VITA TECHNICAL BULLETIN
CONVECTION GRAIN DRYER
This Technical Bulletin contains plans and information for a
natural convection solar grain dryer.
The design is best
suited for use in tropical or other climates where relative
humidity of more than 80 percent and temperatures about 27
are not uncommon.
The dryer was designed and tested as a corn dryer since corn
is one of the heaviest of grains.
The dryer's proven effectiveness
with corn should be reflected when it is used for
smaller, lighter grains.
The design consists of a primary
collector, a drying bin area, a secondary collector, and a
chimney. The dryer
is capable of drying, in eight hours,
enough grain to fill a 55-gallon drum.
This dryer was developed and tested by University of
Maryland students under the supervision of VITA Volunteer
Clifford L. Sayre, Jr. members of the study were:
J. Chesnutis, P. Christis, W. Flensburg, T. Morse, and
Please send testing results, comments, suggestions, and
requests for further information to:
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 * Fax:
Technical Bulletins offer do-it-yourself
technology information on a
variety of subjects.
Bulletins are idea generators
intended not so much to provide a definitive
answer as to guide the user's
thinking and planning. Premises
sound and testing results are provided,
Evaluations and comments based on each
user's experience are requested.
incorporated into subsequent editions,
providing additional guidelines
adaptation and use in a
greater variety of conditions.
Copyright May 1981
SOLAR CONVECTION GRAIN DRYER
There is a need in many countries for an effective,
means for drying grain.
Grain drying is a critical step in
preparing grain for storage.
Drying grain prevents germination
of seeds, inhibits bacterial growth, and reduces insect
damage. The drying
process also drives off insects, while
killing larvae and eggs.
Since grain kernels become harder
during the drying process, they are less subceptible to
attack. Dried grain
can also be stored in air-tight containers,
protecting it from rodent and insect damage.
Currently, the most common method of grain drying is to
the grain on slabs of concrete or on the ground to dry.
method, however, simply increases the chances of insect or
weather damage. More
modern grain-drying methods often consist
of using equipment requiring some form of forced ventilation
and/or fuel-burning heating systems.
This causes a problem in
many parts of the world because of the high cost and
These factors contribute to the need for a low-cost grain
designed to use the natural convection flow of forced air as
the principal drying mechanism.
* Drums, petroleum,
* Lumber, 61cm X
122cm (34 meters)
* Lumber, 30.48cm X
61cm (20 meters)
* Plywood, .95cm
thick (12 square meters)
* Particle board (27
corrugated (72 square meters)
* Plastic film, 4
mil thick (72 square meters)
* Netting, mosquito
(244 square cm)
CONSTRUCTION OF THE DRYER
The Primary Collector
Cut a 244cm X 6.7 meter piece of particle board to form the
base of the collector.
Using 5.08cm X 10.16cm lumber, frame the particle board.
Nail corrugated aluminum to the collector base to form the
The surface of the collector is covered with a sheet of
film. The air
passages at the foot and head of the collector
should be 30.48cm long X 9.20cm high.
If plate glass is
available, it can be used in place of the plastic film.
The Drying Bin
The base is made of plywood, 122cm long X 244cm wide X .95cm
thick. It is framed
with 5.08cm X 10cm lumber.
The bin is 2.4 meters square and should be approximately
The drying bin is large enough to hold four drying
tray should be made from 2.54cm wooden framing, supporting
nylon mosquito netting.
The outside dimensions of each frame
should be 122cm X 122cm.
The trays slide into the bin area on
The roof of the bin is also made of plywood.
The Secondary Collector
The secondary collector is built the same way as the primary
collector. It should
be 244cm wide x 4.8 meters long.
The chimney is made from 55-gallon drums that are welded
together, with the tops and bottoms removed from the five
for the chimney.
Each of the drums should be painted black.
The secondary collector is attached to the bottom of the
chimney where an inlet hole has been cut.
Two additional drums
can be used to form the base of the chimney below the
chimney extends 4.5 meters above the top of the
The completed dryer is shown on the following page.