NBSIR 73-220

Test of a Polyester Composite Wall

Panel for Moisture Accumulation and

Potential Removal of Moisture

Through Venting

C. 1. Siu, W. M. Ellis, and T. Kusuda

Center for Building Technology

Institute for Applied Tectinology

National Bureau of Standards

Washington. D. C. 20234

May 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 73-220

TEST OF A POLYESTER COMPOSITE WALL

PANEL FOR MOISTURE ACCUMULATION AND

POTENTIAL REMOVAL OF MOISTURE

THROUGH VENTING

C. I. Siu, W. M. Ellis, and T. Kusuda

Center for Building Technology

institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Test of a Polyester Composite Wall Panel for Moisture

Accumulation and Potential Removal of Moisture Through Venting

C. I. Siu, W. M. Ellis, and T. Kusuda

Thermal Engineering Systems Section

Building Environment Division

Center for Building Technology

Institute for Applied Technology

ABSTRACT

A polyester composite exterior wall panel was exposed to accelerated

winter temperature and humidity conditions for the purpose of determining

performance with respect to moisture accumulation and release as a result

of pressure and temperature differences. No moisture condensation within

the wall system was detected from visual examinations made at various times

of the testing period; no significant increase in gross weight of the wall

was found from the direct weighings of the wall system. Results also indicate that a wet insulation in such a wall system is unlikely to be dried

out by natural thermal action and convective motion.

Key Words: Composite wall panel; condensation; humidity; moisture;

pressure; temperature

i

1 o Introduct ion

As a result of design changes in one of the systems in Operation

BREAKTHROUGH, the Department of Housing and Urban Development (HUD) requested experimental determination of the performance of the exterior

wall system with respect to moisture accumulation and release as a result of condensation o For this purpose, a representative wall panel

was selected by HUD and submitted to NBS by the manufacturer for testing. The description of the test panel, tests conducted and results

are presented in this report.

2o Test Panel

Two panels were received for testing; one was damaged in transit.

The wall panels received for testing measured about 8' high x 5' wide

X 4" thick. Figure 1 is a schematic drawing of the cross section of

this panel. The wall consists of a corrugated fibrous glass reinforced

polyester core, 3 1/2" thick, two flat fibrous glass reinforced polyester

sheets, 1/8" thick, bonded at the ridges to the corrugated core to form

the inner and outer surfaces of the panel, and nominal 2x4 wooden

plates bonded at the top and bottom of the wallo The grooves and nodes

of the corrugated core were continuous in the vertical direction. The

space within the core was filled with densely packed mineral insulation.

The mineral wool insulation was reported to have been treated prior to

fabrication with a sodium silicate solution which was used as a binder

for the mineral wool fibers to hold the insulation in place during

fire exposure. The exterior surface of the specimen was prepared by

1
the supplier and was composed of beige colored textured elastomeric

material, 1/16" to 1/8" thick. The interior surface was treated with

a primer paint coating. The interior surface was irregular in appearance

having tiny indentations and voids. The interior surface of the panel

was subsequently painted by NBS personnel with latex paint provided by

the supplier of the wall system.

3. Environmental Test Conditions and Test Procedure

The undamaged panel was selected and prepared for testing. It was

found to weigh 309.00 lbs on a calibrated platform balance (precision

of + 0.05 lb at 200 lbs). This weight included an 8' long nominal 2 x

4 wooden stud which was attached to the side of the wall panel for framing

purposes . Insulation material removed from the damaged panel was found

3

to have a density of about 12 lb/ft . Drying of samples of insulation

from the panel to constant weight at an oven at 212 F revealed that the

initial moisture content was less than 0.1% by weight.

The 2x4 plates of the panels did not contain vent holes. To

conform to design, ten 1/2" dia. holes were drilled in the 2x4 plate

located at the top of the panel in such a way that each of the holes

communicated to the corrugated core and to the cold side external

atmosphere; see Figures 1 and 2 . These holes were evenly spaced along

the length of the top plate. In the same way, ten 1/2" dia. holes were

drilled in the 2x4 bottom plate to match the hole positions as

described for the top plate. The 1/2" dia. holes were placed in the

2
top and bottom plates to simulate venting of the wall core space to the

exterior environment through the crawl space and the roof panel facia.

For one half of the width of the specimen, five, 3/4" dia., holes

were drilled through the exterior membrane of the wall panel about 1-1/2"

from the top and bottom edges of the wall. The 3/4" dia. holes in one

half of the panel were to simulate free exchange directly with the outside air. These are shown in Figures 1 and 2. The panel was mounted

with its interior and exterior surfaces facing the warm and cold environmental chambers, respectively. The dimensions of the chambers are shown

in Figure 3.

