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382 CHAPTER 20 1946 Guide Table 2. Unit Fuel Consumption Constants (/) foe Gas3 Based on OF Outside Temperature, 70 F Inside Temperature, and 8-Hour Reduction to 60 F. Hot Water Heating Value or Gar Btu peb Cu Ft .Cu Ft Gas per Degree-Day per Sq Ft Radiator Up to 500 Sq Ft 500 to 1200 Sq Ft Over 1200 8q Ft 500 535 800 1000 0.142 0.132 0.089 0.071 0.135 0.126 0.085 0.068 0.128 0.120 0.081 0.065 Steam . ' Warm Aih Cu Ft Gas per Degree-Day pex 8q Ft Baoiator Up to 500 8q Ft . 300 to 700 Sq Ft Over 700 Sq Ft Cu Ft Gas per Degree-Day per 1000 Btu Hourly Design Heat Loss Gravity Fail Systems 0.242 0.226 0.151 0.121 0.231 0.215 0.144 0.115 0.220 0.206 0.137 0.110 0.855 ' 0.800 0.534 0.428 0.820 0.766 0.513 0.410 1 Therm 100.000 Btu Gas Consumption in Therms per Degree-Day 0.000708 0.000675 0.000642 0.00121 0.00115 0.00110 0.00428 0.00109 Abstracted from Comfort Heating, American Cos Association. 1938. Table 3. Unit Fuel Consumption3 Constants (/) foe OiLb Based onO F Outside Temperature, 70 F Inside Temperature, and 8-Hour Reduction to 55 F.' Unit ErriciEKcr w Pee Cent 40 50 60 70. 80 Gal Oil per Sq Ft Steam Radiator.. 0.00172 0.00137 0.00114 0.00098 0.00086 Gal Oil per Sq Ft Hot Water Radiator........ .............. 0.00108 0.00086 0.00072 0.00062 0.00054 Gal Oil per 1000 Btu per Hour Heat Loss. .... ...... 0.00715 0.00571 0.00476 0.00409 0.00358 Baaed on a heating value of 140,000 Bin per gallop. ^Abstracted by permission from Degree-Day Handbook (Second Edition. 1037), by C. Strock and C. H. B. Hotchkiss. Table 4. Unit Fuel Consumption3 Constants (U) for Coal1* Based on 0 F Outside Temperature, 70 F Inside Temperature, and 8-Hour Reduction to 55 F. Unit 40 Lb Coal per Sq Ft Steam Radiator.. 0.0200 Lb Coal per Sq Ft Hot Water Radiator. _ . ................. 0.0125 Lb Coal per 1000 Btu per Hour Heat Loss. . ........ 0.0825 EmcBNcr m Per Cent 50 0.0160 60 0.0133 70 0.0114 80 0.0100 0.0100 0.0084 0.0072 0.0063 0.0666 0.0550 . 0.0471 .0.0412 Based on a heating value of 12.000 Btu per pound. _ ^Abstracted by permission from Detree-Day Handbook, (Second Edition, 1937), by C. Strock and C. H. B. Hotchkiss. Estimating Fuel Consumption for Space Heating 383 equivalent direct radiator surface. The equivalent heating load for the hot water supply is not included in the latter unit, but it generally includesthe piping load. Since this unit is the one most widely used at present the unit fuel con sumptions given in succeeding paragraphs of this chapter make use of this unit to a considerable extent, although it should be understood that most of these units of consumption can be transposed as desired. Estimating Gas Consumption Values of the Unit Fuel Consumption Constant (/) for gas are given in Table 2 for various gas heating values, and different types and sizes of heating plants. They are based on an inside design temperature of 70 F and an outside design temperature of 0 F and apply only to these con ditions. For other outside design conditions corrections must be made as given in Table 5. The factors in Table 2, as corrected if necessary, are satisfactory for regions having 3500 to 6500 degrfee-days per heating season.- In regions with less than 3500 degree-days the unit gas consumption is higher than given; where over 6500, the unit is less than given. Ten per cent addition Table 5. Coeeection Factoes foe Outside Design Tempeeatuees3 Outside Design Temp. F Deg___ -20 Correction Factor.------ ------- , 0.778 -10 0.875 0 1.000 + 10 1.167 20 1.400 The multipliers in Table 5. which are high for mild climates and low for cold regions are not in error as might appear. The unit figures in Tables 2,3. and 4 are per square foot of radiator or thousand Btu heat loss per degree-day. For equivalent buildings and heating seasons, those in warm climates have-lower design heat losses and smaller radiator quantities than those in cold cities. Consequently, the unit figure, in quantity of fuel per square foot of radiator per degree-day, is larger for warm localities than for colder regions. Since the northern cities have more radiator surface per given building and a higher seasonal degree-day total than cities in the south, the total fuel per season will be larger for the northern dty. or deduction in these cases is recommended by A .G.A. publications. Esti mates for industrial buildings where low inside temperatures are main tained cannot be made from this table. For gas heating values other than those given in Table 2, simply inter polate or extrapolate. It will also be noted that Table 2 applies only to small installations. In general the larger the installation the smaller the unit gas consumption becomes and the values in the table should be used with care, if at all, in large gas-buming installations. Example 6. Estimate the gas required to heat a building located in Chicago, III., which has 6287 degree-days and a gas heating value of 800 Btu per cubic foot. The calculated heating surface requirements are 1000 sq ft of hot . water radiation based on design temperature of --10 F and 70 F. Solution. From Table 2, the fuel consumption for a design temperature of 0 F with 800 Btu gas is found to be 0.085 cu ft of gas per degree-day per square foot of hot water radiation. From Table 5, the correction factor is 0.875 for --10 F outside design tem perature, hence 0.875 X 0.085 = 0.07438. By Equation 4, F = 0.07438 X 1000 X 6287 = 467,000 cu ft. Estimating Oil Consumption Unit fuel consumption factors for oil, similar to those for gas in Table 2, are given in Table 3. The factors in Table 3 apply only to an inside design temperature of 70 F and an outside design temperature of OF. For other outside design temperatures, the constants in Table 3 must be multiplied by the values in Table 5 as explained under Estimating Gas Consumption.