Document pBwqn50wRVEvYKvEjwm5nwOew

426 CHAPTER 17 1951 Guide' Solution. According to Table 6, a store would use 0.624 lb of steam per degree-day per 1000 cu ft heated space. . From Table 1, Philadelphia has 4739 degree-days per normal year. Inserting in Equation 4: F = 0.624 X 250 X 4739 = 739,284 lb of steam. Degree-Day as an Operating Unit The degree-day is also widely used as a means of comparing the efficiency of the fuel consumption of one period with another for the same building. Since the fuel consumption is proportional to the weather (degree-days), and since the periods to be compared may not have the same weather con- Table 7. Heat Consumption Recobd fob Coufabison Col. 1 Col. 2 Col. 3 Total Consumption Consumption Fos Heating Sept.. . . 337,500 Oct. . 834,200 1,446,600 *< Dec_______ 2,176i400 7? Jan.. ____ 2,332,200 o r* Feb_______ 2,131,100 i1 Mar.______ 2,021,900 (O Apr 1,241,500 May..... 672,500 H June__________ 258,600 H July.--------------- 188,400 Aug--------- .. 180,100 Total_____ 13,821,000 Sept__________ Oct.______ . Nov-------------- Dec.......... ......... O Jan. Feb___________ Mar______ 330,200 887,100 1,525,200 2,045,500 1,933,400 1,990,200 1,984,100 170,500 667,200 1,279,600 2,009,400 2,165,200 1,964,100 1,854,900 1,074,500 505,500 .9.1..,6.00 ------- .--------- ___________ 146,200 703,100 1,341,200 1,861,500 1,749,400 1,806,200 1,800,100 Col. 4 Avg Mean Temp. 65 53 44 25 22 28 31 43 55 .. -- _______ 61 52 39 28 30 30 31 Col. 5 Deg Days 65 F Base 146 339 641 1,233 1,297 1,106 1,032 647 303 50 Col, 6 Lb/Deg Day 1,170 1,966 1 QQft L630 1,670 1,775 1,799 1,660 1,670 1,830 _______ 167 410 812 1,120 1,044 1,111 1,021 875 1,718 1,653 1,660 1,670 1,624 1,760 Col. 7 Day/ M Cu Ft 0.575 0.970 0.804 0.822 0.888 0.885 0.818 0.822 0.905 0.431 0.845 0.815 0.817 0.825 0.800 0.868 If, forexample, the heat consumption in March, 1943, is compared with that in March, 1944, it will be found that in the latter the steam consumption is 1799 -- 1760 = 39 lb less which is a decrease of 2.2 percent. ditions, the comparison can be made only after the fuel consumptions have been computed on a comparable weather basis, that is, upon the actual number of degree-days occurring for a given month and year in the city under consideration. Since fuel consumption is proportional to the number of degree-days, plant operators frequently, compute each month the fuel burned pier degree-day by the heating plant. The resulting unit figure, by eliminating the outside tempierature variable, indicates whether the operatingefficiency ofthe plant is above or below the previous month or year. The figures in Table 7 illustrate a typical example of a method of using the degree-day for making heating comparisons for one building for two consecutive heating seasons. The heat quantity figures inserted are pounds of steam, but a similar comparison could be made using pounds of coal, gallons of oil, or cubic feet of gas. For such a comparison, a two-year record is often used, as shown in Table 7. The year under consideration may then be compared, month by month, with the previous year. Column 3, Consumption for Heating, would be used if the same fuel is used for heating and process steam; Some reason able figure must be assumed for the process requirement and should be deducted from the amount shown in column 2. This would leave in column Estimating Fuel Consumption for Space Heating 427 3 only the fuel' chargeable to heating. The degree-day values in column 5 are obtainable from the local Weather Bureau. Figures in column. 6 are obtained by dividing corresponding values in column 3 by the degree-days in column 5. The heating index in column 6 is, then, a figure of heat con sumption, corrected for outdoor temperature, and should be relatively con stant month by month. Column 7 in Table 7 may be used if the heat consumption is to be compared on a building volume basis with average values shown in Table 6. MAXIMUM DEMANDS AND LOAD FACTORS In one form of district heating rates, a portion of the charge is based upon the maximum demand of the building. The maximum demand may be measured in several different ways. It may be taken as the instantane ous peak or as the rate of use during any specified interval. One method Table 8. Building Load Factors and Demands of Some Detroit Buildings Building Classification Load Factor 0.318 0.316 0.287 0.263 0.255 0.238 0.223 0.203 0.158 0.138 0.126 - Lb o? Demand per (Hour) (Sq Ft or Equivalent In stalled Radiator Surface) 0.184 0.207 0.217 0.209 0.225 0.182 0.248 0.158 0.152 0.145 0.151 is to take the average of the three highest hours during the winter. These figures are available for a number of buildings in Detroit, as shown in Table 8.` These maximum demands were measured by an attachment on the con densation meter, and thereforerepresent the amounts of condensation passed through the meter in the highest hours, rather than the true rate at which steam is supplied.' There might be slight differences in these two quantities due to time lag and to storage of condensate in the system, but wherever this has been investigated it has been found to be negligible. The load factor of a building is the ratio of the average load to' the maximum load and is an index of the utilization. Thus, in Table 8, the theaters, operating for short hours, have a load factor of 0.126 as compared with the figure of 0.318 for clubs and lodges. SEASONAL EFFICIENCY The task of predicting fuel consumption within reasonably accurate limits is a simple one where sufficient experience data are available for the fuel in question. Such data can be analyzed to the point where average unit factors can be determined and expressed in such terms as, for example, cubic feet of gas actually burned per (square foot of calculated steam radia tor surface) (degree-day). The unit- U can be inserted directly in Equation 4 without reference to efficiency. Such experience factors are available for gas (see Table 2) and for district steam (Table 6), but not for coal or oil.