Document ExRgxjn210b9aywObeB57DYej

392 CHAPTER 20 1948 Guide pound coal and for other heating values of coal they must be multiplied by the ratio of 12,000 divided by the heating value of fuel used. Example 7. A building in Marquette, Mich., has an hourly-beat loss at design con ditions of 240,000 Btu per hour. Based on an inside design temperature of 70 F and an outside design temperature of- -- 20 F, what will be the estimated normal seasonal coal consumption for heating if 12,000 Btu per pound fuel is burned at a 50 per cent seasonal efficiency, and ryhat part of the total will be used during November, December, and January? Solution. From Table 4, U is 0.0666 lb of coal per 1000 Btu per hour heat loss. Cor recting for the outside design temperature of --20 F from Table 5, the value .of U is 0.778 X 0.0666 = 0.0518. From Table 1, D is 8745 and from the problem, iVis240. Substituting in Equation 4: F = 0.0518 X 240 X 8745 = 108,718 lb. Fuel used over any period is, according to the theory of the degree-day, proportional to the number 'of degree-days during the period. From Table 1, the average numbers of degree-days for November, December, and January in Marquette are 926, 1306, and 1465, a total of 3697. The yearly total is 8745, so that during these three months the estimated consumption is: |f| X 108,718 = 45,961 lb. Estimating Steam Consumption In estimating steam consumption the efficiency is generally assumed at 100 per cent. If for low pressure steam an average heating value of 1000 Btu per pound of steam is used no correction is necessary. In com paring values from different cities, correction should be made for design temperature (see Table 5) when the unit figures are in terms of square feet of radiation but not when the values are in terms of building volume or floor space. Where the heat loss is calculated, in Btu per (hour) (degree difference in temperature) the simple Equation 5 may be used : F H X 24 XD 1000 where F -- pounds of steam required lor estimate period. H = calculated heat loss, Btu per (hour) (degree difference). D = number of degree days for the period of estimation. 1000 = Btu delivered per pound of steam condensed. (5) In this method the number of degree-days automatically takes care of average inside and outside temperature difference. When degree days are taken from Table 1, an average inside temperature of approximately 65 F is assumed throughput the period. If an average inside temperature other than approximately 65 F is to be used, the number of degree-days should be obtained for the new base. Example 8. An eight story building in Pittsburgh maintains daytime temperatures of 70 F but allows night temperature to drop to not lower than 60 F. Its calculated heat loss is 10,500 Btu per (horn-) (degree temperature difference). What is the estimated average yearly steam consumption for building heating? Solution. Since the average inside temperature is approximately 65 F, the degreedays from Table 1, based on 65 F may be used. Therefore, from Table 1, Pittsburgh has 5430.degree-days per normal season. Inserting in Equation 5 10,500 X 24 X 5430 1,000 136,836 lb of steam. Estimating Fuel Consumption for:Space Heating 393 . .Consideration has been given to the difference m .steam utilization of different types of buildings and Table;6 shows,actual .average units' for these various types. These figures were obtained .from operating results in 896 buildings located in. all sections of the . United States- Being averages, and for small groups in. each, type, the. figures may need con siderable modification to allow for'local'variations. It.should be especially noted'that the steam used for heating hot water is.hpt included in the values`given in Table 6. : _, Example 9.. A store in Philadelphia, with a heating system designed to maintain 70 F ' inside in O F Weather has 250,000 cu ft of heated space. What would be the estimated average yearly steam consumption of purchased steam for heating?- Table 6. Steam Consumption op Buildings with-Various Types op Occupancy' Type'op. Building ' - -No.. - Bldgs. Office__ . Office and Bank____ .... . Office and Printing___ Office and Theater Office and Stores or ShopsJ.__:. Bank___ . _ `. Department Store............ Stores___ Loft Warehouse__ Hotel and Club . . Apartment or Residence_________ :__ Theater ................ Garage Manufacturing........... Chtirch... .......... Hospital School........... Municipal or Federal__ ;___ Lodge, Gym, Hall or Auditorium Miscellaneous : 334 49 ... 8 7 26, 16 63 73. 63 24 73 51 22 13 19 9 4 8 15 12 7. Average Volume Heated " Space 1000 Cu Ft ` Steam poa ' Heating' Average ,' ^Houbs 6p~' ' Lb per DD ' Occupancy per 1000 Cu Ft 2160 3000 .1895. . .4950 Y : 1615 806 . 3400 310 865 2230 . 1795 1425 1240 1540 1350 656 3306 1115 . 3215 880 1387 0.685 0.577 1.230 0.412 ; 0.617 0.786 : , . 0.385 0.624 0.588 0.459 . 0.990 0.962 0.482 0.202 : 0.808 . 0.532 1.194 - 6.592 0.587 0.390 0.479 12.1 13.1 17.7 12.9 . 133 ; 11.7' . . 11.1 . 10.4 : \ 10.0 - 9.4 ' . 22.3 21.8 : 12.9 . 21.4 ' 9.5 : 7.9 22.0 . 11.5 : - 15.6 . 12.4 21.4 - Principles of Economical Heating, National Association pf Building Owners and Managers. 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: 1 * F = 0.624 X 250 X 4739 = 739,284 lb of steam : . A;,: 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/or 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 conditions, 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