUING AREA REPLENISHMENT OF EXHAUST AIR STAFF—VENTILATION RATE LOCATION OF EXHAUSTS IN BELOW GROUND ENCLOSURES MONITORING OF ATMOSPHERIC CONTAMINANTS 10 10 10 11 11 11 11 11 12 APPENDICES CA DERIVATION OF THE AIR CLEANING EFFICIENCY EQUATIONS USED IN APPENDIX D, AS 1668 PART CB BASIS OF AIR FLOW RATES FORMULAE FOR CARPARKS CC DERIVATION OF AIR FLOW RATES FOR QUEUING AREAS 13 25 27 AS 1668.2 Supp1—1991 STANDARDS AUSTRALIA Australian Standard The use of mechanical ventilation and air-conditioning in buildings Part 2: Mechanical ventilation for acceptable indoor-air quality—Commentary (Supplement to AS 1668.2–1991) Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited SECTION C1 SCOPE AND GENERAL C1.1 SCOPE Present building regulations (and the Australian Model Uniform Building Code) are based on the assumption that natural ventilation will be the first ‘natural’ choice and arbitrary minimum criteria for such ‘natural’ ventilation are prescribed Presumably the occupants will have control over this aspect of their environment in the type of space where natural ventilation is employed In the event of the criteria not being met, e.g percentage of floor area as openable windows or fixed openings and/or distance from openings are insufficient, then mechanical ventilation or air-conditioning would be required, as a permissible substitute Where the criteria were met, then mechanical ventilation or air-conditioning would be a permissible substitute at the constructor’s option – generally at a higher cost AS 1668, Parts and are references in both State and Territory building regulations and in the recently published Building Code of Australia Where mechanical ventilation is required by such regulations and codes, compliance with AS 1668 is prescribed This therefore places constraints on the wording of the Standard that would not otherwise be necessary AS 1668.2–1980 provided some interpretations of the application of natural ventilation to carparks as prescribed in building regulations Since AS 1668.2 is only referenced in building regulations in respect to mechanical ventilation requirements, consideration was given to the deletion of these natural ventilation interpretations The Australian Uniform Building Regulations Interstate Committee deemed it appropriate that such interpretations remain in AS 1668.2 at this time They have therefore been developed in more detail in the revision for further clarification The wording of the Standard in respect of the use of natural ventilation has also been changed to provide a more logical basis for its inclusion Although AS 1668.2 has been incorporated in State and Territory building regulations, its use has been supplemented or replaced in specific areas by local codes The revision is expected to achieve greater acceptance of AS 1668.2 except where a local code also addresses air-conditioning Although the title of AS 1668.2 has been changed from ‘Ventilation requirements’ to ‘Mechanical ventilation for acceptable indoor-air quality’ the extension of the Standard to include comfort in terms of the control of temperature, humidity, air-movement or noise was still deemed to be inappropriate at this time These elements are therefore only addressed in terms of the definement of limits beyond which health or safety may be impaired C1.2 APPLICATION The applications of the Standard are now more precisely described by direct reference to the specific application of each section To provide greater assistance in the use of the Standard, a logic diagram has also been included COPYRIGHT SECTION C2 AS 1668.2 Supp1—1991 SUPPLY AIR DILUTION PROCEDURE C2.1 SCOPE OF SECTION The term ‘fresh air’ has been deleted entirely from the Standard and term ‘outdoor air’ used in place of ‘outside air’ This has been done to remove possible misunderstandings and to achieve conformity with American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) and other overseas Standards Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited C2.2 OUTDOOR AIR INTAKES C2.2.1 Location The work of Wilson, Halitsky and others indicates the complicated wake effects and the interaction between adjacent obstructions and the intakes and discharges of a building Chapter 14 of the 1989 ASHRAE Fundamentals Handbook contains a comprehensive coverage of air flow around buildings, dispersion of building exhaust gases and design to minimize re-entry Particularly critical cases may warrant wind tunnel testing of models C2.3 OUTDOOR AIR FLOW RATES C2.3.2 Occupancy In some cases, the occupancies used for the purposes of determination of outdoor air flow rates may differ in aggregate for a given floor from those used for egress provisions in the Building Code of Australia This can arise as a result of the use of the maximum occupancy for each area with no account taken of movement of people from one area to another at different times during the period of occupancy An example would be a conference room used substantially by