Document vXwGGBVJamGqNNKDop66B9rb

478__________________________________ CHAPTER 25 1946 Gi4 required to maintain the common air temperature at the 30-in. level is of the order of 13 per cent. In Fig. 3 are shown the results of tests made with the same three convectors and the one large-tube cast-iron radiator, so adjusted in size tbat each gave approximately the same equivalent temperature. in. the No. 3-qjosition in the test room. The difference between the minimum and the maximum amount of heat required to maintain the common equivalent temperature is of the order of 7 per cent. The following statements applying to the use of radiators are based on experience and test results: - - ... I- The heating effect of a radiator cannot be judged solely by the amount of steam condensed within the radiator. Radiators, Convectors Coils 479 to a rate of 0.24 lb. In practice the rate of steam supply to. the heating unit, while heating up, is frequently retarded by controlled elimination of air through air valves or traps. Automatic control valves may also retard the supply of steam. Vacuum types of air venting valves may be used to reduce the length of the venting periods. ENCLOSED RADIATORS The general effect of an enclosure placed about a direct radiator is to restrict the air flow, diminish the radiation and, when properly designed, improve'the heating"effect. Investigations10 indicate that in the design of the enclosure three things should be considered: .. 1. There should be better distribution of the heat below the breathing line level to produce greater heating comfort and lowered ceiling temperatures. . Fig. 3. 1 2 3 4 5.6 i HEIGHT ABOVE flOOR INFECT '. Temperature Gradients and Equivalent Temperatures for Radiator and Convectors with Common Equivalent Temperature .2. Smaller floor-to-ceiling temperature differentials can be maintained with long, low, thin, direct radiators, than is possible with high, direct radiators. 3. The larger portion of the-floor-to-ceiling temperature differential in a room of average ceiling height heated with direct radiators occurs between the floor and the breathing level. 4. The comfort level (approximately 2 ft-6 in. above floor) is below the breathing line level (approximately 6 ft-0 in. above floor), and. temperatures taken at the breathing line may not be indicative of the actual heating effect of a radiator in the roomi The comfort-indicating temperature should be taken below the breathing line levy. 5. High column radiators placed at the sides of window openings do not produce as comfortable heating effects as long, low, direct radiators placed beneath windows. HEATING UP THE RADIATOR AND CONVECTOR The maximum condensation occurs in a heating unit when the steam is first turned on. Tests16 on an old-style column-type cast-iron radiator indicated that in the first 10 min the condensation rate reached a peak of 0.95 lb per square foot of radiator per hour and 10 to 15 min laterdropped Fig. 4. Steam Consumption of Exposed and Concealed Radiators 2. The lessened steam* consumption may not materially change -the radiator heating performance. 3. The enclosed radiator may inadequately heat the space. * . A comparison between a bare or exposed radiator (A) and the same radiator with a well-designed enclosure (B), .with a poorly-designed enclosure (C), and with a cloth cover (D) will illustrate the relative heating effects. In Fig. 4 the curve (Bj reveals that the enclosed radiator used less steam than the exposed radiator, but gave a satisfactory heating performance. A well-designed shield placed over a radiator gives about the same heating effect. Curve (C) shows the unsatisfactory effects produced by improperly-designed enclosures. Curve (D) shows that the effect of a cloth cover extending downward 6 in. from the top of the radiator was to make the performance unsatisfactory and .-inadequate. Some commercial enclosures and shields for use on direct radiators are equipped with water pans for the purpose of adding moisture to the air in the room. Tests 17 show that an average evaporative rate, of about 0.235 lb per square foot of water surface per hour may be obtained from