Document vVX0mLKJQk27VNBGey9DnGbZm

478 CHAPTER 26 1965 Guide And Data Boole air, radiators, or convectors. It is true that warm panel sur faces tend to produce a comfortable environment at a lower room-air temperature, but field experience in the United States has indicated that actual reductions in air temperature are slight in operation. Temperature at Proper Level. However, in making the actual heat loss computations 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 lead is meant, with regard to walls, the air temperature at the mean height be tween floor and ceiling; with glass, the air temperature at the mean height of the glass; with a roof or ceiling, the air temperature at the mean height of the roof or ceiling above the floor of the heated .room; and in the case of floors, the air temperature at the floor leveL' Table 2 .... Winter Indoor Dry-Bulb Temperatures Usually Specified* Type of Bu3dmg Schools-- Classrooms............................ Assembly rooms................ Gymnasiums.......................... Toilets and baths................. Wardrobe and locker rooms Kitchens................................. Dining and lunch rooms.... Playrooms.............................. Natatoriums.......................... Hospitals-- Private rooms............................................... Private rooms (surgical)....... ......... ...... Operating rooms.......................... ............. Wards............................................................. Kitchens and laundries.............. ............. Toilets......... ................................................ Bathrooms..................................................... Theaters--' - Seating space............................................. Lounge rooms............................................... Toilets............................................................ Hotels-- ,i. Bedrooms and baths................................... . Dining rooms.. ......................................... Kitchens'and laundries............................... Ballrooms..... ................. .................... Toilets and service rooms.......................... 72-74 68-72 55-65 70 65-68 66 65-70 60-65 75 72-74 ' 70-80 70-95 72-74 70-80 68-72 68 75 65-68 68 Stores................................................................... Public Buldinqs................................ Warm Air Baths....................................... Steam Baths....................................................... Factories and Machine Shops . . ............ Foundries and Boiler Shops................. Paint Shops......... .................................... 72-74 120 110 * Tbe most eomfortAbW dry-bulb teomeniure to be maintained depends on tbs relative htnrridity snd air motion. These three factors considered together conetitato what to tamed the tSteUee Cempatipe.'(See Chapter 7.) When rela tive humidity ia not controlled aeparately, optimum dry-bulb temperature far comfort will be riixfaUy higher two shown ia Table 9. Temperature at Ceiling. The air temperature at the exiling is generally higher than at the breathing level, due to the stratification of air resulting from the tendency of the warmer or less dense air to rise. An allowance for this fact 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 (1) the type of heating system, (2) the ceiling height, and (3) the indoor-outdoor temperature differential. The type of heating system is particularly impor tant, as the temperature gradient from floor to breathing level to ceiling may depend to a large extent on whether a direct radiation, unit heater, or warm air system is used, and in the latter case, whether the air is moved mechanically or by gravity. The temperature of the heating medium is also a factor. Because of these many variables, it is practically impossible to establish rigid rules for determining the temperature dif ference to use in all eases. However, for residences and struc tures having ceiling heights under 10 ft, the comparatively small temperature differential between the breathing level and ceiling generally may be neglected without serious error. For higher ceilings, an