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ET-159 April 1940
United States Department of Agriculture
"Bureau of Entomology and Plant Quarantine
TEMPERATURE-HUMIDITY CONTROLLED CABINETS
FOR THE STUDY OF INSECTS I/ 2g/
By P. N. Annand and F. H. Harries
The present apparatus was designed for use in studies of the
beet leafhopper (Eutet tix tenellus (Bak.)) in relation to some of the
more important physical factors of the environment as an aid in
interpreting problems of distribution, development, activities, and
abundance in terms of the more significant variables involved. The
cabinets have proved satisfactory for such studies during extensive
use over a period of several years. The description provided is
quite general, since many of the detailed features are arbitrary
and may be modified or improved in many ways.
The equipment may be generally described as consisting of
three major parts, viz, the five air chambers or controlled cabi-
nets, the brine tank and brine circuit through cooling coils in the
different compartments, and the ammonia compressor and expansion
coils for controlling the temperature of the brine (fig. 1).
The cabinets were well insulated to obtain a wide range of
temperatures and greater efficiency in the cost of operation. Dif-
ferent constant-temperature and humidity conditions were obtained by
automatically controlled heaters and humidifiers and the cooling and
dehumidifying action of the brine coils.
i/ The equipment described was constructed in 1932 at the
Twin Falls, Idaho, laboratory of the Bureau of Entomology and Plant
Quarantine, U. S. Department of Agriculture. The writers are in-
debted to R. A. Fulton for suggestions on the design of the equip-
ment, to J. R. Douglass for suggesting certain improvements, and to
E. H. Bean for various suggestions and assistance in construction
of the cabinets and installation of apparatus.
2g/ A brief description of the co:.trolled cabinets was given
Prof. Alvah Peterson in 1933 for inclusion in his manual of entomo-
logical equipment and methods (Plate 124) (A Manual of Entomo-
logical Equipment and Methods, Part I. 1934. Michigan: Edwards
it was possible to produce a wide range of conditions and to
maintain satisfactory control over long periods. The cabinets were
operated at constant temperatures ranging from 5 to 120 F. Dif-
ferences in relative humidity between 10 and approximately 100
percent were obtained within ordinary temFerature extremes for in-
sect development and oviposition activity. Variation in constant
temperatures was about two-tenths of a Fahrenheit degree above or
below the temperature desired, and relative humidity was regulated
within a range of about 1 to 2 percent. The degree of temperature-
humidity control is illustrated by hygrothermograph records in
Structure of the Cabinets
The cabinets were constructed of pressed-cork panels (2 by
12 by 36 inches), suitably strengthened by a wooden framework con-
sisting of 2 by 4's at the upper and lower edges, with uprights
placed at the corners and in the center of the back wall of each
chamber for supporting the brine coils. Single pieces of cork were
cemented and nailed into the structure. The floor, ceiling, and
outer walls were insulated with 4 inches of cork (two layers of
panels), and partition walls between compartments were 2 inches
thick. The floor was supported by a wooden panel laid over 2 by 4
inch cross pieces occurring below the partition walls and the center
of each compartment. Windows were placed in the ceiling of each
chamber and were supported by running the compressed-air line
(1/4-inch steel pipe) and wiring conduit longitudinally through the
ceiling wall on each side of the window frame. (Wooden cross pieces
are also recommended for supporting the weight of the window frames.)
The cork material was also used to build out the back and
side walls of the cabinet for a distance of about 6 inches in each
corner to form a niche in the center for the brine coil (fig. 1).
Pressed-board panels about 6 inches wide were nailed over the cork,
and a removable panel of the same material was mounted over the
center section to separate the brine coil from the remainder of the
chamber (figs. 3 and 4).
The outside of the cabinet measured 13 feet and 10 inches in
length, 4 feet and 6 inches in width, and 3 feet and 4 inches in
height. Inside dimensions of the different compartments were
38 inches in depth from front to back, 30 inches in width, and 32
inches in height.
