Document N2kv2VeooaadgDLywQ82OpmQp

American Society of Heating and Ventilating Engineers Guide, 1934 the value of 5.9 Btu per square foot per degree difference in temperature is obtained for a velocity of 400 fpm and 9.55 Btu per square foot for a velocity of 800 fpm. It will be noted that for these two cases the heat transfer by evapo ration per degree difference in temperature corresponds almost exactly with the heat transfer by convection coils. The similarity may be noted by comparing the formula for heat transfer in parallel flow, where ____ 1_ tfp- 0.026 + 161 v (19) with the heat transfer by evaporation with parallel flow. The relationship will be seen to be very close in both cases and would indicate that the heat transfer by evaporation is actually brought about by a process of con vection. The difference in form of the two formulae may be. due in part to errors in observation at the higher and lower velocities. In cooling air and condensing out the moisture therefrom the heat transfer is considerably more rapid than when the air is dry and no moisture is condensed. In general the rate of heat transmission on the air side is increased an amount which is proportionate to the latent heat removed as compared with the sensible heat removed. That is, if the latent heat removed was 50 per cent of the sensible heat removed, then the conductivity of the surface in contact with the air would be increased approximately 50 per cent. REFERENCES A Review of Psychrometric Charts, by C. O. Mackey (Healing and Ventilating, June, July, 1931). A New Psychrometric Chart, by C. A. Bulkeley (A.S.H.V.E. Transactions, Vol. 32, 1926). Air Conditioning Applied to Cold Storage and a New Psychrometric Chart, by C. A. Bulkeley (Refrigerating Engineering, February,1932). Air Conditioning Theory, by John A. Goff {Refrigerating Engineering, January, 1933). Rational Psychrometric Formula, by W. H. Carrier (A.S.Af.E. Transactions, Vol. 33, 1911). Temperature of Evaporation, by W. H. Carrier (A.S.H.V.E. Transactions, Vol. 24, 1918). Principles of Engineering Thermodynamics, by Kiefer and Stuart. Basic Theory of Air Conditioning, by Lawrence Washington (Western Conference on Air Conditioning, San Francisco, Calif., February 9-10, 1933). Mixtures of Air and Water Vapor, by C. A. Bulkeley (Refrigerating Engineering, January, 1933). Temperature of Evaporation of Water into Air, by W. H. Carrier, and D. C. Lindsay (A.S.M.E. Transactions, 1924). Chemical Engineering, by Lewis, Walker and McAdams. The Psychrometric Chart, by E: V. Hill (Aerologist, April, May, June, 1932). Chapter 2 . VENTILATION AND AIR CONDITIONING STANDARDS Vitiation of Air, Heat Regulation in Man, Effects of Heat, Effects of Cold, Temperature Changes, Acclimatization, Warmth and Comfort, Effective Temperature, Comfort Chart, Comfort Line, Comfort Zone, Application of Comfort Chart, A.S.H. V.E. Venti lation Standards, Natural and Mechanical Ventilation, Recircu lation, Ozone, Ultra-Violet Radiation and Ionization, Heat and Moisture Losses VENTILATION is defined in part as "the process of supplying or removing air by natural or mechanical means to or from any space." (See Chapter 42). The word in itself implies quantity but not necessarily quality. From the standpoint of comfort and health, however, the problem is now considered to be one of securing air of the proper quality rather than of supplying a given quantity. The term air conditioning implies both air quality and quantity. In addition to air change, its scope is to control simultaneously the tempera ture, humidity, air movement and purity. The term is broad enough to embrace whatever other additional factors may be found desirable for maintaining the atmosphere of occupied spaces at a condition best suited to the physiological requirements of the human body. VITIATION OF AIR Under the artificial conditions of indoor life, the air undergoes certain chemical changes and a vitiation which are brought about by the occu pants themselves. The oxygen content' is somewhat reduced, and the carbon dioxide slightly increased by the respiratory processes. Organic matter, which is usually perceived as odors, comes from the nose, mouth, skin and clothing. The temperature of the air is increased by the meta bolic processes, and the humidity raised by the moisture emitted from the skin and lungs. Moreover, according to latest researches1, there is a marked decrease in both positive and negative ions in the air of occupied rooms. Contrary to old theories, the usual changes in oxygen and carbon dioxide are of no physiological concern because they are much too small even under the worst conditions. The amount of carbon dioxide'in air is often used in ventilation work as an index of odors of human origin, but the 1See A.S.H.V.E. research paper entitled. Changes in Ionic Content in Occupied Rooms Ventilated by Natural and Mechanical Methods, by C. P. Yaglou, L. C. Benjamin and S. P. Choate (A.S.H.V.E. Trans actions, Vol. 37, 1931). 19