Reference data. CIBSE Guide C

Transcription

1 Reference data CIBSE Guide C

2 Corrigenda CIBSE Guide C: Reference data Page 4-58: caption to Table should read: 90 swept tees, rectangular, diverging flow: values for... (Issued 16/10/07) Page 4-63: Table 4.A1.1: units for kinematic viscosity (ν) should be m 2 s (Issued 16/10/07) Page 3-25: equation should read: Φ / l = π d op U (θ s θ a) Page 3-25: equation should read: (Issued 15/05/12) d op R = ln (d on / d op ) 2 λ n (Issued 15/05/12) Page 4-25: Figure 4.9(a) should appear as follows: Page 4-22: equation 4.27 should read: (Issued 26/02/14) ζ = (1 A 1 /A 2 ) 2 (Issued 26/02/14)

3 Reference data CIBSE Guide C

4 The rights of publication or translation are reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior permission of the Institution. April 2007 The Chartered Institution of Building Services Engineers London Registered charity number ISBN: This document is based on the best knowledge available at the time of publication. However no responsibility of any kind for any injury, death, loss, damage or delay however caused resulting from the use of these recommendations can be accepted by the Chartered Institution of Building Services Engineers, the authors or others involved in its publication. In adopting these recommendations for use each adopter by doing so agrees to accept full responsibility for any personal injury, death, loss, damage or delay arising out of or in connection with their use by or on behalf of such adopter irrespective of the cause or reason therefore and agrees to defend, indemnify and hold harmless the Chartered Institution of Building Services Engineers, the authors and others involved in their publication from any and all liability arising out of or in connection with such use as aforesaid and irrespective of any negligence on the part of those indemnified. Typeset by CIBSE Publications Printed in Great Britain by Page Bros. (Norwich) Ltd., Norwich, Norfolk NR6 6SA Acknowledgement Permission to reproduce extracts from BS 2869 and BS EN ISO 7726 granted by BSI. British Standards can be obtained from BSI Customer Services, 389 Chiswick High Road, London W4 4AL. Tel: +44 (0) cservices@bsi-global.com Note from the publisher This publication is primarily intended to provide guidance to those responsible for the design, installation, commissioning, operation and maintenance of building services. It is not intended to be exhaustive or definitive and it will be necessary for users of the guidance given to exercise their own professional judgement when deciding whether to abide by or depart from it.

5 Foreword CIBSE Guide C was comprehensively updated for the 2001 edition. Although basic physical data do not change with time, the refinement of measurement and calculation techniques and further research make regular review essential. Many of the changes to this edition are therefore small incremental changes, reflecting such refinement. It was however recognised that section 4, Flow of fluids in pipes and ducts, while heavily revised for the 2001 edition, was at that time unable to take account of the latest European research. The report of this research has now been obtained and its results distilled into this edition of Guide C. The opportunity has also been taken to rewrite and clarify the text and to delete many pages of tabular data providing pre-calculated pressure drops through pipes. It was felt that these tables have outlived their usefulness now that accurate pressure drops can easily be calculated using spreadsheets or computer programs. Such a spreadsheet is provided on the CD-ROM that accompanies this Guide. I would like to express my thanks to all the volunteer authors who agreed to review and update their work and particularly to Peter Koch for his effort and enthusiasm in revising section 4. I would also like to thank all contributors, reviewers and CIBSE staff for their valuable contributions. Finally I hope that you will continue to find this Guide a useful and authoritative source of reference and guidance. Paul Compton Chairman, CIBSE Guide C Authors, contributors and acknowledgements Chapter 1: Properties of humid air Principal author (2001 and 2007 editions) W P Jones (consultant) The tables of psychrometric data are reprinted unchanged from the 1986 edition of Guide C and were prepared by a task group, see below. Task group members W P Jones (Chairman) (consultant) J F Armour B G Lawrence Chapter 2: Properties of water and steam The tables of data are reprinted unchanged from the 1986 edition of Guide C. Chapter 3: Heat transfer This chapter is reprinted from the 2001 edition; the authors and contributors were as follows. Principal authors (2001 edition) D L Loveday (Loughborough University) A H Taki (De Montford University) Contributors (2001 edition) H B Awbi (University of Reading) P D Compton (Colt International Ltd.) R M Harris (Centre for Window and Cladding Technology) M J Holmes (Ove Arup & Partners International Ltd.) B P Holownia (Loughborough University) J Moss (Ove Arup & Partners International Ltd.)