allowance of approximately 1 percent increase in temperature per foot of height above the breathing level may be made for ceiling heights up to 15 ft and approxi mately of 1 deg per foot of height above that level. The values in Table 3 are calculated on this basis. For direct radi ation and gravity warm air systems, the allowance should be increased from 50 to 100 percent over those given in Table 3. These rules should, however, be used with considerable dis cretion, as they do not apply to some types of heating systems, such as those using panel and baseboard radiation, where very low temperature differences between the floor and the ceiling may exist. Temperature at Floor LeveL According to tests at the University of Illinois,*-11 the temperature at the floor level ranged from about 2 to 6 deg below that at the breathing level, or somewhat greater than the difference between the Table 3 .... Approximate Temperature Differentials Between Breathing bevel and Ceiling, Applicable to Certain Types.of Heating Systems* BraofMng level Temperature (5 ft Abov* Flood H 60 65 70 72 74 76 78 80 85 90 10 3.0 '3.3 3.5 `3.6 3.7 3.8 ' 3.9 4.0 4.3 4.5 11 3.6 3 U 4.2 4.3 4.4 4,6 4 7 4.8 5.1 5.4 12 4'.'i 4.6 4.9 ft.t 5.2 5.3 5.5 5.6 6.0 6.3 13 4.8 5.2 5.6 5.8 5.9 6.1 6.2 6.4 6.5 .7.2 14 5.4 59 6 3 6.5 6.7 6.8 7.0 7.2 7.7 8.1 15 6.0 6.5 7.0 7.2 7.4 7.6 7.8 8.0 8.5 9.0 16 17 IS 19 20 '25 30 35 40 45 50 6.1 66 7.1 7.3 7.5 7.7 7.9 8.1 8.6 9.1 6.2 ' 6.7 7 2 7.4 7.6 7.8 8.0 8.2 8 7 9.2 6.3 6.8 7.3 7.5 7.7 7.9 8.1 8.3 . 8.3 9.3 6.4 6 9 7.4 7.6 7.8 8.0 8.2 8.4 8.9 9.4 6.5 7.0 7.5 7.7 7.9 8.1 8.3 8.5 9.0 9.5 8.21 7.0 7.5 8 0 8.4 8.6 8.8 9.0 9.5 10.0 7.5 8.0 8 fi 8,7 8.9 9.1 9.3 9.5 10.C 10.5 8.0 8.5 9.G 9.2 9.4 9.6 9.8 10.0 10.5 11.0 8.6 9.0 9.5 9.7 9.9 10.1 10.3 10.5 11.0 11.5 9.0 9.5 10.0 10.2 10.4 10 6 10 8 11.0 II 5 12,0 9.5 10.0 10.5 10.7 10.9 11.1 11.3 11.5 12.0 12.5 * The figures in this table are bessd on an increaae of 1 percent per foot rf height above the breathing level (4 ft) up to 14 ft and Hoof ana degree far eachfoot above 15 ft. "ITue table a generally applicable to forced air types of heating systems. For direct radiation or gravity warm air, inoreaae valnea SO percent to 100 pocent. 1. . . Heating Load breathing level and ceiling temperatures. Tests at the Uni versity of Wisconsin11 indicated a somewhat smaller differen tial between the floor and breathing level temperatures. As a general rule, if the breathing-level-to-ceiling temperature differential is neglected (as with ceiling heights under 10 ft), the breathing-level-to-floor differential may also be neglected, as the two are somewhat compensating, especially where both floor and ceiling losses are calculated for the same space. In other cases, the 10 ft temperature differentials in Table 3 may be used in arriving at the floor heat loss, these dif ferentials to be subtracted from the breathing level tempera ture. ATTIC TEMPERATURES Frequently, it is necessary to estimate the attic tempera ture, and in such cases Equation 1 can be used for this pur- A,UX + UiArUr + AWUW + AiU.) A,U. + ArUr + + AtU t, ~ attic temperature, Fahrenheit. -- indoor-temperature near top floor ceiling, Fahrenheit. C - outdoor temperature, Fahrenheit degrees. A, * area of ceiling, square feet. A, " area of roof, square feet. A, - area of net vertical attic wall surface, square feet. A, = area of attic glass, square feet U, " coefficient of transmission of ceiling, based on' surface conductance, of 2.20 (upper surface,'see Chapter 24). 2.20 = reciprocal of one-half the.air space resistance. U, " coefficient of transmission of roof, based on surface conductance of 2.20 Gower surface, see Chapter 24). Um " coefficient of transmission of.vertical wall surface. --* U, = coefficient of transmission of glass. Example 1. Calculate the' temperature in an unheated attic, Maiming the following conditions: (, = 70; U = 10; A, = 1000; A, - 1200; A. - 100; A, - 10; U, - 0.50; U, - 0.40; U. 030; U, = 1.13., . Solution: Substituting these values in Equation 1: (1000 X 0.40 X 70) + 101(1200 X 030) __ + (100 X 0-30) + (10 X 1-13)1 " (1000 X 0.40) + (1200 x 030) + (100 X 030) + (10 X 1.13) 34,413 1041 33.1 F Equation. 