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NATL INST OF STANDARDS & TECH R.I.C.

All 102247755

Liu, Stanley T/Experlmental and analytic QC100 .U56 NO.86-3378 1986 V19 C.1 NBS-P Experimental and Analytical

Investigation of Solar Radiant

Flux Distribution on Interior

Surfaces of A Sunspace

Stanley T. Liu

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

March 1986

Issued June 1986

Prepared for Solar Buildings Technology Division

Office of Solar Heat Technologies

-nr—- ~ bailment of Energy

ton, DC 20545

100

- U 5 6

86-3378

1986

C. 2

NBS

research

INFORMATION CENTER NBSIR 86-3378

EXPERIMENTAL AND ANALYTICAL

INVESTIGATION OF SOLAR RADIANT

FLUX DISTRIBUTION ON INTERIOR

SURFACES OF A SUNSPACE

Stanley T. Liu

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

March 1986

Issued June 1986

Prepared for Solar Buildings Technology Division

Office of Solar Heat Technologies

U.S. Department of Energy

Washington, DC 20545

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

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
I' . .

'

*
PREFACE

SOLAR BUILDINGS RESEARCH AND DEVELOPMENT PROGRAM

In keeping with the national energy policy goal of fostering an adequate

supply of energy at a reasonable cost, the United States Department of

Energy (DOE) supports a variety of programs to promote a balanced and mixed

energy resource system. The mission of the DOE Solar Buildings Research

and Development Program is to support this goal, by providing for the

development of solar technology alternatives for the buildings sector. It

is the goal of the Program to establish a proven technology base to allow

industry to develop solar products and designs for buildings which are economically competitive and can contribute significantly to building

energy supplies nationally. Toward this end, the program sponsors research

activities related to increasing the efficiency, reducing the cost, and

improving the long term durability of passive and active solar systems for

building water and space heating, cooling, and daylighting applications.

These activities are conducted in four major areas: Advanced Passive Solar

Materials Research, Collector Technology Research, Cooling Systems

Research, and Systems Analysis and Applications Research.

Advanced Passive Solar Materials Research - This activity area includes

work on new aperture materials for controlling solar heat gains, and for

enhancing the use of daylight for building interior lighting purposes. It

also encompasses work on low-cost thermal storage materials that have high

thermal storage capacity and can be integrated with conventional building

elements, and work on materials and methods to transport thermal energy

efficiently between any building exterior surface and the building interior

by non-mechanical means.

Collector Technology Research - This activity area encompasses work on advanced low to medium temperature (up to 180°F useful operating temperature) flat plate collectors for water and space heating applications, and

medium to high temperature (up to 400°F useful operating temperature)

evacuated tube/concentrating collectors for space heating and cooling

applications. The focus is on design innovations using new materials and

fabrication techniques.

Cooling Systems Research - This activity area involves research on high

performance dehumidifiers and chillers that can operate efficiently with

the variable thermal outputs and delivery temperatures associated with

solar collectors. It also includes work on advanced passive cooling

techniques

.

Systems Analysis and Applications Research - This activity area encompasses

experimental testing, analysis, and evaluation of solar heating, cooling,

and daylighting systems for residential and nonres ident ial buildings. This

involves system integration studies, the development of design and analysis

tools, and the establishment of overall cost, performance, and durability

targets for various technology or system options.
'

