Document Bvv1aMz0NevM5e5BOvx1bgE2k

TFfsr ! : i'l , ; l- iI l : 180 CHAPTER 9 1950 Guide Table 4. Conductivities (fc) and Conductances (C) Used in Calculating Heat Transmission Coefficients (U) in Tables 5 to 18 These constants are expressed in Btu per (hour) (square foot) (Fahrenheit[degree temperature difference). Conductivities () are per inch thickness and conductances (C) are for thickness or construction slated, not per inch thickness. MATERIAL DESCRIPTION CONDUCnVTTT Conductance (i) (O Resistance Per Inch For Thickness listed (i) (f) AIR SPACES 1.10 0.61 0.46 2.17 EXTERIOR FINISHES (Frame Walla) 12.50 2.27 0.03 1.23 1.28 0.44 0.78 0.78 INSULATING MATERIALS Made from mineral or vegetable fiber or 0.27 0.30 0.33 0.27 0.48 3.70 3-33 .3.03 3.70 2.08 INTERIOR FINISHES Gtfsum Board (H t.)-----------------Gtpsgm Lath (M in ) and Piaster.... Insulating Board Lath 0$ 01.) and Plaster thickness assumed H In------------Insulating Board Lath (1 in.) and Plaster-____ -__ ___ ____ --... Plywood (M in.)---------------------- 0.50 3.30 2.00 0.30' 3.70 2.4 0.66 0.80 0.31 4.40 2.12 2.50 MASONRY MATERIALS 3 IN. Clat tils (hollow) ...... 12.00 10 in. Clat tils (hollow)_________ 16 in. Clat tils (hollow)___ _____ 2,50 Sand and gravel aggregate........... .............. 12.00 4 in. Concrete blocks_________ Hollow, gravel aggregate____ --_________ 12 in. Concrete blocks.^__,,______ Hollow, light weight aggregate*1_______ _ 0.89 1.25 2.30 0.08 1.28 1.00 0.64 0.60 0.53 0.40 0.31 0.40 0.08 1.28 1.00 1.00 0.80 0.60 0.53 0.50 0.47 1.66 0.60 0.61 Hollow....................... ...... ......-_________ 0.46 12.50 0.08 12.00 0.08 12.50 0.08 0.27 0.42 1.52 1.67 3.18 0.23 0.47 0.40 1.12 0.80 0.43' 0.78 1.00 1.67 1.67 1.72 2.50 3.23 0.78 1.00 1.00 1.25 1.66 1.88 2.00 2.13 1.64 2.18 Conductance values for horizontal air spaces depend on whether the heat flow is upward or downward, but in most re***"* it is sufficiently accurate to use the same values for horizontal as for vertical air spaces b Expanded slag, burned day or pumice. Heat Transmission Coefficients of Building Materials 181 Table 4. Conductivities (A;) and Conductances (C) Used In Calculating Heat Transmission Coefficients (U) in Tables 5 to 18--Concluded These constants are expressed in Btu per (hour) (square foot) (Fahrenheit degree temperature difference). Conductivities (i) are per inch thickness and conductances (C) are for thickness or construction stated, not per inch thickness. material DESCRIPTION CONDDCriViTI OB Conductance ( (O Resistance Per Inch For Thickness Thickness Usted (*) (*) ROOFING MATERIALS Buiiovcr Roofing-------- ------------------------ SHEATHING Insulating Board in.)-.... ....... Pltwood (*.(# in.)........ --................. .......... Fra or Yellow Pine (1 in.).............. loxo -- SURFACES Ordinary non-refiectivc materials, vertical.... 15 MP3 WIND VELOCITY_____________ ___ Ordinary non-refiective materials, verticaL.. ::: WOODS Fir bhsathino (1 in.) building paper Tfs 0.80 6.00 6.50 3.53 6.50 20.00 1.28 2.82 0.42 2.56 1.02 0.86 1.65 6.00 0.50 -- (Qo = -- 087 1.25 0.17 0.15 0.28 0.15 0.05 0.78 0.35 237 0.39 0.98 1.16 0.61 0.17 2.00 sion Ut of the insulated construction may be compared with the corre sponding coefficient U without insulation. Attention is called to the necessity of applying the insulating material in accordance with the manu facturer's specification. The engineer must evaluate carefully the eco nomic considerations involved in the selection of an insulating material as adapted to various building constructions. Lack of proper evaluation, or improper installation may lead to unsatisfactory results. Computed Heat Transmission Coefficients Computed overall heat transmission coefficients of many common types of building construction are given in Tables 5 to 18, inclusive, each coeffi cient being identified by a serial number, except in Table 18. For example, the coefficient U of a brick veneer, frame wall with wood sheathing and 5-inch of plaster on gypsum lath is 0.27 (Wall No. 28-C in Table 5) and with 2-inches of blanket or bat insulation, the coefficient would be .0.097 (No. 49-B in Table 6). In the analysis of any wall construction for the purpose of calculating the overall coefficient of heat transmission U, it is first necessary'to deter mine the paths of heat flow, that is, whether they are parallel or series, or a combination of both. This is in accordance with the basic laws of heat transfer which state that in parallel flow the conductances are additive, while in series flow the resistances are additive. - Likewise, in order to de termine the total resistance for the wall, the conductance must be known. The importance of this analysis cannot be over-emphasized. This is especially true in wall constructions in which there are parallel paths of heat flow, and one path has a high heat transfer, while others have a low heat transfer. _ The method of making this calculation can best be shown by the fol lowing example and Fig. 4. As this wall was tested by the hot box method