NATIONAL BUREAU OF STANDARDS REPORT

2947

AN APPARATUS FOR MEASUREMENT OF SIMULTANEOUS

HEAT AND WATER VAPOR FLOW THROUGH

4x3 FT INSULATED PANELS

t>y

H. E. Robinson

F. J. Powlitch

M. A. Barron

P. R. Achenbach

Report to

Office of The Quartermaster General

Department of the Army

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section is engaged in specialized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance Measurements. Inductance and Capacitance. Electrical Instruments. Magnetic Measurements. Applied Electricity. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Gage.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenics. Engines and

Lubrication. Engine Fuels. Cryogenic Engineering.

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Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectroscopy.

Nuclear Physics. Radioactivity. X-Rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Instruments Branch.

Chemistry. Organic Coatings. Surface Cheqiistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Aerodynamics. Engineering Mechanics. Hydraulics. Mass. Capacity, Density, and Fluid Meters. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure. Chemistry of Mineral Products.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Machine

Development.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regular Propagation Services. Frequency Utilization Research. Tropospheric Propagation Research. High

Frequency Standards. Microwave Standards.

Ordnance Development. These three divisions are engaged in a broad program of research

Electromechanical Ordnance, and development in advanced ordnance. Activities include

Ordnance Electronics. basic and applied research, engineering, pilot production, field testing, and evaluation of a wide variety of ordnance materiel. Special skills and facilities of other

NBS divisions also contribute to this program. The activity is sponsored by the Department of

Defense.

Missile Development. Missile research and development: engineering, dynamics, intelligence,

instrumentation, evaluation. Combustion in jet engines. These activities are sponsored by the

Department of Defense. • Office of Basic Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-10-4333 December 1, 1953 2947

AN APPARATUS FOR MEASUREMENT CF SIMULTANEOUS

HEAT AND WATER VAPOR FLOW THROUGH

4x3 FT INSULATED PANELS

by

H. E. Robinson

F. J. Powlitcb

M. A* Barron

P, R„ Achenbach

Heating and Air Conditioning Section

Building Technology Division

To

Office of The Quartermaster General

Department of the Army

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, i ,. Approved for public release by the

unleu permission “r r j

25,d.c. such P

. Director of the National Institute of

niiy prepared if Standards and Technology (NIST)

on October 9, 201 5.

>r In part, la prohibited

standard!, Washington

report has been speclfireport for Its own use,

AN APPARATUS FOR MEASUREMENT CF SIMULTANEOUS

HEAT AND WATER VAPOR FLOW THROUGH

4x£ FT INSULATED PANEIS

by

H.E. Robinson, F. J. Powlitch, K.A.Barron and F.R. Achenbach

Abstract

An apparatus designed to subject the opposite faces

of large insulated panels to selected differences

of temperature and vapor pressure, for the study of

moisture condensation and accumulation in panels in

refrigeration service, is described. Provision is

made for periodic measurement of the thermal conductance of the panel, and of the rates of water vapor

flow into the warm side and out of the cold side of

the panel. The apparatus is mounted to rotate on

horizontal trunnions so that a panel can be oriented

in the position of a wall, roof or floor. Because

moisture accumulates slowly in panels, the equipment

is designed for continuous operation for periods of

weeks or months. An account is given of measurements

to evaluate apparatus coefficients needed in calculating heat transfer results, and also of the results of

a few tests made in the apparatus for the chief purpose of

evaluating its operation and performance.

I. INTRODUCTION

A project entitled "Water Vapor Transmission in Refrigerated Warehouses" was initiated at the National Bureau of Standards in May 1952, under the sponsorship and financial support of

the Office of The Quartermaster General, Department of Defense.

Its chief object was to establish practical criteria for the

water vapor permeances of the faces and joints of insulated panels,

used in refrigerated warehouses, to avoid condensation of moisture

and its accumulation in them under operating conditions. Such

moisture accumulation impairs the insulating effectiveness of

panels, leading to serious difficulty in mainining desired low

temperatures in the structure, and causes rapid deterioration of

panels due to decay or corrosion of their components or fasteners.

The problem is basically that of preventing or minimizing

vapor entrance on the warm side of the panel, and allowing, or

impeding as little as possible, its exit through the cold face.

Except for metal sheets, there are few materials available for

panel construction, especially under war conditions, that are

not to some extent permeable to water vapor. Other factors,

such as leaks, methods of assembling and fastening panels, and

requirements for the washability of cold side surfaces of panels,

also must be taken into account.

