li'imriiiSinSf ^'^*^° * TECH RJ.C

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NisrUnited States Department of Commerce

Technology Administration

National Institute of Standards and Technology

NIST Technical Note 1391

NIST Technical Note 1391

Thermal Conductivity of Fibrous Glass Board:

An International Intercomparison for Guarded

Hot Plates and Heat Flow Meters

David R. Smith

Materials Reliability Division

Materials Science and Engineering Laboratory

National Institute of Standards and Technology

325 Broadway

Boulder, Colorado 80303-3328

May 1997

'^TES

U.S. DEPARTMENT OF COMMERCE, William M. Daley, Secretary

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Robert E. Hebner, Acting Director
National Institute of Standards and Technology Technical Note

Natl. Inst. Stand. Technol., Tech. Note 1391, 44 pages (May 1997)

CODEN:NTNOEF

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1997

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
Thermal Conductivity of Fibrous Glass Board:

An International Intercomparison

For Guarded Hot Plates and Heat Flow Meters

David R. Smith

Materials Reliability Division

National Institute of Standards and Technology

Boulder, Colorado 80303-3328

email: drsmith@boulder.nist.gov

In the early 1980s an international round robin was held in which apparent thermal

conductivity of specimens offibrous glass insulation board was measured by users of

guarded hot plates (GHPs) and heat-flow meters (HFMs). The round robin was

performed over a period of several years by laboratories in Europe, North America,

Australia, and the Far East. Participants in this round robin were organized into 12

"loops," 8 for participants with GHPs and 4 for those with HFMs. Each loop in- cluded laboratories located in the same region of the world, and sharing the same set of specimens. In an attempt to obtain insight into the accuracy of the measurements,

participants were also asked to measure the thermal conductivity of a layer of air. The data submitted in this round robin are exhibited and analyzed. The overall

agreement of individual measurements with a least-squares fitted curve, as measured

by one standard deviation o, was o = 2.4% for GHPs and o = 2.7% for HFMs.

Suggestions are made for conducting fiiture round robins of this type.

Key Words: fibrous glass; guarded hot plate; heat flow meter; thermal conductivity;

thermal insulation

1. INTRODUCTION

In October of 1978, under the auspices of the International Organization for Standardization (ISO),

members ofworking group WG 6 of subcommittee SC 1 (Test and Measurement Methods) of ISO

technical committee TC 163 (Thermal Insulation) met to organize a round-robin test program. This

round robin would involve users of guarded hot plates (GHPs), and, optionally, heat-flow meters

(HFMs), measuring apparent thermal conductivity. Those attending this planning meeting represent-
ed Canada, France, Germany, Italy, Japan, the United Kingdom, and the U.S.A. The minutes of the

meeting record that the purpose for this working group was to:

* determine the current world-wide state of the art in GHP and HFM measurement technology, prior to development of ISO standards;

* create uniformity in [GHP and HFM] test methods for measuring apparent thermal

conductivity* of thermal insulation specimens;

* create confidence and credibility in international measurements;

* allow each laboratory and each country to evaluate its measurement capabilities; * provide additional input to the preparation of ISO standardized test methods in the

development stages;

* gather statistical information from a world-wide population of users of GHP and HFM

equipment and techniques; and

* finally, conduct another round robin following the development of the standards, showing

(it is hoped) that precision of measurement has been improved by use of the new

standards.

The recorded objectives of the working group were to:

* coordinate sponsorship of the round robin by ISO;

* conduct the round robin with an international scope;

* complete it within two to three years;

* focus on GHPs, but also include optional HFM data;

* measure thermal conductivities of high-density glass-fiber board and of an enclosed air gap.

Operational considerations were:

* participation in the round robin would be voluntary, at no cost to ISO;

* the number of participants would not be limited unless the number became too large

to accommodate;

* there would be subsets of test specimens circulating within each country or region;

* participants would undertake measurements with their "standard" procedures (their

^Because heat may often be transported through thermal insulation by both radiative and

conductive processes, such a thermal insulation does not have a true thermal conductivity and one

should therefore speak of "apparent" conductivity. However, for brevity, in the rest of the text the

term "apparent" will be dropped.
national standards, where applicable), using appropriate techniques in accordance

with the procedure as they understood it; * thermal conductivity would be measured at two specified mean temperatures; a third

measurement would be performed at a temperature selected by the laboratory; and

* the U.S. National Bureau of Standards (NBS) would supply the needed specimens of

fibrous glass board insulation.

The original members of WG 6 were R. Doussain (France), Convenor; C. Shirtliffe (Canada), R.

Jenish (Germany), F. DePonte (Italy), T. Otouma (Japan), P. Cornish and I. Williams (UK), and F.J. Powell and R.P. Tye (USA). By April of 1979 NBS (now NIST: the National Institute of Standards

and Technology) had organized the round robin with F.J. Powell as Convenor.

2. PARTICIPANTS

Several hundred laboratories around the world were invited to participate in the round robin, with

the understanding that participation would be at no cost to ISO. About 80 laboratories indicated

interest. These respondents were surveyed to determine the types of equipment they had so that the

size(s) of test specimens could be determined to accommodate the needs of all participants. All

participants were assured that test results would be held in confidence; the results, when released,

would not be linked to the name of the source laboratory.

The participants in the round robin are identified in Table Al of Appendix 1.

3. ORGANIZATION OF THE ROUND ROBIN

Because ofthe logistical problems that would have been encountered in distributing round-robin test specimens to a large number of participants around the world, the same set of test specimens was not

distributed to all participants. For each participant was able to accommodate only a specific size of

specimens.

Instead, the round robin was actually an intercomparison of measurements on samples from the same

lot of material. Specimens were distributed among participants in each of 12 small and localized,

round-robin groups, called "loops." Logistical problems arose during the circulation of test specimens within some loops, so in some cases additional specimens had to be introduced to allow all
participants to perform their measurements. However, the whole program will be called a round

robin. The thermal conductivities of the separate loop specimens were not measured. Because all the specimens came from the same lot, it is assumed that their conductivities agree within less than

the standard deviation of the global round-robin measurements.

Within each loop the laboratory requiring the largest specimen size was given the loop specimen first. After each laboratory finished, the specimen was circulated to the next laboratory in order of size

needed. Each laboratory trimmed the received specimen to the proper size for its own test apparatus,

ending with the laboratory needing the smallest specimen.

4. MEASUREMENTS

4.1. Test Specimens

ISO working group WG-6 had selected semi-rigid high-density fibrous glass insulation board with

phenolic binder as the test material. The density was approximately 164 kg-m"^ (10.2 Ib^'ft"^). From

a single lot ofmaterial, the manufacturer supplied boards 1220 mm (48 in) square and 25.4 mm (1 in)

thick to the convenor at NBS, where the test specimens were prepared and distributed to participants.

Other portions ofthis material also became the NBS thermal-conductivity standard reference material

SRM 1450b. The actual specimens were distributed in sizes ranging from squares with an edge

dimension of 1220 mm down to disks 180 mm in diameter.

As a means ofgiving some information on the accuracy of measurements by participant, each laboratory was invited to measure also the apparent thermal conductivity of an inexpensive and universally

available "standard reference material": air. This "standard" was to be an enclosed air gap using the same apparatus (GHP or HFM) that was used to measure the conductivity of the fibrous glass board.

4.2. Test Procedures

Before measuring the thermal conductivity, each laboratory was to dry its test specimen(s) to constant mass in an oven maintaining a temperature of 103 °C. Then the length, width and thickness were to

be measured and combined with the (dry) mass to determine the total "dry" test density. The density

ofthe metered section alone, which would be more representative of the measured conductivity, was

not measured. Due to possible inhomogeneities in the specimen (pair), the density of a specimen may

have shifted slightly as the specimen was passed on to each following participant and cut down to

smaller sizes to accommodate smaller apparatuses.
The dimensions and bulk densities ofeach specimen were to be reported in SI units on the data-entry

form appropriate to each measuring apparatus. Because two specimens were measured in the

guarded hot plate apparatus, two values of density were reported for each corresponding laboratory's

specimens. Participants measuring the thermal conductivity of the fibrous glass specimens with

guarded hot plates were asked to measure the conductivities at mean specimen temperatures of 283 K

and 297 K (approximately 10 and 24 °C) and at a third temperature within the range from 273 K to

3 13 K (0 to 40 °C). As is conventional, the mean temperatures reported are arithmetic means of the

hot-side and cool-side temperatures actually used. Thermal conductivity in HFMs was to be

measured at 23.9 °C (291 K).

