PUBLICATIONS

NBSIR 79-1908

NAT'L INST. OF STAND & TECH R.I.C.

A 11 ID 5 0457^6

Solar Energy Systems:

Methods for Collector

Insulations

Test

McClure Godette

Jack Lee

James Fearn

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

August 1979

Issued October 1 979

Final Report

I

!

,U56

! 79-1908

1979

Prepared for Department of Energy

Office of the Assistant Secretary

Conservation and Solar Applications

20 Massachusetts Ave.

Washington, D.C. 20545

NBSIR 79-1908

SOLAR ENERGY SYSTEMS: TEST

METHODS FOR COLLECTOR

INSULATIONS

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McClure Godette

Jack Lee

James Fearn

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

August 1979

Issued October 1979

Final Report

Prepared for Department of Energy

Office of the Assistant Secretary

Conservation and Solar Applications

20 Massachusetts Ave.

Washington, D.C. 20545

/ V \

s W)"•I4U O*

U S' DEPARTMENT OF COMMERCE. Juanita

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernes, Ambler. Director

ABSTRACT

A preliminary study was performed to evaluate potential procedures for

screening the insulation used in solar collectors. Both ASTM standard

test methods and newly developed non-standard procedures were used to

evaluate twenty-one insulation materials. The insulation parameters

measured in this study were selected on the basis of how and to what

extent they were affected by the unique environmental conditions within

solar collectors. Results of the laboratory tests are discussed and

those procedures which offer a potential for screening insulations used

in solar collectors are presented. It is intended that these procedures

fulfill the first step in the development of a standard set of test

methods for evaluating insulations for solar collectors.

Key words: Accelerated aging; collector insulation; insulation; solar

collector; insulation test methods.

iii
ACKNOWLEDGEMENT

The authors wish to acknowledge the substantial contributions of

Jessie Hairston, John Michalak and Mildred Post of the National Bureau

of Standards for performing much of the laboratory tests described in

this report. We are also grateful to the U. S. Department of Energy

for supporting this study. Finally, we acknowledge the valuable review

comments of Thomas Boone, Leo Skoda and Gary C. Thom.
CONVERSION UNITS

In recognition of the position of the United States as a signatory

to the General Conference on Weights and Measures, which gave official

status to the International System of Units in 1960, SI units of measurement have been used throughout this publication. To assist in conversion to

common U. S. Units of measurement, conversion factors have been provided in

the table below. The reader interested in making further use of the coherent

system of SI units is referred to:

"The International System of Units," National Bureau of Standards,

NBS SP-330, 1977; or "Metric Practice Guide," American Society for

Testing and Materials, ASTM E 380-76 American National Standards

Institute.

Table of Conversion Factors to Common U.S. Units

Physical To Convert

Quantity To From Multiply by

Length m ft 3.28

Area m

2 ft 2 10.76

Volume m

3 ft 3 35. 34

Temperature Celsius Fahrenheit t f = 1.8 t + 32

Density kg/m3 lb/ft 3 6.25 x 10" 2

Thermal

Conductivity

W/m.K Btu .in/h °f t 2 • °F 6.94

Thermal

Resistance

m

2

. K/W h»ft 2 • °F/Btu 5.68
TABLE OF CONTENTS

Page

ABSTRACT ill

ACKNOWLEDGEMENT iv

CONVERSION UNITS . v

1. INTRODUCTION 1

1.1 Background 1 1.2 Objectives 2

2 PROBLEM ASSESSMENT 2

2.1 In-Service Conditions 3

2.2 Primary Function and Requirements 3

2.3 Key Properties and Degradation Factors 3

3. LABORATORY STUDIES 4

3.1 Materials 4

. 3.2 Test Methods 4

3.2.1 ASTM Tests Performed 5 3.2.2 Non-ASTM Test Performed 6

4. RESULTS AND DISCUSSION 9

4.1 ASTM Tests 9

4.2 Non-ASTM Tests 10

5. DRAFT PROCEDURES 11

6. RECOMMENDATIONS FOR FURTHER WORK 11

7. REFERENCES 12

APPENDIX A. Proposed Standard Practice for Screening Insulation Materials for Use in Solar Collectors .... A-l

vi
1 INTRODUCTION

1.1 BACKGROUND

The typical flat plate solar collector has five major components % the

cover plate, the absorber plate, the heat transfer fluid, the thermal

insulation, and the container or enclosure. Of these, the insulation

serves the important function of minimizing the loss of heat from the

back and sides of the collector enclosure (Figure 1). Thus, the effectiveness of the insulation in reducing heat losses is a primary factor

in determining the overall thermal efficiency of the collector. For

maximum efficiency, the insulation should have the properties of low

thermal conductivity, dimensional stability, and chemical compatibility

(i.e. , not react with other collector component materials). Moreover,

of particular importance in solar collector applications, the insulation

must be able to maintain its thermal and dimensional properties over

the lifetime of the collector, and do so under the degrading effects

of high and cyclic temperature and possibly high humidity.

The environmental conditions under which solar collectors must operate

are defined by the diurnal and seasonal variations in temperature, humidity (or moisture), and solar radiation; in addition, the presence of

atmospheric dust and pollutants in combination with the other environsynergistic effect on the degradation of the

conditions depend on the local climate, the design of the collector, and

the materials used in its construction. For example, the maximum absorber

plate temperature will occur on a sunny day when no heat is being removed

from the collector, i.e., stagnant operation. Because the insulation may

be located directly next to the absorber plate, it is also subjected

to temperature extremes.

The effects of extreme environmental conditions on solar collector

components have been well documented in a recent report by Skoda and

Masters [2]. They reviewed the performance of solar collector materials

by conducting on-site inspections of operational solar energy systems,

and surveying both the manufacturers and installation contractors of

these systems. For insulation, they found that the performance problems

included swelling as a result of exposure to elevated temperatures, degradation due to exposure to ultraviolet radiation, and outgassing of

-^Numbers in brackets refer to the references listed in Section 7.

