Document Dvn1kJXZ36BbpQkNmkwOQN4La

394 CHAPTER 20 1948 Guide -plant. The resulting unit figure, by eliminating the outside temperature variable, indicates whether the operating efficiency 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.- Table 7. Heat Consumption Record for Comparison 1942-43 . Col. 1 Col. 2 Col. 3 Total Consumption Consumption For Heating Sept........... Oct-- ---Nov______ Dec__ ____ Jan.._ Feb............ Mar_ -- Apr__ -- May___ Tune.....-- July---------Aug........ 337.500 . 834,200 1,446,600 2,176,400 2,332,200 2,131,100 2,021,900 1,241,500 672.500 258,600 188,400 180,100 Total___ 13,821,000 Sept.......-- Oct.. --...... Nov........... Dec......... . 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 91,600 _______ 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 1,990 1,630 1,670 1,775 1,799 1,660 1,670 1,830 Col. 7 Lb/Dec Day/ M Cu Ft 0.575 . 0.970 0.982 0!804 0.822 0.888 0.885 0.818 0.822 0.905 ......... ' 167 410 '812 11120 1,044 1,111 1,021 875 ' 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 1943-44. If. for example, the heat consumption in March. 1943, is compared with that in_ March. 1944.* ** found that in the latter the steam consumption is 1799 -- 1760 = 39 lb less which is a decrease of 2.2 per cent. Some reasonable figure must be assumed for the process requirement and should be deducted from the amount shown in column 2. This would leave in column 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 consumption, corrected for outdoor temperature, and should be relatively constant 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 Estimating Fuel Consumption for .Space Heating 395 be measured in several different ways. It may be taken as the instan taneous 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. These figures are available for a number of buildings in Detroit; as shown in Table 85. These maximum demands were measured by an attachment on the condensation 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. Table 8. Building Load Factors and Demands of Some Detroit Buildings Building Classification Clubs and I-odges Hotels Printing.. .... .... Auto Sales and .Service Ranks _ . Department Stores . Theaters 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 of Dkuand peb (Houb) (Sq Ft o Equivalent In stalls!) Radiator Surface) 0.184 0.207 0.217 0.209 0.225 0.182 0.248 0.158 0.152 0.145 0.151 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 calcu lated steam radiator 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. Since values of U are not available for oil or coal, an assumed seasonal efficiency E must be used. Selection of a value for this E must be made with caution, for its use implies a meaning not commonly associated with the word efficiency and consequently is frequently misleading. The input of heat to a building consists not only of the energy in the fuel but that from occupants, the sun, appliances, processes, and all other sources. In many cases these make up, over a period, an important percentage of the total heat required, and if they are not taken into account a calculation of efficiency can show a figure over 100 per cent. For this and other reasons the actual seasonal efficiency is a difficult thing to determine. Published data are widely scattered and insufficient.