.
This report is an account of research conducted in the Systems Analysis and

Applications Research area concerning the distribution of solar radiative

flux inside a partially transparent passive solar structure and the

validation of a design and analysis tool that can be used for a parametric

study of those flux distributions.
ABSTRACT

The short wave solar radiant flux distribution inside a sun-space model

with a large south opening was studied experimentally under clear sky

conditions. Miniature photovoltaic pyranometer sensors responsive to short wave radiation were mounted at various locations on the interior surfaces

of the enclosure. It was found that solar flux distribution on an interior

surface not in direct sunlight varies approximately in a linear fashion

from the south opening, so that a limited number of sensors are adequate

for the determination of the flux distribution in an enclosure. A highly

reflective floor or wall surface not under direct irradiation from the sun tends to distribute the incoming solar flux evenly over all indirectly

irradiated interior surfaces having the same solar reflectivity. The flux

values vary only as a function of the distance from the solar opening. The

multiple reflected solar flux within the enclosure increases the amount of

solar energy falling on an area under direct sunlight to a value

significantly greater than would be measured outside of the enclosure. An

NBS developed solar flux distribution program was tested against the

experimental results and was found to give good agreement. The computer

program can be used as a design tool for the evaluation of thermal storage

location and solar physical properties of floor and walls in a passive

solar structure.

Key words: Computer program; partially transparent enclosures; passive

solar structure; solar flux measurement; solar radiation; sun-space model

IV
TABLE OF CONTENTS

Page

PREFACE . i i ABSTRACT . iv

1. INTRODUCTION . 1

2. "SUNFLUX" - THE SOLAR FLUX DISTRIBUTION COMPUTER

PROGRAM 2

3 . EXPERIMENTAL TEST FACILITY 2

4. INSTRUMENTATION AND DATA ACQUISITION 2

5. TEST RESULTS AND DISCUSSIONS 3

5.1 SOLAR FLUX DISTRIBUTION ON AN INTERIOR SURFACE . 3

5.2 SOLAR FLUX DISTRIBUTIONS INSIDE AN ENCLOSURE 4

6. ANALYTICAL PREDICTIONS AND COMPARISONS 4

6.1 COMPARISON OF PREDICTED AND MEASURED FLUX

DISTRIBUTION 5 6.2 APPLICATION OF THE SOLAR FLUX DISTRIBUTION

PROGRAM 5

7. CONCLUSIONS 6

8. ACKNOWLEDGMENT 7

REFERENCES 8

v
_

.
1 . INTRODUCTION

Fundamental to the prediction of the heating and cooling loads in the

design of passive solar buildings is the spatial distribution of the solar

energy flux among the various interior surfaces of a highly solar-driven

zone such as the direct gain sunspace or atrium. Radiant solar energy

transmitted through the large fenestration in a typical sunspace design

undergoes a process of multiple reflections and absorptions. Part of the

entering short-wave solar flux is retransmitted out of the space through

the glazings. The solar energy absorbed and stored at any location on the

interior surfaces and the surface temperature distribution depends on the

amount of the solar radiant flux incident on and absorbed by the surfaces

at that particular location. Currently, none of the existing energy

analysis programs provide for detailed treatment with regard to internal

multiple reflections and re-transmissions out of the space.

McCabe and Van Migom [1,2] reviewed the recent development of the enclosure

theories for specular and diffuse radiative energy transfer among semigray, opaque surfaces [3] and for diffuse radiative energy transfer in

partially transparent enclosures [4,5], and presented a general formulation

for partially transparent enclosures involving both the beam and the

diffuse solar energy transfer through multiple transparent surfaces. In

their development, the shortwave irradiance and radiosity at each surface

in the enclosure are formulated for the diffuse and the beam component

separately. Diffuse reflection of both the beam and the diffuse irradiance

is assumed. The effect of view (angle) factors on diffuse reflection among

the surfaces are considered, and the shading effect of opaque enclosure

surfaces on others for incident beam radiation is also taken into

consideration. The resulting equations for all the surfaces are presented

in matrix form and techniques for matrix manipulation are used to simplify

and solve the equations. Details of the formulation are described in

[ 1 , 2 ].

