334 



VENTILATION 



therefore, somewhat compressed, that is, the air in all the rooms 

 is under somewhat greater pressure than is the air outside the 

 building. Hence the name PLENUM meaning FULL. 



Figure 237 shows the usual construction of the plenum type 

 of heating and ventilating systems. The fresh air enters at 

 the window A. It then passes through a bank of steam 

 pipes called the TEMPERING COILS, or TEMPERING STACK, B. 

 Here the temperature of the air is raised to about 65F. It 

 then passes through a washer, a spray of water, (7, which 



FIG. 237. Showing the plenum system for warming and ventilating a 

 school building. A tempering stack is shown at the right, next (to the left) 

 is an air washer to insure pure and reasonably moist air, next is a fan or 

 blower, and following that a re-heater, which warms the air to any desired 

 temperature. 



washes the air removing all dust particles and increasing the 

 humidity. The air thus warmed to about 65, washed and 

 humidified, passes into the TEMPERED AIR ROOM, D. It then 

 passes into the BLOWER, E, which forces it, blows it, strongly 

 to the left. The upper two-thirds of the exit from the blower 

 contains another bank of steam pipes called the HOT COILS, or 

 RE-HEATER, F. Just beneath the hot coils is a horizontal par- 

 tition, or false floor. The air from the blower may pass through 

 the re-heater into the HOT ROOM, H, or it is equally possible 

 for it to pass beneath the false floor directly into the second 