The maxima and minima in the collector operating

1
degradation products. Depending on the chemical nature of these products,

they may either react with or condense on other collector materials. If

condensation occurs on the underside of the cover plate, transmittance

may be reduced, leading to a lower thermal efficiency for the collector.

Despite the existence of these problems there are few performace standards or test methods which deal specifically with the use of materials

in solar collectors. For example, in the case of insulation, there are numerous standard test methods which may be used to determine its performance in normal building applications but these test methods may not

be fully applicable to the evaluation of insulation for use in solar

collectors. This is particularly true of durability-related tests (aging

tests) where the exposure conditions seldom simulate those experienced

in collectors. Consequently, an urgent need exists for standards which

ensure the satisfactory performance of the insulation used in solar

collectors.

1.2 OBJECTIVES

The purpose of this study was to develop test methods by which the

insulation used in solar collectors may be evaluated. To meet this

goal, four specific objectives were established:

. To identify the performance requirements for insulations used in

solar collectors.

. To identify or develop test methods to measure insulation performance according to these requirements.

. To evaluate and then recommend those test methods which are suitable for the insulation materials that are used in solar collectors.

. To draft a set of standard test methods for solar collector

insulations; these methods will be considered for adoption by the

American Society for Testing and Materials (ASTM).

2. PROBLEM ASSESSMENT

In the evaluation of insulations for use in solat collectors, one must

determine the ability of the insulation to perform its function under A

the environmental conditions within the solar collector. The first step, '* then, is to identify the critical in-service operating conditions and

insulation performance requirements. Using this information one can identify the properties and corresponding tests which must be used in

the evaluation. The following paragraphs are devoted to a discussion of

these topics.

2
2.1

IN-SERVICE CONDITIONS

The in-service operating conditions of a solar collector include the

following factors, which must be taken into consideration in any analysis

of insulation test methods:

. Sustained high or low temperatures. During stagnation, temperatures may be as high as 260° C within the collector on a sunny

day and as low as -40° C outside the collector at night. [l],

. Diurnal temperature-humidity cycling.

. Condensation or accumulation of water within the collector.

. Continuous contact between the insulation and the components

of the collector system.

2.2 PRIMARY FUNCTION AND REQUIREMENTS

The primary function of the collector insulation is to minimize the

thermal losses that result from the transfer of heat from the back and

sides of the absorber plate through the collector enclosure. In order to

attain and maintain maximum thermal efficiency, these losses must be re- duced through the use of an insulation which not only has good initial

insulating properties, but also maintains these properties over the lifetime of the collector. This requires that the insulation withstand the

chemical and/or physical changes which can be brought about by both the

normal diurnal temperature-humidity cycles and sustained high or low

temperatures which occur during stagnation. In addition, unless the

insulation is unreactive toward other collector materials (particularly

metals), and does not absorb water; both the material and performance

degradation of the insulation as well as other collector materials can

take place.

2.3 KEY PROPERTIES AND TEST METHODS

The key properties of insulations which were identified for inclusion

in the laboratory studies were: mass, size, density, water adsorption,

moisture absorption, thermal conductivity, and friability. The degradation factors that could affect these properties and thereby reduce the

ability of insulations to perform as intended are: high and low temperature, water, high relative humidity, mold and vibration. In addition,

the contact compatibility between insulations and other collector materials is an important factor affecting performance. Table 1 lists the

ASTM test methods that were used to determine the effect of these degradation factors on the key properties. Due to the severe environmental

conditions under which the solar collector must operate, some tests had

to be slightly modified. For example, to simulate in service collector

conditions, higher and/or lower temperatures were used in some tests.

Finally, the uniqueness of the solar collector system required that four

3
new non-standard tests be designed to determine the effects of such factors as thermal cycling and corrosion. These test methods are listed in

Table 1 and described in the next section.

3. LABORATORY STUDIES

3. 1 MATERIALS

The twenty-one insulations tested in this study are listed in Table 2.

Insulations were classified according to the four generic types and four

physical forms given in the American Society of Heating, Refrigerating

and Air-Conditioning Engineers (ASHRAE) 1977 handbook [3]. The four

generic types include:

° Mineral fibrous materials such as glass, rock or slag wool.

0 Mineral cellular materials such as calcium silicate, foamed

glass, perlite and vermiculite.

° Organic fibrous materials such as wood, paper or synthetic

fibers.

° Organic cellular materials such as urea-formaldehyde, polystyrene or polyurethane foams.

The above types are available in four basic shapes or forms:

° Loose-fill - This form consists of fibers, granules or nodules which are usually poured or blown into place.

° Flexible - This includes blanket, batt and felt insulation

materials. They have varying degrees of compressibility and

flexibility, and arq available in sheets or rolls of many types

and varieties. The thickness and shape of the insulation may

be of any dimension conveniently handled, although standard sizes are generally used.

° Rigid - These materials are available in rectangular dimensions

called block, board or sheet, and are preformed during manufacture to standard lengths, widths and thicknesses.

° Foamed-in-Place - These materials are available as liquid components which may be poured, frothed or sprayed in place to form

rigid or semirigid foam insulation.

3.2 TEST METHODS

Both ASTM and non-standard test methods were necessary to characterize

the aging process in solar collector insulations and to determine the

effect of the degradation factors and the magnitude of any change in

the several insulation properties given in Table 1. These properties

4
and the factors which affect them had been identified as potentially

contributing to the overall material and performance degradation of a solar collector.. The following gives a brief statement concerning the reasons for selecting each of the ASTM tests listed in Table 1 and what,

if any, modifications were made in the existing test method. For the

non-standard tests the importance of each and a description of the test

is given.

3.2.1 ASTM Tests Performed

C 167 "Thickness and Density of 'Blanket or Batt Type Thermal Insulating

Materials." This is the standard test for determining the density and

thickness of insulations; these two important properties identify the

gross physical characteristics of an insulating material.

