Handbook for heating and ventilating engineers . inglyincreased radiation loss. Fluctuations of temperature, there-fore, are not only undesirable for the occupants, but theyare very expensive as well. 180. Principles of the System:—Temperature control maybe divided into two general classifications,—small plantsand large plants. The control for small plants, i. e., such plantsas contain very few heating unitSj is accomplished by regu-lating the drafts by special dampeo-s at the combustionchamber. This method controls merely the process of com-bustion and has no especial connection with individu
Handbook for heating and ventilating engineers . inglyincreased radiation loss. Fluctuations of temperature, there-fore, are not only undesirable for the occupants, but theyare very expensive as well. 180. Principles of the System:—Temperature control maybe divided into two general classifications,—small plantsand large plants. The control for small plants, i. e., such plantsas contain very few heating unitSj is accomplished by regu-lating the drafts by special dampeo-s at the combustionchamber. This method controls merely the process of com-bustion and has no especial connection with individual reg-isters or radiators, it being assumed that a rise or fall oftemperature in one room is followed by a correspondingeffect in all the other rooms. This method assumes that allthe heating units are very accurately proportioned to therespective rooms. The dampers are operated thr>ough a sys-tem of levers, which system in turn is controlled by a ther-mostat. Fig. 120 shows a typical application of such regu- 272 HEATING AND VENTILATION. Figr. 120. latlon. This may be ap-plied to any system ofheat. In addition to thethenmostaitic controlfrom the room to thedamper, as has just beenmentioned, closed hotwater, steam and vaporsystems should have ^ ^ regulation from the ^—CM pressure within theboiler to the draft. Oc-casionally in the mjorn-i n g- the pressure Ineither system may be-come excessive beforethe house is heatedenough for the thermo-stat to act. With such additional -regulation no hot water heater or steam boilerwould be forced to a dangerous pressure. Fig. 121 shows athermostat manufactured by the Andrews Heating Co., Min-neapolis. The complete regulator has in addi-tion to this, two cells of open circuit baitteryand a motor box, all of which illustrate verywell the thermostatic damper control. The thermostat operates by a differentialexpansion of the Iwo different metals com-posing the spring at the top. Any change Intemperature causes one of the metals to ex-
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