Document nkwkwoJ74yrGqnOpnnk3DYBV8

HEATING VENTILATING AIR CONDITIONING GUIDE 1942 in pounds per hour for the time elapsing after steam is turned into a castiron radiator. The data are from tests on old-style column type radiators. 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. Investigations9 indicate that in the design of the enclosure three things should be considered: CHAPTER IB. RADIATORS AND CONVECTORS 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. Tests10 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. CONVECTORS Although any standard radiator may be concealed in a cabinet or other enclosure so that the greater percentage of heat is conveyed to the room by convection thereby resulting in a form of gravity convector. UFig. 5. Chart Showing the Steam Demand Rate for Heating p a Cast-Iron Radiator with Free Air.Venting and Ample Steam Supply 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 well-designed enclosure (B), with a poorly-designed enclosure (C), and with a cloth cover (D) will illustrate the relative heating effects. In Fig. 6 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 unsatisfactory and inadequate. 'University of Illinois, Engineering Experiment Station Bulletins Nos. 192 and 223. Investigation of Heating Rooms with Direct Steam Radiators Equipped with Enclosures and Shields, by A, C. Willard A. p. Kratz, M. K. Fahnestock and S. Konzo (A.S.H.V.E. Transactions, Vol. 35,1929, p. 77). 260 Fig. 6. Steam Consumption of Exposed and Concealed Radiators generally better, results are obtained with specially designed units which permit a free circulation of a larger volume of air at moderate tempera tures. Since air stratifies according to temperature, moderate delivery temperatures at the outlet of the enclosure reduce the temperature dif ferential between the floor and ceiling and accordingly accomplish the desired heating effect in the living zone. A typical recessed convector is shown in Fig. 7. The heating element consisting of a large percentage of fin surface is usually shallow in depth and placed low in the enclosure in order to produce maximum chimney effect in the enclosure. The air enters the enclosure near the floor line just below the heating element, is moderately heated in passing through the core and delivered to the room through an opening near the top of enclosure. Since the air can only enter the enclosure at the floor line, the cooler air in the room which always lies at this level, is constantly being withdrawn and replaced by the warmer air. This air movement "University of illinois. Engineering Experiment Station Bulletin No. 230. p. 20. 261