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NBSIR 81-2443

Plan for A Round Robin of

Hot Boxes

September 1 981

Issued February 1982

Prepared for National Bureau of Standards

Office of Energy Programs

Washington, DC 20234

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U.S. Department of Energy

Building Energy Science Branch

Washington, DC 20585
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NATIONAL

OF STANDARDS

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NBSIR 81-2443 MAR 4 1982

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PLAN FOR A ROUND ROBIN OF

HOT BOXES

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Erv L. Bales

September 1 981

Issued February 1982

Prepared for National Bureau of Standards

Office of Energy Programs

Washington, DC 20234

U.S. Department of Energy

Building Energy Science Branch

Washington, DC 20585

and

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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TABLE OF CONTENTS

PAGE

I. INTRODUCTION 1

II. NEED FOR ROUND ROBIN 3

III. ASTM ROLE 4

IV. PAST ROUND ROBINS . 5

V. OBJECTIVES 8

VI. POSSIBLE TEST SPECIMENS 9

VII. NUMBER OF SPECIMENS 12

VIII. TEST CONDITIONS. 13

IX. POSSIBLE CONCERNS 14

X. MBS ROLE 15

XI. SCHEDULING 16

XII. EXPECTED RESULTS 18

XIII. RECOMMENDATIONS 19

XIV. REFERENCES 21

XV. APPENDIX '

1. Task Force Membership 22

2. Data Reporting Form 23

3. Fact Sheets on Calibrated Hot Boxes 24

4. Attendance at NBS Workshop 32

5. Parallel Heat Flow Flanking 35

I. INTRODUCTION

The emphasis on energy conservation because of the steep

rise in oil prices since 1973 has created a need to more

accurately specify the thermal performance of typical, composite

building sections. The standard, steady-state, series/parallel,

one-dimensional analytical models (Reference 1) are not precise

enough to make the needed evaluations of competing energy conservation techniques in building construction. The recent, more

sophisticated extensive computer models, such as DOE- 2, require

more accurate data on wall systems under dynamic conditions for

their use and verification. Improved apparatus to test composite

non-homogeneous sections have been constructed and system data is

becoming available.

The first family of such apparatus was the guarded hot box.

It is in wide use and there is an ASTM Standard Test Method (Reference

2) . The apparatus has an electrically heated metering box placed on the

center of the test specimen with a surrounding guard box. The temperature

in the guard box is controlled to be the same as that in the metering box.

Therefore, all energy supplied to the metering box passes through the test

specimen. Another box is attached to the opposite side of the test

specimen to control conditions on that side. The thermal conductance is

the net rate of energy supplied divided by the area and temperature

difference across the specimen. The net rate of energy accounts for

energy transferred through the guard box walls and any flanking losses

around the test area.

When testing full-scale building sections, however, the

apparatus becomes impractically large because of the additional,

necessary guard area,. There are further limitations on the guarded

box which are listed by Sclvason (Reference 3) : (a) the metering

box interferes with the convection over the test wall, so that

forced convection must be resorted to and this may give film

coefficients different from those occurring in practice. It is

difficult to produce equal coefficients for the metering area and

the guard area, so that lateral heat transfer may occur from the

measuring area to the guard area. (b) the metering box placed over

the central portion of the test wall measures only the heat flow

into that portion, but it has been shown by G.O. Handegord and

N.B. Hutcheon that this is not necessarily the average heat flow

for the whole test wall, particularly for walls containing vertical

air spaces; blocking of air spaces in the test area may change the

conductance substantially. (c) Radiation exchange is indefinite,

and it is difficult to produce the same effect on both the metering

area and the guard area of the test wall. Differences in the

radiant exchange from the inner and outer surfaces of the metering

box may require that different air temperatures be provided in the

test box and the guard box in order to maintain zero heat flow

across the test box walls and this may lead to lateral heat transfer

in the test wall. (d) in many cases, the metering box will not

cover a representative complete module of the test wall.

1
With these limitations in mind, Solvason, of the National

Research Council, Canada (Reference 3) designed the first

calibrated hot box to meet his stated requirements.

"First, it was designed to meter the heat flow into

the whole of representative sections of building walls,

and second, to expose the test wall to controlled temperature surroundings as well as to air at controlled

temperature. Third, it was built to operate without

forced air circulation over the warm side of the test

wall in order to produce warm-side film coefficients

approaching those in practice. Fourth, it operates

with the cold-side temperature either constant or

varying according to some predetermined cycle."

The box was built and used for a period but now appears

to be inactive.

There was approximately a fifteen (15) year lag before

another such apparatus was built by Owens-Corning Fiberglas

Corporation (Reference 4) . Since then, five others have been

built and another is under design and construction. See Appendix

5 for brief fact sheets on these boxes. Papers have been presented

on the design of six of the boxes. (References 4, 5, 6, 7, 8,

9 , and 10)

2
II. NEED FOR ROUND ROBIN

The calibrated hot box is a relatively new apparatus; the first

of the presently operational boxes was reported in 1974 (Reference 4

and Appendix 3). The ASTM C16 Committee on Thermal Insulation has

issued a draft Standard Test Method for consideration by its members.

There are six boxes operational and more is expected to be within six

months. As the boxes are being calibrated and used, it has been found

that there are differences in results that cannot be satisfactorily

rationalized. There is an immediate need to know if those differences

are due to errors in measurement or inherent errors in the present design

of the calibrated hot boxes. As a standard calibration specimen is not

available, it is difficult to sort out the sources of the differences.

Also, the ASTM Standard Test Method is required to have a

precision and accuracy statement. As each laboratory has limited

experience, it has been difficult to compare results and define

the expected performance.

A round robin of the calibrated hot boxes and guarded hot

boxes would accomplish:

1. A determination of the resulting differences in

measurement of thermal performance of a common

specimen

.

2. An indication of the magnitude of the precision and

accuracy of the present boxes.

3. Inform each laboratory on a confidential basis how

it is doing relative to all other laboratories.

4. Provide a forum for an exchange of ideas and

information among laboratories.

5. Indicate by analysis of the results how the apparatus

might be improved. « 6. Possibly indicate operational errors.

7. Evaluate calibration procedures in the present draft

ASTM Standard Test Method. Included would be the

examination of the extrapolation of calibration at one

measured thermal resistance to higher thermal resistances.

