Document r3zJyjeLyLO3Nnm3MNq08LgG

-430 ' CHAPTER 20 1949 Guide Solution. According to Tabled, 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 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 per degree-day by the heating plant. The resulting unit figure, by eliminating the outside temperature variable, indicates whether the operatingefficiency of the 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 Table 7. Heat Consumption Recobd fob Compabison Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 .> Total Consumption Consumption For Heating Avg ... Deg Days Mean 65 F .Temp. ' Base Sept_______ 337,500 Oct____ :__ 834,200 Nov.____;__ 1,446,600 Dec............ 2,176,400 % Jan.;___ ,__ 2,332,200 Feb.-- J ... 2,131,100 Mar.______ 2,021,900 CO Apr.'.__________ 1,241,500 . May________ i. 672,500' ttj - June___________ 258,600 July----------- 188,400 'Aug...-------- 180,100 Total-;.- 13,821,000 170,500 667,200 1,279,600 2,009,400 2,165,200 1,964,100 1,854,900 1,074,500 . 505,500 91,600 ..... . _____ 65 53 44 2522 28 .' 31 v 43 _5_5_ . 146 . 339 641 1,233 1,297 -1,106 1,032 647 303 50 ------;. ; -..... ____ . _.... 330,200 Oct.___ ____ 887; 100 rt2 Nov.--__ 1,525,200 Dec.^;.i___ 2,045,500 s Jan.__ _____ .1,933,400 Feb......... _.. 1,990,200 Mar..~ 1,984,100 : ` 146,200 703,100 1,341,200 1,861,500 .1,749,400 1,806,200 1,800,100 61 167 52 410 39 812 28. 1,120; . . 30 .. 1,044 30 1,111 ; 31 1,021 Col 6 Col. 7 Lb/Deg Day Lb/Deg Day/ M Cu FT 1,170 1,966 1,990 1,630 1,670 1,775 1,799 1,660 1,670" 1,830 ' ..... 0.575 0.970 0.982 0.804 0.822 0.888 0.885 0.818 0.822 0.905 -- ..... 875 1,718 1,653 1,660. 1,670 1,624 1,760 0.431 0.845 0.815 0.817 , 0.825 0.800 0.868 " ' >If, for example, the heat consumptionin March, 1943, ia 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 2J per cent, - Estimating Fuel Consumption for Space Heating 431 Table 8`. Building Load Factoes and Demands of Some Detboit Buildings Building Classification Retail Stores.______ _____________ .__ ----- --------- Department Stores..___________ ____ ------------ - , .Load Factor La op Dehand peb (Hour) (So Ft of Equivalent In stalled Radiator Surface) 0.318 0.316 0.287 0.263 0.255 0.238 0.223 0.203 0.158 0.138 0.126 0.184 0.207 0;217 0.209 0.225 0.182 0.248 0.158 0.152 0.145 0.151 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 com 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 is to take the average of the three highest hours during: the winter. Thesefigures are available for a number of buildings in Detroit, as shown in Table 85. These maximum demands were measured by an attachment on the con densation meter and therefore represent 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.