6 T Muneer (Napier University) H K Versteeg (Loughborough University) Acknowledgements American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. British Standards Institution The McGraw-Hill Companies Pearson Education Ltd. Chapter 4: Flow of fluids in pipes and ducts Principal author (2001 and 2007 editions) P Koch (Université Joseph Fourier, Grenoble; Coventry University) Contributor (2001 edition) F Sprenger (Coventry University) Acknowledgements American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. Centre Technique des Industries Aérauliques et Thermiques Coventry University, School of Science and the Environment Sheet Metal and Air Conditioning Contractors National Association Shell Chemicals, Rotterdam Chapter 5: Fuels and combustion Principal author (2001 and 2007 editions) M R I Purvis (Chairman) (University of Portsmouth) Task group members/principal authors (2001 edition) M R I Purvis (Chairman) (University of Portsmouth) R Dando (Coal Research Establishment) M Drew (BP Amoco plc) R J Harris (Advantica Technologies Ltd.) K Mildren (University of Portsmouth) Acknowledgement British Standards Institution Chapter 6: Units, standard and mathematical data Principal author (2001 and 2007 editions) P D Compton (Colt International Ltd.) Editor Ken Butcher CIBSE Publishing Manager Jacqueline Balian

7 Contents 1 Properties of humid air 1.1 Psychrometric data 1.2 CIBSE psychrometric chart ( 10 to +60 C) 1.3 CIBSE psychrometric chart (10 to 120 C) References Tables of psychrometric data 2 Properties of water and steam 2.1 Introduction References Tables of data 3 Heat transfer 3.1 Introduction 3.2 Heat transfer principles 3.3 Heat transfer practice References 4 Flow of fluids in pipes and ducts 4.1 Introduction 4.2 Notation 4.3 Fluid flow in straight pipes and ducts 4.4 Components and fittings 4.5 Flow of water in pipes 4.6 Flow of steam in pipes 4.7 Natural gas in pipes 4.8 Air flow in ducts 4.9 Pressure loss factors for components and fittings 4.10 Pressure loss factors for pipework components 4.11 Pressure loss factors for ductwork components References Bibliography Appendix 4.A1: Properties of various fluids Appendix 4.A2: Pipe and duct sizing Appendix 4.A3: Capacity K, and complex networks Appendix 4.A4: Steam flow in pipes Appendix 4.A5: Compressible flow 5 Fuels and combustion 5.1 Introduction 5.2 Classification of fuels 5.3 Primary fuels 5.4 Secondary fuels 5.5 Specification of fuels 5.6 Combustion data 5.7 Stack losses References Bibliography

8 6 Units, standard and mathematical data 6.1 Introduction 6.2 The International System of Units (SI) 6.3 Quantities, units and numbers 6.4 Metrication in the European Union 6.5 Conversion factors Bibliography Index I-1

