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168 CHAPTER 11 1962 Guide And Data Book ' mends a C factor of 15 for dwellings having a floor area over 1200 sq ft and located in an area having a design temperature difference exceeding 65 F. > Tie use of C factors lower than 18.5 for thoroughly insu lated structures is in accordance with experience records of the electric industry over a wide range of geographical and climatic characteristics. Values of C as low as 12 have been reported on individual ftaudeutiai installations. Application of the C factor is not recommended for commercial and indus trial applications. Operating Coste^Commerdal and Industrial) Energy usage of electrically heated commercial and indus trial buildings, do not follow a pattern like residential. The wide differences in thermal construction, design and type of- building, occupancy habits, magnitude and duration of inter nal heat sources and various other factors combine to make each application somewhat different from any other. A procedure for determining the capacity required is de scribed in Chapter 25 of the 1961 Guide Arm Data Book. A procedure for estimating energy consumption is described in Chapter 12 of this volume. Records of buildings having electric heat have demonstrated that these pro cedures result in higher estimates of required capacity and energy consumed than is actually obtained. Due to thewide variations in actual experience compared to estimates, it is suggested the local power supplier be consulted regarding performance of similar installations in the area involved and also for proper evaluation of electric power rates. Voltage Requirements Voltages stipulated for secondary distribution systems are for the point of service entrance to the building. The preferred nominal system voltage, for single-phase 3-wire systems with space heating, is 120/240 volts, as stipulated by standards of the electrical industry (E.E.I. Publication R-6 and NEMA Publication No. 117 issued May, 1949). For commercial and industrial applications higher power supply voltages of 440 to 480 volts, 3-phase, 3-wire and 3phasa, 4-wire are frequently used. Specific information should be obtained from the local elec tric power supplier on both existing and anticipated future conditions at the location before specifying the capacity and voltage for equipment, wiring and controls. Effect of Voltage Variations The actual electrical input (and consequently heating effect available) can be adjusted for the difference between the rated voltage and service voltage by the following formula: where W, -- actual watts input W, " rated watts input of equipment V. * service voltage or power supply volts V, = rated voltage of equipment n 2 for low temperature coefficient alloy resistors, 1.5 for tungsten resistors, and between 1 and 2 for conductive films and other resistors not included above. BIBLIOGRAPHY <i-dtzj n utuTwiifu c umteawm jar otectrte Vomjort Equipment (National Electrical Manufacturers Associst iication BE 2-1961). BE1-NBMA Preferred Voltage Rating* for A-C System* and Equipment (Edison Electric Institute Publication No. R-6, May 1949, and National Electrical Manufacturers Association Publi cation No. 11, May 1949). Stmdard Handbook for Electrical Engineers (McGraw-Hill Book Co., New York, 1952). R. L. Boyd: Heat schools electrically? (Heating, Piping and Atr Conditioning, December 1956). NEMA Manual for Electric House Heating (National Elec trical Manufacturers Association, June 1957). J. C. Beckett: Cost comparison: resistance space hunting yg ' fuel-fired systems (Electrical Construction end Maintenance. October 1956). ' W. R. New: Serving the all-electric home (Electrical World, March 19, 1956). ^ R. L. Boyd: It's here ... the all electric school (Electrical Construction and Maintenance, February 1957). Handbook of Electrical Applications (Edison Electric Insti tute). A mAntml of electric space heating (Electrical Construction and Maintenance, March 1960). PhQip Sporn and E. R. Ambrose*. Design and application of electric heat (Air Conditioning, Heating and Ventilating, July, I960). Glydewell Burdick: The ABC's of insulation for electric heating(Electricity in Building, November 1960). Minimum Property Standards for One and Two Luting Units (Federal Housing Administration, FHA No. 300). Lawrence Lessing: Electric heating puts on the beat (Archi tectural Forum, October 1959). W. G. Potter and J. P. Gallagher: Electric school heating-- operating result data (American Institute of Electrical Engineer* Paper DP 59-1001). W- J. McGuinees: Electric heat proven favorable for Ohio School (Architectural Forum, November I960). Should your school be electrically heated? (School Management, August 1960). D. B. Anderson, G. R. Erickson, R. C. Jordan, and R. R. Leonard: field laboratory for heating studies (ASHRAE Journal, November 1960). Electric heating survey (Electrical World, June 5,1961). R. L. Boyd: What do we know about infrared comfort heating? (Beating, Piping and Air Conditioning, November I960). R. L. Boyd: Let's get practical about insulation (Electric Heating and Cording, 4th quarter, 1959). R. L. Boyd: Electric beating goes institutional (Catholic Building and Maintenance, January--February 1960). R. L. Boyd: How to solve special heating problems of retail stores (Electric Heating and Cooling, August-September, I960). R. L. Boyd: Annual energy use for electric heating (ASHRAE Transactions, VoL 65, 1959, p. 259). Electric House Heating (Rural Electrification Administration Bulletin 142-1, September 1960). P. H. Rickert: Fossil fuels vs kilowatts for space heating (Load, General Electric Co., September 1960). When, how and why to consider the use of electric heating (Healing, Piping and Air Conditioning, September 1961). CHAPTER 12 estimating fuel consumption or energy FOR SPACE HEATING Bases of Fuel Estimates; Efficiency of Utilization; Calculated Heat Loss Method; Compulation