NBSIR 76-1136

Failure Analysis of Fiberglass

Insulator Rods

Leonard Mordfin and Nixon Halsey

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

July 1976

Final Report

Prepared for

U.S. Coast Guard

Washington, D. C. 20590

NBSIR 76-1136

FAILURE ANALYSIS OF FIBERGLASS

INSULATOR RODS

Leonard Mordfin and Nixon Halsey

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

July 1976

Final Report

Prepared for

U.S. Coast Guard

Washington, D. C. 20590

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Acting Director

CONTENTS

Page

1 . INTRODUCTION 2

2. THE ANGISSOQ INSTALLATION 2

3. THE SPECIMENS 3

4. INSPECTIONS AND MEASUREMENTS 5

4.1 Dimensional Measurements 5

4.2 Coating Loss 7

4.3 Burn Damage 7

4.4 Relationship between Coating Loss and Burn Damage 10

4.5 End Fittings 11

5. CHEMICAL AND MATERIAL-IDENTIFICATION TESTS 12

6. FLAMMABILITY TESTS 12

7. ELECTRICAL TESTS 13

7.1 Specimens 15

7.2 RIV and Visual Corona Tests 15

7.3 Withstand Voltage Tests 16

7.4 Flashover Voltage Tests 18

7.5 Fog Atmosphere Test 19

7.6 Damage Comparisons 19

8. MECHANICAL TESTS 20

8.1 Tensile Tests 20

8.2 Hardness Tests 21

8.3 Diametral Compression Tests 23

9. ON THE CAUSES OF THE DAMAGE 23

9.1 Limitations of the Investigation 23

9.2 Burn Damage 26

9.3 Coating Loss 29

10. ON REDUCING THE INCIDENCE OF DAMAGE 30

10.1 Coating Loss 30

10.2 Burn Damage 30

11. SUMMARY 33

12. REFERENCES 35

i
LIST OF TABLES

1. Rod Designations and Descriptions.

2. Dimensions of Rods.

3. Coating Loss.

4. Burn Damage.

5. Flammability Tests.

6. Visual Corona Tests.

7. Tensile Tests of Insulator Lengths.

8. Diametral Compression Tests.

LIST OF FIGURES

1. Guying arrangement for Angissoq tower, not to scale. All

dimensions in feet (1 ft = 0.3048 m)

.

2. Insulator assembly.

3. Upper end of Rod XI showing two short carbonaceous tracks

adjacent to the end fitting.

4. Lower end of Rod X2 showing two short carbonaceous tracks

adjacent to the end fitting. The upper track is the less

severe of the two, and is situated in a small area in which

the coating is gone.

5. Upper end of Rod X3 showing substantial loss of coating.

Helical markings are faintly visible on the uncoated surface.

6. Upper end of Rod X4 showing substantial loss of coating.

The helical markings on the uncoated surface are clearly

visible

.

7. Upper end of Rod X5 showing substantial loss of coating.

8. Upper end of Rod X6 showing minor losses of coating.

Shallow carbonaceous tracks are faintly visible in the

uncoated areas

.

9. Upper end of Rod X7 showing a 1-in (25-mm) long carbonaceous

track. The longer streak on the left is a scuff mark.

10. Upper end of Rod X8 showing severe carbonaceous tracking

and charring. The rod appeared to have burned almost

completely through, with the last 3 percent of its cross

section having failed in tension. Some small areas of

coating loss are evident along the upper edge of the burn

damage. The fitting from this end of the rod is shown in

Figure 20.

11. Upper end of Rod X9 showing substantial loss of coating.

A carbonaceous track is evident near the middle of the

uncoated area.

li
LIST OF FIGURES

12. Upper end of Rod X10 showing severe carbonaceous tracking

and charring. The rod appeared to have burned almost

completely through, with the last 3 percent of its cross

section having failed in tension. The fitting from this

end of the rod is shown in Figure 21.

13. Upper end of Rod Xll showing a small area adjacent to the

end fitting where the coating had been lost, and a thin

carbonaceous track extending from this area onto the coating.

14. Upper end of Rod X13 showing severe carbonaceous tracking

and charring.

15. Upper end of Rod X15 showing severe carbonaceous tracking

and charring.

16. Upper end of Rod X16 showing severe carbonaceous tracking

and charring. See, also. Figures 17 and 18.

17. Upper end of Rod X16 showing long carbonaceous track on

the surface opposite to that depicted in Figure 16.

18. Lower end of Rod X16 showing carbonaceous track.

19. Upper end of Rod X17 showing substantial coating loss and

intermittent carbonaceous tracking both inside and outside

of the uncoated area.

20. Upper end fitting from Rod X8. See, also, Figure 10.

21. Sectioned (above) and reassembled (below) views of the

upper end fitting from Rod X10. Note the large void in

the potting compound near the tip of the conical wedge.

The void does not appear to have been open to the

atmosphere. See, also, Figure 12.

22. Sketch of end fitting showing coordinate system used for

identifying the angular locations of damage.

23. Dissected end fittings. Top row, left to right: X9 upper,

X14 lower, X9 lower. Bottom row, left to right: X8 upper,

X15 upper, X14 upper.

24. Results of RIV tests.

25. Aluminum-block end fitting for 0.79-in (20-mm) diameter rods.

All dimensions in inches (1 in = 25.4 mm).

26. H3M end fitting for 0.79-in (20-mm) diameter rods. Fitting is

rotationally symmetric about longitudinal center line. All

dimensions in inches (1 in = 25.4 mm).

27. Mod 4 end fiting for 0.79-in (20-mm) diameter rods. Fitting

is rotationally symmetric about longitudinal center line.

All dimensions in inches (1 in - 25.4 mm).

iii

FAILURE ANALYSIS OF FIBERGLASS INSULATOR RODS

by

Leonard Mordfin and Nixon Halsey

ABSTRACT

Failure analyses were carried out on a group

of coated f iberglass-reinforced-plastic insulator

rods that had sustained burn damage and loss of

coating in service on a Loran-C tower. The investigation included chemical, flammability, electrical

and mechanical tests as well as a variety of measurements and inspections. The burn damage, consisting

chiefly of carbonaceous tracking and charring, was

attributed primarily to the occurrence of electrical

discharges, from the energized end fittings to the

rods, under conditions in which the electrical leakage path resistances had been reduced by moisture

from rain, fog and ocean spray. The effects of this

damage on the structural integrity of the rods were

evaluated. Recommendations were made for reducing

the incidence of sucfr damage in the future, based

on the use of skirted insulator rods or more effective coating materials. The principal cause

of the coating loss was not positively identified.

This form of damage was not found to have serious

consequences except as a secondary factor which

may have contributed to the occurrence of some

partial electrical discharges.

Key Words: Breakdown, electrical; failure analysis;

fiberglass-reinforced plastics; flammability; guy

insulators; high-voltage tests; insulators, tower

guy; Loran C; pultruded rods; rods, insulator.
1. INTRODUCTION

Seventeen glass-reinforced-plastic (GRP) rod insulators were removed from a 625-ft (190-m) tower at the U.S. Coast Guard’s Loran-C

station in Angissoq, Greenland, and were shipped to the National Bureau

of Standards (NBS) for study. The rods had originally been installed on

the lower ends of the tower's top-loading elements in 1964, and burning

damage of the rods was discovered in December 1973. NBS was requested

to perform inspections, tests, measurements, and analyses in an attempt

to determine the cause of the burning; to speculate on the conditions

which may have led to the burning; and to provide recommendations for

avoiding burning in the future. This report presents the results of

this investigation.

The work was administered by the Engineering Mechanics Section of

NBS under the sponsorship and with the financial assistance of the U.S.

Coast Guard. High-voltage tests were carried out by A. L. Gabriel, C. M.

Keating, and J. E. Brown of the Bonneville Power Administration (BPA) of

the U.S. Department of the Interior, and flammability tests by Dr. G. D.

Mitchell of the NBS Fire Science Division. Acknowledgements are also

due to W. J. Pummer and Dr. R. W. Burke of the NBS Polymers and Analytical

Chemistry Divisions, respectively, for providing chemical analyses; to

H. Eisenstadt of the Defense Mapping Agency Topographic Center for

furnishing topographic information; and to 0. 0. Owens of the Engineering

Mechanics Section for assistance in mechanical testing.

2. THE ANGISSOQ INSTALLATION

The Angissoq installation is located on a small island near the

southern tip of Greenland, approximately 500 miles (800 km) south of the

Arctic Circle. The Loran tower is a one-megawatt, 100-kHz, top-loaded

monopole antenna. The power is pulsed at a rate of 160 per second with

a pulse duration of 40 to 50 microseconds. At the peak of the pulse the

voltage is 270 kV rms.

The guying arrangement for the tower is shown schematically in

Figure 1. The top-loading elements, fabricated from aluminum-conductor,

steel-reinforced cable, are electrically conducting and an integral part

of the antenna's radiating field. Twenty-four such elements, each 600

ft (183 m) long, are uniformly dispersed around the periphery of the

tower. Each element is guyed with galvanized cable anchored to the

ground, with an insulator assembly separating the top-loading element

from the guy wire. The insulator assembly, shown schematically in

Figure 2, consists of two GRP insulator rods in parallel with a corona

ring at the upper end. (Similar assemblies serve to insulate the structural guys from the tower but these are not of concern in the present

study.

)

2
3. THE SPECIMENS

Seventeen GRP rods with end fittings were furnished for this

study, all of which had been removed from service in the insulator

assemblies of the top-loading elements. As received, each rod carried

one or more numerical designations and four of the rods were also marked

to indicate which end had been oriented toward the top or the bottom of

its insulator assembly. In the case of rods which had served as a companion pair in the same insulator assembly, both carried the same

numerical designation. To avoid confusion, therefore, all of the rods

were renumbered for the purposes of this study. The first column of

Table 1 shows the NBS designation for each rod and the second column

lists the designations and other markings which were attached to the

rods as they were received at NBS.

The rods had been manufactured by a process similar to pultrusion

and consist of unidirectional, continuous, fiberglass roving in an epoxy

matrix. The resin content of the rods was nominally 24+3 percent.

The rods were coated with epoxy resin that was loaded with a titanium

dioxide pigment. The specified diameter of the rods before coating was

0.775 (+0.010, -0.005) in [19.69 (+0.25, -0.13) mm], and the specified

thickness of the coating was 0.005 to 0.010 in (0.13 to 0.25 mm). The

rated tensile strength of the rods was 35 000 lbf (156 kN)

.

The end fittings were conventional open spelter sockets designed

for 3/4-in (19-mm) diameter wire rope. They were forged from steel and

galvanized.

In fabricating an insulator assembly, small holes, 1 in (25 mm)

deep, were drilled concentrically into each end of an insulator rod

having a length of 14.5 ft (4.42 m) . The end fittings were slipped over

the rods and a conical metal wedge, nominally 1-3/4 in (44 mm) long and

0.860 in (21.8 mm) in diameter*, was driven into each small hole. This

split the rod ends and wedged them into a roughly conical shape. The

end fittings then were alined concentrically with the rod, and the

openings in the sockets where the rods emerged were sealed with a plastic

compound. Finally, the sockets were potted with an epoxy-polyamide-grit

mixture, and the mixture was cured.

All of the rods, except for X12, had been put into service in 1964

and were removed some nine or ten years later. Rod X12, which had been

manufactured with the others, was first installed toward the end of this

period as a replacement for Rod X10, and was subsequently removed about

one month later. Thus, while the coatings on sixteen of the rods had

weathered to a pale yellow, the coating on Rod X12 was still white.

*Actual dimensions of one wedge (see Section 5) were 1.79 and 0.88 in

(45 and 22 mm), respectively.

3
TABLE 1. Rod Designations and Descriptions

NBS No. As-received markings Nature of coating Visible helix

XI 1, Cl, 9 of 18 brittle yes

X2 2, C2, bottom, top brittle no

X3 C8 tough; not well-adhered yes

X4 C8 very f laky yes

X5 9, bottom, top f laky yes

X6 10, 6 of 18 britt le no

X7 12 britt le no

X8 C13 , 16 of 18 very brittle no

X9 C13, 4 of 18 brittle yes

X10 15, C15 tough; well-adhered no

Xll 15, 12 of 18 well-adhered no

X12 15A well-adhered no

X13 18, 11 of 18 well-adhered no

X14 18, 13 of 18 well-adhered no

X15 19, 17 of 18 well-adhered no

X16 20, 7 of 18, bottom well-adhered no

XI

22, 2 of 18, bottom f laky no

4
The end fitting on the upper end of Rod X16 was somewhat smaller

than, although of the same general type as, the other end fittings.

Photographs of portions of fifteen rods, showing damage sustained

in service, are reproduced in Figures 3 through 19 and are discussed

below. These figures are arranged in order of the rod designation numbers. Rods X12 and X14 are not included; these rods sustained only

slight, if any, damage.

In general, the rods exhibited two different kinds of damage. The

first was burn damage, which appeared as scorched surface areas (not

visible in the photographs), as carbonaceous tracks (see, for example.

Figs. 9 and 17), or as charred regions (see, for example , Fig. 14),

depending upon the severity of the damage. The second kind of damage

was loss of coating (see, for example, Figs. 7 and 8). Closer examination of the rods revealed that the coatings were not al] the same.

Instead, there appeared to be at least two different kinds. One was

relatively tough and usually tended to be rather well-adhered to the GRP

substrate. The second was relatively brittle and generally tended to

flake off more or less easily with the point of a penknife. The general

nature of the coating on each rod is described in the third column of

Table 1.

During the manufacturing process, before final curing, the rods

were wrapped with a special tape which was later removed before the

coating was applied. This produced a helical track on the surfaces of

most rods (see, for example. Fig. 6) which was visible through some of

the coatings. The last column in Table 1 indicates those rods on which

the helical track was clearly visible through the coatings.

4. INSPECTIONS AND MEASUREMENTS

4.1 Dimensional Measurements

Measurements were made on the rods and are reported in Table 2.

The lengths of the rods, between end fittings, were quite uniform and

averaged 13.91 ft (4.24 m) . The outer diameter of each rod was measured

at five locations and averaged. The coating thickness on most of the

rods was also measured by peeling off a small piece of it. On four

rods, however, the coating was so well-adhered that this could not be

accomplished

In all but one case (Rod X8) the coating thickness was within the

specified limits (Section 3). The uncoated diameters, calculated by

subtracting two coating thicknesses from the respective outer diameters,

also fall within the specified limits, with one exception (Rod X4)

5
TABLE 2. Dimensions of Rods

NBS

No.

Length between

fittings

Average outer

diameter

Average coating

thickness

ft (m) in (mm) in (mm)

XI 13.91 (4.24) 0.789 (20.0) 0.007 (0.2)

X2 13.92 (4.24) .796 (20.2) .006 ( -2)

X3 13.91 (4.24) .783 (19.9) .007 ( -2)

X4 13.91 (4.24) .780 (19.8) .009 ( -2)

X5 13.91 (4.24) .788 (20.0) .006 ( .2)

X6 13.92 (4.24) .794 (20.2) .005 ( .1)

X7 13.91 (4.24) .794 (20.2) .006 ( -1)

X8 13.90 (4.24) .791 (20.1) .004 ( -1)

X9 13.91 (4.24) .792 (20.1) .006 ( .1)

X10 13.92 (4.24) .790 (20.1) .010 ( .2)

Xll 13.93 (4.24) .795 (20.2) .008 ( .2)

X12 13.93 (4.24) .787 (20.0) a a

X13 13.91 (4.24) .789 (20.0) a a

X14 13.90 (4.24) .805 (20.5) a a

X15 13.92 (4.24) .790 (20.1) .005 ( .1)

X16 13.92 (4.24) .792 (20.1) a a

XI

7

13.91 (4.24) .789 (20.0) .006 ( .2)

a. Not measured

6
4.2 Coating Loss

Coating loss ranged from zero, or nearly zero, on seven rods which

had well-adhered coatings, to major losses on six rods which had flaky

or poorly adhered coatings. Four rods with brittle coatings fell into

an intermediate category which experienced only the loss of a chip here

or there. Table 3 shows, for each rod, the amount of coating loss in

square inches (and square centimeters) and the amount of the loss as a percentage of the total surface area. With one trivial exception, on

every rod which experienced some loss of coating more than two-thirds

(and frequently more than 90 percent) of the loss occurred in the upper

one-third of the rod length. (The manner in which the upper ends of the

rods were identified is described later.)

It is interesting that of those rods which had served as companion

pairs in single insulator assemblies (X3 and X4 , X8 and X9, X10 and Xll,

Xll and X12, X13 and X14) both exhibited major coating loss or both

exhibited negligible coating loss. In other words, in none of the five

companion pairs did one rod show major coating loss while its companion

showed negligible coating loss.

Of the six rods which experienced major coating loss, four (Table 1)

had visible helices. Only one rod with a helix visible through its

coating did not experience major coating loss.

4.3 Burn Damage

In this report the expression "burn damage" is used to describe all

damage which apparently resulted from electric arcing, flashover and/or

lightning, whether or not a true ignition ever took place. It thus

includes minor scorching and carbonaceous tracking as well as heavy

charring

Upon receipt at NBS four of the seventeen rods carried markings to

indicate which ends of the rods had been attached to the upper and/or

lower ends of their respective insulator assemblies (Table 1) . On three

of these (i.e., all except Rod X2) most of the burn damage was toward

the upper end. This is consistent with the physical arrangement of the

tower, which ordinarily places the greatest electrical stress on the

upper ends of the insulator rods. On this basis, and strictly for the

purpose of identification, those ends which exhibited the most severe

burn damage were arbitrarily designated as the upper ends.

Table 4 lists the total area of burn damage for each rod. In

making this measurement, surface scorching which produced only a discoloration of the coating and no measurable loss of material was not

included. The figures referenced in the table are those that show the

most severe burn damage for each rod. From the table and the figures it

is evident that five rods suffered severe burn damage, two of them

having burned virtually all the way through near their upper end fittings.

(The upper end fittings from these two rods are shown in Figs. 20 and

21 ).
TABLE 3. Coating Loss

Rod

No.

Fig.

No.

Surface area of

lost coating

Pet of total

surface area

Pet of tot;

in upper l/[

. 2

in (cm

2

) pet pet

XI — 1 ( 6) 0.2 0

X2 — 2 ( 13) .5 75

X3 5 35 (226) 8.5 100

X4 6 55 (355) 13.3 95

X5 7 33 (213) 8.0 76

X6 8 3 ( 19) .7 67

X7 — 2 ( 13) .5 100

X8 — 20 (129) 4.8 90

X9 11 39 (252) 9.4 98

X10 — 0 ( 0) 0 -

Xll 13 ^0 ( 1) ^0 100

XI

2

— 0 ( 0) 0 -

X13 — 0 ( or 0 -

X14 — 0 ( 0) 0 -

X15 — 0 ( 0) 0 -

X16 — 0 ( 0) 0

-

X17 19 16 (103) 3.9 81

a. Only those

principal

figures

area of

which depict

coating loss

the

are

listed

.

8
TABLE 4. Burn Damage

Rod

No.

Fig.

No.

(

a ' Surface

burn

area of

damage

Minimum crosssectional areaAngular location of

most severe burn

in

2 , 2

(cm ) pet deg

XI 3 0.2 ( 1. ) — -15

X2 4 0.5 ( 3. ) — +45

X3 — 0.03 ( 0.2) — -60

X4 — 0.5 ( 3. ) — -90 to 0

X5 — 1.1 ( 7. ) — -90 to +60

X6 — 0.01 ( 0.1) — +75

X7 9 0.2 ( 1. ) — +75

X8 10 22.9 (148. ) 3 -45

X9 11 1.8 ( 12. ) — -75 to -30

X10 12 27.6 (178. ) 3 -90 to +30

Xll 13 0.03 ( 0.2) — -75

X12 — 0.2 ( 1. ) — -30 to 0

X13 14 20.8 (134. ) 58 +90

X14 — 0.00 ( 0.0). — -

X15 15 26.0 (168. ) 79 -60

X16 16 26.2 (169. ) 67 +30

XI

19 0.6 ( 4. ) — +75

a. 'Only those figures which clearly depict

the principal area of burn damage are

listed

9
For the five rods which experienced severe burning, Table 4 lists

the minimum remaining cross-sectional area of each rod as a percentage

of the original cross-sectional area. These percentages are only approximate, since it was impossible to determine the depth of the char on

these rods without introducing additional damage.

It had been suggested that much of the burning damage may have been

caused by arcing from the corona ring to a rod, or by arcing between

rods. In order to examine this possibility consider Figure 22 which

shows, schematically, an end view of the end fitting at the upper end of

a rod. In the physical arrangement of the insulator assemblies, the two

companion rods are closest to each other along axis X-X; the shortest

path between a corona ring and a rod is also along this axis. The

location of the most severe burning damage on each rod was tabulated, in

Table 4, in terms of its angular departure from the X-X axis. The angle

0 was used for this purpose. Since the end fittings are symmetrical

about their Y-Y axes, all of the tabulated angles were arbitrarily

chosen to fall within the semicircle ranging from -90 to +90 degrees.

The fact that the preponderance of angles is not concentrated at 0

degrees suggests that the burn damage was not caused by arcing between

companion rods or between rods and corona rings.

This finding was confirmed by examination of those pairs of rods

that had served as companions in the same insulator assemblies (X3 and

X4, X8 and X9 , X10 and Xll, Xll and X12, X13 and X14). In no instance

was the burn damage on both rods of a pair located in such a way that it

could have resulted from arcing between the rods.

An interesting observation resulted from comparison of Rods X10 and

X12. (X10 was a severely burned rod and X12 was its replacement.)

While the burn damage on X12 was extremely slight, it appeared to be in

essentially the same location as the burn damage on X10.

As pointed out earlier, most of the burn damage on most of the rods

which experienced it was concentrated near one end of each rod. However,

four rods (X2 , X7 , X16, X17) also experienced some burn damage near

their other ends. This is depicted, for example, in Figures 4 and 18.

Fortunately, three of these rods (X2, X16, and X17) were received with

markings designating their upper and/or lower ends.

4.4 Relationship between Coating Loss and Burn Damage

On the basis of the examinations of coating loss and burn damage,’'

certain characteristics of the relationship between the two are evident.

Six rods experienced major coating loss (Table 3), and five rods

experienced severe burn damage (Table 4), but only one rod (X8)

experienced both.

10
Seven rods experienced virtually no coating loss (Table 3), and

four rods experienced negligible burn damage (Table 4) , but only two

rods (Xll and X14) experienced neither type of damage to a substantial

extent

Of the five rods which experienced severe burn damage four had

well-adhered coatings with no coating loss.

On each of the six rods which experienced major coating loss, most

of the burn damage occurred in the uncoated regions of the rods.

4.5 End Fittings

During preliminary examinations of the insulators, before the

formal investigation was started, the upper end fitting from Rod X10 was

cut in half to permit examination of the potted end of the rod. As

shown in Figure 21 a rather large void was found in the center of the

rod, extending from the tip of the conical wedge. The void appeared to

have resulted from entrapment of an air pocket during the potting process. Since this end fitting was adjacent to that part of the rod which

had burned severely, it was suspected that the void may have been a contributing factor. It was hypothesized that the void may have promoted the development of electrical corona or, alternatively, that it

may have accumulated moisture due to rain or ocean spray and thereby

created a conductive path for electrical leakage current.

With a view toward the possible development of a useful qualitycontrol tool, the feasibility of detecting voids inside the end fittings

by nondestructive inspection techniques was explored. Several ultrasonic and radiographic techniques were used but none was adequate for

the task [1]*. The interface between the end fitting and the potting

compound could be detected using fast-neutron radiography, but, because

of the number of material interfaces and the different attenuation

characteristics of the different materials, none of the techniques was

capable of showing the conical wedge with adequate detail.

Subsequently, six end fittings were selected for dissection to

permit visual examination for internal voids. Two of these fittings

were adjacent to severely burned sections of rod and one was near a deep

carbonaceous track. The dissections revealed no voids in any of the six

fittings and showed, in the case of the severely burned rods, that the

burns did not extend more than a centimeter or so into the fittings.

See Figure 23. These observations suggest that the void in the upper

end fitting of Rod X10 was found purely by coincidence, and that such

voids are probably unrelated to the principal cause of burning damage in

the Angissoq insulators.

*Numerals in square brackets refer to similarly numbered references

cited in Section 12.

11
5. CHEMICAL AND MATERIAL- IDENTIFICATION TESTS

The wedge was removed from the lower end fitting of Rod XI 5. Mass

and volume measurements on this wedge showed it to have a density of

0.103 lb/in 3 (2.85 Mg/mJ

) , and hardness tests indicated a hardness of 64

on the Rockwell B scale. These measurements, together with the appearance and the non-magnetic nature of the wedge, suggest that it was

fabricated from a moderately high-strength aluminum alloy.

