NATL INST OF STAND & TECH

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NBS TECHNICAL NOTE 1136

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

NBS Solar Collector Durability/Reliability

Test Program Plan

QC

100

.U5753

NO. 1136

1981

c. 2
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act ot Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities- — Radiation Research — Thermodynamics and

Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and^ technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

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Engineering and Process Technology- — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities: provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

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'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington. DC 20234. -Some divisions within the center are located at Boulder, CO 80303.
NBS Solar Collector Durability/Reliability

Test Program Plan

National Bureau of Standards

Library, £-01 Admin. BIdg,

PEB 2 7 1981

OC/Oo

David Waksman

Elmer Streed

James Seller

1^0. I/S6

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

Prepared for: U.S. Department of Energy

Office of Solar Applications for Buildings

Office of the Assistant Secretary Conservation and Solar Applications

Washington, DC 20585

u.

^^^'^^ °^ oo.

I

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued January 1981
National Bureau of Standards Technical Note 1136

Nat Bur. Stand. (U.S.), Tech. Note 11 36/85 pages /(Jan. 1981) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1981

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402 Price $4

(ADD 25 percent for other than U.S. mailing)
PREFACE

Public Law 93-409, "Solar Heating and Cooling Demonstration Act of 1974," provides for the

development of definitive performance criteria and standard testing methods for use by

industry in evaluating materials, components and systems. Responsibility for the development of these performance criteria and many of these standards has been assigned to the

National Bureau of Standards (NBS) by the Department of Energy (DoE) and the Department of

Housing and Urban Development (HUD)

.

The goal of the experimental program described in this document is to help provide an experimental basis that can be used to prepare consensus standards for assessing the reliability and durability of solar collector assemblies and their materials. The program will

correlate the results of laboratory, accelerated field and simulated operational exposure

tests with the actual operating performance of collectors used for building heating and

cooling applications. This work is intended to be complementary to other collector materials

standards development projects underway at NBS and elsewhere in that it provides a link to the degradation that takes place in commercially available solar collectors.

This report is intended for use as a baseline document describing in detail the experimental

work being conducted and summarizing the types of analyses that are being performed. The

test program described in this plan was initiated in 1977. The experimental work described

in the plan has either been completed or is currently underway. Current program status is

discussed in Chapter 6 of this report.

Ill
ACKNOWLEDGMENTS

This report was prepared by the National Bureau of Standards, Washington, D,C., with the

assistance of the Solar Energy Systems Division, Wyle Laboratories, Huntsville, Alabama.

The comments and assistance of Larry W. Masters and Elizabeth J. Clark of NBS, and Wayne L. Swenson, Louis L. Ullman, Dr. Howard Yen and Joe H. Johnson of Wyle Laboratories are gratefully acknowledged.

Major contributions to the design and construction of exposure boxes for cover and absorber

materials were made by Frank A. Rankin of NBS.

The financial support of the Department of Energy, Office of Solar Applications for

Buildings, is gratefully acknowledged.
ABSTRACT

The test program described In this plan is designed to evaluate both approved and proposed

solar collector test procedures and to correlate laboratory, accelerated field and simulated

operational exposures with actual field data.

The tests and exposure procedures described herein are intended to determine the influence

of environmental exposure parameters that could affect the degradation of solar collectors

and their materials. They are also intended, to the extent possible, to provide a correlation between changes that occur at the materials and the collector component levels.

It is expected that the data obtained through their use will lead to more meaningful

reliability/durability tests for solar collectors and their materials.

A wide variety of commercially available solar collectors and multiple material coupons of

collector components are being tested at sites in different climatic regions. Appropriate

laboratory tests are being conducted during the same time frame to determine physical and

material properties for comparison with field test data and operational collector

experience. The data obtained from these tests will be analyzed and correlated with that

obtained from the current Government Demonstration Program and other related governmentsponsored programs.

Key words: Accelerated aging; durability; environmental exposure; reliability; solar

collectors; solar materials; stagnation testing.
SI CONVERSION UNITS

In view of the present accepted practice in this country for building technology, common

U. S. units of measurement have been used throughout this document. In recognition of the

position of the United States as a signatory to the General Conference of Weights and

Measures, which gave official status to the metric SI system of units in 1960, assistance

is given to the reader interested in making use of the coherent system of SI units by

giving conversion factors applicable to U.S. units used in this document.

LENGTH

1 in. = 0.0254 meter (exactly)

1 ft = 0.3048 meter (exactly)

AREA

2 -4 2 1 in. = 6.45 X 10 meter

1 ft^ = 0.09290 meter^

VOLUME

MASS

1 in."^ = 1.639 X 10 ^ meter"^

1 gal. (U.S. liquid) = 3.785 x lO""^ meter

_2

1 ounce-mass (avoirdupois) = 2.835 x 10 kilogram

1 pound-mass (avoirdupois) = 0.4536 kilogram

PRESSURE OR STRESS (Force /Area)

3

1 inch of mercury (60°F) = 3.377 x 10 pascal

2 3 1 pound-force /inch (psi) = 6.895 x 10 pascal

2 1 pound-force /foot (psf) = 47.88 pascal

ENERGY

1 foot-pound-force (ft-lbf) = 1.356 joule

3 1 Btu (International Table) = 1.055 x 10 joule

POWER

1 Watt = 1 X 10 erg/second

1 Btu/hr = 0.2931 Watt

TEMPERATURE

t°C = 5/9 (t°F - 32)

HEAT

2 -1

1 Btu in. /hr-ft • °F = 1.442 x 10 W/m'K (thermal conductivity)

lBtu/lbm-°F = 4.187 x 10^ J/kg-K (specific heat)

/ 9 9 1 langley = 4.184 x 10 J/m = 1 cal/cm =3.69 BTU /ft
TABLE OF CONTENTS

Page

Preface iii

Acknowledgments iv

Abstract ^

Conversion Units vi

1.0 Introduction 1-1

1.1 Background 1-1

1.2 Purpose 1-3

1.3 Scope 1-3

1.4 Test Program Overview 1-3

2.0 Test Procedures and Exposure 2-1

2.1 General 2-1

2.2 Solar Collector Tests 2-2

2.2.1 Outdoor Exposure Tests 2-2

2.2.1.1 Thermal Performance Measurements 2-2

2.2.1.2 Test Specimens 2-2

2.2.1.3 Environmental Exposure 2-8

2.2.1.4 Data Requirements 2-10

2.2.2 Indoor Simulator Exposure Tests 2-10

2.2.2.1 Thermal Performance Measurements 2-10

2.2.2.2 Test Specimens 2-13

2.2.2.3 Environmental Exposure 2-13

2.2.2.4 Data Requirements 2-13

2.2.3 Indoor Simulator Comparability Testing 2-13

2.3 Collector Material Tests 2-15

2.3.1 General 2-15

2.3.2 Cover Materials 2-15

2.3.2.1 "Real Time" Outdoor Exposure 2-18

2.3.2.1.1 Small Scale Samples 2-18

2.3.2.1.2 Full Size Collectors 2-20

2.3.2.2 Solar Simulator 2-20

2.3.2.3 Accelerated Outdoor 2-21

2.3.2.4 Laboratory Exposure 2-21

2.3.2.4.1 Temperature 2-21

2.3.2.4.2 Temperature and Humidity 2-24

2.3.2.4.3 Temperature and Radiation 2-25

2.3.3 Absorber Materials 2-26

2.3.3.1 "Real Time" Outdoor Exposure 2-26

2.3.3.1.1 Small Scale Samples 2-26

2.3.3.1.2 Full Size Collectors 2-28

2.3.3.2 Solar Simulator 2-28

2.3.3.3 Accelerated Outdoor 2-30

2.3.3.4 Laboratory Exposure 2-32

2.3.3.4.1 Temperature 2-32

2.3.3.4.2 Temperature and Humidity 2-33

2.3.3.4.3 Temperature and Radiation 2-33

2.3.3.4.4 Thermal Cycling 2-34

2.3.4 Non-Routine Property Measurements 2-35

2.3.4.1 Surface Appearance Changes 2-35

2.3.4.2 Surface Chemical Composition Changes 2-35

2.3.4.3 Bulk Material Chemical Changes 2-35

2.3.4.4 Mechanical Property Changes 2-36

VI

1
Page

3.0 Test Specimen Selection 3-1

3.1 General 3-1

3.2 Solar Collector Selection Attributes 3-1

3.3 Selection of Test Specimens 3-1

4.0 Outdoor Test Site Selection 4-1

4.1 Site Considerations 4-1

4.1.1 Climatic Characteristics 4-1

4.1.2 Climatic Requirements 4-1

4.1.3 Site Descriptions 4-3

5.0 Data Analysis 5-1

5.1 General 5-1

5.2 Analyses of Measured Collector Efficiencies 5-1

5.3 Changes in Material Properties 5-4

5.4 Investigation of Stagnation Temperatures of Collector Materials 5-5

6.0 Current Status 6-1

6.1 This Program 6-1

6.2 Related NBS Work 6-1

7.0 References 7-1

Appendix A A-1
INTRODUCTION

1.1 BACKGROUND

The Solar Energy Research, Development and Demonstration Act (Public Law 93-473)

signed into law in October 1974 authorized a vigorous Federal program of research,

development and demonstration to establish solar energy as a viable energy resource for the nation. The primary goal of the program, as stated in the

National Program for Solar Heating and Cooling of Buildings (ERDA 7 6-6) [1]*, is

to work with industry in the development and early introduction of economically

competitive and environmentally acceptable solar energy systems to help meet

national energy requirements.

Responsibility for the management and coordination of the total program has been

assigned to the Department of Energy (DoE) . The Federal program involves many

elements of government, industry and universities. At the Federal government

level, major participants assisting DoE in the program are the Department of

Housing and Urban Development (HUD), the Department of Defense (DoD) , the National

Aeronautics and Space Administration (NASA) and the National Bureau of Standards

(NBS)

.

Interim performance criteria have been developed and published for both residential

and commercial solar energy systems [2, 3] . NBS and other Federal agencies are cooperating with various private sector organizations in the development of consensus standards for the installation, performance and testing of solar equipment.

This effort has resulted in the publication of ASHRAE Standard 93-77, "Methods of

Testing to Determine the Thermal Performance of Solar Collectors" [4] and ASHRAE

Standard 94-77, "Methods of Testing Thermal Storage Devices Based on Thermal

Performance" [5]. The American Society for Testing and Materials (ASTM) is

developing durability and reliability test methods at the materials and collector

levels [6] . Laboratory and field test methods for the evaluation of collector

materials are currently under development at NBS in support of these ASTM consensus standard activities. Collector material studies are also being performed by

the Illinois Institute of Technology Research Institute (IITRI) under DoE contract

[7]. Field test requirements, developed by NBS for the reliability of collectors,

have been incorporated in the HUD Minimum Property Standards (MPS) [8] and the

Interim Performance Criteria (IPC) [2, 3]. Provisional test procedures [9] for

durability and reliability testing of solar collectors have been published by NBS

and are currently undergoing evaluation in a DoE collector testing program [10]

.

The reliability and long-term performance of solar collectors (up to 20 years)

have not generally been demonstrated. One of the few U.S. systems in which the

performance was initially measured and compared with the performance after 18

years experienced about a 30 percent decrease in efficiency [11]. Outdoor

exposure tests [12] of seven collector designs performed under no-flow conditions

for time periods of three to nine weeks resulted in significant decreases in

thermal performance as shown in Table 1-1. In some cases, condensation from

material outgassing products or absorber coating change were visually detected;

however, detailed analytical information on property changes were not reported.

*Figures in brackets indicate references contained in Chapter 1

,

1-1
TABLE 1-1. COLLECTOR THERMAL PERFORMANCE CHANGES AFTER

EXPOSURE TO NO-FLOW CONDITIONS [12]

N COLLECTOR TYPE

EFFICIENCY* % MAX. PLATE

TEMPERATURE (°C) INITIAL"* AFTER EXPOSURE***

1 2 Glass, Selective Paint 49 43 160

2 1 Glass, Black Chrome 65 59 182

3 2 Glass, Black Chrome 57 53 199

4 1 Glass, Black Nickel 47 40 166

5 2 Lexan, Alcoa Selective 52 44 166

6 2 Glass, Black Paint 40 36 149

7 2 Glass, Optical Black 43 43

. . . . . 157

* t. = 60°C, T = 27°C, I = 882 W/m

1 a ** Thermal performance tests performed with an indoor simulator

***Exposure outdoors for three to nine weeks at Langley, Virginia under no-flow

conditions

1-2
1.2 PURPOSE

The purpose of this program is to evaluate and compare existing and proposed test methods which can be used to predict the long-term durability and reliability of

collectors and materials within as short an interval as possible. Specific

objectives of the program are to:

o evaluate test procedures for predicting material deterioration

xates and/or collector performance reliability

o evaluate the effects of collector material deterioration on collector thermal performance

o determine the influence of environmental exposure conditions

on collector materials deterioration

o compare thermal performance measurements of outdoor natural

exposure with those obtained from exposure using a solar

simulator

o correlate data between accelerated tests and normal operation

of collectors and materials

o determine the influence of thermal shock and moisture penetration

1.3 SCOPE

The test program described in this plan is intended to evaluate both approved and

proposed solar collector test procedures and to correlate laboratory, accelerated

field and simulated operational exposures with actual field data. The program

is planned to make full use of existing government and industry studies and

facilities related to collector materials and assembly studies. A wide variety

of commercially available solar collectors and multiple material coupons of

collector components will be tested at sites in different climatic regions and

in solar simulators. Appropriate laboratory tests will be conducted during the same time frame to determine physical and material properties for comparison with

field test data and operational collector experience. The data obtained from

these tests will be analyzed and correlated with that obtained from the current

Government Demonstration Program and other related government-sponsored programs.

