Document Z90MVKRzRxzkMMk4YX36k0D8

246 Chapter 13 . 194$ Guide thermometer are other instruments which have been used to .measure the influence of air temperature, air movement and radiation in an environment. The following statements applying to the use of radiators are based on . experience and test results: 1. The heating effect of a radiator cannot be judged solely by the amount of steam condensed within the radiator. ', 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 5 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 room. The comfort-indicating temperature should be taken below the breathing line level. 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 window openings. 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 later lowered 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. Investigations17 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. 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 welWesigned enclosure (B), with a poorly-desigped enclosure (C), and with a cloth cover (D) will illustrate the relative is^.s.H.V.E. Research Report No. 1067--The Cooling and Heating Rates of a Room with Different Types of Steam Radiators and Convectors, by A. P. Kratz, M. K. Fahnestock and E. L.- Broderick (A.S.H.V.E. Transactions, Vol. 43, 1937, p. 389). 17Loc. Cit. Note 10. *- Radiators arid Convectors 247 heating effects. Iri Fig. 4 the curve (B) 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 unsatisfaictory 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 ln,, "I 100171 Tests18 show that an average evaporative rate of about 0.235 lb per square foot of water surface per hour may be obtained from such pans, when the radiator is steam hot and the relative humidity in the room is between 25 and 40 per cent. This source of supply of moisture, alone is not adequate to maintain a relative humidity above 25 per cent on a zero day. ; ''University of Illinois, Engineering Experiment Station Bulletin No.,230. p. 20.