Document N2xBM7bN4Yw1e16aknRVbr3ab

258 CHAPTER 12 1956 Guide average wind velocity from December through February is 15 mph or higher in only 7 of the cities listed and Column 9 shows that a wind velocity of 15 mph did not occur in any city listed for temperatures equal to or lower than those shown in Column 8 for the years 1935-1939. Conse quently, it will often be desirable to modify the U values in Tables 6 to 9 and 15 to 19 of Chapter 9 to correspond to lower wind velocities. Correc tion factors for wind velocities can be found in Table 21 of Chapter 9. Column 6 in Table 1 lists the average annual minimum temperature which is the average of readings of the one lowest temperature occurring for each year the weather station has been in existence. A comparison of the temperatures listed in Columns 6,8, and 10 of Table 1 offers some guid ance in selecting a suitable outdoor design temperature for particular cities. For the 63 cities in the United States having temperatures listed in all three columns the average annual minimums in Column 6 average 2.3 deg warmer than the design temperature in common use listed in Column 10 whereas the design temperatures in Column 8 average 11.0 deg warmer than those in Column 10. There are variations of 6 deg or more in either direction from these average differences, however, for a few cities in this group. Designers are cautioned against attempting to compensate for internal vagrant heat sources in a structure, the heat generated by electrical equip ment, the approximations that may exist in heat transmission factors and infiltration rates, and the safety factors used in selecting heating plant capacity by adjusting the design temperature difference between indoors and outdoors. These factors should be accounted for by more careful analysis of their existence and magnitude in computing the heating load that must be carried by the heating plant itself. 4 INSIDE TEMPERATURES The inside air temperature which must be maintained within a building is understood to be the dry-bulb temperature at the breathing fine, 5 ft above the floor, or at the seating level, 30 in. above the floor, and not less than 3 ft from the outside walls. Inside air temperatures usually specified, vary in accordance with the intended use of the building. Table 2 presents values which conform to good practice. The proper dry-bulb temperature to be maintained depends upon the relative humidity and air motion, as explained in Chapter 6. In other words, a person may feel warm or cool at the same dry-bulb temperature, depending on the relative humidity and air motion. The optimum winter effective temperature for sedentary persons, as determined at the A.S.H.V.E. Research Laboratory, is 67-68 ET. As explained in Chapter 6 for so-called still air conditions, a relative humidity of approximately 50 percent is required to- produce an effective temperature of 68 ET when the dry-bulb temperature is 72.5 F. However, even where provision is made for artificial humidification, the relative humidity is seldom maintained higher than 40 percent during the ex tremely cold weather, and where no provision is made for humidification, the relative humidity may be 20 percent or less. Consequently, in using the figures listed in Table 2, consideration should be given to the actual relative humidity to be maintained, if provision is to be made for humidifi cation. If no humidification is to be provided, the higher temperatures Heating Load .. ' .259 may not even produce comfort on cold days; if humidity is to be main tained at 50 percent, the lower temperatures will apply.- In rooms having large glass areas, when sun is not shining, or in rooms with walls having a'high transmission coefficient, the lowered surface tem peratime will cause a feeling of coolness even though the air temperature in the room is at or above the temperatures indicated in the table. In rooms of this character, it is desirable to design for even higher temperatures than those listed, unless a compensating higher temperature surface is installed to offset the low temperature surfaces. Table 2. Winter Inside Dry-Bulb-Temperatures Usually Specified Type or Building Deg F Ttpb op Building Deg F Schools^ Class rooms.. ......................... Assembly rooms...................... Gymnasiums............................ Toilets and baths.................... Wardrobe and locker rooms... Kitchens.................................... Dining and lunch rooms........ Playrooms... ......................... Natatoriums.................. .......... HosPiTAia-- ~ ~- Private rooms.............. .;. Private rooms (surgical)., Operating rooms___ WWaards................................ Kitchens and laundries.. Toilets............................... Bathrooms...;............ !. 70-72 68-72 55-65 70 65-68 66 65-70 ' 75 70-72 70-80 70-95 68 66 68 70-80 Theatres-- Seating space................ Lounge rooms.................... Toilets......................... Hotels-- Bedrooms and hath* ........ Thninff mnma Kitchens and laundries__ . Bfdlmoma .................... Toilets and service rnimn ,,. Homes......................................... Stobes................................ . Public buildings...................... Steam baths.............................. Factobies and machine shops Foundries and aon.rn shops. . Paint Shops............................ , 68-72 68-72 68 70 70 66 66-68 68 70-72 65-68 68-72 120 110 60-65 50-60 aCirWmn?t6n"; YhZTtZ ftaTKrya'.U^U"si"Ml.e^re"fpteongiewthreertocoDnestmituatientwaihnaetdisdteeprmenedds tohne tehffeecrteivleatteivmepheummtuirde.ity(8aened wffl CaUghtly higher tE Table 2ntroUed aepamtelY-0pUmum d^-bulb temperature for comfort rut msiue temperatures specined in Table 2 may be used for panel heated spaces as well as for spaces heated by warm air, radiators or con vectors. It is true that warm panel surfaces tend to produce a comfortable environment at a lower room air temperature than when warm panels are not present, but field experience in the United States has indicated that actual reductions in air temperature are slight in operation. Temperature at Proper Level. In making the actual heat loss compu tations, however, for the various rooms in a building it is often necessary to modify the temperatures given in Table 2 so that the air temperature at the proper level will be used. By air temperature at the proper level is meant, in the case of walls, the air temperature at the mean height be tween floor and ceiling; in the case of glass, the air temperature at the mean height of the glass; in the case of roof or ceiling, the air temperature at the mean height of the roof or ceiling above the floor of the heated loom; and in the case of floors, the air temperature at the floor level. Temperature at Ceiling. The air temperature at the ceiling is generally mgher than at the breathing level due to stratification of air resulting from Ihe tendency of the warmer or less dense air to rise. An allowance for this act should be made in calculating ceiling heat losses, particularly in the case of high ceilings. However, the exact allowance to be made may be somewhat difficult to determine as it depends on many factors, including if) the type of heating system, (2) ceiling height, and (3) the inside- outside temperature differential. The type of heating system is par-