Document ZDJKy9wvnMbeRqqgGL3KkYX0

Heating Ventilating Air Conditioning Guide 1939 temperature of 83 F would be cold.. In general, other conditions bei equal, for the range of temperatures normally encountered in iiv;ne quarters on cooling installations, the permissible deviation from avera? room temperature varies from approximately 1 F at the low end of thC range to about 3 F at the high end of the range. In this matter, it 6 important to consider the particular problem in the light of the type occupancy. For instance, greater deviations from room temperature and higher velocities may be permitted in a garage or a hotel hallway than would be permissible in an office or living room. The velocity which mav be considered the permissible maximum differs with the temperature deviation for a given installation, but an absolute maximum under anv conditions might be considered that which would produce a mechanical Chapter 28. Air Distribution ire is counteracted to a certain extent so that an individual may be P^w-ted to higher velocities of warm air without the feeling of disSUb)fnrt occasioned by the same velocities of cool air. In every case, it cpm Id foe the purpose of the designing engineer to keep the conditions ih n the zone of occupancy as nearly uniform as possible, securing W1- 'mum temperature deviations and low velocities. The air velocity Tall points in the room should be at least 25 fpm for good results. * It is impractical to measure momentary temperature differences with v degree of accuracy in the field, but in checking a given installation it Tl generally be found satisfactory to measure velocity only, since on doling installations high velocities normally occur with low temperatures, Td on heating installations high velocities occur with high temperatures. TTiat is, in the former case, the chilled supply air loses its velocity and Undergoes an increase in temperature as it settles into the occupancy "e whereas in the latter case the heated supply air loses its velocity and undergoes a decrease in temperature during this process. Therefore, if the Fig. 5. Elevation View Correctly Located Return Outlet Fig. 6. Elevation View of Improperly Located Return Outlet disturbance, such as the movement of a person's hair or disturbance of papers on a desk. Humidity is amimportant consideration in the determination of one's feeling of comfort; however, if the room generally is assumed to be at a satisfactory value of relative humidity, the designer is justified in neglecting this factor when considering permissible fluctuations in temperature and velocity in the qccupancy zone. This is true because the maximum allowable temperature fluctuation results in an unnoticeable humidity change. The standards that might be set up for maximum allowable room temperature deviation and air velocity would not be the same for both heating and cooling installations. In the former case, any appreciable temperature deviation is likely to be above rather than below the average room temperature, whereas the reverse is most likely to be true on a cooling installation. Further, because air movement has a cooling effect in itself, the feeling of warmth due to temperatures above room tem- 568 'i Fig. 7. Plan View Correctly Located Return Outlet Eliminating Stagnant Space average velocities within the occupancy zone are not excessive, one is fairly safe in assuming that the temperature difference is also within permissible limits. The subject of sound control is covered in Chapter 30 and it is recom mended for detailed review before consideration of the problem of air outlet noise. An understanding of the relation between sound intensity and loudness level in decibels, as well as the effect of the presence of sound absorbent materials in the room, is particularly necessary. A more detailed discussion of the nature of this problem appears later; whereas the following comments refer to what constitutes a satisfactory noise condition. Obviously, the nature of the conditioned space is important when con sidering the allowable outlet noise. In factories, press rooms, and similar spaces where the noise level is 65 db or higher, no complaints of grille noise are likely to be made. On the other hand, some homes, offices, hospitals, and, most of all, radio broadcasting and movie sound studios "present a real problem which must be intelligently attacked if a satis factory installation is to be made. In this chapter the noise of the air outlets (and returns) only is considered, it being assumed that the noise or sound level of the room without the outlet noise includes that which may 569