3
III. THE ROLE OF AMERICAN SOCIETY

FOR TESTING AND MATERIALS

The ASTM has taken on the task of the writing of a Standard Test

Method for the calibrated hot box. The C16 Committee on Thermal and

Cryogenic Insulating Materials has assigned that responsibility to the

C16.30 Subcommittee, Thermal Measurements, chaired by Mr. Charles Pelanne

A task force headed by Mr. Marion Hollingsworth has written the drafts.

Out of the task force work and other discussions, a workshop was held

at the National Bureau of Standards (NBS) to discuss the state-of-theart. It was attended by representatives of each organization with

calibrated hot box and those others interested; the attendance list is

Appendix 4. As the meeting progressed, it became evident that a round

robin would help resolve many of the issues discussed.

At the following C16 meeting in San Diego on April 20-23,

1979, a task force for the hot box round robin was appointed.

A list of the present members is Appendix 1.

Subsequently, the Department of Energy funded the initial

effort to plan the round robin by the NBS for ASTM. This was

done to shorten the time, as the Department of Energy is vitally

interested in seeing data on building composite sections published.

This report is the result of the planning effort. The task

force herein describes the conduct of the round robin for approval

by the C16.30 Subcommittee. It is expected that the Subcommittee

will oversee the testing program, report the results, and continue

to provide a forum for the discussion of hot box testing.

4
IV. PAST ROUND ROBINS.

In planning a round robin, it is natural to examine the

experiences of past efforts. In searching the literature and

talking to those active in thermal measurement, there appears

to have been only three round robins on thermal insulation

reported, one limited round robin conducted by an insulation

company to be reported soon; one currently underway which is

being sponsored by ASTM C16.30 Subcommittee and the Mineral

Insulation Manufacturers Association (MIMA) ; and an international

round robin in the planning stage which is sponsored by the

International Standards Organization (ISO) , Technical Committee

163 on Thermal Insulation. A review of the planning and results

are summarized below:

1. "Interlaboratory Comparison of Thermal Conductivity

Determinations with Guarded Hot Plate" H.E. Robinson

and T.W. Watson (Reference 11).

a. Specimen - corkboard, one inch thick, 18 specimens

at a density of 7.3 pcf and 2 specimens at a density

of 13.3 pcf.

b. Specimen number - one for each apparatus, total

of 20. Because of the wide range of plate sizes

and the number of laboratories participating, it

was considered not feasible to circulate one set

of specimens.

c. Mean temperature - two or more requested between

20 and 130°F. Data presented all show three mean

temperatures

.

d. Specimen reference - After testing, all specimens

cut down and sent to NBS for reference testing.

The cutting caused change in average density,

presumably because of non uniformity in the

specimen material.

e. Results - Data indicate practical value of C177-45.

Difference among the apparatus were pointed out.

The actual data are given with an analysis.

f. Time - the program took between two and five years.

This is an estimate as the dates were not explicitly

reported

.

2. "International Comparative Measurements of Thermal

Conductivity" (Reference 12)

.

a. Specimen - The criterion for selection of a material

were "that it should have a stable and uniform

conductivity over the whole area of a large slab

and that a batch of slabs with closely similar

thermal properties can be obtained. It should be

unaffected by environmental conditions during

transport and testing, and also the conductivity

value should not depend upon the orientation of

the test equipment.

5
A semi-rigid resin-bonded glass fiber board was

used, density being about 5.5 pcf".

b. Number of specimens - "It was decided for several

reasons (not the least being the differing sizes

of apparatus) that samples should not be circulated

from laboratory to laboratory, but that they should

be individual, all emanate from one consignment of

material and be sent out from one source".

There were twenty-two (22) specimens.

c. Mean temperatures - Testing was requested at

32, 50 and 68 of mean temperatures.

d. Specimen reference - National Physical Laboratory

prepared the samples and made tests on a number of

samples over a wider temperature range. The samples

were sent without the reference value from National

Physical Laboratory.

e. Results - Improved design and operation of several

apparatus. The reduction in differences from the

National Physical Laboratory reference data was

from five percent to one percent after changes had

been made in several laboratories. Two laboratories

chose to construct new apparatus which resulted in

the reduction of the difference to one percent.

Several sources of error are listed.

f. Time - A committee was formed in June 1961; the

report is dated 1968. Therefore, the time for the

round robin was about seven years.

3. "An Interlaboratory Comparison of the ASTM C355 Pipe

Insulation Test", M. Hollingsworth, Jr. (Reference 13).

a. Specimen - Resin-bonded glass fiber at a density of

approximately 6.5 pcf. The round robin was not

planned, but grew out of testing by two laboratories.

There was no attempt to select a material based on a

set of criterion. y

-

b. Number of specimens - There was one specimen tested

by two laboratories. As participation was extended

to others, a second specimen was added. Both

specimens were tested by ten laboratories.

c. Mean Temperatures - The range of mean temperature

was 120 to 300°F. Each laboratory ran at least

three mean temperatures, and generally more.

d. Specimen reference - Laboratory 1, the originator,

acted as the distribution center and conducted

several sets of tests on the specimen.

6
e. Results - The data were within - three percent of

the mean value. There was degradation of the

specimen, probably due to handling during shipping

and testing.

f. Time - The total time for the round robin was

seven and one-half years and involved ten testing

laboratories

.

4. ASTM and MIMA-sponsored round robin currently underway

(Reference 14)

.

C. Pelanne is managing the effort in two phases. In

the first phase, a one-inch specimen of fiber glass

is being circulated among the participants. This

phase was begun by MIMA to determine the reproducibility

of testing low density fiber glass with the guarded hot

plate. Pelanne reported preliminary results of three

laboratories at an ASTM C16.30 meeting in San Antonio.

ASTM was added as a co-sponsor. Several preliminary

reports have been made, but the final report has not

been given yet, almost three years later. In this round

robin, a determination of the precision measurement was

the primary objective. It was, therefore, necessary to

have only one specimen.

At the ASTM Albuquerque meeting in May, 1978 Phase II

was added. The objective was to determine the precision

of use thickness testing. The test specimens were to

be 3-1/2, 6 and 8 inches. New specimens were prepared

and testing was expected to begin about June 1978. This

work has not been reported.

