Document 4JLxzYVJ8Mw1yw53pYNZ1bDkp

478 CHAPTER 18 : 1958 Guide Btu per lb 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 6: A building in Scranton, Pa. has a calculated heat loss of 240,000 Btu per hr based on an inside design temperature of 70 F and an outside design tempera ture of -- 10F. What will be the estimated normal seasonal anthracite or coke consumption for heating if 13,000 Btu per lb fuel is burned in a hand-fired boiler, with automatic control, at a seasonal efficiency of 80 percent, and what part of the total will be used during November, December, and January? Solution: From Table 6, U is 0.0444 of coal or coke per 1000 Btu per hr heat loss per degree-day. Correcting for the outside design temperature of --10 F from Table 3, the value of 17 is 0.875 X 0.0444 = 0.0389. From Table 2, D is 6218 and from the problem, N is 240. Substituting in Equation 4, F = 0.0389 X 240 X 6047 = 56,500 lb. Fuel used over any period is, according to the theory of the degree-day, propor tional to the number of degree-days during the period. From Table 2, the average numbers of degree-days for November, December, and January in Scranton are 693; 1057 and 1141 respectively, a total of 2953. The yearly total is 27,000, so that during these three months the estimated consumption is ... 2891 X 56,500 = 27,000 lb. 6047 Estimating Steam Consumption In estimating steam consumption the efficiency is generally assumed at 100 percent. If for low-pressure steam an average heating value of 1000 Btu per pound of steam is used, no correction is necessary. In comparing values from different cities, correction should be made for design tempera ture (see Table 3) when the unit figures are in terms of heat loss 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: H X 24 X D 1000 (6) where ,; F = pounds of steam required for estimate period. H = calculated heat loss, Btu per (hour) (degree difference). 24 = hours in one day. D - number of degree-days for the period of estimation. 1000 = Btu delivered per pound of steam condensed. 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 2, an average inside temperature of approximately 70 F is assumed throughout the period. If an average inside temperature other than approximately 70 F is to be used, the number of degree-days should be obtained for the new base. Example 7: An eight-story building in Pittsburgh is operated with a daytime temperature of 70 F. The calculated heat loss is 10,500 Btu per (hr) (degree temper ature difference). What is the estimated average yearly steam consumption building heating? Solution: Since the average inside temperature is approximately 70 F, the degree- . Estimating: Fuel Consumption for! Space^Heating 479 days from Table 2, based on 70 F maybe used. .Therefore, from Table;2, Pittsburgh has 5048 degree-days per normal season-1 Inserting in Equation 5: 10,500 X 24 X 5048 F= 1000 1,272,000 lb of steam. Consideration has been given to the difference in steam utilization of different types of buildings, and Table 7 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 aver ages, and for small groups in each type, the figures may need considerable modification to allow for local variations. It should be especially noted that the steam used for heating water for service is not included in the values given in Table 7. Table 7. Steam Consumption op Buildings with Various Types op Occupancy* Type of Building No. Bldgs Office........................... Office and Bank...... Offioe and Theater........... Office and Stores or Shops. Bank........... Department Store......... Stores.......... Loft............. ................................. Warehouse__ Hotel and Club . Apartment or RcsiHonre Theater........ Garage.......... Manufacturing ................................ Church..... Hospital.......... School...... Municipal or Federal $dge. Gym, Hall or Auditorium.................... 334 7 26 16 24 73 19 12. Average Volume Heated Space 1000 Cu Ft Steam fob -Heating Lb per DD per 1000 Cu Ft Average Houbs of Occufanct 2160 3000 1895 4950 ` 1615 0.577 1.230 0.412 0.617 12 1 13.1 12.9" 13.2 3400 0.385 11.1 2230 1795 1425 0.962 : 1350 <L'808 n"rfv? i.s 0.390 12l4. Principles of Economical Heating, National Association of Building Owners and Managers 70 ,z?mPje ? A store in Philadelphia with a heating.system designed-to maintain ectHr,118 j 6 ln F weather has 250,000 cu ft of heated space. What would be the unated average yearly steam consumption of purchased steam for heating? to Table 7, a store would use 0.624 lb of steam per degree-day fmrrJ i cu Seated space. From Table 2, Philadelphia has 4523 degree-days per normal year. Inserting in Equation 4: ; ^ F = 0.624 X 250 X 4523 = 706,000 lb of steam. Degree-Day as an Operating Unit Thof 6 fe^ee-day is also widely used as a means of comparing the efficiency Sine thUCf consumPt`on of one period with another for the same building. and'*16 b 1 consumPtion is proportional to the weather (degree-days), ditioSmCfb 6 Per*odstobe compared may not. have the same weather conbeen118' the cornPar^son cal1 be made only after the fuel consumptions have numhCOmf^on a comparable weather basis, that is, upon the actual under61 `degree-days occurring for a given month and year in the city consideration. Since fuel consumption is proportional to the number