On the basis of the analytical formulation described above, a computer

code, "SUNFLUX," was developed at the National Bureau of Standards (NBS)

that models the admission, multiple reflection, and absorption of the solar

radiant flux in partially transparent enclosures. At the same time, an experimental study sponsored by the Department of Energy (DOE) was undertaken to make actual measurements of the distribution of radiant solar

flux incident on the interior surfaces of a direct gain structure. This

paper presents the findings of the experimental investigation and a comparison of the measured results with the analytical prediction obtained

from the computer code. The test facility, instrumentation, and data

acquisition are described, and samples of the experimental results are presented. The test and results are compared with the analytical

predictions produced by the NBS developed computer program "SUNFLUX".

Reasonably close agreement is shown to validate the computer program for

use as a research and design tool in passive solar research and

appl ications

.

1
2 . "STJNFLUX " - THE SOLAR FLUX DISTRIBUTION COMPUTER PROGRAM

The computer program named "SUNFLUX" is a computer model developed by NBS

for the prediction of the amount of short wave solar radiation absorbed by

each of the interior surfaces in a highly solar driven, partially transparent enclosure such as a sunspace or an atrium. The computer program

consists of two parts. The first part generates the geometrical view

(angle) factors and shadow factors due to solar beam radiation among all

the interior surfaces or subsurfaces. It is a simplified version of the

"CONSHAD" subroutine used in the "Simplified Shuttle Payload Thermal

Analyzer Program" (SSPTA) developed by Arthur D. Little, Inc. for the

Goddard Space Flight Center of the National Aeronautics and Space

Administration [6] . The second part of the program uses the algorithm

described in [1] and computes the solar radiant flux distribution and

absorption at the interior surfaces for any time of the day. The program

can handle up to 100 interior surfaces or sub-surfaces in an enclosure of

arbitrary shape, including internally blocking surfaces and multiple

transparent surfaces. The program is developed for use as a design tool

for the evaluation of solar driven passive solar design. It can also be

incorporated into larger general energy analysis programs.

3. EXPERIMENTAL TEST FACILITY

The test facility consists of a one-sixth (1/6) scale model of the direct

gain room of the NBS/DoE Passive Test Facility [7]. The model, as shown in

Figure 1, is a rectangular shaped cell with a 610 mm wide by 1380 mm deep

floor and a 380 mm high ceiling. The fenestration opening at the south end

has a dimension of 610 mm wide by 320 mm high, measured from the floor up.

The model is made of plywood and lined with gypsum wallboard for all

interior opaque surfaces. The surface of the wall is painted latex flat

white color. The measured reflectivity of the painted surface in the solar

wave-length spectrum varies from 0.92 at 500 nm to 0.75 at 2100 nm, with an average weighted solar reflectivity of 0.88. This highly reflective

surface paint was chosen for all surfaces including the floor to give the

maximum possible values of solar radiant flux measured by the pyranometer

sensors located away from the direct beam radiation. No glass cover was used in the south end opening for the same reason.

The scale model is mounted on a wheeled table top on a wood framed base.

The model can be tilted upward at the south end to a maximum of 30° from

the horizontal to artificially change the solar altitude angle. The

ability to vary the altitude angle permitted testing throughout the year.

4. INSTRUMENTATION AND DATA ACQUISITION

Twelve (12) miniature silicon photovoltaic (PV) type pyranometers were used

to measure the incident solar radiant flux on the interior opaque surfaces

of the model at selected locations. This type of sensor responds to the

solar radiation in the wave length spectrum of 400 to 1100 nm . The sensors were factory calibrated against a first class thermopile type precision

spectral pyranometer (PSP) under natural daylight conditions with an absolute error of +5% maximum over the solar spectrum. The sensor is mounted in a fully cosine-corrected miniature head, and according to the

2
manufacturer can be installed in any plane without affecting its performance.

In addition to the 12 PV sensors, a thermopile type precision spectral

pyranometer and a normal incidence pyrheliometer (NIP) mounted on a tracker, away from the scale model, were used to measure the total horizontal and the normal beam solar radiations, respectively. Before the test

was started, the silicon PV sensors were calibrated against the PSP under

various daylight conditions ranging from clear sky to total cloud cover and

during different times of the day. The PV sensors performed according to

the manufacturer's specification as described in the last paragraph.