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To explore and evaluate the problem, which includes knowing the temperature and humidity or moisture conditions at

which the various components of panels must operate in service,

an apparatus capable of tests on full-scale panels (4x$ ft in

size) was constructed, as described herein. In this apparatus,

a panel is exposed to desired temperatures and vapor pressures

on both sides over long periods, during which heat flow through

and vapor flow Into and through the panel can be periodically

observed. Measurements of the heat flow, or of its changes,

are for the purpose of indicating the effect of moisture accumulation on overall insulating value, as well as to indicate

indirectly if moisture is accumulating in the panel. In addition, temperature and humidity measuring elements in the panel

will be used for observing the ambient conditions at which

various components of the panel must function in service. The

latter information is essential for evaluating and selecting

appropriate materials for use as components, since the vapor

permeance of many applicable panel materials depends on the

humidity and temperature conditions to which they are exposed.

Using permeance data for materials at appropriate conditions if they are available, or if necessary/- are obtained by

appropriate measurements, improved designs of panel can be worked out and subjected to trial in the panel apparatus.

The orientation of a panel, that is, whether it is used

as a wall, floor or ceiling of a refrigerated chamber, may

markedly affect its performance, especially?- as regards moisture

accumulation effects. To enable studies in different orientations, the test apparatus was constructed so that it can be

rotated 90 ° in either direction, thus orienting a panel in

either a wall, roof or floor position.

The apparatus was designed for warm side air temperatures

up to about 150°F, with relative humidities up to about 90 percent. The cold side was designed to attain temperatures as low

as 100 degrees under the room temperature, or about -30°F, and

relative humidities from about 20 to ?0 percent.

In the first year of the project, a bibliographical compilation on the subject was made, and the large panel apparatus

was built, instrumented, and subjected to calibration and operating tests. Inasmuch as the sponsoring agency was not able

to continue its expected financial support of the project at

the start of this fiscal year, the following report is presented

to describe the completed apparatus and the results of the tests

thus far made with it.
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II. DESCRIPTION OF THE APPARATUS

A schematic drawing of the apparatus, with its major

elements designated by numbers, is shown in Figure 1. The

main part of the apparatus was constructed as two sections

of a box, which are coupled together by bolts through the

angles (2) at their edges. The test panel (3) ? 4x£ ft in

size, is installed against a gasketed stop ( 23 ) in one section, dividing the enclosure into a warm side and a cold

side, which are separately maintained at the desired temperature and humidity conditions throughout a test. Insulation

is packed into the space at the edges of the panel to prevent chilling of the stop ( 23 ) and possible condensation on

its warm side. The assembled sections are supported on

trunnions attached to the warm side section and resting on

brass bearings, constituting a horizontal axis (A) about

which the apparatus can be rotated 90 ° in either direction.

A small dolly is used to support and move the cold side

when it Is uncoupled from the trunnion-supported warm side.

Both sections were constructed using 2x4 softwood framing with l/4-inch plywood glued and screwed to its inner and

outer faces. Framing was kept to a minimum consistent with

structural requirements to reduce heat conduction through

framing members. The 3 -'§/$ inch spaces between the plywood

sheets were filled with two slightly compressed layers of

2-inch low density fiberglass thermal insulation.

Both sections were lined on the inside and covered on

the outside with 0. 006-inch aluminum sheet for vapor proofing. The aluminum sheet was cemented to the plywood with a rubber-base adhesive, and seams were overlapped and sealed

with an adhesive-surfaced lead tape one inch wide. Heavy

polyethylene sheet was substituted for aluminum sheet on the

inner warm side surface at the stop and the edges of the test

panel to reduce heat conduction to the cold side. All electric

and other lines entering into the enclosed spaces were bunched

into groups, and led through close-fitting holes packed with

permagum and sealed with aluminum sheet and lead tape.

On assembly, the joint between the warm and cold side

sections is made vapor-tight by four lines of rubber gasket

(1), the spaces between which are filled with permagum prior

to closing the joint. The test panel is installed against

the stop ( 23 ), against which it is firmly pressed by means

of wedges (4) bearing on the peripheral shim (21) and the

removable retainers (5). A vapor-seal at the panel edges

is provided by a rubber gasket flanked by permagum.
.

