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Heating Ventilating Air Conditioning Guide 1939 Predictions of fuel consumption are generally based on the average number of degree-days which have occurred over a long period of years and such averages, by months, on a 65 F base, are given by months and heating season totals, for various United States and Canadian cities in Table 3. In general, attempts to apply the degree-day method to fue]' consumptions over a period of less than a month are of questionable value. Formula for Degree-Day Method The general formula for predicting fuel consumption by the Degree- Day Method is: F= UX NXD (3) 1 where F = fuel consumption for the estimate period. U = unit fuel consumption, or quantity of fuel used per degree-day per building load unit. N = number of building load units. D = number of degree-days for the estimate period. i Values of D for use in Equation 3 are given in Table 3. Values of N depend on the particular building for which the estimate is being pre pared and must be found by surveying plans, by observation, or by measurement of the building. Values of U for use in this equation are the Unit Fuel Consumptions per Degree-Day and are obtained as a result of the collection of operating information. Certain of this information is presented later but before referring to these data attention is directed to the nature of the unit. Table 2. Base Temperature for the Degree-Day3 Tm o? BuildtNa Office....................... ......................................... ............. Office and Bank. .......................................... .. ..... Bank.................................. ........................................... Office and Telephone Exchange............................ Office and Stores......... ........................................... Stores. ......... .......... ............................................... Department Stores.................................................... Hotels................................................................ >.......... Apartments...... ........................................................... Residences. ......................................................... Clubs................................ .......................................-- Lodges--................................ ................... ....... :......... Theatres.................................... ................................... Churches............ .......................................... r. Garages......................................................................... Auto Sales and Service.____________ , Newspaper and Printing,.............. .......................... Warehouse and Loft. ______ i Office and Loft...... ..................................................... Manufacturing............... ............................................ Average for 163 Buildings________________ No. or Buildings Akaltzed* 60 4 3 2 6 11 12 7 14 8 4 5 3 2 2 4 3 3 2 8 Temperature F CobRESPONDS TO ZERO Steam Consumption 66.2 65.8 66.2 65.5 67.4 64.0 64.3 66.5 68.8 66.9 65.5 64.9 67.6 65.8 64.8 . 61.2 67.7 67.7 65.2 65.4 66.0 F i i: Report of' Commercial Relations Committee, Proceedings, National District-Heating Association, 1932. 240 Chapter 12. Heat and Fuel Utilization Unit Fuel Consumptions per Degree-Day The quantity of fuel used per degree-day in a given heating plant can he reduced to a unit basis in terms of quantity of fuel (or steam) per dwrree-day per square foot of radiator, per cubic foot of heated building ^ce or per thousand Btu hourly heat loss at design conditions. A less fluently used basis is quantity of fuel per degree-day per square foot of "r flow area. In fact any convenient unit can be used to relate the con sumption to the degree-day and to the building. The choice of these units requires explanation and some discrimination and judgment. The use of heated space in preference to the gross building cubage used by architects is obviously more accurate for this purpose. The architects' cubage includes the outer walls and certain percentages of attic and basement space which are usually unheated. The net heated space is usually about 80 per cent of the gross cubage and can be calcu lated from the latter if it cannot be measured. The cubical content is somewhat inaccurate as a basis of comparison due to differences in types of construction, exposure, and ratio of exposed area to cubical contents. Use of equivalent radiator surface figures is fundamentally the same as using a calculated heat loss and therefore units in terms of fuel per degreeday per equivalent square foot of calculated radiator surface, per 1000 Btu of calculated heat loss, or per Btu of heat loss at design conditions are all of equal accuracy and desirability. It is doubtful if installed radiator surface as determined by count should be used at all. Radiator units are also of questionable value where there is fan coil surface or warm . air systems. In view of all these considerations it is believed that the unit based on thousands of Btu of hourly calculated heat loss for the design hour is probably the most desirable although the one most widely used seems to' be units of fuel (or heat) per degree-day per square foot of equivalent direct radiator surface. 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 (IT) for gas are given in Table 4 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 conditions. For other design conditions corrections must be made as given in Table 5. Estimates for industrial buildings where low inside temperatures are maintained cannot be made from this table. The factors in Table 4, as corrected if necessary, are satisfactory for regions having 3500 to 6500 degree-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 -or deduction in these cases is recommended byrAmerican Gas Association publications. '' - For gas heating values other than those given In Table 4, simply interrpolate or extrapolate. It will also be noted that Table 4 applies only to 241 "1