Figure 2 shows a typical calibration of one silicon PV sensor against the

PSP. The measurements were taken at one minute intervals under various sky

conditions. Because of the differences in time response (very small for

the PV sensor while over 20 seconds for the PSP), some data scattering

during intermittent cloudy weather showing large discrepancies was expected

and should be ignored. A linear least square fit of the data was made for

each of the PV sensors. All data taken in the subsequent measurements are corrected accordingly using these calibration curves.

A microcomputer based data acquisition system is used to collect the 14

channels of data at one minute intervals and the data are stored on floppy

diskette. The data logger has a scanner with an integrated digital

voltmeter having one (1) microvolt resolution.

5. TEST RESULTS AND DISCUSSIONS

5 . 1 Solar Flux Distribution on An Interior Surface

Because of the limited number of the silicon PV sensors that can be

installed on each surface within the scale model it is necessary to select

optimum location. Therefore, preliminary tests were conducted to determine

the pattern of the solar flux distribution along the centerline of an interior surface under clear sky conditions. Figure 3 shows the results of

tests for the flux distribution on the floor of the model. For these

tests, the south to north centerline along the floor was divided into eight

(8) equally spaced segments starting from the south side and seven (7) sensors were installed at the locations X/L = 1/8, 1/4, 3/8, 1/2, 5/8, 3/4,

and 7/8, where L is the length of the floor and X is the distance measured

from the south opening. Figure 3 shows the incident solar flux in the areas not under direct beam radiation. Only data from 5 out of the 7 sensors are shown since the other two are in the direct sunlit area. It is

interesting to note that solar flux distribution varies almost linearly

with respect to the distance from the sunlit area, under both clear and

hazy sky conditions. This phenomenon also holds true for the other

surfaces as shown in Figures 4 and 5 for the east surface and the ceiling,

respectively. It is also interesting to note that while the sun's ray

changed from the west surface in the morning to the east surface in the

afternoon, the flux distributions on the shaded portion of the east surface

under clear sky condition are almost the same. This showed the effect of

multiple reflections of the solar radiant energy among the interior

surfaces

.

3
5.2 Solar Flux Distributions Inside an Enclosure

Based on the flux distribution measurement on the individual surfaces, it

is seen that two sensors on a surface not in direct sunlight is sufficient

to determine the flux distribution on that surface. The locations for the sensors were therefore decided to be that shown in Figure 6. The criteria

for these selections was to have one sensor at each sunlit surface area and

to have two sensors on each shaded surface area to give an average reading

on each half (south and north) of the surface. Throughout the daytime

hours, portions of the floor, east surface, and west surface, will be in

direct sunlight. In Figure 6, the sensors labelled 1, 4, and 5 will be in

direct sunlight in certain times of the day. The rest of the sensors will

be receiving only reflected solar flux. A sample of the test results is

shown in Figure 6. The values beneath the sensors (represented by the

black circles) are the incident solar fluxes measured on a clear day

averaged over a ten minute period near solar noon. Comparing sensors 1 and

2, it is seen that there is nearly 3 to 1 difference in the magnitude of

the solar fluxes, where sensor 1 is in the sun and sensor 2 is in the shade

but near the edge of the sunlit area. It is interesting to note that,

while the total horizontal solar radiation measured by the PSP outside the

test model was 559 W/m , the solar flux on the horizontal floor of the

model in the sunlit region as measured by sensor No. 1 (Figure 6) was much

higher (810 W/m^) . Further examination showed that the difference (251

W/m^) was caused almost completely by the difference in the amount of

diffuse solar radiation received by the two sensors (PSP and sensor

No. 1). While the sky diffuse solar radiation to the PSP was computed to

be 51 W/m^ the solar diffuse radiation as measured by sensor No. 2 which

is located' close to sensor No. 1 was 287 W/m , with a difference of 236

W/m^. It is obvious that this difference is significant when the floor

material is used as a thermal storage medium in passive solar design. Of

course, the difference is expected to become smaller if the solar reflectivity of the floor and/or wall surfaces is decreased.