1
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The air temperature on the warm side is maintained by

small electrical resistance heaters in a cylindrical tube

( 6 ) through which air is circulated by a fan (7). Selected

heaters are energized continuously, and one or two are energized intermittently tinder the control of an electronic

time-proportioning thermostat (ref. N33 Report ho. 20f3

)

having its sensing element at the location (£) on the warm

side. On the cold side, the air is cooled to a temperature

slightly below the desired value, by means of the flooded

direct-expansion cooling coil ( 9 / through which air is circulated by a fan (?)„ An electrical strip heater (10),

controlled by a second channel of the previously-mentioned

thermostat, with its sensing element at (£) on the cold side,

is used to raise the air temperature by the slight amount

necessary to obtain the desired value. Sight fine wire

(I

T o. 30 AV/G) thermocouples (11), connected electrically in

parallel, are used on each side to measure the average air

temperature at a distance of 3 inches from the panel. Ten

individual thermocouples ( 12 ) are used to measure the temperature of each face of the panel. Leads for a number of

thermocouples, and for several Dunmore-type humidity-indicating elements, are brought into the boxes for making measurements of conditions at various locations within the test panel.

Sixteen differential thermocouples (13), connected electrically

in series, are attached to the inside and outside plywood

sheets of the warm side section under the aluminum sheet, for

the purpose described below.

All electrical input to the warm side is measured by an

integrating watt-hour meter with dials readable to one watthour. The heat thus introduced leaves the warm side box by

(a) transmission through the test panel (b) transmission

through the five other faces of the warm side box to the laboratory/ air and (c) conduction around the test panel through the

inner lining of the warm side section. Item (b) is proportional

to the average emf developed by the series-differential thermocouple ( 13 ), and item (c) is approximately proportional to the

air temperature difference of the warm and cold sides. (Perhaps

more satisfactory for evaluating item (c) would be a seriesdifferential thermocouple similar to ( 13 ) with junctions appropriately located on the inner lining on both sides of the panel).

Since the average rate of heat input to the warm side during

a period of a test is known from the watt-hour meter readings,

and items (b) and (c) can be evaluated from the measured thermocouple readings and constants determined by calibration tests,

the average rate of heat transmission through the panel, both

sensible and latent, can be calculated with reasonable accuracy.

By this means, significant changes in the heat transmission of

the panel can be determined as a test is continued. The procedure for determining the calibration constants to be used in

evaluating items (b) and (c) is described in Section IIIA of

this report.
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Water vapor is generated on the warm side as needed to

maintain its humidity at a desired value and to replace

vapor permeating the* test panel. A covered ar.d insulated

aluminum vessel (14) contains water held approximately at

a desired temperature by a constant small current in an

electrical resistance heater cemented to the bottom of the

vessel. When an electronic humidity controller with a Dunmore-type sensing element located at (16) on the warm

side calls for an increase in humidity, a small blower (15)

is energized, forcing air through the hose (20) into the

vessel (14), from which it is discharged carrying an increment of water vapor. The water temperature is adjusted so

that the blower on and off periods are approximately equal.

The water container (14) is suspended from a cantilever

scale (19) (see NBS Progress Report No. 2220 to 0*Q*M*G,)

bv means of which the weight of water evaporated in a given

period can be determined. Figures 2 and 3 show details of

the construction of the cantilever scale, which is mounted

on a horizontal axis with ball bearings so that it remains

in a fixed plane regardless of the angular orientation of

the panel and main apparatus. The deflection of the cantilever beam under load at constant temperature is linearly

proportional to the load, provided the maximum stress in

the cantilever does not exceed the proportional limit.

Consequently/- loads corresponding to intermediate deflections

can be calculated by interpolation between deflections for

two known loads. The cantilever bar is dimensioned so that

its deflection changes about 0. Of inch when the suspended

container (14) is filled with water. Deflections of the

cantilever within this range are indicated by a dial gage

with 0.0001 inch graduations, the dial of which is viewed

through the multiple double-pane window (22). A small buzzer

mounted on the scale is actuated during readings to overcome

frictional hysteresis in the system. Deflections can be read

to within a fraction of a graduation of the dial gage, enabling

calculation of load changes to within less than 1/fOO of the

weight of the water contents of the container. The dimensions

of the cantilever bar and the capacity of the container are

selected to accord with the estimated demand for vapor during

a test run.

