Document EGn1GJarbbL4BLmb13Q7y59n

American Society of Heating and Ventilating Engineers Guide, 1924-25 These .values are now represented on the chart by a %-in. vertical line drawn in the center ofeach of the respective columns. The proper wet-bulb temperature is determined by noting the point of intersection of the "light work line" and the 20-ft. air motion line; this is 55 deg. wet bulb. Since the actual wet-bulb temperature as determined by the test is 58 deg. then the wet bulb difference is 3 deg. This value is plotted in the first column and the penalization as read in the " -- %" portion is -- 5% per cent. For the 10,000 particles of Dust, the penalization is a -- 1 per cent; for the Bacteria, -- 1 per cent; for the Odors, -- 3 per cent; for the COs, -- % per cent;. for Other Injurious Substances, -- 0 per cent, and for Distribution, -- 5% per cent. The sum of all these penalizations is -- 15% per cent. Therefore the Percent of Perfect ventilation in the room is 100 -- 15% =.84% per cent. .This value is then plotted in the last column marked Percent of Perfect. 174 Chapter XVIII . ' HOW TEMPERATURE, HUMIDITY AND AIR MOTION AFFECT HUMAN COMFORT THE sense of warmth experienced by the human body is not due alone to the temperature indicated by the dry bulb thermometer, neither does it depend solely upon the wet bulb temperature. Dry air at a relatively high temperature may feel cooler than air of considerably lower temperature with high moisture content. Human comfort or discomfort depend largely on body temperature and therefore on the relation between the rate of heat production and dissipation. By the process of metabolism heat is constantly generated within the body, while on the other hand, loss of heat is constantly oc curring from the' surface of the body by radiation, convection and evaporation. To maintain a constant body temperature the loss of heat must equal the heat produced. It is therefore apparent that any inter ference with the elimination of heat from the body is accompanied by a rise in temperature and a feeling of discomfort. There are three principal factors affecting loss of body heat: 1. Temperature. 2. Humidity. 3. Air motion. As the temperature of the air and surrounding objects rises, the loss of heat by convection and radiation decreases. When the temperature reaches that of the body, the loss by radiation aiid convection ceases. Finally as the air temperature exceeds that of the body, heat passes from the air to the body. If on the other hand, the relative humidity is increased the heat loss by evaporation decreases. If while the dry bulb temperature increases, the wet bulb temperature decreases sufficiently, the increase in loss of heat by evaporation may be made equal to the decrease in loss of heat by radiation and convection, resulting in no change in body temperature or comfort. From the above, it is concluded that there must necessarily exist cer tain combinations of temperatures and humidities, which produce the. same total body heat loss by radiation, convection and evaporation and therefore the same feeling of comfort or discomfort. Lines passing through such air conditions plotted as a psychrometric chart may be called equal comfort lines. The fact is further substantiated by the general experience of heating engineers in observing that the lower the humidity the higher the dry bulb temperature required for the same degree of comfort. A series of tests have been made in the two psychrometric rooms of the Research Laboratory of the American Society of Heating and Ven tilating Engineers, .in order to locate these lines on the psychrometric chart, both for still and moving air. ; Material for this section was prepared especially for The Cvws by F. C. Hougbten, New York, N. Y. 175