C 209 : Section 13 "Testing Insulation Board (Cellulosic Fiber), Structural and Decorative: Water Absorption." This test was used in conjunction with D 1037: "Evaluating the Properties of Wood-Base Fiber and

Particle Panel Materials", Sections 100-106: "Water Absorption and

Thickness Swelling," to determine the percent water absorption by weight

of all form types of insulation tested. Although these tests are only

strictly applicable to cellulosic fibrous materials, the test procedures

closely simulate the conditions whereby the collector insulation may be

partially or completely submerged in water if it becomes present in the

collector enclosure.

C 553 : Section 13 "Mineral Fiber Blanket and Felt Insulation

(Industrial Type): Moisture Adsorption." This test method is one of

several under C 553 designed specifically for determining the properties

of insulations used on heated or refrigerated surfaces, e.g., the absorber plate or enclosure of a solar collector. The test conditions were

modified in the following way: Samples were exposed for 30 days to 50

and 90 percent relative humidity at 23° C, and to 70 percent relative

humidity at 94° C. The longer exposure time and higher temperature

served to accelerate any possible insulation degradation which might

increase the adsorption of moisture.

C 518 "Steady-State Thermal Transmission Properties by means of Heat Flow

Meter." This is the standard method for measuring the thermal transmission

properties of insulation; it is a comparative method which utilizes C 177

to calibrate a standard comparison sample. For the purpose of this study

results are reported as thermal conductivities (W/m*K).

C 411 "Hot Surface Performance of High-Temperature Thermal Insulation.

This method is specifically designed to determine the performance of

insulation that is used in contact with surfaces hotter than 93° C (viz.

the solar collector absorber). For the purposes of this study, samples were exposed for 96 hours to the following temperatures: 94, 150, 209,

and 260° C. These temperatures are representative of the high temperatures experienced by insulation in a solar collector [1].

5
C 356 "Linear Shrinkage of reformed High-Temperature Thermal Insulation

Subjected to Soaking Heat" - This test is used to determine the change

in the linear dimension and the loss in mass of preformed insulation when

exposed to temperatures greater than 93° C. In the current study temperatures of 150 and 260° C were used — the same temperatures used in the

Hot Surface Performance test. Although the standard 24-hour exposure was used for the linear shrinkage tests, only one-hour exposures were used for

the mass loss tests.

D 3273 "Resistance to Growth of Mold on the Surface of Interior Coatings

in an Environmental Chamber" - Although this standard test was designed

specifically to determine the resistance of a paint film to the growth of

mold that might occur on its surface in a severe interior mold environment (e.g. , high humidity), the procedure is sufficiently general to be

applicable to a variety of materials, including the insulation used in

solar collectors. The tests reported here used the following organisms:

aspergillus niger, aureobasidium pullulus, and penicillin citrinium.

3.2.2 Non-Standard Tests Performed

Thermal Cycling - The diurnal temperature changes both inside and outside

the solar collector may be quite extreme. Thermal cycling may cause insulation to contract, expand or crack which, in turn, could lead to

a general degradation in both the physical and chemical properties of

the insulation. In order to determine the effect of thermal cycling on

the properties of insulation the following test procedure was developed:

1. Insulation samples were conditioned for 48 hours at 23+2° C

and 50 + 5% rh, then placed in the aluminum pan (Figure 1) and

covered.

2. The pan (containing the insulation) was then subjected to 30

cycles of $

° Heating for 7.5 hours at 94, 150, 209 or 260° C^.

° Conditioning at 23+2° C and 50% rh for 30 minutes.

° Cooling at -40° C for 15-1/2 hours.

° Conditioning at 23 + 2° C and 50% rh for 30 minutes.

3. After exposure, the acidity, water absorption and thermal con- ductivity of the samples were measured. In addition, the

samples were examined for expansion, cracking and fluffing;

expansion was measured in terms of the height of the bow

The maximum cycle temperature was established in another test:

Effect of Thermal Cycling on the Appearance of Insulation Materials

(Table 9).

6
formed. Finally, the inside of the cover was visually examined

for the deposition of binder or water.

Out gas sing - The high temperatures within the solar collector are known

to cause the volatile components of an insulation to vaporize and

condense on the cooler cover plate [2]. Volatile components may include

water, organic binders, unpolymerized monomer, and low-temperature

pyrolysis products. The principal effect that these compounds have on

the solar collector is a reduction in the transmittance of the cover

plate when the volatiles condense on its inside surface; this can lead

to reduced thermal efficiency. In order to quantify the transmittance

loss, a newly developed outgassing test method described in [4] was used.

In brief, the outgassing test procedure involves placing a sample into

a heated test chamber; the volatiles released subsequently condense on

the glass collecting plate which is cooled by a measured flow of air

over its surface. The magnitude and effect of outgassing were measured

by the mass lost by the sample, mass gained by the glass plate, and

percent decrease in transmittance of the glass plate after three hours

of heating. For the purposes of this study the test procedure given

in Appendix B was employed with the following modifications:

1. Insulation test samples were cut to a size of about 16 cm . These samples along with the glass plates were weighed to the

nearest 0.01 mg. In addition, the transmittance spectrum of

each plate was recorded between 300 and 2100 nm using a recording spectrophotometer.

2. After the sample chamber was heated to a constant temperature

of 300° C, a sample was placed in the chamber, covered with

a weighed glass collecting plate, and tested for a period of

three hours. To maintain the temperature of the plate below

that of the chamber, the cooling air flow rate was maintained

at 0.55 1 / sec throughout the duration of the test.

3. Data were reported as mass of sample lost, mass deposited on

the collector plate, and percent decrease in transmittance.

Corrosion - Contact between the insulation and the metal components of

the solar collector (e.g. , the absorber plate or enclosure) under the

conditions of high temperature and relative humidity, can result in a significant amount of corrosion to the metal components. This could

result in early failure of these metal components, and, therefore, a reduction in the lifetime of the collector.