A block diagram depicting major program elements and sources for supporting data

is presented in Figure 1-1.

1.4 TEST PROGRAM OVERVIEW

This document is organized as follows:

Chapter 1. INTRODUCTION , contains background information, program

goals and objectives.

Chapter 2. TEST PROCEDURES AND EXPOSURE , contains detailed

descriptions of both field and laboratory tests required to

validate durability and reliability test methods.

Chapter 3. TEST SPECIMEN SELECTION , presents the rationale

used to select test specimens and identifies specimens to be ; tested.

1-3
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1-4
Chapter 4. OUTDOOR TEST SITE SELECTION , describes the effects of various environmental variables on solar collectors and presents criteria and the rationale for

selecting different climatic regions for test sites. Criteria are presented for

choosing test site locations within these regions and representative locations

that meet these criteria are identified.

Chapter 5. DATA ANALYSIS , describes the types of data that will be collected and

compared, tha types of changes that often result from test conditions such as those described in Chapter 2 and the fundamental causes often identified for such

changes.

Chapter 6. CURRENT STATUS , discusses the work performed to date on this program

and on related NBS programs.

Chapter 7. REFERENCES .

Appendix A contains detailed data forms that will be used during the program to characterize site environmental exposure conditions and to report measurements

made on solar collector and materials performance at specified time intervals.

1-5

2. TEST PROCEDURES AND EXPOSURE

2.1 GENERAL

Environmental exposure testing at both the collector component and materials

levels is required to ensure the satisfactory long-term performance of solar

collectors. It is desirable that such tests be capable of predicting the effects

of long-term exposure in a relatively short time and at a reasonable cost.

The stagnation testing of solar collectors is often considered to be an accelerated

test in that it exposes solar collectors to temperatures that would not occur with the heat transfer fluid flowing. However, solar collectors may frequently

be exposed to stagnation conditions in normal service. This can occur either

when the collectors are initially installed, before system start-up, or when the

system is shut down for maintenance or for seasonal considerations. In commercial buildings, time periods of up to a year between the installation and

start-up of equipment have been experienced. Thus, only that portion of stagnation exposure time which would not be attributed to normal service can be considered to represent accelerated aging.

It is possible to devise relatively simple accelerated tests to predict long-term

performance in cases where property changes are independent of the input stress

level, i.e. are dependent only on cumulative dose and not on intensity. However,

this situation seldom occurs because of synergistic effects and changes in the

intensity frequently results in changes in the degradation mechanism that

predominates. For example, exposure of a test specimen to concentrated solar

radiation to accelerate UV degradation can result in abnormal overheating of the

specimen and subsequent thermal degradation that would not occur in normal service.

Similarly, reaction rates in plastics at temperatures above the glass transition

temperature are generally much faster than those below this temperature.

The tests and exposure procedures described herein are intended to determine the

influence of environmental exposure parameters that could affect the degradation

of solar collectors and their materials. They are also intended, to the extent

possible, to provide a correlation between changes that occur at the materials

and the collector component levels. It is expected that the data obtained through

their use will lead to more meaningful reliability/durability tests for solar

collectors and their materials.

2-1
2.2 SOLAR COLLECTOR TESTS

2.2.1 OUTDOOR EXPOSURE TESTS

The four different collector test series selected for use in the program and the

purpose of each test series are summarized in Table 2-1.

Series 1 and 2 are intended to evaluate the effects of "normal" stagnation

conditions. The collectors in Series 1 are allowed to stagnate dry, whereas the

collectors in Series 2 are filled, allowed to stagnate under filled conditions

with a pressure relief valve set to the maximum allowable collector pressure and are subjected to thermal shock/cold fill and thermal shock/ water spray tests at specified time intervals. The purpose of exposing filled collectors to stagnation conditions is to evaluate the combined effects of the temperatures and

pressures that would occur under stagnation conditions.

Series 3 is intended to determine whether or not changes in collector

performance will occur under the reduced plate temperatures characteristic of operational conditions. Augmentation reflectors are used to amplify the

solar radiation to which stagnating collectors are exposed in Series 4. This

series is intended to determine the effects that such reflectors would have when

they are used in actual systems and to determine whether or not reflectors are a practical way of accelerating the degradation of stagnating collectors.

These exposure conditions are intended to subject the solar collectors and their

materials to different thermal stress levels at each outdoor exposure site. The

thermal stress level that would occur in normal use most likely lies between the

Series 1 and 2 and the Series 3 test conditions, with some stagnation being a normal occurrence.

2.2.1.1 Thermal Performance Measurements

Thermal performance measurements are being made on the collectors in each test series in accordance with the schedule summarized in Table 2-1 and described more

fully in Tables 2-2, 2-3, 2-4 and 2-5.

The ASHRAE Standard 93-77 thermal performance test procedure [4] is used in this

program both as a full test (four temperatures, four data points at each

temperature) and as a three-point performance re-test (three temperatures, four

data points at each temperature) . The re-test is conducted to demonstrate the

magnitude of changes in the intercept and slope of the efficiency curve as a function of environmental exposure time. The measurements are required to be

spread over the range of 0.02 to 0.07°C-m2/W. The ASHRAE Standard 93-77 requirements for three-day pre-exposure and measurement of incident angle modifier and

time constant are being performed only when explicitly called for in Tables

2-2, 2-3, 2-4 and 2-5. The term "performance re-test" will be used throughout

this document when the three-point test is specified.

2.2.1.2 Test Specimens

Test specimens include the eight solar collector types whose characteristics are identified in Table 3-1. Type T thermocouples are attached to the center of the

underside of the absorber plate for the measurement of stagnation temperature.

2-2
TABLE 2-1 SUM-MARY DESCRIPTION OF FIELD TEST SERIES ON SOLAR COLLECTORS

TEST

SERIES COLLECTOR PERFORMANCE MEASUREMENT

CONDITIONS FOR WEATHERING

EXPOSURE

PURPOSES OF TEST SERIES***

Series

1 "dry

stagnation"

Initial measurement in accordance with ASHRAE

93-77 except delete

3-day pre-exposure and measurement of time

constant. Performance re-test

after 3, 15, 30, 60, 120 and 240 day exposures.

Each collector pre-conditioned for each weathering

exposure by purging with

dry air to remove the remaining heat transfer

fluid. Successive weathering exposures between

performance re-tests provide

cumulative exposures of

3, 15, 30, 60, 120, and

240 days.*

1. Observation of effects

of dry stagnation on collector performance and other characteristics for various weathering times.

2

.

Provide data for comparison of solar simulator

performance measurement

with field data.

3. Provide data for comparing collector initial

performance with and

without 3-day pre-exposure per ASHRAE 93-77.

Series

2 "no-flow

stagnation"

Initial measurement in accordance with ASHRAE

93-77 after 3-day pre- exposure. Delete measurement of time constant. Performance re-tests

same as in Series 1.

Collectors pre-conditioned

for weathering exposure by

filling per NBSIR 78~1305A

[ 9 ] , capping and allowing

to boil dry. Weathering

exposures same as in Series

1 except that Thermal Shock

Tests per NBSIR 78-1305A

will be performed during

first 30-day exposure on

Ser.ifis 2 test collectors,

only.

1. Observation of effects of no-flow stagnation on collector performance and

other characteristics.

2. Observation of effects of Thermal Shock Tests representing (a) filling

a hot collector with cool

heat transfer medium and

(b) summer rain on a hot collector

.

3. Observation of static pressure leakage after

30 and 120 days of exposure

.

Series

3 "controlled

flow"

Performance of test collectors measured in accordance with ASHRAE

93-77, taking only 3 points. Delete 3-day pre-exposure and time constant measurement. Performance re-tests

same as in Series 1.

During weathering exposure

heat transfer flow rate maintained at 25% of operational flow rate for

liquid.

1. Observation of effects of normal operation on collector performance and

other characteristics.

Series

4 "dry

stagnation

with

augmentation

reflectors"

Initial measurement

same as in Series 1. Performance re-tests

same as in Series 1.

Pre-conditioning and

weathering exposures same

as in Series 1, except

that a reflector** will be used on each collector

during each day of weathering exposure*. Solar

radiation measurements

required both with and

without reflector.

1. Observation of effects of dry stagnation on collector performance and other

characteristics with

solar radiation amplified

by a reflector.

2. Obtaining temperature

history within collectors

for most severe exposure

conditions

.

* Individual days with solar radiation of 17,000 KJ/m-^-day or greater as measured in the plane

of the collector aperture without the influence of a reflector.

** The reflector is described in Paragraph 2.2.1.3.

*** All series include provision of data for comparisons between test series, test sites

(climatic regions), collector designs, etc.

2-3
TABLE 2-2. SERIES 1 COLLECTOR LOG SHEET

Date

Collector Code Number

Collector Manufacturer Name

Collector Serial Number __^_

Test Lab Name

Form Filled Out By

Step No. Test Procedure Date Completed

1 Initial Performance Test (full 93-77 without 3-day preexposure and time constant; with incident angle modifier) . . . 2 Purge with Dry Air

3 3-Day'^ Performance Re-test

4 Purge with Dry Air

5 15-Day* Performance Re-test

6 Purge with Dry Air _^______

7 4-Hour 946 W/m^ Exposure**

8 30-Day* Performance Re-test

9 Purge with Dry Air

10 4-Hour 946 IJ/m2 Exposure**

11 60-Day* Performance Re-test (plus measure incident angle

modifier, if applicable)

12 Purge with Dry Air , 13 4-Hour 946 V//m- Exposure**

14 120-Day* Performance Re-test

15 Purge with Dry Air

16 4-Hour 946 W/m^ Exposure**

17 240-Day* Performance Test (full 93-77 without pre-exposure

and time constant; with incident angle modifier)

*Total number of cumulative days of exposure at 17,000 Kj/m^ day prior to testing.

**First 4-hour 946 W/m^ exposure is mandatory. Subsequent 4-hour exposures are not mandatory. However, it is desired that the number of times this condition is met be

reported.

Form 101

2-4
TABLE 2-3. SERIES 2 COLLECTOR LOG SHEET

Date

Collector Code Number

Collector Manufacturer Name

Collector Serial Number

Test Lab Name

Form Filled Out By

Step No. Test Proceudure Date Completed

1 Static Pressure Leak Test

2 Performance Re-test (after 3-day exposure)

3 Fill and Allow to Boil Dry*

A 15-Day** Performance Re-test

5 Thermal Shock/Cold Fill Test ^____^____

6 Static Pressure Leak Test

7 Thermal Shock/Water Spray Test #1

8 Thermal Shock/Water Spray Test #2

9 Thermal Shock/Water Spray Test #3

10 4-Hour 946 W/m2 Exposure***

11 30-Day** Performance Re-test

12 Fill to Allow to Boil Dry*

13 4-Hour 946 W/m^ Exposure*** ...

14 60-Day** Performance Re-test

15 Fill to Allow to Boil Dry*

16 4-Hour 946 W/m2 Exposure***

17 120-Day** Performance Re-test

18 Static Pressure Leak Test _____________

19 Fill to Allow to Boil Dry*

20 4-Hour 946 W/m^ Exposure***

21 240-Day** Performance Re-test

*Some of the collectors will not reach high enough temperatures to boil dry with the

pressure relief valve settings used. These collectors shall be kept filled for at least one 17,000 Kj/m^-day and may then be drained at the option of the test lab, e.g. to prevent collector freeze up. **Total number of cumulative days of exposure at 17,000 Kj/m^-dav.

***First 4-hour 946 W/m'^^ exposure is mandatory. Subsequent 4-hour exposures are not

mandatory. However, it is desired that the number of times this condition is met be

reported

Form 102

2-5
TABLE 2-4. SERIES 3 COLLECTOR LOG SHEET

Date

Collector Code Number

Collector Manufacturer Name

Collector Serial Number

Test Lab Name

Form Filled Out By

Step No. Test Procedure Date Completed

1 Performance Re-test (without 3-day pre-exposure, time

constant and incident angle modifier)

2 15-Day* Performance Re-test

3 Connected Back in Test Loop**

4 30-Day* Performance Re-test

5 Connected Back in Test Loop**

6 60-Day* Performance Re-test

7 Connected Back in Test Loop**

8 120-Day* Performance Re-test

9 Connected Back in Test Loop**

10 240-Day* Performance Re-test (full 93-77 without pre-exposure

and time constant with incident angle modifier)

*Total number of cumulative days of exposure at 17,000 KJ/m^-day prior to testing.

**Maintain at 25% of recommended operational flow rate.

Form 103

2-6
TABLE 2-5, SERIES 4 COLLECTOR LOG SHEET

Date

Collector Code Number

Collector Manufacturer Name

Collector Serial Number ______^^_______________^

Test Lab Name

Form Filled Out By

Step No. Test Procedure Date Completed

1 Static Pressure Leak Test

2 Initial Performance Test (full 93-77 without 3-day preexposure and time constant, with incident angle modifier). . .

3 Purge with Dry Air

4 Install Augmentation Reflector**

5 15-Day** Performance Re-test

6 Purge with Dry Air

7 Install Augmentation Reflector**

8 4-Hour 946 W/m^ Exposure*

9 30-Day*** Performance Re-test

10 Purge with Dry Air

11 Install Augmentation Reflector**

12 4-Hour 946 W/m^ Exposure*

13 60-Day*** Performance Re-test

14 Purge with Dry Air

15 Install Augmentation Reflector**

16 4-Hour 946 W/m^ Exposure*

17 120-Day*** Performance Re-test

18 Static Pressure Leak Test

19 Purge with Dry Air

20 Install Augmentation Reflector**

21 4-Hour 946 W/m^ Exposure*

22 240-Day*** Performance Test (full 93-77 without pre-exposure

and time constant, with incident angle modifier)

*946 W/m^ flux level as measured without the contribution from the reflector. First

4-hour 946 W/m^ exposure is mandatory. Subsequent 4-hour exposures are not mandatory.

