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410 CHAPTER 17 V . 1950 Guide The correction factor for --20 F outside design temperature from Table 5 is 0.778. Solving, 0.778 X 0.00476 = 0.00370. Making a further correction for'the heating value: 0.0037 X qD[) " 0.0036 gal per 1000 Btu per hr calculated heat loss per degree- day. From Table 1, the normal degree-days for Minneapolis are 7966. pressed in 1000 Btu, N is equal to 192. Substituting in Equation 4: F - 0.0036 X 7966 X 192 = 5506 gal. Since V is ex Estimating Coal or Coke Consumption Coal or coke consumption estimates are made by following exactly the same procedure as for oil. Values of U are given in Table 4 which only apply to an inside design temperature of 70 F. and an outside design tem perature of 0 F. A correction must be made for other conditions by use of the multiplying factors in Table 5. Data in Table 4 are based on 12,000 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 7. A building in Marquette, Mich., has an hourly heat loss at design conditions of 240,000 Btu per hr. 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 lb. fuel is burned at a 50 per cent sea sonalefficiency, and what 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 hr heat loss. " Cor recting for the outside design temperature of --20T 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, N is 240. 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 number 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: jjfv? 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 comparing values from-different cities, correction should be made for design tempera ture (see Table 5) when the unit figures are in terms of square feet of radia tion, 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 B X 24 X D 1000 (5) where * F = pounds of steam required for 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..'.. Estimating Fuel Consumption for Space Heating 411 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 throughout 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 temper atures of 70 F but allows night temperature to drop to not lower than 60 F. Its calcu lated heat loss is 10,500 Btu per (hr) (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: 10,500X24X5435 1,368,360 lb of steam. 1000 Table 6. Steam Consumption op Buildings with Various Types of Occupancy* Type of Building No. Bldgs. Average . Volume ' Heated Space 1000 Cu Ft Office........... .............. ............ Office and Bank Office and Printing.................... ........ Office and Theater .... Office and Stores or Shops_________ Department Store- Sfnrps.-- ---------------------- Hotel and Club___ Apartment or Residence___________ Theater.. Garage. Manufacturing Cthureh-- __ Hospital-- Municipal or Federal..... ................. .. Lodge, Gym, Hall or Auditorium____ Mtscellangnug-_______________i 334 49 8 7 26 16 63 73 63 24 73 51 22 13 19 9 4 8 16 12 7 2160 3000 1895 4950 1615 806 3400 310 865 2230 1795 1425 1240 1540 - 1350 656 3306 1115 3215 880 1387 Steam for Heating Lb per DD per 1000 Cu Ft Average Hours of Occupancy 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 0.592 0.587 0.390 0.479 12.1 13.1 17.7 12.9 13.2 ii.7 H.i 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 Eftnnnmieal Hwating, National Association ofBuilding Ovmert and Managers. Consideration has been given to the difference in 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 aver ages, and for small groups in each type, the figures may need considerable modification to aUow for local variations; It should be especially noted that the steam used "for heating hot water is not. included in the values given in Table 6. Example s. 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 wouldbe the esti mated average yearly steam consumption of purchased steam for heating? f