Corrosion was studied in terms of the amount of pitting which took place

when the metal was put in contact with the insulation under controlled

test conditions. Four types of metals commonly used in solar collector

enclosures and absorbers were tested: 1) stainless steel-type 304;

7
2) aluminum - 6061 T6; 3) brass - composition #24; and 4) copper - cold

rolled, oxygen free.

Procedure:

1. Metal samples (50 x 75 x 3.1 mm) were scrubbed and then ultrasonically cleaned for 30 minutes in 1,1,1-trichloroethane to remove any surface grease. The samples were then rinsed in

distilled water, drained and rewashed if water breaks appeared

on the surface.

2. Samples were dried for one hour in a desiccator at room temperature and then examined under a microscope at 10 to 100 times

magnification to determine the amount of pitting (see 5 below).

3. Each metal sample was placed on a piece of insulation

(180 x 180 mm) and then placed on a ceramic plate in a crystallyzing dish (Figure 2) containing 500 ml of distilled water.

Samples were kept 25 mm above the water level.

4. The crystallizing dish was covered with a watch glass and then

placed in an oven at 100°C for 30 days.

5. At the completion of the test, the metal samples were removed

and examined at 10 to 100 times magnification for corrosion as evidenced by pitting. The amount of pitting was classified as none, very mild, mild, severe, and very severe.

Friability - This property is potentially important because roof-mounted

solar collectors may sustain vibration-induced damage caused by wind,

rain, hail and normal roof maintenance. For the insulation, such damage

takes the form of a breaking-up of the insulation caused by abrasion

and impact between the insulation and the absorber plate or enclosure.

In order to determine the extent of this breaking-up or friability the

following test was devised. This test measured the weight of material

shaken free from a known weight of insulation enclosed in a wire mesh

container.

Procedure

1. An insulation sample was cut to fit snugly into a retangular

75 x 100 x 75 mm container made of 16 mesh (25 mm) wire screen.

2. The tared container and its contents were weighed to the nearest

0.1 mg placed in the base of a sieve (Figure 3), covered, and

shaken for 30 seconds at a rate of 150 cycles per minute.

3. At the termination of the test, the wire mesh container and

insulation were reweighed to 0.1 mg. Any weight change was reported as a percentage of the original weight of the insulation.

8
4. RESULTS AND DISCUSSION

The tests described in the previous chapter are listed in Table 1.

Table 2 contains a description of the insulations tested and their assigned

codes. These codes were used to identify the samples in Tables 3 through

11, which contain the the results. The remaining portion of this chapter

presents a discussion of the test results obtained in this study.

4.1 ASTM TESTS

Density and Thermal Conductivity - Data on these two insulation proper

ties are given in Table 3. Note that the range in densities for the

mineral fiberous and organic cellular insulations was nearly the same:

10 to 150 kg/m . However, ranges for the thermal conductivity showed a considerably greater difference: for the mineral fibrous insulations

values fell between 3.80 and 4.75 X 10 W/m*K — a range of only 0.95

units, while the values for the organic cellular fell between 2.60 and

5.49 X 10” W/m*K — a range of 2.89 units. Thus for this study, the

thermal conductivity parameter appears to distinguish between insulation

types.

Water Absorption and Moisture Adsorption - The water absorption data

(Table 4) show that insulations vary widely in their tendency to absorb

water and whether they absorb more or less moisture after thermal cycling.

In general, fibrous insulations absorbed more water than their cellular

counterparts. On the other hand, the data in Table 5 show that insulations

adsorbed very little moisture, although, at 90% RH and 23° C all but one

of the fibrous insulations were found to adsorb moisture. Finally, the

cellular insulations generally adsorbed less moisture than the fibrous at

all three test conditions — a result anticipated from the water absorption

tests.

Hot Surface Performance - Results of the hot surface performance test are reported in Table 6 as visible changes and percent shrinkage. The data

show that most insulations exhibited visible changes at various temperatures when heated from 94 to 260° C in increments of 55 + 3° C. Three

distinct levels of performance were noted: 1) those insulations that

performed at moderately high temperature (150 and 209° C) with changes

in color or evolution of water without change in linear dimension —

this type of performance was limited to the mineral-type insulations;

2) those insulations that performed at the highest temperature (260° C)

without any observable changes — the mineral-type insulation; and,

3) those insulations that reached their exposure limits at a low temperature (94 or 150° C) with melting and the associated shrinkage — observed

only in organic-type insulations.

Linear Shrinkage and Loss in Mass - Table 7 summarizes the linear shrinkage data for the organic cellular insulations exposed to a soaking heat

of 150 and 260° C for 24 hours. The table does not show data for the
mineral fibrous, mineral cellular, and organic fibrous insulations

because these types suffered no change in linear dimensions under the

test conditions.

The data from the "Loss in Mass" part of this test are given in Table 8.

Although the data indicate a general trend toward increasing loss in mass with increasing temperature, particularly for the organic type

insulations, this test was not considered essential. Any loss in mass from the collector insulation is only important when correlated with the

materials or performance degradation of the collector, such as the loss

in collecter plate transmittance. This correlation was made in the

"outgassing" test discussed in the next section.

Resistance to Growth of Mold - The mold resistance test results showed

that only three of the insulation test specimens supported the growth of

mold: Calcium silicate (11-CS), cellulose (13-CL), and wood fiber (15-WF).

The remaining samples showed no growth. These results indicate that the

growth of mold is not a principal factor in the degradation of insulation.

4.2 NON-STANDARD TESTS

Thermal Cycling - The effects of thermal cycling on water absorption have

already been discussed and the results of this test are given in Table 4.

Table 9 summarizes the effects of thermal cycling on the appearance of

insulations. Note that the mineral-type insulations had the highest

maximum cycle temperature and exhibited relatively minor changes in

appearance compared to the organic-type insulations which had low maximum

cycle temperatures, accompanied by expansion, bowing, crumbling, or com- paction.

Thermal cycling was also used as a degradation factor for the thermal

conductivity of insulation materials. However, data for this test are

not included here because with the exception of a few materials which

showed only a slight decrease in thermal conductivity, little change

in this parameter was observed after thermal cycling.

