Document 0Jdjzk14gx7d5Gv7nBvmojr4O

American Society of Heating and Ventilating Engineers Guide, ig3l / will be 7 X 3, plus 16 X 6, or 117. A 1% in- pipe is slightly too [J, A 1}4 in. pipe would be selected. Instead of making the calculation just described, refer to Table' and note that, for a first-floor radiator, the capacity of a 1J4 in. 9,500 B.t.u. Table 3 is based on an average water temperature ^ 180 deg. When the temperature (average) is higher, the capacities ^ larger. To find the sizes of the radiators, it must be remembered that thSL water is cooled as it traverses the system and. that each success^ radiator is supplied with cooler water and must, therefore, have a larmg surface than the preceding one, if it is to transmit an equal quantity*^ heat. In this particular system, if the first radiator is supplied with 205 deg. water, the sixth one will be supplied with 1843-1; deg. water The average temperatures of the water in the two radiators will then (*' about 195 and 175, respectively. The temperature differences, water to air, will be .125 and 104. The values of U will be (from Fig. 1, for a 3-col 38-in. radiator) 1.34 and 1.28; the heat transmitted will be" 125 X 1.34*4 or 167.5 and 105 X 1.28, or 134.4 B.t.u. per square foot. The firstj radiator must have or 53.7 sq. ft., and the sixth radiator n-a loi.o 134.4' J 66.9 sq. ft. In other words, the last radiator must be about 25 per cent * larger than the first, if it is to deliver an equal quantity of heat. Table 3. Maximum Capacities, in B.t.u., of Risers for One-Pipe Systems Flow Rises, Inches Return Riser, Inches XX Xi ii i IX ix iX IX m ix IX 1X 2 22 Fust Floor 3,000 3,700 5,300 6,400 9,500 10,700 13,000s 16,000 23,000 - Capacities in B.t.u. Second Floor 6,500 8,000 11,400 141400 21,700 25,000 30,200 38,100 55,700 Third Floor 7,800 9,600 13,600 17,100 26,300 30,600 37,900 46,100 66,800 Note.--Length of pipe: First floor--7 ft. 0 in. Second floor--25 ft. 0 in. Third floor--43 ft. 0 in. Each circuit has 16-elbow equivalents. This table is based on a temperature drop of 20 deg. through the radiators and an average water temperature of 180 deg. The resulting pressure heads are: First floor--129 miJ-inches. Second floor--903 mil-inches. Third floor--1,677 mil-inches. If the average temperature is higher than 180 deg. the pressure heads are higher than those shown, and if the average temperature is lower than shown, the pressure heads are lower. 194 JSP'- V- 'Chapter 11--Hot Water Heating _jfnstead 'f making these complicated calculations for every radiator JMSb-Xn^pioe system, it may be sufficiently accurate to adopt the fol- ^pijgDreusilgen e:ach radiator as ifit were supplied with water at the maximum temperature Divide the beating system into four sections so that each section transmits about .med.in the system; ^fouNrtuhmboefrtthheetfootuarlsheecatiot;ns in the order of their distances from the heater, measured a]0Iig the flow main, so that the first section radiators receive the hottest water; 4: Adopt the calculated sizes lor the radiators in the first section and add, respectively 10 per cent, 20 per cent and 30 per cent to the sizes calculated for the radiators of the second, third, and fourth sections of the heatmg system. The one-pipe system with under-foot distribution, designed as out lined, is probably the system which is easiest to construct so that it will Pump - Fig. 8. One-Pipe Heating System op Fig. 4 Changed from Gravity FlovS- to Forced Circulation t function correctly. The most common error committed in the installation of these systems is that the radiators farthest from the heater are not . e'nlTahrgeedonseu-fpfiicpieenstylys.tems with over-head distribution and the two-pipe systems are more complicated, but the underlying principle is the same for all: The friction head in every radiator circuit must be equal to the preTshsueremheetahdodavoafiladbelesifgonrintghatthecirmcuoirte. complicated systems is explained in the respective textbooks to which the reader is referred for additional guidance. FORCED CIRCULATION SYSTEMS The principle difference between a gravity circulation and a forced circulation system is that, in the former, the pressure heads are caused entirely by the difference in the weight of the water in the flow and the return risers, whereas, in the latter, the pressure heads are produced . largely, in some cases almost entirely, by a pump. 195