However, it is desired that the number of times this condition is met be reported.

**Maintain reflector at an angle of 120° to the plane of the collector aperture.

2 ***Total number of cumulative days of exposure at 17,000 Kj/m "day prior to testing.

Form 104

2-7
2.2.1.3 Environmental Exposure

Each type of collector will be exposed using the tests listed for Series 1 and

Series 2 in Tables 2-2 and 2-3 at all four outdoor test sites. Series 3 and

Series 4 tests (shown in Tables 2-4 and 2-5) will be performed at sites 1 and 2 only.* This will result in each collector being exposed for up to 240 days of

17,000 KJ/m^-day or greater incident solar radiation flux.

Series 1 and Series 2 collectors are being exposed in accordance with the

schedules given in Tables 2-2 and 2-3, respectively. It is desired that the

collectors in these two series be exposed to identical amounts of solar radiation

for purposes of comparison of the results of the two test series. For this reason, the Series 1 collectors are being kept covered while the Series 2 collectors

are subjected to the Thermal Shock/ Cold Fill, Thermal Shock/Water Spray and

Static Pressure Leakage tests specified in Table 2-3. These tests are being

performed in accordance with the procedures given in NBSIR 78-1305A [ 9 ]

.

Series 3 collectors are being subjected to the exposure cycles specified in

Table 2-4. During the daytime exposure periods, heat transfer liquid maintained

at a temperature of 71+ 3°C and at 25 percent of the manufacturer's recommended

operational flow rate is being input into each collector. Morning start-up

temperatures are kept in the 49°C - 71°C range, following which the inlet

temperature is maintained at the 71 °C point. This is intended to lower the

costs of heating the heat transfer fluid overnight. The maximum temperature

attained in each collector will thus be a function of collector performance with

these inlet conditions. A typical flow loop for performing this test is shown

in Figure 2-1.

Series 4 collectors will be tested in accordance with the schedule given in

Table 2-5. This test series consists of using a solar augmentation reflector to increase the solar radiation level on the solar collector during dry stagnation

exposure.

Each collector undergoing Test Series 4 is fitted with a flat reflector

constructed from a commercially available material that has a reflectance of

about 0.70 or greater. The width of this reflector is twice the width

(horizontal dimension) of the collector aperture. The length of the reflector

Is equal to the length of the collector aperture, measured along the

vertical axis of the collector. This reflector is maintained at an angle

of 120° to the plane of the collector aperture. The collector is mounted

to a rack and the tilt angle adjusted monthly such that the incident solar

radiation at solar noon is within +10° of the normal to the plane of the aperture.

^'Test sites are identified in Chapter 4 of this report,

2-£
FIGURE 2-1 SERIES 3 "LOW FLOW" TEST APPARATUS

2-9
2.2.1.4 Data Requirements

Detailed data are required to characterize the exposure conditions for correlation

within sites and between sites. In addition to the schedule information requested in the forms given in Tables 2-2, 2-3, 2-4 and 2-5, data sheets are presented

in Appendix A. Forms 201, 201A, 202 and 202A of Appendix A are concerned with

collector thermal performance. Site environmental exposure conditions are addressed by Forms 301, 305, 306 and by the Supplementary Data Requirements

shown in Amendment A-1 of Appendix A.

Weekly visual inspections are being made of each collector and all discernable

changes in the physical characteristics and appearance of the collector recorded.

2.2.2 INDOOR SIMULATOR EXPOSURE TESTS

These tests are intended to evaluate two types of commercially available

solar simulators representing extremes in exposure conditions which have been

proposed for use in the environmental exposure testing of solar collectors. One

of these simulators, (Test Site A) utilizes xenon arc lamps which yield a higher

ultraviolet radiation content than would be found in the terrestrial spectrum

( 8.6% instead of 2.7% at wavelengths less than 0.4um). The other simulator

(Test Site B) , which was designed to perform tests to Mil-Std-810c [13] utilizes

a tungsten lamp array whose output has virtually no ultraviolet radiation content.

Changes in materials and thermal performance of solar collectors caused by outdoor

exposure will be compared with those resulting from solar simulation to determine

if the results can be correlated.

2.2.2.1 Thermal- Performance Measurements

Thermal performance testing at Test Site A were performed at the time

intervals specified in Table 2-6 using the xenon arc simulator. The number of

data points required for the full ASHR.A.E 93-77 performance test and for the

re-test are discussed in Section 2.2.1.1 of this report.

Thermal performance testing at Test Site B were performed outdoors in accordance with the schedule specified in Table 2-7 since this indoor simulator is not

equipped for such testing.

2-10
TABLE 2-6 TESTING AND EXPOSURE SCHEDULE*: TEST SITE A

Step No.

1. Static Pressure Leak Test Per NBSIR 78-1305A

2. Initial Performance Test (full 93-77 without 3-day pre-exposure and time constant,

with incident angle modifier)

.

3. Purge with nitrogen

4. Expose for 3 days** ***

5. 3-Day Performance Re-test

6. Purge with nitrogen

7. Expose for 12 days**

8. 15-Day  Performance Re-test

9. Purge with nitrogen

10. Expose for 15 days**  ***

11. 30-Day  Performance Re-test

12. Purge with nitrogen

13. Expose for 30 days** *

14. 60-Day Performance Test (full 93-77 without 3-day pre-exposure and time constant;

with incident angle modifier)

.

15. Static Pressure Leak Test

* All thermal performance measurements and exposure to be conducted using an indoor

simulator. The performance tests to be made using a spectrum approximating

that of air mass two and then repeated with one approximating air mass zero. The

performance re-tests and environmental exposure to be conducted using the air mass zero spectrum. The simulator chamber temperature is to be maintained at approximately 30°C.

** Exposure Day Cycle : Irradiance will be set at 9A6 W/m^ and slowly increased

for 2.5 hours to 1,108 W/m^ and then decreased back to 946 W/m2 over the next

2.5 hours. The beam will then be doused for one hour to allow the collector to cool and then the cycle repeated.

*** Monitor absorber plate temperature, time, ambient temperature and irradiance at

5 minute intervals on the first, thirtieth and sixtieth exposure day cycles.

**** Cumulative exposure day cycles.

2-11
TABLE 2-7 TESTING AND EXPOSURE SCHEDULE: TEST SITE B

Step No.

1. Initial Performance Test (full ASHRAE 93-77 without 3-day pre-exposure, time

constant and incident angle modifier)

2. Drain collectors

3. Expose for 30 days* **

4. 30-Day*** Performance Test as in initial test

5. Drain collectors

6. Expose for 30 days* **

7. 60-Day*** Performance Test as in initial test

* Exposure Day Cycl e: Average irradiance shall be maintained at 1010 W/m for

five hours. The beam will then be doused for one hour to allow the collector to cool. The chamber shall be maintained at ambient temperatures between 26°C and

38°C.

** Monitor absorber plate temperature, time, ambient temperature and irradiance at

5 minute intervals on the first, thirtieth and sixtieth exposure day cycles.

*** Cumulative exposure day cycles.

2-12
2.2.2.2 Test Specimens

Four of the eight different types of solar collectors exposed outdoors were

used for solar simulator exposure tests. The characteristics of these collectors

(code letters B, D, E and H) are described in Table 3-1. These collectors were

selected from the eight used in the outdoor exposure test program primarily be- cause they used different types of cover plate materials having different spectral

characteristxcs and varying degrees of sensitivity to exposure to ultraviolet

radiation and temperature.

2.2.2.3 Environmental Exposure

Environmental exposure at Test Site' A was performed using the xenon arc simulator in accordance with Table 2-6. Collector thermal performance was checked after 0, 3, 15, 30, and 60 simulated exposure day cycles as described in

Table 2-6.

Testing and expos,ure at Test Site B was conducted in accordance with

Table 2-7. A plate glass filter was placed between the tungsten lamp source

and the solar collectors to absorb the infrared radiation beyond 2.7 ym given off

by the source to provide a better spectral match with the terrestrial solar

spectrum.

2.2.2.4 Data Requirements

Thermal performance was reported in accordance with the requirements of

ASHRAE Standard 93-77. Forms 201, 201A, 202 and 202A of Appendix A show typical

reporting formats for these data. On the first, thirtieth and sixtieth exposure

day cycles, absorber plate temperatures, time, ambient temperature and irradiance

were reported at 5 minute intervals.

Visual inspections were made of each collector and all discernable changes in

the physical characteristics and appearance of the collector recorded.

2.2.3 INDOOR SIMULATOR COMPARABILITY TESTING

These tests are intended to:

(a) determine whether or not thermal performance test data obtained with a xenon

arc lamp solar simulator are comparable to those obtained at outdoor test sites and

(b) determine the influence of individual outdoor test site environmental

parameters on thermal performance test results.

The test program outlined in Table 2-8 is intended to determine the influence of

ambient temperature, tilt, percent diffuse radiation, wind and solar irradiance

level on collector thermal performance.

Two types of solar collectors were used for these studies. The first of these

has a single glass cover and a black chrome selective surface on a steel absorber

and was used in a round robin test program previously conducted by NBS [14], The

second of these collectors, which has two glass covers and a flat black paint on copper absorber, is described in Table 3-1 as collector type B.

All of the thermal performance tests were performed ,'on a xenon solar simulator

filtered for the air mass zero spectrum. The conditions maintained during

thermal performance testing are defined in Table 2-8. Data points were taken

in accordance with ASHRAE Standard 93-77,

2-13
TABLE 2-8. INDOOR SIMULATOR COMPARABILITY TEST CONDITIONS*

AT/I

Selective Non Tilt Diffuse Flux Ambient Wind /"C-m^

Run // Selective (°) (%) (W/in2) (°c ) (m/s)

* Perform with the air mass zero solar spectrum

A-1 X X 60 630 5 0.06

A-IA X X 60 630 5 5 0.06

B-1 X X 60 40 630 5 0.06

D-1 X X 60 1100 5 0.06

D-IA X X 60 1100 5 5 0.06

E-1 X X 60 1100 35 0.06

E-IA X X 60 1100 35 5 0.06

F-1 X X 1100 35 0.06

E-2 X X 60 1100 35 0.02

E-2A X X 60 1100 35 5 0.02

F-2 X 1100 35 0.02

D-2 X 60 1100 5 0.02

D-2A X 60 1100 5 5 0.02

A2X 60 630 5 0.02

A-2A X 60 630 5 5 0.02

B-2 X 60 40 630 5 0.02

B-2A X 60 40 630 5 5 0.02

2-14
2.3 COLLECTOR MATERIAL TESTS

2.3.1 GENERAL

These tests are intended to lead to the development of accelerated materials level

tests that can be used to evaluate the long term performance of cover and absorber

materials in flat plate solar collectors. Indoor laboratory and outdoor environmental exposure tests will be conducted on materials coupon samples. Analytical

studies, as discussed in Chapter 5 of this report, will be conducted (1) to determine the correlations that exist between the various materials level exposure

tests and (2) to determine whether or not changes observed in small scale materials

samples are indicative of those which occur in full sized solar collectors. This

work is intended to be complementary to work currently underway at NBS to develop

draft standards for absorber and cover materials in that it provides a link to the

degradation that takes place in commercially available solar collectors.

Coupon specimens of cover plate and absorber materials cut from full sized collectors of the same make and model as the collectors exposed outdoors, together with

several additional materials, are being subjected to several different types of

laboratory and outdoor environmental exposure tests. Changes in the optical

properties of these materials are being measured as a function of exposure time.

Outdoor exposure conditions at the materials coupon specimen level include

"real time" exposure in simulated collectors and exposure to concentrated radiation in machines having a six to one concentration level. Indoor laboratory tests

being conducted include exposure to (1) temperature, (2) combined temperature and

humidity, (3) combined temperature and radiation, and (4) thermal cycling

(absorber materials only) . Additional materials level exposure tests are being

conducted using the solar simulators described in Section 2.2.2 of this report.

Both the outdoor "real time" and the solar simulator materials level exposures are being conducted concurrently with those on full scale collectors at each test

site.

The exposure conditions used for the cover and absorber materials are summarized

in Tables 2-9 and 2-10, respectively. The exposure conditions summarized in

these tables are intended to simulate a broad range of environmental stress

conditions. Primary emphasis was placed on exposure to temperature, solar

radiation and moisture. Other degradation factors such as hail, pollutants and

dust are localized in nature and will be assessed via their occurrence at the

"real time" outdoor exposure test sites participating in the program.

2.3.2 COVER MATERIALS

The sections which follow contain descriptions of the test procedures and

apparatus that will be used for the environmental exposure testing of cover materials. The specific materials to be used for each test are identified in

tables contained in Chapter 3. A set of control specimens has been provided to each test site performing property measurements for purposes of comparison with

the results of measurements after environmental exposure. These control

specimens are being stored in a dark environment at 21 + 3°C until required for

comparison testing. All outdoor exposure test specimens are being cleaned using

a 0.1% solution of nonionic detergent made with distilled water, using a brush, followed by rinsing and air drying.

2-15
TABLE 2-9. EXPOSURE TESTS FOR COVER MATERIALS

Exposure Condition Value or Range Exposure Time

Temperature (indoor) a)

b)

c)

70°C

90°C

125°C

500, 1,000 and 2,000 hr.

Temperature and Humidity (indoor) a) 50°C and 98% RH 500, 1,000 and 2,000 hr.

b) 70°C and 95% RH

c) 90°C and 95% RH

Temperature and Radiation Xenon arc weathering 500, 1,000 and 2,000 hr.