Beryllium copper was used for the cantilever beams because

of the high limit of proportionality (70-$0,000 psi) of its

stress-strain curve, and its low hysteresis; the maximum stress

occurring during use does not exceed 40,000 psi. Experimental

measurements indicated that the load-deflection curves of the

devices closely approximated straight lines over the working

load range. A pantagraph support for the hose (20) was pro-

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vided to obviate possible forces in the hose between the

fixed blower (15) and the suspended load (14)« Prior to

a test, the load deflection characteristic of the cantilever beam in place is determined by measurements with

known increments of load. A small correction factor has

been evaluated to take account of changes in the elastic

properties of the cantilever and its dimensions with temperature oThe relative humidity on the cold side of the panel is

held constant, and vapor permeating the panel is absorbed,

by means of the desiccant (17) (silica gel) spread out in

eleven wire mesh trays in the external desiccant box. By

means of the flexible metallic hoses (l£) and the two small

blowers (15), air is drawn from the cold side, passed over

the desiccant, and returned to the cold side at a rate of

about 4 CFM. Operation of the blowers is controlled by a humidity controller with a Dunraore-tvpe sensing element

located at position (16) in the cold box. A refrigerating

coil (9) is operated in the desiccant box to keep its air

temperature approximately equal to that in the cold side

box. The construction and vapor-proofing of the desiccant

box is like that of the other boxes; one of its sides is

removable for placement of the trays of desiccant, and the

joint is sealed in the same manner as the joint between the

warm and cold side boxes.

The trays of desiccant are hung from a fixed cantilever

scale (19), similar to but of greater capacity than that in

the warm side box. As much as $0 lb. of dry desiccant can

be placed in the trays, affording capacity for adsorption of

15 or more lb. of water at a low vapor pressure. The desiccant is regenerated, when necessary, by lowering the entire

tray assembly into a chimney-shaped drying oven made of

4-inch foamglas blocks with a 660-watt electric cone heater

at its bottom. An insulated cover is placed over the oven,

and a few small apertures are left open at ton and bottom

for thermal ventilation of the oven. The temperature of the

desiccant reaches 300 °F or more at the end of the drying

period, which requires from 16 to 24 hours. The desiccant

is removed from the oven just prior to a test, and is transferred to the desiccant box while still quite warm, to reduce

moisture pick-up during transferral.

In operation of the cold box, it is necessary to avoid

condensation of vapor on its refrigerating coil (9) or on

that in the desiccant box, if all the vapor permeating the

panel is to be adsorbed by the desiccant. The coils must

therefore be operated at temperatures above the dewpoint of

the air in contact with them. For this reason, the coils (9)

are large and are operated with large air circulation rates;

furthermore, the coils are operated flooded with refrigerant

to obtain maximum capacity with a small air to coil temperature

7

difference „ The coil temperatures are controlled by adjustable evaporator pressure regulating valves; supply of refrigerant to each coil is governed by a thermostatic expansion

valve o To keep the coil flooded, the superheat bulb of the

expansion value is in thermal contact with and responsive to

the temperatures of both the coil suction line and a small

variac-energized electric heater by means of which an artificial superheat is produced. The voltage on the heater is

adjusted so that the coil operates completely flooded, as

indicated by thermocouples on its surfaces, without overflooding back to the compressor. The refrigerant and suction

lines are connected to the cold box by means of flexible

hoses to allow for its range of movement.

In order that the relative humidity in the cold box may

be kept at a reasonably high value if this is desired during

a test, and in view of the limitation on dev/point temperature

to avoid condensation on the cooling coil, the re-heat required

for thermostatic control of the cold side aip temperature,

previously referred to, is kept as small as possible.

To indicate the performance of the arrangement described,

in a test with the average cold air temperature at -23 °F, the

temperatures of the refrigerating coil at its entrance, center

and exit were within 0.5 degree of -27„9°F 0 Under these conditions, condensation on the coil would not occur for cold

side air relative humidities up to 75$»

Eight photographs are attached showing views of the

apparatus and parts as follows:

4 - General view of apparatus with panel in

horizontal plane.

5 - General view of apparatus with panel in

vertical plane.

From left to right: instrument console,

warm and cold side boxes, desiccant box, and

oven for regenerating desiccant.

6 - Apparatus with the two boxes separated.

7 - Close-up of warm side section showing heater

and centilever scale assemblies.

8 - Close-up of cold side section.

9 - Close-up of desiccant box.