5. Jim Walter Research Corporation has conducted a companysponsored round robin on their product with two other

laboratories using the guarded hot box. The results

were presented in December 1979 at the ASHRAE/DOE Conference

(Reference 15)

.

6. International Interlaboratory Comparison of Thermal

Conductivity Determinations with a Guarded Hot Plate

and Heat Flow Transducers.

This ISO 163 sponsored round robin is underway. Thus

far 22 countries worldwide have volunteered to participate

with 122 measurement instruments. It is planned to have

measurements made on dense glass fiber board (^lOpcf),

low-density glass fiber blanket ( 0 . 6 pcf) , a closed

cell plastic insulation, and an air gap. A working

group from ISO 163 chaired by Frank Powell of NBS will

conduct the round robin. Under consideration are

measurements to be made at three mean temperatures,

several thicknesses of material, and if feasible, a density

range. The round robin will be operated with several

"loops" running simultaneously, e.g., a North American

Loop, etc. Specimens will be circulated in series to

about 6-10 laboratories in each loop. The round robin

started in 1981.

7
V. OBJECTIVES

Decisions on the design of the round robin are based on

the objectives. The objectives can either be related to the

apparatus or to the test specimen. In the latter case an

attempt is made to resolve differences in reported data in

thermal properties for an apparatus that has been in use for

some time and is well accepted. In the former case, the

present one, the round robin is used to improve the apparatus.

Accordingly the objectives are as follows in priority order:

1. Alert all concerned to the possibility and sources

of significant errors in design and operation or

measurement of hot boxes, with emphasis on the

calibrated hot box.

2. Evaluate and improve calibration procedure. Develop

standard calibration procedure.

3. Provide present and future operators with confidence

in their apparatus and a basis on how their box

performs compared to all others.

4. Provide information for the overall improvement of

hot box ASTM Standard Test Methods, particularly data

for the writing of a precision and accuracy statement.

5. Compare the measured thermal conductance of various

specimens from the lot of material produced for the

round robin for possible development of a reference

material. This will include results from the guarded

hot box apparatus that participate and from the

guarded hot plate testing of samples of the test specimen.

6. Provide guidelines to improve design of future hot

boxes

8
VI. POSSIBLE TEST SPECIMEN

The thermal insulation selected for the test specimen

depends on the objectives of the round robin. For this round

robin the primary concern is with the development of an apparatus

and not the establishment of a reference material. It is important that the specimen be simple in construction. The issues to

be considered in the selection are:

1. Should the specimen be homogenous of one material or

non-homogenous similar to normal construction? As it

is imperative that data be comparable among the

laboratories, the specimen should be as similar for

each laboratory as possible. The specimen should have

a negligible influence on any differences between two

laboratories or between one laboratory and the mean

values. The draw back to normal construction using

wooden members is the non-uniformity of wood and the

difficulty in controlling moisture changes from one

laboratory to another.

2. What are restrictions on material properties? The

specimen will range in size from 14 x 20 feet to about 6x6 feet for large calibrated boxes and to smaller

sizes for the guarded hot boxes. It must be mechanically

strong enough to stand alone in this range of sizes and

it must be stable with time. The specimen properties

must not change with time or handling. It should also

be impervious to air and moisture. Large quantities

should be reasonably uniform in property values

(particularly thermal conductance and density) and in

thickness

.

3. What thermal resistance should be tested? It would be

desirable to test at several thermal resistance values

to determine performance characteristics over the full

testing capability of the apparatus. More than one value

seems impractical at present due to the testing time

required. Problems with the operation or design are

likely to occur at the larger R values. In addition,

industry and government are recommending higher values

in actual applications. Therefore, the specimen should

be in the range of R = 15 to 20.

t 4. How much material is needed? For the calibrated hot

boxes identified, see Appendix 3, there is 884 square

feet of testing area. The six largest guarded hot

boxes listed in Appendix 3 have a total sample area of

465 square feet. The total area is 1349 square feet.

To allow for all other guarded hot boxes to participate

and for some contingency, at least 50% should be added

which results in a total area of about 2000 square feet.

If there is a specimen for every laboratory, then 2000

square feet of about R=20 material will be required.

9
5. What insulation material should be used? There are

several possibilities. If non-homogeneous specimens

are ruled out, the specimen can be either of one

monolithic material or a single insulation material

with skins to provide the necessary structural strength

and stability. The following are the insulation materials

that were considered:

a. Fiber glass board - This material has recently been

established as a standard reference material by

NBS and has been used in one previous round robin.

It has a thermal resistance of around 4 per inch.

Owens-Corning Fiberglas Corp., a previous supplier,

has enough material on hand for one test specimen.

Another lot of material would have to be made for

this program if all laboratories receive a specimen.

It can be made in 4 x 10 feet boards. For the higher

R value suggested earlier two layers of 2 inch

material would have to be laminated together with

a non-penetrating contact cement. A skin would also

need to be laminated to prevent air and moisture

from passing through the specimen while testing.

b. Extruded polystyrene - This material has an R value

per inch of about 5 but there is some concern with

the stability of the thermal conductance with time.

DOW Chemical, USA, has been able to age and stabilize

the material by holding it at 145°F for six months.

DOW has enough material on hand for one test specimen.

Another lot of material would have to be made for

this program if all laboratories receive a specimen.

DOW considers it impractical to supply the quantity

required for all laboratories due to the aging

process. For the high R values two layers of 2 inch

sheets would have to be laminated together. As

manufactured, the material is impervious to air and

has a low water vapor permeability of about 0.6

perm-in

c. Molded polystyrene - This material has an R value

per inch of about 4. As manufactured the density

variation is about 10%.

W.R. Grace and Company has run a controlled

production of seven billets at 1.25 pcf density.

The billets were characterized for density as a

function of position and for conductivity as a function of density. By using the middle section,

the billets' density was maintained within a 5%

variation

A specimen can be made in one four inch slab which

would eliminate any lamination. The material is

impervious to air and has a water vapor permeability

of about 1.2 perm-in. It is recommended that the

surface be coated with a layer of adhesive, one

coat of primary and two coats of light colored latex

base paint. A 90 lb. Kraft paper facing was not

satisfactory due to shrinkage.

