Document p2vZDjozxzgN206qyzYkybZr7

HEATING VENTILATING AIR CONDITIONING CUIDE 1944 the electric heater serves as a tempering tank, absorbing heat from the basement air and requiring the use of less energy in the electric heater. A typical domestic hot water heater as shown in Fig. 7 is arranged with upper and lower heating elements for the usual type of off-peak heating service. The lower heating element is under the control of the off-peak time switch. However, the upper heating element is usually connected to the line so that in case the supply of hot water in the tank becomes exhausted the top thermostat can turn on the top heater and heat a small supply of water. The top heater will not heat the water in the tank below its location, but when the off-peak period arrives the lower heater is turned on and the entire tank becomes heated. RADIANT DRYING Lacquers and similar surface films can be very effectively dried by radiation. Special electric lamp bulbs have been developed which give off a high percentage of infra-red and similar heat rays*. These are mounted in very efficient reflectors. For continuous manufacturing processes these reflectors are mounted in tunnels through which conveyors pass. For local applications, as for example paint drying in automobile repair shops, they may be mounted on portable racks. In the application of this type of drying the composition of the paint or lacquer is important. In general, lacquers and those enamels using synthetic resins react most favorably. Other applications include the (hying of ink, glue, and water, the softening of celluloid and bakelite for punching or shearing, and a wide variety of other uses5. Objects of relatively large surface area in proportion to their weight, and fabricated materials having a rather high heat absorption, may be satisfactorily heated by such a source. REVERSED CYCLE REFRIGERATION Reversed refrigeration is frequently referred to as a heaipump since the electric motor driving the refrigerating compressor furnishes the motive power to transfer heat from one temperature to a higher temperature: level. The compressor acts as a reversible refrigerating unit to extract heat from the outdoor air in winter and deliver it indoors for heating purposes, and, by a reversal, to extract heat from the indoor air in summer and discharge it outdoors. In normal use a refrigerating machine is arranged to remove heat and the -heat removed is dissipated to the condenser cooling water. The driving energy is converted into heat, most of which is added to the heat removed and extracted. In so-called reversed refrigeration the heat removed together with the heat converted from the driving energy is utilized to heat the building. This conservation of the heat converted from the driving energy enables the reversed refrigeration to show a better performance in heating service than straight refrigeration can show 'Infra-Red Lamps Speed Up Drying Operations (Automotive Industries 82:376-7; April 15,-1940). Invisible Rays Build Visible Profits, by H. M. Archer (Electric Light and Power, May, 1940). Radiant Energy Drying and Baking for Organic Finishing (Metal Industry 38:294-6; May. 1940). Infra-Red Heating, Section IV, Power Sales Manual (Edison Electric Institute). 782 CHAPTER 44. ELECTRIC HEATING in cooling service. In order to overcome the drop in capacity and in efficiency with lower outside temperatures, it is often desirable to use well-water instead of air as the source of heat. For a detailed description of this cycle see Chapter 25. AUXILIARY ELECTRIC HEATING In conjunction with heating systems of other types, an auxiliary elec tric heating arrangement is a convenient means of caring for mild days in the spring and fall which require little heat to make a building com fortable. Likewise, such electric heating might be used on abnormally cold days to help out the main heating system and by this means reduce the necessary size of the system. A few installations have been made using electric heating cable buried in the floors of bathrooms, etc., to provide auxiliary electric heating. At least one airplane hangar is heated in this manner. Because of the feeling of comfort that a radiant type heater gives, bathrooms may be heated electrically with this type of heater while the rest of the house is cared for by some other system. Offices and rooms which require heat at periods when the main heating plant is shut down can be conveniently heated electrically. CONTROL ' Because the efficiency of electric heat production is the same for small and large units, it is possible to reduce heat waste to a minimum by applying local heating, locally controlled. Heaters are often controlled manually but thermostatic control is essential for economical operation. For duct systems having a variable volume of air flow the electric heater control must automatically vary the heat input in coordination with the changes in air volume and demand for heat. CALCULATING CAPACITIES In calculating electric heating capacity one kilowatt is equal to 3413 Btu per hour or 14.2 sq ft equivalent direct steam radiation. POWER PROBLEMS The cost of electric energy varies because of several factors. Distribu tion costs differ for large and small users. The fact that electricity cannot be economically stored, but must be used as fast as it is generated, makes it impossible to operate electric plants at uniform loads; hence, even the time of use may affect the cost of electricity. Special low- rates are some times available during certain prescribed hours of use. Since the cost of production and distribution depends not only upon the quantity of energy used but also upon the maximum rate at which it is used, electric energy is often sold on a demand rate basis. In some cases, the demand charge is based upon the rated connected load, in' other cases, upon the maximum demand as indicated by a demand meter. 783 r