An electrical outlet box was installed at the center of the panel

just above the bottom plate to which it was anchored. The outlet box

was located in the grooved part of the corrugated core. In addition, a

calibrated heat flow meter for measuring heat flux was installed near

the center of the interior wall of the panel. A copper-constantan

thermocouple was located between the heat flow meter and the interior

surface of the wall. A copper-constantan thermocouple and a resistancetype water sensor were installed in the insulation material about 1/4"

from its edge abutting the exterior wall of the panel at each of the

corners of the panel.

The temperature and relative humidity of the air in the warm

chamber were maintained, throughout the testing period, at about 75 F

and 55% R.H. The temperature of the cold chamber was maintained at an

average temperature of about 10 F during the first week of testing. This

3
temperature was changed to a cyclic pulse for the subsequent 2-1/2 weeks.

The period of this pulse was about 24 hours with rise and decay times

of about 3-1/4 and 2-1/4 hours, respectively. The maximum temperature

of the cyclic pulse was about 28+0.5 F for a duration of about 11-1/2

hours. The minimum temperature was about 12 + 0.5 F for a length of

7 hours.

Two types of pressure tests were conducted for the purpose of determining airflow pattern within the wall system. One method utilized

refrigerant vapor to determine its passage through the insulation material

and the wall panel = The second test involved the use of pressurized air

to determine pressure differences between various locations within the

wall. An electric gas detector was used to determine the presence of

refrigerant vapor and a pressures differential manometer (sensitivity

of 0.002 inch of water) was used to determine pressure differences.

To conduct the pressure tests, four additional 3/4" dia. holes were

drilled through the exterior membrane of the mounted panel in order to

test for vapor leakage. These were located along AA' (Figure 2 ) at

distances x = 2, 4, 6, and 7 feet from the top edge of the wall. For

convenience of discussion these locations are denoted by H , where x

X

is the distance in feet as measured from the top edge of the wall panel.

In one pressure test, all of the 3/4" dia. holes were sealed with

rubber stoppers while all of the 1/2" dia. holes were left unsealed.

2 Refrigerant at a gage pressure of 5 lbs/in (at the gas tank) was injected for a period of one minute into the 1/2" dia. hole located at

A' (Figure 2). The upper 1/2" dia. hole to the immediate left of AA'

is denoted by L. The gas detector was used to indicate the presence of

4
refrigerant in the insulation by inserting the probe into each of the

holes drilled into the panel. Sequential observations were made to determine the rate at which the gas permeated through the insulation either

by diffusion through thermal movement or by forces due to differences

in gas densities. These tests were conducted during the minimum

temperature phase of the cyclic condition. Detection of flow of the

refrigerant vapor was continued for a total of 1-1/2 hours.

A similar test was conducted with refrigerant being introduced

through the 1/2" dia. hole at the bottom.

In the second test for determining airflow through the panel, a

2

continuous flow of air at gage pressures ranging from 6 to 11.5 lbs /in

was introduced into the bottom 1/2" dia. hole located at A (Figure 2)

and pressure differences within the wall panel at various locations

on the cold chamber side of the panel were measured relative to H „.

These measurements were taken during the pulse cycle when the temperature

was at a minimum.

Moisture accumulation within the panel was determined through:

(a) direct visual observation of the state of the insulation, (b) direct

weighing of the wall before and after testing, and (c) percent moisture

before and after testing. Water sensors were utilized to indicate

whether the insulation material was wet or dry. In these tests only

the ten 1/2" dia. at the top and bottom 2x4 plate were left opened

to the air in the cold chamber; all other holes were sealed with rubber

stoppers

5
4. Results and Discussion

A. Measured Values of Heat Flux and Temperature Within the Panel

Measured values of the heat flux through the wall panel and average

temperature within the insulation material near the exterior surface, T^,

for various chamber temperature conditions are given in Table 1=

Table lo Representative heat flux, Q, through the

wall panel and mean temperature of the

insulation near its external wall for

various chamber conditions

»

Chamber Air Temperature (F) ^2 "Average Temperature (F)

Cold Warm (Btu/hr ft ) in the Insulation

9.0 (constant) 72.9 5.5 21.0

10.8 (pulse min.) 73.7 ' ' 5.5 20.7

31.0 (pulse max.) 73.9 3.7 37.8

As indicated by four thermocouples within the insulation material near

the abutment to the exterior wall at the corner of the panel.