10
d. Low-density fiber glass - This is the material most

often used in new residential construction and it has

an R value of about 3 per inch. It is being used by

the NBS program for laboratory accreditation. It

would be useful to have the round robin use the same

material although that is not an objective of the

program. NBS has about 1500 square feet on hand which

means that only one specimen could be supplied. The

material is available in 1 inch 4x4 foot sections.

To make up large specimens of R=20 material would

require 6 layers laminated together. It would probably

be mechanically weak and unstable.

11
VI'I - NUMBER OF SPECIMENS

There are two extremes in the number of specimens required

for a round robin. One is to use a single specimen which is

sent to each laboratory in turn for testing. This usually

requires a rigid scheduling so that the apparatus with the

largest test area receives the specimen first and it is trimmed

as it is passed along. The other extreme is to provide each

laboratory with its own specimen from a single lot of suitable

uniform and stable material. In the first case there is no

problem with material variability, assuming that trimming causes

no changes in properties, such as the average density. Results

could be effected by handling damage or long term aging.

In the multiple specimen case the results must be considered

in terms of the variability of the material properties within the

lot of material. If the lot of material is well characterized

this effect can be rationalized. On the positive side, the

handling is reduced and there would be no possible damage due

to trimming.

Of course, there is the intermediate case, at least one

specimen tested by at least two laboratories. Of the calibrated

hot boxes likely to participate, two have the same testing area, 8x8 feet; in addition one guarded hot box has the same sample

area. There are also two guarded hot boxes with a sample area

of 6 x 6 feet. If all participate and their scheduling can be

worked out for multiple specimen testing, an exchange of specimens

by the laboratories with the same area would add significantly to

the results of the round robin.

12
VIII. TEST CONDITIONS

To make the measurements directly comparable the test

conditions must be specified and reported in a standard format.

A sample data sheet is given in Appendix 2 for possible use in

the round robin.

The following are the variables to be specified:

1. Mean temperature of specimen, °F.

o

2. Temperature difference across specimen, F.

3. Room Temperature in which box is located, °F.

4. Relative humidity on both sides of specimen, %.

5. Pressure difference across specimen, inch of water.

One least one mean temperature will be specified and two

others suggested if scheduling permits an organization to do the

testing. A 45°F mean temperature is one that all boxes can attain

with a 40 or 50°F temperature difference, although 75QF is the usual

mean reported for insulation materials (See Reference 1) . In

addition a 95°F mean is usually taken to represent summer conditions.

The room temperature is important as the temperature difference

across the measurement box walls is directly proportional to the

heat loss.

In most boxes the relative humidity cannot be controlled at

a preselected high value but it can be maintained at a relatively

low value. A low relative humidity is necessary to keep frost off

the cooling coils or heat exchange fins on the cold side. The

specification should be such that normal operation will easily

meet the condition.

It is important that relative humidity be measured and

reported as a water vapor gradient in the specimen material

could cause significant effect on the measured thermal conductance.

The pressure difference should be as close to zero as

practical. Any pressure gradient could cause an infiltration of

air across the specimen and a resultant transfer of energy. It

is important that the pressure difference be measured and

reported.

13
I X . POSSIBLE CONCERNS

Experience with the calibrated hot box is limited but some

anomalies have appeared. It is expected that the analysis of

the round robin data will reveal others and offer explanations.

The testing by the guarded hot boxes will be invaluable in

this regard, as it makes an absolute measurement. The following

has been observed:

1. In one laboratory the results of testing of large

area, well characterized fiber glass specimens has

given results different than expected from previous

measurements. The difference is considered to be

likely due to a flanking or by-pass loss around the

specimen in the materials holding the specimen in place.

2. In another laboratory two layers of well characterized,

aged, one inch extruded polystyrene with metal skins

have been laminated to form a calibration specimen.

Measurements in a calibrated box indicate R values lower

than expected. The difference was thought to be due to

flanking losses. Further testing of a specimen from

the same lot of material in a guarded hot box has

confirmed the calibrated hot box result.

3. In a third laboratory the measurements on extruded polystyrene in a calibrated hot box and in a guarded hot

box have been made over a range of R values . The

measured R values in the calibrated box tend to be higher

than those in the guarded box. The difference seems to

get larger with increasing R.

In informal discussions among operators and from computer

analysis of the data the following are possible sources of error:

1. Flanking or by-pass heat transfer around the specimen,

through the materials holding the specimen within the

holding frame.

2. The extrapolation of calibration results at one or two

R measurement to higher values.

3. A weakness in a calibration procedure using the temperature difference between the measurement box and the room.

Appendix 5 offers an example of a simple parallel heat flow

model to make an estimate of the heat transfer through 1/2 inch

thick plywood used to mechanically hold a specimen in place.

It indicates for an R=15 specimen a sizeable flanking of about

5% of the total heat transfer.

14
X. NBS ROLE

The role of the National Bureau of Standards is to provide

guidance and leadership in measurement technology and to dispense reference materials used by the measurement community.

In addition, it acts as a referee in situations where a difference

occurs in measured results on the same material. In the present

case, a new test method and apparatus, the calibrated hot box, is

being developed and the bureau is building its own facility and will

participate in the development process, including the round robin.

NBS will be in a position to make improvements and to mediate

any disputes. In addition, it would be possible to extend the

accreditation program to this apparatus when the test method

appears on the ASTM books.

The Bureau has taken the responsibility to plan and conduct a

round robin for ASTM C16.30. This will require the following:

1. Take the responsibility to physically and statistically

characterize the specimen material in terms of its

density, thermal conductance, and thickness. These

measurements would be done at the Bureau and/or other

places under its supervision.

2. Establish a repository for the specimen material.

3. Ship the materials to the participating laboratories.

If the materials move from one laboratory to another,

make sure schedules are followed.

4. Analyze the resulting data.

5. Report the final results in a manner that keeps each

laboratory's identity confidential.

It is expected that the NBS would work with the supplier of

the specimen material and that the DOE would continue its

support. The DOE is vitally interested in establishing the

performance of building envelopes under steady and dynamic

conditions. Energy conservation depends on knowing accurately

how buildings lose energy.

15
XI. SCHEDULING

It is desirable that the total time for round robin be

as short as possible, on the order of a year or less. The time

for previous round robins has been very long, ranging from three

to eight years. In the following a time projection is made for

the two extremes of one specimen passed to all laboratories in

sequence or a specimen for each laboratory.