In Figure 6, it is also interesting to see that, near the north end, the

flux distributions on all 4 surfaces (sensors 3, 7, 9, and 11) at equal

distance from the south opening are almost of equal magnitude regardless of

the surface orientation. Data at other times of the day showed the same type of variation. This shows that the highly reflective interior surfaces

tend to distribute the solar flux evenly. This phenomenon should be noted

in determining the location of thermal storage material in passive solar

designs

.

6. ANALYTICAL PREDICTIONS AND COMPARISONS

As stated in the beginning of this report, the purpose of the experimental

tests previously described was to provide measured data to validate the

computer program "SUNFLUX" developed on the basis of the theoretical

analysis in [1]. To this end the experimental scale model was used to test

the computer algorithm and codes. On the basis of sun-lit area patterns

observed during the tests, and from the measured solar flux distribution

data, the interior surfaces of the scale model was sub-divided into 13

surfaces as shown in Figure 7. The centers of the subsurfaces correspond

mostly to the locations of sensors shown in Figure 6. The slight variations were in the floor which was divided into four parts instead of three,

4
and in the east and west surfaces which were divided into two equal parts

each instead of three unequal parts. Experimentally measured normal beam

radiation (by the NIP) and the total horizontal radiation (by the PSP)

outside the scale model at solar noon and at 3:00 p.m. solar time were used

as input to the computer program. The ground reflectivity was assumed to

be 0.20 on the basis of prior measurement. The resulting predicted solar

flux distribution on the various surfaces are discussed below.

6.1 COMPARISON OF PREDICTED AND MEASURED FLUX DISTRIBUTION

Table 1 shows the results of the predicted solar flux distribution on the

various interior surfaces of the model together with the test results

measured at the same locations under clear sky conditions at the two time

periods of the day. It is seen that the results compare well (within 10

percent of each other) for most of the interior surface locations. The

major discrepancy between the predicted and the measured results are at the

locations near the south opening, where the measured values are 15 to 23

percent higher. This difference is considered to be the result of two

factors. The first factor is the possible small misalignment of the

sensors' head with respect to the surface, causing errors in measured

data. The second factor concerns the assumption of diffuse reflection in

the theoretical analysis [1] . In the analysis, it was assumed that the

solar fluxes reflected from all the surfaces are diffuse without any

specular reflection. In the experimental study, it is possible that some specular reflections occurred both at the ground around the scale model and

at the model interior surfaces near the south opening where the solar beam

radiation first strikes on the surfaces. This would increase the amount of

radiant energy incident on surfaces near the south opening. This second

factor is considered to be the main factor causing the discrepancy in the

comparison

.

Even with the discrepancy in the comparison just discussed, it is seen from

Table 1 that the analytical model is in good agreement with the experimental data. Thus, the algorithm and codes can be used as a design tool in

the design of passive solar structures such as in the selections of thermal

storage locations and floor covering materials.

6.2 APPLICATION OF THE SOLAR FLUX DISTRIBUTION PROGRAM

As an example of the application of the solar flux distribution program,

the program is used to evaluate the effects of the solar reflectivity of

the floor on the sunspace's energy collection efficiency. The program was run on the same scale model as before, except that the floor's solar

reflectivity is changed from 0.88 to 0.50. The results are shown on Table

2 at a solar time of 3:00 p.m. on November 14. Table 2 gives a comparison

of the solar flux incident on each opaque surface inside the enclosure for

the two values of solar reflectivity, as well as the percentage absorbed

solar energy by the surfaces. Table 2 also gives the total amount of

absorbed solar radiation by the sunspace as a percentage of the total solar

energy entering through the south opening. It is seen that the net effect

of a highly reflective floor surface (r=0.88) is to redistribute the

incoming solar flux to other surfaces. The net absorbed solar flux by the

total floor area was much smaller for the high reflectivity case than the

lower reflectivity case (17.4% at r=0.88 vs. 52.9% at r=0.50), however, the

5
total percentage of absorbed solar energy for the enclosure decreased by

only 16 percentage points, from 76% at r=0.50 to 60% for r=0.88. In both

cases, a significant portion of the incoming solar flux was retransmitted

out of the south opening.

