Document NN0X6KnQqw1XmGmE8ayp9d2LD

HEATINC VENTILATING AIR CONDITIONING GUIDE 1940 improve the heating effect. Recent investigations7 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 well-designed enclosure (3), with a poorly-designed enclosure (C), and with a cloth cover (D) will' illustrate the relative heating effects. In 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 oyer a radiator gives about j CHAPTER 14. RADIATORS AND GRAVITY CONVECTORS CONVECTORS OR CONCEALED HEATERS 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, 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. Fig. 4. .Steam Consumption of Exposed and Concealed Radiators 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. Practically all 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. Tests8 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 Bulletins Nos. 192 apd 223. and 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). University of Illinois, Engineering Experiment Station Bulletin No. 230, p. 20. 262 Fig. 5. Typical Concealed Convector Using Specially Designed Heating Unit Fig. 5 shows a typical built-in convector. The heating element con^ sisting 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 en closure. 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 accom plishes the desired reduction in temperature differentials and assures maximum comfort in the living zone. The Convector Manufacturers Association has adopted the A.S.H.V.E. 263