Document 6B50NMYyKOEG04LDORoM9k6R4

American Society of Heating and Ventilating Engineers Guide, 1937 standard of heating effect allowances for various enclosure heights to be 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 laboratory and that the ratings have been approved by the Standardization Committee of the Convector Manufacturers Association. Concealed heaters or convectors are generally sold as. completely built-in units. The enclosing cabinet should be designed with suitable air inlet and outlet grilles to give the heating element its best performance. Tables of capacities are catalogued for various lengths, depths and heights, and combinations are available in several styles for installations, such as the wall-hung type, free-standing floor type, recess type set flush with wall or offset, and the completely concealed type. Most of these types may be arranged with a top outlet grille in a plane parallel with the floor, although the front outlet is practically standard. In cases where enclosures are to be used but are not furnished by the heater manufacturer, it is important that the proportions of the cabinet and the grilles be so designed that they will not impair the performance of the assembled convector. It is impor tant that the enclosure or housing for the convector fit as snugly as pos sible 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 variable 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's. For steam convectors, as for radiators, 240 Btu per hour may be taken as an equivalent square foot of radiation. RADIATOR AND CONVECTOR SELECTION Since the capacity of a radiator varies as the 1.3 power and a convector5 as the 1.5 power of the temperature difference between the inside of radiator and surrounding air it is obvious that for other than 70 F room temperatures the heat emission will be other than 240 Btu per square foot of rating. Therefore in selecting the size of radiator or convector to be used it is necessary to correct for this difference! - Table 4 shows factors by which radiation requirements, as determined by dividing heat load by 240, shall be multiplied to obtain proper radiator or convector sizes from published rating tables for room temperatures ranging between 50 and 80 F as well as for steam or water temperatures from 150 to 300 F. For other room and heating medium temperatures the factor is determined by the following formulae: For radiators: - _ /215 - 70\i.3 Cs - \~ir-r) 'Factors Affecting the Heat Output of Convectors, by A. P. Kratz, M. K. Fahnestock, and E. L. Brod erick (A\S;H.V.E. Transactions, vol. 40, 1934). 540 Chapter 30--Radiators and Gravity Convectors For convectors: /215 - 65V-5 C6 \ h - k ) where s = correction factor. = steam temperature, degrees Fahrenheit. ^ --- room temperature, degrees Fahrenheit. jj = average inlet air temperature, degrees Fahrenheit. Table 4. Correction Factors for Direct Cast Iron Radiators and Convector Heaters51 Steak Press. Approx. Gage Lb Abe. 22.4 3.7 20J 4.7 17.7 6.0 14.6 7.5 10.9 9.3 6.5 11.5 15.6 21 30 42 67 Steam Water Temp. F 150 160 170 180 190 200 215 230 250. 270 300 Factors por Direct Cast Iron Radiators Room Temperature F Factors por Convectors Inlet Am Temperature F SO 75 70 65 60 55 50 80 75. 70 65 60 55 50 2.58 2.36 2.17 2.00 1.86 1.73 1.62 3.14 2.83 2.57 2.35 2.15 1.98 1.84 2.17 2.00 1.86 1.73 1.62 1.52 1.44 2.57 2.35 2.15 1.98 1.84 1.71 1.59 1.86 1.73 1.62 1J2 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 1.21 1.15 1.84 1.71 1.59 1.49 1.40 1.32 1.24 1.44 1.35 1.28 1.21 1.15 1.10 1.05 1.59 1.49 1.40 1.32 1.24 1.17 1.11 1.28 1.21 1.15 1.10 1.05 1.00 0.96 1.40 1.32 1.24 1.17 1.11 1.05 1.00 1.10- 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 0.92 0.88 0.85 0.81 0.78 0.76 1.00 0.95 0.91 0.87 0.83 0.791 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 0.70 068 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 To determine tne neater size a given spate, tuvruc me uwi . the result by the proper factor from the above table. To determine the heating capacity of a beater at other than standard conditions, divide CODE TEST FOR RADIATORS AND CONVECTORS As previously indicated, t.he output of radiators and convectors is still designated by the terms of older practice, but this is gradually giving place to an engineering method of designating heat emission. The A.S.H.V.E. has adopted the following standards: Code for Testing Radiators (1927); Codes for Testing and Rating Concealed Gravity Type Radiation (Steam, 1932, and Hot Water, 1933). ' For steam services the actual condensation weight is taken without any allowance for heating effect; for hot water services the weight of circulated water is used without allowance for heating effect. In all cases the total heat transmission varies as the 1.3 power for radiators10 and the 1.5 power for convectors11 of the temperature difference between that inside . the radiator and the air in the room, and is expressed in Btu or Mb per hour. Standard test conditions specify either a steam pressure of 1 lb gage (215 F), or hot water at 170 F and a room temperature of 70 F for radi ators, or an inlet air temperature of 65 F for convectors. The heating capacity of a steam radiator or steam convector is, determined as follows: ______ Hi - WjHg (1) "Loc. CiL Note 8. "Loc. Cit! Notes 8 and 9. 541