(indoor) machine

a) 70°C

b) 90°C

Solar Simulator a) Tungsten 30, 60 and 120 cycles*

b) Xenon simulators

with irradiance

of -950 W/m2 and

~70°C

"Real Time" Outdoor 1 sun at ^(d0°C 80, 160 and 240 days**

Accelerated Outdoor — 5 suns at ~70°C 6, 12 and 24 equivalent months***

*Each cyo-le consists of 5 hrs. irradiation and 1 hr. cooling, as defined in Tables

2-6 and 2-7.

**Radiant exposure must exceed 17,100 kj/m^ for each day.

Q 2 ***One equivalent month equals 6.625 x 10 j/m (15,835 Langleys)

2-16
TABLE 2-10. EXPOSURE TESTS FOR ABSORBER MATERIALS

Exposure Condition Value or Range Exposure Time

Temperature (indoor) a) 150°C

b) 175°C

500, 1,000 and 2,000 hr.

Temperature and Humidity (indoor) 90°C and 95% 500, 1,000 and 2,000 hr.

Thermal Cycling (indoor) -10°C to 175°C 5, 15 and 30 cycles

Temperature and Radiation

(indoor)

Xenon arc weathering

machine at 90°C

500, 1,000 and 2,000 hr.

Solar Simulator a) Tungsten

b) Xenon simulators

with irradiance

of —950 W/m2 and — 130°C

30, 60 and 120 cycles*

"Real Time" Outdoor 1 sun at ~140°C and

~160°C

80, 160 and 240 days

Accelerated Outdoor 6 suns at ~150°C 6, 12 and 24 equivalent months***

*Each cycle consists of 5 hours irradiation and 1 hour cooling, as defined in Tables

2-6 and 2-7.

**Radiant exposure must exceed 17,100 kj/m for each day.

8 2 ***One equivalent month equals 6.625 x 10 j/m (15,835 Langleys)

2-17
2.3.2.1 "Real Time" Outdoor Exposure

Cover materials are being exposed to temperatures simulating operational conditions

using the mini-boxes, as described in 2.3.2.1.1, at each of the four outdoor

exposure sites chosen for participation in the program. In addition, property

measurements are being made on materials samples taken from the full size collectors

following the completion of outdoor exposure testing.

2.3.2.1.1 Small Scale Samples

a. Exposure Conditions

These exposures are being conducted concurrently with the outdoor exposure of full

size solar collectors at each of the four outdoor exposure test sites identified

in Chapter 4. The mini-boxes are being exposed at the same tilt and orientation

as the full sized collectors in Section 2.2. Four mini-boxes are being exposed

for each material with one box being pulled after 80, 160 and 240 cumulative days

of exposure to a minimum incident solar radiation flux of 17,000 kj/m^-day.

Depending on the materials property changes measured after 160 days of exposure,

the fourth mini-box will either be pulled at 240 days or exposed for an additional

240 (17,000 kj/m2.day) days.

b. Apparatus and Specimens

Test specimens consist of cover materials mounted onto eight collector mini-boxes

as shown in Figure 2-2. Cover plate test materials are identified in Table 3-2.

Four mini-boxes have been prepared for each test material. One of the four boxes

is instrumented with a type T thermocouple.

c. Property Measurements

Routine evaluation of the cover materials includes visual observation and total

solar transmittance. Visual observation and total solar transmittance are being

determined after each set of test specimens is removed from exposure. Visual

observations include marked changes in appearance, color or shape and notation of

other surface flaws and other changes. The total solar transmittance is being

measured as described in ASTM E424, Method A [15]. Non-routine measurements which

may be performed to further characterize observed changes are discussed in

Section 2.3.4.

d. Test Reports

Test results are to include the following information:

o Test specimen code number (per Chapter 3)

o Location and dates of exposure

o Exposure condition data

o Mini-box absorber plate temperature at solar noon each day

o Notations recorded during visual observation

o Total solar transmittance per ASTM E424, Method A, for both

exposed and control samples

o Actual solar transmittance curves for both exposed and

control samples

Data are to be provided in accordance with the formats given in Appendix A, where appropriate.

2-18
RAIN SHIELD

OUTER COVER

TEST SPECIMEN

SPACER FRAME

INNER COVER

TEST SPECIMEN

SILICONE RUBBER

SEALANT

STAINLESS STEEL

PAN

ABSORBER PLATE

TYPE T THERMOCOUPLE

GLASS FIBER INSULATION

Notes:

Stainless Steel Pan: 22 x 12 x 10 cm without rim

Glass Fiber Insulation: 64 kg/m-^ density

Bottom thickness 10 cm Edge thickness 2 . 5 cm wide x 2.5 cm thick

Baked out at 230°C for 24 hours

Absorber Plate: Black chrome on copper

Silicone Rubber Sealant: Between covers and pan, and covers and spacer

Cover Test Specimens: 26 x 16 cm

Rain Shield: 16 ga stainless steel, clamped to pan

Spacer Frame: 6 mm thick aluminum

FIGURE 2-2 COVER EXPOSURE MINI-BOX

2-19
2.3.2.1.2 Full Size Collectors

Weekly inspections are being made of the solar collectors during the environmental

exposure specified in 2.2.1 and any visual evidence of materials degradation

reported.

Following completion of environmental exposure and testing of these collectors,

the collectors will be disassembled and inspected for degradation of materials.

Materials coupon specimens will be cut from those collectors having polymer

cover materials and total transmittance measurements will be performed in

accordance with ASTM E424. Additional non-routine tests may be performed where

appropriate (see 2.3.4).

2.3.2.2 Solar Simulator

a. Exposure Conditions

Test specimens were exposed concurrently with the full size collectors

utilizing the daily cycles given in Tables 2-6 and 2-7 for Sites A and B, respectively. At Test Site A, where two sets of 60-day cycles are required to expose all four collectors, test specimens were pulled after 30, 60 and 120

daily cycles of exposure for property measurements. At Test Site B, test specimens were pulled after 30 and 60 daily cycles of exposure for property

measurements.

b. Apparatus and Specimens

Test specimens consisted of cover materials mounted onto the collector miniboxes shown in Figure 2-2. Cover plate test materials are identified in Table

3-2. One of the mini-boxes for each test material was instrumented with a type T thermocouple attached to the back of the absorber plate. This box was

the last test specimen pulled.

c. Property Measurements

Routine evaluation of the cover materials included visual observation and

total solar transmittance per ASTM E424. Non-routine measurements which may be

performed to further characterize changes observed are discussed in Section 2.3.4.

Peak mini-box absorber plate temperatures were measured for daily cycles

15, 30, 60 and 120 (Site A) and 15, 30 and 60 (Site B)

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Exposure condition data

o Peak mini-box absorber plate temperatures

o Notations recorded during visual observation

o Total solar transmittance per ASTM E424j Method A, for both

exposed and control samples

o Solar transmittance curves for both exposed and

control samples

2-20
2.3.2.3 Accelerated Outdoor

a. Exposure Conditions

Test specimens are being exposed to concentrated solar radiation in Phoenix,

Arizona (Test Site 1) for periods of 30, 60 and 120 test days (5 test days == 1 month "real time" « 6.625 x 10^ kj/m^) . The test specimens are being air

cooled and subjected to periodic water spray during exposure.

b. Apparatus and Specimens

Cover materials used are identified in Table 3-2. Test specimens are being

exposed to concentrated natural solar radiation using the device referenced in

ANSI Z-97. 1-1975, Paragraph 4.3.2 [16]. Two types of test specimen configurations

are mounted onto the accelerated weathering device. Duplicates of each test

material are being used for each of the two types of specimen configurations shown

in Figures 2-3a and 2-3b. Type T thermocouples are mounted on each specimen.

c. Property Measurements

Routine evaluation includes visual observations and total solar transmittance

per ASTM E424, Method A. Measurements are being made on the same duplicate

specimens after 30, 60 and 120 cumulative test days of exposure. The cover materials are remounted and exposure continued following property measurements until the 120 day cumulative exposure is reached. Temperature measurements

are being made at solar noon on a clear exposure day prior to each time the

specimens are pulled for property measurements. Non-routine measurements per

2.3.4 may be performed to further characterize changes observed.

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative radiative exposure

o Thermocouple temperature at solar noon prior to pulling the sample

o Notations recorded during visual observation

o Total solar transmittance per ASTM E424, Method A, for both

exposed and control samples

o Solar transmittance curves for both exposed and control samples

2.3.2.4 Laboratory Exposure

The test conditions which follow are intended to subject the cover test specimens

to several different levels of environmental stress. Emphasis has been placed on

the primary degradation factors, i.e. temperature, moisture and ultraviolet

radiation. Depending on the test results obtained and their correlation with

properties measured under outdoor "real time" conditions, additional environmental

exposure tests of either lesser or greater severity may be conducted.

2.3.2.4.1 Temperature

a. Exposure Conditions

Two temperature conditions are being used; 70°C and 90°C. Test specimens are

being pulled after 500, 1,000 and 2,000 hours of exposure at each of the above

test temperatures.

2-21
ALUMINUM PAN

(^

'^*

COVER TEST SPECIMEN

SILICONE RUBBER SEAL

TYPE T THERMOCOUPLE

ALUMINUM FOIL ABSORBER

Notes:

Cover Size: 7.6 x 5.1 cm Aluminum Pan: 11.5 x 6.5 x 2 cm Aluminum foil painted black and baked at 230°C for 24 hours

FIGURE 2-3a ACCELERATED EXPOSURE COVER MINI-BOX

2-22
ALUMINUM PLATE

310x140mm (painted black

& baked @ 230°C for

24 hrs.]

COVER TEST SPECIMEN

51x38mm

11 IT T Tl IT

CERAMIC INSULATOR

12.7mm long

TYPE T THERMOCOUPLE

FIGURE 2-3b ACCELERATED EXPOSURE TEST PLATE

2-23
b. Apparatus and Specimens

Cover materials being used are identified in Table 3-2. Three test specimens were provided for exposure at each test temperature; one specimen to be pulled

at each of the exposure time intervals specified (500, 1,000 and 2,000 hours).

The test specimens are being allowed to hang freely in an oven capable of maintaining the above mentioned test temperatures + 3°C.

c. Property Measurements

Routine evaluation includes visual observations and total solar transmittance

per ASTM E424, Method A. Measurements are being made after each exposure time

period. The test specimens are being stored and not returned to the oven

following property measurements. Non-routine measurements per 2.3.4 may be performed to further characterize changes observed.

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure time

o Exposure conditions

o Notations recorded during visual observation

o Total solar transmittance per ASTM E424, Method A, for both

exposed and control samples

o Solar transmittance curves for both exposed and control samples

2.3.2.4.2 Temperature and Humidity

a. Exposure Conditions

Three test conditions are being used: 50°C and >95% relative humidity (RH) ; 70°C

and >95% RH; and 90°C and >95% RH. Test specimens are being pulled after 500,

1,000 and 2,000 hours of exposure at one of the above test temperatures. The

70°C and 90°C test conditions are being conducted first and only those materials

which exhibit significant changes are to be run at the 50°C test condition.

b. Apparatus and Specimens

Cover materials being used are identified in Table 3-2. Three test specimens are being provided for exposure at each test temperature; one specimen to be pulled

at each of the exposure time intervals specified (500, 1,000 and 2,000 hours).

The test specimens are being allowed to hang freely with all surfaces exposed in

a humidity chamber capable of maintaining the above mentioned temperatures + 3°C

and >95% relative humidity.

c. Property Measurements

Routine evaluation includes visual observations and total solar transmittance

per ASTM E424, Method A. Measurements are being made after each exposure time

period. The test specimens are being stored and not returned to the humidity

exposure cabinet after property measurements are completed. Non-routine measure- ments per 2.3.4 may be performed to further characterize changes observed.

2-24
d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure time

o Exposure conditions

o Notations recorded during visual observation

o Total solar transraittance per ASTM E424, Method A, for both

exposed and control samples

o Solar transmittance curves for both exposed and control samples

2.3.2.4.3 Temperature and Radiation

a. Exposure Conditions

Test specimens are being exposed at 70°C and at 90°C (chamber temperature) to xenon arc radiation under dry conditions in an accelerated weathering machine in

accordance with ASTM D2565 [17] . Test specimens are being pulled after 500,

1,000 and 2,000 hours of exposure at one of the above test temperatures.

b. Apparatus and Specimens

Cover materials being used are identified in Table 3-2. Three test specimens are

being provided for exposure at each test temperature; one specimen to be pulled

at each of the exposure time intervals specified (500, 1,000 and 2,000 hours).

The accelerated weathering machine used meets the requirements of ASTM

D2565 and is capable of maintaining the required temperatures.

The test specimens are oriented so that the surface that would ordinarily

face the sun in a solar collector is facing the xenon arc lamp.

In cases where double covers are to be evaluated, the outer and inner covers are

separated by a 6 mm thick air gap and the outer cover faces the xenon arc

lamp.

c. Property Measurements

Routine evaluation shall include visual observations and total solar transmittance

per ASTM E424, Method A. Measurements are being made after each exposure time

period. The test specimens are being stored and not returned to the accelerated

weathering machine after property measurements are completed. Non-routine measure- ments per 2.3.4 may be performed to further characterize changes observed.

d. Test Reports

Test reportsare to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure time

o Exposure conditions

o Notations recorded during visual observation

o Total solar transmittance per ASTM E424, Method A, for both

exposed and control samples

o Solar transmittance curves for both exposed and control samples

2-25
2.3.3 ABSORBER MATERIALS

The sections which follow contain descriptions of the test procedures and

apparatus that will be used for the environmental exposure testing of absorber

materials. The specific materials being used for each test are identified in

tables contained in Chapter 3. A set of control specimens was provided to each test site performing property measurements for purposes of comparison with

the results of measurements after environmental exposure. These control specimens

are being stored in a dark environment at 21 + 3°C until required for comparison

testing.

