Heat Loss from Animals and Man. Assessment and Control PDF
Preview Heat Loss from Animals and Man. Assessment and Control
Published Proceedings of Previous Easter Schools in Agricultural Science SOIL ZOOLOGY* Edited by D. K. McE. Kevan (Butterworths, London, 1955) THE GROWTH OF LEAVES* Edited by F. L. Milthorpe (Butterworths, London, 1956) CONTROL OF THE PLANT ENVIRONMENT* Edited by J. P. Hudson (Butterworths, London, 1957) NUTRITION OF THE LEGUMES* Edited by E. G. Hallsworth (Butterworths, London, 1958) THE MEASUREMENT OF GRASSLAND PRODUCTIVITY* Edited by J. D. Ivins (Butterworths, London, 1959) DIGESTIVE PHYSIOLOGY AND NUTRITION OF THE RUMINANT* Edited by D. Lewis (Butterworths, London, 1960) NUTRITION OF PIGS AND POULTRY* Edited by J. T. Morgan and D. Lewis (Butterworths, London, 1961) ANTIBIOTICS IN AGRICULTURE* Edited by M. Woodbine (Butterworths, London, 1962) THE GROWTH OF THE POTATO* Edited by J. D. Ivins and F. L. Milthorpe (Butterworths, London, 1963) EXPERIMENTAL PEDOLOGY* Edited by E. G. Hallsworth and D. V. Crawford (Butterworths, London, 1964) THE GROWTH OF CEREALS AND GRASSES* Edited by F. L. Milthorpe and J. D. Ivins (Butterworths, London, 1965) REPRODUCTION IN THE FEMALE MAMMAL* Edited by G. E. Lamming and E. C. Amoroso (Butterworths, London, 1967) GROWTH AND DEVELOPMENT OF MAMMALS Edited by G. A. Lodge and G. E. Lamming (Butterworths, London, 1968) ROOT GROWTH* Edited by W. J. Whittington (Butterworths, London, 1969) PROTEINS AS HUMAN FOOD Edited by R. A. Lawrie (Butterworths, London, 1970) LACTATION Edited by I. R. Falconer (Butterworths, London, 1971) PIG PRODUCTION Edited by D. J. A. Cole (Butterworths, London, 1972) SEED ECOLOGY Edited by W. Heydecker (Butterworths, London, 1973) * These titles are now out of print HEAT LOSS FROM ANIMALS AND MAN Assessment and Control PROCEEDINGS OF THE TWENTIETH EASTER SCHOOL IN AGRICULTURAL SCIENCE, UNIVERSITY OF NOTTINGHAM, 1973 Edited by J. L. MONTEITH, PH.D., F.R.S. Professor of Environmental Physics, Department of Physiology and Environmental Studies, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough, Leicestershire and L. E. MOUNT, M.B., B.S.(LOND.), M.D., C.M.(MCGILL) Head of Department of Applied Biology, ARC Institute of Animal Physiology, Babraham, Cambridge and Special Professor of Environmental Physiology in the Department of Physiology and Environmental Studies, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough, Leicestershire LONDON BUTTERWORTHS THE BUTTERWORTH GROUP ENGLAND Butterworth & Co (Publishers) Ltd London: 88 Kingsway, WC2B 6AB AUSTRALIA Butterworths Pty Ltd Sydney: 586 Pacific Highway, NSW 2067 Melbourne: 343 Little Collins Street, 3000 Brisbane: 240 Queen Street, 4000 CANADA Butterworth & Co (Canada) Ltd Toronto: 2265 Midland Avenue, Scarborough M1P4SL NEW ZEALAND Butterworths of New Zealand Ltd Wellington: 26-28 Waring Taylor Street, 1 SOUTH AFRICA Butterworth & Co (South Africa) (Pty) Ltd Durban: 152-154 Gale Street First published 1974 © The several contributors named in the list of contents, 1974 ISBN 0 40870652 X Printed in England by Page Bros (Norwich) Ltd, Norwich PREFACE Food is the source of all the thermal energy which man and animals expend to keep warm and their need for food is related to the rate at which they lose heat to the environment as well as to factors such as age, growth rate and exercise. In practice, the relationship between food needs and the environ ment has been clearly demonstrated for many farm animals, but, by contrast, relatively little unambiguous information is available on the dietary needs of man in relation to the very wide range of natural and artificial climates in which he is able to live and work. Primitive man learned how to control the loss of heat from his body by seeking shelter and by using animal pelts for protection against the weather. Modern man, on the other hand, prefers to heat his environment and, in some parts of the world, gracious living means a thermostat set at 75°F so that a minimum of clothing can be worn. The spectre of a world energy shortage has drawn attention to the enormous amounts of energy used by the industrial nations to make homes, offices and workshops 'comfortable'. The energy used for central heating and air conditioning greatly exceeds the consequent saving of metabolic energy. In contrast, the amount of energy used nationally to heat and ventilate livestock buildings is a trivial fraction of the very large amounts of