As described previously in Section 5.2 of this report, the incident solar

fluxes on the north side of the surfaces have almost equal magnitude

regardless of the surface orientation. Table 2 shows that this phenomenon

is true even for surfaces with unequal values of solar reflectivity as indicated by the incident flux values in the 4th column of Table 2 for a floor solar reflectivity of r = 0.50. It is seen in Table 2 that even though the floor's solar reflectivity is only a little over one-half the

value for the rest of the surfaces (which is 0.88), the incident fluxes for

the north half of the surfaces including the floor (No. 1, 2, 8, 9, 10 and

12) vary only from 51 to 60 W/m .

As described previously in the experimental part of this study (section

5.2), the effect of the surface reflectivity is to increase the amount of

diffuse solar flux incident on the sunlit area of the floor above those

measured on a horizontal surface outside the enclosure. Table 3 shows such

effects by using the computer program for a floor reflectivity of 0.88 and

0.

50. while the reflectivity of the walls are kept at 0.88 for both cases.

It is seen that, as in the case of the experimental study, the total solar

fluxes on the floor in the sunlit area are augmented by the reflected solar

fluxes to values much higher than those measured outside the enclosure.

7 . CONCLUSIONS

Based on the experimental and analytical study on the solar radiant flux

distribution inside a sunspace enclosure, the following conclusions can be

drawn

:

1. The solar flux distribution on any surfaces not in direct sunlit

area can be approximated in a linear fashion from the solar

opening, so that the distribution can be determined with a limited number of sensors installed at the right locations.

2. A highly reflective wall surface such as white painted gypsum

wallboard tends to reflect and distribute the solar radiant

energy evenly over all indirectly irradiated internal surfaces

having equal distance to the south opening.

3. The amount of solar radiation incident on a sunlit floor surface

near the solar opening can be much higher than those measured on

a horizontal surface outside the enclosure under identical

conditions (attenuation by glazing material, for example),

especially if the floor and wall surfaces are highly reflective.

This surface reflected solar radiant flux should be taken into

consideration by designers when the sunlit floor is used as thermal storage medium.

4. The NBS developed solar flux distribution program gives a reasonable estimate of the flux distribution inside an enclosure,

and can be used as a valuable design tool in the design of

6
passive solar structures. It can also be incorporated into other

general energy analysis programs to give a better estimate of the

solar flux distribution on internal surfaces in the overall

energy balance computations of those surfaces.

Finally, it should be emphasized that the experiment and the analytical

model deal only with the reflection and absorption of the shortwave solar

radiation in an enclosure. The exchange of long wave infrared radiation

emitted by the interior surfaces, and convective heat transfer from the

surfaces to the air, are not considered. The analytical model is therefore

not a complete building energy analysis model. Rather, it is a model to be

used to determine the distribution of shortwave solar radiation which is

affected by the solar radiation properties of the surfaces, by the solar

properties of the glazing material, and by the size and location of the

solar openings. However, neglecting the convection and infrared radiation

exchanges do not limit the usefulness of the model for passive solar study

since the shortwave solar energy exchanges do not depend on the surface or air temperature as long as the solar properties of the surfaces remain

constant over the temperature range normally encountered in a passive solar

enclosure

.