9 1-1 1 Properties of humid air 1.1 Psychrometric data 1.2 CIBSE psychrometric chart ( 10 to +60 C) 1.3 CIBSE psychrometric chart (10 to 120 C) Psychrometric tables 1.1 Psychrometric data Basis of calculation The method of formulation suggested by Goff and Gratch (1,2), based on the ideal gas laws with a modification to take account of intermolecular forces, has been adopted for calculating the thermodynamic properties of moist air. This approach remains in line with current practice (3,4). The thermodynamic properties of dry air and saturated water vapour are well established and, although more recent research work (4 6) has been done, the results are not significantly different from those obtained in earlier work (7,8). Hence the thermodynamic properties of dry air and water vapour, determined by the National Bureau of Standards (7) and the National Engineering Laboratory (8), have been retained for the evaluation of the thermodynamic properties of moist air. Since the properties of dry air and saturated water vapour are accurately known, the properties of a mixture of the two can be established for the saturated case. For the enthalpy and specific volume of moist air, at a condition other than saturated, the method is exemplified by the following equations: h = h a + μ (h s h a ) / 100 (1.1) v = v a + μ (v s v a ) / 100 (1.2) where h is the specific enthalpy of moist air (kj kg 1 dry air), h a is the specific enthalpy of dry air (kj kg 1 ), μ is the percentage saturation (%), h s is the specific enthalpy of saturated moist air (kj kg 1 dry air), v is the specific volume of moist air (m 3 kg 1 dry air), v a is the specific volume of dry air (m 3 kg 1 ) and v s is the specific volume of saturated moist air (m 3 kg 1 dry air). The relevant specific property of moist, unsaturated air is determined by adding a proportion of the property of saturated water vapour to the same property of dry air, on a mass basis. A consequence of this is that the humidity of moist air is expressed as percentage saturation (defined in terms of the mass of water vapour present), rather than relative humidity (defined in terms of vapour pressure). The details of the psychrometric calculations are given in references 9, 10 and Standards adopted All data are tabulated for an internationally agreed standard atmospheric pressure (12) of kpa. The zero datum adopted by the National Engineering Laboratory (8) for the expression of the thermodynamic properties of steam is the triple point of water, C. The zero datum for the specific enthalpies of both dry air and liquid water has been taken here as K (0 C) Formulae used for calculations Saturated vapour pressure over water (8) log p s = log (θ ) (θ ) [ / (θ )] (1.3) where p s is the saturated vapour pressure over water at temperature θ (kpa), θ is the temperature, greater than or equal to 0 C ( C).

10 1-2 Reference data Saturated vapour pressure over ice (7) log p s = [ / (θ )] (1.4) where p s is the saturated vapour pressure over ice at temperature θ, less than 0 C (kpa). Moisture content f s p s g s = (1.5) f s p s where g s is the moisture content of saturated moist air (kg kg 1 dry air) and f s is a dimensionless enhancement factor (1 4,11). Percentage saturation 100 g μ = (1.6) g s where μ is the percentage saturation (%) and g is the moisture content of unsaturated moist air (kg kg 1 dry air). Vapour pressure of water vapour in unsaturated moist air p a g p v = (1.7) f s ( g) where p v is the vapour pressure of superheated water vapour in unsaturated moist air (kpa) and p a is the atmospheric (barometric) pressure (kpa). Relative humidity 100 p v φ = (1.8) p s where φ is the relative humidity (%). Wet bulb temperature Knowing the value of the vapour pressure, p v, from equation 1.7 the wet bulb temperature is derived from the following equations by an iterative technique: p v = p sl A (θ θ sl ) (1.9) where p sl is the saturated vapour pressure at temperature θ sl (kpa), A is a coefficient (K 1 ), θ is the dry bulb temperature ( C) and θ sl is the sling or mechanically aspirated wet bulb temperature ( C). Values of A are as follows: A = K 1 when θ sl 0 C A = K 1 when θ sl < 0 C or: p v = p sc B (θ θ sc ) (1.10) where p sc is the saturated vapour pressure at temperature θ sc (kpa), B is a coefficient (K 1 ) and θ sc is the screen wet bulb temperature ( C). Values of B are as follows: B = K 1 when θ sc 0 C B = K 1 when θ sc < 0 C Adiabatic saturation temperature h fg (g sa g) θ* = θ (1.11) (c pa + g c ps ) where θ* is the adiabatic saturation temperature ( C), h fg is the latent heat of evaporation of water at temperature θ* (kj kg 1 ), g sa is the moisture content of saturated air at temperature θ* (kg kg 1 dry air), g is the moisture content of moist air at the particular psychrometric state (kg kg 1 dry air), c pa is the mean specific heat capacity of dry air between temperatures θ and θ* (kj kg 1 K 1 ) and c ps is the mean specific heat capacity of water vapour between temperatures θ and θ* (kj kg 1 K 1 ). In the case of the adiabatic saturation temperature above ice, h fg is replaced by h ig, the latent heat of fusion of water at a temperature θ*. Dew-point For a particular psychrometric state, equation 1.7 is used to calculate the vapour pressure. An iterative technique is then used with equation 1.3 or 1.4 to determine the temperature for which the calculated vapour pressure is a saturated vapour pressure. Specific volume ( θ ) v = [ ] ( p v ) / [A aa x a A aw x a (1 x a ) + A ww (1 x a ) 2 ] (1.12) where v is the specific volume (m 3 kg 1 dry air), θ is the dry bulb temperature ( C), A aa is the second virial coefficient for dry air (4) (m 3 kg 1 ), A aw is the interaction coefficient for moist air (4) (m 3 kg 1 ), A ww is the second virial coefficient for water vapour (m 3 kg 1 ) and x a is the mole fraction of dry air. The mole fraction of dry air, x a, is given by: x a = (1.13) g