the occupants of adjacent areas on the same floor Table A1 and the associated notes comprising Appendix A need to be read together C2.3.3 to C2.3.4 Minimum outdoor air flow rates (Q f ) The minimum outdoor air flow rates required to maintain acceptable air quality depend on the definition of ‘acceptability’ The rates specified in the Standard are consensus values, and have been arrived at after extensive consideration of published research, rates used in the past, changing patterns of occupant behaviour, and changing patterns of pollution emissions within the building The Standard requires outdoor air flow rates in accordance with Appendix A, but allows reductions if a sufficient quantity of recycle air is treated to remove contaminants at an efficiency that meets the requirements of the appropriate formula from Appendix D It should be noted that: (a) The total supply air quantity (i.e recycle air + outdoor air) must exceed the air quantity required by Appendix A, otherwise the formula will require an efficiency greater than 100% (b) The efficiency for removal of particulate contaminants must be as determined using one of the specified test procedures (c) No test procedure for determining efficiency of removal of odours and gaseous contaminants is nominated as there is no recognized procedure It will be necessary for designers proposing such air treatment to justify the method used to determine the efficiency If air treatment is provided that removes particulates, tobacco smoke odours, and body odours, the Standard requires a minimum air flow rate for dilution of other gaseous contaminants that are generated in buildings such as CO2, ozone, formaldehyde and volatile organic hydrocarbons If air treatment is provided that removes only particulates, the Standard requires a minimum air flow rate for dilution of gaseous contaminants and odours, a , that is based on the air quantity necessary to dilute body odours In enclosures where heavy smoking occurs, such as bars, this will not control odours from tobacco smoking, but this is considered acceptable on the basis that occupants have a choice of whether they enter and remain for an extended period in these enclosures For control of body odours, recent studies by Bouwan, Cain, Fanger and others show an outdoor air flow rate of 7.5 to 10 L/s/person to be appropriate and to be a consensus value of minimum ventilation rates in the US, Germany and the UK The Standard requires a rate of 7.5 L/s/person, increasing to 15 L/s/person for enclosures in which temperatures are not kept below 27°C by air-conditioning or other means, as the generation and/or the perception of body odours increase with temperature It was additionally recognized that children are more odorous than adults; the tabulated ventilation rates for some occupancies reflect this For special enclosures, such as operating theatres, a high value of a is specified, so that no reduction in outdoor air flow rates is allowed if recycle air treatment is provided COPYRIGHT AS 1668.2 Supp1—1991 Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited If no air treatment is provided, the Standard requires the minimum outdoor air flow rates to be in accordance with Appendix A The rates in Appendix A take account of contaminants from smoking Based on the work of Wanner, Weber and Johansson, concentration of carbon monoxide may be taken as an indicator of the concentration of contaminants from tobacco smoke A limit of p.p.m of CO from tobacco smoke is considered necessary to maintain acceptable indoor air quality The rates listed in Appendix A, other than those for special enclosures, can be divided into those applying to areas subject to moderate, medium or heavy smoking, for which the rates are 10, 15 and 20 L/s/person respectively For an enclosure in which an excess of environmental tobacco smoke load is anticipated, it is recommended that outdoor air quantities should be increased to an appropriate value Where occupants are required by their employers to enter and remain for an extended period in such enclosures, it is recommended that ventilation systems should be designed so that the employees receive an appropriately higher amount of outdoor air Building ‘leakage’ or a requirement for make-up air may result in a need for higher levels of outdoor air flow than the prescribed minimum C2.3.6 Minimum flow rate of outdoor air into a system serving a group of enclosures (Q F ) The concept of unused ‘outdoor air’ with ‘return air’ is well developed in Appendix D of the Standard Derivation of the air cleaning efficiency equations used in that appendix are included as Appendix CA to this commentary For single enclosures the formulae in Appendix D used to determine the required efficiencies are straightforward (Clauses D2.2.1 and D.2.2.2) For a group of enclosures for which a multiple enclosure factor is applicable, the appropriate formula depends on the location of the air treatment in the system, and the