10 - Refrigerating equipment and controls.

11 - Instrument console and controls.

Figure

Figure

Figure

Figure

Fi gur

e

Figure

Figure

Figure
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III. APPARATUS CALIBRATION, TESTS, AND RESULTS

A. A series of tests was made to determine the calibration

constants for evaluating heat losses from the warm side other

than through the test panel, as previously mentioned, in order

to enable calculation of heat transmission through the test

panel. For this purpose, a 4x£ ft test panel was prepared

with 2x4 framing with l/l6-inch aluminum sheet faces., The

panel was filled full-thick with fiberglass insulation.

With the cold side held at substantially the same temperature (-23°F), three tests were conducted, of several day’s

duration each, with the warm side air temperatures adjusted

to values a) approximately equal to room temperature, b)

25 dego F cooler and c) 25 dego F warmer 0 Heat input to the

warm side was measured, and periodic readings were made of

the various air and panel surface thermocouples, and of the

differential thermocouple ( 1 3 ) » During the initial stage of

these measurements, it was found that the reading of thermocouple (13) varied widely with room air temperature flotations resulting from thermostatic control of the laboratory

heating system. To obviate this difficulty, the outer

aluminum skin of the warm side section was covered with one

inch of fiberglass duct insulation, glued to the aluminum.

This reduced the amplitude of the cyclic variation of the

readings of thermocouple (13) very considerable?- , to such extent that the average of several periodic readings showed

little effect from this .cause. Using the data of the three tests, it was possible to

write a heat balance equation for each test, as previously

discussed, in which the unknowns were the calibration coefficient for thermocouple (13) and the equivalent thermal conductance of the panel including the heat conduction to the

cold side around its edges. By simultaneous solution of these

equations taken in pairs , the unknown coefficients were determined. Coefficients determined from different pairs of

the heat balance equations agreed with their average value

within 2.1 percent. The equivalent thermal conductance of

the panel so determined included both heat flow through it,

and heat flow around its edges. To estimate the latter, and

a coefficient for it, the thermal conductance of the test

panel was calculated using data as to the thermal conductivity

of its components, and the desired coefficient was obtained

from the difference between the observed equivalent conductance and the calculated, conductance.
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Taking the average values of the coefficients determined

in this manner, the heat balance equation for calculating the

average thermal conductance of a 4x0 ft panel was found to be

Cp x A t

s _ s = 0.106W + 0.706 ( ±D) - 0.0302 A t a _a

where Cp = average thermal conductance of panel,

Btu/hrft^ ( deg. F)

W = average electrical input to warm side, watts

±D = emf (millivolts) of differential thermocouple (13),

with appropriate polarit}7, At s „ s = average surface to surface temperature

difference of panel, deg.F

Ata -a = average air to air temperature difference

across panel, deg. F

The validity of the above equation was shown in a test

on a homogeneous foamed plastic panel described under C in

this report.

B. An operational test of seven day f s duration was made to

observe the performance of the vapor generating and vapor

absorbing systems and controls on the warm and cold sides of

the apparatus. The test panel used for this purpose (see

Figures 12 and 13) consisted of a frame of 2x4 f s on 16 inch

centers and at the edges, to the warm side face of which was

fastened a 4x0 ft sheet of l/l6-inch aluminum. Fiber glass

duct insulation one inch thick was glued to the cold side

of the aluminum sheet and, like the frame, was exposed to the

cold side air. Six l/4-inch diameter holes were drilled in

the aluminum sheet along each of two horizontal lines 6 ft

apart vertically, the insulation being chamfered around the

holes. Under the test conditions (warm side air at 0O°F and

51$ R.H. ; cold side air at 30°F and 66$ R.H.), convective

circulation of air between the warm and cold sides through

these holes caused a steady net flow of vapor from the warm

to the cold side.

The major findings based on the test of this panel were:

(a) The cantilever weighing devices for determining vapor release and adsorption rates on the two sides of the panel performed satisfactorily, as did the onerating control systems

on both sides. Both cantilever scales indicated constant

rates of vapor transfer; the cold side cantilever scale showed

a rate of vapor adsorption twice as great as the warm side

vapor release rate, which is believed to have been due to

vapor entering from the laboratorv air through a small leak

which was later found in a connection of the flexible hose

carrying air to the desiccant box.
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(b) The vapor flow from the warm side through the holes in

the panel was measured as equivalent to 3.4 grains per hour

per square foot of panel. This is in agreement with the

vapor flow that would be calculated on the basis of a coefficient of discharge of 0.76 for the holes, for convective

air 'flow due to stack action under the conditions of the test.