Originally the conductivity of an enclosed air gap 6 mm thick was to be measured at a mean

temperature of 23.9 °C (291 K), and with a temperature difference of 28 K. Somehow a thickness

value of 25 mm, rather than 6 mm, was introduced into the instructions communicated to the

participants.

5. INPUT OF DATA BY PARTICIPANTS

Participants were requested to record their measurements on standard data-entry forms supplied by

the convenor. Facsimiles of each data-entry form distributed to participants are given in Appendix

2. The data forms requested the entry (in SI units) of raw data: oven-dried mass (g), specimen

dimensions (mm), total specimen density^ (kg-m'^), mean specimen temperature, temperatures of each

plate, temperature difference AT across the specimen, and ambient temperature (all in kelvins), thick- ness of specimen as tested (m), ambient relative humidity (%), metering area A (m^) and power input

Q (W) to the metering heater, and emissivities of hot and cold plates. From the raw data the

participant was asked to calculate the thermal resistance R^ = A-AT/Q (m^-K-W^), the thermal

conductance C^, = Q/(A-AT) = IfR^ (W-m'^-K"^), and then the thermal conductivity

k = (Qa/A)/(AT/AX) = Cfl,-AX (W-m"^-K''). The steps in the calculations just outlined here requested

the participants to follow a logical order from the raw data to a final calculation of thermal

conductivity.

^This "total" density, total mass divided by total specimen area, is not necessarily equal to the

density of the central metered area. Also, the specimens within a regional loop were sent to

laboratories in order of decreasing size of measurement apparatus, and so total densities of the

specimens may have varied as the specimens were reduced in size.
To analyze the round-robin data, we used spreadsheet templates for recording the data in formats

very similar to those originally used by the participants to submit their data. Minor changes were made in the formats for ease of data entry and analysis by computer, but all the original data were

faithfully preserved. The purpose of this part of the analysis was to allow the data to be regrouped

for various useful comparisons, as desired.

6. ANALYSIS OF RETURNED DATA

Several important factors were assessed while entering the returned data into the spreadsheet

templates for analysis. First, each data sheet was carefully examined for internal consistency among

the reported values. Calculated values, such as density, thermal resistance, and thermal conductivity,

derived from the data submitted by each participant, were checked for accuracy by recalculation. In

this stage several types of questionable data were found.

A few data were obviously in error, but it was apparent in most cases that simple errors in

transcription had probably occurred. We assumed that this was the source of the discrepancy, and

corrected such data. For example,

(a) a temperature difference was in error as listed on the data form, but the thermal conductivity

had been correctly computed from the correct value of difference between the warm- and

cool-side temperatures. In this case, because the correct temperature difference had obviously

been used, the correct (not that originally listed) temperature difference was used in reporting

the data here. This correction of submitted data more faithfiiUy reflected the intent (and

results) of the participant.

(b) in a very few cases an improper (but easily detectable) conversion of temperature difference

was made from degrees Celsius to kelvins. That is, a temperature difference of, say, 25 "C,

had been converted by the participant to 298. 1 K, an error that was corrected by using the

correct value of 25 °C. (In this case the participant had used 25 °C to compute the thermal

resistance, thermal conductance, and thermal conductivity.) This error was also corrected to

reflect the true results.

Two serious types of error occurred when (a) the values of thermal resistance, conductance, and

conductivity were internally inconsistent, or (b) the raw data were incomplete (lacking the value of

heater power used, for example). In the latter case no test of internal consistency could be per-
formed. In these two cases the values of thermal resistance, conductance, and conductivity were

listed as submitted by the participant. Only small benefits of the doubt were given to the submitted

data.

6.1. Outliers

Ifthe purpose of a given set ofconductivity measurements were to determine the thermal properties

of a material, then it would be proper to test for the presence of outliers according to accepted

statistical guidelines. However, the purpose ofthis set of measurements is not to establish the thermal

properties of fibrous glass board, but rather to compare the resuUs of measurements by different

laboratories around the world so that each laboratory can evaluate its measurement apparatus and

technique. Thus the concept of "outliers" has no application to this present case. No "outliers" have

been excluded fi^om presentation in this work, except as explained next.

In one particular case detailed later, a least-squares curve was fitted to measurements of thermal

conductivity versus temperature by the GHP apparatus so that HFM data could be evaluated by

comparison. For this special case alone, three deviant points were treated temporarily as outliers and

so were excluded fi^om the curve fit determining the dependence of conductivity on temperature as indicated by GHP measurements.

In summary, because the purpose ofthis exercise was to perform an interlaboratory comparison, and

not to determine the thermal properties of a material, all data submitted have been used in the roundrobin intercomparison. Submitted values were changed only when the error was easily and obviously

identifiable, based on common sense, and justified by the internal consistency of related data. If there

was any doubt about the source of error in a questionable value, it was left unchanged and reported

as submitted.

7. PRESENTATION OF DATA

Sets of data are first presented for the complete population, and then identified according to three

individual major groupings. The first grouping, "Asia," actually includes participants in Afiica, Asia,

and Australia, but these laboratories are grouped together under one title for convenience, and

reflecting their participation in a common loop. The second group is Europe, and the third is North

America.
7.1 Thermal Conductivity of Fibrous Glass Board

7.1.1 Measurements with Guarded Hot Plates

Characteristics of the GHP apparatuses used by participants are described in table 7.1 (North

America, loops 1 and 2), table 7.2 (Africa, Asia, and Australia; loops 4 and 5), and table 7.3 (Europe,

loops 7, 8, 10, and 11).

Measurement data for GHPs for all participants are tabulated in table 7.4 (Africa, Asia, and AustraUa), table 7.5 (Europe), and table 7.6 (North America). The data sets have been sorted in order of

increasing thermal conductivity (first datum in the set of three) to conceal the identity of the

submitting laboratory. The data are grouped in sets of three, one measurement for each of three

different temperatures (283 K, 297 K, and approximately 3 10 K). Some participants did not submit

a complete set ofthree measurements. Values in parentheses were not reported but were computed

from the other data and listed here if the calculated values were consistent with other submitted data.

Values that appear to be in error and that could not be self-consistently recalculated were used as submitted.

The complete GHP data set for thermal conductivity as a fiinction of temperature is plotted in figure

7. 1. The solid curve is a least-squares fit to all the data; however, in performing the fit, the three

highest data points (asterisks) were excluded. The fianction fitted was of the form

X = \ + AjD + AjT + A3T'

,

(1)

where A is thermal conductivity in mW'm"*-K'\ D is density in kg-m'^, and T is mean specimen

temperature in K. The physical justification of this representation is that the conductivities of both

the gas and solid vary approximately linearly with temperature, but the solid fibers in low-density

insulation should also contribute a term to the conductivity directly proportional to the density;

finally, any radiative transport should contribute the term in T^ The least-squares values found for

the coefiBcients in eq (1) were:

Ao = 9.578 mW-m-'-K-\

A, = 0.0265 mW-m'-kg-'-K"'

,

A2 = 0.0457 mW-m-''K-2

,

A3 = 2.552xlO-'mW-m-^-K-^.
Table 7.1. Characteristics of guarded hot plate apparatuses and specimens for North American

participants (loops 1 and 2). In column 7, "H" denotes a horizontal direction for heat flow, and "V"

denotes a vertical direction. "NR" = "not reported."

