SUPPLEMENTARY NOTES ON BODY RADIATION* 



By L. B. ALDRICH 



WALL TEMPERATURES AND BODY RADIATION 



In present-day ventilation, three basic factors are considered: 

 (i) air temperature, (2) relative humidity, and (3) air movement. 

 The results of my previous report indicate that, in addition, considera- 

 tion should be given to a fourth factor, the temperature of the walls 

 and surrounding objects. 



For normal indoor conditions, with the surrounding objects all at 

 the temperature of the air in the room and with the subject clothed 

 and at rest, the radiation loss of a human subject is nearly one half 

 of his total heat loss. This radiation emitted from skin and clothing 

 has been shown to be nearly that of a " black body." We may assume 

 that, by virtue of repeated reflections from the other walls and sur- 

 rounding objects in a closed room, the radiation from the walls to the 

 subject is also nearly " black." Then the radiation loss of the sub- 

 ject is proportional to the difference of the fourth powers of the 

 absolute temperatures of the subject and the surroundings, in accor- 

 dance with the Stefan-Boltzmann law. Suppose the mean surface 

 temperature of a clothed subject to be 32° C. and the mean tempera- 

 ture of surrounding walls and objects to be the same as the air 

 temperature, 23° C. The difference of the fourth powers of the 

 absolute temperatures is 977 X 10". Now imagine the air temperature, 

 humidity, and air movement to stay constant and the wall tempera- 

 ture to be lowered 10°. The difference of the fourth powers becomes 

 1963 X 10'^% an increase of 100 per cent in the radiation loss. On a 

 winter day the temperature of exposed walls might easily be 10° 

 below air temperature, and the inner surface of window panes prob- 

 ably would be considerably more than 10° below air temperature. 

 Thus a subject, particularly if on the exposed side of the room, would 

 radiate at least twice as much on one side as on the other, and his 

 total loss of heat would be increased some 25 per cent or more. 



Of even greater importance is the consideration of surrounding 

 objects which are at higher than air temperature. As before, suppose 



* See A study of body radiation, Smithsonian Misc. Coll., vol. 8l, no. 6, 

 1928. 



Smiihsonian Miscellaneous Collections, Vol. 85, No. 11 