11 Properties of humid air 1-3 In the original work (1,2) and in later research (4), a third virial coefficient for water vapour (A www ) appears in equation 1.12 but it is complicated to calculate and its influence is insignificant. It is ignored here, without any loss of accuracy. Equation 1.2 yields answers of adequate precision and is easier to use than equation Specific enthalpy h = h a + g h g (1.14) where h is the specific enthalpy of moist air (kj kg 1 dry air), h a is the specific enthalpy of dry air (7) (kj kg 1 ), g is the moisture content (kg kg 1 dry air) and h g is the specific enthalpy of water vapour at the dry bulb temperature (8) (kg kg 1 dry air). Equation 1.1 gives answers having the same accuracy as those obtained from equation 1.14 and is simpler to use Psychrometric properties at non-standard barometric pressures The tabulated psychrometric data are accurate within the range of barometric pressure from 95 kpa to 105 kpa and Table 1.1 Corrections to specific enthalpy at non-standard pressures Adiabatic saturation temperature / C hence are suitable for the whole of the UK. For pressures outside these limits an application of the ideal gas laws will give answers of a little less accuracy. Better answers may be obtained by the use of equations 1.15 and p s g s = (1.15) (p a p s ) ( g) ( θ ) v = (1.16) p a Corrections to specific enthalpy may be taken from Table 1.1. Figure 1.1, which gives the relationship between height above sea level and barometric pressure, is drawn from the equation: p a = exp[( 9.81 ρ z) / ( )] (1.17) where p a is the particular atmospheric (barometric) pressure (kpa), ρ is the density of air (kg m 3 ) and z is the altitude above sea level (m). Alternatively, the standard relationship (12) for altitude, atmospheric pressure and temperature may be used. This is reproduced in Table 1.2. Approximate additive corrections to specific enthalpy (/ kj kg 1 dry air) at stated barometric pressure / kpa