It is expected that all laboratories with a calibrated hot

box will volunteer to take part in the round robin and each is

represented on the task force. In addition those laboratories

with guarded hot boxes with large sample areas will be encouraged

to take part. Others may also participate if they request

specimen material. All laboratories that are known to have hot

boxes will be informed that a round robin is beind conducted.

The primary effort and the impelling reason for the program is

to test a single material in the calibrated hot boxes. A

preliminary report will be issued when all testing has been

finished in the calibrated hot boxes and the large sample area

guarded hot boxes.

The operators of the calibrated hot boxes estimate about two

weeks time to mount a specimen and measure its thermal conductance

at one mean temperature. About one month advance notice is needed

to schedule time in the apparatus. It is estimated that time for

a guarded box would be similar.

There are two known calibrated hot boxes and one guarded hot

box with 8x8 foot specimen areas. As pointed out, it would be

of great value if the specimens could be exchanged and rerun. In

addition, there are two guarded hot boxes with 6x6 foot specimen

areas, they could also exchange.

Based on these considerations the following time estimates have

been made:

1. One specimen circulated to all laboratories. In addition

to test time an allowance would be required to trim the

specimen and to package and ship it to the next laboratory.

A reasonable time for each laboratory is six weeks , two

weeks testing, two weeks for trimming, and two weeks for

shipping. The total time is 72 weeks for twelve laboratories

If 6 weeks is added for reporting, the total time is 1-1/2

years

Obtaining a well characterized specimen would be negligible

as only one sample is required. At least two sources

have enough material on hand.

16
2. A specimen for each laboratory. Each laboratory would

need about two weeks for testing. Additional time should

be allowed for scheduling and reporting, the total time

would reasonably be one month. As a great deal more

material is required, time should be allowed to characterize

the material lot, estimated at three months. The total time

may be on the order of six months.

It is expected that the results of the round robin will generate

a need for more information and further testing, either on the same

specimen or on other specimens, e.g., a built-up stud wall section. If

each laboratory has its specimen in hand it will be somewhat easier

to have further testing done.

The final report will include all data from

that choose to participate and will be issued by

C16.30.

all those laboratories

ASTM Subcommittee

17
XII. EXPECTED RESULTS

The "hard" results will be in two reports, the present one

on planning and a final report on the results of the testing.

The "soft" results will be the many discussions, formal and

informal, of the many people involved in the measurements. The

round robin and the task force will provide a focal point for the

general advancement of the calibration hot box apparatus and

thermal measurements of large, full-scale wall sections in general.

Analysis of the data will provide the basis on which a

precision and accuracy statement can be made for the ASTM Standard

Test Method. It is likely that a single calibration procedure

will evolve.

A general upgrading of measurement techniques and instrumentation is also likely when the operators compare the way data are

measured and recorded. This will be an informal result, as

specific instrumentation and data reduction apparatus are not

specified and will probably not be cited in the final report.

The final report of the data and its analysis will state the

mean values and the differences and give some indication of the

types and possible sources of such differences. As each laboratory is aware of its performance compared to all others, there

will be a general upgrading in performance and techniques.

Finally, the results will be useful to the NBS laboratory

accreditation program when it considers the calibrated hot box.

18
XIII. RECOMMENDATIONS

There are several issues on which all those who intend to

participate should agree:

1. Selection of a test specimen.

2. Setting of the number of specimens.

3. Specimen R-value. * 4. Test conditions of mean temperature, temperature

difference, relative humidity, and pressure

difference

.

5. Number of test points to be run.

6. General specifications, such as adhesive to join sections

of the specimen, material used to seal the specimen into

the frame, and the tape used to mount the surface thermocouples . Based on the discussions in this report, the following

recommendations are made:

1. The test material should be molded polystyrene. If

satisfactory tolerance cannot be held in the manufacturing

process, then fiber glass board should be used by laminating two 2-inch boards and a plastic skin. Owens-Corning

Fiberglas Corp. can supply the material, and DOW Chemical

USA, can do the laminating on their line.

2. Each laboratory should be provided with a specimen that

will fit its sample area.

3. The specimen R-value should be a nominal R=16. For the

recommended material, this will require a single

monolithic 4-inch specimen made up of 4 foot wide sections.

4. The test conditions should be:

a. Mean temperature = 45°F.

b. Temperature difference = 50°F.

c. Relative humidity as low as possible on both sides

of the test section. Control and research pressure

difference at zero.

5. A minimum of one test point should be run. If resources

permit it, other suggested points are mean temperatures of

75°F and 95°F with a 50°F temperature difference.

19
6 . The adhesive used to join sections of molded polystyrene and the polystyrene edges to the test forms

should be a one component urethane. The joint

between the specimen and the frame should be sealed

with a silicone rubber caulk.

7. The surface thermocouple should be mounted with the

tape. Finally, it is recommended that all data

should be reported on the data form in Appendix 2.

20
XIV •. REFERENCES

1. "Handbook of Fundamentals'; ASHRAE , 19 77.

2. "Standard Test Method for Thermal Conductance and Transmittance

of Built-Up Sections by Means of the Guarded Hot Box"

C236-66, ASTM .

3. Solvason, K.R. "Large-Scale Wall Heat-Flow Measuring Apparatus"

ASHRAE Transactions , 65, 1959.

4. Mumaw, J.R., "Calibrated Hot Box: An Effective Means for

Measuring Thermal Conductance in Large Wall Sections,"

ASTM STP 544 , 1974, pp. 193-211.

5. Mumaw, J.R., "Thermal Research Facility — Large Calibrated

Hot Box for Horizontal Building Elements," DOE/ASTM Conference

STP 718, 1980.

6. Rucker, J.L., and Mumaw, J.R., "Calibration Procedures and

Results for a Large Calibrated Hot Box", ASHRAE/DOE Conference

ASHRAE SP 28, 1979.

7. Miller, R.G., Perrine, E.L., and Linehan, P.W.,

"A Calibrated/Guarded Hot Box Test Facility,"

ASTM STP 660 , 1978, pp. 329-341.

8. Perrine, E.L., Linehan, P.W., Howanski, S.W., Shu, L.S.,"

"The Design and Construction of a Calibrated/Guarded Hot

Box Facility" ASHRAE/DOE Conference, ASHRAE SP28 , 1979.

