Document qdyd42x2b6mn7mDQa2vpEj415

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 cold atmospheres compensation by increased metabolism becomes inade quate. The body temperature falls and the reflex irritability of the spinal cord is markedly affected. The organism may finally pass into an unconscious state which ends in death. A moderate amount of variability in temperature is known to be beneficial to health, comfort, and the performance of physical and mental work. On the other hand, extreme changes in temperature, such as those experienced by passing from a warm room to the cold air out-ofdoors, appear to be harmful to the tissues of the. nose and throat which are the portals for the entry of respiratory diseases. Experiments show that chilling causes a constriction of the blood vessels of the palate, tonsils, throat, and nasal mucosa, which is accom panied by a fall in the temperature of the tissues. On re-warming, the palate and throat do not always regain their normal temperature and blood supply. This anaemic condition favors bacterial activity and it probably plays a part in favoring infection with common colds and other respiratory diseases. Lowered resistance may also be related to a dimi nution in the number and phagocytic activity of the leucocytes (white blood cells) brought about by exposure to cold and by changes in tem perature. Sickness records in industries seem to strengthen this belief. The Industrial Fatigue Research Board of England19 found that with the workers exposed to high temperatures and to changes in temperature, namely, steel smelters, puddlers, and general laborers, there is an excess of all sickness, the excess among the puddlers being due chiefly to respira tory diseases and rheumatism. The causative factor was not the heat itself but the sudden changes in temperature to which the workers were exposed. The tin-plate millmen who were not exposed to chills, since they work almost continuously throughout the shift, had no excess of rheumatism and respiratory diseases. On the other hand, the blastfurnacemen, who work mostly in the open, showed more respiratory sickness than the steel workers. This experience in British factories is well in accord with the findings in American industries20,21. According to these data the highest pneumonia death rate is associated with dust, extreme heat, exposure to cold, and to sudden changes in temperature. In the ordinary dwelling not equipped with a fan system during the winter season, air movement is likely to be minimal and the only air movements affecting comfort are those due to cold walls or convective heating. Below an air temperature of 77 F, for the clothed, semi-reclining body, sweat secretion is at a minimum and, even with high atmospheric humidity, all the moisture available is evaporated. Under conditions'of low air movement, and with a relative humidity of 30-35 per cent, the evaporative heat loss is only 1.5 Btu per square foot of body surface greater than with a relative humidity of 75-80 per cent. This is the equivalent of decreasing the air temperature by less than 1 F. . "Fatigue and Efficiency in the Iron and Steel Industry, by H. M. Vernon (Industrial Fatigue Research Board Report No. 5. 1920, London). "Iron Foundry Workers Show Highest Percentage of Deaths from Pneumonia (Statistical Bulletin. Metropolitan Life Insurance Co., New York, N. Y., 1928). "The Pneumonia Problem in the Steel Industry, by D. K. Brundage and J. J. Bloomfield {Journal of Industrial Hygiene, 14, December, 1932). , 48 CHAPTER 2. PHYSIOLOGICAL PRINCIPLES RELATION of air conditioning needs to metabolism The major objective of heating and ventilation is to balance heat losses from the human body. The basic factor is human metabolism. The desirable environment, from the standpoint of heat loss, depends directly on the heat produced' in the body and this heat may be five times as great when a man is exercising violently as when he is reclining and at rest. Table 4. Relation Between Metabolic Rate and Activity3 Activity Hourly Metabolic Rate tor Avq Person or Total Heat Dissipated, Btu per hour Hourlt Hourlt Sensible Latent Heat Dis Heat Dis sipated, sipated, at 79 P, at 79. F, Btu per Btu per Hour Hour Moisture Dissipated per Hour Grains Pounds Basal................................................-........................ 291 Seated at Rest--......................--...................... 384 Reading Aloud (Seated)-...................................... 420 Standing at Rest...... ............................................... 431 Hand Sewing (Seated)............................................ 441 Knitting 23 stitches per minute on Sweater..... 462 Dressing and Undressing. .................................. 468 Tailor......................................................................... 482 Singing....... ........................... ...........I....................... 486 Office Worker Moderately Active--................... 490 Light Work Standing.........:................................... 549 Typewriting Rapidly.............................................. 558 Ironing with 5 lb iron--.......................................... 570 Dishwashing--Plates, Bowls, Cups and Saucers 600 Clerk Moderately Active Standing at Counter.. 600 Book Binder.-....... -................................................. 626 Shoemaker...... ....................................................... 661 Sweeping Bare Floor 38 Strokes per Minute.... 672 Pool Player. ..................... -.................................... 680 Walking 2 mph, Light Dancing- _ ................. 761 Light Metal Worker (at Bench)--....................... 862 Painter of Furniture (at Bench)........................... 876 Carpenter.................................................................. 954 Restaurant Serving................................................. 1000. Pulling Weight ..................................................... 1041 Walking 3 mph. 1050 Walking 4 mph, Active Dancing, Roller Skating . 1390 Walking Down Stairs............................................. 1444 Stone Mason............................................................. 1490 Bowling........................;................................... 1500 . Man Sawing Wood.... ................................ 1800 Swimming.-.:.... .............;............................. 1986 Running 5.3 mph_____........................................... .2268 ' Walking 5 mph._ ___ .............. ............... 2330 Walking Very Fast 5.3 mph,,_ ........................ 2580 Walking Up Stairs................................... 4365 Maximum Exertion Different People___ 3000-4800 145 145 225 159 225 195 225 206 225 216 225 237 225 243 225 257 225 261 225 265 225 324 225 333 225 345 225 375 225 375 225 401 225 436 229 443 230 450 250 511 277 585 280 596 307 . 647 325 675 335 708 339 .711 452 . 938 467 977 490 1000 490 1010 590 . 1210 979 1070 1316 1390 1458 1600 1640 1740 1762 1790 2187 2248 2329 2530 2530 2710 2940 2990 3040 3450 3950 4020 4367 4556 4745 4750 6330 6595 6750 6820 8170 0.140 0.153 0.880 0.199 0.208 0.229 0.234 0.248 0.252 0.256 0.312 0.321 0.333 0.362 0.362 0.387 0.420 0.427 0.434 0.493 0.564 0.575 0.624 0.651 0.677 0.679 0.904 0.942 0.964 0.974 1.167 ------- aThese metabolic rates were compiled by the A.S.H.V.E. Research Laboratory from actual tests,.from other authoritative sources, and from estimates based upon various considerations. Division of the'total heat dissipation into latent and sensible rates is based on actual test data and on various considerations for metabolic rates up to 1250 Btu per'houf;:and extrapolated for higher rates. Valuesfor total heat dissipa tion for a person at rest apply for.a_dry-bulb temperature range From approximately 60 to 90 F; for otherthan rest conditions the values apply for a similar but lower temperature range. Below these temperature ranges metabolic rates and total rates of heat dissipation increase, while above these ranges metabolic ratesincrease slightly and total heat dissipation rates decrease rapidly. Division of total dissipation rates into sensible and latent heat holds only for a dry-bulb temperature of 79 F. For lower temperatures, sensible heat dissipation increases and latent heat decreases, while for higher temperatures the reveree is true........... 49.