Handbook for heating and ventilating engineers . ge. There is some questionconcerning the advisability of doing this. Some prefer toinstall a high pressure steam heater, as in Art. 160, to beused independently of the exhaust steam heaters. Thisremoves all possibility of having excessive back pressureon the engine piston, as is sometimes the case where highpressure steam is admitted with the exhaust steam. It has been the experience of some who have operatedsuch plants that where more heat is needed than can besupplied by the exhaust steam, it is better to resort to heat-ing boilers and economi
Handbook for heating and ventilating engineers . ge. There is some questionconcerning the advisability of doing this. Some prefer toinstall a high pressure steam heater, as in Art. 160, to beused independently of the exhaust steam heaters. Thisremoves all possibility of having excessive back pressureon the engine piston, as is sometimes the case where highpressure steam is admitted with the exhaust steam. It has been the experience of some who have operatedsuch plants that where more heat is needed than can besupplied by the exhaust steam, it is better to resort to heat-ing boilers and economizers, than to use high pressure steamfor heating. 244 HEATING AND VENTILATION 160. Hleh Pressure Steam Heater:—When this heater Isused it Is located above the boiler so th<at all the condensa-tion freely draios back to the boilers by gravity as in In calculating the tube surface, use formula 82 withthe full value of the steam and the steam temperatureschanged to suit the increased pressure. Such a heater asthis gives good Fig. 117. 161. Circulating Pumps:—Two type& of pumps are Ingeneral use: centrifugal and reciprocating. Each type issomewhat limited in its operation. The centrifugal pumphas difficulty in operating against high heads and the recip-rocating pump is very noisy when running at a high pistonspeed. Since each type is in successful operation in manyplants, no comparisons will be made between them furtherthan to say that the former, being operated by a steam en-gine, may be run more economically than the latter becauseof the possibilities of using the steam expansively. It will DISTRICT HEATING 245 be noted, however, that this same steam is to be used in theexhaust steam, heaters for warming the circulating- waterand hence there would be little, if any, direct loss from thissource in the use of the reciprocating pump. Having given the maximum amount of water to becirculated per hour, consult trade catalogs and select thenumber of pumps and t
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