Document YGjvwam5D5xOR6xoLrY01m5NE

Heating Ventilating Air Conditioning Guide 1939 expensive in construction, is effective and quite suitable for cathedrals and large public buildings (Fig. 3). To provide a uniform floor temperature, special consideration should be given to the design of the air ducts so that equal distribution is obtained. 4. By attaching separate heated metal plates or panels to the interior surfaces. These plates or panels are placed either in an insulated recess so that the surface of the panel is flush with the surface of the walls or ceilings, or they may be secured to the face of the wall. They may be covered with wood veneers and decorated to harmonize with other parts of the room, or they can be cast into panels to imitate oak or other wood designs. With flat plate panels it is a common practice to use a frame of plaster, wood, metal or composition around the panels to allow for expansion.' These plates may be heated with either hot water or steam and connected similarly to an ordinary radiator system. Fig. 3. Diagram of Air Ducts for Floor Heating 5. By electric heated metal plates or panels. These plates or panels are either placed in insulated recesses of walls or ceilings or fastened to the face as desirable. They should not have a surface temperature above 160 to 200 F. Some electric panels have a much higher surface temperature but a lower temperature gives a more comfortable condition and is more efficient. 6. By electrically healed tapestry mounted on screens and on the wall. For this purpose the screen is woven with an electric continuous conductor being the warp and wool or silk being the weft. Such screens are useful to plug in at any position for emergency local heating without taking care of a large room or office. Note. If all of the heating panel is installed at one end of a large room there may be a marked difference between the BET on the two sides of the body. . It is usually desir able therefore that the heat be distributed at different parts in the room so that no uncomfortable effects will be felt from unequal heating. CALCULATION PRINCIPLES The calculations for radiant heating are entirely different from those for convective heating. The purpose of thelatter is to determine the rate of heat loss from the room by conduction, convection, and radiation when maintained in the desired condition; radiant heating involves the regu lation of the rate of heat loss per square foot from the human body. The first step in the calculations for radiant heating is to ascertain the necessary mean radiant temperature (MRT); next, the size, temperature, and disposition of the heating surfaces required in the room to produce this MRT are estimated; and after this the determination of the convec tive heat is made. Mean Radiant Temperature If the whole of the interior surface of a room were at the same tempera ture, this temperature would represent the MRT. Such a condition 774 Chapter 41. Radiant Heating Table 1. Total Black Body Radiation to.Surroundings at Absolute Zero3 Boor OB Mean Radiant Temper ature Deg Fahr Radiation ip Btu per square foot per hour . emitted to surroundings with a tempera- ' ture of absolute zero by bodies at various temperatures and with emissivity factor e 1.00 6 0.9S e 0.90 0.80 : Boot OB' Mean Radiant Temper ature Deg ' Fahr Radiation in Btu per square foot per hour emitted to surroundings with a temperature .of absolute zero by bodies at various temperatures and with emissivity .factor e 9 1.00 , .e 0.95 9 0.90 9 0.80 . 30 99.3 35 103.5 40 107.6 45 . 112.1 46 112.9 47 113.9 48. 114.8 49 . 115.6 50 116.5 51, 117.5 52 118.4 53 119.4 54 120.2 55 121.1 56 122.1 57 123.1 58 124.0. 59 124.9 60 125.8 61 126.6 62 127.7 63 128.6 64 129.6 65 130.5 66 131.6 67 132.5 68 133.5 69 134.5 70 135.5 94.3 98.3 102.4 106.5 107.3 108.2 109.1 109.9 110.6 111.6 112.5 113.4 114.2 115.1 116.0 117.0 117.8 118.6 119.5 120.3 121.4 122.2 123.1 124.0 125.0 125.9 126.8 127.8 128.8 89.4 93.2 96.8 100.9 101.6 102.5 103.4 104.1 104.9 105.8 106.5 107.4 108.2 109.0 109.9 110.9 111.6 112.4 113.4 114.0 114.9 115.8 116.7 117.5 118.4 119.3 120.1 121.1 121.9 79.4 82.8 86.1 89.7 90.4 91.1 91.9 92.4 93.2 94.0 94.7 95.5 96.2 96.9 97.7 98.5 99.2 99.9 100.7 101.4 102.2 102.9 103.7 104.4 105.4 106.0 106.8 107.6 108.4 71 72 73 74 , 75 . 80 85 90 100 110 120 130 140 150 160 170 .180 190 200 210 220 250 300 350 400 450 500 550 600 136.5 137.4 138:4 139.6 141.0 146.6 152.3 157.9 169.6 181.6 . 194.8 210.1 223.2 237:1 251.1 270.5 288.0 306.5 325.2 348.0 371.5 437.8 575.0 740.0 942.1 1176.0 1464.0 1791.0 2405.0 129.6 130.5 131.5 132.6 133.9 139.4 144.6 149.9 161.1 172.5 185.0 199.6 212.1 225.2 238.8 257.0 '273.8 291.0 309.0 330.6 353.0 415.9 546.1 703.0 895.0 1117.0 1390.0 1701.0 2284.0 122:9 123.6 124.5 .125.6 ' 126.9 132.0 137.1 142:1 . 152.6 163.5 175.4 189.1 201.0 213.5 226.0. 243.5 259.1 .275.8 292.8 313.1 334.4 394.0 517.5 666.0 847.5 1059.0 1318.0 1613.0 2165.0 109.3 109.9 110:6 111.7 . 112.8 117.4 . 121.9 126.4 135.7 145.4 155.9 168.1 178.5 189.7 201.0 216.4 230.4 245.1 260.3 278.4 297.1 350.2 460.0 592.0 753.5 941.0 1171.0 1434.0 1925.0 These factors are calculated from the formula where , /Q ( 0.1723 X T*\ \ 100 000.000 0 =* total black body radiation, Btu per square foot per hour. e '** emissivity. T " absolute temperature, degrees Fahrenheit. seldom exists, however, since the actual surface temperature in any heated space having surfaces exposed to the outer air varies greatly for different sides of the enclosure. It is therefore necessary to ascertain by calculation the mean of these interior surface temperatures. The mean temperature in this sense is not the arithmetic average of the actual thermometric temperatures of the surfaces, but the temperature corresponding to the average rate of heat emission per square foot of surface. The temperature corresponding to this mean emission can be taken from Table 1. Conversely, the emission at different temperatures and also the emissivity factors can be obtained from this table. For instance, 1 sq ft of surface at 50 F will emit 104.9 Btu per square foot per hour to surroundings at absolute zero if the emissivity of the surface is 0.9. 775