A small piece of Rod X9 was ground up and formed into a pellet, and

its infrared transmission spectrum was determined using a spectrophotometer. This determination revealed that the resin used in manufacturing

the rods was, indeed, epoxy and not polyester, which is more commonly

used in pultrusions.

In view of the marine atmosphere to which the insulators had been

exposed, some indication of the salt contamination of the insulator

surfaces was considered desirable. A relatively sensitive indicator of

the presence of sodium chloride, the "taste test", was dutifully applied

to all seventeen of the insulator rods with negative results in every

instance. In order to arrive at a more quantitative measure, four short

lengths of rod with intact coatings were then cut from Rod X9. Each was

immersed in a 10-percent hydrochloric acid solution for fifteen minutes

and removed, and then the sodium content in the solution was determined

by flame emission spectrometry with repetitive optical scanning. The

results for the four samples, expressed as the quantity of sodium per

unit of surface area of the rod samples, were 1.30, 0.385, 0.910 and

1.56 g/m2

. The significance of these measurements is discussed in

Section 9.1.

6. FLAMMABILITY TESTS

A series of tests was conducted to evaluate the flammability of the

rod material and to explore the influences of the coating and of salt

contamination on the flammability. An adaptation of the Limiting Oxygen

Index (LOI) test [2] was selected for this purpose. This test method

provides a means for studying the effect of changes in a material on its

flammability. While the results do not necessarily correlate with

actual use conditions, the method has been described as the most reproducible test available for fire-retardant materials [3]. In the basic

method a thin flat specimen is vertically supported in a column containing a slowly rising mixture of oxygen and nitrogen, the top of the

specimen is ignited, and the minimum concentration of oxygen (the LOI)

that will just support combustion under conditions of candle-like burning

is measured.

Since the insulator rods are cylindrical in shape rather than flat,

preliminary tests were performed to see whether cylindrical specimens

could be used. Undamaged lengths of Rod X16 were employed for this purpose. A thin flat specimen machined from one length of rod was tested

first. It produced an LOI of 24 percent. Next, a length of full cross

12
section was tested. Again, an LOI of 24 percent was obtained, suggesting

that either (a) the shape of the specimen was not a significant factor,

or (b) the shape effect was effectively canceled by an opposite effect

resulting from the removal of the coating on the flat specimen. Finally,

a test was conducted on a thin disk of full cross section, supported

vertically. While an accurate determination of the LOI was not possible

with this configuration, this test revealed that the coating material by

itself was far more flammable than the basic GRP rod material, although

this was not obvious in tests of full-sized specimens. Presumably, the

mass of the full-sized specimens acts as a heat sink under candle-like

burning conditions, preventing separate combustion of the coatings.

In the main series of tests, in which a similar but different test

apparatus was used, eight full-sized specimens were tested after having

been preconditioned as follows:

two specimens were tested in the as-received condition;

two specimens were washed with a small amount of warm water and

detergent and wiped dry;

two specimens were immersed in a five-percent saltwater solution for seven days, then removed and wiped dry; and

the coatings were carefully peeled from the last two specimens.

The first six of these specimens were cut from an undamaged part of Rod

X10 which had a well-adhered coating. The last two specimens were cut

from an unburned part of Rod X8 which had an easily removable coating.

The results of the flammability tests are given in Table 5. The

standard deviation of the mean LOIs from the first three sets of tests

is less than one percentage point; this is within the range obtained

with nominally identical specimens [2], This suggests that the flammabili ties of the specimens from Rod X10 were not significantly affected

by the three preconditioning treatments that were applied to them. On

the other hand, the specimens from Rod X8, which had their coatings removed, appeared to be somewhat less flammable than the specimens from

Rod X10. It is not immediately obvious whether this difference is due

to the relatively high flammability of the coating or whether it results

from more basic differences in the material characteristics of the two

rods

.

7. ELECTRICAL TESTS

In order to explore the possibility that burning was caused by

leakage currents in the insulator rods, an attempt was made to measure

the electrical resistances of the rods. For this purpose a megohmmeter

having a range of 10 14 ohms (100 Tft) and an applied voltage of 1 kV dc

was used with the leads spaced 1 in (25 mm) apart on the rod. A meter

i
TABLE 5. Flammability Tests

Test

No.

Rod

No. Condition

Limiting

Oxygen Index

volume pet

FI X10 as received 30

F2 X10 as received 27

Avg 28.5

F3 X10 washed 28

F4 X10 washed 27

Avg 27.5

F5 X10 saltwater immersed 30

F6 X10 saltwater immersed 27

Avg 28.5

F7 X8 coating removed 28

F8 X8 coating removed 35

Avg 31.5

14
reading of infinity was consistently obtained. The test was repeated on

lengths of rod that had been immersed in saltwater for several days and

then dried. The same result was obtained, suggesting that substantially

higher voltages or high frequencies, or both, would be required to

produce measurable leakage currents. Subsequently, eight insulators were

preconditioned and submitted to the Bonneville Power Administration for

a series of high-voltage tests.

The unavailability of high-voltage, high-frequency testing apparatus

necessitated that these tests be conducted with 60-Hz voltages, although

it is recognized that this leaves some question as to the applicability

of the test results to the problem at hand.

7.1 Specimens

The eight insulator rods selected for this purpose had all experienced only minor burn damage. They were preconditioned in the same

manner as the flammability specimens (Section 6). In order to possibly

gain some additional information from the high-voltage tests, seven of

the insulator rods chosen had brittle or flaky coatings while the eighth

(Xll) had a well-adhered coating. The two insulator rods which were

preconditioned by having their coatings removed had already suffered

major coating loss. Of the other six rods, five were chosen with only

minor loss, while the sixth (X17) had major coating loss. The rod

designations and their preconditioning treatments were as follows:

X6 and XI

7

X2 and Xll

XI and X7

X4 and X5

as received

washed

immersed in saltwater

coatings removed.

Except as noted hereafter, all of the high-voltage tests were

with pairs of similarly conditioned rods mounted in insulator

(see Fig. 2) with corona rings at the upper (energized) ends,

results of the tests [4] are summarized and discussed below.

performed

assemblies

The

7.2 RIV and Visual Corona Tests

A radio influence voltage (RIV) is a high-frequency voltage generated as a result of ionization and may be propagated by conduction,

induction, radiation or a combination of all three. The RIV of an

insulator is the radio-frequency voltage produced, under specified

conditions, by the application of a 60-Hz voltage. In certain situations

increased RIV levels are believed to indicate a degradation of dielectric

quality. Results of RIV tests on the four insulator pairs are shown

graphically in Figure 24. The results for the insulators in the three

coated conditions all plot within a band that is relatively narrow in

comparison with the probable test-to-test variability on nominally

identical insulators. The insulators which had their coatings removed

showed higher RIVs up to applied voltages of approximately 200 kV.

Above this voltage level the results for the uncoated rods plot within

the same band as those for the coated rods.

15
Using the same power supply, visual corona tests were performed on

the four insulator assemblies to assist in locating the sources of the

radio-influence voltages. As the applied voltage was increased, the

first visual corona on each insulator assembly appeared at the junction

of an insulator rod with its upper end fitting. The inception voltages

for these visual coronas are listed in Table 6. Note that these voltages

are different for the two insulators in each assembly. Note, also, the

low inception voltages for the two rods whi ch had their coatings removed.

This observation correlates with the higher RIVs measured with the

insulator assembly that was fitted with these rods.

As the applied voltage was further increased, corona appeared

around the corona rings of the insulator assemblies. The onset voltages

for these coronas were all in the narrow range of 189 to 207 kV rms

,

which is consistent with the relatively uniform RIV response of the four

assemblies above 200 kV.

None of the insulator rods experienced any visible damage as a result of these tests.

7.3 Withstand Voltage Tests

Following the RIV and visual corona tests the applied voltage on

each insulator assembly was quickly raised to 500 kV and maintained for

one minute. Again none of the rods experienced any visible damage.

The applied voltage was then removed and the assemblies were exposed to a simulated rainfall. After being thoroughly wetted the assemblies were subjected to a voltage of 100 kV, with the following results:

The insulator assembly containing the rods which had been immersed

in saltwater (XI and X7) failed immediately. Heavy corona appeared at

the junctions of the rods and their upper end fittings and Rod X7 developed a carbonaceous track over a length of about 12 in (300 mm) from

its upper end fitting. This track penetrated the coating and passed

directly through a 1-in (25-mm) long track (Fig. 9) that existed prior

to the test. The GRP substrate did not appear to have been damaged

significantly. Both sides of the track were covered with soot. Rod XI

suffered little, if any, burn damage.

The insulator assembly containing the rods which were tested in the

as-received condition (X6 and X17) failed approximately 15 seconds after

energization. Scintillation developed along the upper part of Rod X6

and produced a carbonaceous track, approximately 2 in (50 mm) long, near

the upper end. Interestingly, this track developed on a previously

undamaged portion of the rod’s surface, although prior damage, in the

form of short carbonaceous tracks and lost coating, existed nearby (Fig.

8). Rod X17 (which had major coating loss) was undamaged.

16
TABLE 6. Visual Corona Tests

Rod

No. Condition

Inception

voltage

kV

X6 as received 141

X17 as received 186

Avg 164

X2 washed 185

Xll washed 192

Avg 188

XI saltwater immersed 147

X7 saltwater immersed >205

Avg >176

X4 coating removed 65

X5 coating removed 58

Avg 62

17
The other two insulator assemblies survived one minute at the 100-

kV level without burning and the voltages on these were then increased

to 200 kV.

The insulator assembly containing the washed rods (X2 and Xll)

failed after approximately 30 seconds at this voltage. Heavy corona

appeared at the junctions of the rods and the upper end fittings and

scintillation developed along the upper portions of the rods. A 1 1/2-

in (38-mm) long carbonaceous track near the upper end of Rod X2, which

existed prior to this test, was extended for another 2 1/2 in (64 mm)

with considerable soot formation. The new damage penetrated the coating

at intermittent points but did not appear to have damaged the substrate.

Rod Xll suffered some localized scorching of the surface which did not

look like anything more severe than a permanent discoloration of the

coating.

The insulator assembly containing the rods which had their coatings

removed (X4 and X5) survived one minute at the 200-kV level without

failure. Scintillation developed along the upper part of Rod X5 and

aggravated a 3-in (76-mm) long carbonaceous track near the upper end

that existed prior to the test. Rod X4 was not damaged in this test.

7.4 Flashover Voltage Tests

Two insulator assemblies were then subjected to both dry and wet

flashover tests, one with coated rods and one with the rods which had

their coatings removed. Because of the damage to the coated rods in the

previous tests, a matched pair was not available and, accordingly, Rods

XI (saltwater immersed) and Xll (washed) were tested together.

In the dry tests a voltage of 400 kV was applied and was then increased at a rate of 10 kV/s until the insulators flashed over. In

the wet tests 50 kV were applied and then increased at the same rate

until flashover occurred. The observed flashover voltages were as

follows

Dry Wet

flashover flashover

Rod Nos. voltage vol tage

kV kV

XI & Xll 943 486

X4 & X5 883 530

These tests caused only minor burn damage in regions of the rods where

damage from previous tests already existed. Rod Xll experienced further

scorching of its surface over a length of approximately 24 in (600 mm)

18
from its upper end fitting. The 3-in (76-mm) long track on Rod X5,

mentioned above (Section 7.3), was widened from about 1/8 in (3 mm) to

about 3/16 in (5 mm) at some points.

7.5 Fog Atmosphere Test

The insulator assembly with Rods XI and Xll was then installed in a fog chamber and a voltage of 280 kV was applied and thereafter maintained

constant. Fog generation was initiated and allowed to accumulate. As

the surfaces of the rods became wetted, leakage current increased and

burning spots began appearing near the ends of the rods. Eventually,

scintillation developed over the full lengths of the rods and smoke and

steam were observed rising from the surfaces. As the fog became denser,

long arcing paths appeared and after 87 minutes severe burning and

flashover developed on Rod XI.

As a result of this test. Rods XI and Xll suffered carbonaceous

tracking over most of their lengths, with the worst damage occurring

near their lower ends. Rod XI was the more severely burned of the two,

with tracks up to 1/2 in (13 mm) wide. Most of the tracking on Rod Xll

had the appearance of fine black lace, consisting of thousands of disconnected hairline tracks generally oriented in the transverse direction.

The more severe tracks on both rods were surrounded by considerable soot.

7.6 Damage Comparisons

Comparisons of the burn damage experienced in service at Angissoq

with that suffered in the above electrical tests provided some interesting observations.

The carbonaceous tracks produced in the electrical tests tended to

be wider but not as deep as those sustained in service. The tracks produced in the tests were accompanied by considerable soot, on both sides

of the tracks, whereas the rods as received from Angissoq were clean.

It is considered unlikely that soot had accumulated at Angissoq and had

subsequently been washed away by rain. NBS attempts to remove the soot

from the rods used in the electrical tests met with only limited success

when plain water was used. A mildly abrasive cleanser had to be used to

remove all of it.

In situations where burning was experienced, whether in service or

in the tests, all or most of the damage to an insulator assembly tended

to be concentrated in only one of the two companion insulator rods.

19
8. MECHANICAL TESTS

8.1 Tensile Tests

A series of tensile tests was performed to investigate the effects

of service-incurred burn damage on the structural integrity of the rod

insulators. Except as noted, all of these tests were carried out in a 100 000-lbf (445-kN) capacity, horizontal, hydraulically powered testing

machine [5] at a crosshead speed of 0.75 in/min (0.32 mtn/s).

The first two tests were conducted full-scale on complete insulators.

To mount the insulators in the machine, lugs which were clamped in the

machine's wedge-type jaws were used to grip the clevis pins in the

insulator end fittings. Rod X14, which had experienced no visible

damage of any kind in service, was tested first in order to establish

baseline data for comparison purposes. At a load of 44 000 lbf (196 kN)

a thin sliver of the rod material, about 3/8 in (10 mm) wide, split off

at the lower end fitting. The remainder of the rod continued to carry

load and attained a maximum load of 53 200 lbf (237 kN) , at which point

it disintegrated explosively. This value exceeds the 35 000-lbf (156-

kN) rated capacity of the rods by a comfortable margin.

The second full-scale test was performed on Rod X15, which had been

severely damaged in service. This rod had burned about a fourth of the

way through at about an inch from its upper end fitting (Fig. 15).

Measurements indicated that about 79 percent of the original crosssectional area remained, but it was impossible to determine how much of

this remaining cross section was structurally functional and how much of

it was char. The rod sustained a maximum tensile load of only 16 000

lbf (71 kN). At this point the rod sheared in two longitudinally, the

split emanating from the base of the burn. The remainder of the rod

broke off from the charred region just inside the upper end fitting.

The low value of maximum load suggests that relatively little of the

remaining cross section of the rod was undamaged by the burning.

In order to establish the degree of damage which rods can withstand

without a degradation of structural performance, three lengths of rod

were then tested to determine the full strength of the product. These

were cut from undamaged sections of rod insulators. Since commercial

end fittings, including those used in the Angissoq system, generally

introduce geometric discontinuities and stress concentrations which

prevent the full strengths of pultruded rods from being attained [6],

special end fittings had to be used for these tests. Three such end

fittings have been developed at NBS; the aluminum-block end fitting [7],

the H3M end fitting [8], and the Mod 4 end fitting [8]. It is usually

impossible to determine beforehand which of these three end fittings

will work best on a given type of pultruded rod. Consequently, it was

decided to use all three. The three had originally been developed for

1/2-in (13-mm) diameter rod; scaled-up versions (Figs. 25-27) were therefore fabricated for the present tests. The end fittings were mounted on

their respective rod specimens with NBS C2W3 potting compound [8].

20
The results of the tests are given in Table 7. It may be seen that

the Mod 4 end fitting worked best with this rod material, and that the

rods have full strengths of at least 65 700 lbf (292 kN).* By contrast,

the full-scale test of undamaged Rod X14, with the manufacturer's end

fittings, attained only 53 200 lbf (237 kN) , which is 19 percent less.

It would seem, therefore, that an insulator rod, of the type under consideration here could sustain a 19 percent loss of cross-sectional area without any loss of load-carrying capacity because the strength of the insulator would still be determined by the limitations of the end fittings.

(This, of course, does not apply to losses of cross-sectional area that

are produced by sharp notches, which introduce high stress concentrations

of their own, but rather to more gradual losses such as would be expected

from burn damage.) This conclusion is supported by the results of other

studies which showed that, depending upon the efficiency of the end

fittings, losses of cross-sectional area of 10 to 30 percent could be

sustained without any loss of tensile load-carrying capacity [7,9].

Considering that the insulators have undamaged strengths which far

exceed their 35 000 lbf (156-kN) rated strengths it would appear that

even greater losses of cross-sectional area — up to 47 percent — could

be sustained without reducing their load-carrying capacities below the

rated value.** The significance of this is that insulator rods which

have experienced minor bum damage do not pose a threat to the structural

integrity of the antenna system and do not have to be replaced for this

purpose. On the other hand, rods which have suffered major burn damage

should be replaced even if the loss of cross-sectional area appears to

be less than 47 percent because charring may have rendered part of the

remaining cross section unsound.

8.2 Hardness Tests

Hardness tests were made on the cylindrical surfaces of several of

the insulator rods to obtain some indication of the degree of cure of

the material. In general, these tests were unrewarding. The measurements exhibited abnormally high scatter, even from one location to

another on the same rod. It is surmised that this scatter may have

resulted from differences in the coating thickness and in the degree of

adhesion of the coating to the substrate from one point to the next. To

eliminate these variables, the tests were then repeated on transverse

cross sections of short lengths of the rods. In this case, hardness

numbers of 69 or 70 on the Rockwell E scale were consistently obtained.

This exceeds the hardnesses of uncoated, post-cured, polyester pultrusions [10]. Since polyester and epoxy laminates generally exhibit

*This suggests a tensile strength of approximately 140 000 lbf /in 2

(970 kPa) on the basis of the cross-sectional area of the uncoated rod.

**Note that on the only two rods which actually sustained complete failure

in service (X8 and X10), the tensile fractures were not incurred until

about 97 percent of the cross-sectional areas had been burned away. This

suggests that the tensile loads on the rods, at the instants of failure,

were of the order of only 2000 lbf (9 kN).

21
TABLE

7.

Tensile

Tests

of

Insulator

Lengths

co CO 3 3 3 3

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22
hardnesses within the same range [11], it is reasonable to conclude that

the epoxy-based insulator rods from the Angissoq installation were, in

fact, fully cured. There is no way of determining, however, whether the

rods were in this condition at the time they were installed or whether

the curing process gradually proceeded to completion under the ambient

service conditions over the years since installation.

8.3 Diametral Compression Tests

A previous study [12] showed that changes in the wet dielectric

strength of a pultruded rod product, resulting from changes in the

material constituents or the manufacturing conditions, could be correlated with changes in the transverse tensile strength of the product.

Accordingly, diametral compression tests were performed on 0.2-in (5-mm)

thick disks cut from undamaged portions of several of the insulator rods

in order to measure their transverse tensile strengths. The procedure

developed in previous investigations on other pultruded rod products

[8,13] was followed. Although reasonably good consistency was obtained

with disks from the same rod, Table 8 shows rather large differences

between rods.

These differences are not immediately explainable. The range of

transverse tensile strength values falls within the range of values

measured on a variety of commercially available pultruded rod products;

but variations of this magnitude have not previously been observed with

any single product, except when comparing virgin material with that

which had been weathered outdoors for several months or years.

9. ON THE CAUSES OF THE DAMAGE

9.1 Limitations of the Investigation

The design of this investigation, like most, was based upon certain

reasonable assumptions. In this case, however, there is evidence that

some of these assumptions were invalid and, as a consequence, the interpretation of the test results is less than straightforward. It is

important to recognize this limitation before proceeding to a discussion

of the central questions addressed by the investigation.

Table 8 indicates a major difference between the transverse tensile

strengths of three of the insulator rods as compared with the strengths

of three other rods. It is unlikely that the lower strength values

resulted from a degradation of the fiber/matrix bonds due to solar

radiation or moisture absorption, or that the higher values are indicative of a more complete cure of the matrix having been attained in

service, since all of the insulator rods (except Rod X12) were exposed

to essentially the same environment. Similarly, it is unlikely that the

lower values resulted from damage incurred by electrical discharges

within the rods (punctures) , since there was no evidence of internal

tracking damage or voids in any of the rods. On the other hand, it is

significant that the three insulator rods which had low transverse

23
TABLE 8. Diametral Compression Tests

Rod No. Average transverse tensile strength

lbf/in 2

(MPa)

X3 1800 (12)

X8 2000 (14)

X9 2000 (14)

X10 3400 (23)

X13 3500 (24)

X16 3600 (25)

24
strengths also had poorly adhered coatings, while those rods that exhibited high transverse strengths also had well-adhered coatings. This

observation suggests a reasonable likelihood that all of the insulator

rods were not manufactured identically; and that there were, in fact, at

least two distinct batches of rods involved in the group which was

received for study. (Consideration of the helices observed on certain

rods (Table 1), and comparison of those data with Table 8, suggest that

there may have been even more than two batches involved.) Thus, the

various tests which were designed to detect differences attributable to

service-induced damage or to laboratory-imposed conditions may actually

have yielded results which are clouded by unexpected, inherent, manufacturing differences.

In a similar vein, the preconditioning treatments applied to the

rods for some of the test series were based upon the assumption that the

rods, as received, were highly contaminated with salt as a result of

prolonged exposure to a marine environment. It appears that this may

not actually have been the case. Consider the sodium contamination

measured on the surface of one of the rods (Section 5). If it is assumed

that this sodium was present principally as sodium chloride, and that it

was deposited on the rod by airborne ocean spray, then it may be shown

by calculations that the quantity of sodium present represents the

residue from the evaporation of a film of seawater only about 0.1 mm

thick. This is an extremely small quantity of salt in comparison with

the extensive depositions which were observed on GRP rods that had been

exposed to a simulated marine environment in the laboratory for only

2000 hours [13]. Consider, also, the differences in appearance between

the burn damage on the as-received rods and that experienced in the

electrical tests. While the latter tests produced considerable soot on

the rod surfaces, the as-received rods were totally devoid of it. It

seems unlikely that the salt and the soot had been washed away by rain,

since the soot could not be removed by simple rinsing (Section 7.6), and

since rain would be expected to foster additional arcing and soot formation (Section 9.2) — unless the power to the antenna system had been

turned off some time prior to the removal of the rods. The cleanliness

of the as-received rods remains unexplained but, nonetheless, these

observations indicate that the washing treatment, which was subsequently

applied to some of these rods at NBS, was largely ineffectual.

Another factor which inhibits the proper interpretation of the test

results is the difference in the voltage characteristics between the

Angissoq installation (100-kHz pulsed) and the electrical tests (60-Hz

continuous wave (CW)). A cursory review of the literature suggests that

the effects of this difference on the burning behavior of rods is largely

unknown. Early work [14] showed that the threshold voltages for corona

inception and for sparkover in air were relatively independent of frequency up to 1 kHz, while at 40-kHz CW the threshold voltages appeared

to be somewhat less than at 60-Hz CW, except for highly polished surfaces.

On the other hand, with pulsed voltages the threshold for sparkover was

higher than with continuous waves. Recent work has added little to the

characterization of high-frequency effects on the inception voltages for

25
corona [15], but the reduction in sparkover voltage at high frequency

has been confirmed [16]. Regarding the effects of pulsed voltages, the

sponsor reported that an insulator rod was burned up in only two minutes

at 150 kV and 100-kHz CW, even though the rods at Angissoq survived for

years at 270 kV and 100-kHz pulsed. It appears, in summary, that

measurements of voltage levels for corona inception, arcing and flashover, made at 60-Hz CW, provide little more than general indications of

behavior under 100-kHz pulsed voltages.

9.2 Burn Damage

The possibility that the burn damage on the Angissoq insulators was

caused by lightning cannot be ruled out categorically. While the extent

of the damage appeared to be greater and more dispersed than that which

might be attributable to a single stroke, it is not beyond reason that

it was the cumulative result of numerous strokes over a period of months

or years. Certainly, the terrain and the climate at Angissoq would tend

to favor the possibility. On the other hand, if the tower had been

struck by lightning on a series of occasions, one would not expect all

of the damage to have been restricted to the insulators on the toploading elements. Local blackening of the metal structure and burning

of the insulators on the structural guys (Fig. 1) would also have occurred. Since only minor coating losses on some structural guy insulators were reported, it is assumed, for the purposes of this report, that

lightning was not, in fact, the principal cause of the observed burning

damage

This leaves corona, arcing, flashover, and similar phenomena related to the operating voltage of the system as the probable causes of

the burning damage. Several factors and mechanisms, which had originally been considered as having possibly contributed to the development

of burn damage, were ruled out by the tests and measurements performed

in this study: (1) It was found that most of the end fittings on the

most severely burned rods did not contain voids. (2) It was shown that

there was no simple correlation between coating loss and the incidence

of burn damage. If anything, rods with well-adhered coatings tended to

experience more burn damage. However, the burn damage on rods which

experienced major coating loss usually occurred where the coating had

been lost. (3) It was also shown that the burn damage was probably not

due, in general, to arcing between companion rods or between rods and

their respective corona rings.

