Handbook for heating and ventilating engineers . lant, it would be well to allow a small marginin excess so that one or two boilers may be thrown out ofcommission for repairs and cleaning without interferingwith the working of the plant. Case 2 seems to be the betterarrangement. Assuming 1800 total boiler horse-power wemight very well put in six 300 H. P. boilers arranged in threebatteries. 171. Cost of Heatlne from a Central Station (DirectFIrlngr):—It will be of interest in dhis connection to estimateapproximately the cost in supplying heat by direct firing toone square foot of hot water rad
Handbook for heating and ventilating engineers . lant, it would be well to allow a small marginin excess so that one or two boilers may be thrown out ofcommission for repairs and cleaning without interferingwith the working of the plant. Case 2 seems to be the betterarrangement. Assuming 1800 total boiler horse-power wemight very well put in six 300 H. P. boilers arranged in threebatteries. 171. Cost of Heatlne from a Central Station (DirectFIrlngr):—It will be of interest in dhis connection to estimateapproximately the cost in supplying heat by direct firing toone square foot of hot water radiation per year from theaverage central station. In doing this make the boiler as-sumptions to be the same as Art. 166. Take ooal at 13000B. t. u. per pound, 2000 pounds per ton, and a boiler effi-ciency of 60 per cent. Water enters the boiler at 155 degreesfrom the returns, and is delivered to the mains at 180 de-grees. From the value of the ooal as stated, we have15600000 B. t. u. per ton given off to the water. This is DISTRICT HEATING 259. POWER PLANT 118, 260 HEATING AND VENTILATION equivalent to heating 624000 pounds, or 74910 gallons, ofwater. If one ton of coal costs $ at the plant, we have 200 -f- 74910 = .0027 cents This represents the amount paid to reheat one gallon ofw^ater, or to supply one square fOOt of heating surface onehjour at an outside temperature of zero degrees. Take theaverage temperature for the seven cold months at 32 de-grees. This is the average for the coldest year in the twentyyears preceding 1910, as recorded at the U. S. Exp. Station,I^aFayette, Indiana. We then bave an average differencebetween the Inside and the outside temperatures in anyresidence of 70 — 32 = 38. This makes the formula forthe heat loss, Art. 28, reduce to 38 -f- 70 = .54 of its formervalue. Now, if It takes one gallon of water per square footof radiation per hour under maximum conditions, we havefor the seven months .54 X- 7 X 30 X 24 = 2722 gallons ofwat
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