Document RabRnDXVnxMyrnYkQyM0N8BXV

HEATINC VENTILATING AIR CONDITIONING GUIDE 1944 will not impair the performance of the assembled convector. It is desirable that the enclosure or housing for the convector fit as snugly as possible 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 radiators, 240 Btu per hour may be taken as an equivalent square foot of radiation. When more than one heating unit is used, one mounted above the other in the same cabinet, the output of the upper unit or units will be materially less than that of the bottdnrunit. 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 roorrt, 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 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). 254 CHAPTER 13. RADIATORS AND CONVECTORS 1931 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. For hot water the standard test conditions call for a mean temperature of the water in the convector of 170 F. The Convector Manufacturers Association has adopted the A.S.H.V.E. standard in the formulation of its ratings and has compiled a tentative 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 Table 3. Correction Factors for Direct Cast-Iron Radiators and Convectors3 Steam Press. Heating Medium Factors for Direct Cast-Iron Radiators Factors fob Convectors Approx. Temp F Gage Aba. Steam FRoom Temperature Am FInlet Temperature Vacuum Lb per OB Id. Hg. Sq In. Water 80 75 70 65 60 55 50 80 75 70 65 60 55 50 22.4 20.3 17.7 14.6 10.9 6.5 LbperSqln. 1 6 15 . 27 52 3.7 4.7 6.0 7.5 9.3 11.5 15.6 21 30 42 67 150 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 1.84 160 2.17 2.00 1.86 1.73 1.62 1.52 1.44 231 2.35 2.15 1.98 1.84 1.71 1.55 170 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 1.40 180 1.62 1.52 1.44 1.35 1.28 1.21 US 1.84 1.71 1.59 1.49 1.40 1.32 1.24 190 1.44 1.35 1.28 1.21 1.15 1.10 1.0S 1.59 1.49 1.40 U2 1.24 1.17 1.11 200 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 1.00 215 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 0.87 230 0.96 0.92 0.88 0.85 0.81 0.78 0.76 1.00 0.95 0.91 0-87 0.83 0.79 0.76 250 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 . 270 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 0.56 300 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 aTo determine the size of a radiator or a convector for 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. To determine 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 radiator, and the inlet air 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. in accordant with the A.S.H.V.E. Code by an impartial and disinterested 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, within the convector3. For hot water the arithmetical average between entering and leaving water temperatures is used. These laws may be expressed as correction factors to change from output under standard A.S.H.V.E. Research Report No. 998--Factors Affecting the Heat Output of Convectors, by A. P. Kratz. M. K. Fahnestock, and E. L. Broderick (A.S.H.V.E. Transactions, Vol. 40, 1934, p. 443). 255