Document gDk9Mnr3gZQOpR80M4zM2e18a

HEATING VENTILATING AIR CONDITIONING GUIDE 1940 In Tables 7, 8, 9 and 10 the unit of concentration is the mol. A M molal solution is defined as a solution containing M X 42.37 grains of anhydrous lithium chloride per 1000 grains of water. The formula con necting concentration in mols with weight in per cent is equivalent to: [100 X M X 42.37] - [1000 + (M X 42.37)]. Example If. Calculate the dew-point, wet-bulb, relative humidity and absolute humidity of air in equilibrium at 100 F with pure lithium chloride solution of density 1.27S0o.lution. From Table 8 the concentration of a solution of density 1.270 at 100`F is 18.0 M. From Table 7 the dew-point of 18 M lithium chloride at 100 F is 43.7 F. From Table 6, Chapter 1, the partial pressure of water over the solution is 0.28S8 in. of Hg,, the absolute humidity is 42.00 grains per pound dry air, and the wet-bulb is 65.8 F. The relative humidity is 14.0 per cent. Example 6. Calculate the boiling point, and freezing point of 18 M lithium chloride soluStoioluntsio. n. From Table 10, boiling point (standard) is 285.8 F, freezing point is 58.1 F. The salt precipitated on cooling to this temperature has the composition LiCl-2H,0. Example 6. Calculate the heat of vaporization of 1 lb of water from a large amount of lithium chloride solution at the boiling point. Solution. The heat of boiling is equal to the heat of mixing plus the heat of boiling pure water at the same temperature. The heat of mixing from Table 10 at 18 M and 285.8 F is (145 -- 0.186 X 285.8) = 92 Btu per pound. The heat of vaporization of water from steam tables at 285.8 F is 920 Btu per pound. Therefore the heat of vapori zation of water from the solution is 920 + 92 = 1012 Btu per pound. Example 7. One thousand pounds of air per minute at 100 F dry-bulb with a dew point of 70 F and a relative humidity of 39 per cent is passed over 18 M lithium chloride solution. The rate of flow of the solution is 200 gpm and the entering temperature is 80 F. The air leaves the absorber at 85 F dry-bulb and dew-point of 35 F. Calculate (a) the heat to be removed from the lithium chloride solution to maintain these con ditions, and (6) the temperature rise of the solution in passing through the absorber. Solution, (a) The heat content of the entering air: From Table 6, Chapter 1, weight of vapor at 70 F dew-point is 0.01574 lb times heat content of steam at 100 F dry-bulb is 1104.2 (Table 8, Chapter 1) equals 17.41 Btu per pound plus heat content of dry air at 100 F is 24.0 (Table 6, Chapter 1) resulting in heat content of mixture as 41.41 Btu perSpimouilnadr.ly, the heat content of the leaving air: Weight of vapor at 35 F dew-point is 0.004262 X 1097.5 = 4.68 Btu per pound plus heat content of dry air at 85 F is 20.39 resulting in heat content of mixture as 25.07 Btu per pound. Heat to be extracted from air is 1000 X (41.41 -- 25.07) = 16.340 Btu per minute. Add to this the heat of mixing of 18M lithium chloride at 80 F equals 145 -- (0.186 X 80) = 130 Btu per pound (Table 10) or for 1000 lb of air X (0.01574 -- 0.00426) X 130 = 1494 Btu per minute. Heat to be removed from solution is 16.340 + 1494 = 17,834 Btu(bp)eTrhmeinwuetieg.ht of solution circulated is 200 X 1.275 (Table 8) X 8.33 = 2124 lb per minute. Its heat capacity is 2124 X 0.631 (Table 10) = 1340 Btu per minute per degree Fahrenheit. The temperature rise is 17,834 1340 = 13.31 F. .44 Chapter 3 PHYSICAL AND PHYSIOLOGICAL PRINCIPLES Chemical Vitiation of Air, Physical Impurities in Air, Thermal Changes Between the Body and Its Environment, Adaptation to Hot Conditions, Adaptation to Cold Conditions, Relation of Air Conditioning Needs to Metabolism, Acclimatisation, Effective Temperature Index, Physiological Objectives of Heating and Ventilation, Relation of Air and Wall Tempera tures, Influence of Humidity, Influence of Air Movement, The Four Vital Factors 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 46). 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 in its broadest sense implies control of any or all of the physical or chemical qualities of the air. More particularly, it is often used to include the simultaneous control of temperature, hu midity, movement and quality of air. The term is broad enough to embrace whatever factors may be found desirable, in a given case, for maintaining the atmosphere of occupied spaces at a condition best suited to the physiological requirements of the human body. CHEMICAL VITIATION OF AIR Under the artificial conditions of indoor life, the air undergoes certain physical and chemical changes which are brought about by the occupants 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 metabolic processes, and the humidity raised by the moisture emitted from the skin and lungs. Contrary to old theories, the usual changes in oxygen and carbon dioxide are of no physiological concern because they are too small to produce appreciable effects even under the worst conditions of normal human occupancy. The amount of carbon dioxide in air is often used in ventilation work as an index of odors of human origin, but the information it affords rarely justifies'the labor involved in making the observation1,1. 1A.S.H.V.E. Research Report No. 959--Indices of Air Change and Air Distribution, by F. C. Hotigb- ten and J. L. Blackshaw (A.S.H.V.E. Transactions, VoL 39, 1933, p. 261). 2A.S.H.V.E. Research Report No. 1031--Ventilation Requirements, by C. P. Yaglou. E. C. Riley and D. J. Coggins (A.S.H.V.E. Transactions, Vol. 42, 1936, p. 133). 45