Book - School of Science and Technology

Convective heating 197DamperFinnedtubeFigure 7.19 Skirting heaterAir inletAir outletCasing setwithinchannelcast in slabHeatingelementFigure 7.20 Trench convector heater (Multibeton)Forced (fan) convectorsUnits of this type are best described by reference to an illustration such as Figure 7.21which, for a commercial size of convector, shows the various component parts in separation.The finned tube element will probably differ from the pattern used in a naturalconvector in that the headers, to which pipe connections are made, are likely to be oneabove the other at the same end of the casing, the tubes being in hairpin form to make upa `two deep' arrangement. In the earliest models made, propellor type fans were used.These were superseded by small quiet running centrifugal units having long-life motorsmounted within the suction eye, which in turn were replaced in some models by tangentialfans.The heating element and fans are contained within a casing which, where free-standing,is similar to that provided for a natural convector. For the type of unit illustrated,provision is made at the fan discharge for an air filter. This is often a washable type,