Document gLwJQpBgKZbOjeVeQbQMyDQ

nr 1 514 CHAPTER 22 : : "1950:'G(iide Leonard Greenburg, I; M. Moriyama and ;E. J: Rbdee.' (The American Joumai of Hygiene, Vol. 22, No. 1, July, 1935, pp. 137-156). ., . 11 The Globe Thermometer in Studies of Heating and Ventilation, by T. Bedford and C. G. Warner. (The Journal of Hygiene, \ol. 34, No. 4). 11 A.S.H.V.E. Research Report No. 1067--The Cooling and Heating Rates'of a Room with Different Types of Steam Radiators and Convectors, by A. P. Kratz, M. K. Fahnestock and E. L. Broderick (A.S.H.V.E. Tbansacitons, Vol. 43,1937, p. 389). "Humidification for Residences, by A. P. Kratz (University of Illinois, En gineering Experiment Station Bulletin No. 230, p. 20). \ CHAPTER 23 PANEL HEATING AND RADIANT HEATING Influence of Heat Radiation on Human Comfort, Objectives of Radiant Heating, Practical Problems of Radiant Heating from a Physiological Standpoint, Fundamental Computations, Application Methods, Calculation Principles, Measurement and Control IT has been pointed out in Chapter 6 that the human body loses heat to its environment in three ways: by convection, radiation, and evapo ration. The Effective Temperature Chart takes account of convection and evaporation, but does not provide for such radiative effects as occur when room air and its surrounding surfaces differ widely in temperature. INFLUENCE OF HEAT RADIATION ON HUMAN COMFORT When, however, the body is exposed to radiation from a hot surface or is radiating to a cold surface, the factor of radiative heat gain or heat loss may be important. This phenomenon is most marked in the case of expos ure to the sun's radiative heat. On a cold day, with no wind blowing,' while standing in the sunshine, one may feel perfectly comfortable but, when a cloud passes over the sun, one may instantly feel much cooler. The cloud acts as a shield to interrupt the. radiant heat from the sun. The change in feeling of comfort is due to the instant change in rate of heat loss from the body caused by the shielding effect of the cloud. A shielded ther mometer under the same condition would register no change in temperature.. The rate of heat loss by convection depends upon the average tempera ture difference between the surface of the body and the surrounding air, the shape and size of the body, and the rate of air motion over the body. The rate of heat loss by radiation depends upon the exposed surface area of the body, and upon the difference between the mean surface temperature of the body and the mean surface temperature of the surrounding walls or other objects. This latter temperature is called the Mean Radiant Tem perature (MRT). Because these two types of heat loss supplement each other, a required rate of total heat loss can result either from a`relatively low air temperature and a relatively high MRT, or vice versa. At the temperature which produces comfort (and at all lower tempera tures) the production of sweat is low and the heat loss by evaporation is relatively low and relatively constant, irrespective of the relative humidity of the atmosphere. Under such conditions the heat loss from the body is chiefly related to the combined effect of convection and radiation. For,, unclothed subjects in a reclining posture, the heat demand of the environ ment, so far as these two factors of radiation and.convection are concerned, may be measured by Operative Temperature, which is defined by the follow ing formula, modified from that of Gagge1 by the expression of air velocity in feet per minute and the various temperatures in Fahrenheit degrees, 515