The interior of the cabinets was made tight arid waterproof by
covering the surface of the cork with a thick layer of emulsified
asphalt. Floors of the cabinets were covered with a hard pressed-
asbestos board placed over the cork. The interiors of the compart-
ments were finished with aluminum paint to give a better surface
for reflecting light. The front of the cabinet, including the outer
doors, was constructed by a cabinet maker as a unit or panel that
was attached by means of large lag scrc'.'s .c-ntering the 2 by 4's of
the wooden f mr'. work (fig. 3). Large doors, x'.,:d to give f:, ac-
cess to the cabinets, were insulated with 4 Inch,-s of pr:A--.d cork
and were properly fitted with rubber gaskets to prevent air lenl-.ae.
Inner doors were made of three-ply pin'-;, veneer, coatcd with asj:halt
paint, and provided with an observation windc.'.' and smaller doors to
permit examinations or adjustments of the control equipment without
disturbing the experimental conditions (fig. 1). (Since some ex-
pansion of the innpr doors occurred under moist condition-s, con-
struction of pressed-board material instead of veneer would evidently
prove more satisfactory.) Electrical outlets 'were placed in each
compartment for the convenient attachment of control ap.:aratus.
The front surface, including the outer doors, was constructed of
finished birch, and the remainder of the exterior was covered with
pressed board having a smooth, durable surface and good insulating
properties. The cabinet was finished by staining and varnishing
The Brine Tank and Cooling Circuits
The brine tank (fig. 1) was constructed of 10-gauge steel and
was insulated with a 4-inch layer of pressed cork and an outer
protective casing of wood. Inside dimensions of the tank were
2 by 6 by 3 feet, giving a capacity of about 200 gallons. The
refrigeration coil consisted of about 150 linear feet of 1-inch
ammonia pipe that was arranged to leave the center of the ta"-. free
for accommodating containers used in making ice (fig. 1). The
inside of the tank and the outside of the rmnimmonia ex-."r.rzion coil
were covered with a protective coating of tar to prevent oxidation
and corrosion. The tar was melted and applied with a brush while e
the metal surfaces ,"ere heated. (Since some leakage has occurred
after several years of use, a wooden brine tank is evidently to be
The brine circuit consisted of 1-inch pipe conr.ected through
ordinary wall-type heating radiators in the controlled chambers by
appropriate fittings. As is shown in figure 3, the pipe ,'.is i.l.Lced
along the back of the cabinet and was connected through the coils
by a by-pass arrangement so that the flow of brine to different
compartments could be independently regulated or shut off by means
of hand-operated valves. The brine pipe was covered with pressed-
cork pipe insulation, 2 inches in thickness (fig. 3). Brine was
circulated through the pipe and coils by a centrifugal pump operated
by a 3/8-horsepower motor. The temperatu,-e of the brine was auto-
matically regulated within a range of about 2 by the starti:..g and
stopping of the ammonia compressor under the control of an immersion
thermostat placed in the brine tank (fig. 1).
Temperature control was obtained through the counter action
of the cooling coils and resistance heaters controlled by thermo-
stats. The heaters were adapted from a common type of heat con-
vector and consisted of resistance wire mounted over porcelain
insulators on a metal frame. The heaters were usually employed at
about 200 watts capacity, but the load could be increased if neces-
sary by changing the line wires to different terminals. Heating
elements were mounted directly in front of the circulating fans
(figs. 3 and 4) to give a minimum of lag before and after operating.
These were controlled by mercury-glass thermoregulators of the
sealed type containing dry hydrogen to dampen the spark and prevent
failure through oxidation at the contact. The thermostats were used
with small relays designed to reduce voltage and current on the
Since the temperature of the brine could not be independent-
ly regulated for different temperatures in the various compartments,
the amount of cooling and heating was controlled to a considerable
extent by limiting the passage of air over the brine coils. Un-
necessary cooling and heating at the higher temperatures was reduced
in this way by closing the air vents or adjustable ventilators in
the panel in front of the brine coil (figs. 3 and 4).