8 . ACKNOWLEDGMENTS

The author wishes to acknowledge Mr. Bonn Ebberts of NBS who constructed

the test scale model. Dr. Michael McCabe of NBS who developed the algorithm

for the computer program, and Ms. Virginia McGurrin of NBS who wrote the

codes for the program. The work reported here was sponsored by the Solar

Buildings Technology Division, Office of Solar Heat Technologies,

U. S. Department of Energy, Washington, D.C. 20545, under Interagency

Agreement No. EA-77A-01-6010

.

7
REFERENCES

1. McCabe, ¥. E. and M. Van Migom, "Solar Energy Absorption by

Vertical Cylindrical - Tnbe Absorbers in Snnspace

Enclosures," ASME Winter Annual Meeting, Boston, MA, 1983,

paper no. 83-WA/ Sol-6,

2. McCabe, M, E. and M. Van Migom, "Application of Transparent

Enclosure Theory to Solar Energy Absorption by Cylindrical

Tubes in Sunspaces," ASME Journal of Solar Energy

Eng ineering , Vol. 107, Feb. 1985.

3. Bobco, R. P., "Radiation Heat Transfer in Semigray Enclosures

with Specularly and Diffusely Reflecting Surfaces," ASME

Journal of Heat Transfer , Vol. C86, 1964, p. 123.

4. Siegel, R., "Net Radiation Method for Enclosure Systems

Involving Partially Transparent Walls," NASA TND-7384, Aug.

1973.

5. Arumi, F. N., "The Multispace Thermal Coupling Algorithm of

the DEROB System,” Heat Transfer in Energy Conservation, ASME

Winter Annual Meeting, Atlanta, GA, 1877, pp. 9-15.

6. "Program Manual for the Simplified Shuttle Payload Thermal

Analyzer," Arthur D. Little, Inc., Cambridge, MA, Sept. 1979.

7. Mahajan, B. M., "National Bureau of Standards Passive Solar

Test Facility - Instrumentation and Site Handbook," National

Bureau of Standards, NBSIR 84-2911, Aug. 1984.

8
Table 1

Comparison of Measured and Predicted Solar Radiant

Flux Distribution Incident on Surfaces

Inside A Sunspace Enclosure

Surface Solar Time of Dav

No. Location 12.00 noon 3:00 o

.

m. Test Predict % Diff. Test Predict % Diff.

1+2 FL., N. Half 185 179 3.2 123 126 -2.4

3 FL. , S . Mid

.

542 495 8.7 23 8 195 18.1

4 FL . , S . End 808 739 8.5 400 369 00

t"

7 E. Vail, S. Half 365 309 15.3 510 413 19.0

8 E. Wall, N. Half 191 182 4.7 124 122 1.6

9 N. Wall 186 172 7.5 123 119 3.3

10 W. Wall. N. Half 188 182 3.2 133 131 1.5

11 W. Wall, S. Half 370 309 16.5 231 209 9.5

12 CL, N. Half 193 191 1.0 128 128 0.0

13 CL, S • Half 433 335 22.6 267 221 17.2

Notes: 1. All fluxes in unit of W/m

2. Surface NO. in accordance to Figure 7.

3. Clear day on Nov. 14, 1984 at 39® N. latitude.

9
Table 2

Effects of Different Floor Solar Reflectivity on the

Surface Solar Radiant Energy Flux Distribution

Inside an Enclosure

Surface Incident Flux (W/m^) % Net Absorl >ed Enerav

No. Location r=0 . 88 r=0 .50 r=0 . 8 8 r=0.50

1+2 FL, N. Half 126 60 5.35 10.70

3 FL, S. Mid. 195 164 4.17 14.66

4 FL, S. End 369 309 7.91 27.57

7 E. Wall, S. Half 413 326 11.21 8.84

8 E. Wall, N. Half 122 51 3.30 1.38

9 N. Wall 119 51 2.81 1.20

10 W. Wall, N. Half 131 59 3.55 1.60

11 W. Wall, S. Half 209 122 5.67 3.30

12 CL, N. Half 128 53 5.50 2.28

13 CL, S. Half 221 127 9.46 3.91

5 Header, S. Open. 221 131 0.79 0.47

TOTAL ABSORBED 59.72 75.91

Notes: 1. Data are for 3:00 p.m. solar time.

