Document nm20rMm4DY1EGr7XMawM8kKZm

130 Am. Soc. of Heat.-Vent. Encineers Guide, 1922 EFFECT OF ENCLOSING THE RADIATOR It is very often desirable to partly enclose or conceal a radiator by means of screens or grills. All such enclosures in general reduce the heat transmission from the radiator, the effect being both to reduce the radiant heat and the converted heat. As in most radiators, the converted heat is at least two-thirds of the heat transmission, these enclosures or screens largely affect the convected heat. It is therefore very desirable that the current of air passing over and through the radiator should be restricted as little as possible. There has been some experimental work done, particularly abroad, with reference to these screens. There are, however, so many different cases that may arise that it will not be possible to discuss all of them but only to take up typical ones. Case No. 1. In this case, Fig. 8, the radiator is enclosed in a box with a screen in front and at the bottom, and a screen at the top, these screens extending the full length of the radiator. This arrangement reduces the heat transmission of the radiator from 7 to 10 per cent, and in all cases, the spaces between the radiator and the wall and the spaces between the casing and the radiator should be at least 2j4 inches. The reduction of heat transmission will be more in narrow radiators than in wide radiators. Experiments show'that the best results are obtained when the opening at the top has twice the width of the opening at the bottom, and for radiators of ordinary type the width of opening at the bottom should be 5 inland the opening at the top, 10 in. Case No. 2. It is sometimes desirable to place a screen in front of the radiator, leaving the top entirely open with an opening at the' bottom in front for the cold air to enter the radiator, as in Fig. 9., In a case of this kind the effect of the screen is to produce a strong current of air and if this screen is high enough it may even product a chimney effect which will increase heat transmission from the radiator due to increased circulation. The effect of such screens depends entirely upon their hejght. Professor Brabbee states that, with a screen 72 in. high and a 49 in. radiator, the heat transmission will be increased 12 per cent. Case No. 3. Radiators often have placed over them a flat shelf, as shown in Fig. 10. In such case, they should-be provided with a deflector as shown. The effect of the shelf very largely depends upon the height of the shelf above the radiator. When the distance D--that is the height of the shelf above the radiator--is 5 in. or over, the effect of the shelf may be neglected. When the distance D is reduced to 4 in., the heat effect may be reduced by 4 per cent. Case No. 4. Radiators are often enclosed in boxes with a grill in front or recessed in the wall with a grill placed in front of them as in Fig. 11. In such cases, the height, D, is very important. With D equal to 2in., the heat transmission will be reduced 20 per cent., and with D equal to 6in., the heat transmission is reduced 10 per cent. It is assumed in this case that the entire front of the box is provided with an open grill. Case No. 5. Sometimes a grill, as shown in Case 4, is partly replaced by a solid panel -with openings above and below as in Fig. 12 . With the openings the full length of the radiator and 6 in. in height and with D not less than 4 in., the heat transmission will be reduced 25 per cent. As D is reduced in height, the heat transmission will also be reduced and with D, 2j4 in., the reduction will be 40 per cent. . - Am. Soc. of Heat.-Vent. Encineers Guide, 1922 DIFFERENT ARRANGEMENTS OF RADIATORS IN ENCLOSURES