Outgassing - The results of the outgassing test and the effects of outgassing on transmittance through the cover plate are shown in Table 10.

The few insulations tested showed only slight decreases in the weight

with a corresponding increase in the weight of the glass plate and decrease

in its transmittance. The only exception was the single organic cellular

insulation tested (polyurethane) which lost nearly one-fourth of its original

weight; this resulted in an effective decrease in cover plate transmittance

of 8 percent.

Corrosion - The results of this test, which are given in Table 11, are reported in terms of the amount of pitting that took place on the metal

surface. Note that only the fibrous insulations caused severe pitting

of the metal surfaces, whereas the effect of the cellular insulations

was restricted to mild or no pitting.

10
Friability - Results from this test showed that only two of the twentyone insulations tested lost mass when subjected to vibration. As a result, the data from this test are not included in this report.

5. DRAFT PROCEDURES

Based upon the laboratory tests and results described in sections 3 and 4,

the following tests have been included in the "Draft Procedures for

Screening Insulation Materials used in the Solar Collectors" which is

given in Appendix A.

The tests included were either identical with existing ASTM tests or newly developed tests, as indicated below:

Water Absorption - ASTM C 209

Thermal Conductivity - ASTM C 518

Linear Shrinkage - ASTM C 356

Corrosion - Newly developed

Hot Surface Performance - ASTM C 411

Outgassing - Newly developed

Thermal Cycling - Newly developed

These tests, in combination, are presented as a methodology for screening

insulation materials used in solar collectors with respect to the level

of performance and relative stability of solar collector insulation under

simulated in-service conditions. The tests are applicable to both flexible, semirigid and rigid, loose-fill, and f oamed- in-place insulation

materials. Moreover, tests were chosen to allow testing of all types of

insulations: mineral fibrous and cellular, and organic fibrous and cellular.

Finally, although correlations between performance under laboratory and

actual in-service conditions have not yet been firmly established, the

proposed standard should aid significantly in the assessment of the longterm performance of insulation materials by the type of before/after and

comparative testing utilized in the above tests.

6. RECOMMENDATIONS FOR FURTHER WORK

The tests and results discussed in this report represent a small portion

of the research which must be done to identify the degradation factors

affecting not only the properties of solar collector insulation but also

the other solar collector components. Thus, this report may be considered

as a preliminary investigation. Further work should be directed toward

conducting more extensive, quantitative studies of those degradation factors and properties found to be important in this study, i.e., those

which are part of the tests included in the Draft Procedures. In addition, particular attention should be paid to conducting studies which

will show if correlations exist between two or more insulation properties,

e.g., mass lost from outgassing as a function of temperature and its

affect on the loss of cover plate transmittance. These and similar

11

/
in-depth correlation-type studies should lead to a greater understanding

of insulation properties and solar collector performance. Finally, these

studies will provide a firmer data base for proposing new recommended

testing practices for the insulation and other components used in the

solar collector system.

7. REFERENCES

1. Masters, L. W. , and Wolfe, W. C. , The Use of Weather and Climatological Data in Evaluating the Durability of Building Components

and Materials , NBS Technical Note 838, National Bureau of

Standards, Washington, D.C., August 1974.

2. Skoda, L. F., and Masters, L. W. , Solar Energy Systems - Survey

of Materials Performance , NBSIR 77-1314, National Bureau of

Standards, Washington, D.C., October 1977.

3. "ASHRAE Handbook & Product Directory - 1977 Fundamentals," American

Society of Heating, Refrigerating and Air-Conditioning Engineers,

Inc., New York, 1977.

4. Stiehler, R. D. , Hockman, A., Embree, E. J. , and Masters, L. W.

,

Solar Energy Systems - Standards for Rubber Seals , NBSIR 77-1437,

National Bureau of Standards, Washington, D.C., March 1978.

12
Table 1. Test Methods Used to Evaluate Solar Collector

Insulations

ASTM Tests

C 167

C 209: Section 13

C 553: Section 15

C 518

C 411

C 356

D 3273

Non-standard Tests

"Thickness and Density of Blanket- or Batt-Type

Thermal Insulating Materials"

"Testing Insulation Board (Cellulosic Fiber)

,

Structural and Decorative: Water Absorption"

"Mineral Fiber Blanket and Felt Insulation

(Industrial Type) : Moisture Adsorption

"Steady-State Thermal Transmission Properties

by Means of Heat Flow Meter"

"Hot Surface Performance of High-Temperature

Thermal Insulation"

"Linear Shrinkage of Preformed High-Temperature

Thermal Insulation Subjected to Soaking Heat"

"Resistance to Growth of Mold on the Surface

of Interior Coatings in an Environmental

Chamber"

Thermal Cycling

Outgassing

Corrosion

Friability

13
Table 2. Description of Insulations Tested

Generic Sample No. and Thickness

Type Description3 Form (mm)

Mineral 1-FG Fiber Glass Batt 87.5

Fibrous

2-FG Fiber Glass Batt 87.5

3-FG Fiber Glass Board 48.4

4-FG Fiber Glass Board 25.0

5-FG Fiber Glass Batt 21.9

6-FG Fiber Glass Batt 37.5

7-FG Fiber Glass Batt 31.3

8-SW Slag Wool Batt 100.0

9-SW Slag Wool Batt 31.3

10-RW Rock Wool Batt 31.3

Mineral 11-CS Calcium Silicate Tubular 25.0

Cellular

12-GF Foam Glass Board 46.9

Organic 13-CL Cellulose Loose-fill N. A.

* Fibrous

14-CL Cellulose Loose-fill N. A.

15-WF Wood Fiber Board 12.5

Organic 16-UF Urea Formaldehyde Foamed-in-place 21.9

Cellular

17-PS Polystyrene Board 50.0

18-PS Polystyrene Board 12.5

19-PS Polystyrene Board 50.0

20-PU Polyurethane Board 23.4

21-RB Foamed Rubber Tubular 12.5

* N. A. -- Not Applicable.

a These descriptions are based on the classification of insulations

given in the "ASHRE Handbook of Fundamentals-197 7

,

and, therefore

are not necessarily the same as those given by the manufacturer.

