Document 3Q0q5Xw4dqBzKv8rRDQye4pka

224 Chapter 11_________________________ 1945 Guide . ---using-the degree-day-for makifigTieating comparisons forone-building for, two consecutive heating seasons. The heat quantity figures inserted are pounds of steam, but a similar comparison could be made using pounds of coal, gallons of oil, or cubic feet of gas. For such a comparison, a two-year record is often used, as shown in Table 8. The year under consideration may then be compared, month /by month, with the previous year. Column 3, Consumption for Heating, would be used if the same fuel is used for heating and process steam. Some reasonable figure must be assumed for the process requirement and should be deducted from the amount shown in column 2. This would leave in column 3 only the fuel chargeable to heating. The degree-day values in column 5 are obtainable from the local Weather Bureau: Figures in column 6 are obtained by dividing corresponding values in column 3 by the degree days in column 5. The heating index in column 6 is, then, a figure of heat consumption, corrected for outdoor temperature, and should be relatively constant month by month. Column 7 in Table 9. Building Load Factors and Demands of Some Detroit Buildings BtnLDiNQ Classification Load Factor Clubs and Lodges:............................ ........................... Hotels...... Printing.................................... ....................... Offices . Apartments................ .................................. .......... Retail Stores Churches... Department Stores Theaters 0.318. 0.316 0.287 0.263 0.255 0.238 0.223 0.203 0.158 0.138 0.126- Lb or Demand pee Houb psa Sq Ft of Equiyalbnt Installed Radiator Surface 0.184 0.207 0.217 0.209 0.225 0.182 . 0.248' 0.158 0.152 0.145 0.151 Table 8 may be used if the heat consumption is to be compared on a building volume basis with average values shown in .Table 7. MAXIMUM DEMANDS AND LOAD FACTORS In one form of district heating rates, a portion of the charge is based upon the maximum demand of the building. The maximum demand may be measured in several different ways. It may be taken as the instan taneous peak or as the rate of use during any specified interval. One method is to take the average of the three highest hours during the winter. These figures are available for a number of buildings in Detroit, as shown in Table 96. These maximum demands were measured by an attachment on the condensation meter and therefore represent the amounts of condensation passed through the meter in the highest hours, rather than the true rate at which steam is supplied. There might be slight differences in these two quantities due to time lag and to storage of condensate in the system, but wherever this has been investigated it has been found to be negligible. The load factor of a building is the ratio of the average load to the maximum load and is an index of the utilization. Thus, in Table 9, the The Heat Requirements of Buildings, by J. H. Walker and G. H. Tuttle (A.S.H.V.E. Transactions, Vol. 41. 1935, p. 171).- Estimating Fuel Consumption_____________________ __________________________________________ 22S. theaters, operating for short hours, have a loid factor of 0.126 as compared with the figure of 0.318 for clubs and lodges. SEASONAL EFFICIENCY The task of predicting fuel consumption within reasonably accurate limits is a simple one where sufficient experience data are available for the fuel in question. Such data can be analyzed to the point where average unit factors can be determined and expressed in such terms as, for example, average gallons of oil actually burned per square foot of calculated steam radiator surface per degree-day. The unit U can be inserted directly in Equation 2 without reference to efficiency. Such experience factors are available for gas (see Table 3) and for district steam (Table 7), but not for coal or oil. Since values of U are not available for oil. or coal, an assumed seasonal efficiency E must be used. Selection of a value for this E must be made with caution, for its use implies a meaning not commonly associated with the word efficiency and consequently is frequently misleading. The input of heat to a building consists not only of the energy in the fuel but that from occupants, the sun, appliances, processes, and all other sources. In many cases these make up, over a period, an important percentage of the total heat required, and if they are not taken into account a calculation of efficiency can show a figure over 100 per cent. For this and other reasons the actual seasonal efficiency is a difficult thing to determine. Published data are widely scattered and insufficient. From the available published material it is found that the seasonal effi ciency varies over a wide range, depending on the fuel used, and it varies widely even for a given fuel. For example, in a recent survey of 30 houses in one locality there was found a variation of from 45 to 75 per cent in the utilization efficiency depending on the fuel7. 7Heat Losses and Efficiencies of Fuels in Residential Heating, by R. A. Sherman and R. C. Cross (A.S.H.V.E. Transactions, Vol. 43, 1937, p. 185).