Document MZ4YYeZJM3aoXyY7QGpzrL2k

American Society of Heating and Ventilating Engineers Guide, 1925-26 American Society of Heating and Ventilating Engineers Guide, 1925-26 HEAT LOSSES FROM INSULATED SURFACES Fig. 68 shows the losses from appropriately insulated surfaces compared with losses from bare surfaces. It will be noted that it was necessary to plot the upper part of the bare surface curve to a greatly reduced scale in order, to show it on the same sheet with the curves for losses through insulation. Therefore, for a true measure of the relative losses from bare and insulated surfaces, compare the numerical value of the ordinates of the curves rather than the apparent spaces between the curves on the chart. . The chart, Fig. 68, is based on still air conditions, room temperature of 70 deg. fahr., and 5 in. pipe size. The effect of pipe size on losses through insulations of various thicknesses is shown in Fig. 69. (Trans. A. S. H. & V. E., Vol. 26, p. 375). Fig. 68. Losses from Appropriately Insulated Surfaces as. Compared with Losses from Bare Surfaces Note.--The scale showing Dollars loss per sq. ft. per year is based on a unit cost of $1.00 per 1,000,000 B.t.u. The actual cost is usually less than this where heat is derived directly from burning coal or oil, but may be greater where illuminating gas or electricity is the source of'heat. However, the use of $1.00 as the unit greatly simplifies the use of the chart in connection with any cost per 1,000,000 available B.t.u. All that is necessary is to multiply the values from the chart by the ratio of the actual cost to. $1.00. For example, if the cost of heat is $.50 per 1,000,000 B.t.u., multiply values from the chart in dollars by 0.5, ctc._ 182 Fig. 69. Variation with Pipe Size of Rate of Heat Transmission Through a Given Thickness of Insulation For equations by means of which heat losses may be calculated for any thickness of-insulation on any pipe size see Trans. A. S. H. & V. E,, Vol. 26, p. 360. Refer also to Manufacturers' Data for heat losses and efficiencies of different insulations on various sizes of pipes. RADIATING SURFACE OF PIPES . In order to determine heat losses per linear foot of pipe from known losses per square foot, it is necessary to know the number of square feet area per linear foot of pipe. Table 86 gives these areas for various standard pipe sizes. 183