Document rBpJ7BKjzBD06OD7Ooxq88wj0

708 CHAPTER 27 1957 Guide Therefore, the thickness at which the sum of the costs is a minimum, is the most economical. The method of using the chart Fig. 6 is as follows: From the number of hours of operation per year at the bottom of the chart proceed upward to the line showing value of heat in dollars per million Btu using the appropriate scale A or B. Proceed right to tempera ture difference line using either scale A or B. Move upward to the line representing conductivity of the insulation being considered, then left to discount line, upward to the percent fixed charge line, right to the pipe size or flat surface line and read the economic thickness at top on the scale corresponding to the scales selected, for value of heat and temperature difference. For example; with Scale B Heat Value and Scale A tempera ture difference or vice versa, use scale A-B economic thickness. If the intersection with the flat surface is on the flat surface continued curve, the economical thickness is read on the prime scales A'-A', A'-B' or B'-B'. Cost of insulation refers to incremental cost in place; i.e., average in cremental cost per unit thickness after the first unit. The first inch of Table 7. Thickness op Pipe Insolation Ordinarily Used Indoors* Steam Pressure Psig or Condition Steam Temperature Fahrenheit Degrees Thickness op Insulation Pipes Larger Than 4 In. Pipes 2 In. to 4 In. Pipes . X In. to IX b. 0 to 25 25 to 100 100 to 200 Low Superheat Medium Superheat High Superheat 212 to 267 267 to 338 338 to 888 388 to 600 500 to 600 600 to 700 ' 1 in. "Ifc 2M in. 3 in. 3X in. . 1 in. 1 in. 2X in. 3 in. 1 in. 1 in. 1 in. * 2 in. * All piping located outdoors or exposed toweather is ordinarily insulated to a thickness X in. greater thso shown in this table, and covered with a waterproof jacket. insulation will usually cost more than each; additional inch. This is due to cost of finish, contractor's set-up and operating costs, which do not increase in proportion with thickness. The first inch of insulation, except in very unusual cases, provides enough saving in heat cost out of bare surface cost to more than cover these extra first costs. To obtain discount from insulation list price, first obtain applied prices for the desired type'of insulation in one-inch, two-inch, etc., thickness.- Then determine the average incremental cost per inch above one-inch thickness. Incremental cost in percent discount from list is where X = average incremental cost in place per inch above one inch Y = list price lor one inch Note that in figuring pipe insulation, use the list price for one-inch thickness for a pipe size consistent with the average incremental cost per inch. f or example, if the average incremental cost per inch is based on applied pncj for one, two, and three inches, the incremental cost of the second Pipe and Industrial Insulation CHART FOR DETERMINING ECONOMIC, THICKNESS OF. INSULATION 709 KWHS or OPCfflTION PCB ru* *IQ- 6. Chart fob Determining Economical Thickness of Pipe Insulation (From Reference (2) used by permission. Not to be reprinted without permission.)