edge piling is
greatly superior to flat piling where the heating system is below the
lumber.

From experiments and from study of conditions in commercial kilns the
idea was developed of so arranging the parts of the kiln and the pile
of lumber that advantage might be taken of this cooling of the air to
assist the circulation. That this can be readily accomplished without
doing away with the present features of regulation of humidity by
means of a spray of water is clear from Fig. 30, which shows a
cross-section of the improved humidity-regulated dry kiln.

In the form shown in the sketch a chamber or flue B runs through the
center near the bottom. This flue is only about 6 or 7 feet in height
and, together with the water spray F and the baffle plates DD,
constitutes the humidity-control feature of the kiln. This control of
humidity is affected by the temperature of the water used in the
spray. This spray completely saturates the air in the flue B at
whatever predetermined temperature is required. The baffle plates DD
are to separate all entrained particles of water from the air, so that
it is delivered to the heaters in a saturated condition at the
required temperature. This temperature is, therefore, the dew point of
the air when heated above, and the method of humidity control may
therefore be called the dew-point method. It is a very simple matter
by means of the humidity diagram (see Fig. 93), or by a hygrodeik
(Fig. 94), to determine what dew-point temperature is needed for any
desired humidity above the heaters.

Besides regulating the humidity the spray F also acts as an ejector
and forces circulation of air through the flue B. The heating system H
is concentrated near the outer walls, so as to heat the rising column
of air. The temperature within the drying chamber is controlled by
means of any suitable thermostat, actuating a valve on the main steam
line. The lumber is piled in such a way that the stickers slope
downward toward the sides of the kiln.

M is an auxiliary steam spray pointing downward for use at very high
temperatures. C is a gutter to catch the precipitation and conduct it
back to the pump, the water being recirculated through the sprays. G
is a pipe condenser for use toward the end of the drying operation. K
is a baffle plate for diverting the heated air and at the same time
shielding the under layers of boards from direct radiation of the
steam pipes.

The operation of the kiln is simple