Document Rp0pjX6Qp49v1eEL6B1bJ2MDX

Vr'Hi HEATING VENTILATING AIR CONDITIONING CUIDE 1941 ment of comfort with relative humidities as high as 80 per cent, provided the effective temperature is between 70 and 75 deg. The second school favors a higher dry-bulb temperature, according to the prevailing outdoor dry-bulb, with a comparatively low humidity (well below 50 per cent), the main purpose being to reduce temperature contrasts upon entering and leaving the cooled space and to keep the clothing and skin dry. This second scheme requires more refrigeration with the present conventional type of apparatus. In connection with summer cooling mention should be made of the Table 5. Desirable Inside Conditions in Summer Corresponding to Outside Temperatures1 Occupancy Over 40 Min OUTSIDB DbT-BuLB . Dbg F Effective . Temperature Inbidb Aib Conditions Dry-Bulb Deg F Wet-Bulb Deg F Dew-Point Deg F Relative Humid ity Per Cent 100 75 83 66 56 40 75 82 67 59 45 75 81 68 61 51 |t 75 80 70 65 60 I 95 74 82 . 64 53 36 74 81 66 57 44 74 80 67 60 51 74 79 68 62 57 74 78 70 66 68 90 73 81 63 52 36 73 80 64 54 41 73 79 66 59 50 73 78 67 61 56 85 72 80 61 48 32 72 79 63 53 41 72 78 64 56 46 72 77 .... : 66 60 56 . SO .-. . 71. 78 ` - - . .61 49 36 . .- 71.. 77 63 54 45 71 . ,73 64 57 52 ' 7l ` ?'5 66 61 61 Applicable to Individuals engaged in sedentary or light muscular activity. danger of over-doing it. `Possible impairment to health may have resulted from the sharp contrast between air conditioned trains and the outside atmosphere in the early days of this practice. Current practice in theaters,' restaurants, etc., follows a schedule similar to that shown in Table 5. This schedule should. be used with considerable judgment, depending on the occupancy and local climatic conditions. There are some in dications that a definite indoor effective temperature may be applicable throughout the cooling season, but other observations seem to show that changing indoor conditions are desirable with violently changing outdoor weather conditions. It is questionable whether entirely satisfactory air conditions could be adduced for practical use to meet the changing / requirements of patrons from the time they enter to the time they leave ^ a cooled space. Too many uncontrollable variables enter into the prob 62 CHAPTER 2. PHYSIOLOGICAL PRINCIPLES lem. Work now going on at the A.S.H.V.E. Research Laboratory and other institutions may throw considerable light on this complex problem. For cooled banks and stores where the customers come and go, spending but a few minutes in the cooled space, observations indicate a schedule about 1 deg of effective temperature higher than that shown in Table 5. Laboratory experiments with exposures of 2 to 10 min indicate tem peratures 2 to 10 F higher than those in Table 5, but with much lower relative humidities. It should be kept in mind that southern people, with their more sluggish heat production and lack of adaptability, will demand a comfort zone several degrees higher than that for the more active people of northern climates. Instead of the summer comfort lines standing at 71 deg ET as here given, it was found to be much higher for foreigners in Shanghai where climatic conditions are similar to those of our gulf states. This difference in adaptability of people forms a very real problem for air conditioning engineers. Cooling of theaters, restaurants, and other public buildings in southern climates cannot be based on northern standards without considerable modification. RELATION OF AIR AND WALL TEMPERATURES In the previous discussion, it has generally been assumed that air and wall temperatures are alike and, of course, this is roughly the case. In a room heated by pure convection, the walls are generally heated by the warm air and in a room heated by pure radiation, the air is gradually warmed by convection from surfaces which have themselves been warmed by absorption of radiant heat. In ordinary indoor spaces, whatever the heating method, the mean of floor, ceiling and all four walls, is not likely to differ more than 3 F from the air temperature; but individual walls which have a dominant effect on certain areas of the room may be 20 F below air temperature46 (see Fig. 9). With an open fire, or a high temperature radiant heater the influence of radiant heat may be considerable; and with large window areas the converse cooling effect may be important. Outdoors in the sun, the influence of radiation is, of course, enormous. Where substantial differ ences between air and surrounding surfaces (or special radiant heat sources) do exist, this factor must be taken into account. An interesting point indicated by the studies at the John B. Pierce Laboratory, is that when a given operative temperature (that is, the temperature which should physically exert a certain heat-demand upon a body of fixed surface temperature) is produced by (1) air and walls at approximately the same temperature, and (2) colder air and warmer walls (in the zone of body cooling), the skin temperature falls to a lower point for the cold air warm wall situation, thus decreasing the actual rate of heat loss. The reason for this effect is somewhat obscure but it is believed to be related to local stimulation by the colder air exerted on the mem branes of the nose and throat and to the greater chilling of the exposed skin surfaces when those parts of the body are moved. Wall Surface Temperatures, by A. C. Willard and A. P. Kratz (A.S.H.V.E. Transactions, Vol. 36, 1930. p. 447). 63