Document npy93b8poJra4NgXZBqD6pxYR

HEATINC VENTILATING AIR CONDITIONING: GUIDE 1940 ELECTRIC HOT WATER HEATINC Electric water heating, using an electric boiler in place of a fuel burning boiler, like electric steam heating, is generally confined to auxiliary or other limited applications. The use of insulated water storage tanks in which to store , heat generated by electricity during off-peak hours at extremely low rates, is a development which has some special applications. In this system of heating, the primary storage tank is simply a large, well-insulated, pressure type steel tank, equipped with electric heating elements connected to line with automatic time switches, which also have automatic limit controls for temperature and pressure. The heating system installed in the building' may be of any standard individual radiator or fan-served indirect type or with provisions for the heating and- CHAPTER 41. ELECTRICAL HEATINC hours of off-peak load, while the regular heating element is a stand-by at all times. Storage of this two-element type of water heater is larger than average to carry over the periods when the off-peak element is timed out, without too frequent demands on the regular heating element which takes the higher domestic lighting service rate. Some utilities now offer a schedule which, beyond a stipulated minimum, lowers the rate for all service if an electric water heater is installed. A comprehensive survey covering United States arid Canada shows a rapidly growing use of electric water heaters, although the per cent of saturation, based on the total number of domestic power customers, is still low. Public acceptance is effected by the cost of other competitive fuels, by the electric power rate, and by the temperature of the cold water supply. Competition with other fuels, especially gas, seems to be the major controlling factor. The first cost of electric storage heaters is also greater Fig. 6. , Diagrammatic Arrangement of an Electrode Boiler humidification phases of an air conditioning system. A system of this kind requires very careful design to avoid excessive overall radiation losses during periods of low heat demand. ..It is also important to provide for sudden changes in heat demand. A typical hot water heating boiler is illustrated in Fig. 5. - HEATINC DOMESTIC WATER SUPPLY1 Electric water heaters of the automatic storage type for domestic hot water supply are simple and reliable, and in many sections of the country low electric rates have been established by the electric utilities to secure this load. In some districts, rate schedules divide the current used for water heating into two classifications, regular and off-peak. A time switch automatically limits use of the off-peak heating element to the 'Test Results of Electric Water Heaters, by C. G. Hillier (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, November, 1936, p. 632). ' Fourth Annual Survey, by B. J. Martin (Electric Light and Power, March, 1937). 710 Fig. 7. Piping Arrangement for Connecting Electric Water Heater to Fire-Box Coil Fig. 8. Domestic Hot Water Heater for Off-Peak Service than for gas, owing to the need for larger tank storage due to off-peak service and slower recuperating capacity. It is often desirable to connect an electric heater to a residential system having a coil in the fire-box of the furnace. In this case it is im portant to make the proper connections in order to benefit by any heat obtained from the furnace and at the same time to prevent dangerous overheating. The proper piping connections are shown in Fig. 7, and in this case the electric heater will only furnish heat when insufficient heat is supplied from the furnace. This arrangement has a further advantage in the summertime in that the bare tank through which the cold water passes on its way to the electric heater serves as a tempering tank, absorbing considerable warmth from the basement air and re quiring the use of less energy in the electric heater. A typical domestic hot water heater as shown in Fig. 8 is arranged with upper and lower heating elements for the usual type of off-peak heating service for which most utilities have especially attractive low power rates. The lower heating element is under the control of the off- 711