Document 7M9zNLr68o523MQj23OMwyVb8

222 CHAPTER 12 1949 Guide thorities give 0.3 to 1 deg increase of room temperature to compensate for 1 deg depression of the MRT. APPLICATION OF PHYSIOLOGIC PRINCIPLES TO AIR CONDITIONING PROBLEMS In order to estimate cooling loads in occupied spaces it is necessary to know the metabolic rate (heat production) of man. This has been studied extensively and found to remain relatively constant per unit of body sur face area in a subject fasting and resting quietly after a good night's sleep. The rate is high in children, and diminishes gradually with age; it increases in certain diseases and in the presence of fever. The metabolic rate is some what lower in women. Heat production goes up sharply with work and physiological Principles 1223 Combinations of temperature, humidity, and air movement which induce the same feeling of warmth are called thermo-equivalent condi tions. A series of studies22 at the A.S.H.V.E. Research Laboratory estab lished the equivalent conditions for practical use. This scale of thermoeouivalent conditions not only indicates the sensation of warmth, but jjso to a considerable degree determines the physiological effects on the varies widely in different persons doing the same work. Figsi 5; 6, and. 7 and Table 24 of Chapter'15 give sufficient basic data for estimating heat pro duction and heat loss under various conditions. \ EFFECTIVE TEMPERATURE INDEX AND COMFORT ZONES There is no precise physiologic observation by which comfort can be evaluated. Mean skin temperature offers some promise. The zone of thermal neutrality differs with clothing, season, activity, and'all the other factors controlling heat production (Table 4). The comfort zone is very similar to the zone of thermal neutrality. Sensations of warmth or cold depend, not only on the temperature of the surrounding air as registered by a dry-bulb thermometer, but also upon the temperature indicated by a wet-bulb thermometer, upon air movement, and upon radiation effects. Dry air at a relatively high tem perature may feel cooler than air of lower temperature with a high moisture content. Air motion makes any moderate condition feel cooler. Radia tion to cold or from warm surfaces is another important factor under certain conditions affecting the comfort reaction of the individual:"' 30 40 50 60 70 80 90 100 110 EFFECTIVE TEMPERATURE DEG Fig. 5. Relation Between Total Heat Loss from the Human Body and Effective Temperature for Still Air* 14 * Curve A--Persons working, metabolic rate 1310 Btu per. hour. Curve B--Persons working, metabolic rate 850 Btu per hour. Curve <7--Persons working, metabolic rate 680 Btu per hour. Curve D--Persons seated at rest, metabolic rate of 400 Btu per hour. Curves B and D based on test data covering a wide tern* perature range. Curves A and C based on test data at an Effective Temperature of 70 deg and extrapolation of Curves B and D.. All curves are averages of values for high and low relative humidities; variation due to humidity is small. body induced by heat or cold: For this reason, it is called the effective temperature scale or index, and it denotes sensory heat level. Effective temperature is an empirically determined index of the degree of warmth perceived on exposure to different combinations of temperature, humidity, and air movement. It was determined by trained subjects who compared the relative warmth of various air conditions in two adjoining conditioned rooms by passing back and forth from one room to-the other. The numerical value of the index for any given air conditions is fixed by the.temperature of slowly moving (15 to 25 fpm air movement) saturated air which induces a like sensation of warmth or cold. Thus,. any air condition has an effective temperature of 60 deg, when it-induces a sensa-