Document mbqG083gZvMVO88z28LMqzYZ

; AMERICAN SOCIETYOE HEAMG & VENTILATING ENGINEERS GMHE192L 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 pro portionate 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. The late John R. Allen, while Director of the Society 's Research Laboratory, submitted a paper as a report (A. S. H. V. F.. Journal, January, 1920), 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. EFFECT OF HUMIDITY Fig. 3 shows the effect of increasing the humidity upon the heat transmission. It will be 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. Humidity can have very little, if any effect upon radiation, and the effect of humidity must there-, fore change the convected heat lost by the radiator. This change of convected 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 con vection. No exact data are available on the effects that may be intro duced by increasing these velocities over radiator surfaces, but in rooms with moving machinery the heat transmission is increased approximately 10 per cent. - EFFECT OF PAINTING The effect of painting was originally determined by experiments made; with a cast iron rectangle, and in applying these to radiators of standard; type, corrections must be made to allow for the difference between; the; 26 AMERICAN SOflETYIff AMONG & VENTILATING ENGINEERS6PM1923^ area of the radiating and convecting surfaces. The effect of painting is to change the radiation constant of the radiating surface and has prac tically no effect upon the heat lost by convection. It is, therefore, a sur face effect and it makes no difference what paints are placed on the radi ator as a priming coat, the results are always dependent upon the last coat of paint put upon the radiator. In radiators having a large proportion of radiating surface such as pipe coils or wall coils, the effect of painting will be more marked than in four-column radiators having a compara tively small radiating surface in proportion to convecting surface. All __-- k.**.._ luumuuil LUUO Ldl1 L 1 IltJTC* fore all paints having finely ground pigments will give about the same effect. Metals have a poor radiating effect so that any paint involving flake metal, such as the bronze, will have a low radiating constant. The following Table 23 shows the heat loss frpm a two-column 38-in. radiator, 10 sections long, when painted with different kinds of paints: TABLE 23. EFFECT OF PAINTING ON TWO-COLUMN 38-IN. RADIATOR. STEAM TEM PERATURE 215 DEG. ROOM TEMPERATURE 70 DEG. FAHR. Condition of Surface Per Cent Condition of Surface Per Cent Cast iron bare...................................... 240 Painted with white enamel........ ...... 242 Painted with aluminum bronze..,___ 200 " " maroon Japan............. 240 11 ** gold bronze..... .............. 205 ** ** white zinc paint...;.-..... 242 Painted with no-lustre green enamel 230 It is often very important to know the maximum condensation that occurs in a radiator when steam is turned on_ -Fig. 4 shows the condensa tion rate in pounds per hour for the time elapsing after steam is turned into the radiator. It will be noticed that the maximum condensation occurs 10 min. after steam is turned on, and in that case it amounts to 27