formula can be complicated Clause D2.3 of Appendix D provides formulae for some configurations, for which the derivations are set out in Clause CA2.3 of this Commentary For any other configuration proposed, the appropriate formula would have to be derived by the designer C2.3.7 Variable air volume systems Clauses 2.3.6 and 2.3.7 are both designed to take account of variations in air flows in variable air volume systems Table A1 in Appendix A of the Standard specifies the minimum outdoor air flow rates that must be supplied to one enclosure to maintain an indoor air quality that, in the present state of knowledge, should eliminate possible adverse effects of the indoor air on healthy adult occupants remaining in this enclosure for unrestricted periods Quite often one air-handling plant supplies air to more than one such enclosure The question then arises: How much outdoor air has to be introduced to the air-handling plant so that the minimum air quality required by this Standard will be maintained in all enclosures served by this air-handling plant? The formula given in Clause 2.3.6(a) provides the answer to this question and is known as the Multiple Enclosure Formula, and yields the Multiple Enclosure Factor ‘M’ The derivation of this formula can be found in Appendix D of the Standard and a nomogram is provided (Figure 2.2 of the Standard) to simplify the computation of M The factor M is usually greater than one The reason for this is obvious from the derivation and Example D1 in Appendix D One way of satisfying the requirements of this Standard, would be to introduce into the air-handling plant, sufficient outdoor air, so that the outdoor air content in the air supplied by the air-handling plant, would be determined by the use of the highest ratio of outdoor air to total supply air for any enclosure, applied to the total of air supplied to all enclosures This would certainly satisfy the Standard but would not be economical since all enclosures with lower ratios would be oversupplied with outdoor air The Multiple Enclosure Formula is based on the fact that the air returned from enclosures oversupplied with outdoor air still has some potential to dilute pollutants to satisfactory levels when introduced into the supply duct from the air-handling plant to enclosures It should be evident that further economies can be achieved by the grouping of enclosures with like ratios of outdoor air to total air on the same air-handling plant This of course may not be possible or appropriate in many cases for a variety of reasons C2.5 OUTDOOR AIR MIXING AND DISTRIBUTION The purpose of this Clause is to ensure that all enclosures supplied with air by an air-handling plant receive at all times the minimum amount of outdoor air required by the Standard As it is not practicable to measure the outdoor air content and its distribution in the air supply duct, the requirements of this Clause will be satisfied if the system design provides for – (a) minimum outdoor air to be carried at all times by the supply ducts from the air-handling plant to all enclosures; and (b) sufficient mixing of outdoor air with the recycle air in the air-handling plant to supply all enclosures with air of about the same ratio of outdoor to recycle air COPYRIGHT AS 1668.2 Supp1—1991 A well designed mixing chamber before the main fan in a single supply duct system would satisfy this Clause It would also satisfy the clause for other systems if the design provides for the minimum outdoor air to be delivered to each enclosure under all possible conditions of operation, i.e from full heating to full cooling The Standard accepts that this condition will be met if all supply ducts carry the same fraction of outdoor air The other requirement of this Clause of the Standard that outdoor air be well distributed within the occupied zone of an enclosure is to ensure the elimination of pockets of stagnant air where pollutants could accumulate Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited C2.6 OUTDOOR AIR FLOW C2.6.1 Systems serving enclosures in which the temperature may exceed 27°C under normal operation It is well recognized that additional body odour is generated at elevated temperatures The determination of outdoor air flow rates in Table A1 of Appendix A of the Standard for the ‘no smoking’ requirement is usually based on odour control Recognize that, in the majority of applications, air-conditioning would be used Where this is not the case, or for some other reason, temperatures in excess of 27°C occur under normal operation, rates must be adjusted upwards to compensate for increase in body odour generation by occupants C2.6.2 Systems serving enclosures with transient or variable occupancy The intent of this Clause is to conserve energy use in terms of the hours of operation of mechanical ventilation systems related to periods of occupancy of the enclosures served This provision was introduced by ASHRAE into its Standard on Ventilation For