2. Surface No. in accordance to Figure 7.

3. Solar reflectivity on surfaces other than floor is r=0.88.

4. Clear day on Nov. 14, 1984 at 39° N. latitude.

10
Table 3

Augmentation of Solar Flnx on Sunlit Floor Area

Due to Surface Solar Reflectivity

Solar Outside of the Enclosure Floor Inside the South Onenins. Sunlit

Time Normal Horizontal Horizontal Horizontal Total Horizontal Diffuse

(11/14) Beam Total Diffuse r=0 . 88 r=0 .50 M

IIo 00 GO o «n o

ll 14

Noon 956 559 51 739 623 231 115

3:00 pm 825 301 41 445 3 85 184 124

Notes: 1.

2 . 3.

All fluxes in unit of T/m . Solar reflectivity on surfaces other than floor is r-0.88.

39°N latitude, on Nov. 14.

11
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DISTANCE

(from

South)

TO

LENGTH

RATIO

-

X/L
00

o O) 3 Tt • CO

C* co

-•O)

c

KB

r he

d>

o

in

So

h* • h*

CM CO

O# 00

CO

0 - - I

CO

5

o

o

.5

o

cn

CM

E

5

o

00

CM • 00 w CM

CO

2*00

o

o

CM

oo

LL

S*” Sco ^ • CD

CO

1^# o>

CO

CO

UJ

CO

£

s£>

00

17

North

wall

Total

horizontal

-

559

W/m

2

Direct

normal

-

957

W/m

2
00

Fig. 7 Sub-division of Sunspace Interior Surfaces for

Computer Modelling

18
U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions

)

REPORT NO.

NBSIR-86/3378 June 1986

4. TITLE AND SUBTITLE

EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF SOLAR

DISTRIBUTION ON INTERIOR SURFACES OF A SUNSPACE

RADIANT FLUX

5. AUTHOR(S)

Stanley T. Liu

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

8. Type of Report & Period Covered

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

Solar Buildings Technology Division

Office of Solar Heat Technologies

U.S. Department of Energy

Washington, D.C. 20545

10. SUPPLEMENTARY NOTES

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

11.

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

bibliography or literature survey, mention it here)

The short wave solar radiant flux distribution inside a sun-space model

with a large south opening was studied experimentally under clear sky

conditions. Miniature photovoltaic pyranometer sensors responsive to short

wave radiation were mounted at various locations on the interior surfaces

of the enclosure. It was found that solar flux distribution on an interior

surface not in direct sunlight varies approximately in a linear fashion

from the south opening, so that a limited number of sensors are adequate

for the determination of the flux distribution in an enclosure. A highly

reflective floor or wall surface not under direct irradiation from the sun tends to distribute the incoming solar flux evenly over all indirectly

irradiated interior surfaces having the same solar reflectivity. The flux

values vary only as a function of the distance from the solar opening. The

multiple reflected solar flux within the enclosure increases the amount of

solar energy falling on an area under direct sunlight to a value

significantly greater than would be measured outside of the enclosure. An

NBS developed solar flux distribution program was tested against the

experimental results and was found to give good agreement. The computer

program can be used as a design tool for. the evaluation of thermal storage

location and solar physical properties of floor and walls in a passive

12.

KEY tries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Key words: Computer program? partially transparent enclosures; passive

solar structure; solar flux measurement; solar radiation; sun-space model

13.

AVAILABILITY

[_Xj Uni imited

| | For Official Distribution. Do Not Release to NTIS

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

20402.

[J] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

25

15. Price

$9.95

USCOMM-DC 80.3-PS0