Document 8rGevkyXjd3xdg9wj3Mvzwko

American Society of Heating and Ventilating Engineers Guide, 1928 Solution.--17,200 + 70 per cent = 24,500 B.t.u. Table 3, column for 45 in. indicated 19, as the required number of sections. Pipe coils- should be of the header type, with provision made for expansion by a mitre piece. The steam supply should be at the mitre end and all coils should be securely anchored at the return header so as to throw the expansion toward the mitre end. The coils should be made of. IK or \x/i in. pipe and not over 60 ft. in length, not including the mitre, which should be at least one-tenth the length of the coil. RADIATION FOR ROOM TEMPERATURES The following table from the Establishment of Standard Methods of Proportioning Direct Radiation, by James A. Donnelly (Transactions, Vol. 21, p. 535) gives the proportionate heat losses from buildings, the Table 14. Effect of Room Temperature on Heat Loss and Size of Radiator Room Temperature Proportionat b Loss in B.t.u. Difference in Temperature Between Radia tor and Room Proportionate Transmission in B.t.u. Room Temperature Proportionate Surface Required Sq. Ft. 35 40 45 50 55 60 65 70f. 75 80 85 90 95 100 105' no 115 120 0.50 0.57 0.64 0.71 0.79 '0186 0.93 l.OOf 1.07 1.14 1.21 1.29 1.36 1.43 1.50 1.57 1.64 1.71 175 170 165 160 155 150 145 140f 135 130 125 120 115 110 105 100 95 90 r~/1.34 1.29 1.24 1.19 1.14 1.09 1.05 l.OOf 0.95 0.91 0.87 0.82 0.78 0.74 0.70 0.66 0.62 0.58 35 40 45 50 55 60 65 70f 75 80 85 90 95 100 105 no 115 120 0.37 0.44 0.52 0.60 0.69 0.78 0.89 l.OOf 1.12 1.26 1.40 1.56 1.74 1.93 2.15 2.39 2.66 2.95 t Standard Conditions. Assuming that the rate of beat loss from a building varies directly with the difference be tween the outride temperature and the building temperature, and considering the heat loss for zero outside, 70 deg. inside as the standard, or 100 percent; the second column shows the proportionate loss of heat from a building when the outside temperature is zero, and the inside temperature is as given in the first column. Assuming that the rate of transmission from a direct radi ator to the air of a building is in proportion io their difference in temperature, with a variation in the rate of transmission of 2 per cent, greater or less, for each 10 deg. increase or decrease in their temperature difference, and considering 140 deg. differ ence in temperature (steam 210 deg., building 70 deg.) as standard, or 100 per cent trans mission, the second column shows the proportionate trans mission when the difference in temperature is as given , in the first column. Assuming that under stand ard conditions of outride tem perature zero, building tempera ture 70 deg., and radiator tem perature 210 deg. (or 140 deg. difference between the. radiator and room) the amount of radia tion necessary is 100 per cent, the proportionate amounts of radiation given in the second column are those necessary to heat a building to the tempera tures given in the first column, when the outside temperature is zero. Note.--(The amount of surface required for heating is always obtained by dividing the heat loss-from the building by the amount of heat transmitted per squire foot of radiation. Therefore, as may be seen from the above tables, the proportionate amount of surface required for heating is obtained by dividing the proportionate heat loss from the building by the proportionate transmission of the radiator, in each case. < 72 Chapter II--Heating by Radiation nroDortionate transmission from direct radiators, and the proportionate radiation required (with steam at 210 deg.) for various room temper atures, when the outside temperature is zero. The preceding table may be used to find the proportionate amount of radiation necessary to heat a room to any desired inside temperature, other than 70 deg., when the outside minimum temperature is other than zero and with a radiator temperature other than standard. Find the difference between the outside temperature and the room temperature in the first column; divide the proportionate heat loss opposite this amount, in the second column, by the proportionate transmission opposite the difference in temperature between the radiator and the room, as given in the- fourth column, and the result will be the proportionate amount of radiation required. Example.--What is the proportionate amount of radiation required to heat a room to 90 deg., with a temperature of 20 deg. below zero outside, and a steam temperature of 240 deg. Solution.--The difference in temperature between 20 deg. below outside, and 90 deg. inside, is 110 deg. Opposite 110, the propor tionate heat loss or 1.57 is found in the second column. The difference in temperature between the radiator and the room (steam 240 deg., room 90 deg.) is 150 deg. Opposite this, the proportionate transmission 1.09 is found in the fourth column. Divide 1.57 by 1.09 and the quotient, 1.44 is the proportionate amount of radiation required. EFFECT OF HUMIDITY The late John R. Allen, while Director of the Society's Research Laboratory, submitted a paper as a report (A. S. H. V. E. Transactions, Vol. 26, p, 11), which in addition to the treatise on the heat emitted by various types of radiation, from which the preceding tables were calcu lated gives other data from which the following is taken, Fig. 1 shows the effect of increasing the humidity upon the heat transmission. It will & noted that with extreme change of humidity there is a slight change in the heat transmission, the heat transmission reducing slightly as the humidity increases. Humid ity can have very little, if any effect upon radiation, and the effect of humidity must therefore change the convected heat lost by the radiator. This change of converted heat is probably due to the change in the density of the air passing over the radiator. EFFECT OF AIR CIRCULATION The amount of heat given off by a radiator may also be increased by increasing the velocity of the air over the surface of the radiator. This increase in velocity will increase the amount of heat carried off by convection. No exact data are available on the effects that may be introduced by increasing these velocities over radiator surfaces, but in rooms with moving machinery the heat transmission is increased approximately 10 per cent. WARMING THE RADIATOR It is often very, important to know the maximum condensation that occurs in a radiator when steam is turned on. Fig. 2 shows the condensation rate in pounds per 73