Acceptable Indoor Air Quality in 1979 and is included in ASHRAE 62–1989 The rationale provided in the ASHRAE Standard is included as Appendix J in AS 1668.2–1991 It should be recognized that although a system may be turned off during periods of non-occupancy a period of post-purging will be required after departure of occupants to clear pollutants generated by the occupants Also a period of pre-purging may be required before entry of occupants to clear accumulation of pollutants generated by furnishings and other materials, etc., within the space COPYRIGHT 13 AS 1668.2 Supp1—1991 APPENDIX CA DERIVATION OF THE AIR CLEANING EFFICIENCY EQUATIONS USED IN APPENDIX D, AS 1668 PART In the interests of space, the equations connecting efficiency of air cleaning equipment and the outdoor air intake in mechanical ventilation systems are set out in Appendix D of AS 1668 Part Although in some cases an indication of the approach taken in arriving at the equations is given, generally they are presented without explanation This Appendix contains the derivations not included in Appendix D of the Standard Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited DE FINITION OF SY MB OLS An af1, af2, afn = area of the nth enclosure = the minimum outdoor air flow rate per person, given in Appendix A of AS 1668 Part 2, or other approved rates, for the n enclosures N1 , N2 N n qfn = the occupancies (see Clause 2.3.2 of AS 1668 Part 2) of the n enclosures = the minimum outdoor air flow rate, for adequate air quality, to be supplied to the nth enclosure When there is no air cleaning, q fn = afn N n = the minimum outdoor air flow rate per person to be supplied to an enclosure for dilution of body odour (see Clause 2.3.4 of AS 1668 Part 2) = the supply air flow rates to enclosures 1, n a0 qs1 , qs2, q sn COPYRIGHT Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited AS 1668.2 Supp1—1991 14 Qs qF qs = = = Σ qsn = qs1 + q s2 + + qsn = total air supply rate in a multiple enclosure system the rate at which outdoor air is taken into a system comprising a single enclosure the supply air flow rate in a system comprising a single enclosure qr qsc = = Nc rc r c’ = = = the flow rate of air, treated by a recirculating air cleaning unit, that is delivered to an enclosure the supply air flow rate to the critical enclosure, i.e the enclosure with the largest value of q fn /qsn in a multiple enclosure system the occupancy of the critical enclosure the largest ratio q f1/qs1 , qf2/q s2, q fn /qsn the second highest ratio q fn /qsn (r c) (r c) 0’ (r c) cd QFU = = = = QFP = QFO = ε0 = ε1 = ε2 = the highest ratio a0 N/qsn the second highest ratio a N n /qsn the highest ratio (larger of 2.5 N n and 0.35 An )/qsn M Σ (afn N n ), the minimum rate at which outdoor air is to be taken into the multiple enclosure system when there is no air cleaning, where M is the multiple enclosure factor (see Clause 2.3.6 of AS 1668 Part 2) based on qfn = afn N n M Σ (a0 N n), the minimum rate at which outdoor air is to be taken into a multiple enclosure system when there is adequate filtration of particulates, where M is the multiple enclosure factor (see Clause 2.3.6 of AS 1668 Part 2) based on q fn = a0 Nn M Σ (larger of 2.5 N n or 0.35 A n ), the minimum rate at which outdoor air is to be taken into a multiple enclosure system when there is adequate filtration of particulates and adequate reduction of odours, where M is the multiple enclosure factor (see Clause 2.3.6 of AS 1668 Part 2) based on qfn = (larger of 2.5 N n or 0.35 A n ) the percentage efficiency of the air cleaning unit for particulates as determined in accordance with either – (a) AS 1132.5, using test dust No 1; or (b) BS 3928, Sodium flame test; or (c) AS 1324, Hot DOP test the percentage efficiency of the air cleaning unit for odours and for gaseous irritants in tobacco smoke, under all operating temperatures, determined by means of an approved test the percentage efficiency of the air cleaning unit for body odours under all operating temperatures, determined by an approved test CA2.2 Single enclosure CA2.2.1 Air treatment for particulates (a) Air treatment of the supply air stream Assume that the amount of particulate-free air in the supply stream to the enclosure is just enough to satisfy the requirements of the enclosure, viz a f N COPYRIGHT 15 AS 1668.2 Supp1—1991 There is at least qF of particulate-free air in the supply stream via the outdoor intake; the rest must come from the ‘clean up’ of the return air stream, i.e (a f N - qF) must come from filtration of (qs - qF ) This is expressed as For fixed q F, we have: Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited (b) Recirculating air cleaner to the enclosure Assume that just enough particulate-free air is supplied to the enclosure (viz a f N ) so that no particulate-free air emerges from it If this is the case, there is no clean air in the return stream and the amount of particulate-free air in the supply stream is q F Any