Atmospheric humidity was controlled through the dehumidify-
ing action of the brine coils and automatic operation of spray-jet
humidifiers. The humidifiers consisted of a common type of atom-
izer mounted over a reservoir made of sheet copper. A small baffle
was placed in front of the jet to increase the rate of humidifica-
tion by breaking the spray in finer particles. The upper half of
a glass bottle was inverted over the reservoir to trap the larger
spray droplets (fig. 3). The humidifiers were later modified by
soldering the air line through the bottom of the reservoir and con-
necting the atomizer in a vertical position. A band of copper wire
screen around the top of the reservoir served to trap the larger
drops of water (fig. 4). The atomizers were operated with com-
pressed air at 15 to 20 pounds of pressure and were controlled
by humidostats through the action of solenoid valves placed in the
air line (fig. 3). Humidostats of a common commercial type, em-
ploying human hair as the sensitive element, were used with small
three-wire relays to prevent jumping of the valve through arcing
on the instrument contacts during completion and breaking of the
pilot circuit. The rate of dehumidification was controlled by
regulating the temperature of the brine and the passage of air over
the brine coils. Water condensing on the brine coils was trapped
and returned to the reservoirs of the humidifiers (fig. 3). When
brine temperatures were below freezing there was a gradual accumu-
lation of ice on the coils and it was necessary to add water to the
reservoirs at intervals to maintain the supply. When brine tEmlri;ra-
tures were above 32- F. it was occasionally necessary to siphonl off
an excess accumulmction of water resulting from transpiration of the
Since the different chambers were operated with brine at the
same temperature to obtain different temperature-humidity conditions,
the rate of dehumidification at higher humidities (especially in
combination with higher temperatures) was much more rapid thln
necessary and required a corresponding excess amount of compressed
air to operate the humidifiers in counter action. For better oper-
ation as well as greater efficiency in current consumption and cost
of operation, ventilators or air valves were used to regulate the
amount of air passing over the brine coil (figs. 3 and 4). By this
method the rate of dehumidification was regulated satisfactorily
to obtain widely different temperature-humidity conditions in dif-
ferent chambers with brine at the same temperature.
Cost of Materials and Apparatus
Cost of the equipment, exclusive of the air and ammonia
compressors and considerable part-time labor of laboratory workers,
is estimated at about $1,000. The following list of materials and
apparatus is appended as a guide in estimating the approximate cost
of similar cabinets or particular features of the control equip-
Pressed cork $70.00
Cement for joining cork panels 25.00
Lumber and nails 6.50
Screws and bolts 2.00
Cabinet front with outer doors (materials and labor) 84.00
Hinges and fasteners for outer doors 15.50
Inner doors (materials and labor) 21.50
Emulsified asphalt for interior of cabinets 25.00
Glass for windows 4.00
Asbestos board for floors 19.00
Pressed board for paneling brine coil chambers 10.00
Pressed board for exterior of cabinet 18.00
Lights and electrical wiring 50.00
Metal base or stand for cabinet 26.00
Brine tank and brine circuit
Brine tank and expansion coil (materials and labor) $100.00
Pipe and plumbing connections (materials and labor) 70.00
Centrifugal pump and motor for circulating brine 70.00
Five gate valves 8.75
Automatic ammonia expansion valve 20.00
Five wall radiators (in cabinets) 21.00
Five relays (two-wire)
Five electric heaters
Five 10-inch electric fans
Five relays (three-wire)
Five solenoid valves (in compressed-air line)
Cabinets and apparatus for the precise control of tempera-
ture and atmospheric moisture over a wide range of conditions are
described. Constant temperatures were obtained through the counter
action of cooling coils, and of resistance heaters controlled by
thermostats. Constant humidity conditions were obtained through
the dehumidifying action of low-temperature coils and humidifiers
controlled by humidostats. Cost of the equipment is roughly esti-
mated at about $1,000, exclusive of the air compressor and the re-
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Figure 1.--Exterior of cabinet and brine tank.
Digitized by the Internet Archive
in 2012 with funding from
University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation
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Figure 4.-Front view of cabinet interior showing
panel and ventilators in front of the brine coil.
UNIVERSITY OF FLORIDA
3 1262 08537 1036
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