The electrical tests showed that the corona inception voltages for

the junctions between the rods and their upper end fittings, and for the

corona rings, are less than the operating voltage of the Angissoq installation. Thus, corona may have been present as a normal operating condition on rod ends and corona rings at Angissoq, although this was not

reported. The presence of corona facilitates electrical breakdown by

increasing the electrical surface of the conductor, and by degrading the

dielectric quality of insulation over a long period of time. But corona.

26
by itself, does not produce carbonaceous tracking and charring; this

was substantiated by tests on other GRP rods which were subjected to

violent corona for 17 hours at 400 kV (60 Hz) without corona rings and

sustained no visible damage [17].

The withstand and flashover tests showed that the voltages required

to cause burning damage on dry insulators were sufficiently high, in

comparison with the Angissoq operating voltage, to effectively rule out

this mechanism as an explanation of the observed burning damage. The

situation with wet insulators was entirely different, however. The

electrical tests showed that insulators which had been wetted by rain or

dense fog could sustain burn damage under voltages which are significantly

less than, or equal to, that used at Angissoq.

With these observations in hand it is not difficult to postulate a realistic damage mechanism which is consistent with the bulk of the data

available. Tiny droplets or rivulets of water are electrically conductive

when they contain even the minutest amount of salt or other contaminant.

The presence of such a droplet on the rod, immediately adjacent to or

near the upper end fitting, can provide a terminal for a partial discharge

from the fitting, either by direct conduction or by means of an arc from

the fitting to the nearby droplet. The leakage currents thus produced

cause a localized heating of the rod surface which, in time, would

oxidize the polymeric surface leaving a thin carbonaceous track. The

track, being electrically conductive even after it had dried, would

provide a jumping-off point for an arc to the next water droplet slightly

further down the rod, extending the track or starting a new one. At the

same time, since it continued to carry current each time an arc developed,

the original track would grow deeper and wider. In a heavy fog or a rainfall of such duration as to produce long rivulets of water on the

rod, the process could continue until complete flashover of the rod

would result. This would explain why four of the rods received from

Angissoq had sustained burn damage at their lower, as well as their

upper, ends.

This damage mechanism also serves to explain why no more than one

rod, out of each companion pair, tended to experience severe burning.

The two rods in each insulator assembly are not constrained to remain at

exactly the same elevation above the ground. Rather, the assembly can

rotate about its longitudinal axis, due to twisting and untwisting of

the wire rope guys, thus placing one rod somewhat above the other in the

general case. During a heavy rainfall, with water rivulets coursing

down the top-loading elements from the tower, nearly all of this water

would run down the lower of each pair of rods, with the upper one being

wetted solely by the raindrops directly incident upon it. This, in

turn, would tend to produce far more arcing and tracking on the lower

rod than on the upper one.

27
I—

The postulated damage mechanism can also be used, with some elaboration, to explain why the worst burn damage was sustained by rods

having negligible coating loss, while on those rods which had experienced

major coating loss most of the burn damage occurred in the uncoated

regions. Where coating loss had occurred, the rod surfaces were rougher

and more porous than the coating and, therefore, tended to be wetted and

to retain moisture more easily than the coating. As a result, these

uncoated regions were more likely to provide termination points for arcs

from the upper end fitting or from a nearby carbonaceous track. (Incidentally, the greater roughness of the uncoated regions also explains

why the corona inception voltages were less for the rods which had their

coatings removed than for the coated rods.) On the other hand, it was

found that the coating is more flammable than the GRP substrate material

so that it would tend to carbonize and track more readily than uncoated

rod in the presence of leakage currents. This explains why the uncoated

rods experienced less damage than the coated rods in the electrical

tests. Since, as pointed out earlier, there is reason to believe that

there were at least two different coating materials used in the manufacture of the rods, it is entirely possible that the well-adhered

coating had a higher flammability than the flaky coating and was, therefore, more susceptible to carbonaceous tracking in the presence of surface leakage currents. If so, this would explain why the worst burn

damage was sustained primarily on rods which had experienced little, if

any, coating loss.

The principal thrust of the above paragraph is, simply, that arcing

was more prone to occur where coating loss had been experienced, but the

worst burn damage was still apt to take place on a rod having a relatively

flammable coating even if coating loss had not occurred and the incidence

of arcing was less.

The flammability tests showed that the rods have LOIs in excess of

21 percent and it follows, therefore, that they are basically self-extinguishing in air. This explains why the rods, once ignited, did not

invariably burn to destruction. Instead, the proposed damage mechanism

suggests that burn damage was only incurred while surface leakage currents were present, i.e., while there was actual arcing from the upper

end fitting or from an established carbonaceous track to the next water

droplet on the rod, or while there was complete flashover. Once a rain

had ceased to fall, or a fog had dispersed, the moisture on the surface

of a rod would quickly vaporize, due to the leakage current, to the

point where further arcing would cease.

(An alternative, though similar, damage mechanism has also been

proposed, which also merits presentation here. According to this theory,

the electrical failure of the Angissoq insulators

28
"... is attributed to the intrusion of salt into

the weather-deteriorated polymeric coating. These

salt deposits are probably limited to the immediate

area of any crack, chip, or other surface damage and

do not extend into the interface area. When wetted,

these deposits create many small, highly conductive

paths for current flow and places high electrical

stresses on the undamaged surface areas. This, in

turn, causes arcing across the undamaged areas and

once the polymeric material is burned, it remains

conductive. In addition, this new surface damage

creates additional areas for salt entrapment . " [4

]

This damage mechanism may, indeed, have been responsible for the failures

observed in the electrical tests, since, in those tests, the rods which

had been preconditioned by washing and by having their coatings removed

performed significantly better than those rods which had been preconditioned

by immersion in saltwater. On the other hand, it does not appear likely

that this mechanism was principally responsible for the failures at

Angissoq since the worst burn damage, on the as-received rods, was confined primarily to rods that had experienced no coating damage.

(Research has shown that epoxy films are relatively permeable to

chloride ions [18] and this suggests the possibility that the salt may

have been able to penetrate the coatings by diffusion even where the

coatings were intact. However, the permeability of epoxy resins decreases rapidly with temperature [19]so it Is improbable that salt

diffusion was a significant factor at Angissoq.)

9 . 3 Coating Loss

It has been pointed out that of those rods which had served as companion pairs in single insulator assemblies both exhibited major coating

loss or both exhibited negligible coating loss. At first, this suggests

the possibility that the loss of coating may have resulted from companion

rods striking or rubbing against each other due to wind-induced vibration;

or that the rods may have become twisted together due to the twisting or

untwisting of the wire rope guys. However, if either of these were the

case, then most of the coating loss would probably have occurred near

the midlengths of the rods rather than in their upper thirds.

Another possibility is that the coating loss was caused by icing

and repeated freeze-thaw cycles. Icing is most commonly formed when the

air and the affected surface temperatures are slightly above, at, or

below 0 °C (32 °F), and supercooled moisture is present. The average

0 °C (32 °F) isotherm passes very close to Angissoq during six months of

the year (Dec-May) and, similarly, the southern part of Greenland experiences a relatively high frequency of occurrence of supercooled fog,

throughout the year. Also, Angissoq is near a region that has a high

frequency of occurrence of supercooled clouds for six months of the year

29
(Dec-May), a condition which is conducive to the development of glaze

storms [ 2 0 J . The deficiency in this explanation is also that it would

appear to affect all parts of the insulator rods equally rather than

their upper portions preferentially.

The fact that most of the coating loss occurred in what is believed

to be the upper parts of the insulator rods suggests that corona may

somehow have been responsible. It is known that ozone is invariably

generated whenever corona is present and that most organic compounds are

readily oxidized by ozone. But this does not explain why the incidence

of major coating loss was apparently confined to companion pairs of

rods

.

10. ON REDUCING THE INCIDENCE OF DAMAGE

10.1 Coating Loss

Although the principal cause of the coating loss on the Angissoq

insulator rods is unknown, the remedy is obvious. It is abundantly

evident, from seven of the seventeen rods which were examined, that

well-adhered coatings which are resistant to peeling and flaking can be

manufactured. Unfortunately, it appears that the formulation of the

well-adhered coating may have compromised its flammability qualities, so

that the use of the coating may have avoided coating loss at the expense

of a greater susceptibility to burn damage. The formulation of a suitable

coating with high resistance to combustion and/or carbonaceous tracking

is discussed later.

10.2 Burn Damage

In accordance with the postulated damage mechanism, there are three

general approaches that can be considered, either singly or in combination, for reducing the incidence of burn damage in GRP insulators for

top-loading elements:

1. Reduce the electrical stress at the top of the insulator

rods, where burn damage apparently begins.

2. Raise the leakage path resistance of the insulator rods

to reduce the tendency for electrical discharges to occur.

3. Enhance the flame-retarding and anti-tracking qualities

of the insulator rods to reduce the burn damage incurred

in the presence of arcing and leakage currents.

Each of these approaches are discussed here.

While there is no evidence that corona, in itself, was a direct cause

of the observed burn damage, it could have been a contributing factor.

It has been pointed out that corona could lead to coating loss; but more

important, the presence of corona at the junction of a rod and its upper

30
end fitting can effectively increase the distance over which an electrical

arc from the fitting can strike in order to reach some receptive terminal

point on the rod. The inception of corona at the rod/fitting junctions

can be eliminated by suitable redesign of the corona rings [17]. However,

given the 270-kV operating voltage of the Angissoq system, it does not

seem likely that a corona ring — even a very effective one — could

avert partial discharges from the energized end fittings in the presence

of water droplets or rivulets on adjacent portions of rod. Furthermore,

the voltages required to produce complete flashover do not appear to be

influenced by the design of the corona rings [17].

(In this connection, and with relevance to lightning protection, it

was shown by means of high-voltage impulse tests on other GRP rods, that

flashover could be diverted from the rod surfaces when corona rings were

used on both ends of the rods [7]. Flashover occurred in the air between

the rings, and the rods were not damaged thereby. However, these tests

were conducted under dry conditions and, again, it seems likely that if

the rods had been sufficiently wet the rod surfaces would have provided

a preferential path for the flashover.)

The tendency for arcing to occur along the surface of a rod could

be reduced by avoiding the development of sites on the rod surfaces

where water droplets can momentarily accumulate. This can be achieved,

to some extent at least, by keeping the rod surfaces clean of contamination particles, and by using rods with extremely smooth, nonporous

surfaces to reduce wettability.

While some users clean their GRP insulator rod surfaces regularly,

this does not seem to be a feasible practice for highly inaccessible

rods on installations situated in remote geographical locations.

With regard to the desirability of having smooth rod surfaces, it

has been observed that uncoated rods, as produced by many pultrusion

manufacturers, are substantially smoother than coated rods, at least

when they are new*. It may be noteworthy that of the four communications

systems that had burn damage problems with GRP insulators (three of them

Loran-C installations), and which are known to the authors, all involved

coated rods. This may not be a meaningful observation, however, since

it is possible that uncoated rods are not widely used in high-voltage

*For the purposes of this discussion, rods manufactured with a transparent, integral gel coating of the matrix material are considered

uncoated; the term "coatings" is reserved for compositions that differ

from the matrix material of the rod, being added chiefly for enhanced

weatherability

.

31
outdoor applications. There is evidence* that uncoated rods, exposed to

sunlight for extended periods, develop a condition known as "blooming"

or fiber prominence. The outer surfaces of the matrix material deteriorate

under the sustained action of ultraviolet radiation, leaving glass

fibers exposed. In this state the surfaces are neither smooth nor

nonporous, and may be expected to be particularly susceptible to arcing

when wet.

Given, therefore, that some coating is needed on the rods for longterm weather resistance, it would appear desirable to add a second

coating to reduce wettability. Such water-repellant coatings have been

developed and have, in fact, demonstrated significant increases in

surface electrical leakage resistance in the presence of moisture [21].

An entirely different technique for reducing the tendency for

arcing involves the use of GRP insulators fabricated with regularly

spaced, transverse skirts [22-24]. The shapes of these insulators

provide inherently longer leakage paths and, in addition, inhibit the

formation of rivulets by shedding water at the lower extremities of the

skirts. These insulators have been finding increased acceptance in

European power-transmission systems.

Arcing and leakage current, though undesirable, do not necessarily

lead to the formation of carbonaceous tracks. Most plastics, including

most epoxies, oxidize in the process of combustion or in the presence

of electric arcs, leaving elemental carbon from the polymeric structure

as a solid residue. By adding a strong oxidizing agent such as aluminum

hydrate to the polymer formulation, the decomposition process is changed

so that the carbon is carried away in the form of carbon monoxide and

volatile hydrocarbons. Effectively, then, the material erodes; but the

tracks are not carbonaceous and, therefore, non-conducting. In the case

of insulator' rods, this would inhibit the growth and the spread of

tracks and virtually avoid surface flashover.

Some thermoplastics also offer anti- tracking qualities by virtue of

their chemical constitutions. Po ly tetraf luoroethy lene (PTFE) is particularly notable in this regard, since it is also exceptionally weatherresistant. Numerous commercial formulations, suitable for use as coatings

or jacketing materials, have also been developed in recent years and,

reportedly, offer exceptionally high resistance to fire [25].

Unfortunately, the aluminum hydrate additive, in the proportions in

which it must be used, reduces the mechanical properties of GRP. Similarly, PTFE is not a suitable matrix material for pultruded rod. Thus,

*Unpublished results of real-time weathering tests conducted by a pultrusion manufacturer, and of a survey, by another manufacturer, of

pultrusions in outdoor service.

32
while these materials can be used to provide anti-tracking or flameresistant coatings, a different approach would be required for the GRP

substrates. It has been reported that aramid-reinf orced epoxy offers

flammability and electrical properties which are equal or superior to

those of glass-reinforced epoxy [26], while NBS research has shown that

the wet dielectric strength of aramid-reinf orced polyester is less than

that of glass-reinforced polyester [12]. Considerable work has been

done, in recent years, on the development of fire-retarding agents for

glass-reinforced polyester [27].

11. SUMMARY

A group of damaged GRP insulator rods, which had been removed from

service on a Loran tower in Angissoq, Greenland, were submitted to NBS

for failure analyses. The rods, which had sustained both, burn damage

and loss of coating, were subjected to a variety of inspections, tests

and measurements. There was evidence that the rods may not all have

been manufactured identically; this complicated the failure analyses.

The burn damage, which had led to complete failure of some rods,

was attributed primarily to the occurrence of electrical discharges from

the energized end fittings. It appeared that most of the discharges had

been only partial but there was also evidence that complete flashover

probably had occurred on some rods. The principal factor which contributed to the occurrence of the discharges was the presence of moisture

from rain, fog and/or airborne ocean spray, which significantly lowered

the leakage path resistances of the rods. Other factors which may have

contributed include salt contamination, electrical corona at the junctions

of the rods with the energized end fittings, and the loss of coating on

some of the rods. The poor flammability and tracking resistances of the

rods and their coatings contributed to the severity, if not the incidence,

of the burn damage.

The principal cause of the coating loss, which was extensive on

some rods, could not be identified, but climatic conditions and the

presence of electrical corona are believed to have been contributing

factors. The coating loss did not impair the structural integrity of

the rods; but as mentioned above, it may have been a secondary factor

contributing to the occurrence of electrical discharges.

One approach toward reducing the incidence of burn damage would be

to use skirted insulator rods, which effectively increase the leakage

path resistances in moist environments. A second approach, which might

be less expensive in the long run, would be to select or develop an

improved coating material for the rods. Ideally, such a coating should

be tough and well-adhered, weather resistant and water repellant, arc

resistant, track resistant and fire resistant. Regardless of which of

these approaches is used, the basic GRP rod material should also be made

more fire resistant if this can be accomplished without serious compromise of its mechanical properties. The design of more effective

33
corona rings and the use of such rings on the lower, as well as the

upper, ends of the insulator rods, might also provide some protection

against damage due to lightning.

The insulator rods can tolerate moderate carbonaceous tracking

without any loss of tensile load-carrying capacity. Even burns that

consume rather substantial percentages of a rod's cross-sectional area

do not pose an immediate threat to the structural integrity of the

system. However, rods that sustain major burn damage should always be

replaced because burned rods are more susceptible to further burn damage

and because undetected charring beneath the burned surface may have

rendered some of the remaining material unsound.

34
12. REFERENCES

1. Sushinsky, G. F. and Mordfin, L., Nondestructive Examination of

Glass-Reinforced-Plastic Rod End Fittings, NBSIR 76-1084 (April

1976)

.

2. American Society for Testing and Materials, Standard Method of Test

for Flammability of Plastics Using the Oxygen Index Method, ASTM

Designation D2863, 1975 Annual Book of ASTM Standards , Part 35

(1975).

3. Parvin, K. , Polyester Resins of Reduced Fire Hazard, Proc. Reinf orced Plastics /Composites Institute , 30th Anniversary Conf .

,

Washington, Feb. 4-7, 1975, paper 2-F (Society of the Plastics

Industry, N.Y., 1975).

4. Gabriel, A. L. and Brown, J. E. , Electrical Tests on Fiber Glass

Guy Insulators, Technical Report No. ERF-75-128, Bonneville Power

Administration (Vancouver, Wash., July 10, 1975).

5. Chwirut, D. J., coordinator. Research and Testing Facilities of the

Engineering Mechanics Section, National Bureau of Standards,

Washington, D. C., NBS Spec. Publ. 370 (1973).

6. Halsey, N. , Mitchell, R. A. and Mordfin, L., Evaluation of GRP Rod

and Rope Materials and Associated End Fittings, NBSIR 73-129

(Dec. 1972).

7. Halsey, N., Properties of Glass Fiber-Reinforced Polymers for Application to Guy-Insulator Systems of Communication Towers, Phase

2, Test Methods and Evaluations of Glass Fiber-Reinforced Polymer

Rods for Use in Guy-Insulator Systems of Loran C Towers, NBS Report

10261 (June 1970).

8. Marlowe, D. E., Halsey, N., Mitchell, R. A. and Mordfin, L., NonMetallic Antenna-Support Materials, First Annual Interim Report,

NBSIR 73-233 (April 1973).

9. Halsey, N., Glass Reinforced Plastic Rod Insulators, NBS Report of

Test on U.S. Coast Guard MIPR No. Z-7099-1-13072 (Feb. 18, 1971).

10. Halsey, N. , Marlowe, D. E. and Mordfin, L., Non-Metallic AntennaSupport Materials, Second Annual Interim Report, NBSIR 74-557

(June 1974)

.

11. Gross, S. (editor), Modern Plastics Encyclopedia 1973-1974 , (McGraw-Hill, N.Y., Oct. 1973).

12. Halsey, N. , Marlowe, D. E. , Mitchell, R. A. and Mordfin, L., NonMetallic Antenna-Support Materials, Final Report, AFML-TR-76-42

,

Air Force Materials Lab (Wright-Patterson AFB, Ohio, May 1976).

35
13. Halsey, N. and Mordfin, L. , Environmental Effects on the Strength

of a Glass Fiber-Reinforced-Plastic Rod Material, NBSIR 76-1069

(March 1976)

14. Peek, F. W. Jr., Dielectric Phenomena in High Voltage Engineering , 2nd edit., pp 65-66 and 106-111 (McGraw-Hill, N. Y., 1920).

15. Loeb, L. B., Electrical Coronas, Their Basic Physical Mechanisms , PP 569-586 (Univ. of Calif. Press, Berkeley, 1965).

16. Hotter, F. R. , A Study of Air-Gap Breakdown at 28.5 Kilohertz,

NBSIR 75-731 (June 1975)

17. Gabriel, A. L. and Brown, J. E., Electrical Tests on U.S.C.G.

Designed Grading Ring Assemblies, Technical Report No. ERD-75-235,

Bonneville Power Administration (Vancouver, Wash., Dec. 4, 1975).

18.. Matsui, E. S., Permeation of Chloride and Sodium Ions through Protective Coating for Naval Shore Structures, Report No. TN-1373,

Civil Engineering Laboratory, Naval Construction Battalion Center

(Port Hueneme, Calif., Feb. 1975).

19.. Parham, J. L., Specific Permeability of Epoxy Resin Systems, Report

No. RL-TR-71-5, U.S. Army Missile Command (Redstone Arsenal, Ala.,

June 14 , 1971).

20.. Sanderson, J. I., Occurrence of Ice in the Form of Glaze, Rime and

Hoarfrost with Respect to the Operation and Storage of V/STOL Aircraft, Report No. ETL-SR-73-1, U.S. Army Engineer Topographic Laboratories (Fort Belvoir, Va. , Jan. 1973).

21. Baker, H. R. and Bolster, R. N., The Prevention of Surface Electrical

Leakage in the Presence of Moisture, NRL Report 7326, Naval Research

Laboratory (Washington, Oct. 26, 1971).

22. Polvara, A., Plastics as Insulating Materials for Traction and High

Voltage Lines [in Italian], Materie Plastiche ed Elastomeri

(June 1969) . Also English translation, PTFE/Polyester Glass Fibre

Insulators for Power Transmission, Imperial Chemical Industries

Ltd. (Welwyn Garden City, Hertfordshire, England, March 1970).

23. Anon., Rodurflex Plastics Insulators for Overhead Transmission

Lines, Rosenthal Technik AG (Selb, W. Germany, June 1973).

24.

Anon., Second Generation of High-Voltage Insulator, Publication

No. 2554-H, Ohio Brass Co. (Mansfield, Ohio).

36
25. Hughes Aircraft Co., Improved Cable Fire Protection, report to

Naval Ship Engineering Center on Contract No. N0024-74-C-5083

(Fullerton, Calif., Jan. 1974).

26. Sturgeon, D. L. G. and Venkatacha 1 em, T. K., Potential Contribution

of High Strength, High Modulus Aramid Fibers to the Commercial

Feasibility of Lighter than Air Craft, Proc. Interagency Workshop

on Lighter than Air Vehicles , edited by J. F. Vittek, Jr., FTL

Report R75-2, MIT Flight Transportation Laboratory, pp 243-255

(Jan. 1975).

27. See annual Proc . Reinforced Plastics /Composites Institute (Society

of the Plastics Industry, N.Y.).

37

TOP-LOADING

ELEMENT

ID

toZ

Figure

1.

Guying

arrangement

for

Angissoq

tower,

not

to

scale.

All

dimensions

in

feet

(1

ft=

0.3048

m).

Figure 3. Upper end of Rod XI showing two short carbonaceous tracks

adjacent to the end fitting.

Figure 4. Lower end of Rod X2 showing two short carbonaceous tracks

adjacent to the end fitting. The upper track is the less

severe of the two, and is situated in a small area in which

the coating is gone.

Figure 5. Upper end of Rod X3 showing substantial loss of coating.

Helical markings are faintly visible on the uncoated surface.

Figure 6. Upper end of Rod X4 showing substantial loss of coating.

The helical markings on the uncoated surface are clearly

visible

.
Figure 7. Upper end of Rod X5 showing substantial loss of coating.

Figure 8. Upper end of Rod X6 showing minor losses of coating.

Shallow carbonaceous tracks are faintly visible in the

uncoated areas.

Figure 9. Upper end of Rod X7 showing a 1-in (25-mm) long carbonaceous

track. The longer streak on the left is a scuff mark.

Figure 10. Upper end of Rod X8 showing severe carbonaceous tracking

and charring. The rod appeared to have burned almost

completely through, with the last 3 percent of its cross

section having failed in tension. Some small areas of

coating loss are evident along the upper edge of the burn

damage. The fitting from this end of the rod is shown in

Figure 20.
Figure 11. Upper end of Rod X9 showing substantial loss of coating.

A carbonaceous track is evident near the middle of the

uncoated area.

Figure 12. Upper end of Rod X10 showing severe carbonaceous tracking

and charring. The rod appeared to have burned almost

completely through, with the last 3 percent of its cross

section having failed in tension. The fitting from this

end of the rod is shown in Figure 21.

Figure 13. Upper end of Rod Xll showing a small area adjacent to the

end fitting where the coating had been lost, and a thin

carbonaceous track extending from this area onto the coating.