shortfall in meeting the requirement of the enclosure has to be made up by the recirculating air cleaner, i.e ( a f N - qF) must be provided by ‘won’ from the recirculating air stream by a filter of efficiency ε % Therefore ≥ ( a f N - qF) hence ε q r ≥ ( a f N - qF) x 100% CA2.2.2 Air treatment for particulates and odour (a) Air treatment of the supply air stream Exactly the same reasoning as for CA2.2.1(a) leads to the following expressions: (i) (ii) COPYRIGHT , the clean air AS 1668.2 Supp1—1991 16 (b) Recirculating air cleaner to the enclosure Exactly the same reasoning as for CA2.2.1(b) leads to the following expressions: (i) ε qr and ε qr ≥ (a f N - qF ) x 100% (ii) ε qr ≥ (a0 N - qF) x 100% Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited CA2.3 Multiple enclosure systems CA2.3.1 Central air cleaning unit serving all enclosures (a) Particulate filtration only To meet the requirements of the critical enclosure, there must be at least of particulate-free air in the supply stream The amount in the supply stream is the sum of three components— (i) the amount of particulate-free air taken into the system from outside, Q F; (ii) the amount of unused clean air in the return stream after spilling Q F , viz (iii) the amount obtained by filtration of the particulate-contaminated air reaching the filter, viz The result of this summation must equal Manipulation of the terms yields the expression for the necessary value of ε given in Appendix D of AS 1668 Part 2: COPYRIGHT 17 AS 1668.2 Supp1—1991 This may be expressed as Dividing numerator and denominator by the term in parentheses yields But so we have Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited When Q F is set to the minimum permissible value, Q FP, substitution yields the expression given in Appendix D of AS 1668 Part 2, viz The reverse situation, considered in this section of Appendix D of AS 1668 Part 2, viz choosing a value of ε and calculating the necessary value of Q F, is handled by simple algebraic manipulation of the expression yielding (b) Particulate filtration and odour reduction The expressions relating to ε (and ε ) are unchanged from (a), above, whereas the expression for ε is derived in an exactly analogous manner Similarly, the compact forms, where Q F = Q FO, may be shown to be valid by substitution and expansion of terms, as was done in (a) CA2.3.2 Recirculating air cleaning units to each enclosure (a) Particulate filtration only COPYRIGHT AS 1668.2 Supp1—1991 18 The amount of odour-free air in the supply stream must be at least in order to satisfy the requirement of the critical enclosure This is achieved when Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited It is proposed that the particulate-free air ‘mimic’ the odour-free air, i.e that there be the same amount of particulate-free air in the supply stream as there is odour-free air, and that this surplus of particulate-free air supplied to each enclosure, over and above each enclosure’s requirement, should be the same in magnitude as the surplus of odour-free air emerging from each enclosure If this is done there will be equilibrium in the amount of particulate-free air in the supply, and all enclosures will be satisfied, because this is the case for the odour-free air, which it mimics With the proportion of particulate-free air in the supply equal to (r c)0 , the nth enclosure receives q sn x (r c) of particulate-free air It is required that this amount, together with that supplied by the recirculating air cleaner (call this later amount Z), should exceed the requirement for particulate- free air by the extent to which the odour-free air exceeds the requirement for odour-free air That is [q sn x (r c) + Z] - af Nn = qsn x (r c) - a Nn From this it is seen that Z = af Nn - a 0N n The quantity Z is obtained by filtering, with efficiency ε %, the recirculating amount of the enclosure air, q r n Since the filter acts only on particulate-contaminated air, it is necessary to find the amount of contaminated air in the recirculating stream This quantity is— x (Amount of contaminated air in the enclosure) The amount of contaminated air in the enclosure is q sn - (q sn x (r c) - a 0N n) since there is to be a surplus of particulate-free air emerging from the enclosure of (q sn x (r c) - a Nn ) Thus the amount of contaminated air in the recirculating stream is With a filter of efficiency ε % the amount of particulate-free air, Z, is equal to Since Z is to be equal to a f Nn - a0 N n, simple algebra yields (b) Particulate filtration and odour reduction COPYRIGHT 19 AS 1668.2 Supp1—1991 The reasoning here is as for (a) except that the particulate-free (and now, the odour-free) air has to ‘mimic’ the carbon dioxide (or building contaminants)-free air, which is to be present in the supply stream in the proportion That proportion is achieved when Q F = QFO Following this reasoning yields the expressions for ε (and ε ) and ε2 given in Appendix D of AS 1668.2 