Document e7kJxnaQOeRg1V8DVwRbdge3E

432 CHAPTER 18 1953 Guide opening of windows, abnormal heating of the building, poor design of heat ing system, sun effect, and other variations. The Degree-Day Method is the more practical since it is based, in part, on actual consumption data. The presentation of the two illustrative estimating, methods will be pre ceded by a discussion of seasonal efficiency. SEASONAL EFFICIENCY The seasonal efficiency differs from the measured efficiency of the fuelfired heating unit because it is affected by the many minor sources of extraneous heat gain and-heat loss.: Throughout a season* useful heat is supplied to a building not only, by the heating unit, but also by the external surfaces of the heating unit, the flue pipe, and the chimney. In addition, heat is gained from lights, occupants, cooking and other appliances, and from the sun. Indeterminable amounts of heat are lost through radiation directly to basement or .utility-room walls and floors, from the heating unit, the distribution system, and the flue pipe, :from stand-by operation of the unit, from opening of doors and windows,'and from-faulty adjust ment and operation of the combustion unit. Fortunately, data which are : available permit the making of reasonable estimates of seasonal efficiency for residences. The average fuel consumption of various types of approved gas-fired equipment has been obtained from a large number of heating systems.1 .Corresponding seasonal efficiencies can be calculated from these data. They show a variation from approximately. 72 to; 88 percent, depending .upon the type and size of system.. Laboratory tests on a gas;conversion burner in a heating boiler operated with on and of cycles gave about 72 percent efficiency.1.; Other tests on coal-fired room heaters indicate sea sonal efficiencies of 65 to 75 percent, when the heat from the flue pipe was included,3 A survey of 30 residences in one locality showed a variation ;of 45 to 75 percent in utilization efficiency., depending upon the condition of the equipment and the fuel used.4 A summary3'6 of many tests in two research residences at the University . .of Illinois, using many fuels and systems, gave values of 67 to 90 percent for overall house efficiency (the ratio of the heat loss from the structure to the heat input to the unit for an average test day). -These data were used by the Small Homes Council1. of .the University of Illinois in a tabulation of the comparative costs of heating the same build ing with various fuels. . " ., '. ' The approximate seasonal efficiencies shown in Table 1. are suggested . as a guide. Table 1. Approximate Seasonal Efficiency Approximate Sea Approximate Sea . Type op Fuel-Burning Unit sonal Efficiency, Type of Fuel-Burninq Unit sonal Efficiency, Percent ,. Percent'- Gas, designed unit................... Gas, conversion unit................. Oil, designed unit..................... Oil, conversion unit.................. Bituminous coal, hand fired with controls............... ........ Bituminous coal, hand ' fired ,. without controls.................... Bituminous coal, stoker-fired... 75-80 60-80 65-80 60-80 50-65 40^60 50-70 Anthracite, hand-fired with controls.............................. Anthracite, hand-fired without controls...........\........ Anthracite, stoker-fired.......... Coke, hand-fired with con trols..................` ............... Coke, hand-fired .without con' trols__ _.............................. Direct electric heating........ 60-80 50-65 60-80 60-80 '50-65 .100 EstimatihgFuel Consumption for Space Heating ' .433'' CALCULATED HEAT LOSS METHOD In the Calculated Heat-Loss Method a constant average outdoor temper ature is assumed throughout the heating season.. This average tempera ture is. considerably above the design temperature given in Chapter 12. The method,becomes unreliable whenever data ori/the seasonal average temperature are not available for the particular locality. If the' length of time is shown over which the degree-day data apply in' the, particular locality, it is possible to calculate the average temperature from the definition of the degree-day (see Chapter 1). When this is done, the two meth ods described in this chapter become identical: The average temperature for the period October to April inclusive, is listed in Table 1, Chapter 12, ' for U. S. and Canadian cities. Computation , and Application In order to apply the Calculated Heat-Loss Method, the hourly heat loss from the building under maximum load, or design condition, is. com puted following the principles discussed in Chapters 9, .11, and 12, The fuel requirement is then computed by the equation . Hit - QN Eiu - QC (1) where F = quantity of fuel or'energy required (in the units in which C is expressed). H = calculated heat loss including infiltration loss, Btu per hour, during the design hour, based on l0 and U. t = average inside temperature maintained during heating period, Fahrenheit. = average outside temperature through estimate period, Fahrenheit (for cities with an Oct. 1-May 1 heating season--see Table 1, Chapter 12). id = inside design temperature, Fahrenheit (usually 70 F). to = outside design temperature, Fahrenheit (see Table 1 in Chapter 12). N = number of heating hours in estimate period (for an Oct. 1-May 1 heating season, 212 days X 24 hr = 5088). E -- efficiency of utilization of the fuel over the period, expressed as a decimal; not the efficiency at peak or rated load condition. C = heating value of one unit of fuel, or energy. . Although the assumption of an Oct. 1-May i heating season is reason ably accurate in the well-populated New York-Chicago zone, it is not valid as far north as Minneapolis nor farther south than Washington, D, C. and St. Louis. Consequently, it is suggested that allowance be made for this variation, especially in the far north or southern cities. . , Example 1: A residence building is to be heated to 70 F from 6 a.m. to 10 p.m. and 65 F from 10 p.m. to 6 a.m. The calculated hourly heat loss is 120,000 Btu per hour based on,70F inside at --lOFoutside. If the building is to be heated by metered steam, how many pounds would be required during an average heating season? Solution: The heating value of steam may be taken as 1.000 Btu per lb, and since it is purchased steam, the efficiency can be assumed.as 100 percent. Assume average outside temperature as 36.4 F. The average inside temperature is: (16 X 70) + (8 X 65) .= 68.3 F.