Prior to the installation of test specimens, ten specimens selected at random

of each coating material were measured for absorptance in accordance with ASTM

E424, Method A, and for emittance in accordance with ASTM E408, Method A [18] to determine the uniformity of coating optical properties. In cases where sample lot

differences greater than 0.01 exist in absorptance or 0.02 in emittance, each test

specimen was measured for absorptance and emittance prior to environmental

exposure. The test specimens were indexed in the measurement apparatus in such a manner that the same area can be measured following environmental exposure.

2.3.3.1 "Real Time" Outdoor Exposure

Absorber materials are being exposed to temperatures simulating operational conditions using the test collector boxes described in 2.3.3.1.1, at each of the four

outdoor exposure sites chosen for participation in the program. In addition,

property measurements will be made on materials samples taken from full size

collectors following the completion of outdoor exposure testing.

2.3.3.1.1 Small Scale Samples

a. Exposure Conditions

These exposures are being conducted concurrently with the outdoor exposure of full

size solar collectors at each of the four outdoor exposure test sites identified

in Chapter 4. The outdoor absorber exposure boxes are being exposed at the same

tilt and orientation as the full size collectors in Section 2.2. Test specimens are being pulled from the selective surface and non-selective sides of the

outdoor absorber exposure boxes after 80, 160 and 240 cumulative days of exposure

to a minimum incident solar radiation flux of 17,000 kj/m^-day. Depending on the

materials property changes measured after 240 days of exposure, the test specimens

may be exposed for an additional 240 days of 17,000 kj/m2 exposure.

b. Apparatus and Specimens

Test specimens consist of coupon samples of absorber materials mounted onto

the selective and non-selective surfaces of the outdoor absorber exposure box

shown in Figure 2-4. Absorber test materials are identified in Table 3-3- In general, three test specimens are installed on both the selective and non'- selective sides of the exposure box (a total of six) . In some cases where a limited amount of test material was available, lesser numbers of samples were

used as identified in Chapter 3. Where three samples were used, one Is being

pulled at 80, 160 and 240 cumulative days of exposure for property measurements.

Type T thermocouples are attached to the centers of both the selective and

non-selective test box absorber plates.

2-26
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2-27
c. Property Measurements

Routine evaluation of the absorber materials includes visual observation,

total solar absorptance and emittance. Property determinations are being made

after each set of test specimens is removed from exposure. Visual observations

include any marked changes in appearance, color or shape, and notation of

other surface flaws and other changes. The total solar absorptance is being measured in accordance with ASTM E424, Method A. Emittance is being measured in

accordance with ASTM E408, Method A. Non-routine measurements which may be performed to further characterize changes observed are discussed in Section 2.3.4.

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Selective and non-selective absorber plate temperature at solar noon each day

o Notations recorded during visual observation

o Total solar absorptance for both exposed and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance for both exposed and control samples

Data are to be provided in accordance with the formats given in Appendix A, where

appropriate.

2.3.3,1.2 Full Size Collectors

Weekly inspections are being made of the solar collectors during the environmental

exposure specified in 2.2.1 and any visual evidence of materials degradation

reported.

Following completion of environmental exposure and testing of these collectors,

total solar absorptance and emittance measurements will be made on samples cut

from the absorber plates using ASTM E424 and ASTM E408, respectively. Additional

non-routine tests may be performed where appropriate (see 2.3.4).

2.3.3.2 Solar Simulator

a. Exposure Conditions

Test specimens were exposed concurrently with full size collectors

utilizing the daily cycles given in Tables 2-6 and 2-7 for Sites A and B, respectively. At Test Site A, where two sets of 60-day cycles were required to expose all four collectors, test specimens were pulled after 30, 60 and 120

daily cycles of exposure for property measurements. At Test Site B. test speci- mens were pulled after 30 and 60 daily cycles of exposure for property

measurements

b. Apparatus and Specimens

Test specimens consisted of absorber materials mounted onto the absorbers of

the test boxes shown in Figure 2-5. Two boxes were used at each site, one having a selective surface absorber and the other having a non-selective flat

black absorber. Sufficient samples of each material were provided for each

box to permit pulling a sample at each of the exposure time periods identified in

a. above. Absorber test materials are identified in Table 3-3. A type T thermocouple was attached to the center of the absorber plate in each box.

2-28
COVER

GLASS FIBER

INSULATION

AIR SPACE

Z7Z7Z7Z7Z7Z7

Z7^Z7Z7£^^-

^>>p?^wSmm^

ABSORBER

WOOD CASE

METAL PAN

ABSORBER TEST SPECIMENS

Notes:

Cover Material: Polytetrafluoroethylene film

Wood Case: 122 x 61 x 10 cm Glass Fiber Insulation: On bottom and edges

64 kg/m density

5,1 cm thick

Baked out at 230°C for 24 hours

Absorber: Selective box - Black chrome on copper

Non-selective box - Black paint on pan baked out at 230°C for 24 hours

Type T thermocouple attached to center of absorber

Metal Pan: 43 x 28 x 2.2 cm

Test Specimens: 7,6 x 5,1 cm screwed to absorber

FIGURE 2-5 SOLAR SIMULATOR ABSORBER BOX TEST ASSEMBLY

2-29
c. Property Measurements

Routine evaluation of the absorber materials included visual observation,

total solar absorptance per ASTM E424, Method A, and emittance per ASTM E408,

Method A. Non-routine measurements which may be performed to further characterize

changes observed are discussed in Section 2.3.4. Peak absorber plate temperatures were measured for daily cycles 15, 30, 60 and 120 (Site A) and 15, 30 and 60

(Site B)

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Exposure condition data

o Peak absorber plate temperatures

o Notations recorded during visual observation

o Total solar absorptance per ASTM E424, Method A, for both exposed

and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance per ASTM E408, Method A, for both exposed and control samples

2.3.3.3 Accelerated Outdoor

a. Exposure Conditions

Test specimens are being exposed to concentrated solar radiation in Phoenix,

Arizona (Test Site 1) for periods of 30, 60 and 120 test days (5 test days

1 month "real time" =6.625 x 10^ kj/m2) .

The test specimens arebeing air cooled and exposed without water spray.

b. Apparatus and Specimens

Absorber materials being used are identified in Table 3-3. Test specimens are being exposed to concentrated natural solar radiation using the device referenced in

ANSI Z-97. 1-1975, Paragraph 4.3.2. Test specimens, constructed in accordance with

Figure 2-6, are mounted onto the accelerated weathering device. Type T thermocouples are mounted on each specimen as shown in Figure 2-6. Duplicate specimens

of each test material are being used.

c. Property Measurements

Routine evaluation of the absorber materials includes visual observation,

solar absorptance per ASTM E424, Method A, and emittance per ASTM E408, Method A. Measurements are being made on the same duplicate specimens after 30, 60 and 120

cumulative test days of exposure. The absorber materials are remounted and

exposure continued following property measurements until the 120 day cumulative

exposure is reached. Temperature measurements are being made at solar noon on a clear exposure day prior to each time the specimens are pulled for property

measurements. Non-routine measurements which may be performed to further characterize changes observed are discussed in Section 2.3.4.

2-30
HLM COVER ABSORBER TEST SPECIMEN

ALUMINUM PAN

TIEDOWN WIRE

TYPE T THERMOCOUPLE

Notes:

Film Cover: Polytetrafluoroethylene

Absorber Test Specimen: 7.5 x 5.1 cm Aluminum Pan: 11.5 x 6.5 x 2 cm Interior painted black and baked at 230°C for 24 hours

FIGURE 2-6 ACCELERATED EXPOSURE ABSORBER MINI-BOX

2-31
d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative radiative exposure

o Thermocouple temperature at solar noon on a clear day prior to pulling the sample

o Total solar absorptance per ASTM E424, Method A, for both

exposed and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance per ASTM E408, Method A, for both exposed and control samples

2.3.3.4 Laboratory Exposure

The test conditions which follow are intended to subject the absorber test specimens to several different levels of environmental stress. Emphasis has been

placed on the primary degradation factors, i.e. temperature (both constant and

cyclic) , moisture and ultraviolet radiation. Depending on the test results

obtained and their correlation with properties measured under outdoor "real time"

conditions, additional environmental exposure tests of either lesser or greater

severity may be conducted.

2.3.3.4.1 Temperature

a. Exposure Conditions

Two temperature conditions are being used: 150°C and 175°C. These temperatures

approximate those that occur in the tion-selective and selective absorbers,

respectively, of the outdoor absorber test box (see 2.3.3.1.1) under clear day

conditions. Test specimens are being pulled after 500, 1,000 and 2,000 hours of

exposure at one of the above test temperatures.

b. Apparatus and Specimens

Absorber materials being used are identified in Table 3-3. Three test specimens are provided for exposure at each test temperature; one specimen to be

pulled at each of the exposure time intervals specified (500, 1,000 and 2,000

hours) . The test specimens are being allowed to hang freely in an oven capable

of maintaining the above mentioned test temperatures + 3°C.

c. Property Measurements

Routine evaluation includes visual observations, total solar absorptance per

ASTM E424, Method A, and emittance per ASTM E408, Method A. Measurements are

being made after each exposure time period. The test specimens are being stored

and not returned to the oven following property measurements. Non-routine measure- ments per 2.3.4 may be performed to further characterize changes observed.

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure time

o Exposure conditions

o Notations recorded during visual observations

o Total solar absorptance per ASTM E424, Method A, for both

exposed and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance per ASTM E408, Method A, for both exposed and control samples

2-32
2.3.3.4.2 Temperature and Humidity

a. Exposure Conditions

Test specimens are being pulled after 500, 1,000 and 2,000 hours of exposure in a chamber maintained at 90°C and >95% RH.

b. Apparatus and Specimens

Absorber materials being used are identified in Table 3-3. Three test specimens are provided for exposure at the test temperature; one specimen to be pulled

at each of the exposure time intervals specified (500, 1,000 and 2,000 hours).

The test specimens are being allowed to hang freely with all surfaces exposed in

a humidity chamber capable of maintaining 90° + 3°C and >95% RH.

c. Property Measurements

Routine evaluation includes visual observations, total solar absorptance per

ASTM E424, Method A, and emittance per ASTM E408, Method A. Measurements are

being made after each exposure time period. The test specimens are being stored and

not returned for further exposure following property measurements. Non-routine

measurements per 2.3.4 may be performed to further characterize changes observed.

d. Test Reports

Test reports shall include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure time

o Exposure conditions

o Notations recorded during visual observations

o Total solar absorptance per ASTM E424, Method A, for both

exposed and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance per ASTM E408, Method A, for both exposed, and control samples

2.3.3.4.3 Temperature and Radiation

a. Exposure Conditions

Test specimens are being exposed at 90°C to xenon arc radiation under dry conditions in an accelerated weathering machine in accordance with ASTM D2565. Test

specimens are being pulled after 500, 1,000 and 2,000 hours of exposure in the

machine.

b. Apparatus and Specimens

Absorber materials being used are identified in Table 3-3. Three test specimens are provided for exposure; one to be pulled at each of the exposure time

intervals specified (500, 1,000 and 2,000 hours).

The accelerated weathering machine used meets the requirements of ASTM D2565

and is capable of maintaining the required temperature. The test specimens are oriented so that the absorber surface is facing the xenon arc lamp.

2-33
c. Property Measurements

Routine evaluation includes visual observations, total solar absorptance per

ASTM E424, Method A, and emittance per ASTM E408, Method A. Measurements are

being made after each exposure time period. The test specimens are being stored and

not returned for further exposure following property measurements. Non-routine

measurements per 2.3.4 may be performed to further characterize changes observed.

d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure time

o Exposure conditions

o Notations recorded during visual observations

o Total solar absorptance per ASTM E424, Method A, for both

exposed and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance per ASTM E408, Method A, for both exposed and control samples

2.3.3.4.4 Thermal Cycling

a. Exposure Conditions

Test specimens are being exposed to test cycles consisting of the following:

o '^' 8 hours at 175°C

o 5 minutes to equilibrate at room temperature

o r\,16 hours at -10°C

o 5 minutes to equilibrate at room temperature

Test specimens are being pulled after 5, 15 and 30 test cycles as specified above.

b. Apparatus and Specimens

Absorber materials being used are identified in Table 3-3. Three test specimens are being provided for each material; one specimen to be pulled at each of the

exposure intervals (5, 15 and 30 cycles) . Two test chambers are being used; one maintained at 175 + 3°C and the other at -10 + 3°C.

c. Property Measurements

Routine evaluation includes visual observations, total solar absorptance per

ASTM E424, Method A, and emittance per ASTM E408, Method A. Measurements are being

made after each of the specified exposure intervals. The test specimens are

being stored and not returned for further exposure following property measurements.

Non-routine measurements per 2.3.4 may be performed to further characterize

changes observed.

2-34
d. Test Reports

Test reports are to include the following information:

o Test specimen code number

o Location and dates of exposure

o Total cumulative exposure cycles

o Exposure conditions

o Notations recorded during visual observations

o Total solar absorptance per ASTM E424, Method A, for both

exposed and control samples

o Solar reflectance curves for both exposed and control samples

o Emittance per ASTM E408, Method A, for both exposed and control samples

2.3.4 NON-ROUTINE PROPERTY MEASUREMENTS

Many techniques are available that can be used to characterize degradation

phenomena in materials [19, 20] . The techniques identified below will be used, as required, to characterize initial composition and topography, and changes in cover and absorber materials resulting from environmental exposure.