viz Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited CA.2.3.3 Air cleaners on supply to each enclosure (a) Particulate filtration only As in CA.2.3.2, it is arranged that the particulate-free air ‘mimics’ the odour-free air The proportion of particulate-free air in the supply is to be (r c)0 - largest of the values This is achieved when Q F = Q FP When this is the case, it means that amounts q sn (r c)0 (direct) and (via filtration) of particulate-free air reach the nth enclosure This total amount is to exceed the requirement, a fN n, by the same amount as the odour-free air supplied to the enclosure exceeds the odour-free air requirements of the enclosure That is – Thus, re-arranging terms COPYRIGHT AS 1668.2 Supp1—1991 20 (b) Particulate filtration and odour reduction The reasoning here is the same as in (a), except that Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited Following this reasoning yields: CA2.3.4 Air cleaners for the critical enclosure only CA2.3.4.1 Particulate filtration only Let Q F = Q FP Assume that the air treatment applied to the critical enclosure just satisfies the requirements of that enclosure For there to be equilibrium, there must exist a proportion of particulate-free air in the supply stream, CPF , such that the surplus particulate-free air emerging from the non-critical enclosures, attenuated by the spilling of Q FP from the return air, and then added to the uptake of Q FP of outside air, gives rise to an amount of particulate-free air in the supply of Q s CPF That is The term may be expressed as COPYRIGHT 21 AS 1668.2 Supp1—1991 Σ (q sn CPF ) - qsc C PF = (Σ(a f N n ) - a f N c ) i.e Q s CPF - q sc CPF = Σ a f N n + a f N c Substituting and rearranging terms leads to which is given in Appendix D of AS 1668.2 It has been assumed that the air treatment will take care of the needs of the critical enclosure, so it is necessary to consider the enclosure with the second highest ratio If CPF > , then all enclosures will be satisfied and the next step is to calculate what is needed of the air cleaning equipment to ensure that the requirement of the critical enclosure is satisfied (a) If there is a filter on the supply to the critical enclosure, then q sc (1 - CPF) of particulate-contaminated air is supplied to the filter, of efficiency ε0 % Thus is to be added to the qsc CPF supplied directly to the Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited enclosure Since the total is to equal the requirement a f N c it may be seen that (b) If there is a recirculating air cleaner, then an amount equal to (a f N c - qsc CPF) has to be provided by ε0 qr ≥ (a f N c - qsc CPF) x 100% If CPF < , more air than Q FP must be taken into the system from outside so that C PF reaches the value QF for QFP, and Substituting for C PF in the expression for C PF gives From this, the necessary value of Q F can be found as follows: Multiplying numerator and denominator by Q s gives Multiplying out the parentheses gives hence Gathering terms gives – Multiplying both sides by -1 and isolating Q F yields – With this value of QF, and with the proportion of particulate-free air in the supply stream equal to as applied earlier gives: (i) Filter on supply to the critical enclosure – COPYRIGHT , the same reasoning AS 1668.2 Supp1—1991 22 (ii) Recirculating air cleaner to the critical enclosure – ε0 ≥ (a f N c - qsc ) x 100% CA2.3.4.2 Particulate filtration and odour reduction The reasoning applied to CA2.3.4.1 applies here, when considering the provision to the various enclosures of adequate amounts of clean air The chain of steps it is necessary to follow are the same as before, complicated by the fact that there are two sets of requirements involved It is first assumed that the requirement of the enclosure that is critical for particulate-free air is just satisfied when Q F is equal, in this case, to QFO, and the requirement of the next most critical enclosure is considered If this cannot be met, an adequate value of Q F must be calculated In either event, the next step is to consider the situation from the odour-free air point of view Analogous expressions are derived, employing a0N and a f N and (the second largest value of instead of CA2.3.5 Combination of a central air cleaning unit and a recirculating air cleaning unit for the critical enclosure Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited (a) Particulate filtration only QF is set at QFP, which ensures that the proportion of odour-free air in the supply streams is (rc)0 = the largest value of The purpose of the filters and recirculating air treatment equipment is to add particulate-free air to ensure that although only QFP is being taken into the system, the particulate-free air requirements of all the enclosures are met Since it may be assumed that the critical enclosure will be satisfied, attention must be directed to the enclosure with the next highest value of This value is defined as If ≤ (rc)0, no central filter will be