Figure 14. Upper end of Rod X13 showing severe carbonaceous tracking

and charring.
Figure 15. Upper end of Rod X15 showing severe carbonaceous tracking

and charring.

Figure 16. Upper end of Rod X16 showing severe carbonaceous tracking

and charring. See, also, Figures 17 and 18.

Figure 17. Upper end of Rod X16 showing long carbonaceous track on

the surface opposite to that depicted in Figure 16.

Figure 18. Lower end of Rod X16 showing carbonaceous track.
Figure 19. Upper end of Rod X17 showing substantial coating loss and

intermittent carbonaceous tracking both inside and outside

of the uncoated area.

!

|

Figure 20. Upper end fitting from Rod X8

.

See, also, Figure 10.
Figure 21. Sectioned (above) and reassembled (below) views of the

upper end fitting from Rod X10. Note the large void in

the potting compound near the tip of the conical wedge.

The void does not appear to have been open to the

atmosphere. See, also, Figure 12.
X

>

Figure

22.

Sketch

of

end

fitting

showing

coordinate

system

used

for

identifying

the

angular

locations

of

damage.
Figure

23.

Dissected

end

fittings.

Top

row,

left

to

right:

X9

upper,

X14

lower,

X9

lower.

Bottom

row,

left

to

right:

X8

upper,

X15

upper,

X14

upper.
250

>

a. >

O'

A>l '39VHOA ddllddV

Figure

24.

Results

of

RIV

tests.
Figure

25.

Aluminum-block

end

fitting

for

0.79-in

(20-mm)

diameter

rods.

All

dimensions

in

inches

(1

in

=

25.4

mm).
Figure

26.

H3M

end

fitting

for

0.79-in

(20-nun)

diameter

rods.

Fitting

is

rotationally

symmetric

about

longitudinal

center

line.

All

dimensions

in

inches

(1

in

=

25.4

mm)

.
Figure

27.

Mod

4

end

fitting

for

0

.

79-in

(20-mm)

diameter

rods.

Fitting

is

rotationally

symmetric

about

longitudinal

center

line.

All

dimensions

in

inches

(1

in

=

25.4

mm)
NDi-l I 4A (REV. 7-73)

U.S. DEPT. OF "COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1136

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Failure Analysis of Fiberglass Insulator Rods

1

5. Publication Date

July 1976

6. Performing Organization Code

7. AUTHOR(S)

Leonard Mordfin and Nixon Halsey

8. Performing Organ. Report No.

NBSIR 76-1136

9. PERFORMING ORGANIZATION NAME AND ADDRESS

1 NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

2130445

11. Contract /Grant No.

MIPR Z-70099-5-51020

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U. S. Coast Guard Headquarters

400 Seventh Street, S.W.

Washington, D. C. 20590

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

Failure analyses were carried out on a group of coated f iberglass-reinforcedplastic insulator rods that had sustained burn damage and loss of coating in service

on a radar tower. The investigation included chemical, flammability, electrical and

mechanical tests as well as a variety of measurements and inspections. The burn

damage, consisting chiefly of carbonaceous tracking and charring, was attributed

primarily to the occurrence of electrical discharges, from the energized end fittings

to the rods, under conditions in which the electrical leakage path resistances had

been reduced by moisture from rain, fog and ocean spray. The effects of this damage

on the structural integrity of the rods were evaluated. Recommendations were made

for reducing the incidence of such damage in the future, based on the use of skirted

insulator rods or more effective coating materials. The principal cause of the

coating loss was not positively identified. This form of damage was not found to

have serious consequences except as a secondary factor which may have contributed to

the occurrence of some partial electrical discharges.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of die first key word unless a proper name; separated by semicolons)

Breakdown, electrical; failure analysis; fiberglass-reinforced plastics; flammability;;

guy insulators; high-voltage tests; insulators, tower guy; Loran C; pultruded rods; —rnris., insulator.

18. AVAILABILITY [Xl Unlimited

For Official Distribution. Do Not Release to NTIS

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Washington, D.C. 20402, SD Cat. No. 03

I X' Order From National Technical Information Service (NTIS)

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19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

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UNCLASSIFIED $4.50

USCOMM.DC 2904 2- P 7 4

NBSIR 76-1137

Thermal Data Requirements and

Performance Evaluation

Procedures for the National

Solar Heating and Cooling

Demonstration Program

E. Streed

M. McCabe

D. Waksman

J. Hebrank

T. Richtmyer

Office of Housing and Building Technology

and Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

August 1976

Prepared for

Energy Research and Development Administration

Division of Solar Energy

Washington, D.C. 20545

and

Department of Housing and Urban Development

Division of Energy, Building Technology and Standards

Washington, D.C. 20410

NBSIR 76-1137

THERMAL DATA REQUIREMENTS AND

PERFORMANCE EVALUATION

PROCEDURES FOR THE NATIONAL

SOLAR HEATING AND COOLING

DEMONSTRATION PROGRAM

Office of Housing and Building Technology

and Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D C. 20234

August 1 976

Prepared for

Energy Research and Development Administration

Division of Solar Energy

Washington, D.C. 20545

and

Department of Housing and Urban Development

Division of Energy, Building Technology and Standards

Washington, D.C. 20410

V A?

AU 0* S

U S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

PREFACE

The overall goal of the National Solar Heating and Cooling Demonstration Program is "to

stimulate industrial and commercial capability, including that of small businesses, to

produce and distribute solar heating and cooling systems, and through widespread applications, reduce the demand on present fuel supplies." To help achieve this goal, the

Demonstration Act further provides that solar heating and combined heating and cooling

systems will be installed in a substantial number of buildings in the climatic regions

existing in the different United States geographic areas. Evaluation of the performance

and reliability of the current technology can be expedited by testing under carefully

controlled conditions and by demonstration in the field.

The purpose of this document is to provide the rationale and description of the data

requirements, instrumentation types and data analysis methods used to monitor and evaluate

the field demonstration systems. It is recognized that complete instrumentation and subsequent technical evaluation of each system/building/ climate combination cannot be

performed because of the cost and data analysis limitations. Therefore, only selected

unique installations will be completely instrumented and as the exact design and location

of all sites becomes available, optional measurements will be made to evaluate significant

features

.

The report has been prepared at the National Bureau of Standards under the general guidance

and review of the Solar Heating and Cooling Performance Evaluation Committee, Mr. H. J. Hale,

Solar Division, Energy Research and Development Administration (ERDA) , Chairman. Members

of the committee include:

M. McCabe National Bureau of Standards (NBS)

W. Christensen Department of Defense

W. Freeborne Department of Housing and Urban Development

A. Kromis NASA - Marshall Space Flight Center (MSFC)

W. Littles NASA - MSFC

F. Morse ERDA

E. Streed (Secretary) NBS

Specific acknowledgments are extended to Dr. Dan Ward, Colorado State University, for providing operational data and technical inputs and to David E. Galehouse, Consulting Engineer,

for sensitivity and error analysis calculations. The consultation and technical reviews of

Dr. J. Wayne Littles, NASA-MSFC , Dr. Mike Nash and Mr. John Bartlett, International Business

Machines, and Dr. James E. Hill, NBS, have contributed significantly to this document.

Thanks are also expressed to Mr. Frank Bridgers, Dr. Jack Duffie, Dr. Gerald Lowery, Prof.

John Yellott, and Dr. George 0. G. Lof for general review and comments regarding organization,

completeness, and terminology. The encouragement and support of Mr. Jack Hale, ERDA, and

Mr. Robert Dikkers, NBS/CBT, Solar Program Manager, to prepare the document in final form,

is gratefully appreciated.

i
This report was prepared as a reference document to prescribe a standard list of thermal

performance factors and data analysis methods that can be used to evaluate solar heating

and cooling systems for the National Demonstration Program. In describing these factors

and the associated measurements, specific solar energy system designs have been identified

and their features characterized to illustrate the type and location of sensors. Inclusion

of a particular design in this report in no case implies a recommendation or endorsement

by the Federal government, and the presentation should not be construed as a certification

that any component, subsystem, or system is preferred at the current state of technology

development. Similarly, the omission of a component, subsystem, or system does not imply

that the capabilities are less than those that are included. The designs presented were

obtained primarily from the open literature and are intended to be used for illustration

purposes only.

The thermal performance data obtained from the Demonstration Program are intended to serve a variety of users including architects, engineers, manufacturers, developers

and homeowners, code officials, standards writing organizations, and government planners

for energy conservation, economic and building technology applications. An attempt has

been made to identify and determine the many factors needed to satisfy the interest and

needs of these diversified disciplines. However, recognizing that requirements or technology will change during the course of a five-year program, the evaluation factors and

measurements can be modified.

Comments and suggestions are welcome and should be sent to:

Manager, Solar Energy Program

National Bureau of Standards

Building 225, Room A-114

Washington, D.C. 20234

ii
NOMENCLATURE

A

c

C

P COP

h

FG

K

M

M

N

Q

Q

u

T

TI or x UA

GREEK LETTERS

Collector gross area

Specific heat

Coefficient of Performance

Collector panel heat removal factor

Latent heat of vaporization

Sampling interval factor

Total incident solar radiation in plane of array

Mass

Mass flow rate

Performance index, number of samples

Cummulative thermal energy

Rate of useful energy extraction from collector

Temperature

Time

Overall heat transfer coefficient

Collector heat loss coefficient

(«t)

e

A

n

a

T

T

SUBSCRIPTS

Collector panel solar absorptance

Effective product of solar absorptance and transmittance

of cover and absorber panel

Difference

Efficiency

Sensor or measurement uncertainty, standard deviation

Integration time 1, etc.

Collector cover transmittance at air mass 2 or time

a Air, ambient

f Mass flow

f ,i Fluid inlet

I Insolation

in Inlet

out Exit

at, td Temperature difference

s Sampling rate

w Water, Flow

iii
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

1 in

2 = 6.45 x 10

-42

meter

1 ft = 0.09290 meter

Volume.

1 in = 1.639 x 10 meter __ . 1 gal (U.S. liquid) = 3.785 x 10 meter

Mass

_o

1 ounce-mass (avoirdupois) = 2.834 x 10 kilogram

1 pound-mass (avoirdupois) = 0.4536 kilogram

Pressure or Stress (Force/Area)

1 inch of mercury (60°F) = 3.377 x 10

3 pascal

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

3 pascal

Energy

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

1 Btu (International Table) = 1.055 x 10

3 joule

Power

^ 1 watt = 1 x 10 erg/second

1 btu/hr = 0.2929 watt

Temperature

to

c = 5/9 (to

p

" 32)

Heat

1 Btu-in/h-f

2 - F = 1.442 x 10-1 W/m-K (thermal conductivity)

1 Btu/lbm - °F = 4.184 x 10 3 J/kg-K (heat capacity)

1 langley = 4.184 x 104 J/m2 = 1 cal/cm2 = 3.69 Btu/ft 2

iv
TABLE OF CONTENTS

PAGE

1.0 Introduction

3 2.0 Program Objectives

4 3.0 Performance Evaluation Procedure

3.1 Standard Designations for Sensors and Subsystems 4

3.2 General Solar Energy System Description and Energy Balance 5

4.0 Active Systems Description and Performance Calculations 11

4.1 Energy Collection and Storage Subsystem

4.2 Hot Water Subsystem 15

4.3 Space Heating Subsystem 17

4.4 Space Cooling Subsystem 2G

5.0 Passive Systems Description and Performance Calculations 23

5.1 Roof Water Pond 25

5.2 Wall Collector 27

5.3 Performance Evaluation 27

6.0 Systems Performance Evaluation Summary (Active Systems) 30

6.1 Performance Factors - General 30

6.2 Energy Saved - General 32

6.3 Climatic Primary Performance Factors 33

6.4 Energy Collection and Storage Subsystem (ECCS) Primary 34

Performance Factors

6.5 Hot Water Subsystem (HWS) Primary Performance Factors 36

6.6 Space Heating Subsystem (SHS) Primary Performance Factors 38

6.7 Space Cooling Subsystem (SCS) Primary Performance Factors 40

6.8 Solar Energy System/Building Summary 42

6.9 Secondary Performance Factors and Measurements 45

7.0 Uncertainty Analysis of Solar Performance Factors 52

7.1 Sensitivity Analysis Methods 52

7.2 Derivation of the Overall Instrumentation Accuracies 55

7.3 Summary 64

8.0 Application of Performance Factors 66

8.1 Solar Energy System Thermal Performance 66

8.2 Solar Energy System Thermal Effectiveness 66

8.3 Analytical Predictions 59

8.4 Solar Collector Array 59

8.5 Component Predicted Performance 71

8.6 Climatic Data 71

8.7 Recommendations 74

9.0 Conclusions 76

10.0 References

v
TABLES AND FIGURES

TABLES PAGE

1.

Primary Performance Evaluation Factors 6

2 a&b. CSU Sampled Data Using Different Sampling Intervals 60

3. Range of Measured Daily Variance with Data Extrapolated for 61

Weekly, Monthly and Yearly Periods

4. Sampling Rate as a Function of Time Interval for Several 62

Data Requirement Types

5. Instrumentation Range, Accuracy and Measurement Frequency 65

6. Comparison of Collector Performance Coefficients Derived 72

from Testing and Analysis

7. Application of Specific Performance Factors to Evaluation Areas 75

FIGURES

1. Flow Chart of Elements Comprising Monitoring of System 2

Performance and Operation

2. Energy Flow Diagram for a General Solar Heating, Cooling 7

Hot Water System

3. Energy Collection and Storage Subsystem Flow Schematic, 12, 13

Sensors and Performance Calculations

4. Hot Water Subsystem Flow Schematic, Sensors and Performance 16

Calculations

5. Space Heating Subsystem Flow Schematic, Sensors and Performance 18, 19

Calculations

6. Space Cooling Subsystem Flow Schematic, Sensors and Peformance 21

Calculations

7. Passive Solar Energy Systems Schematics and Sensors 24

8. Calculation Sequence for Building Load Program 29

9. Accuracy in Calculated Solar Energy Collected (Q100) 57

10. Accuracy in Calculated Solar Used for Hot Water (Q300) 58

11. Monthly Heating and Cooling Loads and Auxiliary Energy 67

Requirement

12. Cummulative Energy Use for the MIT Solar House IV During 68

Two Winter Heating Seasons

13. Comparison of Collector Panel and System Collector Array 70

Performance

14. Illustration of Detecting Collector Degradation from Thermal 73

Performance Measurements

vi
DATA REQUIREMENTS AND THERMAL PERFORMANCE EVALUATION PROCEDURES FOR THE

NATIONAL SOLAR HEATING AND COOLING DEMONSTRATION PROGRAM

1.0 INTRODUCTION

A major objective of the Solar Heating and Cooling Demonstration Program, described

in ERDA-23A [1], is to provide data on the technical performance of solar heating

and cooling systems.* This data, following its collection, analysis, and evaluation

will be used to provide the information and data base needed to evaluate subsystem

and system performance, to develop definitive performance criteria and to formulate

analytical models for use as design guidelines for solar heating and cooling systems.

This report is intended to provide a description and rationale for the instrumentation

selection and resultant data required to monitor and evaluate the thermal effectiveness and reliability of solar heating, cooling and hot water systems in meeting

building thermal loads and in conserving conventional fuels or energy.

A basic assumption utilized in the preparation of this report concerns the purpose

of the data to be acquired by the described instrumentation. Because of the demonstration nature of the program, the data acquired must be sufficient to allow for

the evaluation of the thermal effectiveness of the solar components and system, but

is not intended to be utilized directly in the development of specific components.

Because nationally accepted test procedures for building heating and cooling systems

do not exist at the present time and because of the relatively large number of combinations possible for solar and conventional HVAC systems, the data requirements,

measurement procedures and equations used to determine the performance factors

dicussed in this report will require modifications dictated by the characteristics

of the specific system being evaluated.

The approach and methodology employed to obtain, evaluate and compare thermal

performance data is shown in Figure 1. Measurements from the on-site sensors are used to determine the solar system energy contribution, the auxiliary energy requirements, the building heating or cooling load, the climatic conditions and the comfort

level maintained by the system. Selected buildings and certain type solar systems will

be analytically modeled to predict system performance and building thermal response

as a function of the measured climatic conditions. The resulting predictions will

then be compared with the experimental data and the analytical modeling procedures

validated. Validated analytical models will be used to predict performance on similar solar system/building types having either reduced levels of instrumentation

or none at all.

*Solar heating and cooling systems are referred to as Solar Energy Systems in this

report

1
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Additional laboratory or field test data on critical components as a function of time

and operating conditions should also be made to the extent necessary to characterize

their performance and resolve differences between predicted and measured system

performance

.

2.0 PROGRAM OBJECTIVES

Technical performance evaluation of each solar energy system/building/climatic region

demonstration will be based upon the following factors:

1. Determining the savings in fossil fuel and electrical energy resulting from the use of solar energy for space heating, space cooling and/or hot water.*

2. Determining the total heating, cooling and/or HW thermal energy loads and the

fraction of each load supplied by solar energy for monthly, seasonal and/or

annual periods.

3. Measuring the solar energy system efficiency for converting solar radiation into useful

thermal energy for monthly and seasonal or annual periods

.

4. Measuring the thermal performance of major subsystems or components and the

thermal interactions between collector array, storage and energy conversion equipment

5. Measuring the occupants use of the system by means of parameters such as the

temperature level maintained and hot water demand.

6. Determining the major system operational characteristics and degradation over

the life of the demonstration (1 to 5 years)

.

7. Obtaining records of the incident solar radiation and other pertinent site

environmental nparameters that could affect the performance of the system over

the life of the demonstration.

* The term hot water (HW) as used in this report includes both residential domestic hot

water (DHW) and commercial service hot water (SHW) . The commercial service hot water

may either be potable or nonpotable depending on its intended use.

3
3.0 PERFORMANCE EVALUATION PROCEDURE

Performance factors and associated data requirements have been classified into

three categories. Category one (primary) items are required for a data summary

that is considered essential to adequately measure the solar energy system or subsystem thermal effectiveness and determine the energy saved by the solar energy

system in comparison with the energy that would have been used by a conventional

hot water, space heating, or space cooling systems. Without this data, comparative

evaluations of different solar energy subsystems and systems would be incomplete

or impossible. These primary performance evaluation factors are shown in Table 1

and described in detail in Section 6.0.

Category two (secondary) requirements are for data deemed important and useful in

evaluating different subsystems or components. Such data make it easier to

understand the component interactions that occur in system operation and serve

as an aid in comoarative analysis or simulation but are not essential. In general

second category data can be determined by appropriate calculations or approximations using category one measurements however in some cases the data can only be

direct measurements.

An example of a secondary performance factor is the storage efficiency. The

average storage medium temperature is the significant parameter in determining the

amount of stored energy available. The change of storage medium temperature during

a time period with no addition or withdrawal of energy can provide a measure of the

storage efficiency. The storage medium temperature is thus very useful but is not

unique to the system thermal evaluation.

Category three data are obtained from special measurements which are not particularly

essential for current analysis needs, but which serve to define system operational

conditions. Wind direction and velocity are examples of such measurements.

The building load, particularly infiltration, and collector losses are related to

wind effects. However, most analyses to data have not incorporated corrections

or used detailed calculations to correlate performance with wind data.

3.1 Standard Designations for Sensors and Subsystems

In order to standardize the performance calculations and identify sensors according to type and location, an alpha-numeric name is provided for each performance factor and sensor. A five character name is used consisting of one or

two letters which designate either the sensor type or the measured or calculated

quantity and a three digit number which identifies the subsystem or data group as follows

4
Letter Designations

C = Specific Heat

D = Direction or Position

EE = Electric Energy

EP = Electric Power

F = Fuel Flow Rate

I = Incident Solar Flux (Insolation)

N = Performance Parameter

P = Pressure

PD = Differential Pressure

Q

= Thermal Energy

T = Temperature

TD = Differential Temperature

V = Velocity

W = Heat Transport Medium Mass Flow Rate

TI = Time

Subsystem Designations

Number Sequence

001 to 099

100 to 199

200 to 299

300 to 399

400 to 499

500 to 599

600 to 699

Subsystem/Data Group

Climatological

Collector and Heat Transport

Thermal Storage

Hot Water

Space Heating

Space Cooling

Building /Load

Thus the sensor designation T101 defines an absolute temperature measurement

in the collector subsystem and the variable name Q600 defines a heat flow

measurement or calculation for a building load grouping.

3.2 General Solar System Description and Energy Balance

Prior to discussing the performance evaluation and measurement requirements of

solar energy systems, it is useful to describe in general terms the equipment

and subsystems that comprise a solar energy system and to describe the flow of

thermal energy from the solar equipment, through the energy conversion and

distribution equipment to the building. As shown in Figure 2, the basic elements

of a solar hot water, space heating and space cooling system include a solar

energy collection and storage subsystem (ECSS) , an energy conversion and distribution subsystem (ECDS) and the building.

5
6

TABLE

1

PRIMARY

PERFORMANCE

EVALUATION

FACTORS
OCCUPANT

ENERGY

TO

LIGHTS

METABOLIC

APP. &

NON-IIVAC

ENERGY

EQUIPMENT 7

FIGURE 2

ENERGY

FLOW

DIAGRAM

FOR A

GENERAL

SOLAR

HEATING,

COOLING

HOT

WATER

SYSTEM
3.2.1 Functions

The function of the collector subsystem, collector energy transport subsystem, and

storage subsystem (ECSS) is to convert the relatively variable incident solar

radiation to a relatively steady source of thermal energy in the form of elevated

temperature heat transport fluid or storage medium. This solar source acts as a

significant thermal energy source for the building's energy conversion equipment.

The major purpose of the ECSS is to reduce the consumption of non-renewable energy

sources such as natural gas, oil, and electricity normally used to provide the hot

water, heating, and cooling for the building.

The energy conversion and distribution subsystem is comprised of three subsystems

to provide the distinct functions of HW heating, space heating and space cooling

and utilizes conventional HVAC equipment such as electric or fuel fired heating

furnaces, hot water heaters, heat pumps, absorption chillers and their associated

pumps, fans, heat exchangers, controls, piping and ductwork. The function of this

equipment is to combine the energy available from the solar subsystem with the

auxiliary energy available from the conventional energy sources when the supply

of solar energy is inadequate, and to convert the solar energy to a useful energy

form for the building. To accomplish this conversion and distribution function,

additional electrical energy is required to power the pumps, fans, and controls.

The building consists of the various structural elements in which

of thermal energy between the outdoor and indoor environments occurs primarily

by the process of conduction, convection, radiation, and infiltration. When

the solar heat gain and the structural heat losses and gains are combined with the

internal heat gains from the lights, appliances and other equipment and the

metabolic heat from the occupants, and these loads are absorbed by the air in

the temperature controlled spaces of the building, they comprise the building

thermal load. If the HVAC equipment's rate of heat removal or addition to the

building is exactly equal to the building thermal load, the air temperature is

stabilized and the building is in balance. In the context of this report, hot

water is also treated as a building thermal load in that the HW subsystem capability

to provide the thermal energy required at the desired temperature must be balanced

against the actual rate of hot water consumption.

3.2.2 Thermal Energy Flow

A primary tool which can be used in the location and choice of measurements is the

concept of heat balances. For a given component, the amount of energy input must

equal the energy output plus the change in stored energy within the component.

8
This tool can be particularly useful as a check on the installed instrumentation.

By obtaining the heat balance periodically on a component or subsystem, evaluation

of the losses and accuracy of the installed data instrumentation can be made. Only

when the heat balance "error" is no longer within acceptable limits will selected

investigation (on the particular subsystem) be required to determine the need for

sensor recalibration or subsystem maintenance.

The performance evaluation factors can be defined in terms of the thermal energy

quantities shown for the generalized system of Figure 2, in which an arrow leading

into a box represents the net flow of a particular thermal energy quantity into a

subsystem. The quantities shown represent the integrated rate of thermal energy

flow over a sufficient period of time such that thermal storage in each subsystem

(with the exception of the storage subsystem) is negligible. For example, in

Figure 2 the quantity Q203 represents the net flow of thermal energy out of the ECSS

system and into the energy conversion and distribution subsystem. The quantity Q602

represents the net flow of thermal energy between the building and the energy con- version and distribution subsystem; i.e. , the total building energy load.

3. 2. 2.1 Subsystem Heat Loss

Examination of Figure 2 indicates a quantity called "heat loss" (or "heat gain")

associated with each subsystem element. This quantity represents the difference

between the total energy that originally entered the subsystem and the thermal

energy delivered by the subsystem. In most cases, the subsystem heat loss represents thermal energy transferred to the subsystem environment by heat loss through

the component insulation.

