Book - School of Science and Technology

Direct systems ± electrical (primarily convective) 111buildings which are used only intermittently and for relatively short periods such aschurches, etc.Direct systems ± electrical (primarily convective)Natural convectorsA considerable variety of patterns and sizes of such heaters is available, most nowcomprising a metal sheathed element or elements fitted within a rectangular casing. Theenclosure is arranged to promote air flow over the elements via an opening at the baseand a louvred outlet at the top. Convectors may, alternatively, be floor standing andportable or wall mounted: in the latter case, mounting brackets may provide means foreasy access to the rear face for cleaning. Ratings range from 500 W to 3 kW, the largersizes having multiple elements for control purposes. The temperature of the casingremains relatively low in most cases and output by radiation is minimal in consequence.Convectors of this and other types are particularly responsive to thermostaticcontrol.Skirting heatersThese are a variant of the convector type heaters noted above having a height of about150 mm with a slotted casing, as in Figure 4.15, to promote air flow over the element.Most are arranged for either floor or wall mounting and have ratings of between 550 and750 W per metre length. They may be fitted in small rooms or mounted below tallwindows.Oil filled radiatorsSimilar in appearance to the pattern of steel panel radiators used in hot water heatingsystems, these have a light oil filling within which is an immersion heater element. The oilbegins to circulate when heated and thus acts to transfer heat to the outer surfaces. With amaximum surface temperature of about 90 C, output ratings vary with size up to anormal maximum of 1.5 kW. Wall mounted or portable models on feet are available:the former are useful in circulation spaces.ElementSlottedcasingFigure 4.15 Electrical skirting heater (Dimplex)