required since the odour-free air will be sufficient to cope with the particulate-free air requirements If > (rc)0, the proportion of particulate-free air in the supply stream must be increased to by means of filtration of the contaminated portion of the recycle air At equilibrium, and ignoring the critical enclosure, which is looked after by the recirculating air treatment unit, we have (q sn x the spilling of air, Σ( - a f N n ) surplus from the nth enclosure In total there is, before qsn - a f N n ) (excluding the critical exposure), and after the spill, an amount A, equal to— Thus the amount, B, of particulate-contaminated air approaching the central filter is— Filtration of this air is to provide the amount of particulate-free air needed for equilibrium, viz Q s r c - Q FP - A That is – Substituting for A and B yields the expression given in Appendix D for the necessary efficiency of the central filter COPYRIGHT 23 AS 1668.2 Supp1—1991 The efficiency of the filter in the recirculating air cleaner is derived by considering that an inadequate amount, q sc is supplied directly, a f N c is required, and is supplied via the filter, thus ε qr ≥ (a f N c - qsc ) × 100% Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited (b) Particulate filtration and odour reduction QF is set at QFO, which ensures that the proportion of carbon dioxide-free air in the supply streams is The purpose of the air-cleaning equipment is to add particulate-free and odour-free air to ensure that although only Q FO is being taken into the system, the requirements of all the enclosures are met Since it may be assumed that the critical enclosure will be satisfied by the recirculating air cleaner, attention must be directed at the enclosure ‘next most critical’ The ‘r values’ of interest are , the second highest value of , and , the second highest value If , ≤ (r c)cd, no central air cleaner for reduction of body odour will be required since the carbon dioxide-free air will be sufficient for the purpose If > (rc)cd, the proportion of odour-free air in the supply stream must be increased to by means of air cleaning of the contaminated portion of the recycle air In a manner exactly analogous to that of (a) it may be shown that for the central air cleaner – Similarly, following the argument in (a), it may be shown that for the recirculating air cleaner applied to the critical enclosure: ε2 qr ≥ [a0 Nc - qsc ] × 100 Next consider the requirements for air free of particulates and the odours and gaseous irritants of tobacco smoke If ≤ (rc)cd, no central air cleaner for filtering particulates and reducing the level of odours and gaseous irritants of tobacco smoke will be needed COPYRIGHT AS 1668.2 Supp1—1991 24 If r’c > (rc)cd, the proportion of air in the supply stream that is free of particulates and the odours and gaseous irritants of tobacco smoke must be increased to r’ c In a manner analogous to that in (a) above, it may be shown that for the central air cleaning unit: and for the recirculating air cleaning unit applied to the critical enclosure— ) x 100% Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited ε0 qr and ε1 qr ≥ (af Nc - qsc COPYRIGHT 25 AS 1668.2 Supp1—1991 APPENDIX CB BASIS OF AIR FLOW RATES FORMULAE FOR CARPARKS CB1 FLEET AVERAGE CO EMISSION RATES (Based on 1990 fleet mix, 25% catalyst): 1st minute 35 g/min 2nd minute 24 g/min 3rd minute 17 g/min 4th minute 13 g/min 5th minute 10 g/min Hot g/min CB2 AVERAGE CARSPEED IN CARPARK: km/h (0.01 minutes per metre) CB3 AMBIENT CO CONCENTRATION 10 p.p.m Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited NOTE: Although ambient CO concentrations exceed 10 p.p.m during peak periods at street level, the increasing proportion of catalyst cars in the fleet will reduce the excess in time CB4 PARKING TIMES (a) Parking: car drives at km/h to space, and takes one minute to park (b) De-parking: car takes 0.5 minute to leave space, and then takes 0.5 to 1.5 minutes to leave zone (c) Cars exiting from other areas are in the second minute of operation CB5 CO CRITERIA The formula aims for a one-hour average of 60 p.p.m (50 p.p.m rise) on the basis that – (a) this is intended to ensure that peak concentrations for short periods not exceed 100 p.p.m rise; (b) if CO monitoring devices are set to reduce ventilation when the CO concentration drops below 40 p.p.m., this would ensure that the eight hour average does not exceed 50 p.p.m.; and (c) this is intended to ensure that the eight hour average does not exceed 50 p.p.m CB6 FORMULAE For a typical commercial carpark, peak movements occur at morning and evening peak hours, when 50% of the total car spaces may be filled or emptied within one hour Generally, the evening peak hour generates more CO as the cars start cold so, for most car parks, the exit formula produces the highest requirement However, many carparks require entering cars to drive through all levels until a space is found, but allow exiting cars to leave by a comparatively