requirements, and yet use the capacity of the plant but a small part of the total time, as developed in the next two sections.



Plotting an atmospheric temperature curve, based on Weather Bureau records, upside down, so that a decline in temperature will go upwards, as shown in Figure 10, a graphical index of the consumer's capricious demand for heating service is obtained. The maximum demands are at the peaks of the curve and are, therefore, called peak loads.

Referring to Figure 10, note there are only nine peak demands where temperatures were 15° and only one were temperature was under 9°. The peak demand requires about one-third of the heating equipment and is used only about one and one-half per cent of the total 8,760 hours of the year.



For a number of years an eight-room brick house, 29 feet by 34 feet – which would be an average size – has been heated exclusively with gas. The room-heating equipment is a hot-air furnace with 80 per cent efficiency; the water heater will run about 80 per cent efficiency. For room heating, water heating, cooking, and burning the garbage, this house requires:
                                                    


The annual plant capacity for the 8,760 hours in the year just to meet the maximum hourly demands equals 8,760 by “1,000 cubic feet” or 8,760 “1,000 cubic feet.” The 560 “1,000 cubic feet” actually used, therefore, represents 6 ½ per cent of the total 8,760 “1,000 cubic feet” capacity needed to meet the peak demand. Therefore, the annual sales represent 6 ½ per cent of the total plant capacity that must be held in readiness to serve and meet the peak-load conditions.

The maximum hour peak of 1,000 cubic feet an hour does not occur every winter; in fact, has not occurred for two years. About 600 cubic feet an hour represents the maximum hourly demand of the usual winter, but when the extreme demand does come, if the gas service is unable to meet it, there will be an immediate complaint of the gas shortage and poor service.


 



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