Labora- Speci- L W Plate Density Heat Ambient Ambient

tory men (oven-dried) size

(edge)

flow

dir.

temperature

relative

humidity

(mm) (mm) (mm) (kgm-^) (K) (%)

1-1 1 ANA 1245 1243 1219 156 H 295.4 28

4 ANA 1243 1243 158 295.4 28

1-2 1 ANA

4 ANA

'1016 M016 164.57 V 308.65

297.05

40

1-3 1 ANA

4 ANA

M020

"1018

406 158.39 V 294.11

294.11

33

30

1-4 1 ANA

4 ANA

610 610 610 156 H 302.6

297.2

NR

NR

1-6a 1 ANA

4 ANA

610

610

609

609

610 155.1

154.1

V NR NR

1-6b 20-1

20-2

610 610 610 125.18

130.12

V NR NR

2-1 SANA 312 311 305 182.5 V 300.5 28.0

7ANA 310 310 154.0 300.5 25.0

2-2 SANA

7ANA

305 305 305 168 V 297.15

292.15

40

2-7 8-1

8-2

432 432 M06.4 166 V 283

297

<30

<30

2-8 7-1 7-2

457.2 457.2 457 164.8

172.5

H 296.5

283.1 --

2-11 17-1

17-2

581 581 610 151 H 282.88

295.87

20

20

"diameter
Table 7.2. Characteristics of guarded hot plate apparatuses and specimens for "Asian" participants

(loops 4 and 5). In column 7, "H" denotes a horizontal direction for heat flow, and "V" denotes a

vertical direction. "NR" = "not reported."

LaboratorySpecimenL

(oven

(mm)

W

-dried)

(mm)

Plate

size

(edge)

(mm)

Density

(kgm-^)

Heat

flow

dir.

Ambient

temperature

(K)

Ambient

relative

humidity

(%)

4-1 6A-AA

8A-AA

614.0

616.5

613.5

613.5

605 164.56 NR 308

297

26

33

4-2 6A-AA

8A-AA

320 320 318 167.6 H 304.0

304.5

62

69

4-3 6A-AA

8A-AA

320 320 305 147.8 V 298.0

295.5

71

73

4-4 6A-AA

8A-AA

308.4

308.0

306.3

308.4

300 168 H 271.7

281.2

45

65

4-5 6AAA

8AAA

^200.9

"200.0

"203 167.5 V 301

314

<5

<5

4-6 6AAA

8AAA

NR NR "200 168.5 H 288

288

63

54

4-8 6AAA

8AAA

306

308

309

308

300 167 H 297

294

51

54

5-4 9A-AA

18A-A

311.5 311 305 167.2 H 291.2 30

5-6 9A-AA

18A-A

311 311 210 167 H 296 30

'diameter

10
Table 7.3. Characteristics ofguarded hot plate apparatuses and specimens for European participants

(loops 7 and 8). In column 7, "H" denotes a horizontal direction for heat flow, and "V" denotes a

vertical direction. "NR" = "not reported."

Laboratory

SpecimenL

(oven

(mm)

W

-dried)

(mm)

Plate

size

(edge)

(mm)

Density

(kgm-^)

Heat

flow

dir.

Ambient

temperature

(K)

Ambient

relative

humidity

(%)

7-2 17AE

20AE

502

502

505.2

505.2

500 152.7

162.6

V 293.5

293.5

60

7-4 17AE

20AE

500 500 500 159.7 NR 296

296

50

7-6 11-1

11-2

305 305 305 172 V 293.4

293.4

40

7-7 19-1

19-2

304.8

305.4

304.0

305.7

305 157

159

V 293.4

295.3

37

45

7-9 5-1

5-2

305 305 305 148

177

V 293 40

7-1 1a

7-1 lb

6-1

6-2

6-1

6-2

M50

M50

370

450 (D)

150.0

147.8

150.0

147.8

V

V

290

290

301

298

NR

NR

7-13 3-1

3-2

600 600 610 170 V 293

293

65

65

7-14 17AE

20AE

613.2

613.3

614.8

616.5

610 153.86 V 293 55

8-1 11AE

15AE

1003 1003 1000 174 V 286.8

287.1

40

8-2 11AE

15AE

805 805 800 165.4

173.1

V 296.05

283.15

35

30

8-5 11AE

15AE

602

602

601

601

600 170.0

168.6

V 284.9

285.0

28

30

"diameter

11
Table 7.3. (cont.) European, loops 10 and 11.

Labora- Speci- L W Plate Density Heat Ambient Ambient

tory men (oven-dried) size

(edge)

flow

dir.

temperaturerelative

humidity

(mm) (mm) (mm) (kgm-^') (K) (%)

10-1 a 21?

25?

855 855 850 161 V 293

293

NR

NR

10-1b 21?

25?

802 800 800 161 V 293

293

NR

NR

10-3 21 803 802 800 165.0 V "Trm" NR

25 801 801 162.0 "Trm"

(293?)

NR

10-5 12

770 770 770 160.5

158.7

NR 294.60

294.60

40

40

11-1 24:AE

27:AE

500 500 500 168 V 283.15

296.15

17

17

11-2 24:AE

27:AE

501 499.75 500 170 V 283.17

296.19

17

11

11-3 24:AE 502.2 500.2 500 175.77 V 286.35 26

27:AE 501.8 502.4 161.48 291.85 25

11-4 24:AE NR NR 246 168.3 V NR 60

27:AE NR NR NR 70

11-6 24:AE

27:AE

300.5 300.4 300 171 V 293

294

68

68

11 -7a 24:AE

27:AE

250 250 250 178.8 V 296.35 47

11-7b 24:AE

27:AE

249 249 250 161.3 V 273.12

296.81

48

11-8 9-1

9-2

^203.8

'204.5

203 (D) 171.0 V 296 62

"diameter

(Values in parentheses were not reported, but were computed from the given data)

12
Table 7.4 Thermal conductivity data (GHP) for Africa, Asia and Australia.

Test Temp Thick- Power Metering Rth Cth Kth Tmean Mean

run: diff. ness area Density

(K) (mm) (W) (m^ (Km^W-^) (Wm-^K-^) (mWm-^K-^) (K) (kgm-^)

1 30.1 25.4 0.722 0.01 0.834 1.198 30.3 283.3 167

2 31.3 25.3 0.782 0.800 1.249 31.6 297.5 167

3 33.8 0.879 0.769 1.300 32.9 308.3 167

1 28.8 25.4 ^35.00

(3.25)

0.0929 0.823 1.215 30.9 298 164.56

2 29.1 25.4 "38.24

(3.544)