14
Table 3. Density and Thermal Conductivity of Insulation Materials

Generic

Type

Sample

No.

Density

(kg/m3

) Thermal Conductivity

(W/m*K x 10 3 )

Mineral 4-FG 144.0 b

Fibrous

10-RW 104.0 b

3-FG 72.0 3.80

8-SW 52.8 3.99

9-SW 44.5 3.77

6-FG 19.2 4.60

7-FG 16.0 4.49

5-FG 16.0 b

1-FG 12.0 4.75

2-FG 10.0 4.60

Mineral 11-CS 184.0 b

Cellular

12-GF 140.8 5.49

Organic 21-RB 86.0 b

Cellular

19-PS 35.2 3.17

17-PS 32.0 4.50

20-PU 32.0 2.60

16-UF 24.0 b

18-PS 14.9 3.17

a The organic fibrous insulations were not tested,

b Not determined.

15
Table 4 . Water Absorption Before and

Thermal Cycling

After

Generic Sample Water Absorption, °l by Mass

Type No. Before After % Change

Mineral 1-FG 3064 1548 -49.5

Fibrous

2-FG 1853 1893 + 2.1

7-FG 1874 1892 + 1.0

6-FG 1300 1830 +29.0

9-SW 1136 474 -58.3

8-SW 586 473 -19.3

4-FG 113 35 -69.0

3-FG 89 105 +15.2

5-FG 43 40 - 7.0

10-RW 20 15 -25.0

Mineral 11-CS 371 379 + 2.1

Cellular

12-GF 14 18 +22.2

Organic 13-CL 2273 2279 + 0.2

Fibrous

14-CL 1774 1491 -16.0

15-CL 45 38 -15.2

Organic 16-UF 308 364 +15.4

Cellular

17-PS 92 45 -51.1

18-PS 56 41 -26.8

20-PU 38 56 +32.1

19-PS 34 30 -11.8

21-RB 26 8 -69.2

16
Table 5 . Moisture Adsorbed by Insulations during

30-day Exposure to Different Temperatures

and Levels of Relative Humidity

Moisture Adsorbed, % by Mass

3 ’*5 Generic Sample 23 °C 94 °C

Type No. 50% RH 90% RH 70% RH

Mineral 1-FG 0.4 5.3 1.0

Fibrous

3-FG 1.7 4.0 -

2-FG - 4.0 0.4

8-SW - 1.7 -

6-FG - 1.0 -

5-FG 0.4 0.8 -

7-FG - 0.5 -

4-FG 0.1 0.4 -

9-SW - 0.1 -

10-RW - - -

Mineral 11-CS 0.5 13.2 0.2

Cellular

12-GF - - 0.1

Organic

Fibrous

15-WF 1.5 10.3 -

13-CL 1.7 4.0 -

14-CL 0.2 1.8 -

Organic

Cellular

16-UF 0.5 8.8 -

21-RB - 4.0 -

20-PU - 0.7 -

19-PS - - 0.1

17-PS, 18-PS - -

a Where no value is recorded, there was no measurable gain in mass.

b Note that Sample Nos. 10-RW, 17-PS and 18-PS showed no moisture

adsorption.

17
Table 6. Effect of Hot Surface Contact on the Appearance and

Linear Shrinkage of Insulations

Generic Sample Surface Temperature at which Linear Shrinkage*

3 Type Nos. First Observable Change at 150 and/or

Takes Place3 260 °C

Mineral 1-FG, 2-FG 209 °C - Discolors and chars None

Fibrous 3-FG, 5-FG

8-SW, 10-RW 209 °C - Discolors None

4-FG 150 °C - Discolors and chars None

6-FG, 7-FG, 9-SW None

Mineral 12-GF None None

Cellular

11-CS 209 °C - Evolves water None

Organic 13-CL 209 °C. - Evolves water c Fibrous

14-CL 94 °C - Evolves water c

15-WF 94 °C - Discolors 3% at 150 °C >95% at 260 "C e

Organic 20-PU 150 °C - Meltsd and chars 18% at 260 °C Cellular

17-PS, 18-PS

19-PS

150 °C - Melts® >95% at 150 °<f

21-RB 94 °C - Discolors 18% at 150 °C

16-UF 94 °C - Bows 14% at 150 °C >95% at 260 °C e

a All observations made after 96 hours pf exposure to the hot surface; samples were

exposed successively to 94

,

150, 209 and 260 °C to determine the lowest temperature

required to induce an observable change.

b Linear shrinkage calculated as the percent reduction in the original length of the

sample.

c Shrinkage not applicable to cellulosic loose-fill insulations,

d Sample melts on side exposed to hot surface,

e Sample melts completely.

18
Table 7 . Linear Shrinkage of Cellular Insulation Materials

Exposed to High Temperature

Generic

Type

Sample

No. 150 °C 260 °C

Organic 20-PU 0.0 % 25.0 %

Cellular

3

16-UF 5.0 25.0

21-RB 27.0 40.0

19-PS 82.0 >95.0

17-PS 86.0 >95.0

18-PS 93.0 >95.0

a All other insulations showed no shrinkage under• the same test conditions

.

