. Power, heating and ventilation ... a treatise for designing and constructing engineers, architects and students. can be determinedin any particular case by computing the saving in fuel by the useof a condenser, taking into account the interest and depreciationon the first cost of the condensing apparatus, and the cost ofwater, if it must be purchased, and comparing it with the cost ofheating with live steam. Usually, however, in the case of office buildings and institu-tions, and commonly in the case of shops and factories, especially EXHAUST STEAM HEATING 171 in northern latitudes, it is ad
. Power, heating and ventilation ... a treatise for designing and constructing engineers, architects and students. can be determinedin any particular case by computing the saving in fuel by the useof a condenser, taking into account the interest and depreciationon the first cost of the condensing apparatus, and the cost ofwater, if it must be purchased, and comparing it with the cost ofheating with live steam. Usually, however, in the case of office buildings and institu-tions, and commonly in the case of shops and factories, especially EXHAUST STEAM HEATING 171 in northern latitudes, it is advantageous to use the exhaust forheating, even if a condenser is installed for summer use only. Effect of Back-Pressure.—The principal objection to the useof exhaust steam for heating has been the higher back pressurerequired on the engine, resulting in a loss of power nearly pro-portional to the ratio of the back pressure to the mean effectivepressure. There are two ways of offsetting this loss; one byraising the initial or boiler pressure, and the other by increasingthe cut-off of the engine. BY-PASSVALVE. Fig. 120. Float Trap. Fig. 121. Bucket Trap. Engines are usually designed to work most economically at agiven cut-off, so that in the majority of cases, it is undesirable tochange it to any extent. Raising the boiler pressure, on the otherhand, is not so objectionable if the increase amounts to only afew pounds. To Offset Back Pressure.—The necessary change in eitherinitial pressure or cut-off to offset a given rise in back pressureis easily obtained. Computations for an engine having a clearance of 5 per cent,supplied with steam at 80 pounds pressure and cutting off at ^4stroke, show that raising the back pressure 3 pounds calls for acorresponding increase of only 5 pounds in the boiler pressure tomaintain the same power of the engine. The indicator card shows a back pressure of about 3 poundswhen an engine is exhausting into the atmosphere, so that an in-crease of 3 p
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectventilation, bookyear
