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American Society of Heating and Ventilating Engineers Guide, 1929 \ %Table 5. Final Temperature of Air Leaving in. Pin, Cast-Iron, Gravity Indirect Radiators Temperature Entering Ant Dbg. Fahr. AmCubic Feet of (at 70 deg.) per Hour per Square Foot Radiation 75 100 125 150 175 200 | 225 250 275 300 I 325------- 350 -10 0 10 20 30 40 SO 60 132* 136 140 144 148 152 156 160 130 134 128 132 126 123 130 127 121 125 119 123 138 136 134 131 129 127 142 140 138 135 133 131 246 144 142 139 137 135 150 148 146 143 141 139 154 152 150 147 145 143 158 156 154 151 149 147 --1st Floor- --2nd Floor-- --3rd Floor-- 116 113 111 108 120 117 115 112 124 121 119 116 128 125 123 120 132 129 127 124 136 133 131 128 140 137 135 132 144 141 139 136 105 103 109 107 113 111 117 115 121 119 125 123 129 127 133 131 as Tlst IFloor1^deg.*riow^^2ndCFloo8r81deg.a^wert<3rdWFl(X5i^ "^de^^wer.0^ ^ *Cav`nf: rac^ato1 Table 5 is for % in. pin-type radiation using steam at I lb. pressure. For 1 in. pin-type the temperature rise of the air is about 95 per cent of the corresponding rise for % in. pin-tvpe and for hot water at 170 deg. fahr. the temperature rise of the.air ranges from 80 to 85 per cent of the corresponding temperature rises with steam at 1 lb. pressure. From Tables 4 and 5 the heat emission of an indirect radiator may be calculated as follows: Example.--Determine the B.t.u. transmitted per hour per square foot of surface, from a % in. pin-type cast-iron radiator, supplying a first floor register; entering air at 0 deg. and steam at 1 lb. pressure. Solution.--From Table 4, it will be found that 150 cu. ft. of air will flow per hour per square foot and from Table 5 it is determined that the final temperature of the air is 127 deg. The temperature rise of the air -- 127 -- 0 = 127 deg. and the B.t.u. trans- mitted per hour per square foot -- ~1o5o0r X 0.24 X 127 -- 333, where Id.do 0-24 - B.t.u. required to heat 1 lb. of air 1 deg. la.do -- cubic feet of air per pound at 70 deg. For a 1 in. pin-type radiator the transmission will be 333 X 0.95 = 316 B.t.u. per square foot per hour and with water at 170 deg. the trans mission in either case would be 84 per cent of the respective figures for steam. For performance data on radiators and heaters where air is forced through them by fans see Chapter XXIV. LOCATION AND SELECTION OF CAST IRON RADIATORS It should be made a rule to install radiators beneath or near the space of greatest heat loss. The best place is underneath an outside window. This seems logical for the following reasons : 1. Heat emitted by radiation from the radiator will counteract the effect of heat radiated out through the window from occupants in the room. 2. Cold air leaking in through the window is warmed before it reaches the interior of the room. 72 r-` Chapter II--Radiators and Heaters 3. Air currents from the radiators pass upward, mingling with the cold infiltering air and form a screen of warm air protecting against cold window drafts. 4. There is less discoloration of walls from dust arising from the radiator. If the heater cannot be placed underneath the window, then it should be located as near the window as possible, near outside doors, underneath skylights, near to very exposed walls or corners, etc. Heat emission by a radiator at the ceiling or floor will differ little, provided the surrounding air and objects are at the same temperature. The effect bn heating the room or on temperature distribution in the room, however, may be very great. Heat applied near the ceiling will tend to stratify, resulting in a hot ceiling and cold floor, unless there is mechanical disturbance to produce circulation. As the total heat emitted from the radiator varies with type, height, width, length, steam pressure, etc., the selection of the heater should be done in the following way: 1. Figure the total heat loss of the room as outlined in Chapter I, making proper allowances for exposure, wind velocity, height of ceiling, etc. 2. Next, decide upon the type (design, height, width, etc.) and the number of radia tors to be used. Then find in Tables 1 to 3, or in tables of guaranteed performance published by the various manufacturers, the number of sections' necessary for each radiator. Example.--The heat loss from a given room calculated in accordance with Chapter I is estimated to be 14,200 B.t.u. per hour. How many sections are required in a threecolumn, 38-in., radiator for heating this room? Solution.--Table 1 indicates that a 3-column, 38-in. radiator emits 211 B.t.u. per .square foot per hour for intermediate sections, and 380 B.t.u. per square foot per hour for end sections. Each section has 5 sq. ft. of area. Intermediate sections will emit 5 X 211 = 1055 and each end section will emit 2)4 X 211 + 2)4 X 380 or 1277.5 B.t.u. per section per hour. The two end sections will emit 2 X 1277.5 = 2555, leaving 14,200 -- 2555 = 11,645 B.t.u. per hour to be supplied by the intermediate sections. 11,645 -5- 1055 = 11. Hence, 11 intermediate and 2 end sections, or a total of 12 sections, will be required. Example.--How many sections of 5-tube radiation are required to heat a room having an estimated heat loss of 15,000 B.t.u. per hour? Solution.--Total radiation required under the new ratings is 15,000 -5- 240 = 62.5 sq. ft. Select the radiator from the manufacturer's catalog. Example.--How many square feet of radiation are required to heat a room having a heat loss of 15,000 B.t.u. per hour if the pressure of the steam in the radiator.is 2 lb. gage and the room temperature is 50 deg. fahr.? Solution.--The factor from Table 3 for 2 lb. gage and 50 deg. fahr. room temperature is 1.220. Under these conditions 1 sq. ft. will emit 240 X 1.220 = 293 B.t.u. per hour. The number of square feet required is 15,000 4- 293 = 51.2. Select from a manufac turer 's catalog. Example.--How many square feet of hot-water radiation are required to heat a room having a heat loss of 15,000 B.t.u. per hour if the mean water temperature is 170 deg. fahr. and the room temperature is 70 deg. fahr. Solution.--The factor from Table 3 for a temperature of 170 deg. fahr. in the radiator and a room temperature of 70xieg. fahr. is 0.617. Under these conditions 1 sq. ft. will emit 240 X 0.617 -- 148 B.t.u. per hour. The number of square feet required is 15,000 4- 148 = 101.3. Select from a manufacturer's catalog. 73 s