9. Achenbach, E.R., "Design of a Calibrated Hot Box for Measuring

the Heat, Air and Moisture Transfer of Composite Building Walls"

ASHRAE/DOE Conference, ASHRAE SP 28 , 1979.

10. Fiorato, A.E., "Laboratory Tests of Thermal Performance of

Exterior Walls" ASHRAE/DOE Conference, ASHRAE SP 28 , 1979.

11. Robinson, H.E., and Watson, W.W., " Inter laboratory Comparison

of Thermal Conductivity Determinations with Guarded Hot Plates,"

Symposium on Thermal Insulating Materials" ASTM STP 119 , 1951,

pp. 36-44.

12. "International Comparative Measurements of Thermal Conductivity"

HR TOME XLVIII, No. 1 , 1968.

13. Hollingsworth, M. , Jr., "An Inter laboratory Comparison of the

ASTM C 335 Pipe Insulation Test," ASTM STP 660, 1978 , pp, 50-59.

14. ASTM 16.30 Subcommittee minutes for 1977 and 1978.

15. Sherman, Morton, "Aged Thermal Resistance (R-value)'of Foil-Faced

Polyisocyanurate Foam Therma Insulation Board"

ASHRAE/DOE Conference, ASHRAE SP 28 , 1979.

21
APPENDIX 1

ASTM - Cl 6. 30 Thermal Measurements Task Force - Hot Box Round Robin

1. Erv Bales, Chairman 202/252-9187

Building Energy Science Branch

Office of Conservation and Renev/able Energy

U.S. Department of Energy

Washington, DC 20585

2. Dr. Anthony Fiorato 312/966-6200

Construction Technology Laboratories

5420 Old Orchard Road

Skokie, Illinois 60077

3. Mr. David Greason 614/587-4362

Dow Chemical, USA

Granville Research & Development Center

P.O. Box 515

Granville, Ohio 43023

4. Mr. Marion Hollingsworth, Jr. 614/587-0610

Owens-Corning Fiberglas Corporation

Technical Center, Energy Measurements Laboratory

P.O. Box 415

Granville, Ohio 43023

5. Mr. Jack Howanski

6. Dr. Diana Kirkpatrick 301/921-2946

National Bureau of Standards

24408 Kakaf Drive,

Damascus, Maryland 20750

7. Dr. Gerry Miller 813/576-4171

Jim Walter Research Corporation

10301 Ninth Street, North

St. Petersburg, Florida 33702

8. Mr. Frank Powell 301/921-3275

National Bureau of Standards

Building 224, Room B.120

Washington, DC 20234

9. Mr. Ronald Tye 207/282-5911

Energy Materials Testing Laboratory

Biddeford Industrial Park

Biddeford, Maine 04005

22
APPENDIX 2

THERMAL LABORATORY REPORT

TEST NUMBER TEST DATES

CALIBRATED HOT BOX

. METERING AREA =

TEST PANEL CONSTRUCTION:

HOT SIDE COLD SIDE

SURFACE TEMPERATURE

AIR TEMPERATURE

AIR VELOCITY

SURFACE COEFFICIENT

AVERAGE POWER INPUT =

MEAN TEMPERATURE

THERMAL CONDUCTANCE, C =

' THERMAL RESISTANCE, R

THERMAL TRANSMITTANCE, U = THERMAL RESISTANCE, R

COMMENTS:

OPERATORS

23
APPENDIX 3

Summary fact sheets for each known Calibrated

Hot Box in the United States are in this

Appendix. In summary, table is as follows:

ORGANIZATION SPECIMEN SIZE

1. W.R. Grace fit Company 8 ft. X 8 f t

2. DOW Chemical, USA 9.8 ft

X 13. 1 ft

3. Construction Technology 8 f t

X 8 ft

Laboratories 7 inch

4. Owens-Corning Fiberglas 9 f t

X 14 ft.

5. Owens-Corning Fiberglas 14 ft

X 20 ft

6. Jim Walter Research Corp. 8 ft

X 8 f t

7. National Bureau of Standards 10 ft. xl5 ft.

REMARKS

Can be used in

Guarded mode

Can test for

dynamic testing

Vertical heat flow

Vertical heat flow

Can be used in

Guarded mode

Can be used for

dynamic, moisture

and infiltration

heating
1. Organization: W.R. Grace & Company

2. Contact Person: Mr. Larry Shu

3. Test Specimen Size: 8x8 feet (6x6 feet in Guarded Mode)

4. Temperature Range: Cold Side -30 to 160°F

Hot Side 59 to 120°F

5. Design R Value: 4 to 3 2

6. Method of Temperature Control: Cold Side - external 5 hp;

Refrigeration unit which supplies chilled air.

Hot Side - water/air heat exchanger in box. The water

flow and temperature rise are controlled.

7. Calibration Technique: Measure a shell coefficient and

a frame coefficient so that Q,loss

T Cold

8. Specimen fixture configuration: Not firm in design at this time.

NOTE: This facility is under construction and will be ready for

operation about May 1980. This facility will be able to

test under dynamic conditions with a maximum rate of change

of 35oF/hr at 80°F heating and 20°F/hr at 15°F cooling.

In addition, the test section can be positioned vertically

or horizontally and can be operated in the Guarded Mode.

25
1. Organization:

2. Contact Person:

3. Test Specimen Size:

4. Temperature Range:

Dow Chemical, USA

Dr. David Greason

9.84 x 13.12 feet (3x4 meter)

Cold Side -50 to 70°F

Hot Side 70 to 140°F

5. Design R. Value: Have tested over R=40

6. Method of Temperature Control: Cold side - Refrigeration

unit which supplies chilled air. Controlled electrical

heaters are used for fine tuning the temperature.

Hot Side - SCR controlled electric heaters (three) in the

box

7. Calibration Technique: Use thermal piles on walls to

determine correction factor for the

total heat

8. Specimen fixture

Configuration

Specimen is built into frame inside

a 1/2" plywood skin. The seams are

caulked. May eliminate plywood to

reduce possible flanking losses.

NOTE: The test section may be positioned vertically or horizontally.

The environment of the CHB is controlled so that the

temperature difference across the hot side wall can be made

nearly zero. This makes the operation somewhat similar

to a Guarded Mode.

