Document mBB1aNGdg2NnbQL78YngLjZX0

HEATINC VENTILATING AIR CONDITIONING GUIDE 1944 resistance to heat flow inherent in the insulation itself. The maximum increase in heat loss due to air velocity ranges from about 15 per cent in the case of 1-in. thick insulation, to about 5 per cent in the case of 3-in. thick insulation, provided that the insulation is thoroughly sealed so that air can flow only over the surface. If the conditions are such that the air may circulate through cracks and crevices in the insulation, the increases may be far greater than those given. Therefore, it is essential that insulation be sealed as tightly as Fig. 3. Heat Loss Through 2 In. Thick 85 per cent Magnesia Type Covering possible. Pipe insulation exposed to the elements should be thoroughly waterproofed. Example 3. If the steam line given in Examples 1 and 8 is covered with 1 in. thick 85 per cent magnesia, determine the resulting total annual toss through the insulation: Also compute die monetary value of the annual saving and the percentage of saving over the heat loss from the bare pipe. , Solution. By referring to Fig. 1, the coefficient for I in. magnesia on a 2-in. pipe is found to be 0.285 Btu per hour per linear foot of pipe per degree temperature difference at a temperature difference of 169.4 F. ' The total hourly loss per linear foot of pipe will then be 0.285 X 169.4 = 48.3 Btu. The total annual loss through the insulation- = 48.3 X 165 (linear feet) X 4000 (hours) - 31,900 Mb. The annual bare pipe loss as CHAPTER 18. PIPE INSULATION determined in the solution of Example 1 was found to be 181,600 Mb. The saving due to insulation is then 181,600 -- 31,900 = 149,700 Mb per year. From the solution of Example 3, it was found that the heat supplied to the system cost $0,804 per thousand Mb. Therefore, the monetary value of the saving = 0.804 (dollars) X 149.7 (thousand Mb) -- $120.36, or 82.4 per cent of the cost when using uninsulated pipe. Table 8. Conductivity (k) of Various Types of Insulating Materials for Medium and High Temperature Pipes4 Expressed, in Btu per hour per squarefoot per degree Fahrenheit . . --' 'r------ inch thickness Mean Temperature. Deg F Types of Insulating Materials 100 0.359 0.495 200 0.403 0.618 300 0.448 0.741 400 0.493 0.864 (4 Plies per 1 in. thick) 0.505 0.598 0.692 0.786 (8 Plies per 1 in. thick) Laminated Asoestos i ypc- # . .. (30-40 Laminations per 1 in. thick; Laminated Asbestos Type.--. (14-20 Laminations per 1 in. thick; Mineral Wool Type------------------------------------ HIfDiatbmaceous Earthand Asbestos) 0.326 0.374 0.350 0.576- 0.338 0.380 0.445 0.410 0.614 0.396 0.434 0.518 0.470 0.652 0.453 0.488 0.589 0.530 0.689 0.510 (Felted Fiber) 500 0.539 -- _________ 0.543 0.662 0.590 0.726 0.568 From tests conducted at Mdlm Institute. Table 9. Pipe Covering Factors Temperature Difference, Pipe to Air. Deg F Types of Insulating Materials 100 200 8ZwCM5Zorprprevu.rgc--ae-t-e-n--d-tt---M-A-A--s-a-b1-_g,,_e_n-_-s-ei-t-.o-s-.-si-.a-- TTT.ymypae(4: 1Plies per 1 in. thick; -o,rugated Asbestos Type.. 1.050 1.024 1.425 1.465 1.435 1.437 (8 P1 luiecas ppevir 1* in*. thick) Laminatedu Absbuecasmtoas T* yjppev-.,..-..-.-------- 0.969 0.960 (30-40 Laminations per 1 in. thick) Laminated Asbestos Type 1.103 1.104 (14-20 Laminations per 1 in. thick) Mmiinueurcaul Wiiwoo.l T-yjpx-e---.---------High Temperature Type-------------------- 1.023 1.560 1.028 1.489 (Diatomaceous Earth and Asbestos) Brown Asbestos Type____ : 1.003 0.997 (Felted Fiber) ' 300 0.997 1.505 1.438 0.951 1.105 1.033 1.418 0.990 400 0.971 1.545 1.440 0.942 1.106 1.038 1.347 0.984 500 0.944 0.933 1.107 1.043 1.276 0.977 600 0.918 0.924 1.108 1.048 1.205 0.971 LOW TEMPERATURE PIPE INSULATION Surfaces maintained at temperatures lower than the surrounding air are insulated to reduce the flow of heat and to prevent condensation and frost. The insulating material should absorb a minimum amount of moisture, because the absorption of moisture substantially increases the conductivity of the material. This property is particularly important in