Chapter 3: HIGH-TEMPERATURE HEATERS
Over the years, high-temperature radiant heaters have been used in many industrial applications and, to a lesser extent, in commercial and space heating. These heaters take on various shapes ranging from flat surfaces to tubes to cylindrical surfaces. A hydrocarbon fuel or electricity via resistive elements can heat these heaters. The definition of a high-temperature heater is one whose surface is greater than 300 F, but they may range up to as high as 1800 F. Due to the high temperature of these heaters, safety dictates location and distance from combustible surfaces.
As energy efficiency and employee comfort are becoming more important issues, engineers have sought a better design and application of these heaters. The following sections introduce types of high-temperature radiant heaters and discuss heat transfer implications of these heaters. The discussions also include some design parameters to size and locate heaters for their optimum operations.
3.1 TYPES OF HIGH-TEMPERATURE RADIANT HEATERS: DIRECT AND INDIRECT
For residential thermal comfort utilization, a direct radiant heaterrefers to a radiant heater that typically consists of a porous ceramic or metal screen as a flat combustion surface. One type of direct radiant heater is illustrated in Fig. 3.1. In ASHRAE s Handbook of HVAC System and Equipment,these types of heaters are classified as surface combustion heaters.Often, the manufacturer s literature refers to these types of heaters as high-intensity radiant heatersbecause of their high temperature at the burning surface. The gas and air are premixed, and the combustion takes place on the burner face.