26
1. Organization:

2. Contact Person:

3. Test Specimen Size:

4. Temperature Range:

Construction Technology Laboratories

Dr. Anthony E. Fiorato

8 ft x 7 inches x 8 ft x 7 inches

Cold Side -20 to 120°F (Outdoor)

Hot Side 65 to 80°F (Indoor)

5. Design R Value:

6. Method of Temperature

Control

7. Calibration Technique:

2 to 20

Cold side - Refrigeration controllers

on cooling coils and heating elements

in indoor and outdoor chambers.

Heating elements SCR controlled.

Calibrate base conditions for each

test run by holding THot . Then determine wall coefficient with:

T

T

T7 , and T„ , - T_ , , AMB = Hot Hot Cold A T.

Can also calibrate for Ttt = T_ . ,= T‘ Hot Cold AMB

and correct for losses.

8. Specimen Fixture

Configuration

Specimen is built into 12-inch square

urethane frame inside a 1/4" plywood

skin.

NOTE: This facility has the ability to test under dynamic

conditions with a maximum rate of change of 50 to 100 F

per hour (plenum air) . Rate depends on absolute value

of set point temperatures

.

27
1. Organization: Owens-Corning Fiberglas Corp.

2. Contact Person: Mr . J ohn Mumaw

3. Test Specimen Size: 9 x 14 feet

4. Temperature Range: Cold Side -40 to 58°F

Hot Side 32 to 150°F

5. Design R Value: 1 to 35

6. Method of Temperature

Control

Cold Side - Direct expansion system

to cold temp, reheat with 6 step

electrical resistance. Heaters

with on/off controller.

Hot Side - no cooling - heating same

as cold side.

7. Calibration Technique: Measure a shell coefficient and a

frame coefficient so that:

OW =C (T —T ) + c (t —T ) LOSS 1

v HOT AMB' 2

v HOT COLD ;

8. Specimen Fixture

Configuration

Specimen built into frame inside

a 1/16 " FRP skin.

28
1. Organization: Owens-Corning Fiberglas Corp.

2. Contact Person: Mr. John Mumaw

3. Test Specimen Size: 14 x 20 feet

4. Temperature Range: Cold Side -50 to 150°F

Hot Side 15 to 145°F

5. Design R Value: 1 to 40

+

6. Method of Temperature

Control

Cold Side - refrigeration unit

with SCR control on electric heaters

Hot Side - on/off control - thermometer sensor with electrical

heater or brine system refrigeration

7. Calibration Technique: Measure a shell coefficient and a

frame coefficient so that:

qloss

= c

i (thot ” tamb ) + C

2

^ thot " t

cold^

8. Specimen Fixture

Conf iguration

Specimen layed on end of bottom box

for support. The specimen is in a

frame with a 1/16" FRP skin.

29
1. Organization: Jim Walter Research Corporation

2. Contact Person: Dr. Gerry Miller

3. Test Specimen Size: 8x8 feet (6x6 feet in Guarded Mode)

4. Temperature Range: Cold Side -20 to 80°F

Hot Side 70 to 160°F

5. Design R Value: 20

6. Method of Temperature

Control

Cold Side - refrigeration unit which

supplies cold air. Controlled

electrical heaters are used for fine

tuning the temperature.

Hot Side - SCR controlled electrical

heaters (three) in the box with a

Leed and Northrup control unit.

7. Calibrated Technique: Measure a shell coefficient and a

frame coefficient so that:

QLOSS

= C

1

(THot

" TAMB ) +

C

2

^ T

Hot

“ T Cold^

8. Specimen Fixture

Configuration:

Specimen is built into frame inside

a 1/2" plywood skin.

NOTE: The test section may

horizontally and can

be positioned vertically or

be operated in the Guarded Mode.

30
1. Organization: National Bureau of Standards

2. Contact Person: Mr. Frank Powell

3. Specimen Size: 10' by 15'

4. Temperature Range: Cold Side -40 to 150°F

Hot Side 50 to 150°F

5. Design R Value: 2 to 50

6. Method of Temperature

Control

Cold Side - Refrigeration unit with

SCR to control electric resistance

heaters. Hot Side - Laboratory water

supply and SCR to control electric

resistance heaters.

7. Calibration Technique:: Heat flow meters to measure metering

chamber wall heat transfer to water

jacket. Determine thermal resistance

of calibration wall from Guarded

Hot Plate tests of material. Determine

flanking heat transfer coefficient by

difference.

8. Specimen Fixture

Configuration

Frame lining will be plywood or FRP

.

Specimen will be gasketed, caulked,

or taped at perimeter to eliminate

leakage.

NOTE: This facility has the ability to test under dynamic

conditions with a maximum rate of change of 20°F/hr at 82°F.

This facility is in the construction stage and will be

ready for operation about Spring, 1982.

31
APPENDIX 4

NBS/DOE WORKSHOP ON CALIBRATED MOT BOXES

MARCH 30, 1979

NBS - GAITHERSBURG

P.R. Achenbach

NBS - 740

Washington, DC 20234

301/921-3106

Michael Argie

Smith, Hinchman & Grylls

455 W. Fort Street

Detroit, Michigan 48226

313/964-1000

Erv Bales - Workshop Chairman

M.E. Department

Stevens Institute of Tech.

Hoboken, New Jersey 07030

201/273-2574

Donald K. Baxter

U.S. Department HUD

451-7th Street, SW

Washington, DC 20410

202/755-5930

D.M. Burch

NBS - 742

Washington, DC 20234

301/921-3501

G.A. Berman

NBS - 782

Washington, DC 20234

301/921-2427

W.L. Carroll (NBS-742)