heat produced by farm animals. According to one estimate, farm animals in Britain produce 50% more heat by metabolism than the whole human population. Because there is a strong link between food and energy, the study of heat loss from animals and man is fundamental both to efficient agricultural production and to the efficient use of fuel. The programme of this Easter School was designed, therefore, to explore the theme of heat loss, beginning with statements about physical principles and progressing through a review of physiological and behavioural knowledge to a final session on a few of the economic implications of attempting to control human and animal environ ments. The last topic could not be explored in depth, but if our knowledge of thermal physiology is to make a significant contribution to world food production, much more effort will be needed to assess the economic implica tions of progress in building schemes and animal husbandry. PREFACE The titles of the 20 papers submitted to the Easter School reveal the wide range of disciplines represented on the platform and the list of participants indicates the variety of interests and backgrounds which helped to sustain discussion both inside and outside the lecture hall. Although a comprehensive account of these discussions would have limited value, one topic worth pursuing was that of thermal neutrality. All participants were asked, therefore, to comment on a paper circulated after the meeting, and a final chapter was then added to the Proceedings in an attempt to reach a common view on this controversial matter. As far as possible, consistent symbols and units are used throughout the volume. S.I. units have been used but equivalents are included in the text where they are appropriate. In some cases, manuscripts needed considerable revision for the sake of conformity, and we are grateful for the willing co operation of authors which made this possible. The principles which guided our choice of symbols are explained, followed by a list of all the main symbols which are used in the text. J. L. Monteith L. E. Mount ACKNOWLEDGEMENTS We are grateful to all those who agreed to present papers at the meeting, and who showed great patience and good humour in their negotiations with the editors. The Vice-Chancellor of the University, Dr W. J. H. Butterfield opened the meeting by welcoming delegates who represented many different nationalities and the smooth running of the following sessions was a tribute to the skill of individual chairmen: Dr O. G. Edholm, Dr K. L. Blaxter, Professor A. D. M. Greenfield, Professor G. E. Lamming and Mr. Seaton Baxter. We are also grateful to Professor G. E. Folk for providing a film concerned with studies of thermoregulation at Point Barrow, and to all those who brought equipment, diagrams and photographs for demonstration during the meeting. Many of these demonstrations involved a substantial amount of preparation and their value was widely appreciated. The University of Nottingham acknowledges its gratitude to a number of firms which made financial contributions towards the expenses of overseas speakers: Dow Chemical Company Ltd, Vic Hallam Ltd, Milk Marketing Board, RHM Research Ltd and TAC Construction Materials Ltd. AGA (UK) Ltd met the additional cost of printing colour thermograms. The visit of Dr G. Alexander to Britain was made possible by a travel grant from the Underwood Fund administered by the Agricultural Research Council. Several members of the Department of Physiology and Environmental Studies were concerned with arrangements for the meeting, in particular Dr K. Cena, Dr J. A. Clark and Dr M. H. Unsworth. Miss Edna Lord handled all secretarial matters with the skill and enthusiasm which she has brought to many previous Easter Schools. SYMBOLS A common set of symbols is used throughout the text, chosen to conform as far as possible with current literature in environmental physics and physiology, modified by the following conventions: 1. Quantities of the same class are represented by symbols of the same alphabet, fount and case, for example τ—transmissivity, p—reflectivity. 2. As a corollary of 1., quantities which have different dimensions are not given the same symbol. This practice may create confusion even when a distinguishing subscript is added. The use of h as a heat coefficient and as a mass transfer coefficient is a familiar example. 