19
Table 8. Percent Loss in Mass After Heating Insulation

for One Hour

Materials

Generic

Type

Sample

No. 94 °C 150 °C 209 °C 260 °C

Mineral 3-FG 7.0 % 10.1 % 15.3 % 42.0 %

Fibrous

5-FG 1.7 1.7 3.8 4.0

2-FG 0.8 0.8 2.9 3.0

1-FG 1.1 1.1 2.8 3.0

7-FG 0.9 2.1 2.1 2.0

4-FG 0.2 0.6 1.0 2.0

9-SW 0.3 0.3 1.0 1.3

6-FG 0.9 0.9 0.9 1.0

8-SW 0.5 0.5 0.5 0.8

10-RW 0.2 0.2 0.4 0.8

Mineral 11-CS 0.7 0.7 2.6 3.5

Cellular

12-GF 0.2 0.2 0.2 0.2

Organic 15-WF 4.1 5.3 83.1 83.1

Fibrous

13-CL 31.0 36.8 73.3 74.0

14-CL 5.6 6.4 5.2 64.0

Organic 18-PS 1.2 1.2 21.4 82.5

Cellular

16-UF 3.0 9.7 60.0 71.4

17-PS 1.4 1.4 11.3 63.7

19-PS 1.2 3.1 25.8 62.0

20-PU 1.7 10.7 32.3 44.7

21-RB 0.8 1.8 25.0 32.0

20
Table 9. Effect of Thermal Cycling on the Appearance

of Insulation Materials

Generic Sample

Type No. Max Cycle Temp - Change in Appearance

Mineral 3-FG, 4-FG 94 °C - Deposits binder

Fibrous

8-SW, 9-SW 260 °C - Deposits binder

1-FG, 2-FG, 5-FG 260 °C - Fluffs, Deposits binder

6-FG, 7-FG 260 °C - Fluffs

Mineral

Cellular

11-CS, 12-GFb

94 °C - None

Organic 15-WF 94 °C - None

Fibrous

13-CL, 14-CL 94 °C - Evolves ^0, compacts

Organic 16-UF 94 °C - Cracks then crumbles

Cellular

20-PU 94 °C - Expands, forming 66 mm bow

17-PS, 18-PS , 19-PS 150 °C - Expands, forming 50, 40, and

30 mm bows, respectively

a Thirty-cycle test; minimum cycling temperature for all samples was -40 °C.

b Cracked after extended 45 cycle test.

\

21
Table 10. Effect of Insulation Outgassing on Cover Plate Transmittance

Generic

Type

Sample

No. a Mass of Sample

Lost, mg (%)

Mass Deposited

on Plate, mg

Decrease in

Transmittance

of Plate, %

Mineral 8-FG 6.39 (0.99) 0.32 0.69

Fibrous

2-FG 1.64 (1.0) 0.13 0.21

9-SW 2.27 (0.28) 0.24 0.16

10-RW 1.61 (0.27) 0.66 0.14

1-FG 2.24 (0.70) 0.56 0.04

Organic 20-PU 130.53 (24) 0.48 8

Cellular

a Sample numbers not listed were not tested.

22
Table 11. Corrosion of Metals by Insulation Materials3

Degree of Pitting

Generic Sample Stainless

Type No. Steel Brass Copper Aluminum

Mineral 7-FG Severe Severe Severe V. Mild

Fibrous

1-FG, 4-FG, 9-SW — Mild Mild —

3-FG Mild — — —

2-FG, 6-FG, 7-FG — — —

8-FG, 10-RW

Mineral 11-CS Mild

Cellular

12-GF — — —

Organic 13- CL Severe Mild Mild

Fibrous

14-CL Severe Mild Mild Mild

15-WF — — Mild —

Organic 20-PU Mild Mild Mild

Cellular

16-UF — Mild Mild Mild

17-PS , 18-PS, — Mild Mild —

19-PS, 21-RB

a Results reported as severe or mild pitting of the metal surface after 30-day

contact with insulation; where nc> pitting occurred, no result is given •

23
Figure 1. Essential features of a flat plate solar collector.

24
Figure 2., Diagram of the aluminum pan used in the

25
Figure 3 . Crystallizing dish containing water and metal specimens in

contact with insulation, as used in the chemical compatability

test

26
Figure 4. Insulation sample enclosed within the wire mesh container and

sieve pan as used in the friability test.

27

APPENDIX A

Draft Procedures for Screening Insulation Materials

Used in Solar Collectors

1.

Scope

1.1 This set of draft procedures provides a methodology to screen

insulation materials used in solar collectors with respect to their

level of performance and relative stability under simulated in-service

conditions. Test methods are given to measure water absorption, thermal

conductivity, corrosion, hot surface performance, outgassing, and

thermal cycling. It is intended that these procedures fulfill one of the steps in the development of a standard set of test methods

for evaluating insulations used in solar collectors.

1.2 The methods are applicable to flexible, semirigid, and rigid

board, loose-fill, and f oamed-in-place insulation materials. Tests were chosen to allow testing of all types of insulation: mineral

fibrous and cellular, and organic fibrous and cellular.

1.3 The assumption is made that elevated temperature, temperature

cycles, moisture and their resulting stresses are the primary factors

that cause degradation of the insulation materials used in solar collectors .

1.4 Test methods included in the document are both property measurement tests and aging tests. Property measurement tests are tests

which provide for measurement of various properties of insulation,

e.g., thermal conductivity.

Aging tests are tests which provide for exposure of insulation to

environments that may induce changes in the properties (degrade)

of test specimens. Measuring properties before and after aging

test provides a means of determining the possible effect of aging.

2.

Significance and Use

2.1 This draft set of procedures is intended to aid the assessment of

long-term performance by comparative testing of insulation materials.

However, correlations between performance under laboratory and actual

in-service conditions have not been established.

3.

Applicable Documents

ASTM C 209 Testing Insulating Board (Cellulosic Fiber), Structural

and Decorative.

A1
ASTM C 411 Test for Hot-Surface Performance on High-Temperature

Thermal Insulation.

ASTM C 518 Steady State Thermal Transmission Properties by

Means of the Heat Flow Meter.

3.

Test Specimens

3.1 Specimens for each test condition shall be randomly selected from

the original sample lot so as to be as representative as possible.

3.2 At least three specimens shall be measured for each property tested

3.3 The size and shape shall be as specified in the property measurement test.

4.

Conditioning

4.1

Unless otherwise specified, test specimens shall be conditioned at

73 + 5°F (23 + 2° C) and 50 + 5% rh for at least 48 hours before testing

5.