0.763 1.311 33.3 313 164.56

1 38.0 25.4 1.9263 0.04 0.791 1.264 32.1 283.0 167.6

2 30.0 1 .6478 0.729 1.371 34.8 296.0 167.6

3 31.0 1.8063 0.686 1.457 37.0 304.0 167.6

1 20.6 24.8 0.86 0.03223 0.772 1.29533679 32.15 284.2 167.2

2 28.3 1.225 0.745 1.34228188 33.36 297.0 167.2

3 27.7 1.236 0.723 1.38312586 34.36 307.0 167.2

1 20.6 24.8 0.86 0.03223 0.772 1.29533679 32.15 284.2 167.2

2 28.3 1.225 0.745 1.34228188 33.36 297.0 167.2

3 27.7 1.236 0.723 1.38312586 34.36 307.0 167.2

1 36.0 25.38 0.3859 0.0084 0.782 1.279 32.47 283.2 167.5

2 36.0 25.38 0.4021 0.751 1.332 33.81 296.2 167.5

3 36.0 0.4181 0.722 1.384 35.13 309.2 167.5

1 28.2 24.9 (0.303) 0.0081 0.7582 1.319 32.8 283.0 168.5

2 28.1 (0.313) 0.7298 1.370 34.1 296.2 168.5

3 28.0 (0.325) 0.7018 1.425 35.5 308.9 168.5

1 29.7 25.5 1.75 0.0225 0.764 1.31 33.4 288.0 168.0

2 27.2 25.4 1.65 0.742 1.35 34.4 296.8 168.0

3 27.6 1.75 0.710 1.41 35.9 310.9 168.0

1 18.0 24.8 0.4023 0.01628 0.7283 1.373 34.1 301.2 167

2 20.0 0.4511 0.7217 1.386 34.4 303.7 167

3 20.5 0.4773 0.6991 1.430 35.5 313.1 167

1 28 25.4 1.0625 0.0231 (0.6088) (1.643) 41.73 283 147.8

2 28 1.1405 (0.5671) (1.763) 44.79 296 147.8

3 28 1.368 (0.4728) (2.115) 53.71 313 147.8

Value as submitted

13
Table 7.5. Thermal conductivity data (GHP) reported by European participants.

Test Temp. Thick- Power Metering Rth Cth Kth Tmean Mean

run: diff. ness area Density

(K) (mm) (W) (m^ (Km^W-^) (Wm-^K-^) (mWm-^K-^) (K) (kgm-^

12

3

9.42

10.16

9.89

25.5 0.1193

0.1295

0.1277

0.01056 0.8333

0.8279

0.8173

1.2000

1.2078

1.2235

30.6

30.8

31.2

300.13

296.18

297.60

178.8

178.8

178.8

13

2

9.40

9.49

9.37

25.4 0.1215

0.1235

0.1235

0.01056 0.8167

0.8115

0.8013

1 .2244

1.2323

1.2480

31.10

31.30

31.70

273.12

296.82

296.81

161.3

161.3

161.3

3

2

1

28.4

28.2

27.9

25.4 8.740

9.023

9.422

0.25 0.805

0.781

0.750

1.242

1.280

1.333

31.6

32.5

33.8

274.35

283.25

296.20

169.2

169.2

169.2

3

2

1

29.57

31.14

32.43

25.5 4.580

5.180

5.812

(0.0625) (0.8070)

(0.7514)

(0.6975)

(1.239)

(1.331)

(1 .434)

31.6

33.9

36.6

283.46

298.13

309.89

168.3

168.3

168.3

12

3

29.15

33.93

27.65

25.4 6.908

8.295

7.018

0.1898 0.8010

0.7763

0.7477

1 .2484

1 .2882

1 .3374

31.71

32.72

33.97

287.75

297.15

304.50

158.56

158.56

158.56

12

3

29.5

30.4

31.4

25.7

25.2

6.991

7.340

7.774

0.0948 0.800

0.785

0.765

1.251

1.275

1.307

31.8

32.4

33.3

283.4

290.3

296.4

169.3

169.3

169.3

3

2

1

32.36

30.70

29.98

25.43 5.845

5.766

5.732

0.07211 0.7935

0.7679

0.7544

1 .2524

1.3022

1.3256

31.85

33.12

33.71

284.44

297.55

303.25

148.9

148.9

148.9

3

2

1

31.70

30.51

29.95

25.43 2.131

2.131

2.140

0.02657 0.7905

0.7608

0.7437

1.2651

1.3144

1.3447

32.17

33.43

34.19

283.55

297.29

302.93

148.9

148.9

148.9

13

2

28.1

27.9

28.7

25.5 46.74

48.14

49.97

0.6561 0.789

0.761

0.754

1.27

1.32

1.33

32.2

33.4

33.7

281.2

289.1

294.3

174

174

174

3

2

1

28.0

28.2

28.0

25.63 2.913

3.064

3.167

0.04129 0.793

0.761

0.730

1.260

1.315

1.371

32.3

33.7

35.1

283.0

296.3

309.2

158

158

158

12

3

26.80

28.30

27.20

25.7 6.10

6.72

6.71

0.09 (0.791)

(0.758)

(0.730)

(1 .264)

(1.319)

(1.370)

32.5

33.9

35.3

282.6

296.3

310.2

161

161

161

12

3

29.1

28.2

26.9

25.7 (2.954)

(2.950)

(2.952)

0.04 0.788

0.765

0.734

1.268

1.307

1.362

32.6

33.6

35.5

282.75

292.75

303.15

162

162

162

14
Table 7.5. (cont.) European GHP data. Test Temp. Thick- Power Metering Rth Cth Kth Tmean Mean

run: diff. ness area Density

(K) (mm) (W) (m^ (Km^W-^) (Wm-^K-^) (mWm-^K-^) (K) (kgm-3)

1

2

3

3

2

1

11.90

10.90

10.40

26.24

28.97

28.17

25.4

25.5

25.7

26.0

4.0

4.0

4.0

16.59

18.91

19.01

0.25

0.25

(0.744

(0.681

(0.650

0.791

0.766

0.741

1.264

1.305

1.349

'32.6

(34.2)

'33.6

(37.3)

'34.9

(39.1)

32.7

33.7

34.9

285.3

294.4

304

286.94

295.48

304.91

163.5

163.5

163.5

159.6

159.6

159.6

12

3

28.5

28.4

28.5

25.4 2.315

2.369

2.467

0.063 0.776

0.755

0.726

1.288

1.324

1.376

32.71

33.64

34.94

283.0

296.4

313.3

157.6

157.6

157.6

12

3

28.37

33.00

31.96

25.7 2.995

3.629

3.618

0.040 0.784

0.751

0.730

1.276

1.331

1.370

32.8

34.2

35.2

282.02

296.65

307.29

172

172

172

12

3

30.21

29.62

30.24

25.42 5.002

5.096

5.398

0.064 0.773

0.744

0.717

1.293

1.344

1.394

32.87

34.16

35.46

283.17

296.19

309.17

170

170

170

12

3

27.96

27.80

28.01

25.62 4.565

4.754

4.981

0.063 0.777

0.742

0.714

1.285

1.346

1.400

32.99

34.55

35.93

283.11

296.16

308.26

168

168

168

12

3

"27.146

"28.134

"30.475

25.4 4.442

4.764

5.326

0.062 0.763

0.738

0.715

1.309

1.354

1.398

33.2

34.4

35.5

"282.567

"296.038

303.18

168.62

168.62

168.62

12

3

29.40

28.40

27.70

25.7 19.4

19.5

19.5

0.25 (0.758

(0.728

(0.710

33.3

34.7

35.7

285.75

297.95

309.70

162

162

162

12

3

27.65

26.55

21.2

25.4 4.553

4.561

3.778

0.062 0.759

0.728

0.701

33.5

34.9

36.2

283.7

297.7

308.6

159.7

159.7

159.7

12

8

30

25.4

(4.02)

0.1 0.74

0.75

1.35

1.33

34.3

34

296

313

170

170

12

3

30.30

28.80

29.60

25.4 1.842

1.915

1.939

0.022 0.740

0.677

0.686

1.351

1.477

1.460

35.0

37.5

37.0

283.0

296.2

303.4

171

171

171

12

3

29.23

28.29

27.79

25.4 0.683

0.696

0.697

0.008 0.694

0.660

0.636

1.441

1.516

1.572

36.6

38.5

39.3

281.64

296.71

306.86

171.0

171.0

171.0

"Value as submitted

Unrealistic precision

15
Table 7.6. Thermal conductivity data (GHP) reported by North American participants.

Test Temp. Thick- Power Metering Rth Cth Kth Tmean Mean

run: diff. ness area Density

(K) (mm) (W) (m^ (Km'W) (Wm-'K-^) (mWm-^K-^) (K) (kgm-3)

3 "22.544 25.4 9.216 0.1662 0.8154 1 .2264 31.15056 158.39

2 "26.400 11.362 0.7725 1.2945 32.8803 "297.422 158.39

1 "27.262 12.285 "0.7014

(0.7376)