(c) The vapor generating and vapor absorbing systems on the

two sides of the panel had ample capacity for the vapor flow

rates experienced.

(d) The heating and refrigerating systems, and their automatic controls, operated very satisfactorily throughout the

seven-da^r test period.

C. A full-scale test of eight days T duration was made to

determine the performance of the apparatus in testing a homogeneous, non-hygroscopic , test panel of low thermal conductance and moderate vapor permeance. The test panel was composed of four planks of foamed polvstyrene insulation

(Styrofoam 22) each 6 ft long, one foot wide and 3-1/16 inches

thick, glued edge to edge to form a panel 4x6 ft in size and

3-1/6 inches thick. The three joints which were glued with

a polymerizing adhesive called Weldwood were very strong, and

appeared to be continuous and without leaks.

The findings of the test, which was conducted with the

warm side air at 62.0°F and 55 * 57$ R.H. and the cold side air

at 32.1°F and 35.5% R.H., were as follows:

(a) The thermal conductance of the panel was determined to

be 0.093 Btu/hrft2(d eg F), using the equation given previously.

This compares with a calculated conductance of 0.092 Btu/hr

ft^(deg F) for the 3-1/16 inch panel based on the thermal conductivity of similar material as measured in a guarded hot plate

apparatus

.

(b) The average water vapor permeance of the test panel, as

determined from the warm-side vapor generation rate, was 0.40

perm ( grains/hr ft^ ( inch Hg) )

,

indicating an average permeability

of the material of 1.22 perm-inch. Dry-cup tests of samples

of the material 0.6 and 3.0 inches thick, at a uniform temperature of ?3°F in an ambient at 50% R.H., yielded an average

permeability of 1.5 perm-inch, which is in good agreement considering the different temperature and vapor pressure conditions.
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(c) The cold side vapor adsorption rate exceeded the warm

side generation rate, as in the previous test. Since there

was no wood or hygroscopic material exposed in this panel,

the excess moisture could be accounted for only by moisture

ingress to the cold side from the humid laboratory air

through a leak. A leak of considerable magnitude at one of

the desiccant box hose connections was detected by introducing Freon 12 vapor into the cold side and inspecting all

joints and seals with a halide torch. The leak was sealed,

and further examination indicated an absence of discoverable leaks.

(d) The thermal conductance of the panel did not change perceptibly during the test. There was no evidence of moisture

accumulation in the cells of this homogeneous, moderately

permeable, panel material under the conditions of this test,

based upon observation of a piece of the panel cut therefrom

immediately on termination of the test. Analysis of the

vapor pressure and temperature conditions in the panel

material (based on the method described in BF3 63 ) showed

that condensation in the material was unlikely under the

conditions of this test. It was planned to repeat the test

with the cold side at a much lower temperature to obtain conditions favoring moisture or frost accumulation in the panel

material but curtailment of the project occurred before this

test could be undertaken.

IV. SUMARY

A description is given of an apparatus for making simultaneous heat and vapor transmission tests of 4x# ft insulated

panels over periods of time of weeks or months. Temperatures

and relative humidities on both sides of the panel can be controlled at selected values. Check tests made on a few panels

indicated that the thermal conductance and vapor permeance

of panels can be measured with good accurac}?-.

The apparatus was constructed for the conduct of research

measurements to determine criteria for the water vapor permeance

of the surfaces of insulated panels to avoid moisture condensation difficulties in refrigeration service, and to study

moisture accumulation and its effect in impairing the insulating effectiveness of panels as a result of improper vapor

permeances, or vapor leaks, in their construction. The research program, including other phases of the work for which

this apparatus was intended to serve as a guide in exploring

the nature of moisture problems in panels, was originally expected to cover a period of three or more years. The essential preparatory/- steps to carry out the project as planned--

namely, a bibliographical research and construction and operational checks of the major item of the necessary apparatus--
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, , rnmni cstpd Feasureraents of the vapor permeance

Tlaltts caFtherefore be undertaken at once if financial

support for such measurements is provided.

TRUNNION

AXIS

[

PANEL

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THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of the National Bureau of Standards ($1.00). Information on calibration services and fees can be

found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.