Document mqRQ24vx3bLME25aXyXe3B0J0

u' 242 . __________ Chapter 13 . 1945 Guide so that the air to be heated must pass through; the convector and cannot' be by-passed in the enclosure. ' " The output of a convector, for any given length and depth, is a function of the height. Published ratings are generally given in terms of equiva lent square feet, corrected for heating effect. 'However,.an extended surface heating unit is entirely different structurally and physically from a direct radiator and, since it has no area measurement corresponding to the heating surface of a radiator, many engineers believe that the per formance of convectors should be stated in Btu. For steam convectors, as for raidiators, 240 Btu per hour may be taken as an equivalent square foot of radiation. When more than one heating unit is used, one mounted aboye the other in the same cabinet, the output of the upper unit or units will be materially less than that of the bottom unit. , }- RADIATOR AND CONVECTOR RATINGS A standard method of testing radiators was adopted by the A.S.H.V.E. in 19271. This Code provides for a standard test room, the temperature of which is to be maintained at 70 F, measured in the center of the room at an elevation of 5 ft above the floor, The steam temperature in the radi ator is to be 215 F, which corresponds to 15.6 lb per square inch absolute. The weight of .condensate per hour, under these standard conditions, multiplied by the difference in the enthalpy of the steam entering the radiator and that of the condensate leaving the radiator, gives the radiator output in Btu per hour. This output divided by 240 gives the steam rating of the radiator in square feet. Similar test methods for convectors are the A.S.H.V.E. Codes for Testing and Rating Concealed'Gravity Type Radiation, (Steam Code 1932 and Hot Water Code 1933). These Codes recognize a different type of test booth, and the air temperature used is that of the air entering the convector casing instead of the temperature in the center of the room. The entering air temperature for standard test conditions is 65 F.' Fqr hot water the standard test conditions call for a mean temperature of the water in the convector of 170 F. I The Convector Manufacturers Association has adopted the A.S.H.V.E. standard in the formulation of its ratings and has compiled a tentative V | ' standard of heating effect allowances for various enclosure heights to be ii; . included in the ratings by its members. All published ratings bearing the title C.M.C. Ratings {Convector Manu facturers Certified Ratings) indicate that the convectors have been tested in accordance with the A.S.H.V.E. Code by an impartial and disinterested I:f ' laboratory and that the ratings have been approved by the Standardiza > tion Committee of the Convector Manufacturers Association. Effect of Operating Conditions The heat output of a radiator is proportional to the 1.3 power of the temperature difference between the air in the room at the 60 in. level and ' the heating medium in the radiator. The heat output of a convector is proportional to the 1.5 power of the temperature difference between the air entering the convector and the heating medium, steam or hot water, *A.S.H.V.E. Code for Testing Radiators (A.S.H.V.E. Transactions, Vol. 33, 1927, p. 18). -- 'A.S.H.V.E. Standard Code for Testing and Rating Concealed Gravity Type Radiation (Steam), (A.S.H.V.E. Transactions, Vol. 37, 1931, p. 367); (Hot.Water), (A.S.H.V.E. Transactions, Vol. 39, 1933. p. 237). (See also A.S.H.V.E. Transactions, Vol. 41, 1935, p. 38, and Vol. 42, 1936. p. 29). . Radiators and Convectors 243, within the convector. For hot water the arithmetical average betweeri entering and leaving water temperatures is used. These laws may be expressed as coiTection factors to change from output under standard rating-test conditions to output under other operating conditions. Such' factors are given in Table 3. ' 1 ABLE d. CORRECTION r ACTORS FOR DIRECT, CAST-IRON RADIATORS AND CONVECTORS* Steam Heating Factors por Direct Press. Medium Cast-Iron Radiators Factors for Conyxctoeb ' Approx. Temp F Gage Vacuum In. Hg. Abe. Lb per Sq In. Steam OB Water 80 75 EMPERATURS F 70 65 60 55 50 80 Inlet Air Temperature F. 75 70 65 60 55. SO 22.4 20.3 17.7 14.6 10.9 6.5 LbperSqlo. 1 6 IS 27 52 3.7 150 4.7 160 '6.0 170 7.5 180 93 190 11.5 200 15.6 215 21 230 30 250 42 ' 270 67 300 2_58 236 2.17 2.00 1.86 1.73 1.62 3.14 2.83 2.57 2.35 2.15 1.98 131 2.17 2.00 136 1.73 1.62 1.52 1.44 237 2.35 2.15 1.98 1.84 ;1.71 139 1.86 1.73 1.62 1.52 1.44 1.35 1.28 2.15 1.98 1.84 1.71 1.59 1.49 1.40 1.62 1.52 1.44 1.35 1.28 131 1.15 1.84 1.71 1.59 1.49 1.40 1.32 L24 1.44 1.35 1.28 1.21 1.15 1.10 1.05 1.59 1.49 1.40 132 1.24 1.17 1.11 1.28 1.21 1.15 1.10 1.0S 1.00 0.96 L40 1.32 1.24 1.17 1.11 1.05 1.00 UO 1.05 1.00 0.96 0.92 0.88 0.85 1.17 1.11 1.05 1.00 0.95 0.91 0.87 0.96 0.V2 038 0.85 0.81 0.78 0.76 1.00 0.95 0.91 0.87 6A3 0.79 0.76 0.81 0.78 0.76 0.73 0.70 0.68 0.66 0.83 0.79 0.76 0.73 0.70 0.68 0.65 0.70 0.68. 0.66 0.64 0.62 0.60 0.58 0.70 0.68 0.65 0.63 0.60 0.58 0.56 0.58 0.57 0.55 0.53 0.52 0.51 0.49 0.56 0.54 0.53 0.51 0.49 0.48 0.47 h,, 2n of a, radiator or a convectorfor a given space, divide the heat loss in Btu per hour by 240 and multiply the result by the proper factor from the above table. ,, Tdetermine the heating capacity of a radiator or a convector under conditions other than the basic ones with the heating medium at a temperature of 215 F. and the room temperature at 70 F in the case of a 5?.- th',nlcf hir temperature at 65 F in the case of a convector, divide the heating capacities at the basic conditions by the proper factor from the above table. When it is desired to change the output under any test conditions to the corresponding output under standard Code test conditions, the reciprocal form of correction factor may be derived. The equations for steam units are: for radiators: for convectors: r, - f215 - rcy-3 /215 - 6S\1 (3) The output under standard conditions,will be: where HB -- CB Ht .. G = correction factor. tB = steam temperature during test, degrees Fahrenheit, tr = room temperature during test, degrees Fahrenheit, h = inlet air temperature during test, degrees Fahrenheit. #s = heat emission rating under standard conditions, Btu. per hour. . ~ heat output under test conditions, Btu per hour. (4) , f re^at*on between the size of the radiator or convector and the size Th k e?t room will affect the results obtained in a capacity-rating test. he height and location of the radiator and the insulation of the test room are other important factors that are not specifically regulated by the Code. Kratz, M V p . No. 998--Factors Affecting the Heat Output of Conveciore. uy . <F ' K' Fahnestock, and E. L. Brodenck (A.S.H.V.E. Transactions. Vol. 40, 1934. p. 443). (A.S.H.V E ?ot?"tf IHfStors- A- C Dav">- w- M- Sawdoi and David Diopkin Bulletin NTo" 29^A^SI1iS42Vo1' 42' 1B42- P' 185 and Corne11 University, Engineering Experiment Station ,y