B. Refrigerant Vapor Leakage Test

The locations in the panel and times of detection, t^, of the refrigerant are given in Table 2.

6
Table 2„ Measured time of detection, t^, of escaping

refrigerant gas at various hole locations

R^o The end of the gas injection is taken

as t(j = 0; detection of refrigerant was initiated at this time.

Location

t , (min o

)

a

'0.1* "2 H,

Number in subscript is distance (ft) as measured

from the top of the panel.

L is a 3/4" diameter hole located to the immediate

left of H„ ,

.

Refrigerant was detected at each of the holes listed in Table 2

even after 1-1/2 hour of the introduction of tb'^^ vapor; however, no

refrigerant was observed at and .

Refrigerant was detected passing through the interior surface of

the wall at various locations. Small pin hole openings at which refrigerant was detected were distributed over an area several corrugations wide and extending from the top of the wall down to mid-height.

Except for a profusion of refrigerant vapor at the electrical outlet box, similar results were obtained for the test where refrigerant

was introduced through the bottom 2x4 plate at A (Figure 2)o

7
C. Air Pressure Test

The pressure of the air in the cold environmental chamber, during

the pulse condition, was measured to be 0.01 inch of water above that in

the warm chamber. Such a pressure difference corresponds to a wind speed

of about 5 miles per hour'-. Measured pressure differences are given in

Tables 3 and 4.

Table 3. Measured pressure difference (inch water) at

selected locations within the panel relative

to location x = 7o9o The distance x (feet) is

measured from the top of the panel» P^, P^ are pressures in cold, warm chambers » P^ pressure

at which air is injected into the panel

P^ (Ib/in^) P_ „ - P H„ T H_ H. H, P - P

a 7.9c 0.1 z 4 6 cw

(inch water)

0 .01

6 .17 .17 .17 ol7 ol7 .02

6* .15 .165 .162 .15 .15 .02

10 .192 .197 .192 .190 .190 .03

Electrical outlet taped to complete seal

8
Table 4. Measured pressure difference - P with

/ 9 ^ C P^ = 11.5 Ib/in^ for various locations

within the panel.

X Ool 2 4 6 7.9

P - P 0 0 .005 .010 ,020 X c

X denotes distance (feet) measured from the top of the panel

D. Moisture Accumulation

No frosting or moisture condensation was observed within the insulation on visual examinations made at various times throughout the entire

testing period. Readings from the water sensor indicated that the insulation material adjacent to the external surface was not wet at any time

during the testing period.

On direct weighing of the wall panel before and after testing, it

was found that there was a gain of about 0.9 lbs in the total weight

of the panel; of course, total weight includes weights of structural

elements as well as that of the insulation material. This would lead to

about a 0.1 lb increase in weight per square foot of panel over a period

of 4 months of wintry weather: too Insignificant an increase for causing

condensation damage to the insulation material.

9
The percent moisture content of the insulation in the wall was

determined before and after its exposure to all test conditions. The

results are given in Table 5.

Table 5. Percent moisture content of the

insulation within the wall panel

Specimen Location Time of Determination Moisture Content

Damaged panel Before testing <0.17o

Bottom of tested panel After testing 1%

Top of tested panel After testing .8%

In view of the low moisture accumulation, no attempts were made to

remove it through ventilation.

The objectives of this series of tests were to determine if moisture

would accumulate within the wall system, when exposed, in the laboratory,

to simulated wintry temperature and humidity conditions; if moisture

accumulation did occur could it be dissipated by natural means of convection venting.

The increase in the percent moisture content of the insulation,

Table 5, shows that a slight amount of moisture accumulated within the

panelc This, of course, results in an overall gain in the total weight

of the panelo Based on the measured percent moisture content increase.

5. Concluding Remarks

10
an extrapolated moisture content increase of about 5 percent may be expected over a four to five month period of exposure o It should be pointed

out that a 21 day exposure time can be considered adequate to indicate

only the most serious problems. Significant amounts of moisture would

take considerably longer periods of exposure.

It seems apparent from the results of both pressure tests, Sec. 4,

that a wet insulation in such a wall system is unlikely to be dried out

by natural thermal and convective forces. The insulation material was

so densely packed that it greatly impeded air passage. In addition, results of the refrigerant detection test indicate the inner wall surface

to be porous at random locations; spaces within adjoining corrugations

are not airtight; and air passes very slowly through the densely packed

insulation

.