Depending on the physical location of the component, the subsystem environment can be outside the building either above or below ground or inside the building either

in a temperature controlled or a non-controlled space. No further use is made of

the heat lost by components located outside the building and above ground. However,

the heat lost by components in the other locations can affect the performance of

the solar energy system.

For example, with a buried non-insulated storage unit some heat lost to the environment when the storage medium temperature is relatively high may eventually be

recovered when the storage medium temperature is low. In addition, for those

components located within the building, some or all of the subsystem's heat loss

may find its way into the temperature controlled portion of the building which is

shown in Figure 2 as a miscellaneous heat loss/heat gain for the building. The

entire subsystem heat loss for those components located within a temperature

9
controlled space will be effective in reducing the building's heat load during the

heating season and in increasing the building's cooling load during the cooling

season

.

In the case of a subsystem having components located in a non-temperature controlled

room in a building, the effects of subsystem heat loss on the solar energy system

performance are difficult to assess. The heat loss from a storage unit located in

an unheated basement will certainly raise the air temperature of the room, which

will reduce the heat losses for the heating equipment and increase the heat gains

for the cooling equipment located in that room. However, little benefit of the

subsystem heat loss will be realized unless specific means are provided to utilize

the heat loss to reduce the building heating requirements.

Examination of each subsystem element in Figure 2 reveals the energy quantities

that must be either measured or estimated to determine the subsystem heat balance.

Subsystem heat loss is probably the most difficult quantity to measure, therefore,

it must be determined from the heat balance by measuring or calculating all the

other quantities.

In the following description of subsystem equipment measurements and performance

evaluation, the basic approach to performance measurement is to instrument all

energy flow quantities except subsystem heat loss and to determine this quantity

by the energy balance method. Additional instrumentation is recommended for the

solar collector subsystem and storage subsystem to enable correlation of heat loss

with observed temperature differentials and thus more effectively monitor these

important subsystems. It is recognized that this approach to instrumentation may

not always be practical, because of other constraints such as sensor cost,

reliability and performance, available data channels, etc. When such reductions

in measurement are considered, it will be necessary to assess the impact on overall evaluation and accuracy of the stated objectives of performance analysis.

In the subsequent sections describing the performance evaluation of solar energy

systems, the performance equations are developed on the basis that subsystem heat

loss does not affect the performance of a solar energy system with respect to such

primary evaluation factors as energy saved, heating and cooling load, and the

solar fraction of the heating and cooling load. However, it is necessary that the

heat loss for solar energy transport and storage subsystems located in temperature

controlled spaces be determined. When significant losses are calculated , the

pertinent equations (energy saved, heating and cooling load, and solar fraction of

the heating and cooling load) must be modified to indicate heat loss effects.

10
4.0 ACTIVE SYSTEM DESCRIPTIONS AND PERFORMANCE CALCULATIONS

The following section describes the flow schematic drawings and instrumentation

requirements for several typical solar energy systems, which are used for hot water,

space heating and space cooling, to illustrate the methods of evaluating performance.

The objectives of this section are to define the various subsystems sufficiently to

enable an analyst to convert a site contractor's solar energy system mechanical

drawings (showing the equipment, piping, ducting, controls etc.) into the various

system, subsystems and components as shown in Figures 2, 3, 4, 5 and 6. The location

and type of sensors can then be selected and the performance evaluation equations

defined based on the guidelines established herein.

In order to illustrate the sensor locations and performance evaluation factors,

the subsystem component configurations shown in Figures 3, 4, 5 and 6 were assumed

to represent reasonable subsystems that are capable of utilizing solar energy to

reduce the consumption of conventional energy. It is recognized that numerous

variations on these subsystem and component configurations are possible. It is

therefore re-emphasized that the schematic drawings are illustrative only and should

not be interpreted as recommendations by the government as to the most efficient means to use solar energy to reduce conventional energy consumption in satisfying

the hot water heating and space heating and cooling requirements of buildings.

In order to provide some flexibility in the selection of sensors, three different

categories of performance evaluation have been defined; primary, secondary and

special. Primary factors are deemed mandatory for each system and therefore all

sensors used to calculate primary performance factors must be provided. Secondary

performance factors are desireable and these data will normally be provided as a

fallout of the data provided with the primary sensors, however, whenever additional

non-primary sensors are required to calculate a secondary performance factor,

the requirement to provide the additional sensor is optional. Special performance

factors are calculated from data taken with special sensors, which are provided

as determined by the needs of each particular system and site.

4.1 Energy Collection and Storage Subsystem

Figure 3 describes the flow schematics, instrumentation and performance calculations

required to characterize two alternate energy collection and storage subsystems

(ECSS) and to define the required sensor locations and performance evaluation factors.

Subsystem elements common to both systems include a collector subsystem, energy

transport subsystem and a storage subsystem. In System A, the heat transfer

medium is a liquid and the storage subsystem is in series with the collector subsystem and the energy conversion and distribution subsystem (ECDS) therefore all thfe

11
SYSTEM A

(Liquid Medium, Series Storage) SOLAR HEATED

LIQUID TO

CIRCULATING

PUMP

SYSTEM B (Air Medium, Parallel Storage)

SOLAR HEATED

AIR TO

AUXILIARY AND

LOADS

MD 5 MEASUREMENTS

0=0PEN

MD POSITION C=CLOSED

/4>YA0LAR RADIATION NO. MODE 1 MODE 2 MODE 3 $ TEMPERATURE 1 0 0 C

m FLOW 2 C C 0

/ WIND VEL. DIRECTION 3 0 c C

Q, ELEC . POWER 4 C 0 0

5 C 0 0

FIGURE 3 SPACE HEATING SUBSYSTEM FLOW SCHEMATICS AND SENSORS

12
CATEGORY VARIABLE

P Q001

SM Q002

(1)

P Q100

S Q101

S Q102

S Q103

S Q200

S Q201

S Q202

P Q203

S Q204

s Q205

s N1QQ

s N101

s N1Q2

S N103

s N104

s N105

s N106

s N107

s N108

SM N109

s N11Q

p Nlll

s N112

p N113

SM N114

SM N115

SM N116

SM N117

FIGURE 3

description

Total Solar Incident

Direct Solar Incident

Solar Energy Collected

Collector Eeat Loss

ECSS Operating Energy ( 2 )

Collector Transp. Heat Loss

(3)

DEFINING EQUATION

/IOOldx

/ (I001-I002)dt

(1/Ac) mOO • C100 • TDlOOdx

/IIOOl-Cl/Ac) (WlOO-ClOO-TDlOO)dx, WIOO^O

f 3413/EPlOldx, SYSTEM A

I 3413/0 -EPAOldr, SYSTEM B

A^ Q100+NPUMP -Q102-Q200 , SYSTEM A

A • Q100+NFAN • Q102-Q200 , SYSTEM B/MODE 1

A

c

’ Q100+NFAN"Q102-Q203 , SYSTEM B/MODE 2

Energy to Storage

Energy from Storage

Hourly Increase in Stored Energy

Total Solar Energy Utilized

Storage Heat Loss

ECSS Total Heat Loss

Daily Integrated Collector Efficiency

Instant, Collector Efficiency

Collector Panel Efficiencv Factor

Collector Panel Factor Fp

(x*)

Collector Panel Factor Fp

U.^

Collector Hx Effectiveness

DHW Hx Effectiveness

Collector Transp. Efficiency

Storage Efficiency

Storage Heat Loss Parameter

ECSS Coefficient of Performance

ECSS Conversion Efficiency

ECSS Utilization Efficiency

Avg. Ambient DB Temperature

Avg. Wind Velocity

Avg. Wind Direction

Avg. Collector Pressure Differential

Avg. Storage Pressure Differential

Q2C1+NFAN-Q102-Q203

’/W100 -C101 -TDlOldx mOO• C101 • TDlOldx

Q

Q300+Q400+Q500

0

/W400-C101- TDlOldx

(HC ) [T200(x)-T200(x-l)l

P s

SYSTEM B/MODE 3

SYSTEM A

SYSTEM B/MODE 1

SYSTEM B /MODES 243

SYSTEM A

SYSTEM B/MODES 142

SYSTEM B/MODE 3

, SYSTEM A

, SYSTEM B/MODE 1

, SYSTEM B/MODES 2 4 3

Q300+Q400+Q500

0

t /W400 • C401 -TD401dx

Q200- (Q201+Q202)

qiQl+qi03+Q2Q4

/QlOQdx / /QQOldx

W100 • C100 -TDIOO/Ac • 1001 , QUASI-STEADY CONDITIONS

(1/T3jf[ (T100-T0Ql/I0Ql]dx, QUASI-STEADY CONDITIONS (4)

(4) COMPUTER SUBROUTINE, QUASI-STEADY CONDITONS

(4) COMPUTER SUBROUTINE, QUASI-STEADY CONDITIONS

(1/TI/ [TD101/ (T101-T200) ]dx , WIOO^O, SYSTEM A

(1/TI)/ [TD300/ (T200-T300) ] dx , W300^0, SYSTEM A

(1/TI) / [ (Q100-Q103) /Q100 ] dx , W1OO0O

/ (Q201+Q202) dx//Q200dx

Cl/Tl)/(T200-T201)dx

/Q203dx/ Q102dx

/Q203dx/Ac -/QOOldx

/Q203dx/Ac-/Q100dx

(l/TI)/T001dx

Cl/TI)/V001dx

a/TI) /DOOldx

(1/TI) /PDlOOdx , W1OO0O

Q/TI) /PDlOldx , SYSTEM B/MODES 14 3

(1) Provided for concentrating collectors only

(2) 0 = Ratio of Pressure Drop in ECSS to Total Pressure Drop

(3) NPUMP, NFAN = Ratio of pump or fan shaft work to electrical energy input

(4) QUASI-STEADY Conditions occur when 1001, T001, T100, W100 are essentially constant for 15 minutes.

PRIMARY AND SECONDARY PERFORMANCE FACTORS FOR SPACE HEATING SUBSYSTEMS

13
thermal energy collected is transferred through the storage tank before going to

the ECDS - In System B, the heat transport medium is air and the storage subsystem

is in parallel with the collector subsystem and the ECDS, thus permitting collected

solar energy to be transferred to either the storage subsystem or to the load.

In System A, during sunny periods the collector circulation pump circulates the

heat transport fluid through the collector array where it is heated by absorbed

solar radiation. The absorbed energy is transferred to the storage tank via the

collector heat exchanger.

In SYSTEM B a fan combined with five motorized dampers (MDS) permits operation of the

system in three different modes. In Mode 1 on a sunny day when there is no demand

for space heating, the fan circulates air between the collector and storage unit and

thereby temporarily stores thermal energy for future use. In Mode 2 when a demand

exists for space heating and there is solar radiation available, the fan circulates

air between the collector and the building load. In Mode 3 when a demand exists

for space heating and there is insufficient solar radiation available, the fan circulates

air between the storage unit and the building load and thus makes available the

previously stored thermal energy for space heating. In Modes 2 and 3, whenever

the building heating load is not satisfied hy the available energy either from

the collector or from storage, a final stage of heating is provided by an auxiliary

source using conventional fossil fuel or electrical energy.

To obtain data for full evaluation of all performance factors, the sensor types and

locations shown in Figure 3 are required. These include the sensors for a local

weather station which consists of total (direct plus diffuse) solar radiation at the

solar array tilt angle and ambient dry bulb temperature. Wind velocity and

direction sensors are provided on certain selected sites as special measurements.

On solar energy systems using concentrating collectors, an additional sensor measuring diffuse radiation is also required. The collector and heat transport

subsystems have temperature sensors at the collector array inlet, on the absorber

plate of one panel and at the collector heat exchanger inlet in addition to

differential temperature sensors across the collector array and collector heat

exchanger. The storage subsystem temperatures include the average storage

medium and exterior ambient temperatures. Storage subsystems utilizing stratification to improve performance should measure interior temperatures at specific

locations rather than average storage medium temperature.

14
In SYSTEM A, a single mass flow sensor is required to determine the liquid flow

rate between the collector and storage subsystems. In SYSTEM B, two mass flow

sensors are required. One flow sensor measures the air flow rate through the

collector and the second sensor measures the air flow rate to the load. The air

flow rate to the storage system is determined by the difference in flow rate to

the two sensors, assuming negligible air leakage. Operating power measurement

is required for the circulating pump of SYSTEM A, or the building fan of SYSTEM B

and for the operating controls of both systems. Since the building fan of SYSTEM B

also provides the energy to move air through the non-solar equipment and the

building, only a portion of this power is charged against the solar energy system.

Pressure differential sensors are provided across the collector arrays in both

systems and across the storage unit in SYSTEM B as special measurements.

Figure 3 also defines the performance calculations necessary for each type of

energy system. As indicated, many of the equations are appropriate for both

system types and where different equations are required, the particular system is

noted. However, not all active solar system types to be considered for the

demonstration program can be described by the listed equations. In that case, the

equations must be rewritten as required, to define the desired performance

factors for the specific systems to be evaluated. In addition to the performance

calculations noted, several of the calculated quantities are considered of

special significance and are categorized as primary performance evaluation factors.

These variables will be discussed in greater detail in Section 6.

4.2 Hot Water Subsystem

Figure 4 shows the flow schematic, instrumentation requirements and performance

calculations required for the HW subsystem. The subsystem selected for

illustration consists of the HW storage tank, circulation pump, auxiliary heat

exchanger, piping and controls but does not include the HW heat exchanger which

is located within the solar storage tank and is therefore considered a part of

the storage subsystem. (Had the HW heat exchanger been located on the outside

of the solar storage tank, it would have been considered a part of the HW

subsystem)

In operation, heat is transferred from the storage subsystem to the HW storage

tank by circulating potable water through the HW heat exchanger which is located

in the storage tank. Whenever a demand is made for hot water, solar preheated

water is withdrawn from the top of the HW storage tank and replaced by cold make-up

water at the bottom. If the temperature of the water leaving the HW tank is

15
Q302

HW

LOAD

/W301

C301

(TD301+TD302

)

Ax

16
insufficient, auxiliary energy is added either electrically or by combustion

of fuel to provide the desired HW temperature.

Temperature sensors are located at the HW heat exchanger inlet and at the

makeup to the HW storage tank and across the auxiliary heating unit.

Liquid flow measurements are required for the HW circulation loop and for

the HW flow to the load. Operating power measurements include electrical

energy consumed by the pump and controls. Electrical power or fuel flow rate

must be measured depending on the auxiliary energy source.

Figure 4 also lists the performance calculations required for the HW subsystem. A further discussion of the primary performance factors is given in

Section 6.

4.3 Space Heating Subsystem

Figure 5 shows the flow schematic, instrumentation requirements and performance

calculations for two alternate space heating subsystems using a liquid

heat transport medium. In SYSTEM A, an all-electric heating system ,

a liquid-to-air heat exchanger is located in the air duct as the primary

solar heating component, a liquid-to-air heat pump i s the secondary

solar -heating component and an electric resistance heating coil is the

backup auxiliary component which is used when the solar energy storage is

depleted. In SYSTEM B, an all fossil fuel heating system, solar heated

liquid is passed through a liquid-to-air heat exchanger located in a con- ventional fan-coil heating unit. Auxiliary energy is provided in the heat

transport loop by a conventional gas or oil fired furnace to supplement

the solar energy source during peak demand periods or when insufficient

solar energy is available. In both systems the building supply

air is heated as it flows across the various heat exchangers located in

the air duct and this increase in sensible energy represents the amount

of heat provided to the space heating load.

In SYSTEM A, four distinct modes of operation are considered, which are numbered in order of increasing electrical energy consumption and therefore

decreasing preference. In Mode 1, when the temperature of the storage

medium is sufficiently high to carry the building heating load, the two-way

17
SYSTEM A

Supply Air

F400

(Fossil Fuel Auxiliary)

FLOW

FIGURE 5 SPACE HEATING SUBSYSTEM FLOW SCHEMATICS AND SENSORS

18
category

s

s

t>

s

s

s

s

s

s

s

s

s

s

s

s

p

s

p

s

s

s

s

s

p

s

VARIABLE

g400

040 L

Q402

Q403

Q404

Q405

Q406

Q407

Q408

Q409

Q410

Q411

Q412

Q413

Q414

Q415

Q416

Q417

>!400

N401

N402

N403

M404

1J405

'1406

M407

description

Solar Used for Space Heating

Auxiliary for Space Heating

Space Heating Load

Operating Energy

Heat Pump Compressor Energy

Solar to Heat Pump

Solar to Building Air

Heat Pump Load

Heating Loop Load

Electric Energy for Aux.

Fossil Energy For Aux.

DEFINING EOLATION

/W400 C400 • TD400dx

l*/W600 • C602 (TD600-TD601)

^/W400 • C401 • TD401dx

/W600 • C600 • TD600dr

3413/ (EP401+EP402) dr

3413/F.P403dx

/W400 • C400 • TD402dx

/W400-C401-TD401dx

/W600 • C601 • TD601dr

/W400-C402'TD402dT

3413/EP400dr

HVF/F400dx

t , system a/modes 3 6 4

, system b

, SYSTEM A/ MODES 263

, SYSTEM A/ MODES 263

, SYSTEM A/MODE 1

, SYSTEM A/MODES 263

, SYSTEM B

, SYSTEM A/ MODES 3 6 4

, SYSTEM B

Total Energy Consumed

SHS Fraction of ECSS Elec. Energy

Elec. Engy. for Solar Space Htg.

Q400+Q403

Q400+Q403+Q404

Q400-KJ403+Q404+Q409

Q403+Q409

Q400+Q403-KJ410

Q400/N110

^Q403+Q412

I Q403+Q404+Q412 ^ Q403+Q404+Q409+Q412

\ Q403+Q409

\J5403+Q412 ,

, SYSTEM A/MODE 1

, SYSTEM A/MODE 2

, SYSTEM A/MODE 3

, SYSTEM A/MODE 4

, SYSTEM B

, SYSTEM A/MODE 1

, SYSTEM A/MODE 2

, SYSTEM A/MODE 3

, SYSTEM A/MODE 4

, SYSTEM B

Elec. Engy. for Conv. Space Htg.^^

Elec. Energy Saved

Fossil Engy. for Conv. Space Htg.

^

Fossil Engy. Saved

Solar Fraction of Heating Load

Solar Fraction of Energy Consumed

SHS Coefficient of Performance

Heat Pump Coefficient of Perf.

Elec. Aux. Thermal Efficiency

Fossil Aux. Thermal Efficiency

Avg. Bldg. DB Temp.

Avg. Bldg. Supply Air DB Temp.

{

Q402/HHTE

Q414-Q413

Q402/NHTF , SYSTEM B

0416-Q410 , SYSTEM B

7 (Q405+Q406) dt//0402 , SYSTEM A

/Q400dx//Q402dt , SYSTEM B

/Q400dx//Q411dx

/Q402dx//(0403-K}404+0409)dT , SYSTEM A

/Q407dx//(Q403+Q404)dx , SYSTEM A/MODES 263

/Q401dx//Q409dx , SYSTEM A/KODES 364

/Q401dx//0410dx , SYSTEM B

(1/TI) /T600dx

(1/TI) /(T600+TD600) dx

(1) HVF = Heating Value of Fuel

(2) :IHTE = Thermal Efficiency of Conventional Electric Heating Unit

(3) NHTF = Thermal Efficiency of Conventional Fossil Fuel Heating Unit

FIGURE 5 PRIMARY AND SECONDARY PERFORMANCE FACTORS

FOR SPACE HEATING SUBSYSTEMS

19
valve directs the flow of solar heated liquid to the heating loop load

heat exchanger. If the temperature of the solar heated liquid is insufficient

to carry the building load, Mode 2 operation is initiated in which the two-way

valve diverts the heating loop flow to the heat pump's evaporator heat exchanger

and the heat pump is turned on. This mode uses solar energy indirectly in

that the solar heated liquid is used to increase the heat pump's Coefficient

of Performance (COP) and thus reduce the consumption of electrical energy

required to carry the building heating load. In Mode 3, the heat pump's

heating capacity is augmented by the electric resistance heaters in the air

duct and in Mode 4 the heat pump and heating loop circulation pump are

off and the entire building heating load is carried by the electric resistance

heaters.

Figure 5 shows the measurements required for the space heating subsystem.

Absolute temperature sensors are located at the heating loop inlet to the

solar storage subsystem and at the building return air duct inlet to the heat

pump or fan coil unit. Differential temperature sensors are located in the

heating loop across the solar storage subsystem, across the heat pump heat

exchanger in SYSTEM A and across the heating loop load heat exchanger. A

differential temperature sensor is required in the building air loop to sense

the dry-bulb temperature difference between the building air supply and return

and in SYSTEM A to sense temperature difference across the combined heat

pump condensor heat exchanger and the electric auxiliary coil. A liquid

mass flow sensor is located in the heating loop and an air mass flow sensor

is located in the building air flow circuit . Operating power measurements

are required for the heating loop pump, building fan and controls for both

systems, and for the heat pump compressor of SYSTEM A. Auxiliary energy

consumption, using an electric meter for SYSTEM A and a fuel flow sensor for

SYSTEM B are also required.

The performance calculations required for the space heating subsystem are also listed in Figure 5. The primary performance evaluation factors used to

characterize the operation of the subsystem are further described in Section 6.

4.4 Space Cooling Subsystem

Figure 6 shows the flow schematic, instrumentation requirements and detailed

performance calculations for the space cooling subsystem using a thermal energy

actuated absorption chiller as the cooling component. In operation, the solar

heated liquid from storage is circulated through the absorption chiller's

generator by way of the auxiliary heat exchanger and this provides the re- quired thermal energy source.

20
21

FIGURE

6

SPACE

COOLING

SUBSYSTEM

FLOW

SCHEMATIC,

SENSORS

AND

PERFORMANCE

CALCULATIONS
The absorption chiller's useful thermal output consists of the energy indirectly

removed from the building air using an intermediate heat transfer fluid (chilled

water or brine) which is pumped through the evaporator. The heat rejection

required by the absorption thermodynamic cycle is provided by another intermediate

heat transfer fluid (water) which absorbs heat in passing through the absorber

and the condensor sections and then rejects this heat to ambient air via "a

cooling tower. The energy removed from the building air flowing over the load

heat exchanger represents the space cooling load. Since most space cooling

applications include both sensible cooling and dehumidification processes,

it is important to account for the removal of water vapor from the building air

in determining the building's cooling load.

Figure 6 shows the measurements required to fully evaluate performance of a

solar assisted space cooling subsystem. The temperature, flow and power sensors

for the heating loop and fan coil unit are identical to those previously described for the system B configuration space heating subsystem. Additional

temperature and flow sensors are required to measure absorption chiller heat

rejection and building air dehumidification. Building air dehumidification

is determined using a modified rain gauge to determine the rate of condensation

at the building load heat exchanger. An additional power sensor is required

to measure the operating power of the various pumps, fans and controls used in

the absorption chiller.

In measuring wet-bulb temperature (or alternatively measuring relative humidity)

it is recognized that the relative high expense and reduced accuracy of the

commercially available sensors may not be justified, particularly for the

residential portion of the demonstration program. Alternatively , the building

cooling load could be defined as the energy added to the chilled water circulating between the absorption chiller and load heat exchanger at the load

heat exchanger. This approach does not account for the energy gains in the

fan coil unit but does eliminate the requirement for the condensate measurement.

Measurement of the alternative building cooling load at the absorption chiller

requires coolant mass flow and inlet temperature to the load heat exchanger

and temperature difference across the load heat exchanger.

Figure 6 also lists the performance calculations required for the space

cooling subsystem and the primary items which characterize the operation of the

subsystem and are reported in the overall performance summary. These items are further discussed in Section 6.

22
5.0 PASSIVE SYSTEMS DESCRIPTION AND PERFORMANCE CALCULATIONS

The influence of the building envelope materials and construction, particularly

the area and location of windows, on building heating and cooling loads are

well established. The application of windows, walls, roof sections with sky

lights and roof ponds as part of the architectural design to utilize solar energy

as a significant fraction of the total 1 oad is commonly referred to as a passive

solar energy system. Additional requisites for a building design using windows

to qualify and be evaluated as an alternative energy source have been stated

in reference [2] as (1) operable insulating shutters or other devices which,

when drawn or closed, shall cause the window area to keep maximum outward heat

flows below a selected value, and (2) the window areas are shaded to otherwise

protected from the direct solar rays during the cooling season.

Generally the same functional elements such as the collector, storage and energy

conversion subsystems exist in passive systems but physical distinction between these

elements and the building elements is not always possible. Direct measurement

of the thermal energy flows will probably not be possible because of the

dependence on natural heat transport phenomena such as free convection, radiation

and evaporation. Therefore, the heat balance approach previously described for

active systems will have to be greatly modified for passive system evaluation .

