Honeywell AUTOMATIC CONTROL Engineering Manual page 59

This converts to:
0.848 x 60 minutes = 50.9 gallons per hour
Recalling that the steam added 11.6 Btu per pound of dry air,
the total heat added is:
714.3 x 11.6 = 8286 Btu per minute
This converts to:
8286 x 60 minutes = 497,160 Btu per hour
Summarized, a steam humidifier always adds a little sensible
heat to the air, and the Process Line B–C angles to the right of
the 90F starting dry-bulb line because of the added sensible
heat. When the process line crosses the moisture content lines
along a constant dry-bulb line, only latent heat is added. When
it parallels a constant, horizontal moisture line, only sensible
heat is added.
AIR WASHERS
Air washers are also used as humidifiers particularly for
applications requiring added moisture and not much heat as in
warm southwestern climates. A washer can be recirculating as
shown in Figure 19 or heated as shown in Figure 20. In
recirculating washers, the heat necessary to vaporize the water
is sensible heat changed to latent heat which causes the dry-
bulb temperature to drop. The process line tracks the constant
enthalpy line because no total heat is added or subtracted. This
process is called "adiabatic" and is illustrated by Figure 21.
Point A is the entering condition of the air, Point B is the final
condition, and Point C is the temperature of the water. Since
the water is recirculating, the water temperature becomes the
same as the wet-bulb temperature of the air.
SUPPLY FAN
Fig. 19. Recirculating Air Washer.
SUPPLY FAN
HWS
HWR
HEAT EXCHANGER
Fig. 20. Heated Air Washer.
PUMP
C2598
PUMP
C2599
49
PSYCHROMETRIC CHART FUNDAMENTALS
C
B
Fig. 21.
The next two psychrometric charts (Fig. 22 and 23) illustrate
the humidifying process using a heated air washer. The
temperature to which the water is heated is determined by the
amount of moisture required for the process. Figure 22 shows
what happens when the washer water is heated above the air
dry-bulb temperature shown at Point A. The temperature of
the water located at Point B on the saturation curve causes the
system air temperature to settle out at Point D. The actual
location of Point D depends upon the construction and
characteristics of the washer.
As the humidity demand reduces, the water temperature
moves down the saturation curve as it surrenders heat to the
air. This causes the water temperature to settle out at a point
such as Point C. The final air temperature is at Point E. Note
that the final air temperature is above the initial dry-bulb
temperature so both sensible and latent heat have been added
to the air.
C
E
A
Fig. 22.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
CONSTANT
ENTHALPY
LINE
A
C1843
SATURATION
CURVE
B
D
C1844