The insignificant increases in moisture determined in these tests

does not, of course, preclude moisture problems in field situations

arising from rainfall, and the melting of snow and ice on the exterior

surface of the panel with cracks and loose joints. These are then the

primary factors to be considered when examining moisture problems in

field tests. In addition, effects of any cumulative action of moisture

pick-up over other seasonal conditions must be determined for a more

accurate assessment of moisture accumulation over an extended period.

11
6 . Acknowledgment

The authors wish to thank T. Faison for his valuable suggestions,

, 7. Reference

"'"ASHRAh Handbook of Fundamentals, American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., New York, p. 333

(1972).

12
PLASTIC

COATED

ALUMINUM

FOIL

HOT

i

ELECTRIC OUTLET

BOX 2"x3" OPENING^^»."

-STAINLESS STEEL DOOR FRAME

1/2" THICK LOOSE GLASS FIBER INSULATION

i i

L )

3/4" OPENING WITH RUBBER STOPPER

-MINERAL WOOL INSULATION

(DENSITY: ~I2 lb/ft')

COLD

EPOXY

GLUE'

PLASTIC COATED

ALUMINUM FOIL^

1-1/2" THICK LOOSE

GLASS FIBER

INSULATION

FIBROUS GLASS

POLYESTER REINFORCED

COMPOSITE

INSIDE

SECTION A-A

-3/4" OPENING WITH RUBBER STOPPER

'VENT HOLE 1/2" DIAMETER

3-7/8'

2x6 SUPPORTS

y THERMOCOUPLE

O WATER SENSOR . (H>HEAT FLOW METER

Figure 1 Schematic diagram of a sectional view of the instrumented

test wall panel mounted between environmental chambers

13
,10 VENT HOLES 1/2 DIAMETER

FIBROUS GLASS

POLYESTER

REINFORCED

COMPOSITE

L A' 64-1/2

1-1/2

I/- r\\ rti rtr

5 HOLES 3/4 DIAMETER

WITH RUBBER STOPPER

Oh.

Oh,

OHg

6-1/2

5 HOLES 3/4 DIAMETER

WITH RUBBER STOPPER

Ijj' — j|J L|j 1|J Lji ^ -Lji IjJ yA

10 VENT HOLES/

1/2" DIAMETER

I I

.11 2x4 WOOD

/

2"x6" SUPPORTS

Figure^ 2 Exterior wall surface of test

wall panel on frame support

14
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BLDG. 226

RM. A-118

WARM/HUMID

CHAMBER

35"

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TEST WALL PANEL

(5'-4"x8')

20'

Figure 3 Floor plan giving dimensions of environmental

chamber facilities

15

NBS-n4A II. -I) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PMIU.K .'\ l iON CR Kl-;PC)K r NO. NBSIR 73-220

2. Gov't Acofssion

No.

4. rn i.i-: -wn sl'b n ri.i- Testing of a Polyester Composite Wall Panel for Moisture

Accumulation and Potential Removal of Moisture Through Venting

3. lUt ipil'!!!''. \c( cssion Nc

5. Huh! I. 1 1 i!>i) 1 ),uc

6. Performing Organization Code

7. .AinHORlS) Co I Siu, W. M. Ellis, and T. Kusuda

8. Performing Organization

NBSIR 73-220

10. Projecl/Task/'Work Unit Nc 4600370

9. PERFOR.MING ORG.-W'IZATION NAMl- AND ADDRESS

NATION.AL BUREAU OF STANDARDS

DEPARTMENT OF COM.MERCE

WASHINGTON, D.C. 20234

11. Contract/Grant .No.

12. Sponsoring Organization .N.tine and .'\ddress

Housing and Urban Development

Washington, D. C. 20410

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLE.MENTAR^' MOTI-",S

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

bibliograph) or iitcraiiire ,-urvey, mention it here.)

5igni

A polyester composite exterior wall panel was exposed to accelerated winter

temperature and humidity conditions for the purpose of determining performance with

respect to moisture accumulation and release as a result of pressure and temperature

differences c No moisture condensation within the wall system was detected from visual

examinations made at various times of the testing period; no significant increase in

gross weight of the wall was found from the direct weighings of the wall system. Results also indicate that a wet insulation in such a wall system is unlikely to be

dried out by natural thermal action and convective motion.

17. KEY UORDS 'Alphabetical order, separated by semicolons) Composite Wall panel; Condensation; humidity;

moisture; pressure; temperature

18. A'/AILABILITY STATEMENT

X' UNLIMITED.

FOR OFFICIAL DISTRIBUTION. DO NOT RELliASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

21. NO. OF pac;es

22. Price

UNCLASSIFIED

USCOMM-DC 66244-P71

I
}