Lawrence Berkeley Laboratory

Energy-Efficient Bldgs. Pgm

Berkeley, California

415/486-6651

S.C. Dangel

Dynatech R/D Company

99 Erie Street

Cambridge, MA 02139

617/868-8050

Andre' Desjarlais

Dynatech R/D Company

99 Erie Street

Cambridge, MA 02139

617/868-8050 x 270

Merv W. Dizenfeld

U.S. Department HUD

451-7th Street, SW

Washington, DC 20410

202/755-6590

C. Donaldson

Division of Energy and Product

Information

Federal Trade Commission

7313 Star Building

Washington, DC 20580

202/724-1537

Anthony E. Fiorato

Portland Cement Association

5420 Old Orchard Road

Skokie, Illinois 60077

312/966-6200

J.B. Funkhouser

Dynatherm Engineering

595 Marshan Lane

Lino Lakes, MN 55014

612-786-1853

C. F. Gilbo

Consultant

201 East Ross Street,

Lancaster, Pennsylvania 17602

717/392-0520

D. Greason

Dow Chemical, USA

Granville Research Center Bldg. F

P.O. Box 515

Granville, Ohio 43023

614/587-4362

32
H.H. Mackey, Jr.

U.S. Department of HUD

415-7th Street, SW #6178

Washington, DC 20410

202/755-5929

D.J. McCaa

Certain Teed Corporation

1400 Union Meeting Road

Blue Bell, PA 19422

215/542-0500

Michael McCabe

MBS - 742

Washington, DC 20234

301/921-3871

P.E. McNall

NBS - 742

Washington, DC 20234

301/921-3637

M.H. Hahn

Dennis Industries

19444 St. Johnsbury Lane

Germantown, MD 20757

301/428-0471

M. Hollingsworth

Owens/Corning Fiberglas

P.O. Box 415

Granville, Ohio 43023

614/587-0610

J.W. Howanski

W.R. Grace Company

Construction Products Div.

62 Whittemore Avenue

Cambridge, MA 02140

R.R. Jones

NBS - 742

Washington, DC 20234

301/921-3637

J.F. Kimpflin

Certain Teed Corporation

Valley Forge, PA 19481

215/687-5000 x 7526

Diana Kirkpatrick

NBS - 782

Washington, DC 20234

301/921-2946

H.N. Knickle

Department of Chem. Eng.

University of R.I.

Kingston, RI 02881

401/792-2655

Stephen Lane

NBS - Rm B26 Bldg. 225

Washington, DC 20234

301/921-3481

W.C. Louie

Smith, Hinchman & Grvlls

455 W. Fort Street

Detroit, MI 48226

313/954-3000

R.G. Miller

Jim Walter Research Corporation

10301-9th Street, North

St. Petersburg, Florida 33702

813/576-4171

Murnaw

Owens/Corning Fiberglas

P.O. Box 415

Granville, Ohio 43023

614/587-0610

Henry Oms on

Radco, Incorporated

218 North Lee Street

Alexandria, Virginia 22314

703/836-2527

B

.

A. Peavy

NBS - 742

Washington, DC 20234

301/921-3501

C. M. Pelanne

Johns Manvi lie R/D

P.O. Box 5108

Denver, Colorado 80217

303/979-1000

J.W.

33
E„L. Perrine

Wiss, Janney, Elstner & Assoc.

330 Pfingsten Road

Northbrook, Illinois 60062

3 12/ 272-7 400

F.J. Powell

NBS - 790

Washington, DC 20234

301/921-3275

Edwin Randall

NBS - 782

Washington, DC 20234

301/921-2946

B. Rennex

NAHB Research Foundation

627 Southlawn Lane

P.O. Box 1627

Rockville, Maryland 20850

301/762-4201

Mary Reppert

NBS - 742

Washington, DC 20234

301/921-3637

Ben Reznek (NBS Consultant)

3501 Forest Edge Drive,

Unit 14-2G

Silver Spring, MD 20906

James N. Robinson

Oak Ridge National Lab.

Energy Division

P.O. Box X

Oak Ridge, TN 37830

615/574-5208

Glen Schuyler

NBC - CANADA

C. Seal

Reynolds Metal Company

Williamsburg Road & Goddin St.

Richmond, Virginia 23235

804/788-7357

Mort Sherman

Jim Walter Research Corporation

10301-9th Street, North

St. Petersburg, Florida 33702

813-576-4171

Marvin K. Snyder

Butler Manufacturing Company

Research Center

135th and Botts Road

Grandview, Missouri 64030

816/648-4009

Henry Taylor

Architectural Testing, Inc.

1360 North George Street

York, PA 17404

717/846-7700

Ron P. Tye

Dynatech R/D Company

99 Erie Street

Cambridge, MA 02139

617/868-8050

Foster Wilson

Owens/Corning Fiberglas Corp.

Technical Center

P.O. Box 415

Granville, OHIO 43023

614/587-0610

Mike Zieman

RADCO, Incorporated

P.O. Box 5506

Carson, California 90749

215/532-3842

34
APPENDIX 5 PARALLEL HEAT FLOW FLANKING

For a 1/2 inch frame of plywood around a test specimen the ratio

of areas would be:

Aspecimen _ HW

Aplywood 2t (H+W) +4t^

where the terms are defined by a sketch:

Plywood

The ratio of the heat transfer through the two materials is,

neglecting terms of t2;

Q U A • ZJ9. . Q +Q

p s U

sA

s

R A

- s- P

R A

p s

For H = 10 feet, W = 14 feet, t =1/2 inch, and

R = 15, and R = 1.25(3), where the insulation is

s p

assumed to be 3 inches thick.

.054

35
NBS-114A (REV. 2-80) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NRSIR 81-2443

2. Performing Organ. Report No. 3. Publication Date

February 1982

4. TITLE AND SUBTITLE

"Plan for a Round Robin of Rot Boxes”

5. AUTHOR(S)

Dr. Ervin L. Bales

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

National Bureau of Standards

Department of Commerce

Washington, DC 20234

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

A plan for an interlaboratory round robin series of tests sponsored by the American

Society for Testing and Materials (ASTM) using calibrated or guarded hot-box

equipment is described. These testing methods are designed to measure the thermal

conductance of full-scale building sections such as walls, roofs and floors.

Results from about 25 hot boxes in the U.S. and Canada are expected to produce

improved calibration techniques and repeatability and uncertainty information

12. useful for improving ASTM specifications.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) interlaboratory round robin-tests, calibrated and guarded hot boxes, ASTM C-236,

thermal conductance of building sections

13. AVAILABILITY 14. NO. OF

(XXI Uni imited

| 1 For Official Distribution. Do Not Release to NTIS

PRINTED PAGES

37

1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

15. Price 20402.

[XJCOrder From National Technical Information Service (NTIS), Springfield, VA. 22161 $7.50

USCOMM-DC 6043-P80

II