Document 8Va1yYbXYdNL61YgEZMQp5Qre

American Society of Heating and Ventilating Engineers Guide, 1931 air is 1.34, based on the values given in Table 1, and when increased by the factor 3 to allow for moving air, the outside surface coefficient is 3 X 1.34 or 4.02 B.t.u. per hour per square foot per degree fahrenheit difference between the surface and the air in contact with it. The overall transmission of any wall for a wind exposure other than 15 miles per hour, can be computed by assigning the proper outside sur face coefficient, but in most cases the accuracy involved does not warrant this degree of refinement, and it is sufficiently accurate to base all calcu lations on the one wind exposure. For example: If the heat transmission coefficient of a certain wall is 0.20 based on the outside surface coefficient of 4.02 for a 15-mile wind velocity, this coefficient would not vary more than 1 per cent, plus or minus, for a variation in the wind velocity of 5 miles per hour, plus or minus, based on data contained in Table 2. Computed coefficients are not accurate to this degree of variation in most cases, particularly when it is considered that overall coefficients will often vary to a much greater extent with the density of the materials used in the construction, the moisture content, the mean temperature, the quality of workmanship, and other factors. Conductivities and Conductances The majority of the conductivities and conductances of the building materials and insulations given in Tables 4, 5, 6, 7 and 8 were determined by the hot-plate method of testing.5 Attention is called to the fact that conductivities per inch of thickness of materials or insulations do not afford a true basis for comparison, although they are frequently used for that purpose. Correct comparisons should take into consideration many different factors, including conductivities or conductances, thicknesses installed, manner of installation, etc., while the selection of an insulation should also give consideration to structural qualities, as well as material and application costs. At present there is no universally recognized method of rating insulations. Conductivities and conductances of build ing materials and insulations are useful to the heating engineer in deter mining overall coefficients of heat transmission of walls, floors, roofs and ceilings. Computed Transmission Coefficients As previously stated heat transmission coefficients of many common .types of building construction are given in Tables 9 to 33, inclusive, each construction being identified by a serial number. For example: The co efficient of 'transmission (U) of a 12-in. brick wall, furring strips, and %-in. of gypsum plaster on metal lath; is 0.216, and the number assigned to a wall of this construction is S-B, Table 9. . ' The coefficients in these tables were determined by' computations similar to those shown in Fig. 2, using the value of k (or C) indicated. The authorities for the conductivities used for computing these coefficients are given in Tables 4, 5, 6, 7 and 8. As in the case of the examples in Fig. 2, the average value of 1.34 given in Table 1 for/i was used for all surfaces in still air. The value of/0 for outside walland roof surfaces was taken as 3 X fi, or 4.02, corresponding to a wind velocity of approxi- *SeeStandard Test Codefor Heat Transmission through Walls (A.S.H.V.E. Transactions, Vol. 34, 1928). 30 . Chapter 3--Heat Losses by Transmission . Table 4. Conductivities (k) and Conductances (C) of Building Materials and Insulations Tests Conducted at the U. S. Bureau of Standards.P Insulation Tests Based on Samples Submitted by Manufacturers Not, --the coefficients in Tables 4-8. incl.. are expressed in B.t.u. per hour per square * ,___-- ,,.,,n r>n 1 .% 'ruirrunrcc fnitrec fYnUTDWIQR INTWCATHD RV NOTE b. Material Description Density (Lb. per Cu. Ft.) Mean Temp. (Dec. Fahr.) ' CONDUC-a TIVJTY (k) OR Conduc tance (O Asbestos Wood---------Asbestos Mill BoardBalsam Wool**--------- Cabots Quiltb---------Cabots Quiltb.---------Celotex-------------------- Corkboard.. Corkboard------Corkboard., Corkboard (Eureka).. Dry Zerob---------------Fibrofeltb................... Flaxlinumb--------------Gyplap............ ........... Hairinsulb.-- Hairinsulb_'... Hair Feltb-- Hair Feltb.. Insulex or PyrocellInsulex or Pyrocell.. Insulex or Pyrocell.. Insulex or Pyrocell.. rnsulite.......-............ Linofeltb.,,....... .. ..... Lith............. ............. Magnesia (Rigid)----Plaster-- Regranulated cork--. Rock cork.------------Rock wool-------------Rock wool................ Rock wool................ Rock wool................ Sawdust.................... Shavings__________ Sheetrock................. Sprayo*Flake............ . Thennofeltb,,.......... . Thermofeltb_______ Thermofill____ ,,....... Thermofill.... .............. Thermofillb______ _ Torfoleum______ ___ Asbestos and cement compressed-- Pressed asbestos..Chemically treated wood fiber be tween layers of paper. Eel grass between Kraft paper------- .... Eel grass between Kraft paper----------Rigid insulation made from sugar cane fiber_____ ------- ------------------Pure; no added binder---------------------Pure; no added binder________ ______ Pure; no added binder Asphaltic binder-- Kapok between burlap or paper-- Flax and rye fiber__________ __ Flax fiber.. Gypsum between layers of heavy paper (H in. thick)----------------------75% hair; 25% jute50% hair; 50% jute___ Felted cattle hair.. Felted cattle hair-. Cellular gypsum--dry....... Cellular gypsum--dry...... 'Cellular gypsum--dry----Cellular gypsum--dry. Rigid insulation made from wood pulp. Flax fibers between paper. Rock wool, flax and straw pulp with binder. 85% magnesia. 15% asbestos.. Gypsum-------- -----------About % in. particles.. Rock wool block with binders.------Fibrous material, made from rock.. Fibrous material, made from rock.. Fibrous material, made from rock.. Fibrous material, made from rock.. Ordinary.-------------- 1......................... OrdinaryGypsum mixed with sawdust between layers of heavy paper (0.39 in. thick) Shredded paper with silica binder------Jute and asbestos fibers, felted----------Hair and asbestos fibers, felted_______ Dry, fluffy, flaked gypsum.................... Dry, fluffy, flaked gypsum.................... Dry, fluffy, flaked gypsum................... Peat moss compressed into sheet form 123.0 60.5 2.2 4.6 3.4 13.2 14.0 10.6 7.0 14'. 5 1.0 13.6 13.0 53.5 6.3 6.1 13.0 11.0 30.0 24.0 18.0 T2.0 16.9 4.9 14.3 19.3 46.2 8.1 16.7 10.0 14.0 18.0 21.0 -- 60.7 4.2 10.0 7.8 34.0 26.0 19.8 10.2 86 86 . 90 * 90 90 90 ' 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 86 86 90 86 90 90 90 90 86 86 90 94 90 90 90 90 90 91.5 2.70 0.84 0.27 0.26 0.25 0.34 0.34 0.30 0.27 0.32 0.24 0.32 0.31 2.60b 0.27 0.26 0.26 0.26 1.00* 0.77* 0.590.44' 0.34 0.28 0.40 0.51 2.32> 0.31 0.37 0.27 0.28 0.29 0.30 1.04 0.71 3.6Qb 0.28 0.37 0.28 0.60 0.52 0.35 0.29 Woods: Balsa wood.. Balsa wood__.___ Balsa wood......... Cypress______ Maple--........... Mahogany._____ Virginia Pine___ White Pine......... Across grain__ Across grain__ Across grain__ Across grain__: Across grain__ Across grain__ Across grain.__ Across grain.__ 20.0 90 0.58 8.8 90 0.38 7.3 90 0.33 28.7 86 0.67 44.3 86 1.10 . 34.3 80 0.90 34.3 86 0.96 . 31.2 86 .0.78 In addition to the conductivity values for the authorities listed, considerable work of importance per taining to the heat transmission of various types of construction and materials has been done by the late Prof. John R. Allen and Prof. A. J. Wood of the Engineering Experiment Station of Pennsylvania State College. # bFor thickness stated or used in construction, not per 1 in. thickness. faNot compressed. ,., ,, A The conductivity of plaster varies with the composition. Note range of values from 2.32 to 8.0. The average value fot plaster is .probably about 6.0. On account of the comparatively high conductivity of- plaster and the fact that it is seldom applied more than H in. thick; this material does not appreciably effect the overall transmission of a construction, excepting in the case of thin, uninsulated walls. /. , pSee .Chapter LX, by Chas. H. Herter of the Report of the. Insulation' Committee. A.'S. R. E,, Annual' Meeting 1922, Revised to 1924. entitled, Heat Transmission of Insulating Materials for.a more compre hensive collection of heat transmission data relating,tobuildingand-insulating-materials. 31 /