Book - School of Science and Technology

188 Heat emitting equipmentOpen front to sectionsSections extended at frontFigure 7.12 Elevations on two types of cast iron radiatorThere seems to be no modern substitute for the 75 mm deep cast iron `Hospital'-typeradiator which, in terms of neatness and an ability to withstand maltreatment by eitherphysical impact or by untreated water, represented the ultimate of its type. Imported castiron radiators seem generally to be of the sectional column type, not unlike the patternsmade familiar in the British Isles during the 1930s. Erection of the sections is by means ofleft- and right-hand threaded nipples at the top and bottom ports. In some cases theprofile of the sections is now arranged to present a front elevation which resembles apanel, thus increasing the output per unit area by about 10%. Figure 7.12 illustrates thedifference between the two types, and a summary of typical ratings is included in Table7.5 for a temperature difference, water to air, of 60 K which is the accepted standard fortests. Table 7.6 provides correction factors which enable these ratings to be adjusted forother conditions. The radiant component of output for column radiators varies between30 and 17% as will be noted later.Pressed steel radiatorsThe place of cast iron seems now to be taken by radiators fabricated from light gauge mildsteel sheet pressings, welded together, a technique which originated in Scandinavia. Steelis more susceptible to corrosion than cast iron and thus some form of water treatment forthe content of the heating system is prudent. The particular merits of steel radiators resultfrom their small mass and their comparatively narrow waterways: they are light to handleon a building site and respond quickly to temperature control.In consequence of the versatility of the manufacturing process, there is an almostinfinite variety of shapes and patterns of steel radiator available. These fall, however,into a number of categories which divide into two clearly recognisable groups, the first ofwhich is illustrated in Figure 7.13:(a) The simple convoluted panel type which may be single, double or more. Each panel isnormally fabricated from two identical sheets, seam welded at top, bottom and endsbut some of the better patterns are made from a single sheet folded over to provide arounded top.(b) The column type which, in effect, reproduces the appearance of a similar cast ironradiator.(c) A sinuous coil panel type which is very similar to the radiant panels discussed earlier.(d) A tubular type, using top and bottom headers with elegant pipe arrays between them:may be used as a room divider or barrier rail.