1.3512 34.32048 "311.316 158.39

1 (28.17) 25.6 3.264 0.09266 0.7996 1.251 32.04 283.18 151

2 (28.04) 3.370 0.7709 1.297 33.24 296.19 151

3 (28.11) 3.568 0.7300 1.370 35.10 313.45 151

3 27.73 25.4 8.966 0.1299 0.8041 1.244 32.10 283.08 161.4

2 27.80 25.4 9.419 0.7665 1.305 33.64 297.00 161.4

1 27.81 9.865 0.7324 1.365 35.24 310.83 161.4

1 28.0 25.4 2.30 0.0648 0.790 1.27 32.2 283.0 166

2 27.7 2.43 0.740 1.35 34.3 297.1 166

3 26.7 2.54 0.685 1.46 37.1 316.3 166

3 27.78 25.4 11.64 0.165 0.786 1.271 32.3 283.15 156

2 27.78 12.16 0.754 1.328 33.7 297.05 156

1 27.78 12.69 0.722 1.385 35.2 310.93 156

2 38.44 25.65 4.623 0.1898 (1.578) (0.6336) 32.7 285.0 154.6

1 36.27 25.93 4.489 (1.533) (0.6521) 33.6 295.7 154.6

3 39.16 5.099 (1.457) (0.6861) 35.4 312.2 154.6

3 27.78 25.1 2.994 0.0825 0.7645 1.308 32.8 283.15 168

2 27.78 3.117 0.735 1.361 34.2 297.05 168

1 27.78 3.247 0.706 1.417 35.6 310.93 168

1 28.2 25.0 "7.9 0.0225 0.766 1.305 32.9 283.0 168.2

2 28.0 25.4 "8.2 0.741 1.350 34.0 296.0 168.2

3 28.0 "11.3 0.722 1.385 34.9 303.0 168.2

2 28.4 25.48 3.14 0.0852 0.77 1.30 33.0 283.2 168.6

1 29.4 3.30 0.76 1.31 33.5 296.3 168.6

3 29.7 3.44 0.73 1.37 34.8 308.4 168.6

3 21.2 25.4 11.78 0.211 0.759 1.32 33.4 289.7 157

1 22.3 12.60 0.747 1.34 34.0 297.1 157

'Unrealistic precision

''Value as submitted

16
^55

>- 45

>

o

IDQ

oO 35

Ld

n:

25

00000 ASIA

nnnnn EUROPE

OOOOO N. AMERICA

Eq. (1)

I I I I I I I I I 270 280

I I I I I I

I

I I I M I I I I

I

I I I 290 300I I I I I

I

I I I I I I I I I 310 320

TEMPERATURE, K

Figure 7.1 Measurements with guarded hot plates (GHPs) of thermal conductivity of fibrous glass

board specimens as a flinction oftemperature, for all participants (ASIA: Asia, Africa and Australia;

Europe, and North America). The solid curve is eq (1), a least-squares fit to all the data except the

three highest-conductivity data points (asterisks).

17
LJO

LJ

Q_

o

<

>

LJ

o

>

LjJ

15

10-

5-

-10

n D

D

D

d>

GHP, All

00000 ASIA

nnnnn EUROPE

OOOOO N. AMERICA

a

^

D — 1 5 I

I I I I I I I I I

I

I I I I I I I I I I

I I I I I I I I I

I

I I I I I I I I I

I

I I I I I I i I I 270 280 290 300 310

TEMPERATURE, K

320

Figure 7.2 Deviations of GHP data in figure 1 from the fitted curve, eq (1), for all participants. The

mean density of each individual specimen pair was used in eq (1) to compute each deviation. To

allow precise examination of deviations, the deviations for the three highest-conductivity points

(asterisks in figure 7. 1) are not shown here.

18
The deviations ofthe GHP data from the fitted curve in figure 7. 1 are plotted in figure 7.2. In order

to show the value of each deviation more precisely, the data showing the three largest deviations

(data represented by asterisks in figure 7.1) are not included in figure 7.2. The relative standard

deviation of the data from the fitted curve is 2.4%. In figure 7.2, the two parallel solid lines, one

above, and one below the central zero-deviation line, are separated from the central line by one

standard deviation (2.4%).

Statistically, lines lying above and below the central zero-deviation line and separated from it by two

standard deviations (±4.8%, or about 1.65 conductivity units at 300 K) should include about 95%

ofthe data in the complete set, if the data are normally distributed. The two parallel dashed lines in

figure 7.2 are separated from the central line by two standard deviations (4.8%). Clearly the data are not normally distributed about the fitted curve, as there are about 22 data points (19 of which are shovm in figure 7.2) that deviate from the fitted curve by more than 5%, out of a total population of

124 points.

The same conductivity data for GHPs, separated into three geographical groupings ("Asia," Europe,

and North America) are plotted in figures 7.3 through 7.5. In figures 7.3, 7.4, and 7.5 the solid curve

is a plot of eq (1) using D = 164 kg-m"', which is the mean value of density for all the specimens

represented by this data.

19
^55

T

E

>. 50H

E

25

00000 ASIA

Eq. (1)

I I I I I I I I I

I

I I I I I I I I I II I I I I I I I I

I

I I I I I I I I I II I I I I I I I I 270 280 290 300 310

TEMPERATURE, K

320

Figure 7.3 Measurements with guarded hot plates (GHPs) of thermal conductivity of fibrous glass

board specimens as a function of temperature, for participants in the "Asian" (Asia, Africa and

Australia) measurement loops. The solid curve is eq (1), a least-squares fit to all the data except the

3 highest-conductivity data points (asterisks in figure 7.1).

20
^55

E

• 5:

50

E

>-'^45

\—

>

\—

o 40

_j

n

2:

35

_i

<

^

on 30

LU

X

25

nnnnn EUROPE

Eq. (1)

D

D

D

*

D

iffir tPlD D

D'

D

D

I I I I I I I I

I

I I I I I I I I I

I

I I I I I I I I I

I

I I I I I I I I I

I

I I I 270 280 290 300 310I I I I 320

TEMPERATURE, K

Figure 7.4 Measurements with guarded hot plates (GHPs) of thermal conductivity of fibrous glass

board specimens as a function of temperature, for participants in the European measurement loops.

The solid curve is eq (1), a least-squares fit to the data.

21
^55

i 50-

OOOOO N. AMERICA

Eq. (1)

25 II I I I I 270

I I I

I

I I I I I I I I I

I

I i I I I I I I I

I

I I I I I I I i I I

I I I I I I I I I 280 290 300 310

TEMPERATURE, K

320

Figure 7.5 Measurements with guarded hot plates (GHPs) of thermal conductivity of fibrous glass

board specimens as a fiinction of temperature, for participants in the "North American" (U.S.A. and

Canada) measurement loops. The solid curve is eq (1), a least-squares fit to the data.

22
7.1.2 Measurements with Heat Flow Meters

Characteristics of the HFM apparatuses used by participants are described in table 7.7 (North

America, loop 3), table 7.8 (Africa, Asia, and Australia, loop 6) and table 7.9 (Europe, loops 9 and

12).

The HFM measurement data are tabulated in table 7.10 (Africa, Asia, and Australia), table 7.11

(Europe) and table 7.12 (North America). The data sets have been sorted in order of increasing

thermal conductivity (first datum in the set of three) to conceal the identity ofthe submitting laboratory. Values in parentheses were not reported but were computed from the other data submitted by

the participant and listed here if the calculated values were consistent with all other submitted data.

Values that appear to be in error and that could not be self-consistently recalculated were used as submitted.

Figure 7.6 shows the complete data set for HFMs as a function of specimen density for all participants. The solid curve is the least-squares fit to all the GHP data, eq (1), and calculated for an assum- ed mean specimen temperature of 297 K. The mean specimen temperature for the five "Asian"

participants' data displayed here was 297.4 K; that for the 15 European participants' data was

297.9 K; and that for the 21 North American participants' data was 297.6 K. The global mean

specimen temperature for all 41 participants was 297.7 K. Plots of eq (1) (dashed lines) for mean

specimen temperatures of295 K and 300 K are almost equally separated from the mean temperature

ofmeasurement, 297.7 K. These are shown for comparison, to illustrate the effect of mean specimen

temperature on the submitted data.

Figure 7.7 plots deviations ofHFM data in figure 7.6 from the fitted curve, eq (1), for all participants.

The mean density of each individual specimen pair was used in eq (1) to compute each deviation. The

standard deviation from the curve for the "Asia" data is 2.7% (for all 26 data points; the mean

deviation for 23 points left after excluding the three highest conductivity points for "Asia" is - 1.9%);

the standard deviation for the European data is -0.6%; and that for North American data is - 1.0%.

23
Table 7.7. Characteristics of heat flow meter apparatuses and specimens:

for loop 3 (North America [U.S.A. and Canada]). In column 5, "V" denotes a vertical direction for heat flow; Vdn, downward heat flow; Vup, upward

heat flow. "NR" = "not reported." Specimens grouped together without

spacing were measured by the same participant.