2.3.4.1 Surface Appearance Changes

Techniques that will be considered to characterize changes include:

o Stereoscopic Microscopy

o Nomanski Differential Phase Interference Microscopy

o Scanning Electron Microscopy (SEM)

The Nomanski and SEM techniques have the advantages of high resolution and good

depth of field.

2.3.4.2 Surface Chemical Composition Changes

Techniques that will be considered to characterize changes include:

o X-Ray Fluorescence (XRF) in conjunction with an electron microprobe

o Auger Electron Spectroscopy (AES)

o Electron Spectroscopy for Chemical Analysis (ESCA)

o Attenuated Total Reflectance (ATR)

The AES and ESCA techniques are suitable for analyzing elements having an atomic

number greater than two, whereas XRF is primarily of value with relatively heavy

elements. The electron probe can be used to get a picture of the material

surface, however, it will not be of the quality that can be obtained with a SEM.

The ATR technique is an infrared spectroscopy technique that will primarily be of

value in analyzing surface degradation of cover materials, i.e. carbonyl formation

and hydrolysis.

2.3.4.3 Bulk Material Chemical Changes

Techniques that will be considered to characterize these changes include:

o Secondary Ion Mass Spectrometry (SIMS)

o Electron Spin Resonance (ESR)

o Infrared Transmittance

2-35
The SIMS technique will primarily be used to characterize localized degradation

such as pitting of coatings. By etching through the defect with an ion beam, it

is possible to get an in-depth profile of the chemical composition of the defect.

SIMS is an especially powerful tool when used in conjunction with AES or ESCA.

ESR and Infrared Transmission will primarily be used to characterize compositional

changes in polymeric cover materials.

Potassium bromide pellet techniques may be of value for those materials which

exhibit poor infrared transmission.

2.3.4.4 Mechanical Property Changes

Primary emphasis will be placed on tensile properties of organic cover materials

using ASTM Methods D638 [21], D882 [22] or D1708 [23].

The D638 method is primarily applicable to sheet materials (up to 14 mm thick)

whereas the D882 method is intended for use with films (less than 1 mm thick)

.

The D1708 method is a microtensile technique that can be used on specimens up to 3.2 mm thick; however, it cannot be used for the determination of modulus of

elasticity unlike the D638 and D882 methods. Additional stiffness and/or bending

tests will be devised where appropriate.

2-36
3. TEST SPECIMEN SELECTION

3.1 GENERAL

Solar collectors presently available on the commercial market show a wide range

of variation in materials, construction and operational characteristics. These

variables include type of solar collector (flat plate, concentrating, evacuated

tube, etc.), heat transfer medium (air or various liquids), absorber plate

materials, absorptive coatings, number of cover plates and their materials, type

of insulation, and flow tube/passage material and design. With this vast number

of variables, it is not possible to define a typical solar collector that is

representative of all collectors commonly in use. Due to the large number of

variables, it is necessary to develop selection criteria to optimize the choice

of a limited number of test specimens.

3.2 SOLAR COLLECTOR SELECTION ATTRIBUTES

The criteria which follow were used to select test specimens:

Criterion 1 : The collectors selected for testing must be commercially available

and have a history of "real time" use in the solar heating and cooling demonstration program. This is to permit a comparison of changes observed as a result of

environmental exposure in the test program with those that occur in operational

systems.

Criterion 2 : The manufacturer's specification must not prohibit prolonged stagnation exposure. This criterion eliminates the use of tracking concentrators which

would not ordinarily be designed to track the sun under stagnation conditions.

Criterion 3 : The collectors must be capable of being tested for thermal performance'

by ASHRAE Standard 93-77 by qualified test laboratories located in each of the climatic regions selected _.for use in the test program. This criterion would eliminate

those collectors which require non-aqueous heat transfer fluids as well as air

collectors since a limited number of test sites have these capabilities.

Criterion 4: Cover and absorber materials coupon specimens removed from the

collectors must not require special protection during environmental exposure. In addition, the test specimens must be amenable to optical and mechanical property

measurements using standard test methods. This would eliminate the use of

evacuated tube collectors where the test specimen configuration requires special

measurement techniques and a vacuum is required to simulate the actual in-use

environment.

Criterion 5 : The products selected must be representative of the broad range of

materials and construction commonly in use. Primary emphasis is to be placed on cover and absorber materials.

3.3 SELECTION OF TEST SPECIMENS

Consideration of the criteria in 3.2 has narrowed down the choice to the following

primary variables:

Collector Type: Flat Plate

Heat Transfer Fluid: Aqueous Liquid

Number of Covers: One and Tvro

3-1
Cover Materials: Glass

o Ordinary Plate Glass

o Water White

o Low Iron

Sheet Plastics

o Glass Fiber Reinforced Plastic (FRP)

o Polymethyl Methacrylate

o Polycarbonate

Films

o Polytetra Fluorethylene (FEP)

o Polyethylene Terephthalate (polyester)

o Polyvinyl Fluoride

Absorber Coatings: Selective

o Black Chrome

o Black Nickel

o Copper Oxide

o Lead Oxide

o Aluminum Oxide (conversion coating)

o Aluminum Oxide (anodized)

o Selective Paint

Non-Selective

o Porcelain Enamel

o Paint - Alkyd

o Paint - Epoxy

o Paint - Urethane

o Paint - Silicone

Absorber Substrate: Aluminum

Copper

Carbon Steel

Stainless Steel

Polymeric Material

Insulation Material: Glass Fiber

Glass Foam

Organic Foam

There are many other secondary variables such as collector case material, gasket

and sealant materials, etc., that were not considered in the selection process

since they do not normally directly affect thermal performance.

A total of eight different types of solar collectors were selected for use in the

test program. Key features of these collectors are summarized in Table 3-1.

Testing will be performed at the materials coupon specimen level on as many

other cover and absorber materials as can be obtained. Materials level test specimens are identified in Tables 3-2 and 3-3 for cover and absorber materials

respectively.

3-2
TABLE 3-1. SOLAR COLLECTOR TEST SPECIMENS

Code

Cover Mat erial 5 Absorber Mat arial ^ Outer Inner Coating Substrate

A Glass Black Nickel Steel

B

2 Glass Glass Black Velvet Paint Copper

C Glass FEP Film

Heat Trap

Black Velvet Paint Copper

D Glass

^'^ Glass ^'^ Black Chrome Steel

(nickel flashed)

E FRP - Type la Flat Black Paint

(lacquer primer)

Copper

F Glass

"" Copper Oxide Copper

G FRP - Type II FEP Film Procelain Enamel Steel

H Polyester Film FEP Film Flat Black Paint

(siliconized polyester)

Aluminum

Water White Glass

Low Iron Glass

Ordinary Plate Glass

Etched Anti-Reflection Treatment

Obtained from collector manufacturer literature

3-3
TABLE 3-2. COVER TEST MATERIALS

Code

"^ Cover Material Transmittance (Controls)

E FRP Type la 0.85

G FRP Type II 0.84

H^ Polyester/FEP

(outer) (inner)

0.85/0.96

J Polycarbonate 0.88

K Polyvinyl Fluoride 0.89

L FRP Type lb 0.84

M FRP Type III 0.78

N Polymethyl methacrylate

(acrylic)

0.90

0^ 4 Glass /Polyvinyl Fluoride

(outer) (inner)

0.86/0.89

Code letters E, G and H indicate materials coupon specimens cut from solar collectors E, G and H. Codes J, K, L, M, N and tested at the materials level only.

Materials to be exposed as a combination in the cover mini-boxes (see 2.3.2.1 and 2.3.2.2)

and in the accelerated weathering machine (see 2.3.2.4). Materials to be exposed

individually in all other tests. Glass and FEP materials are not to be used for

individual tests because of proven stability.

These properties are dependent on the formulations and manufacturing processes used.

Other products within a generic class of materials may have significantly different

properties.

Ordinary plate glass.

3-4
TABLE 3-3. ABSORBER TEST MATERIALS

Code '- Absorber Material

, 2 Optical Properties

Coating Substrate Absorptance ^ Emittance -'

A Black Nickel Steel 0.87 0.13

C Flat Black Paint Copper 0.98 0.92

D Black Chrome Steel

(nickel flashed)

0.97 0.07

E Flat Black Paint Copper 0.95 0.87

F Copper Oxide Copper 0.96 0.75

G Black Porcelain Enamel Steel 0.93 0.86

H Flat Black Paint Aluminum 0.95 0.89

I Black Chrome Stainless Steel 0.88 0.19

J Black Chrome Aluminum 0.98 0.14

L Lead Oxide Copper 0.99 0.29

M Oxide Anodized Aluminum 0.94 0.10

N Oxide Conversion Coating Aluminum 0.93 0.51

P Black Chrome Copper 0.96 0.08

Code letters A through H indicate materials coupon specimens cut from solar collectors

A through H. Codes I through P tested at the materials level only.

These properties are dependent on the formulations and manufacturing processes used.

Other products within a generic class of materials may have significantly different

properties.

Average values based on a minimum of ten test specimens.

3-5

4. OUTDOOR TEST SITE SELECTION

4.1 SITE CONSIDERATIONS

Factors that have been considered in the selection of test sites include:

o Climatic conditions in major regions of the United States

o Population density in these areas

o Test site availability in these major climatic regions

The first factor is concerned with the environmental exposure conditions to which

solar collectors will be exposed. The second with the probability that solar will

be used and the third with whether or not testing can be performed in areas having

desired climatic and population characteristics.

4.1.1 CLIMATIC CHARACTERISTICS

The six major divisions of world climates have been identified by Trewartha [24] as follows:

A. Tropical Rainy Climates

B. Dry Climates

C. Humid Mesothermal Climates

D. Humid Microthermal Climates

E. Polar Climates

F. Undifferentiated Highlands

Examination of the population distribution for the 1970 census as a function of

climatic region indicates that about 96% of the people in the U.S. live in two major

climatic regions: C, Humid Mesothermal, and D, Humid Microthermal, as shown in

Table 4rl [25] . The more extreme climates in terms of precipitation such as A, Tropical Rainy, and B, Dry, account for about 4%. The Polar and Undifferentiated

Highlands contain a relatively small percentage of the continental U.S. population.

The tropical Savanna subdivision of Tropical Rainy Climates are found in Hawaii

and the southern tip of Florida. The Dry Climates include large areas of

New Mexico, Arizona and Nevada, and portions of Texas, Colorado, Utah, Oregon,

Idaho, Montana, Wyoming, California, the Dakotas, Nebraska and Kansas. Humid

Mesothermal Climates prevail in the Southeast, northern California and the western

part of Oregon and Washington. Humid Microthermal Climates include the New

England states. New York, Michigan, Minnesota, Iowa, Pennsylvania, Wisconsin, and

parts of Maryland, West Virginia, Ohio, Illinois, Indiana, Missouri, Kansas,

Nebraska, Alaska and the Dakotas. Highlands Climate occurs in Arizona, Colorado,

Utah, Wyoming, Idaho, Montana, California, Oregon and Washington. The Polar

Climate is found in Alaska only.

4.1.2 CLIMATIC REQUIREMENTS

A meaningful validation of durability/reliability tests for solar collectors and

their materials must consider the broad range of climatic and other environmental

exposure conditions that can be found in the United States. These variables in

the approximate order of decreasing importance are:

o The annual solar radiation at a test site and its seasonal distribution

o Humidity

o Ultraviolet radiation in the solar flux

o Average and extreme high temperatures

o Low temperatures

o Total and seasonal precipitation (and type)

4-1
TABLE 4-1. ESTIMATED DISTRIBUTION OF POPULATION IN THE UNITED STATES*

AMONG VARIOUS CLIMATES [25]

A. TROPICAL RAINY CLIMATES 1.1 percent

Am, Monsoon Rainforest ... 0.3 percent

Aw, Tropical Savanna 0.8 percent

B. DRY CLIMATES 2.9 percent

BSh, Tropical and Subtropical Steppe .... 0.6 percent

BSk, Middle Latitude Steppe. , . . - 1.6 percent

BWh, Tropical and Subtropical Desert .... 0.7 percent

C. HUMID MESOTHERMAL CLIMATES 46.2 percent

Cs, Mediterranean 9.3 percent

Caf, Humid Subtropical (no dry season) . . . 35.5 percent

Cb, Marine West Coast (cool summer) 1.4 percent

D. HUMID MICROTHERMAL CLIMATES 49.6 percent

Daf, Humid Continental (warm summer;

no dry season) ... 31.9 percent

Dbf, Humid Continental (cool summer;

no dry season) ... 17.5 percent

Dcf, Subarctic (no dry season) 0.2 percent

Total 99.8 percent

*Including all 50 states, the District of Columbia and Puerto Rico.

4-2
o Average and maximum wind velocities and their directions

o Concentrations of suspended particulate matter from dust and pollution

o Pollution oxidants and acid gases (ozone, nitrogen oxides and sulfur

oxides) that attack collector materials, particularly plastic cover plates

The importance of these environmental variables to collector durability and

reliability, and their wide variation throughout the United States require that:

1) test sites be selected that represent suitable combinations of these variables

and 2) their effects on collector performance be carefully monitored during the

test program.

An important caution is that climatological data and pollution data can vary

widely, depending on the local terrain and locations with respect to major bodies

of water, heat-producing sources (such as a steel mill) and other geographical

factors. Weather characteristics (which are typically measured at airports) show

wide variations even over a distance of a few miles. Such variations are even more evident in pollution measurements which are usually taken near sources of

suspected air pollution. Accordingly, if any test site is to rely upon another

location for data on climatological or other environmental conditions, the

organization conducting the test must demonstrate that the recorded data is valid

for that test site.

