(BQ) Part 2 book "Refrigeration and air conditioning technology" has contents: Creating user interfaces, 2D graphics, 3D graphics, graphics and sound, useful internet links. | 6 SECTION Air Conditioning (Heating and Humidification) UNIT 30 Electric Heat UNIT 31 Gas Heat UNIT 32 Oil Heat UNIT 33 Hydronic Heat UNIT 34 Indoor Air Quality UNIT 30 Electric Heat OBJECTIVES After studying this unit, you should be able to ■ discuss the efficiency and relative operating costs of electric heat. ■ list types of electric heaters and state their uses. ■ describe how sequencers operate in electric forced-air furnaces. ■ trace the circuitry in a diagram of an electric forced-air furnace. ■ perform basic tests in troubleshooting electrical problems in an electric forced-air furnace. ■ describe typical preventive maintenance procedures used in electric heating units and systems. SAFETY CHECKLIST ✔ Be careful that nails or other objects driven into or mounted on radiant heating panels do not damage the electrical circuits. ✔ Any heater designed to have air forced across the element should not be operated without the fan. ✔ Always observe all electrical safety precautions. This unit briefly describes several types of electric heating devices. Emphasis, however, is placed on central forced-air electric heat because it is frequently serviced by technicians in this industry in some areas of the country. PORTABLE ELECTRIC HEATING DEVICES Portable or small space heaters are sold in many retail stores and by many industrial distributors and manufacturers, Figure 30–1. Some have glowing coils (due to the resistance of the wire to electron flow). These transfer heat by radiation (infrared rays) to the solid objects in front of the heater. The radiant heat travels in a straight line and is absorbed by solid objects that warm the space around them. Radiant heat also provides heating comfort to individuals. The heat concentration decreases by the square of the distance and is soon dissipated into the space, Figure 1–13. Quartz and glass panel heaters are also used to heat small spaces by radiation, Figure 30–2. INTRODUCTION Electric heat is produced by .
