ADAPTATIONS OF HUMAN BODY TO VARYING THERMAL CONDITIONS 



301 



variations in physiological status occur, it is 

 to be expected that hot conditions, well 

 within the range of thermal equilibrium, may 

 be accompanied by sensations of discomfort. 



The fundamental studies on this latter 

 point were made at the Research Labora- 

 tories of the American Society of Heating 

 and Ventilating Engineers (to which full 

 reference will be found in the current issue of 

 their Guide (2) . These tests were based pri- 

 marily on indications of preference expressed 

 by subjects passing from one carefully regu- 

 lated room to another room with shghtly dif- 

 ferent temperature or humidity. The major 

 result of these studies was the development 

 of what is laiown as the Effective Tempera- 

 ture Index. This index was determined for 

 clothed subjects not engaged in active physi- 

 cal work and exposed to minimal air move- 

 ment (15-25 feet per minute). It repre- 

 sents, for these conditions, the net effect 

 upon comfort of variations in atmospheric 

 temperature and humidity. The Effective 

 Temperature is defined as that temperature 

 of completely saturated air which will pro- 

 duce the same subjective sensation of com- 

 fort as the particular combination of tem- 

 perature and humidity observed (in both 

 cases with minimal air movement). Similar 

 charts have been dra\vn for higher air veloci- 

 ties ; and the way in which the scale works is 

 illustrated in Table XII, showing various 

 combinations of air conditions, all producing 

 an Effective Temperature of 17.2°C. 



Fig. 9, again reproduced by the courtesy 

 of the American Society of Heating and 

 Ventilating Engineers, shows the zones of 

 dry-bulb and wet-bulb temperatures that 

 correspond to maximum comfort as deter- 

 mined in the Pittsburgh studies. It will be 

 noted that two separate zones are indicated 

 for winter and for summer comfort, respec- 

 tively, since it was found that the subjects 

 in the summer preferred distinctly higher 

 temperatures than in winter. The winter 

 comfort zone extends from an Effective Tem- 

 perature of 63°F (17.2°C) to one of 71°F 

 (21 .7°C) . The summer comfort zone ranges 



between 66°F (18.9°C) and 75°F (23.9°C). 

 An optimal area for all seasons is indicated 

 between 66°F and 71°F (18.9°C and 21.7°C) 

 with relative humidities between 30 and 

 70 percent. 



The Effective Temperature data were ob- 

 tained in rooms with air and walls at approxi- 

 mately the same temperature. Later 

 A.S.H.V.E. studies have led to the conclu- 

 sion that an elevation or lowering of the 

 mean radiant temperature of the enclosure 

 1°F above or below the air temperature can 

 be balanced by a 0.5°E.T. lowering or raising 

 of Effective Temperature. The correction 

 for mean radiant temperature is obviously a 

 very rough approximation. The relative 



TABLE XII 



Air Temperatures, °C, Producing Equivalent 

 Sensations of Comfort, Equal to an Effec- 

 tive Temperature of 17.2 °C, with Varying 

 Degrees of Relative Humiditt and Air 

 Movement 



influence of air and wall temperatures can 

 only be evaluated by the factor of Operative 

 Temperature discussed earlier. It would be 

 much sounder to determine operative tem- 

 perature directly and then apply it, in place 

 of air temperature, in the Comfort Chart. 

 A.S.H.V.E. studies (2) on both resting and 

 working subjects have shown the striking 

 effects of High Effective Temperature on 

 rectal temperature and pulse rate as given 

 in Table XIII. This table affords ample 

 evidence of the stress imposed by saturated 

 environments (or their equivalent) above 

 32.2°C (90°F) on either resting or working 

 subjects. From the standpoint of service 

 engineers, the details of this stress are less 

 important than a clear realization of the 

 reality of the severe physiological stress that 