4.1.3 SITE DESCRIPTIONS

A comparison of the major populated climatic regions and the availability of

exposure sites with the capability of performing thermal performance tests in

accordance with the ASHRAE Standard 93-77 [26 J resulted in the selection of four

test sites. The location of these sites with respect to U.S. geographic and

climatic regions is shown in Figure 4-1.

A summary of the major climatic features of each site is listed below.

DSET Labs, Inc., Phoenix, Arizona (Test Site 1):

o Hot, dry

o High solar radiation

o High UV

o Rural, desert environment

Florida Solar Energy Center, Cape Canaveral, Florida (Test Site 2):

o Hot, humid

o High solar radiation

o Low to moderate UV

o Coastal, salt air environment

Lockheed Palo Alto Research Laboratory, Palp Alto, California (Test Site 3):

o Moderate, dry

o High solar radiation

o Moderate UV

o Urban environment

National Bureau of Standards, Gaithersburg, Maryland (Test Site 4)

o Moderate, humid

o Moderate solar radiation ^ o Moderate to low UV

o Suburban environment

4-3
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5 . DATA ANALYSIS

5.1 GENERAL

The large amounts of thermal performance, material properties and environmental

data to be collected during the entire program and the associated correlations

between variables will require the data reduction to be computerized. To the

extent feasible, this computer data reduction and analysis will be performed con- currently with the experimental program to improve the quality of subsequent data

and to identify modifications in procedures if they become apparent. A summary

of the available data, and the purpose and application of the results is shown

in Table 5-1.

A general description of the three categories of data analysis and correlations

are described as follows.

5.2 ANALYSES OF MEASURED COLLECTOR EFFICIENCIES

The data and results of measuring thermal efficiencies of 96 collectors in a series of from 4 to 6 tests on each collector (approximately 640 efficiency

graphs) will be analyzed to correlate thermal performance changes with elapsed

time and the collector environment. Graphical and statistical analyses of the

data will be completed to identify effects of the different test series including

enhanced solar radiation by plane reflectors, thermal shock and simulated solar

radiation.

A. Data Organization and Standardization

The results from the efficiency tests will be organized and arranged for

correlation studies. The measured efficiency curves for the individual

collectors will be plotted on a common graph with accumulated exposure days

as a parameter. Linear and second-order polynomial "least-squares" curve

fits to the data will be used. The primary performance parameters Fp(Ta)g

and Fj^U^ will be tabulated for linear fits. The appropriateness of secondorder fits and the corresponding performance parameters will be considered

in tabulating results. The relative scatter of efficiency values around the

correlating curves will be evaluated by the Chi-square, i.e.

Zjj[ri( experiment) - n(curve)]2.

B. Analyses of Change in Thermal Performance Parameters

Various trial correlations will be carried out to investigate the change with

respect to time of the primary collector performance parameters. The specific

correlations to be emphasized depend on the results of initial trials and

analyses. The following analyses and correlations will be considered:

1. Representative graphs for individual collectors will be prepared to show the change of FR(Ta) and Fj^Ul with elapsed time and the effects

of the four test series. The parameters will be normalized with

initial values and survey plots made to identify overall similarities

and differences in trends. Graphs will also be prepared for each of

the eight collector models with the results from all test sites shown

collectively. The scatter in the results is a measure of site

dependence. Furthermore, for each of the test sites, changes with

respect to time in the normalized values will be depicted collectively

for all collectors. Finally, these results will be depicted collectively for all sites and collectors. The measured changes in the

5-1
TABLE 5-1. SUMMARY OF AVAILABLE DATA, PURPOSE AND RESULTS

Available Data Purpose

1. Solar simulator measured performance and

outdoor measured performance.

2. Measured performance before and after 3-

day exposure on the same collector

[Series 1]; also initial performance with

[Series 2] and without [Series 3] preexposure on same type of collector.

3. Measured performance on the same type of

collector at different outdoor test sites

[all series and applicable sites]

4. Measured performance after dry stagnation

without reflector [Series 1], no-flow

[Series 2], controlled flow [Series 3]

and dry stagnation with reflector [Series

4].

5. Temperature history of internal collector

components (cover plates and absorber

plate) [all series and applicable sites]

.

6. Weather data:

Total solar radiation history

UV solar radiation history

Maximum daily ambient temperature

Minimum daily ambient temperature

Rainfall

Snow, sleet, hail, etc. Wind speed and direction

Pollutants

[all series and sites]

7. Thermal shock/cold fill test results

8. Thermal shock/water spray results

9. Static pressure leakage test results

[all four series at applicable sites]

1. Comparison of thermal performance measured on the solar simulator and that

measured at the outdoor test sites.

2. Determine requirement for 3-day preexposure before thermal performance mea- surements in ASHRAE 93-77.

Comparison check of instrumentation,

technique and analysis of performance at different test locations.

Evaluation of solar collector performance

degradation and durability under different accelerated aging conditions and when

exposed in different climatic regions.

Validate 30-day exposure test.

Evaluation of test criteria for testing

solar collector components in the

laboratory. Comparison of test conditions

with maximum and minimum temperatures

specified in ASTM E44.04 test methods.

Correlate maximum temperature of collector components with solar radiation and

ambient temperature for each collector

type. Correlate performance and material

degradation with UV dosage. Correlate

performance and material degradation with

pollutant measurements.

7. Evaluation of test procedure in NBSIR

78-1305A for testing the ability of the

solar collector to withstand the thermal

shock induced through filling a hot

collector with relatively cool heat

transfer fluid during daytime start-up.

8. Evaluation of test procedure in NBSIR

78-1305A for testing the ability of the

solar collector to withstand thermal

shock caused by heavy rains falling on

the heated collector.

9. Evaluation of test procedure in NBSIR

78-1305A for determining leakage and

indication of damage induced by other

tests.

5-2
TABLE 5-1 (Contd.)

Available Data Purpose

10. Property measurements of material coupon

specimens exposed to the same environments as solar collectors.

11. Property measurements of material coupon

specimens exposed to accelerated field

and laboratory tests.

12. Collectors with significant degradation

available for tear down unless exposure

to recontinue [all series] . Results of

laboratory tests on collector components,

13. Incident angle modifier data for preand post-exposure.

10. Evaluation of outdoor weathering methods

of material coupons. Assess value of

various measurement techniques as indicators of change.

11. Evaluation of accelerated aging methods

for materials. Assess value of various

measurement techniques as indicators of

change.

12. Identify fundamental causes of collector

performance and other changes. Estimate

whether such changes would increase if

aging had been continued. If possible,

verify by continuing aging at some sites.

13. Provide a basis for correlating change

in incident angle modifier with change

in thermal performance, exposure time

and conditions.

5-3
efficiency parameters will be compared with the changes justified by

differences in the test environments during various tests. Bands

corresponding to the most and least favorable environments will be

established and used to identify changes in collector performance or possible experimental error.

The results of the studies involving changes in the key performance

parameters will be used to validate or refute currently-recommended

test procedures. The significance of the HUD-prescribed thirty-day

thermal exposure test procedure will be considered. Efficiency tests

obtained with natural (outside) solar radiation will be compared for

several identical collector models with the results using a solar

simulator.

2. The kinetics and mechanisms of changes in the collector performance

parameters will be correlated with environmental characteristics during

the exposure period. The weather data base furnished by the test sites

will be used along with test results to make selected cross-plots of

the changes versus elapsed hours at incremental weather parameters.

Tabulations showing the time above incremental solar radiation levels and

ambient temperature combinations will be used to identify weather parameters which are important in correlating material property changes. The

integrated total daily radiation over the elapsed exposure time will be

compared with elapsed time at incremental exposure levels as a means of

correlating changes. Comparisons will be made to establish possible

dependence on humidity and UV levels, design configurations, mounting

and array effects. The differences in material property deterioration

resulting from the four test series, which include the effects of thermal

shock, solar radiation (and UV) enhancement by reflectors, etc., will be

evaluated.

After the stronger correlating weather parameters have been identified,

analyses will be carried out in an attempt to establish functional

dependence on the environmental parameters. For example, plots will be

made to determine whether the key collector performance parameters have an Arrhenius type rate dependence on solar radiation and stagnation

temperature.

Data and results from the test program will be compared with the limited

results available from actual field experience. Trends in the change of

collector parameters from the different test procedures will be compared

with data from actual operating systems to determine which test series

corresponds closer to actual aging trends.

5.3 CHANGES IN MATERIAL PROPERTIES

Property changes in samples of solar collector materials will be analyzed in an approach similar to that described above. The effects of cover and absorber

material deterioration on the thermal performance of typical solar collectors

will be evaluated with a mathematical model.

A. Kinetics of Material Property Changes

The primary properties of material samples that will be considered are absorptance (a), emittance (e) and solar transmittance (is)- Investigations

will be made to correlate property changes with exposure time above selected

I values of solar radiation and ambient temperatures. The effects of concentrated

radiation will be evaluated and compared with the conventional aging methods and

with field experience. Investigations will be made to identify possible

dependences on regional weather characteristics such as humidity and UV level.

Similar studies may be performed using the non-routine property measurements

discussed in 2.3.4.

5-4
B. Effect of Material Property Changes on Collector Thermal Performance

Measured changes in material properties will be used in a mathematical model

to calculate corresponding changes in the thermal efficiency of the types of

collectors used in the test program. The accuracy of the mathematical model

will be established by comparing results with the initial measured efficiencies.

Subsequently, the primary performance parameters, FRda) and FrUl, will be

calculated on the basis of measured values of sample material properties and

compared with those from the collector efficiency measurements after various

exposure times. While most of the collectors used in the test program are of

conventional design, three (C, G and H) have unusual design features which may

necessitate a more approximate mathematical model. In these cases, the

experimental results will be used to identify effective properties such as solar transmittance and convection suppression effects, and confirm the model.

The overall results will be reviewed and recommendations made as to the

applicability of the material exposure procedures for predicting changes in

materials during long-term collector operation.

5.4 Investigation of Stagnation Temperatures of Collector Materials

Analytical and experimental data will be evaluated to compare the stagnation

temperatures of absorbers, covers and insulating materials for conventional

tube-in-sheet collectors. This study is useful to apply modeling results to collector designs which are different from those used in the program.

A. Mathematical Model

In contrast to thermal performance models, transient effects, longwave

radiation transmittance and temperatures of specific components of the

collector are important considerations in developing an accurate model for

predicting stagnation temperatures. A tentative mathematical model

incorporating these essential features currently under development will be

compared to experimental results and, if necessary, further developed to support the overall objectives of the research program.

B. Experimental Applications

It is anticipated that stagnation temperature is an important parameter in

correlating changes in material properties. The experimentally-verified

mathematical model would then become an essential tool to develop

accelerated aging procedures. The model, consisting of a FORTRAN computer

code and supporting documentation, would likely be useful to establish the

long-term durability of collector materials.

5-5

6. CURRENT STATUS

This chapter summarizes the status (as of August 1, 1980) of the various elements of the

reliability/durability test program described in this plan and of related solar collector

materials test programs also being conducted at NBS.

6.1 THIS PROGRAM

The status of various program elements is summarized in Table 6-1. As a result of

thermal performance test results obtained following the exposure of full size

solar collectors for periods of up to 120 days (>17,000 KJ/m^-day), the outdoor

exposure of the Series 1 and Series 2 collectors as well as the small scale "real

time" cover and absorber specimens has been extended for an additional 240 days.

Additional property measurements will be made following that exposure. Materials

level tests will also be conducted with somewhat less extreme combined temperature

and humidity exposure conditions because of the severe degradation observed with

several materials [27]. Exposure to combined temperature, radiation and humidity

using the accelerated weathering machine referred to in 2.3.2.4.3 will also be

studied.

6.2 RELATED NBS WORK

An experimental program was recently completed in which the properties of ten types of cover materials were evaluated following exposure to natural weathering,

heat aging and combined heat and xenon-arc radiation [28]. Properties measured

included solar energy transmittance, dimensional stability, warpage and dirt

retention. Laboratory work to aid in the development of evaluation standards for

absorber materials [29] has also been completed. In this program, coupon specimens

of twelve different absorber materials were subjected to various types of laboratory

exposure (temperature, moisture, xenon-arc radiation) and to natural weathering

in simulated collectors. Optical properties (absorptance and emittance) and

visually detectable changes were determined following this exposure. Data from

these two programs are being incorporated into the analyses being performed in the

present program. Comparisons will be made to ascertain that the degradation

observed at the materials level is indicative of that which occurs in actual solar

collectors.

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7 . REFERENCES

1. "National Program for Solar Heating and Cooling of Buildings," Report No. ERDA 76-6,

Energy Research and Development Administration (now Department of Energy) , Washington,

DC 20545, November 1976.

2. Holton, J.K., et . al., "Interim Performance Criteria for Solar Heating and Cooling

Systems in Residential Buildings - Second Edition," NBS Report NBSIR 78-1562, November

1978. Available from NTIS, Order No. PB 289 967.

3. Waksman, D., et . al., "Interim Performance Criteria for Solar Heating and Cooling

Systems in Commercial Buildings," prepared for ERDA by NBS, NBS Report NBSIR 76-1187,

November 1976. Available from NTIS, Order No. PB 262 114.

4. "Methods of Testing to Determine the Thermal Performance of Solar Collectors," ASHRAE

Standard 93-77, February 1977. Available from the American Society of Heating,

Refrigerating and Air Conditioning Engineers, Inc., Publications Sales Department,

345 E. 47th Street, New York, NY 10017.

5. "Methods of Testing Thermal Storage Devices Based on Thermal Performance," ASHRAE

Standard 94-77, February 1977. Available from ASHRAE, 345 E. 47th Street, New York, NY

10017.