In general, the only direct measurements practical will be with temperature

sensors, heat flow meters, scanning radiometers and pyranometers . The performance

evaluation will rely upon measurements of the auxiliary fuel usage and the interior

comfort level. Determination of the energy saved will be obtained from load

calculations for similar buildings without the solar energy system or, when

possible, measured energy consumption in an adjacent similar structure without

a solar energy system.

The following section describes the energy flow, instrumentation requirements

and performance evaluation for two alternate designs assumed for illustrating

the use of passive solar energy for space heating and cooling. The systems

are considered passive because no auxiliary energy is required for the transfer

of thermal energy between the collecting and storage elements and the building

load. Figure 7 illustrates conceptually the two passive solar energy systems

and indicates the required instrumentation for performance evaluation.

One design consists of a water pond with a movable insulation cover that is

thermally integrated into the building structure. The other design consists of

a wall solar collector with a movable insulating device and thermal storage

23
Movable

Cover

Roof

o .-h o o

<u X>

Go

G 'r o

OO

as

nG

H

.-I

O

o l» CO o

0)

GO 3 o

aG

4J

O 00 C 5^ O OO

CL,

U

<w

G

O rM o o

OH c/5

aGum

5>-v on

60GOOo

T3C

60G

•HUGG

asG>

•H

00

0)G

CL,G

Li3

60

•H

Pm

Go

•H

4JO

cG

o 60

M

•H

U •rl

u <D

Q cd <D C

*H

Uw

A

X) 3 •

CT3 4J

u

G

PS nj •H Li

G

u

u 3 > 0) u W

03 Cu ^ u CO x>

pH

s

o <2J

G

G

O <D pH rH Li *r1 CO H Ph w PM » 1o D * X /

oswHo

I-S PmH

<3Ma

24
that is also thermally integrated into the building structure. These two

designs are considered representative of current passive technology but many

other innovative architectural approaches have been built for private use and

their evaluation is in a relatively primitive stage. It is apparent that the

building solar heat gain, thermal resistance, thermal mass and thermal time

constant are the basic parameters governing the building thermal performance.

Figure 7 shows the daytime position of the movable insulating cover during the

heating season. In operation, the roof pond is uncovered during the heating

season daytime, thereby enabling solar energy to be stored by raising the irternal

energy of the water in the roof pond. At night, the pond is covered to

reduce heat losses and enable the stored energy to be used for space heating by

free convection and radiation from the ceiling. During the cooling season, at

night the roof panel is uncovered and the pond rejects heat by radiation to

the night sky and by evaporation. During the daytime, the roof panel is

covered to prevent absorption of solar energy. Space cooling is provided during

the day because the cool water in the roof panel can absorb the heat that is

released in the space and transferred through the walls and fenestrations.

Roof water ponds can be evaluated in the same manner as conventional solar

collectors. In order to do this, the overall heat transfer coefficient (UA)

must be known as a function of the temperature difference between the roof

average pond water (T ) and the average building air (T ) . This relationship

can be quantitatively established by heating the roof pond with solar energy

until a maximum temperature for the day is obtained at which time the roof

water pond is covered with the insulated panels. The rate at which the water

temperature decreases times the water mass (m) and specific heat (c p

) gives

the rate of heat transfer to the building, assuming that the heat loss through

the insulated panels is either negligible or can be calculated. Once this

quantitative relationship is established, the useful heat delivered by the water

roof pond to the building can be calculated knowing the value of the aforementioned

temperature difference.

The solar energy collected between time x^ and > Q100 is calculated by:

5.1 Roof Water Ponds

T 2 Q100 = m-c

p

[Tw(x

2 )-Tw

(T

1

)] + /

T UA(T -T ) dx w a (5.1)

1

25
where DA is the overall heat transfer coefficient between the pond and the ceiling,

and T (t„)-T (t,) is the increase in the average pond temperature during the

W 2 w 1

selected time intervals when the pond is uncovered. From a practical standpoint,

daily collector efficiency is the minimum time to obtain reasonable accuracy for

performance evaluation. The efficiency can be expressed by:

2 2 N100 = / Q100 d t// Q001 di (5.2)

T

1

T 1 where the energy collected and the incident solar radiation quantities

are summed each day when the pond is uncovered.

The rate at which heat is removed from a building during the summer can be

determined in a similar manner. Just before sunrise, the roof water pond is

covered with the insulated roof panels. The rate of water temperature increase

times the water mass and specific heat product gives the rate at which heat is

removed from the building (if the heat transfer through the insulated roof

panels is either negligible or can be calculated) as a function of the temperature difference between the water and building air.

It is imperative that the internal air temperature be carefully recorded because

performance will depend significantly on the temperature excursions permitted.

In addition, it is extremely important that the roof pond water depth also be

carefully recorded because it will also affect performance.

The fraction of the annual heating and cooling load furnished by a roof water

pond is strongly dependent on the temperature excursions permitted before auxiliary

energy is used. Therefore, internal temperature is required for space heating

and cooling and relative humidity measurements are needed for the evaluation

of space cooling. The electrical power expended for humidity control must

be measured also.

Measurements of the fossil or electrical energy used for auxiliary purposes

(E400/F400 and E500/F500) are used to determine the total auxiliary energy,

Q401 (heating) and Q501 (cooling). The heating or cooling load, Q402 or Q502

respectively, are obtained by adding the solar and auxiliary contributions as follows

:

t

2 Q402 = / [UA(T -T )dx + Q401

T 1

(5.3)

26
(5.4)

T

2 Q502 = f [UA(T -T )dx + Q501

T 3 f.T w

1

Because of the building modification to accommodate the roof pond, energy

saved calculations will require analytical prediction of the building load for

conventional design and construction.

The operation of the wal] solar collector is shown in Figure 7 during the heating

season for sunny days; the insulating device is removed thereby exposing

the high thermal capacity wall to solar radiation. At night, the deployed

insulating device and transparent cover reduce heat losses to ambient and the

heat stored in the wall during the day is transferred by convection and radiation

to the space for heating. The wall collector is primarily a heating device

so that the useful output during the cooling season is limited to the ventilation

capability of the system. To limit solar heat gains during the cooling season,

the insulating device must be deployed and the overhanging roof designed to

provide shading from direct solar radiation.

For the generalized system schematic in Figure 7 the possible heat flows are

the solar input, 1001, heat losses from the wall (a function of the wall or window temperatures T119, ambient temperature T001, wind characteristics

V001 and D001, and radiation exchange with the exterior surrounding) and

the heat delivered or removed from the building heated space.

Figure 7 shows the sensors utilized for performance evaluation of the passive

type solar systems. Although temperature sensors are indicated for the energy

storage elements, heat flow meters would also be appropriate. Because of the

passive nature of the solar system, air flow measurements are probably impractical and energy transfer and storage must be determined from the measured

temperatures and a knowledge of the thermal characteristics of the building.

Thus, performance analysis of the passive solar system must rely primarily on transient thermal analysis of the integrated building and solar system,

considering the outdoor climatic conditions and the energy release within the

building. It should be noted that the exact number and location of the temperature/

heat flow sensors are very dependent on the design of the particular instrumentation

deemed necessary for passive system evaluation.

The heat transfer calculations for room temperature predictions are similar to

5.2 Wall Collector

5.3 Performance Evaluation

27
the building heating/cooling load calculations performed by available computer

programs. However, the temperature calculations are more complex because they

require exact heat balances considering the room air, surrounding walls and

infiltration of the outdoor air. Since the major variable in passive system

performance is the hourly room temperature, it is necessary to account for the

transient heat conduction and thermal storage of the building and internal mass.

Determination of the temperature and humidity in non-air conditioned rooms

responding to randomly fluctuating outdoor climatic conditions can be determined

using hourly simulations of heat gain and storage obtained with standard

algorithams published by ASHRAE [3].

A computer program employing these algorithms is available [4]. The calculation

sequence as depicted in Figure 8, requires detailed data input for the building,

weather and operating schedule. Building data includes geometric characterization

of the construction and materials used for the exterior envelope, interior

partitions, ceilings and floors and their associated thermophysical properties.

Weather data is provided in the form of a National Weather Service Tape or provided as measured data including wet and dry bulb temperature, wind, and solar

radiation. The operating schedule is used to determine energy release profiles for

the appliances and lights and metabolic heat release by the occupants.

Normal solar radiation inputs corrected for local cloud cover, collector tilt

angle and shading can be calculated for conventional building construction heat

gain or for solar modified construction using roof ponds and window collectors.

Routines to calculate the transmission, reflection and absorption for direct

and diffuse solar radiation are used to calculate the solar heat gain through

fenestrations. The thermal response of the various building structural

components and furnishings are calculated using conduction, radiation and convection

heat transfer routines to provide the necessary inputs to the room temperature

calculation (RMTMP) [4], This subroutine compares the prescribed room temperature

with the calculated temperature, and variances beyond the prescribed limits result

in calculation of the heating or cooling loads to satisfy the temperature.

28
29
6 . SYSTEMS PERFORMANCE EVALUATION SUMMARY (ACTIVE-SYSTEMS)

As indicated in Figures 3 to 6, numerous calculations are performed for the

elements comprising a system, subsystem or for the individual components in

the solar assisted heating and cooling system. As previously described,

performance evaluation factors are classified into three categories, primary,

secondary and special. The primary performance evaluation factors are listed

in Table 1 and consist of those evaluation factors that summarize the

performance of each subsystem, the solar energy system, the building and

climate and the utilization of the solar energy system by the occupant.

The secondary performance evaluation factors include the detailed performance

of the solar collectors, storage tanks, heat exchangers and other solar energy

components as well as the components of the conventional HVAC equipment used

such as hot water heaters, furnaces, heat pumps and other energy conversion

equipment. Special evaluation factors include those calculations performed

using data from certain optional sensors such as the diffuse pyranameter or

the collector absorber panel temperature.

This section will describe each term of the primary system performance

evaluation summary to clearly define the terminology and calculation method.

In addition, some of the more important terms of the secondary and special

performance calculations are described.

6.1 Performance Factors - General

Two types of performance factors are indicated in Table 1; a thermal energy

quantity defined by the letter "Q", and a performance index defined by the

letter "N".

6.1.1 Performance Factors Based on Thermal Energy Quantity

In the evaluation of the net thermal energy flow into or out of a subsystem,

the general expression for energy addition to a fluid flowing through a subsystem or component is determined by integrating the measured instantaneous

rate of heat addition as follows:

Q = /

2 me (T - T. )dx

p out in

T

1 where m is the fluid mass flow rate in LB/HR ,

( 6 . 1 )

0 ^ is the fluid specific heat at constant pressure in BTU/LB °F,

30
- T is the fluid temperature rise in the subsystem or component

F and

tare the initial and final times of the integration period*

In general, both T _ and T. are functions of time, m is a function of both

time and temperature and c^ is a function of temperature: therefore, evaluation

of Equation (6.1) usually involves a numerical integration procedure in which

the total time interval is broken down into subintervals that are sufficiently

small so that during the subinterval each variable in the integrand can be

considered constant.

Ideally continuous data measurement is desired, however, in the actual data

acquisition system the sensors are scanned at periodic intervals and the

instantaneous measured values are used to evaluate equation (6.1). Changes

in the variables between data scans are not determined and errors are introduced

into the calculated results. Section 7 describes these errors due to data

sampling and presents the results of a study of sampling errors based on

data from one of the solar demonstration houses at the Colorado State

University

In general, for all thermal energy quantities the smallest integration period

desired will be one hour, with additional integration periods to provide

cumulative daily, monthly, and seasonal or annual data.

6.1.2 Performance Indices

In the evaluation of a performance index which depends on the ratio of

two thermal quantities such as the energy conversion efficiency, the index N

is given by

V Ql

dT

N = — (6.2)

T

2 / Q

2 dt

T 1

In this equation and are hourly thermal energy quantities calculated by

Equation (6.1). For meaningful results the integration times must be sufficiently

long, not only to preclude division by zero, but to assure that a true average

value is obtained. Thus, the performance index calculations involving the ratio

of thermal energy quantities may require evaluation on a daily, monthly, or

annual basis using hourly values of the thermal energy quantity.

31
Other performance indices such as average temperature are determined by

integrating the measured temperature and dividing by the integration period as follows

dx ( 6 . 3 )

where is the actual temperature measurement,

x^ and x2 ate the initial and final times of the integration period and

TI= T

2 ~ x^ represents the total time period over which the average

temperature is evaluated.

The minimum integration period varies depending on the particular temperature.

For example, outdoor dry bulb temperature would be desired for hourly, daily and

monthly periods whereas storage tank ambient temperature might be evaluated on

a monthly basis.

6 . 2 Energy Saved - General

Since the energy sources for both conventional and solar assisted heating and cooling

include different energy types such as gas, oil or electrical, it is important to

distinguish between at least the fossil sources and the electrical sources. It

is conceivable that when a conventional system is replaced with a solar system,

the solar system could require more electrical energy to run (due to operating power

for the solar pumps, fans or controls) than the conventional system; however, the

solar system should significantly reduce the consumption of fossil energy. Due to

the difference in energy costs in various parts of the country, the same solar

system and same type building in different locations may have wide variance in the

cost effectiveness or payback period.

The basic approach to determining the energy saved is to first measure the total

electrical energy and the total fossil fuel energy consumed by the solar assisted

system to provide a given building energy load at a given occupant utilization

level. An assessment of a non-solar system must then be made to determine the

type of equipment that would be provided if there were no solar equipment.

Since available performance data of energy conversion equipment are usually

based on measurements taken at a design condition for steady state equipment

operation, the effects of off-design operation and duty cycling on equipment

performance must be estimated to improve the accuracy of the predicted energy

consumption. Alternatively, equipment performance based on seasonal efficiency

rather than design point efficiency should be used. The electrical energy

32
and fossil energy consumption of the non-solar system must then be calculated

assuming some equipment performance coefficients and operating efficiencies

based on the same building load and occupancy utilization that was measured

for the solar system. The energy saved is then the difference between the

calculated value of energy consumed by the non-solar system and the measured

value of energy consumed by the solar system. In reporting these results,

the assumed non-solar system must be described as well as the assumed performance

characteristics and efficiencies.

6.3 Climatic Primary Performance Factors

6-3.1 Total Solar Energy Incident (Q001 »Q002*)

Total incident solar radiation is measured by a sensor mounted in the plane

of the collector array on either a continuously integrated or frequently

sampled basis. Data are recorded at specified intervals for use in the calculation of collector and system efficiencies. For those solar energy systems

having a significant dependence on direct solar radiation (such as concentrating

collectors) , diffuse insolation will also be measured independently with a separate sensor located in the plane of the collector array and the direct

component of incident solar radiation is determined by subtraction of diffuse

from the total incident solar radiation. The total and direct integrated

values of incident solar radiation are calculated by integrating the

instantaneous values as follows:

Q001 = / 1001 dx (6.4)

Q002* = ;

2 (1001-1002) dx (6.5)

Where 1001 and 1002 are the instantaneous values of incident total

solar radiation and diffuse solar radiation respectively, and x. , x

? are the integrating time intervals.

Q002* is not identified as a primary performance factor in Table 1

however, its importance for certain solar collectors warrants

inclusion as a special measurement for some active and passive solar

energy systems.

33
6.3.2 Average Ambient Dry Bulb Temperature (N113)

Average ambient dry bulb temperature is a significant parameter in determination

of system performance and comparison of alternate solar energy systems in

different climatic regions. It is obtained by integration of the instantaneous

ambient dry bulb temperatures as follows:

x„

N113 =

/

TI

T001 dx ( 6 . 6 )

6.4

where T001 is the instantaneous dry bulb temperature, and TI is the

integration period T

2 -Ti‘

N113 should be obtained for the hourly, daily and monthly data summaries.

Energy Collection and Storage Subsystem (ECSS) Primary Performance Factors

The primary performance factors are based on the ECSS shown in Figure 3.

6.4.1 Solar Energy Collected (QlOO)

The amount of solar energy collected in a given time period is obtained by

evaluating Equation 6.1 using the appropriate sensors in the ECSS as follows:

1 T

o QlOO = — f W100-C100- TD100 dx (6.7)

A. c x

x Where A is the total collector area defined by the outside dimensions

c of the collector array, *

W100 = Collector array fluid mass flow rate,

C100 = Specific heat of collector fluid,

TD100 = Fluid temperature increase across the collector array.

Additional data may be required to correct the fluid specific heat for temperature,

concentration, etc.

6.4.2 Total Solar Energy Utilized (Q300, Q400, Q500, Q203)

For the demonstration program, solar energy is used in as many as three applications

i.e., hot water heating, space heating, and space cooling. For each application,

^Proposed Solar collector test procedure [6] rates flat plate collector performance

on transparant frontal area instead of total area, therefore, thermal comparison of

result will require adjustment by appropriate area ratio.

34
Equation (6.1) is evaluated using the appropriate measurements in the HW loop

and in the heating or cooling loop. Since some of the measurements used for

the heating and cooling calculations are the same, additional information must be

supplied (such as the operating status of the absorption unit) to determine

whether the calculation pertains to heating or cooling. The following equations

are used to calculate each component for the ECSS using a liquid heat transfer

medium (SYSTEM A in Figure 3):

6.4.2.

Solar Used for Hot Water

T 2 Q300 =f W300-C301-TD301 dx (6.8)

6. 4. 2.

Solar Used for Space Heating

T

2 Q400 = / W400 • C400 • TD400 dx

T 1

6.4.2.Solar Used for Space Cooling

T 2 Q500 = f W400 • C400 * TD400 dx

(6.9)

( 6 . 10 )

6.4. 2.4 Total Solar Energy Utilized (Liquid Heat Transfer Medium)

The total solar energy utilized is the sum of the solar energy used in each

application and is given by:

Q203 = Q300 + Q400 + Q500 (6.11)

6. 4. 2.Total Solar Energy Utilized (Air Heat Transfer Medium)

For the ECSS using air as the heat transfer medium (SYSTEM B in Figure 3)

the total solar energy utilized is given by:

T

2 Q203 =f W400 • C401 * TD401 dx (6.12)

T 1

6.4.3 ECSS Conversion Efficiency (Nlll)

The ratio of total solar energy actually utilized to the total solar energy

incident on the collector array is termed the solar subsystem conversion

35
efficiency and is a measure of the ability of the ECSS to convert incident

solar radiation into useful thermal energy. ECSS conversion efficiency is

calculated by:

T T r\ Nlll = /

2 Q203 dx/A

c / Q001 dr (6.13)

Because of the solar energy storage time dependence, ECSS conversion efficiency

(Nlll) should be determined only for the monthly, seasonal and annual data

summary

6.5 Hot Water Subsystem (HWS) Primary Performance Factors

6.5.1

Hot Water Load (Q302)

The total thermal energy required for heating HW from the inlet (makeup)

to delivery temperature is given by:

T 2 Q302 =f W301-C301- (TD301 + TD302)di (6.14)

The HW load (Q302) should be obtained for the hourly, daily, monthly and annual

data summary.

6.5.2

Solar Fraction of the HW Load (N300)

The solar fraction of the HW load is calculated by:

N300 = / dx, W301^0

2 TD301

TI ' TD301 + TD302

T 1

(6.15)

where TD301 and TD302 are the temperature differences across the HW

storage tank and auxiliary heat exchangers, respectively, when

there is a flow to the HW load (W301^0)

This parameter should be evaluated on a daily, monthly and annual basis.

6.5.3

HW Electrical Energy Saved (Q311)

The measured electrical energy used by the HW subsystem of Figure 4 is given by

Q309 = Q303 + Q305 + Q308 (6.16)

where Q303 is the energy required to operate the circulation pump,

Q305 is the energy input to the auxiliary heater (Q305=0 for a

fossil auxiliary)

and Q308 is the HWS fraction of the ECSS operating energy.

36
The calculated electrical energy required to operate a conventional hot water

subsystem is given by:

Q310 = Q302/NHWE (6.17)

where Q302 is the hot water load previously described,

and NHWE is the thermal efficiency of a conventional HW subsystem using

electricity as an energy source.

The electrical energy saved is the difference between the calculated electrical

energy to operate a conventional system having the same source and

delivery temperature and usage rate as the solar energy system and the

measured electrical energy required to operate the solar energy system as follows:

Q311 = Q310-Q309 (6.18)

If a negative value is obtained for Q311 this implies that the particular

solar HWS consumes more electrical energy than the assumed conventional

system it is replacing.

6 . 5.4 HW Fossil Energy Saved (Q313)

The fossil energy used by the solar HWS is calculated in the following manner:

T

2 Q306 = HVF / F300 dt (6.19)

T 1

where HVF is the fuel heating value in BTU/LB and F300 is the measured

mass flow rate of fuel to the auxiliary in LB/HR.

The fossil fuel energy required to operate a conventional HWS is calculated from:

Q312 = Q302/NHWF (6.20)

where Q302 is the HW load and NHWF is the thermal efficiency

of a conventional HW system using fossil fuel as an energy source.

The fossil fuel energy saved is the difference between the calculated fossil

energy required to operate a conventional HW system and the measured fossil

energy required to operate a solar energy system as follows:

Q313 = Q312-Q306 (6.21)

37
6.6 Space Heating Subsystem (SHS) Primary Performance Factors

The primary performance factors are based on the SHS shown in Figure 5.

b.6.1 Space Heating Load (Q402)

The space heating load is the sensible energy added to the air in the building

and is given by:

Q402 = / W600-C600-TD600 dx ( 6 . 22 )

where W600 is the building air flow rate,

C600 is the specific heat,

and TD600 is the temperature rise of the air flow across all the heat

exchangers in the air handling unit

.

The space heating load should be determined for the hourly, monthly

and seasonal data summary.

6.6.2 So lar Fraction of Space Heating Load (N400)

The solar fraction of the space heating load for the SHS comprised of a heat

pump and electric auxiliary (SYSTEM A) is given by:

N400 = / (Q406 + Q407)dx// Q402 dx (6.23)

where Q406 is the energy delivered to the heating loop load heat

exchanger in mode 1,

and Q407 is the energy delivered to the heat pump evaporator in modes 2 and 3.

The solar fraction of the space heating load for the SHS comprised of the fossil

fuel auxiliary (SYSTEM B) is given by:

N400 = / Q400 dx// Q402 dx (6.24)

where Q400 is the energy delivered to the heating loop load heat

exchanger

,

and Q402 is the space heating load previously described.

This parameter should be determined for the daily, monthly and seasonal data

summary

.

6.6.3 Space Heating Electrical Energy Saved (Q415)

The electrical energy used by the heat pump system shown as system A in Figure

38
(6-25)

5 is given by:

Q413 = Q403 + Q404 + Q409 + Q412

where 1^403 is Che energy consumed by the heating loop circulation

pump, building fan and all controls,

0404 is the energy to operate the heat pump compressor,

Q409 is the energy to the electric auxiliary heat exchanger and

Q412 is the SHS fraction of the ECSS operating energy.

The electrical energy consumed by a non-solar heat pump heating system is

given by:

Q414 = Q402/NHTE (6.26)

where Q402 is the measured space heating load,

and NHTE is a modified coefficient of performance of the non-solar

heat pump system which as defined in reference [ 2 ] includes

electrical energy required to operate the compressor, supply fan,

return fan, outdoor air fan and HVAC control circuit.

The modifications to the equipment COP include the supplemental energy reauired

for defrosting and auxiliary heating and the reduction in performance due to

cyclic operation at off design conditions. Reference [ 7j presents data

describing off-design heat pump performance and the discrepancy between manufacturers

performance data and measured performance primarily due to defrosting requirements.

The electrical energy saved is therefore the difference between the calculated

electrical energy required to operate a conventional heating system and the

measured electrical energy required to operate the solar energy system as follows:

Q415 = Q414-Q413 (6.27)

6.6.4 Space Heating Fossil Energy Saved (Q417)

The fossil energy saved by an all electric-heating system is obviously zero,

therefore, to illustrate this calculation, the fossil energy used by the alternate

SYSTEM B is given by:

T

2 Q410 = HVF / F400 dx (6.28)

T 1

where HVF is the heating value of the fuel,

and F400 is the mass flow rate of fuel consumed by the auxiliary.

The fossil-energy consumed by a non-solar heating system must be calculated for

the measured load conditions based on the performance characteristics and/or

component efficiencies of the equipment as follows:

Q416 = Q402/NHTF (6.29)

39
where Q402 is the space heating load and,

NHTF is the assumed thermal efficiency of the equipment.

The fuel energy saved is given by the difference between the calculated

fossil energy consumption of the non-solar heating system and the

measured fossil energy consumption of the solar energy system as

follows

Q417 = Q416-Q410 (6.30)

6.7 Space Cooling Subsystem (SCS) Primary Performance Factors

The primary performance factors of the space cooling subsystem are based on

the SCS shown schematically in Figure 6.