Methods of Test

5.1 Property Measurement Tests

5.1.1 Water Absorption

5.1. 1.1 Determine water absorption of the insulation material in

accordance with ASTM C 209.

5.1. 1.2 Determine the quantity of water absorbed (expressed as a percentage by weight and by volume) by the insulation material.

5.1.2 Thermal Conductivity

5.1. 2.1 Measure thermal conductivity according to ASTM C 518.

5.2 Aging Tests

5.2.1 Corrosion

5.2.2 Determine the contact corrosion between the insulation and

metals (e.g., absorber plate or enclosure) using the following

p roeedu re

:

A2
a. Cut metal samples to a size 50 X 75 X 3.1 mm and then

scrub samples and clean them ultrasonically for 30 minutes

in 1,1,1-trichloroethane. Rinse samples with

distilled water. Drain. If water breaks appear, rewash.

b. Dry for one hour in a desiccator at room temperature.

Examine each sample under a microscope at 10 to 100 times

magnification and record the amount of pitting (see "e"

below)

.

c. Place each sample on a 180 X 180 mm piece of insulation,

and then place both in a crystallizing dish containing

500 ml of distilled water.

d. Cover the crystallizing dish with a watch glass and

place in an oven at 100° C for 30 days. Keep samples

25 mm above the water level by adding make-up water as necessary.

e. At the completion of the test, remove metal samples

and examine the contact side for corrosion under a microscope at 10 to 100 times magnification. The

corrosion Is based on a subjective visual evaluation of

the amount of pitting which has occurred on the surface

of the sample; five classes of pitting are used to

describe the results: none, very mild, mild, severe

and very severe.

5.2.2 Hot Surface Performance

5. 2. 2.1 Hot surface performance shall be determined in accordance

with ASTM C 411. Test at 200 + 10° F (94 + 5° C) and 500 + 10° F

(260 + 5° C) if maximum temperature conditions are unknown.

5.2.3 Outgassing

5.2.3. 1 Determine the effect of outgassing products in cover plate

transmittance using the method described in Appendix B with the

following modifications to the procedure: 1) weigh test specimen

and the glass plate to the nearest 0.01 mg, and 2) adjust the temperature of the test apparatus to a temperature which is representative

of the maximum in-service temperature.

5.2.4 Thermal Cycling

5.2.4. 1 Determine the effect of thermal cycling on the properties

of insulation using the following test procedure:

a. Condition insulation samples for 48 hours at 73 + 5° F

(23 + 2° C) and 50 + 5% rh, then place in a suitable

aluminum pan and cover.

A3
b. Subject the pan (containing the insulation) to 30 cycles

of

:

o Heating for 7.5 hours at the maximum in-service temperature.

o Conditioning 73+5° F (23 + 2° C) and 50% rh for

30 minutes.

o Cooling at the minimum in-service temperature.

o Conditioning at 73+5° F (23 + 2° C) and 50% rh for

30 minutes.

6. Procedure

6.1 Select 4 sets of specimens for each insulation material to be

evaluated. Each set shall consist of at least three identical test

specimens.

6.2 Water absorption (5.1.1) and thermal conductivity (5.1.2) of Set 1 specimens. Measure the dimensions of Set 4 specimens.

6.3 Expose Set 1 specimens to thermal cycling as described in 5.2.4.

6.4 Remeasure the water absorption and thermal conductivity of Set 1 specimens as decribed in 6.2. Also, visually examine specimens

for expansion, cracking and fluffing and examine the inside of the

cover for deposition of binder or water.

6.5 Expose Set 2 specimens to the corrosion test (5.2.1). After exposure, determine extent of corrosion as described in 5.2.2.e.

6.6 Expose Set 3 specimens to the outgassing test described in 5.2.3.

6.7 Expose Set 4 specimens to the hot surface performance test

described in 5.2.2. After the exposure, visually inspect

the insulation and remeasure the dimensions of specimens.

Report

7.1 The report should include:

7.1.1 Complete identification of the insulation material

7.1.2 Water absorption and thermal conductivity obtained from 6.2 and

6.4.
7.1.3

Results of the corrosion test (6.5).

7.1.4 Results of outgassing of test (6.6)

7.1.5 Results of hot surface performance test (6.7).

__ 4 7.1.6 Test temperature used, the thermal cycling test (6.3) and the

hot surface performance test (6.7).

7.1.7 Documentation of instrument and procedures for measuring

transmittance in the outgassing test (6.6).

7.1.8 Deviations from specified procedures or conditions.
-

;
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 79-1908

4. TITLE AND SUBTITLE

Solar Energy Systems: Test Methods for Collector

Insulations

5. Publication Date October 1979

7. AUTHOR(S)

McClure Godette, Jack Lee, James Fearn

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

/Work tinit No.

;

:

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP)

Department of Energy, Office of the Assistant Secretary,

Conservation and Solar Applications, 20 Massachusetts

Avenue, Washington, DC 20545

13. Type of Report & Period Covered

jency Code

15. SUPPLEMENTARY NOTES

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

16. ABSTRACT (A 200-word or leas factual summary of most sighi ficant information. If document includes a significant bibliography or

literature survey, mention it here.)

A preliminary study was performed to evaluate potential procedures for

screening the insulation used in solar collectors. Both ASTM standard

test methods and newly developed non-standard procedures were used to

evaluate twenty-one insulation materials. The insulation parameters

measured in this study were selected on the basis of how and to what

extent they were affected by the unique environmental conditions within

solar collectors. Results of the laboratory tests are discussed and

those procedures which offer a potential for screening insulations used

in solar collectors are presented. It is intended that these procedures

fulfill the first step in the development of a standard set of test

methods for evaluating insulations for solar collectors.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter ol the first key word unless a proper name;

separated by semicolons)

Accelerated aging; collector insulation; insulation; solar collector;

standard insulation test methods.

18. AVAILABILITY fex) Unlimited

For Official Distribution. Do Not Release to NTIS

| Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

| Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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