and Application, Short Methods for Estimating Heat Loss; Degree-Day Method: Computation and Application, Unit Fuel Consumption per Degree Day, Estimating Consumption for Various Fuels, Degree Day as an Operating Unit; Industrial Degree Days; Maximum Demand and Load Factor* IT IS often necessary to estimate the anticipated heat re quirements and fuel consumptions of heating plants for either short or long terms of operation. These quantities can be much more difficult to calculate than design beat loss or required system capacity, since they involve essentially the summing up of the net result over the period in question of the influence of many factors which may vary greatly with time. It will seldom be possible to predict with any great ac curacy the way in which all the factors involved.will vary throughout the prediction period. In addition to this, the caldilations required to take all such variations into account become very involved. For these and other reasons records of past operating experience, when these are available, pro vide the most reliable and usually the most accurate basis for the prediction of future requirements. Records of past heat requirements or of fuel consumption of a particular building are a better basis for estimates than are averages of records from similar buildings. In the absence of past records for a particular building the data from sim ilarplants in the same locality may have to be used. Averages of consumption figures taken from many types of plants in many types of buildings in various localities can only pro duce an average estimate which may prove to be inaccurate when applied to a particular building. Where unusual operating conditions exist due to factors such as excessive ventilation, abnormal inside temperatures, and heat gains from external sources, or where, in the case of proposed buildings of unusual design,-no information is avail able regarding former consumption, it is necessary to estimate fuel consumption from the computed heat losses. In preparing fuel consumption estimates it is well to real ize that any estimating method used will produce a more reliable result over a long period operation than over a short period. Nearly all of the methods in common use will give trustworthy results over a full annual heating season, and in some cases such estimates will prove consistent within themselves for monthly periods. As the period of the estimate 13 shortened, there is more chance that some factor not taken into account directly in. the estimating method will deviate from its long-time average value, and thus lead to serious error in the predicted heat requirement. Except when specific statement is made to the contrary, the data in this chapter are based on the performance of residential heating installations. The application of these data to commercial or industrial installations may produce misleading results. EFFICIENCY OF UTILIZATION Any method of estimating fuel requirements baaed pri marily on calculation of heat losses must, of necessity, also take into account considerations of the efficiency with which the heat in the fuel is used. Efficiency can be defined in a variety of ways for various purposes, and the values in any given case can vary widely depending on the con ditions. For estimating purposes, as will be shown later, it is the efficiency of utilization of the fuel over the calculation period which is wanted. This is distinct from heating unit, efficiency which expresses the heat delivered by a furnace or boiler as a percentage of the heat provided in the fuel and which is the efficiency normally used in describing the per formance of a unit under rated, or stated, load conditions. It has been shown, at the University of Illinois for example,1 that in the case of a dwelling with an intide chimney, as much * as 35 percent of the heat delivered to the chimney which is normally considered to be a loss so far as efficiency of the heating unit is concerned may be delivered to the house through the heated chimney walk. This recovered heat amounted to as much as 12 percent of the heat required by a house. Much of this recovered beat may be available for heating. It has been said in connection with the same study that at times only about 50 percent of the heat utilized by a house was supplied by radiators, while the other 50 percent of the heat utilised was supplied from such sourcesaschimney, piping, boiler jacket and smoke pipe, people, lights, etc. A summary*4 of many tests in two research residences at the University of Illinois using many fuek and systems give values of 67 to 90 percent for overall house efficiency (the ratio of the beat loss from the structure to the beat input to the unit). The efficiency of utilization of the fuel burned can at times be relatively very high for houses. It can. also vary quite widely from one house to another because of variations in chimney location and design, utilization of heat lost to the basement from the heating unit and smoke pipe, utilization of electricity, occupancy of the house, water heating require ments, etc. The efficiency of utilization may also vary with time of year as the average load on the furnace varies. Some of the reasons for this in the case of intermittently-fired oil furnaces have been demonstrated.4 In buildings other than houses the efficiency of utilization of the heat supplied in the fuel may also vary widely. There will, in general, be less tendency in many larger buddings toward effective use for heating purposes of the beat which is normally lost from chimney, furnace, and piping surfaces, and, consequently, efficiency is seldom likely to be as high as in the case of many houses. The average fuel consumption of various types of ap proved gas-fired equipment has been obtained from a large number of heating systems.* Corresponding efficiencies of utilization over the heating season can be calculated from 169