6.7.1 Space Cooling Load (Q502)

The space cooling load is the total energy, including sensible and latent,

removed from the air in the building and is given by:

X 2 Q502 = f [ W600 '0600' TD600+W601 • h„_, ] dx (6.31)

r (j T i

where W600 is the building supply air flow rate,

TD600 is the temperature differential across the fan-coil unit^

W601 is the flow rate of condensed water vapor from the cooling coil,

and h is the latent heat of vaporization of the condensate,

r G

Alternatively if air side measurements are not practical, the space cooling

load can be approximated from Q507 shown in Figure 6 which is the measured

absorption chiller load.

6.7.2 Solar Fraction of Space Cooling Load (N500)

The solar fraction of the space cooling load is given by:

T T

,

N500 = /

2 Q500 dx// 2 Q506 dx (6.32)

T 1 T

1 where Q500 is the solar energy delivered to the SCS,

and Q506 is the total thermal energy delivered to the absorption

chiller generator consisting of solar and auxiliary thermal energy.

This parameter should be determined for the daily, monthly and seasonal data

summary

.

40
6.7 3 Space Cooling Electrical Energy Saved

The electrical energy used by the solar assisted space cooling subsystem is given

by:

Q510 = Q503 + Q509 (6.33)

where Q503 is the cooling subsystem operating energy including

power for the heating loop circulation pump, building fan, absorption

unit pumps, cooling tower fans and all subsystem controls,

and Q509 is the space cooling subsystem fraction of the ECSS

electrical energy consumption.

The electrical energy consumed by a non-solar cooling system must be calculated

for the measured load conditions, source and sink temperatures using the appropriate conversion efficiency as follows:

Q511 = Q502/NCLF (6.34)

where Q502 is the measured cooling load,

and NCLF is the electrical efficiency of the non-solar cooling

equipment

The electrical energy saved is the difference between the calculated electric

energy consumption of the conventional cooling system and the measured electric

energy consumption of the solar energy system as follows:

Q512 = Q511-Q510 (6.35)

6.7.4 Space Cooling Fuel Energy Saved (Q514)

The fossil fuel energy used by the solar space cooling subsystem

is given by:

t

2 Q508 = HVF f F500 dr (6.36)

T 1

where F500 is the fuel mass flow rate to the auxiliary unit,

and HVF is the heating value of the fuel.

The fuel energy consumed by a non-solar cooling subsystem must be calculated

for the measured load conditions based on the component performance characteristics

and/or efficiency as follows:

41
Q513 = Q502/NCLF (6.37)

where Q502 is the measured space cooling load,

and NCLF is the thermal efficiency of the non-solar equipment.

The fossil fuel energy saved' is given by the difference in the calculated fossil

energy consumption of the non-solar cooling system and the measured fossil

energy consumption of the solar energy system as follows:

Q514 = Q513-Q508 (6.38)

6.8 Solar Energy System/Building Summary

The following primary performance factors summarize the performance of the

overall solar energy system and the building.

6.8.1

Average Building Dry Bulb Air Temperature (N407)

Average building temperature is an occupant utilization parameter that will have a

strong influence on system performance for both heating and/or cooling and is

therefore useful for comparison of alternate systems. Average dry bulb temperature

should be evaluated as follows

:

N400 = JL

TI

T600 d-r (6.39)

where T600 is the measured building air dry bulb temperature.

This parameter should be determined for the hourly, daily, monthly and seasonal

data summary.

6.8.2

Total Auxiliary Energy (Q301, Q302, Q303, Q600)

Auxiliary energy is required for HW, space heating and space cooling whenever

the solar system is not capable of meeting the demand. The amount of auxiliary

energy required is determined using the same basic approach described in Section

6.4.2

for solar energy utilized and is calculated as follows:

6. 8. 2.1 Auxiliary Used for HW

X

2 Q301 = / W301-C302- TD302 dx (6.40)

42
6.S.2.2 Auxiliary Used for Space Heating

For SYSTEM A of Figure 5, the auxiliary energy used for space heating is given

by:

T 2 Q401 = / W600 • C602 (TD600-TD601) dx (6.41a)

For SYSTEM B of Figure 5, the auxiliary energy used for space heating is given

by:

Q401 = / W400 • C401 * TD401 dr (6.41b)

6. 8.2.3 Auxiliary Used for Space Cooling

T

2 Q501 = / W400-C401- TD401 dx (6.42)

6. 8.2.4 Total Auxiliary Energy Utilized

The total auxiliary energy utilized is the sum of the auxiliary energy used for

each application and is given by:

Q600 = Q301 + Q401 + Q501 (6.43)

Total auxiliary energy should be determined for hourly, daily, monthly and

seasonal/annual data summary.

6.8.3 Total Operating Energy (Q601)

The total operating energy is the thermal equivalent of the electrical energy

required to run the pumps, fans, compressors and controls but excludes the

electrical energy used for auxiliary heating purposes. The total operating

energy is composed of the individual components as follows:

Q601 =

where

Q102 + Q303 + Q403 + Q503 (6.44)

Q102 is the solar subsystem operating energy defined in Figure 3,

Q303 is the HW operating energy defined in Figure 4,

Q403 is the space heating operating energy defined in Figure 5,

Q404 is the heat pump compressor energy defined in Figure 5,

Q503 is the space cooling operating energy defined in Figure 6.

43
Total operating energy should be determined for the hourly , daily , monthly and

seasonal/annual data summary.

6.3.4 Total Energy Delivered to Building Load (Q602)

The total building energy load is the sum of the HW load, the space heating load

and space cooling loads previously defined, and is calculated by:

Q602 = Q302 + Q402 +Q502 (6.45)

The total building energy load should be determined for the hourly, daily,

monthly, seasonal/annual data summary.

6.8.5 Total Energy Consumed (Q603)

Total energy consumption consists of the total solar, fossil and electric

energy consumed by all of the subsystems as follows:

Q603 = Q102 + Q307 + Q411 + Q515 (6.46)

where Q102 is the ECSS operating energy.

Q307 is the HWS total energy consumption defined in Figure 4,

Q411 is the SHS total energy consumption defined in Figure 5,

and Q515 is the SCS total energy consumption defined in Figure 6.

Total energy consumed should be determined for the hourly, daily, monthly and

seasonal/annual data summary.

6.3.6 Total Electric Energy Saved (Q604)

The total electric energy saved is given by:

Q604 = Q311 + Q415 + Q512 (6.47)

where Q311, Q415 and Q512 are the electric energies saved for HW,

space heating and space cooling, respectively.

6.3.7 Total Fossil Energy Saved (Q605)

The total fuel energy saved is given by:

Q605 = Q313 + Q417 + Q514 (6.48)

where Q313, Q417 and Q514 are the fossil fuel energies saved for

HW, space heating and space cooling respectively.

Energy saved should be determined for the hourly, daily, monthly and seasonal/

annual data summary.

44
6.S.8 Solar Fraction of Building Load (N601)

The solar fraction of the building load is determined by averaging the solar

fractions of the individual subsystem loads as follows:

T 1 [N300-Q302 + N400 Q402 + N500 Q502]dt

(6

f

2 [Q302 4- Q402 + Q502]dx

where N300, N400 and N500 are the solar fractions, respectively, of

the HW load, heating load and cooling load,

and Q302, Q402 , Q502 are .respectively , the HW load, heating load

and cooling load.

6.8.9

System Performance Factor (N602)

The ratio of the total energy delivered to the building load to the total

equivalent fossil fuel energy expended is defined to be the system performance

factor and is calculated as follows:

T T N602 = /

2 Q602 dr//

2 [Q306 + Q410 + Q508 + (0601 + 0305 + 04 09) 3dt (6.50)

T x NELEC

1 1 where Q306, Q410 and Q508 are the fossil fuel energies consumed,

respectively, for the HW, space heating and space cooling auxiliaries,

Q305 and Q409 are the electrical energies consumed respectively for

the HW and space heating auxiliaries,

NELEC is the overall thermal efficiency for conversion of fossil energy

at the power plant to electrical energy at the building.

The system performance factor should be determined for the daily, monthly and

seasonal/annual data summary.

6.9

Secondary Performance Factors and Measurements

In addition to the primary system performance factors described in Section 6.3

to 6.8, certain secondary performance evaluation factors for the ECSS and ECDS

are of sufficient importance to warrant further discussion.

45
6.9.1 Daily Integrated Collector Efficiency (N100)

The ratio of the daily integrated solar energy collected by the array to the daily

integrated total solar energy incident on the array is termed the daily integrated

collector efficiency and is a measure of the ability of the solar collector to

convert daily incident solar radiation into thermal energy available either

immediately or for storage and subsequent use thereof to support the building

thermal energy load. Daily integrated collector efficiency is calculated by:

N100 = / Q100 dx// Q001 dx (6.51)

where the numerator represents the total thermal energy collected

per day for one square foot of collector and the denominator represents

the total solar radiation incident on one square foot of collector

per day.

6.9.2 Collector Array Instantaneous Performance (N101, N102, N103, N104 )

The performance of a flat plate collector operating under steady state

conditions can be described by the following equation:

A

c

F

s

t(IT) (T«) e

- U

L

(Tf>1

- T

a

)] (6.52)

where = rate of useful energy extraction from the collector

= collector area, aperature

F

R

= Actual useful energy collect ed

useful energy collected if the entire

collector were at the inlet fluid temperature

l,p = total incident solar radiation

(x«)

e = effective transmission absorptance product of collector

U

T = heat transfer loss coefficient for the collector

T^

^ = fluid temperature entering collector

T

a = ambient air temperature

Defining the solar collector efficiency as the ratio of useful energy extracted

from the collector to the total solar radiation incident, equation (6.52) is

rearranged to give collector efficiency as follows:

N101=F

r

[(x“)

e

- u

L (6.53)

46
A plot of equation (6.53) as a function of (Tf ^ - Ta )/lT for a range of

operating conditions yields a first or second order curve with the y axis

intercept equal to FR

(t °0 e and slope equal to Fpl^.

If an individual collector panel is instrumented the same as the collector

array with inlet and exit temperatures and flow rate monitored, or if the

entire collector array is co-planer, then by evaluating the two factors

F (t^) and F U over the life of the demonstration, degradation of the array

K S R L

due to changes in the t® product or (heat transfer loss coefficient) will

be revealed.

Meaningful efficiency measurements are obtained when essentially steady state

is achieved for the previous 15 minutes (three data scans, if the scan occurs every five minutes). The following measurements should be constant:

T001 (ambient dry bulb air temperature)

T100 (array inlet temperature)

W100 (array flow rate)

1001 (total incident solar radiation)

Other constraints for the procedure as obtained from reference (6 ) are to

limit the calculation to times during which the angle between the sun and the

collector array normal is less than 30° degrees and the total incident solar

2 2 radiation is greater than 630 w/m (200BTU/hrft ). If all the above constraints

are satisfied, then data taken at the last data scan are used to calculate the

following performance indicies.

6. 9. 2.1 Instantaneous Collector Array Efficiency (N101)

N101 W100 • C100 • TD100

A -1001

c

6. 9.2.2 Collector Panel Efficiency Factor (N102)

N102 = (T100-T001) / 1001

(6.54)

(6.55)

6. 9.2.3 Collector Panel Factors (N103, N104)

The newly calculated values of the parameters N101 and N102 are used together

47
with previously calculated values of N101 and N102 using the previously described

slope/intercept linear curve fit and new values of the collector panel factors

N103 and N104 are obtained, where:

N103 = F_ (t*) R e (6.56)

and

,

N104 = F U

R L (6.57)

The above described procedure should be performed at the start of each hour

until a data scan occurs which satisfies all specified constraints. For that

scan, the calculated values of N101, N102 , N103 and N104 are reported in the

hourly data summary and no further scans are required for the remainder of the

hour. At the start of the next hour the procedure is repeated.

6.9.3 Collector Heat Exchanger Effectiveness (N1Q5)

For the ECSS where the thermal capacitance of the storage container is much

greater than the flow capacitance of the collector loop, the collector heat

exchanger effectiveness is given by:

1

X 2 N105 = 1 (TD101)/ (T101-T200) dx (6.58)

T 1

Evaluation of collector heat exchanger effectiveness can be done on a monthly

and annual basis.

6.9*4 HW Heat Exchanger Effectiveness (N106)

The hot water heat exchanger effectiveness is determined as follows:

N300 ('TF300) / (T200rT300)dT

(6.59)

Due to the requirement for double walled heat exchangers to prevent any possible

contamination of potable water with non-potable water, the HW heat exchangers

may present a substantial thermal resistance to heat transfer and thereby

reduce the amount of solar energy available. Any tendency for fouling of the

heat exchangers would be revealed by changes in the calculated values of heat

exchanger effectiveness.

48
6.9.5 Storage Subsystem Efficiency (N108, N109)

The storage subsystem efficiency is defined as the ratio of the sum of the

output of stored thermal energy and the increase in stored thermal energy to

the input of thermal energy to storage as follows:

=

T 1 (Q201 + Q202)dx

t

2 / Q200 dx

(6.60)

where Q201 is the hourly output of thermal energy from the storage

device,

Q202 is the hourly increase in stored energy,

and Q200 is the hourly input of thermal energy to the storage device.

The normal source of thermal energy input to storage is from the solar energy

collectors, however, other thermal energy sources, such as off-peak auxiliary

energy must also be included. Where more than one storage container is used,

individual evaluation is required.

Storage efficiency is related to the subsystem heat losses which may be

either deliberate (such as the dumping of energy to ambient) or non-deliberate

due to air leakage or insulation losses. Heat loss through insulation is related

to the following parameter:

1

T

2 N109 = Yf- / (T200-T201)dx (6.61)

T 1

where T200 is the average storage medium temperature, and

T201 is the ambient temperature surrounding the storage container.

Evaluation of these parameters (N108 and N109) should be performed for the

monthly and seasonal/annual data summary.

6.9.6 Average HW Load Temperature (N307)

The average HW delivery temperature to the load is a significant parameter

in the comparison of alternate HW solar systems, in that this temperature

is controlled by the occupants and subsystem performance will depend

on the actual control point setting.

1

t 2

N307 = / (T301 + TD301 + TD302)dr (6.62)

49
where T301 is the make-up water temperature,

TD301 is the temperature difference across the hot water storage

and TD302 is the temperature difference across the HW auxiliary

heat exchanger.

6.9.8

Average Gallons HW Consumed (N308)

The time of day at which hot water is used and the total daily consumption

are significant parameters in evaluating performance and comparison of

alternate HW solar systems. The average HW consumption in gallons is given

by:

Energy Conversion Equipment Coefficient of Performance

Enegry conversion equipment uses electrical or thermal energy to

raise heat from a low temperature source to a higher temperature sink and

is rated by the ratio of the useful heat transferred to the energy input.

Useful heat transferred consists of heat delivered to the sink in the heating

mode and heat extracted from the source in the cooling mode.

Measurement of the Coefficient of Performance (COP) is desired for energy

conversion equipment such as heat pumps in which the useful thermal energy

delivered to the building is significantly greater than the electrical

energy consumed. Referring to the heat pump system shown as SYSTEM A in

Figure 5, Space Heating COP is calculated from:

2 N308 = .12 / W301 dr ( 6 . 63 ) T 1

where W301 is the measured flow rate in lbs/hr.

The HW consumption should be determined for the hourly, daily, monthly

and annual data summary.

Space Heating Equipment COP (N404)

T N404 = / (6.64)

T

1 where Q407 is the useful thermal energy added to the building

supply air from the heat pump,

Q403 is the electrical energy required to operate the SHS pumps

fans and controls.

50

i
Q404 is the electrical energy required to operate the heat pump

compressor.

This parameter should be determined for the daily, monthly and seasonal

data summary.

Measurements of the Coefficient of Performance {COP) are desired for thermally

actuated equipment such as the absorption chiller for Figure 6 and for other

equipment such as solar assisted Rankine Cycle equipment or dessicant

dehumidification systems as appropriate.

Referring to the absorption chiller shown in Figure 6, the Coefficient of

Performance is calculated as:

6. 9. 8.

2

Space Cooling Equipment COP (N503)

T 2 T

2 N503 = / Q507// Q506 dx (6.65)

T

1

T 1

where Q507 is the useful thermal output of the absorption

chiller as defined in Figure 6,

and Q506 is the thermal energy input to the absorption chiller

as defined in Figure 6.

51
7.0 UNCERTAINTY ANALYSIS OF SOLAR PERFORMANCE FACTORS

The uncertainty of determining the performance evaluation factors Lor a particular solar energy system/building/climate combination is related to the data

requirement accuracy for sensor signal conditioning, data acquisition sampling

rate and data processing method. Non-instrumentation variables such as building

heating or cooling load, occupancy, conventional heating and air conditioning

equipment operation and meteorological parameters must also be considered when

comparing the performance of solar energy systems in different buildings or

climatic regions.

To establish acceptable tolerances in the performance evaluation factors, the

contribution of sensor accuracy and sampling rate error to the total performance

factor uncertainty must be derived and set in perspective by comparison with

the pertinent non-instrumentation sources of the performance factor uncertainty.

The approach, rationale and sensitivity analysis for several performance factors

are described in the following sections:

° Sensitivity Analysis Methods

° Specific Error Analysis

° Overall Instumentation Errors

° Recommended Sampling Rates and Data Requirement Accuracies

7.1 Sensitivity Analysis Methods

Two methods are in general use for combining precision errors in measuring

several variables to estimate the error in a calculated function of those

variables. The particular method used depends on whether the component errors

are considered to be absolute limits or statistical bounds (such as 3a limits)

the form of the relationship between the variables and the calculated function,

and the specification of component errors (percent of reading or absolute in

terms of measured units)

.

7.1.1 Absolute Limits

If the component precision errors are considered to be absolute limits and a functional relationship exists such that

T = f(x,y,z) (7.1)

If the component errors in x, y, and z are Ax, Ay and Az respectively,

and f(x,y,z) is expanded in a Taylor series; then:

52
f(x + Ax, y + Ay, z + Az) = f(x,y,z) +

3f

A

x , 3fAy 3f Az

3x 3y 3z

+1/2 (7.2)

Neglecting the second order and larger terms because Ax, Ay, Az are assumed

small (^1%), the total measurement error is:

Af + (7.3)

In the general case for a function R (a function of any number of variables)

the error can be expressed as:

i*l

1

7.1.2 Statistical Bounds

In the absence of a function relating the component error sources, a general

equation can be used to find the measurement error. If the measurement is

defined by R(X, , X„ X ), where R is the desired measurement and AX,, AX

are the individual error sources, the following equation can be used:

ar = (7.5)

This equation assumes that the errors are random and uncorrelated. The precision

errors will be expressed as + AX. As a probable error in either of the two

cases (functional or non-functional relationship) , the true value of R will be

between R - AR and R + AR for some percentage of all readings. The percentage

involved depends upon the error expressions used for the component errors.

7.1.3 Error Analysis - Daily Integrated Collector Array Efficiency

An error analysis of the calculations of daily integrated collector array

efficiency is presented to illustrate using both methods discussed in the

preceding paragraphs.

53
From Figure 3, the daily integrated collector array efficiency is calculated as:

N100 = /Q100dx//Q001dx = f W100-C100-TD100 dx/Ac f IOOldx (7.6)

If the component errors are independent of time than the uncertainty in the

integrated daily efficiency is the same as the uncertainty in the instantaneous

efficiency given by performance factor N101 as:

N101 = W100-C100-TD100

Ac- 1001

(7.7)

For purposes of illustration, the following reference conditions and tolerances

in each variable are assumed:

2 2 A^ = 32 ft +1% (assumption) (+.32 ft ), collector area

W100 = 1 GAL/HR ft

2 x 32 ft2 = 269.91 lb/hr. +2% FS (+5.4 Ib/hr) , collector flow

C100 =1.0 BTU/lb

TD100 = 18 + 1.7%

1001 = 300 BTU/hr

°F , specific heat (NO TOLERANCE)

(+ 0.3°F), temperature rise through collector

2 2 ft +3% (+9 BTU/hr ft ) , incident solar radiation

The nominal array efficiency is determined from equation (7.7) by substitution

of the assumed variables at the reference point as:

N101 =

LB BTU

(270)HR (1.0) LB °F (18.0) °F

2 2 (32 )ft z (300) hr ft

.506

Equation 7.7 is differentiated with respect to each variable having a non-zero

tolerance and each partial derivative is evaluated at the reference condition

as follows

:

3N101

= C101-TD100

3W101 A -1001

c

(1.0) (18 .

)

(32.) (300.)

.0019

3N101

= W100-C100

3TD100 “ A -1001

c

(270 . ) (1 . 0)

(32.) (300.)

.0281

54
3N101 (270) (1.0) (18.0) = -0.0158

9A

c

W100 • C100 • TD100

A

2 -1001

c (32)

2 (300.)

3N101

31001

W100 • C100 'TD100

A -(1001)

2 C

(270) (1.0) (18.0)

z

(32) (300)

.0017

The error by absolute limits is obtained by substitution of the partial

derivatives and tolerances in equation (7-4) as follows:

AN101 = {( . 0019) (5 . 4]Jd|( .0281) ( . 03 j+J(-0.

0158) ( . 32^+|(- .0017) (9 . 0) | AN101 = .0390

N101 = .506+. 039

Thus the calculated value of instantaneous efficiency based on absolute error

limits indicates an uncertainty of + 7.7 percent.

The error by statistical bounds is obtained by substitution of the partial derivatives and tolerances in equation (7.5) as follows:

N101 =£(.0019 x 5 . 4)

2+( . 0281 x 0 . 3)

2+(-0 . 0158 x .32)

2+(-.0017 x 9.0)

2

AN101 = .021

N101 = .506+. 021

1/2

The statistical or rms method indicates about a + 4.1 percent uncertainty in the

calculation of collector efficiency. As indicated by the sample calculations

the absolute limit method gives a larger error value than the statistical method.

Because of the randomness of the measurement process for the solar energy systems

(i.e., errors among the many different sensors are not correlated), the statistical

method is used for the uncertainty and error analysis calculations reported in

this document.

7.2 Derivation of the Overall Instrumentation Accuracies

Instrumentation accuracies are caused by sampling errors and by systematic

sensor errors due to inaccurate calibration, drift, and non-linearities. To

evaluate the effect of sensor and sampling errors on the performance factors,

the following information is necessary: the analytical expression for each

55
performance factor, the range of loads and operating points for the solar energy

systems and the sampling period. Application of the error analysis method to

determine the uncertainty in solar energy system conversion efficiency is

described to illustrate the analysis performed for most of the primary factors.

There are several ways of expressing temperature sensor accuracy. If all

temperature sensors used to compute energy flows are differential sensors,

meaning that a temperature rise or drop, not an absolute temperature is

measured then accuracy of measuring a temperature differential is expressed as

percent (degrees accuracy in measuring the differential divided by the total

differential). If the differential is to be measured using two sensors, then

the accuracy is the square root of the sum of the individual accuracies squared

divided by the temperature difference of.

Thus, a 2% load temperature accuracy requirement and 20°F assumed load temperature

difference means that the temperature accuracy should be .4°F for a differential

sensor and .3°F for individual sensors. Similarly, a 4% accuracy and 10°F

rise across a collector requires a temperature accuracy of .4°F differential

or ,3°F for individual sensors.

Other combinations of flow and temperature sensors which fulfill instrumentation

accuracy requirements can be determined from Figures 9 and 10. These two

graphs were computed from the two error equations that constrain flow and

temperature sensor errors.

Sampling errors develop when a signal waveform is not sampled quickly enough

so that the exact waveform can be reproduced. Because many solar parameters

change quite rapidly (e.g., auxiliary fuel flow or insolation), it is not

feasible to sample to reproduce the entire waveform. However, it is

possible by sampling a large number of times to statistically reproduce the mean of a waveform. For instance, for a monthly measurement period and a 10-minute sample interval, each parameter mean is based on approximately 2,000

samples. It is the statistics of large numbers which governs sample accuracy

(provided correlation effects do not arise)

.

7.2.1 Temperature Sensor Accuracy

(7.8)

7.2.2 A Description of Sampling Errors

56
Q100

=

/WlOO

•

ClOO

•

TDIOO

di

3 '-n cr u

•H *H J <

Ul«- OJ

oo ro

^ co

U.