12 1-4 Reference data Barometric pressure / Pa Altitude / m Figure 1.1 Variation of barometric pressure with altitude Table 1.2 Standard atmospheric data for altitudes to m Altitude / m Temperature / C Pressure / kpa Atmospheric pressures and temperatures from 5000 m to m may be accurately calculated (3) using the following equations: p a = ( z) (1.18) θ = z (1.19) where p a is the barometric pressure (kpa), θ is the atmospheric temperature ( C) and z is the altitude above sea level (m). 1.2 CIBSE psychrometric chart ( 10 to +60 C) The chart has been designed (13) and constructed using the two fundamental properties of mass (moisture content) and energy (specific enthalpy) as linear co-ordinates. Other physical properties are not then shown as linear scales (13,14). The 30 C dry-bulb line has been constructed at right angles to lines of constant moisture content, which are horizontal. The scale of specific enthalpy is obliquely inclined to the vertical scale of moisture content. In this way, lines of constant dry bulb temperature are approximately vertical, diverging slightly on each side of the 30 C line, and the traditional appearance of the chart is preserved. The wet-bulb values shown are those read from a sling or mechanically aspirated psychrometer and lines of percentage saturation are plotted instead of relative humidity. Within the comfort zone, there is no practical difference between percentage saturation and relative humidity. In any case, the difference diminishes as saturated or dry conditions are approached. The psychrometric data used were taken from the tables of the properties of humid air presented in this chapter of CIBSE Guide C. 1.3 CIBSE psychrometric chart (10 to 120 C) The psychrometric chart for 10 to 120 C has been based on the ideal gas laws. This does not give a significant difference when compared with a chart constructed using more accurate data, based on the method of Goff and Gratch (1,2). The principles of calculation and drawing are detailed elsewhere (14). References 1 Goff J A and Gratch S Thermodynamic properties of moist air Trans. ASHVE (1945) 2 Goff J A Standardisation of thermodynamic properties of moist air Trans. ASHVE (1949) 3 Psychrometrics ch. 6 in ASHRAE Handbook Fundamentals (Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers) (2005) 4 Hyland R W and Wexler A Formulations for the thermodynamic properties of dry air from K to K and of saturated moist air from K to K at pressures to 5MPa Trans. ASHRAE 89(2A) (1982) 5 Hyland R W and Wexler A Formulations for the thermodynamic properties of the saturated phases of H 2 O from K to K Trans. ASHRAE 89(2A) (1983) 6 Stimson H F Some precise measurements of the vapour pressure of water in the range from 25 C to 100 C J. Res. NBS 73A (1969) 7 Tables of thermal properties of gases NBS Circular 564 (Gaithersburg, MD: National Bureau of Standards) (November 1955) 8 National Engineering Laboratory steam tables (London: Her Majesty s Stationery Office) (1964) 9 Jones W P and Lawrence B G New psychrometric data for air Technical Memorandum No. 11 (London: Polytechnic of the South Bank) 10 Some fundamental data used by building services engineers (London: Institution of Heating and Ventilating Engineers) (1973) 11 Jones W P A review of CIBSE psychrometry Building Serv. Eng. Res. Technol. 15(4) (1994) 12 US Standard Atmosphere (Washington DC: U.S. Government Printing Office) (1976) 13 Jones W P The Psychrometric Chart in SI Units J. Inst. Heating and Ventilating Engineers (1970) 14 Bull L C Design and use of the new IHVE psychrometric chart J. Inst. Heating and Ventilating Engineers (1964)

13 Specific enthalpy / (kj. kg 1 ) Properties of humid air Sensible/total heat ratio for water added at 30 C Wet-bulb temperature / C (sling) Based on a barometric pressure of kpa Specific volume / m 3. kg Percentage saturation / % Moisture content / (kg. kg 1 dry air) Specific enthalpy / (kj. kg 1 ) Dry-bulb temperature / C Specific enthalpy / (kj. kg 1 ) Figure 1.2 CIBSE psychrometric chart ( 10 to +60 C)

14 Reference data Relative humidity / % Moisture content / (kg. kg 1 ) Sensible/total heat ratio for water added at 30 C Specific volume / m 3. kg Specific enthalpy / kj. kg 1 0 Wet bulb temperature / C (sling) Dry bulb temperature / C Specific enthalpy / kj. kg 1 Figure 1.3 CIBSE psychrometric chart (+10 to +120 C)

15 Properties of humid air C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl

16 1-8 Reference data 9 C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl

17 Properties of humid air C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl

18 1-10 Reference data 7 C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl

19 Properties of humid air C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl

20 1-12 Reference data 5 C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl

21 Properties of humid air C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl C DRY-BULB temperature, Screen, Sling, content, g enthalpy, h volume, ν θ * θ sc θ sl