Specimen L W Plate Heat Ambient Ambient

(oven-dried) size flow temp. relative

(edge) direc- humidity

(mm) (mm) (mm) tion (K) (%)

14 ANA 1218 1218 1016 V 295 28

14 ANA 914 914 914 V 295 28

14 ANA 914 914 914 NR NR NR

14 ANA 914 914 NR NR 295.9 50

14 ANA 610 610 NR NR NR NR

14 ANA 610 610 NR V 294.66 30

14 ANA 610 610 1016 V 294 22

7-3 305 305 305 Vdn 296.0 52

7-4 610 610 NR V 296.0 52

8-1 432 432 381 NR 297 30

8-2 432 432

1 ANA NR NR 610 NR NR NR

4 ANA NR NR NR NR NR

20-1 NR NR 610 NR NR NR

20-2 NR NR NR NR NR

3AAA 610 610 610 Vup 294 22

24
Table 7.8 Characteristics of heat flow meter apparatuses and specimens:

for loop 6 (Africa, Asia, and Australia). In column 5, "V" denotes a vertical

direction for heat flow; Vdn, downward heat flow; Vup, upward heat flow.

Specimen L W Plate Heat Ambient Ambient

(oven--dried) size

(edge)

flow

directemp. relative

humidity

(mm) (mm) (mm) tion (K) (%)

3A-AA 301 301 300 Vdn 295 64

3A-AA 311.5 311 300 Vdn 291.2 30

3A-AA 265 265 265 Vup 291 69.5

3AAA 308 308 NR Vdn NR NR

10 AE 1000 1000 1000 Vup 296 50

25
Table 7.9. Characteristics of heat flow meter apparatuses and specimens:

for loops 9 and 12 (Europe). In column 5, "V" denotes a vertical direction

for heat flow; Vdn, downward heat flow; Vup, upward heat flow. "NR" =

"not reported." Specimens grouped together without spacing were

measured by the same participant.

Specimen L W Plate Heat Ambient Ambient

(oven-dried) size

(edge)

flow

directemp. relative

humidity

(mm) (mm) (mm) tion (K) (%)

12 AE 705 705 700 Vdn 297.55 35

12 AE 610 610 610 Vup 294 22

NA 400 400 400 Vdn 297 NR

5-1 305 305 305 Vup 293 40

10A-1 300 300 305 V 293.5 NR

16 AE 610 610 610 NR 294 22

24 AE NR NR NR NR NR NR

27 AE

16 AE 500 500 500 Vdn 296.15 22

16 AE 500 500 500 Vdn 303.2 20-30

16 AE 306.5 305.5 305 Vdn 296.15 53

16 AE NR NR #250 V 292.2 54

17 AE 500 500 NR NR 296 50

20 AE 500 500 NR 296 50

26
Table 7. 10. HFM data for participants in Africa, Asia, and Australia.

Temp. Thick- Power Metering Rtli Cth Ktfi Tmean Mean

diff. ness area density

(K) (mm) (W) (m^) (Km^W-^) (Wm-^K-^) (mWm-'K"') (K) (kgm-3)

27.8 25.4 35.5

41.05

0.04 0.782 1.278 32.5 297.1 159

31.41 25.4 (W/m^)

41.56

0.209 0.765 1.307 33.2 296.82 164.7

31.02 25.0 (W/m^) 0.0121 0.7463 1.3399 33.49 297.34 155.37

53.18 25.4 NR 0.0144 0.729 1.370 34.80 298.6 165.1

29.3 25 -0.423 0.0103 0.73 (1.370) 35.0 297.0 165.0

(Values in parentheses were not originally reported, but were computed from the data submitted)

27
Table 7.11. HFM data for European participants.

Temp. Thick- Power Metering Rth Cth Kth Tmean Mean

diff. ness area density

(K) (mm) (W) (m^ (Km^W) (Wm-^K-^) (mWm-^K-^) (K) (kgm-3)

35.3

(28) 25 (W/m^

17.45

0.008 0.79 1.26 31.5 297 141.9

27.26 50.23 (W/m^) 0.04 1.562 0.640 32.2 296.5 172

27.8 25.8 2.36 0.0645 0.777 1.29 32.9 297.0 163

6.4 25.4 "3 0.008 0.765 1.31 33.2 298.2 169

27.8 25.9 2.32 0.0645 0.764 1.31 33.5 297.1 178

28.03 25.4 1.842 0.0576 0.754 1.327 33.7 297.05 181.6

27.2 25.9 (0.2865) 0.008 0.760 1.317 34.1 297.6 148

12.2 25.4 2.08 0.0625 0.733 (1 .364) 34.6 299.5 155

11.6 25.4 ^2 0.0625 0.725 1.37931 35.0 299.1 164.4

NR 25.64 NR NR NR NR 34.76 297.05 NR

8.86 25.52 (0.494) 0.04 0.717 1.395 35.6 296.78 166.1

9.7 25.5 (3.404)

39.77

0.25 0.712 1.404 35.8 303.2 167.8

28.06 25.4 (W/m^) 0.01 0.706 1.417 36 296.93 167.6

'Value as submitted

(Values in parentheses were not originally reported, but were computed from the data submitted)

28
Table 7. 12. HFM data for North American participants.

Temp. Thick- Power Metering Rth Cth Kth Tmean Mean

diff. ness area density

(K) (mm) (W) (m^ (Km^VV^) (Wm-^K-^) (mWm-^K-^) (K) (kgm-^

24.02 25.86 (1.947) (0.0645) -0.796 (1.257) 32.5 297.06 125.18

-27.8 25.4 (3.325) 0.0929 (0.777) (1.29) 32.7 297.0 163

24.12 25.90 (1.976) (0.0645) (0.787) (1.270) 32.9 297.16 130.12

28.66 25.4 2.43 0.0645 0.762 1.31 33.0 297.3 158

27.1 26.1 (2.31) 0.0645 0.775 1.29 33.3 296.7 157

23.96 25.86 (2.002) (0.0645) (0.772) (1.295) 33.5 297.05 155.1

21.9 25.4 (6.05) 0.209 0.756 1.32 33.6 297.0 165

24.02 25.90 (2.010) (0.0645) (0.771) (1.297) 33.6 297.15 154.1

22.2 25.4 (6.05) 0.209 0.756 1.32 33.6 297.1 165

21.7 25.4 (6.02) 0.209 0.753 1.33 33.7 297.0 165

22 25.6 (2.70) NR (0.759) (1.32) 33.8 297.3 (162)

27.8 25.4 2.377 0.0645 0.75 1.33 33.8 297.1 162.6

27.8 25.4 (2.39) 0.0645 (0.750) (1.33) 33.9 297.0 160

27.6 25.4 0.380

29.8

0.0103 0.75 1.34 33.9 297.1 157.1

22.2 25.4 (W/m^) 0.0413 0.745 1.34 34.1 297 166.0

22.200 25.4 -1.936 0.0645 (0.739) 1.352 34.35 296.888 159.83

(Values in parentheses were not originally reported, but were computed from the data submitted)

29
I

T

>-

>

o

o

o

_j

<

LxJ JO

00000 ASIA

nnnnn EUROPE

36- OOOOO N. AMERICA D

Temp. = 295 K °

Temp. = 297 K ^ Temp. = 300 K

^ _^ -^ D ^^''' ^^ o ^— ^ D 0--^"^^^^--"'^^ -

"

D

.-'^'^^^-^^0

—

7 1 —

D

o 1 1 1 1 1 1

1 1 1 1 11 1 1 1 1

1 1 1 1 1

1 1 1 1 1

1 1 1 1

1

1 1 1 1 120 130 140 150 160

DENSITY, kg m

170 180

-3

190

Figure 7.6 Measurements with heat flow meters (HFMs) of thermal conductivity of fibrous glass

board specimens as a function oftemperature, for all participants (Asia, Africa and Australia; Europe,

and North America). The solid curve is eq (1), a least-squares fit, calculated for an assumed mean

specimen temperature of 297 K. The mean specimen temperature for the five Asian participants' data

displayed here was 297.4 K; that for the 1 5 European participants' data was 297.9 K; that for the 21

North American participants' data was 297.6 K. Plots of eq (1) for mean specimen temperatures of

295 K and 300 K are shown for comparison, to illustrate the effect of mean specimen temperature.

30
LUO

LU

CL

O

<

>

LJQ

> -5-

<

ct:

190

DENSITY, kg.m

Figure 7.7 Deviations of HFM data in figure 7.6 fi-om the fitted curve, eq (1), for all participants.