6. Waksman, D. , Pielert, J.K., Dikkers, R.D., Streed, E.R. and Niessing, W.J., "Plan for

the Development and Implementation of Standards for Solar Heating and Cooling

Applications," NBS Report NBSIR 78-1143A, June 1978. Available from NTIS, Order No. PB 283.

7. Gilligan, J.E., Brzuskiewicz, J. and Brzuskiewicz, J.E., "An Extended Test Program for

Solar Collector Optical Materials," Proceedings of 1977 Flat Plate Solar Collector

Conference, Orlando, FL, March 1977. Available from Florida Solar Energy Center,

Cape Canaveral, FL.

8. "Intermediate Minimum Property Standards Supplement - Solar Heating and Domestic Hot

Water Systems," 1977 Edition, prepared for HUD by NBS. Available from GPO, Order No. SN 023-000-90161-7.

9. Waksman, D., Streed, E.R., Reichard, T.W. and Cattaneo, L.E., "Provisional Flat Plate

Solar Collector Testing Procedures: First Revision," NBS Report NBSIR 78-1305A, June

1978. Available from NTIS, Order No. PB 283 721.

10. Ibid, Appendix C.

11. Ward, J.C. and Lof, G.O.G., "Long-Term (18 Years) Performance of a Residential Solar

Heating System," Solar Energy, 18_, 301, 1976.

12. Knoll, R.H. and Johnson, S.M., "Baseline Performance of Solar Collectors for NASA

Langley Solar Building Test Facility," Presented at Flat Plate Solar Collector

Conference, Orlando, FL, March 1977.

13. "Environmental Test Methods," MIL-STD-810C, March 10, 1975. Available from ASD/ENYESS,

Wright-Patterson AFB, OH 45433.

14. Streed, E.R., Thomas, W.C, Dawson III, A.G., Wood, B.D. and Hill, J.E., "Results and

Analysis of a Round-Robin Test Program for Liquid-Heating, Flat-Plate Solar Collectors,"

NBS Technical Note 975, August 1978. Available from GPO, Order No. 003-003-01959-3.

7-1
15. "Standard Methods of Test for Solar Energy Transmittance and Reflectance (Terrestrial)

of Sheet Materials," ASTM Standard E424-71. Available from American Society for

Testing and Materials, 1916 Race Street, Philadelphia, PA 19103.

16. "American National Standard Safety Performance Specifications and Methods of Test for

Safety Glazing Material Used in Buildings," ANSI Z97. 1-1975, September 26, 1975.

Available from American National Standards Institute, 1430 Broadway, New York, NY 10018.

17. "Standard Recommended Practice for Operating Xenon Arc-Type (Water-Cooled) Light- and

Water-Exposure Apparatus for Exposure of Plastics," ASTM Standard D2565-76. Available

from ASTM.

18. "Standard Test Methods for Total Normal Emittance of Surfaces Using Inspection Meter

Techniques," ASTM Standard E408-71. Available from ASTM.

19. Czanderna, A.W., ed., "Methods and Phenomena of Surface Analysis," Vol. 1, Elsevier,

Amsterdam, 1975.

20. Kane, P.P. and Larrabee, G.R., eds., "Characterization of Solid Surfaces," Plenum Press,

New York, NY, 1974.

21. "Standard Test Method for Tensile Properties of Plastics," ASTM Standard D638-77a,

Available from ASTM.

22. "Standard Test Methods for Tensile Properties of Thin Plastic Sheeting," ASTM Standard

D882-75b. Available from ASTM.

23. "Standard Test Method for Tensile Properties of Plastics by Use of Microtensile

Specimens," ASTM Standard D1708-66. Available from ASTM.

24. Trewartha, G.T,, Robinson, A.H. and Hammond, E.H.. "Fundamentals of Phyical Geography,"

McGraw Hill Book Company, Inc., 1961.

25. 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, August 1974, National Bureau of Standards, Washington, DC 20234.

26. Niessing, W.J,, "Laboratories Technically Qualified to Test Solar Collectors in

Accordance with ASHRAE Standard 93-77: A Summary Report," NBS Report NBSIR 78-1535,

November 1978. Available from NTIS, Order No. PB 289 729.

27. Waksman, D. , Streed, E. and Dawson, A,, "The Influence of Environmental Exposure of

Solar Collectors and Their Materials," Proceedings of 1980 Annual Meeting of the

American Section, International Solar Energy Society , held in Phoenix, AZ, June 1980,

28. Clark, E., Roberts, W., Grimes, J.W. and Embree, E.J., "Solar Energy Systems - Standards for Cover Plates for Flat Plate Solar Collectors," NBS Technical Note 1132.

29. Masters, L., Seller, J., Embree, E. and Roberts, W., "Solar Energy Systems - Standards

for Absorber Materials," NBS Report NBSIR (in review).

7-2
APPENDIX A. DETAILED DATA REQUIREMENTS

Form 105, Coupon Specimen Log Sheet

Form 201, Instantaneous Efficiency Data

Form 201A, Instantaneous Efficiency Plot

Form 202, Incident Angle Modifier Data

Form 202A, Incident Angle Modifier Plot

Form 203, Coupon Data Form

Form 204, Coupon Optical Properties Data Sheet

Form 301, Monthly Test Site Weather Conditions

Form 302, Maximum Daily Cover Plate Box and Absorber Box Temperature

Form 303, Maximum Daily Collector Absorber Plate Temperature

Form 304, Maximum Daily Collector Absorber Plate Temperature

Form 305, Exposure Conditions for 4-Hour 300 Btu/f t2.hr Exposure

Form 306, Pollutants

Amendment A-1, Supplementary Data

A-1
For NBS Use

COUPON SPECIMEN LOG SHEET

Specimen

Code No. Date Time Test Description Sample Disposition

Form 105

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A-6
Test Site

COUPON DATA FORM

(use when changes are observed or measurements made)

Date

2 Total Days Exposure (1500 Btu/ft minimum)

Total Calendar Days Exposure

Date Exposure Started

Form Filled Out By

Cover Materials

Specimen

Code No. Visual Change Report

Transmission

Measured* Comments

Yes No

Absorber Coatings

Specimen

Code No. Visual Change Report

a, e Measured*

Comments

Yes No

*If yes, report on Fomn 204

Form 203

A-7
COUPON OPTICAL PROPERTIES DATA SHEET

Test Site Date

Form Filled Out By

Cover Coupons

Sample

Code No.

Number

Removed

for Test

Samples

Returned to Test

Days Exposure

1500 Btu/ft2

Calendar

Days

Exposure

*

T Comments

Yes No

Absorber Coating Coupons

Sample

Code No.

Number

Removed

for Test

Samples

Returned to Test

Days Exposure

1500 Btu/ft2

Calendar

Days

Exposure

* k

Z Comments

Yes No

*Describe method (equipment) used

Form 204

A-8
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A-9
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A-12
EXPOSURE CONDITIONS FOR

4-HOUR 300 BTU/Ft2-HR EXPOSURE

Collector Code Number

#1500 Btu/ft^.day - Exposure Days

Test Site

Form Filled Out By

Date of 4-Hour Exposure

* Solar.

Time

hr:min

It

*' T

( amb

= F)

Wind

(mph)

21 22 23 24 25J26 27 28 29 30 31 32 33 — ,

,

1

,

* Record at half hour intervals during the 4-hour exposure period.

**Instantaneous solar flux (Btu/ft -hr).

Form 305

A-13
POLLUTANTS

(To the extent available from a local EPA or other facility)

Test Site

Form Filled Out By

Date _

Month

Year

Day of

Month

Pollution

Particulate

Sulfur

Dioxide

yg/m^

Carbon

Dioxide

mg/m^

Oxident/

Ozone

yg/m

Nitrogen

Dioxide

yg/m^

Total

Hydrocarbons

yg/m^

1

2

34

5

6

7

8

9 10

11

12

13

14

15

16

1718

19

20

21

22

23

24

25

26

27

2829

30

31

Form 306

A-14
AMENDMENT A-1

SUPPLEMENTARY DATA

The following detailed measurements shall be made and reported in addition to the data

previously requested

1. Solar Radiation

a) The irradiance of the incident solar radiation at the exposure tilt angle shall be

measured at 5 minute intervals or less. A daily plot of irradiance (W/m ) as a function of time during the sunlight hours shall be provided as indicated in

Figure A-1.

b) A determination of the number of hours each month with irradiance values greater

than 950, 1000, 1050, and 1100 W/m shall be made. Time intervals at each of the

specified irradiance levels must exceed 15 minutes to be counted. In addition the

time shall be segregated by occurrence above ambient temperature levels of 15°,

20°, 25°, and 30°C. The data shall be reported by total hours per month as indicated in Table 1.

2 c) The integrated total daily radiation in W hr/m shall be determined and reported

in tabular form for each month as illustrated in Table 2 . The data shall be

obtained from measurements made at 5 minute intervals or less.

2. Ambient Temperature

a) Ambient temperature measurements shall be made at intervals not greater than 30

minutes during the sunlight hours. The measurements shall be made at coincident

times with the plate temperature measurements described in Section 3(a) below.

The data shall be reported in daily plots of the temperature versus time as shown

in Figure A-1.

3. Absorber Plate Temperature

a) Absorber plate temperatures shall be made at intervals of not greater than 30

minutes during the sunlight: hours. The data shall be obtained for each Series 1 and Series 4 collector of each manufacturer. The data shall be plotted on the same curve as the ambient temperature and irradiance shown in Figure A-1.

4

.

Wind

a) The average hourly wind velocity for the sunlight hours shall be measured and

reported for each day. The data shall be reported as a curve plotted as shown

in Figure A-1.

A-1

5
(s/uij A1I3013A QNIM

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O Cd ^ ?? c>« *- (3oJaiinivH3dN3iiNaraiiv

-J I I I I I L

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<

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o

A-16
Ambient Temp °C

2 Irradiance (W/m )

950 1000 1050 1100

15

20

25

30

Table 1 Hours of exposure with conditions

exceeding the conditions shown, June 1979,

A-17
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A-18

c

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n)

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CO en u

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43

CO H

6 U. S, GOVERNMENT PRINTING OFFICE : 1981 340-997/364
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBS TN 1136

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

I January 1981

4. TITLE AND SUBTITLE

NBS Solar Collector Durability/Reliability Test Program Plan

5. AUTHOR(S)

David Waksman, Elmer Streed, James Seller

6. PERFORMING ORGANIZATION (If joint cr other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

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

Office of Solar Applications for Buildings

Department of Energy

Forrestal Building

Washington, DC 20585

10. SUPPLEMENTARY NOTES

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

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

bibliography or literature survey, mention it here) The test program described in this plan is designed to evaluate both approved and

proposed solar collector test procedures and to correlate laboratory, accelerated

field and simulated operational exposures with actual field data.

The tests and exposure procedures described herein are intended to determine the

influence of environmental exposure parameters that could affect the degradation of

solar collectors and their materials. They are also intended, to the extent

possible, to provide a correlation between changes that occur at the materials and

the collector component levels. It is expected that the data obtained through

their use will lead to more meaningful reliability/durability tests for solar

collectors and their materials.

A wide variety of commercially available solar collectors and multiple material

coupons of collector components are being tested at sites in different climatic

regions. Appropriate laboratory tests are being conducted during the same time

frame to determine physical and material properties for comparison with field test

data and operational collector experience. The data obtained from these tests will

be analyzed and correlated with that obtained from the current Government

Demonstration Program and other related Government-sponsored programs.

e entries; alphabetical order; capitalize only proper names; and separate key words t ivironmental exposure; reliability; solar

collectors; solar materials; stagnation testing.

12. KEY WORDS (Six to twelve entries; aipnaoeticai oraer; capitalize only proper nan Accelerated aging; durability; environmental exposure;words by semicolons)

13. AVAILABILITY

[^ Unlimited rn Foi" Official Distribution. Do Not Release to NTIS rn Order From Sup. of Doc, U.S. Government Printing Office, Washington, DC ^^ 20402.

[2Z\ Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

85

15. Price

$4.00

USCOMM-DC 6043-P80
There's

anew

look

. . . the monthly

magazine of the National Bureau of Standards.

Still featured are special articles of general interest on

current topics such as consumer product safety and building

technology, in addition^ new sections are designed to . . . PROVIDE

SCIENTISTS with illustrated discussions

of recent technical developments and

work in progress . . . INFORM INDUSTRIAL

MANAGERS of technology transfer activities in

Federal and private labs. . . DESCRIBE TO MANUFACTURERS advances in the field of voluntary and

mandatory standards. The new DIMENSiONS/NBS also

carries complete listings of upcoming conferences to be

held at NBS and reports on all the latest NBS publications,

with information on how to order. Finally, each issue carries a page of News Briefs, aimed at keeping scientist and consumalike up to date on major developments at the Nation's physical sciences and measurement laboratory.

(please detach here) SUBSCRIPTION ORDER FORM

Enter my Subscription Subscription To DIMENSIONS/NBS DIMENSIONS/NBS at $11.00. $11.00. Add S2.75 for foreign foreign mailing. mailing. No additiona postage is required for mailing within the United States or its possessions. Domestic

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test methods, and performance criteria related to the structural and

environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's tech- nological marketplace. Order the above NBS publications from: Superintendent of Documents, Government Printing Office. Washington, DC 20402. Order the following NBS publications—F/PS and NBSIR's—from

the National Technical Information Services, Springfield, VA 22161

.

Federal Information Processing Standards Publications (FIPS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amendet^

Public Law 89-306 (79 Stat. 1127), and as implemented by E>

ecutive Order 11717 (38 FR 12315, dated May 11, 1973) and Pan u

of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Services, Springfield, VA 22161,

in paper copy or microfiche form.
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