3. In general, lower case subscripts are used to identify the position or region to which the main symbol refers, for example I is tissue insulation. Upper t case subscripts are used to identify entities or processes, for example h, a heat transfer coefficient for convection. Accepted usage requires a c few exceptions such as c, the specific heat of air at constant pressure. p 4. Quantities representing a flux density, i.e. a rate of transfer per unit area, are represented by bold symbols, for example M for metabolic heat production per unit body surface area. A fuller list of consistent symbols is given in Monteith, J. L. (1973). Prin ciples of Environmental Physics, Edward Arnold. A Area of body subscripts: D intercepting direct solar radiation R exchanging long-wave radiation with environment c Specific heat of air at constant pressure p C Rate of loss of sensible body heat from animal by convection per unit body surface area Heat loss from animal house by convection per unit floor area e (T) Saturation vapour pressure of water vapour in air with respect to w temperature T SYMBOLS D Wind direction e Vapour pressure subscripts: a air o interface r respired air s skin surface E Rate of loss of latent heat from body by evaporation per unit body surface area subscript: r respiratory component F Rate at which metabolisable energy is consumed as food per unit area of body surface f Depth of fleece g Gravitational acceleration G Rate of heat transfer from skin surface to surface of coat per unit area of skin surface Gr Grashof number h Generally, coefficient expressing rate of heat transfer from animal or house per unit temperature difference and per unit area subscripts: B sensible heat from respiratory system i.e. by breathing C convection CR convection and radiation as parallel modes of heat transfer E coefficient for latent heat transfer with same dimensions as h and h c R (Exceptionally, the symbol h has also been used for rate of water vapour transfer per unit area and per unit difference of water vapour concentration subscripts: d diffusion through skin M mass transfer from skin to air) I Insulation; temperature difference needed to produce unit heat SYMBOLS flux across insulator subscripts: a coat/air interface e external / fleece t tissue p fleece to depth penetrated by radiation / Depth of coat / Length of stretched hair s L Characteristic dimension of body k Thermal conductivity of (still) air K Rate of heat loss from animal by conduction per unit body area; heat loss from animal house by conduction, per unit floor area L Flux density of long-wave radiation subscripts: b emitted by body d downwards from atmosphere e received from environment u emitted upwards by ground m Flux of water vapour by diffusion through skin per unit area d m Flux of water vapour from skin to atmosphere per unit area M Rate of metabolic energy production per unit body surface area (i.e. rate of transformation of chemical energy into heat and mechanical work) subscripts: S sensible component of metabolic heat loss B metabolic heat expended on internal work D metabolic heat expended by departure from thermo- neutral state Nu Nusselt number p Interception function for ray in unit depth of coat Total air pressure Pr Prandtl number r Radius r Resistance for transfer process subscripts: H heat (by convection) V water vapour SYMBOLS R Net flux density of radiation loss from body, i.e. radiant energy n exchange per unit of surface in unit time R Universal Gas Constant (8.31 J mol"1 K"1) Ratio of wall surface area to floor area of house S Flux density of short-wave, solar radiation subscripts: e received from environment p normal to solar beam t total (i.e. direct and diffuse) T Temperature subscripts: a air c colon e effective, for example of coat surface g ground h required house temperature hy hypothalamus min minimum s skin o interface V Thermodynamic wet bulb temperature 17 Conductivity used in building science; heat transfer through material per unit temperature difference V Windspeed V Ventilation rate; volume of air inspired or expired in unit time W Rate of mechanical work by animal per unit body surface area W Body weight V Rate at which energy is retained by animal; weight gain of animal per unit area of body surface a Fraction of absorbed radiation; absorption coefficient of individual hair ß Thermal coefficient of expansion of air y Thermodynamic value of psychrometer constant ( = 0.66 mbar K"1 at20°C)
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