The mean density of each individual specimen pair was used in eq (1) to compute each deviation.

31
7.1.3. Thermal Conductivity of a Layer of Air

The second type of specimen to be tested in the round robin was a layer of air approximately 25 mm

thick, either on GHP or on HFM apparatuses. Some laboratories did not perform this measurement.

The participants were not directed to correct their data for the (appreciable) effects of radiative

transfer that could have been present in their apparatuses, between the plates bounding the air layer.

No participants indicated that they did so. Thus the measurements here probably include the

combined effects of conductive and radiative transfer, and can be compared only qualitatively with

accepted values for the thermal conductivity of air. Table 7. 13 lists the conductivity data obtained

from laboratories that measured the thermal conductivity of the air layer in a GHP apparatus. The

data sets have been randomized by sorting in order of increasing thermal conductivity to conceal the

identity of the submitting laboratory. Values in parentheses were not reported but were computed

from the other data and listed here if the calculated values were consistent with other submitted data.

Values that appear to be in error and that could not be self-consistently recalculated were used as submitted.

Table 7. 14 lists the data obtained from laboratories that measured the air layer with a HFM apparatus,

and have also been randomized, as previously explained. In both tables the data have been sorted in

order of increasing thermal conductivity to conceal the identity of the submitting laboratory. The

values for the thermal conductivity ofthe air layer versus temperature as measured on both GHPs and

HFMs are plotted in figure 7.8 for comparison. Only one point (lowest open square: 32 mW-m"'-K"'

at 297 K), for a measurement with a GHP, is near the value of the conductivity of air (about 26

mW-m'*-K'* at 300 K). However, in the absence of information submitted by this participant about

whether the total heat transfer was corrected for the effects of radiative transfer, even this point

cannot be assumed necessarily to represent a valid measurement of the conductivity of air.

All the measured values obtained with heat flow meters lie far above the value of the thermal

conductivity of eiir at 297 K, and do not represent a measurement of true conductivity. The signifi- cance of these data will be discussed in the next section.

32
Table 7.13. Thermal conductivity of a layer of air as measured with a GHP apparatus

for North American (loops 1 and 2), "Asian" (loops 4 and 5), and European (loops 7,

8, 10, and 11) participants. H = horizontal; V = vertical; W^ = vertical, down; NR =

not reported.

Plate Heat Tmean Kth Temp.

emittances flow diff. top bottom direction (K) (mWm-^K-^) (K)

NORTH 0.8 0.8 H 297 141.4 27.78

AMERICA: 0.9 0.9 H 297.05 152.8 27.78

0.89 0.89 V 297 170 27.8

0.95 0.95 V 297.19 175.9 12.038

0.86 0.86 H 296.8 180 19.4

0.9 0.9 H 295 187 22.9

0.89 0.89 H 296.16 191.3 27.86

0.96 0.96 V 297 191.8 28.3

ASIA: 0.35 0.35 NR 297 119.6 27.9

0.8 0.9 H 299.0 123 31.4

0.41 0.41 V 296.9 127.5 28

NR NR V 297.5 132 28.9

0.85 0.95 H 306.6 143.4 17.2

0.8 0.8 H 296.9 148 28

0.88 0.88 V 297.0 174.5 28.1

EUROPE: NR NR V 297 32 10

0.15 0.15 V 297 72 28

0.64 0.64 V 296.6 86.1 9.86

NR NR V 297.7 167 20.8

NR NR NR 297.33 168.33 24.39

0.9 0.9 V 290.97 168.9 16.20

0.9 0.9 V 296 170 27.3

NR NR V 297.02 171.5 28.00

NR NR V 297.7 173 26.3

0.82 0.82 V 297.08 174.0 28.42

0.9 0.9 V 297 177.5 28.0

0.92 0.92 V 297.1 178 28.1

0.9 0.9 V 300.4 181 3.9

0.95 0.95 V 296.93 184.8 28.08

0.9 0.9 V.n 296.96 191 28.03

0.9 0.9 V 296.95 204 23.20

33
Table 7.14. Thermal conductivity of a layer of air as measured with a HFM apparatus

by North American (loop 3), "Asian" (loop 6), and European (loops 9 and 12), participants. H = horizontal; V = vertical; Y^ = vertical, down; NR = not reported.

Plate Heat Tmean Kth Temp.

emittances flow diff. top bottom direction (K) (mWm-^K-^) (K)

N. AMERICA: 0.9 0.9 H 297 77.8 22.2

0.86 0.86 Vdn 297.1 152 27.6

0.94 0.94 Vup 297.03 184.4 16.74

ASIA: 0.8 0.8 Vdn 301.9 87.78 24.2

NR NR Vdn 297.1 117 27.8

NR NR Vdn 302.2 172 19.5

EUROPE: NR NR Vdn 297.04 142 28.07

NR NR Vdn 294.8 144.3 3.30

NR NR Vdn 297.1 147 27.8

0.9 0.9 Vdn 297.05 151 37.2

0.85 0.85 Vdn 297.15 156 27.2

black black Vup 298 205 27.8

NR NR Vup 298.09 207 25.00

34
• T

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£ o ^£ D

- D

^ A

1— — A > 150-

1—

A %

o

Q

:

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o

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- AIR Measurements:

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:2 50- 00000 ASIA

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0- 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 1 2£)0 300 31

TEMPERATURE, K

Figure 7.8 Measurements with GHPs and HFMs of the thermal conductivity as a function of

temperature of an air layer 25 mm thick, by all participants (GHPs: diamonds, "Asia"; squares,

Europe; circles, North America; HFMs: all participants).

35
8. FUTURE ROUND-ROBIN STUDIES: DISCUSSION AND RECOMMENDATIONS

8.1. Measurement of the EfTective Conductivity of a Still Layer of Air

Asking the participants to measure the thermal conductivity of air offers the potential of using the air "specimen" as an in-house "standard reference material" freely and inexpensively accessible to all

participants. The air layer would then be available to each laboratory as a permanent and reusable

reference material for regular use. However, the very wide scatter in data for the conductivity of air suggests that almost all participants did not understand at all how to perform this measurement.

Measuring the conductivity of air, although not difficult when correctly done, is on the other hand

not a trivial exercise. Because of the great difficulty apparently encountered by the participants in

measuring the conductivity of air for this round robin, the procedures to be followed (several small

thicknesses) in measuring the conductivity of air in any future round-robin program will have to be

carefully spelled out in the next round-robin protocol. A paper by Jaouen and Klarsfeld [1] clearly

describes a straightforward procedure for obtaining both the plate emittance and thermal conductivity

of air in either a GHP or HFM apparatus. Each participant of any fliture round robin on GHPs or HFMs should at least be provided with a copy of this paper. Better would be to supply each

participant with a detailed protocol for this measurement. Because a world-wide distribution of

participants could include some located at altitudes as high as 1.5 km or higher, guidance should be

given on how to correct for the small, but measurable, effects of atmospheric pressure.

The important feature in performing this measurement is that the conductivities of at least two or three different layers of air of different thicknesses should be measured. To promote stable stratification of the air layer, the flow of heat should be downward only, and the thickness of each layer

should be ofthe order of only a few millimeters, to guard against the occurrence of convective heat

transfer. This can be accomplished by the use of a set of two plastic annular rings, each having an

annular (radial) width of4 or 5 mm and an outer diameter equal to that of the usual specimen. If one

ring is, say, 3 mm thick and the other, twice as thick (6 mm), then the conductivity of air may be

measured at three different thicknesses: 3, 6, and (stacking the two rings together) 9 mm. The exact

thicknesses are of course subject to choice, but should be fairly uniformly spaced.

