August, 1919 
WISCONSIN HORTICULTURE 
173 
Efficiency of Common Storage 
Houses for Apples 
By F. W. Allen, Assistant Horti- 
culturist Fruit Storage Investi- 
gations, Bureau of Markets, U. 
S. Department of Agriculture. 
As prerequisites for success in 
storing fruit of any kind, whether 
in cold or common storage, it 
should be sufficient to mention the 
necessity of having good fruit well 
grown, picked at the proper stage 
of maturity, carefully handled and 
stored as soon after picking as pos 
sible. With the importance of 
these fundamental factors fully 
appreciated, the efficiency of air- 
cooled storages depends directly 
upon three things : The location 
of the house, its construction, and 
the way in which it is managed. 
The terms “air-cooled” and 
“common” storage are synony- 
mous, but in using the former we 
imply the medium by which the 
fruit is cooled. In this type of 
house there is no artificial means 
of refrigeration, only the natural 
circulation of air. The cooler the 
air as compared with the tempera- 
ture of the house the faster the cir- 
culation and the more rapid the 
cooling. In most of the apple sec- 
tions of the Northwest the nights 
are generally quite cool, even 
though the days are warm. Any 
section having these cool nights is 
well adapted for successful air- 
cooled storages. In localities where 
the days are warm, with little re- 
duction in the night temperature 
until quite late in the fall, the 
value of the storage is considerably 
reduced. In fact, the construc- 
tion of this type of house in such 
regions should probably be looked 
upon with some discouragement. 
In planning a common storage 
we should never lose sight of the 
fact that the building is to be 
cooled entirely by air circulation. 
A few small windows located here 
and there where they will fit in 
most conveniently will not accom- 
plish the purpose intended. Air 
circulation is induced by the differ- 
ence in weight of air at different 
temperatures. The weight of a 
cubic foot of warm air is less than 
a cubic foot of cold air. Warm 
air therefore seeks the higher level 
Interior view of air ducts to a base- 
ment where the air inlet is built in the 
wall. With the intake doors on the 
outside at the level of the ground the 
cold air is delivered under the false 
floor. 
and cold air the lower. For this 
reason intake air vents should be 
placed in the foundation wall, in 
order that the cold air may enter 
at the lowest point. After being 
drawn into the house this cool air 
expands, its weight becomes lighter, 
and with the continuous flow of 
cold air through the intakes it 
seeks an outlet through vents or an 
air shaft in the ceiling. The stor- 
age room floor should be not less 
than eighteen inches above the 
ground level and of open construc- 
tion. Two by fours or two by sixes 
spaced three- fourths of an inch 
apart are recommended. 
With this construction the ven- 
tilating system may be compared 
to a heating stove, where the cold 
air is taken in under the grate and 
the heated air passes up and out 
through the chimney. If we de- 
sire more heat, the stove is given 
more draft, that is, the intake 
openings are made larger. In 
order to cool the fruit in an air 
storage more rapidly, we do the 
same thing. The same principle 
applies, only the difference be- 
tween the temperature of the in- 
take and outlet air in the storage 
house is much less than that in a 
stove, consequently the circulation 
is much slower. For this reason 
the air vents must be numerous 
and of proper size. Eighteen by 
thirty inches is none too large and 
one such opening should be pro- 
vided for every ten or fifteen feet 
on both sides and ends of the 
house. In extremely large build- 
ings inlet openings should be twen- 
ty-four by thirty-six inches. The 
insulated or refrigerator type of 
door is much better than those 
made of only one or two layers of 
boards. 
The flues or outlet ventilators 
should lead up from the ceiling of 
the storage room and out through 
the ridge of the house. By mak- 
ing these from four to six feet 
square only one or two such out- 
lets should be necessary for the 
average individual grower’s house. 
As in the case of the inlets, these 
should be likewise fitted with trap 
doors in the ceiling of the storage 
room. By installing such a sys- 
tem of ventilators the house is 
equipped with the cooling machin- 
ery. The efficiency of this machin- 
ery will depend upon the method 
of operation, as we shall see subse- 
quently. Most air-cooled houses 