direct route For these carparks it is necessary to consider the requirement of entry formula CB7 DERIVATION OF FORMULAE (a) Exit formula CO generated per car movement on exit = n1 x (0.5 @ 35 g/min + 0.5 x (35 - 24)) + n1 d1 x 0.01 min/m x 24 g/min + n2 t1 x 0.01 min/m x 24 g/min = 23n1 + 0.24 n1d1 + 0.24 n2t1 = 0.24 (100 n1 + n1d1 + n2t1) = 0.872 x 0.24 (100n1 + n1 d1 + n2t1) grams CO litres CO Required air quantity for 50 p.p.m rise, P car exit movements per car space per hour = P x 0.872 x 0.24 x (100 n1 + n1 d1 + n2t1) x = P x 1.16 x (100 n1 + n1 d1 + n2t1) = P x 1.2 x (100 n1 + n1d1 + n2 t1 ) (b) Entry formula CO generated per car movement on entry = n1 x (1 @ g/min) + n1d2 x 0.01 min/m x g/min + n2t2 x 0.01 min/m x g/min = n1 + 0.08 n1 d2 + 0.08 n2t2 grams CO = 0.872 x 0.08 (100 n1 + n1 d2 + n2t2) litres CO Required air quantity for 50 p.p.m rise, P car exit movements per car space per hour = P x 0.872 x 0.08 x (100 n1 + n1 d2 + n2t2) x = P x 0.39 x (100 n1 + n1 d2 + n2t2) = P x 0.4 x (100 n1 + n1d2 + n2 t2 ) COPYRIGHT AS 1668.2 Supp1—1991 26 (c) Minimum air quantity Based on one engine operating at 20 g/min (5 cold start average), for 100 p.p.m rise Required air quantity = = 2906 L/s, say 3000 L/s (d) Limit on n2 Based on required air quantities for cars passing through the zone or level not exceeding the requirements for cars moving through the level at 12 m centres (approx m space between cars) in short peak periods for which 100 p.p.m CO rise is acceptable If cars are closer together or stopped, they would be queuing, and subject to Clause 4.6 of the Standard For exit lanes, assuming 24 g/min CO (average emission rate for second minute) – Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited This limit has the effect of limiting the through ventilation component to a rate equivalent to that for queuing areas of exiting cars For entry lanes, assuming g/min CO (hot engine emission rate) This limit has the effect of limiting the ventilation to about 56% of the rate applicable to queuing cars However, entry queuing areas would extend out from the carpark rather than back into the carpark CB8 BASIS OF TABLE 4.1 Values obtained for some commercial parking stations indicate the following: Example 1: 865 car spaces Peak entry movements occurring in 9th hour: 425 entries (4 exits) Peak exit movements occurring in 18th hour: 317 exits (6 entries) Example 2: 900 car spaces Peak entry movements occurring in 9th hour: 284 entries (13 exits) Peak exit movements occurring in 18th hour: 273 exits (28 entries) Counting entries as equal to exits, the actual usage factors would be as follows: For Example 1: Entry peak hour = 0.496 Exit peak hour = 0.373 For Example 2: Entry peak hour = 0.33 Exit peak hour = 0.33 The table nominates 0.5 as the commercial parking usage factor Factors for other categories are notional and should be discussed It would be desirable to get some factual data on the ventilation requirements of diesel engines CB9 BASIS OF AREA MINIMUM (a) The minimum air quantity in AS 1668.2–1980 for a simultaneous operation factor of 0.06, and for 25 m per car space, is equivalent to L/s/m2 This has been in use before the introduction of catalytic convertors If a comparison is made between the emission rates of non-catalyst cars and the average emission rates during the first three minutes after starting for catalyst cars, there is a reduction by a factor of 0.56, resulting in an equivalent minimum standby of 3.5 L/s/m2 for catalyst cars (b) 3.5 L/s/m2 corresponds to six air changes per hour for a space 2.1 m high, which is an established rate for general ventilation COPYRIGHT 27 AS 1668.2 Supp1—1991 APPENDIX CC DERIVATION OF AIR FLOW RATES FOR QUEUING AREAS CC1 EXIT LANES Based on average emission rate for 3rd to 5th minute = 13.33 g/min For 100 p.p.m rise: Required air quantity = = 1937 L/s Assume 6.5 m per car in queue Required air quantity per metre = 298 L/s, say 300 L/s CC2 ENTRY LANES Based on hot engine emission rate = g/min For 100 p.p.m rise: Required air quantity = = 1163 L/s Licensed to LUU MINH LUAN on 25 Feb 2002 Single user licence only Storage, distribution or use on network prohibited Assume 6.5 m per car in queue Required air quantity per metre = 178 L/s, say 200 L/s CC3 DIESEL VEHICLES Assume length per vehicle rises in same proportion as air flow required per vehicle COPYRIGHT ... in AS 1668.2 at this time They have therefore been developed in more detail in the revision for further clarification The wording of the Standard in respect of the use of natural ventilation has... also the basis of the ventilation rate for the lift shaft C4.5.5 Areas used by special purpose vehicles The values in Table 4.3 of the Standard were derived from the American Conference of Governmental... meet the requirements of the critical enclosure, there must be at least of particulate-free air in the supply stream The amount in the supply stream is the sum of three components— (i) the amount