O ^X

<0 cvi

li_ O

o CO

't. —

u.

ooo

>

o

<

cn3

o

o

<

cnO 2

co Ld

z: huj c

o

TM 3

>

co

Ld

cn cn 6< 5

cn

Ld

CL2

Ld

h3

<

h-Z

Ld

cnLd

U_

U.

cno

o

o

AOVUnOOV d0SN3S MOU

57

Figure

9

Accuracy

in

Calculated

Solar

Energy

Collected

(
58

4°F

.6°F

.8°F

I.O°F

(Liquid)

(l.4°F)

(2.I°F)

(2.8°F)

(3.5°F)

(Air)

DIFFERENTIAL

TEMPERATURE

SENSOR

ACCURACY

FOR

LIQUID

(AIR)

SYSTEM
In general, lengthening the sampling period (e.g., from one month to one year)

by some factor k decreases sampling error by 1/ J""k. Similarly, shortening the

sampling interval (e.g., from 30 minutes to 5 minutes) decreases sampling error.

The errors due to sampling can be predicted for the three common types of signals.

"ON-OFF," "slowly varying," and "rapidly varying." Error in measuring "ON-OFF"

signals is a function of the total number of samples N and the duty cycle, d

a (ON-OFF) (7.9)

For "slowly varying" signals (signals that cycle much fewer than once in 2n

samples) error is a function of the number of samples, N, and the mean percent

change of the signal during one sample interval, a:

a < (slowly varying) (7.10)

For "rapidly varying" signals (signals that cycle much faster than once every

2tt samples), error is a function of the number of samples, N, and the ratio of

the varying to steady signal component, b:

a < ~z (rapidly varying) (7.11)

/N (1-b)

Decreasing the sample interval by a factor of k results in an error decrease

of approximately 1/k for "ON-OFF", 1/kJ k for "slowly varying" and 1/ •T

r for

"rapidly varying." Examples of "ON-OFF", slowly varying, and rapidly varying

signals might be auxiliary input to load, storage temperature, and insolation,

respectively, for a 2 minute to 60 minute sampling interval. Actual standard

deviations for different sampling rates and periods have been computed for

insolation, collector output, auxiliary output, etc., using Colorado State

House No. 1 data [5]. Typical data for insolation values integrated from

measurements made at different intervals are listed in Tables 2 a and 2b.

Assuming the 2 minute sampling rate represents the most accurate value obtained,

the actual sampling error results are listed in Table 3 and scaled to different

sampling intervals and periods. There is wide variation in the monitoring interval

required by the different parameters. For example, the analysis indicates

insolation need only be monitored once every 15 minutes to maintain a weekly

variance below 1%, but auxiliary sampling with a non-integrating sensor roust be made.

59
Table 2a CSU Sampled Data Using Different Sampling Intervals (Summer 1975)

Parameter Insolation

[ 5 ]

Minutes

Date 2 5 10 20 30 60

6/21 1132.9 1130.0 1118.9 1128.3 1124.2 1160.7

7/9 1111.3 1119.0 1089.9 1100.4 1035.5 995.4

7/13 1768.2 1776.2 1772.6 1763.9 1759.3 1765.7

7/17 1255.3 1266.6 1270.9 1273.0 1242.9 1227.0

7/21 1248.0 1271.6 1254.3 1241.1 1153.9 1072.2

7/23 1263.4 1246.8 1253.1 1204.3 1259.7 1271.7

7/25 1815.2 1811.4 1809.0 1799.1 1792.0 1767.3

7/27 1850.4 1846.6 1840.5 1827.7 1815.1 1779.6

7/29 1564.5 1558.1 1534.4 1515.9 1633.1 1513.0

7/31 1205.6 1207.8 1245.6 1229.3 1219.8 1233.3

S.D per day 0.8% 1.3% 2.0% 3.3% 5.3%

: 2b Parameter Insolation (Winter 1974-75)

Date 2 Minutes

5 10 20 30 60

12/21 455.0 449.1 446.4 455.2 466.6 465.9

12/23 165.9 159.5 158.0 152.2 159.7 143.7

12/25 1478.9 1476.0 1472.7 1457.4 1445.9 1396.3

12/27 1238.6 1235.8 1235.1 1228.9 1251.7 1270.1

12/29 948.0 937.8 933.3 916.6 896.7 846.5

12/31 1108.1 1102.0 1086.0 1034.4 1045.6 976.0

1/4 1248.4 1242.6 1246.7 1246.2 1205.9 1224.6

1/6 1395.4 1388.1 1380.4 1345.3 1327.4 1228.9

1/15 730.9 741.1 725.0 735.6 778.2 755.0

1/17 1022.4 1017.6 1015.6 1112.4 111.3 1173.3

S.D. per day 0.7% 1.1% 4.3% 5.1% 9.6%

60
TABLE 3

RANGE OF MEASURED DAILY VARIANCE WITH DATA EXTRAPOLATED

FOR WEEKLY, MONTHLY, AND YEARLY PERIODS.

SAMPLING

INSOLATION

FREQUENCY (MIN) 5 10 20 30 60

Daily .7 - .8 1.1-1.

3

2.0-4.

3

3. 3-5.1 5. 2-9.

6

Weekly .3 .4 - .5 .8 - 1.6 1. 2-2.0 2. 0-3.

6

Monthly .1 .2 .4 - .7 .6 - .9 1.0-1.

7

Yearly .1 .1 .1 - .2 .2 - .3 .3 - .5

SAMPLING

FREQUENCY (MIN) 5 10

COLLECTOR

OUTPUT

20 30 60

Daily 3. 3-4.

6

5.3-11.1 13.9-20.1 18.2-21.5 19.7-23.8

Weekly 1.2-1.

7

2. 0-4.0 5. 2-7.

5

7. 0-8.0 7. 5-9.0

Monthly .6 - .8 .9-2.0 2. 5-3.

7

3. 3-3.

9

3. 6-4.

3

Yearly .2 .3 - .6 .7-1.0 .9-1.1 1.0-1.

3

SAMPLING

FREQUENCY (MIN) 5 10

AUXILIARY TO

LOAD

20 30 60

Daily 6.7-23.6 6.3-30.9 10.2-43.3 15.8-66.5 23.3-111.8

Weekly 2. 5-9.0 2.5-11.5 4.0-16.5 6.0-25.0 9.0-42.0

Monthly 1.2-4.

3

1.1-5.

6

1. 8-8.0 2.8-12.0 4.2-20.0

Yearly .7 .7 1.1 1.7 2.6

61
Using the CSU data and the suggested sampling accuracies from Section 7.2.2,

sampling rates for various sensors are determined as listed in Table 5.

Data Requirements Weekly Summations Monthly Summations Yearly Summations

(minutes) (minutes) (minutes)

load flow <5 5 30

collector flow and

temperature 5 10 60

auxiliary input <5 5 60

* insolation 30 60 60

Based on insolation at Colorado State University, Fort Collins, Col. 1974-74.

Table 4 Sampling Rates as a Function of Time Interval for Several Data Requirements Types

Sensors requiring sampling rates greater than once every five minutes can be

continuously integrated and then sampled. It is recognized that the data

utilized is for a specific system, load and climatic conditions and will only

provide estimates of sample rates for other combinations of these factors. For

example, insolation sample rates are a function of the weather variability and

a rate of 3 minutes is used in the Washington, D.C. area to obtain an uncertainty

of about 1% [8]. A sampling rate of 5 minutes or less is recommended for both

insolation and auxiliary energy related measurements.

7.2.3 S olar Energy Conversion Efficiency (Nlll)

The conversion efficiency of a heating and HW solar energy system is determined

by dividing the solar energy delivered to the load by the available insolation.

Instrumentation uncertainty (°jN

g) is given by:

INS =

(a

2 + a

2 + a

2 W

1 TD

1

S

l*)(

Q300

Q300 + Q400 ) + (°

2 2 2

, t + a +a W c 2 TD

2

S

2 V Q400 \

Jc)300 + Q400 J

, 2 , 2 +

°I + a S001 (7.12)

where aw ando^ are uncertainties in solar-to-load flow and temperature

difference sensors, a is the sampling uncertainty, Q300 and Q400 is

solar energy to hot water and heating respectively, is insolation

sensor uncertainty, and °gQQ-^ is the insolation sampling uncertainty.

62
Assuming conditions such that Q300>>Q400, the instrumentation accuracy is:

(7.13)

The sensor accuracy and sampling rate accuracy necessary to achieve a 6%

instrumentation uncertainty is determined as described in the following sections.

The two worst case RMS instrumentation error equations that determine necessary

sensor accuracies for system and collector array efficiencies respectively are

°TD301

= ^oa<^ temperature sensor accuracy (20°F differential)

°TD100

= array temperature sensor accuracy (10°F differential)

°I001

= ’• nso-*- a ti°n sensor accuracy

a S300

= samP-*-^ n8 error for solar or auxiliary to load

°S001

= sampling error for insolation

°S100

= sampling error for collector output

On the basis of performance a reasonable strategy for initial selection of

sensor accuracy and sampling rate is to balance the error terms of the error

equations. For example, using the instrument error equation for system

conversion efficiency and a 6% instrument error criterion, the error terms

would be balanced according to:

7.2.4 Sensor Accuracy

where

°W301 °W100

= flow sensor accuracies

W301 - a TD301 - a !001 - °S300 - a S001 (7 ’ 16)

63
Using this term balancing strategy, sensor and sampling accuracies are selected

and iteratively refined to reasonable values using tradeoff charts shown in

Figures 9 and 10. The results for the projected sensor accuracy and sampling

requirements are as follows:

Sensor Sensor Accuracy Sampling Accuracy

load flow + 2% + 2%

load temp. + 2% —

collector flow + 2% (liq)+ 3%(air) + 2%

collector temp. + 4%(liq)+ 3%(air)

insolation + 3% + 2%

auxiliary input + 2.5% + 2%

7 . 3 SUMMARY

The final instrumentation accuracy and performance factor uncertainty will

depend upon economic tradeoffs of sensor cost, installation and maintenance.

Using the instrument error equations and selecting a desired instrumentation

uncertainty of 6% as being reasonable and achievable, the values of sensor

accuracy and sampling rate were assigned to the various measurements as shown in

Table 5.

64
TYPE DESIGN DATA REQUIREMENT RANGE ACCURACY MEASUREMENT FREQUENCY

1001 Total Radiation 0-350 + 3% Btu/f

t

2 -hr FS 5 min or less

1002 Diffuse Radiation 0-100 + 6% Btu/ft^-hr FS 5 min

T001 Outdoor DB Temperature -20 to 120 + 2°F Avg/hr

<8 V001 Wind Velocity 0 to 100 + 3 mph Avg/hr

D001 Wind Direction 0 to 360 + 20°F Avg/hr u T002 Outdoor Wet Bulb Temp 32 to 90 + 2°F Avg/hr

s

V T100 Collector Inlet Temp 40 to 220 + 0.5°F (L) + 1°F (A) 5 min

>s TD100 Collector Temp Diff -10 to +50 + 0.3°F (L) + 1.2 >F (A) 5 min

c xs T101 Storage Inlet Temp 60 to 230 + 0 , 5°F (L) + 2°F (A) 5 min

in TD101 Storage Temp Diff 0 to 100 + 0 . 3°F (L) + 2.5 ’F (A) 5 min

0 T102 Collector Absorber Temp 30 to 450 + 3°F Daily at noon

CJ 0 W100 Collector Flow Rate varies + 27. (L) + 37. (A) FS 5 min

03c

O S3 u uH

PD100 Collector Press Diff varies + 27. FS Daily at noon

E

0) 0> QC 4J T200 Storage Media Ave Temp 60 to 230 + 2°F hr, T201 Storage Ambient Temp -20 to 120 + 3°F hr,

kJ X)

in a

c/9 PD101 Storage Press Diff (Air) 0 to 4"H2 0 + 2% FS hr,

T301 Makeup Water Temp 30 to 90 + 0 . 5°F Avg/hr

.

T300 HX Inlet Temp 40 to 160 + 0.5°F 5 min

a) d TD300 HX Temp Diff 0 to 50 + 0. 3°F 5 min

sq os TD301 Storage Temp Diff 0 to 75 + 0 . 3°F 5 min

CO TD302 Auxiliary Temp Diff 0 to 100 + 0 . 3°F 5 min or less

0 3

SC C/9 W300 Circulation Flow Rate varies + 27. FS 5 min

W301 Load Flow Rate varies + 37. FS 5 min

E

QC d

T400 Load Return Temp 70 to 180 + 0.5°F (L) + 2°F (A) 5 min TD400 Storage Temp Diff 0 to 50 + 0 . 3°F (L) + 2°F (A) 5 min

09 TD401 Auxiliary Temp Diff 0 to 100 + 0. 3°F (L) + 2°F (A) 5 min

QJ 09 W400 Circulation Flow Rate varies + 27. (L) + 37. (A) FS 5 min

0) -C X 3

cn TD402 HTG Load Temp Diff 0 to 100 + 0 . 3°F (L) 5 min

E

o

4J T500 Load HX Inlet Temp 40 to 60 + 0.5°F 5 min

Ss TD500 Load HX Temp Diff 0 to 75 + 0. 3°F 5 min or less

•O T501 Cooling Tower Inlet Temp 40 to 120 + 0.5°F 5 min

C/9 TD501 Cooling Tower Temp Diff 0 to 20 + 0.3°F 5 min or less

QC W500 Load HX Flow Rate varies + 27. FS 5 min or less

i-Ho

oo

W501 Cooling Tower Flow Rate varies + 27. FS

EP10I Collector Circ Pump Power AKW varies + 5 7 FS 5 min

EP301 HW Circ Pump Power AKW varies + 57. FS 5 min

QC EP401 HTG Loop Circ Pump Power AKW varies + 57. FS 5 rain u o EP402 Bldg Fan Power AKW varies + 5 7 FS 5 min

EP403 Heat Pump Compress Power AKW varies + 27. FS 5 min or less

a- >x EP501 Absorp Chiller Oper Power AKW varies + 27. FS 5 min or less

QC 03 EP300 HW Elec Aux Power AKW varies + 27. FS 5 min or less H t—

(

EP400 HTG Elec Aux Power AKW varies + 27. FS 5 min or less

03 X F300 HW Aux Fuel Flow varies + 27. FS 5 min or less

O < F400 HTG Aux Fuel Flow varies + 27. FS 5 min or less O wa F500 Cooling Aux Fuel Flow varies + 27. FS 5 min or less

T600 Bldg Return Air DB Temp 50 to 90 + 2°F 5 min TD600 Supply/return Air Temp Diff 0 to 80 + 2°F 5 min

T601 Bldg Return air WB Temp 20 to 80 + 2“F 5 min

T602 Bldg Supply Air WB Temp 20 to 80 + 2°F 5 min

•H d W600 Building Air Flow Rate varies + 27. FS 5 min

r-J 09 W601 Condensate Flow varies + 57. 5 min

s w HF600 Heat Flow Meter 0.25 to 30 °F AT + 57. 5 min

TD601 HT Pump Cond & Load HX Temp

Diff

0 to 80 + 2°F 5 min

Table 5 INSTRUMENTATION RANGE, ACCURACY AND MEASUREMENT FREQUENCY

65
8.0 APPLICATION OF PERFORMANCE FACTORS

The performance factor data generated during the Demonstration Program will provide

the basis to directly determine parameters such as energy saved, thermal efficiency

and energy contributions to the various functional loads. However, to fulfill

the program national goals the data will also be applied to determine correlations

between building types, climates and heating and cooling system designs, to verify

design methods and to establish reasonable performance goals.

Although exact system or subsystem comparisons must await the selection of specific

solar system/building/climate combinations, examples of the format and general use

of performance factors are presented as illustrations of how the data can be

utilized.

8.1 Solar Energy System Thermal Performance

The technical selection of a solar system is based primarily on the thermal

performance in terms of energy collected on monthly or annual/seasonal periods.

Data such as shown in Figure 11 presents the amount of energy utilized for

auxiliary energy as well as for the heating and cooling functions and the total

energy supplied for a single site. Individual comparisons of solar energy systems

(in similar climates) and collector areas can be made using this type of chart.

For systems with varying collector size, the energy quantity can be expressed per

unit collector area. Comparisons are made for each unique type of solar system

to include air, liquid, active and passive. The data should be tabulated for

monthly, seasonal and annual time periods to cover the following functional areas

as appropriate.

Functions

A. Hot Water

B. Space Heating

C. Space Cooling

D. Space Heating and Space Cooling

E. Space Heating and Hot Water

F. Space Heating and Cooling and Hot Water

G. Space Cooling and Hot Water

8.2 Solar Energy System Thermal Effectiveness

The effectiveness of a solar energy system to meet the total functional loads on a cumulative basis for each building type can be illustrated for a single site as shown in Figure 12. Comparison of the effectiveness of similar solar system types

66
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and climates on a seasonal basis is done by normalizing the building size and load

per degree day of heating or cooling and presenting the data in tabular form for

monthly, seasonal and annual time periods.

8.3 Analytical Predictions

The design of solar systems is currently based on analytical models and calculated

performances. The demonstration program will provide the measured data for com- parison with prediction of the following performance factors:

(1) Energy Delivered to Load (HW, heating, cooling, total)

(2) Solar Fraction of Load (HW, heating, cooling, total)

(3) Solar Energy Conversion Efficiency

(4) Energy Saved (Electric and Fossil)

(5) Collector Array Efficiency

Comparisons can be made on an individual site basis as illustrated in Figures 11

and 12 or tabular data for many sites can be used to determine standard deviations

as a function of climate and building characteristics for monthly and annual

periods

.

8.4 Solar Collector Array

The greatest technical innovations are needed in the development of collectors,

therefore, comprehensive characterization, measurement, and comparison of operating

performance data for the many collector varieties will be necessary. Because of

the influence of site integration and operating mode, comparison of preinstallation

performance data for individual panels and the array performance, as illustrated

in Figure 13, is desirable using instantaneous and daily, monthly and annual

efficiencies. Other comparisons based upon design or material properties are listed

as follows:

A. Flat Plate

1. Absorber Coating

a. Flat Black

b. Selective

2. Covers

a. Number

b. Material Type

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and

System

Collector

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Performance

[10]
B. Concentrator

1. Cylindrical

2 . Tubular

3. Trapezoidal

4. Other

8.5 Component Predicted Performance

It is not the intent of the test and evaluation program to develop components

but the influence of the operating mode and environment will be determined on major subsystems or components as listed below:

A. Collector Array

B. Storage

C. Energy Transport

D. Energy Conversion Equipment

An example of the comparisons in collector performance between predicted and

experiment are shown in Table 6 for the three key heat transfer areas: (a) solar

absorptance-transmittance product (“t)^ (b) heat removal efficiency factor

(F ) ; and (c) heat loss coefficient (U ) . These values are obtained by

reducing the collector performance data during selected periods of quasi-steady

state to plot in the slope-intercept form.

An example of the use of the slope-intercept plot to illustrate collector

material degradation is shown in Figure 14. Tabular values of a x and for

similar materials as a function of climatic exposure will reveal the differences

related to environmental conditions.

8.6 Climatic Data

Climatic data measured during the program will be reported for hourly, monthly and

annual data as follows

A. Total solar radiation at collector tilt angle

B. Direct solar radiation at collector tilt angle for selected sites

C. Ambient dry bulb temperature

D. Ambient wet bulb temperature at selected sites

E. Wind direction and velocity at selected sites

These data will be tabulated and plots indicating variations over the continental

United States will be available.

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Table 6

Comparison

of

Collector

Performance

Coefficients

Derived

from

Testing

and

Analysis

[11]
COLLECTOR

EFFICIENCY.

T).

(aJ BLACK PAINT. 2 GLASS MYLAR HONEYCOMB COLLECTOR.

Figure 14 Illustrations of Detecting Collector Degradation From

Thermal Performance Measurements.

73
8.7 Recommendations

Table 7 lists a number of data correlations and evaluations possible with the

available measurements and calculated performance factors. Due to the large

number of building types solar energy systems and climatic regions, it is

obvious that computerized data reduction will be necessary to perform the necessary

evaluation. It is therefore recommended that additional study of the data format

and computerized data reduction requirements be under taken to more efficiently

implement the various correlations studies planned and to assure availability of the

results to the potential users on a timely basis.
PERFORMANCE

FACTORS

EVALUATION

AREA

75

TABLE

7

Application

of

Specific

Performance

Factors

to

Evaluation

Areas
9.0 Conclusions

The quantity and type of measurements described reflect a level of instrumentation

that will provide a capability for full evaluation of each solar energy system

and for each building, partial evaluation of most components performance and

measurement of local climatic data.

To reduce instrumentation costs, an assessment of the significance of the performance factors should be made for each proposed demonstration unit. The four

factors considered essential for the performance of solar energy systems are:

° conventional energy saved by the solar energy system

0 solar fraction of total load

° solar energy system conversion efficiency

° solar energy collected per unit collector area.

The primary tool used to determine the data requirements and the selection of

instrumentation is the analytical heat balances. Sufficient heat balance calculations are required to equate the total energy input to the total energy output

for the subsystem or component plus an acceptable heat loss to provide an energy

balance closure of about ten percent. Errors greater than approximately ten percent

for active systems and fifteen percent for passive systems will not permit useful

comparison between different systems. Error analysis of most performance evaluation

factors for active solar energy systems have shown that the experimental data can be

obtained with accuracy of about + 5 percent using commercially available sensors.

76
10.0 REFERENCES

1. National Plan for Solar Heating and Cooling (Residential and Commercial Applications)

ERDA-23A, October 1975.

2. ASHRAE Standard 90-75, "Energy Conservation in New Building Design," 1975, Available

American Society of Heating and Refrigerating and Air Conditioning Engineers, Inc.,

345 East 47th Street, New York, N.Y. 10017

3. "Procedures for Determining Heating and Cooling Loads for Computerized Energy

Calculations", The Task Group on Energy Requirements for Heating and Cooling, ASHRAE,

345 East 47th Street, New York, 1971.

4. T. Kusuda, "NBSLD, Computer Program for Heating and Cooling Loads in Buildings", NBS

Report NBSIR 74-574, November 1974.

5. Personal Communication, Dr. Dan S. Ward, Colorado State University, Ft. Collins,

Colorado; and Study on "Instrumentation Type, Range, Accuracy, and Measurement

Frequency Required to Monitor and Evaluate the Thermal Effectiveness of Solar Heating

and Cooling and Hot Water Systems", NBS Purchase Order No. 608692, March 1976.

6. ASHRAE Standard 93-P "Method of Testing for Rating Solar Collectors Based on Thermal

Performance", August 1976 (Available ibid ASHRAE).

7. G. E. Kelly, "Potential of Air-to-Air Heat Pumps for Energy Conservation in

Residential Buildings", NATO Advanced Study Institutes, Series E: Applied Science

No. 15, Noordof f-leyden, 1976 (Available from National Bureau of Standards, Washington,

D C 20234)

8. Personal Communication, Dr. William H. Klein, Radiation Biology Laboratory,

Smithsonian Institution, Rockville, Maryland, January 1976.

9. Engebretson, C. D. , The Use of Solar Energy for Space Heating, M. I. T. Solar

House IV, "Proceedings of the United Nations Conference on New Sources of Energy",

Rome, August 21-31, 1961, Vol. 5 III e.2 pp. 159-172.

10. J. E. Hill, T. E. Richtmyer and J. Jenkins, "Initial Test Results for a Solar Cooled

Townhouse in the Mid-Atlantic Region", National Bureau of Standards, Washington, D C

20234, Presented at ASHRAE Semi-Annual Meeting, June 1976.

11. J. W. Ramsey, J. T. Borzoni and T. H. Holland, "Development of Flat-Plate Solar

Collectors for the Heating and Cooling of Buildings, "NASA CR-134804, June 1975.

77
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1137

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Thermal Data Requirements and Performance Evaluation

Procedures for the National Solar Heating and Cooling

Demonstration Program

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

E. Streed, M. McCabe, D. Waksman, J. Hebrank, T. Richtmyer

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4606500 and 4606505

11. Contract/Grant No.

ERDA - 49(1) - 3800

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Energy Research & Development Admin. Dept, of Housing and

Division of Solar Energy Urban Development

Washington, DC 20545 Division of Energy

Washington, DC 2Q410

13. Type of Report & Period

Covered

Interim

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

This report presents the results of a study to determine the data requirements and

performance evaluation factors to be used in the National Solar Heating and Cooling

Demonstration Program. Solar energy systems used for heating hot water, space heating,

and space cooling have been considered and specific measurements and analytical procedures have been recommended to determine the thermal effectiveness for daily,

monthly, seasonal, or annual operating periods. The sensor accuracy and sampling rate

effects on measurement uncertainty for several performance factors is presented.

Application of the individual performance factors for the comparison of subsystem and

system thermal performance as a function of building type and climatic region is

discussed

.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated v semicolons)

Data requirements; measurement uncertainty; solar energy systems evaluation; thermal

performance

.

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