By measuring the heat transfer through the air layers at different thicknesses, one can obtain a line

whose slope and intercept contain information from which both the plate emittance and thermal

conductivity of air may be readily obtained. The use of at least three different thicknesses allows a

line to be fitted by linear least squares, with consequent partial averaging out of the contributions

from random experimental errors. This test provides not only a test of the ability to measure the

36
thermal conductivity of a "standard material" (still, nonconvecting) air, but also provides an estimate

of the plate emittance in the apparatus.

In retrospect, it seems clear that the choice of a thickness for the air layer of 25 mm, rather than 6

mm, was unfortunate. This thickness is too large to ensure accurate measurements of thermal

conductivity of a (fluid) gas. Also, in order to stratify the air layer and minimize the possibility of

convective heat transfer, the conductivity should have been measured for only a single layer of air,

with the top boundary (hot plate) at a greater temperature than that of the bottom boundary (cold

plate). For guarded hot plates this involves operation in a "one-sided" mode, a procedure with which

many or most participants may not have been familiar. For both apparatuses care must be taken to

set up a thermally stratified, stable (nonconvective) layer of air for measurement.

The data for the air measurements do not prove, but are consistent with, the possibility that (a) convective effects permitted by the large thickness, and (b) effects of unknown but variable plate emittances, had a strong influence on the total heat transfer. The participants did not have the procedure

outlined by Jaouen and Klarsfeld [1] available to them. As a result, total heat transfer, not simply

thermal conductivity, was the actual physical variable actually measured by both types of apparatus

in the round robin.

8.2. Reporting of Data by Participants

The two data sheets sent to participants for submitting their conductivity results were quite detailed.

One form asked for information on the preparation of the specimens for the measurements. The

second asked for all the experimental data as input. It asked the participant to calculate as output

values the heat-flux density and thermal resistance, conductance, and conductivity from the input

data. The forms were, in effect, worksheets. The forms for reporting measurements of air were

practically identical to those for reporting measurements of fibrous glass board. The only difference

was the number of determinations to be made.

Both the input and the output data formed somewhat redundant sets of data. For example, in the set of input data, either the set of both surface temperatures or the set of mean temperature and

temperature difference suffice to calculate the output quantities needed. However, asking for both

sets oftemperature values provided a valuable tool for checking for internal consistency of the input

data. Similarly, asking for heat flux, thermal conductance, thermal resistance, and thermal

conductivity provided sufficient redundancy for checking for internal consistency of the output data

by the author, especially if certain data were not included.

37
At the cost ofadditional labor, the redundancy of input and output data allowed, in a few cases, some

minor errors to be corrected in both input and output, and the appearance of error, where none really

existed, to be avoided. It also revealed, in the case of inconsistent input data, a genuinely erroneous

data point that did not truly reflect the experimental input values. However, such an outlier was not

rejected from the population of data; the ability to report the values correctly is certainly part of what

is (or should be) tested in a round robin. The use of redundancy in the submitted information

therefore turned out to be a resource of some significant value in identifying where problems exist.

An interesting problem arose with some laboratories that undertake routine testing of thermal

properties regularly. They submitted their round-robin data on the same forms usually used for

reporting data to clients. These "in-house" forms did not contain all the information that was asked

for on the "ofiBcial" round-robin forms drawn up by the convenor of the round robin, and this

situation prevented any testing for internal consistency. The same defects arose when one report was

submitted on raw computer printouts, forcing a search of the output for data that would lead to the

requested information.

On a related topic, in some cases the data were not submitted in the (SI) units requested and had to

be converted by hand. This leads to the possibility of errors creeping into the output data, where the

participant is not the source of the errors.

Submitting reports on unique sizes of paper or in official binders made filing of the whole set of

round-robin forms difficuh. Whoever analyzes the data handles the report forms many times in entering the data, in double-checking for accuracy, and in going back to answer any questions that

may arise. Thus it is wise to emphasize in any round robin that all data should be submitted on the

forms supplied to the participants for that purpose, and in the exact units requested.

8.3. Criteria for Measurements

The results show that organizers of any fliture round robin must ensure that a clear set of criteria are established for conducting the measurements of thermal conductivity. Whether the use of either

national or ISO standards are to be left to the choice of the participant, or specified by the planning

committee, must be decided upon in advance in order to promote uniformity of measuring conditions

among a community of world-wide participants. If only one standard is to be adhered to (or a few

uniform, widely accepted standards such as ASTM and/or ISO), care should be taken to ensure that

all participants have access to the relevant measurement standards. Participants should then indicate

clearly which standard they are using in performing their measurements. For uniformity in submission

38
ofdata, SI units should again be specified. It should be clearly stated that only data in SI units will

be accepted into the round robin.

Deciding on the ambient conditions to be established or permitted is complicated of course by the fact

that in any world-wide round robin or intercomparison, ambient conditions can vary widely with

geographic location, as well as with seasons of the year. Some participants may have laboratories

with carefully controlled ambient conditions, while others may have open-window exposure to local

conditions of weather and climate.

In particular, such important parameters as mean temperature of measurement, temperature

difference, measured thickness, the range of ambient temperature, pressure and humidity permitted or established in the laboratory during the measurement, and the order in which data points are to be

measured, must all be carefully considered. Some conditions (general laboratory ambient) may of

necessity have to be lefl to the participant to decide upon, while other, more critical conditions (such

as specimen conditioning for measurement of density and thermal conductivity) may have to be

specified as mandatory. Care must be taken in specifying in advance the ambient conditions for

measurement of related parameters such as density and thickness.

In this round robin the conditions for measurement of density were carefully specified. However, the

period of time allowed to elapse between measurement of density and measurement of thermal

conductivity was not specified or even addressed. If a specimen whose density has been measured were then to be permitted to be exposed to the moist air of a humid climate or weather condition for a period of several days or more before having its conductivity measured, the "conductivity specimen"

could conceivably be different from the "density specimen," both in density and in conductivity.

8.4. Formal Submission of Data

It is prudent to make it a mandatory requirement that all data from each participant be submitted on

the forms supplied by the director of the round robin. As indicated earlier, problems arose in this

round robin when data were submitted on report forms other than those provided by the convenor.

In every such case the forms either presented irrelevant data or failed to supply some of the requested

data, or both. This leaves the analyst with the necessity of converting units and the burden of not

making errors that would reflect pooriy (and unfairiy) on the submitting participant. (When such

conversion was required, every effort was made by the analyst to double-check calculations of unit

conversions to avoid generating errors.) Such examples complicate the testing of internal consistency or result in incomplete submission of data critical to the round robin.

39
8.4.1 Statistical Considerations

Repeating measurements after attaining the highest or lowest mean temperature should, if permitted,

also be clearly described. In any case it should be made clear what number of conductivity

measurements are to be performed by each participant, and that only those submitting this exact

number ofmeasurements will have their data accepted into the intercomparison. It is very important

to have a uniformly sized set of data from each participant, for uniform statistical weighting of data

among the total population of participants. The analyst cannot supply missing data.

In some instances a set of data larger than that requested was submitted. Participants, not convenors

and/or analysts, should be the ones deciding which specific set of data is being submitted by the

participant as the official entry of a set of data into a round robin. Ultimately, only the participant

is fijUy qualified to make such a decision.

Frank J. Powell (now retired from NBS/NIST) was the convenor of WG 6 and organized this

international round robin, coordinated the logistics of getting specimens to the participants, and

collected the reports ofmeasurements. He provided much background material to the present author

to assist in preparing this report. The Building Environment Division at NIST fianded the preparation

ofthis report. Owens-Coming Fiberglas Company, of Toledo, Ohio, USA kindly donated a specially

manufactured lot of fibrous glass insulation board used as the round-robin test material.

9. REFERENCES

[ 1 ] J.-L. Jaouen and S. Klarsfeld, "Heat Transfer Through a Still Air Layer," in Thermal

Insulation: Materials and Systems: ASTMSTP 922, F. J. Powell and S.L. Matthews, Eds.

(American Society for Testing and Materials, Philadelphia, 1987), pp. 283-294.

*U.S. GOVERNMENT PRINTING OFFICE 1 B97-0'B73-0 1 8/40062


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