1 neglects the effect of'any interchange of air such as would take place through attic vents.or louvers in tended to preclude attic condensation. Test data**-1* indi.cate that reduction in temperature difference between attic air and weather is linear with attic;ventilation rates between 0 and 0.5 cfm per sq ft of ceiling area. A ventilation rate of 0.5 cfm per sq ft reduces this attic-to-weather temperature difference by approximately 50 percent, while a ventilation rate of 0.1 cfm per sq ft reduces this temperature difference about 10 percent. When attic ventilation meets the require ments of Table 3 in Chapter 23, 0.5 cfm per sq ft is the ap proximate ventilation rate under design conditions. There fore, the attic-temperature found from Equation 1 above can be reduced accordingly, depending upon the estimated ventilation rate. However,1 once this affects the overall heat loss of a residence with an insulated ceiling only one or two percent, it can be neglected without serious error. , This equation does not take into consideration such factors 479 as heat exchange between chimney and attic, or solar radi ation to and from the roof. Because of these effects, actual attic temperatures are frequently higher than the calculated values derived by using Equation 1. The attic temperature may be calculated in the usual manner by of Equation 1, allowing the full value of the roof. The error resulting from this assumption will generally be considerably less than that resulting if the roof were neglected (as is sometimes the prac tice) and the attic temperature assumed to be the same as the outdoor temperature. When relatively large louvers are in stalled, as is customary in the southern states, the attic tem perature is often assumed as the average between the indoor and outdoor temperatures. For a shorter approximate method of calculating heat losses through attics, the combined ceiling and roof coef ficient may be used, as described in Chapter 24. TEMPERATURES IN UNHEATED SPACES The heat loss from heated rooms to untreated rooms or spaces must be based on the estimated or assumed tempera ture in such unheated spaces. This temperature will lie in the range between tbe indoor and outdoor temperatures, de pending on the relative areas of the surfaces adjacent to the heated room and those exposed to the outside. If the re spective surface areas adjacent to the heated room and ex posed to the outdoors are approximately the same, and if the coefficients of transmission are approximately equal; the temperature in the unheated space may be assumed to be the mean of the indoor and outdoor design temperatures. If, however, the surface areas and coefficients are unequal, the temperature in the' unheated space should be estimated by means of Equation 2. k(Ai(/| + A,Ui + AtUt + etc.) + UA.U. + A*U> + A,Ut + etc.) A,U, + AtU, + AU + etc. .. + A.U + A(7 + A,U, + etc. tthere tu " temperature in unheated space, Fahr enheit. . U = indoor design temperature of heated room, Fahrenheit. t, -'outdoor design temperature, Fahren heit. At, At, At, etc. - areas of surface of unheated space ad jacent to heated space, square feet. 'A., At, A0 etc. - areas of surface of unheated space ex- 'posed to outdoors, square feet. Ui, Ut, Ui, etc. " coefficients of transmission of surfaces of At, At, At, etc. U,, Ut, Ua etc. " coefficients of transmission of surfaces A,, At, At, etc. Example 9: Calculate tee temperature in an unheated space y adjacent to a heated room having surface areas (At, At, ana At) ' in contact therewith of 100, 120, and 140 sq ft, and coefficients (Ui, Uh and f/) of 0.15, 0.20, and 0.25, respectively. The surface areas of.the unheated space exposed to the outdoors (A, and A*) are, respectively, 100 and 140 sq ft, and tee corresponding coeffi cients are 0.10 and 0.30. The sixth surface is on the ground and is neglected in this example. Assume - 70 and f. - -- 10. Solution: Substituting in Equation 2: 70((100 X 0.15) + (120 X 030) + (140 X 035)1 + -101(100 X 0-10) + (140 X 030)1 * " (100 x 0.15) + (120 X 030) + (140 X 035) + (100 X 010) + (140 X 030) 4660 126 37 F