Influence of material properties on the hygrothermal performance of a high-rise residential wall

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Influence of material properties on the hygrothermal performance of a

high-rise residential wall

Karagiozis, A. N.; Salonvaara, M. H.

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I nflue nc e of m a t e ria l prope rt ie s on t he hygrot he rm a l pe rform a nc e of

a high-rise re side nt ia l w a ll

N R C C - 3 7 9 1 3

K a r a g i o z i s , A . N . ; S a l o n v a a r a , M . H .

J a n u a r y 1 9 9 5

A version of this document is published in / Une version de ce document se trouve dans:

ASHRAE Transactions,

ASHRAE Symposium (Chicago, IL, USA, January,

1995), pp. 647-655, 1995

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379/3

ｃｾＭＹｰＭＳＭＵ

INFLUENCE OF MATERIAL PROPERTIES

ON THE HYGROTHERMALPERFORMANCE

OF A HIGH-RISE RESIDENTIAL WALL

A.hiDesN. Karaglozis is a research officer at the National Research Council Canada. Institute for Research in Construction, Building Per-formance Laboratory, Ottawa, ON. Mikael Salonvaara is a research scientist at the Technical Research Centre of Finland, Espoo.

Achilles N. Karagiozis, Ph.D.

ABSTRACT

Knowledge of the expected long-term peiformance of building envelopes subjected to the simultaneous heat and moisture transport is critical during the design stage. In-creased incidents ofrapid deterioration ofhigh-rise building envelopes have further extended this concern to the rehabili-tation of such structures. For durable and energy-efficient constructions, the knowledge of how the structure/construc-tion behaves when subjected to a persistently harsh environ-ment is needed. Recently this behaviorhas been simulated by sophisticated computer models that incorporate the trans-port physics ofheat and moisture in porous construction ma-terials.

This paper investigates the influence ofthe variability of measured moisture transport properties on the overall hy-grothermal peiformance of a high-rise construction wall. The analysis was carried out using a state-of-the-art hygro-thermal model. The LATENITE model is a two-dimensional heat and moisture transport program tailored specifically for building envelope investigations. For the present simula-tions, the model was adaptedfor one-dimensional conditions and hourly simulations were predicted for a one-year peifor-mance of a high-rise wall section. Three types of facade cladding were used: two with red brick (one with an ex-tremely high water vapor permeance, one with normal per-meance) and one with a sandlime stone facade. Several cases for the wall systems were tested to determine the rela-tive influence ofmoisture transport properties of the wall on the predicted results.

For these particular high-rise wall structures, the re-sults showed that by significantly varying the vapor perme-ability and the liquid diffusivity, the monthly and year-round heat flows and moisture contents were not influenced much for the brick facade walls. A similar behavior was found with the sandlime stone facade bur, in this case, the exhibited dif-ferences were more noticeable. The high-rise wall hygrother-mal peiformance was found to be extremely sensitive to the sorption isotherm material property.

INTRODUCTION

Moisture has been identified as one of the main reasons for building envelope deterioration in North America and

Mlkael Salonvaara

Europe. In North America alone, the cost of premature dete-rioration, mainly due to moisture, is estimated to be between $20 and $40 billion annually. Building consultants, design engineers, and construction materials and system manufac-turers have had limited or no modeling tools to assist them in the prediction of hygrothermal (heat-air-moisture transport) performance. Even with the recent development of several hygrothermal models (a detailed analysis may be found in Hens and Janssens [1992]), very few have included all the important transport physics; obstacles are primarily of a computational/numerical nature. Today, some of the most sophisticated models, such as TRAlMO-2 (Salonvaara and Ojanen 1991), LAlENITE (Karagiozis 1993), MATCH (pedersen 1990), and FSEC (1992), have demonstrated good agreement with both experimental and field test data (KioBl

1993; Hens 1991).

The predictive ability of hygrothermal model simula-tions depends on the accuracy and reliability of the material properties used, such as dry and wet heat capacity, dry and moist thermal conductivity, sorption and desorption iso-therms, suction curves, water vapor permeability, moisture diffusivity, thermal moisture diffusivity, and air permeability in both dry and wet stages. Even though test methods are available, but not standard, agreement within laboratories on transport properties is not acceptable (some properties, such as liquid diffusivity, in a round-robin testing show disagree-ment on the order of 40% [Kurnaran 1992]). Traditionally, this has discouraged researchers from enhancing the model capabilities by citing material properties discrepancies as a major contributor in the disagreement of model predictions and field tests.

It becomes apparent that a systematic transient heat and moisture transport investigation is required to determine the sensitivity of the hygrothermal performance of a wall system to material properties. This step is important before effective guidelines can be deduced from any modeling analysis. This paper addresses this concern and investigates the effect of the accuracylvariability of material moisture transport prop-erties on the performance of three high-rise wall systems. These walls differ only to the extent of the material used on their exterior facade. In this study, three important material properties were significantly varied-the sorption isotherm,

Macroporous moisture flux

The equation for moisture flux can be written for macropor-ous materials and for capillary materials using slightly dif-. ferent potentials; howeverdif-. they are similar and are described

by

GOVERNING EQUATIONS Moisture Balance

The moisture balance is considered for two classes of materials-macroporous and capillary-type materials. As-suming that the dry density of the material remains un-changed during the moistening process (i.e.• no excessive swelling or shrinkage phenomena occur), the moisture trans-port balance is given as

(2) (I)

vapor permeability (kgls Pa·m) and vapor pressure (pa) in the porous material. density of thedryporous material (kglm3).

moisture content (kg,./kg,u. time (s). and

moisture flux (kglm2·s). where

introduced prior to the spatial discretization. which allows the equations to be written in operator notation that retains a parallel structure to the original partial differential equations. This also allows easy extensionlDemploying the delta form and provides the best stabilityｾｴ･･ｴｩｯｮＮ especially when the hygroscopic capacity varies significantly along the

sorp-tioncurve. . .

In LATENITE. the solution domain is divided into con-trol volumes over which the differential equations of heat and moisture flow

are

integrated and then approximated by nonlinear algebraic equations. The model employs two dif-ferent types of solution procedun:s-the approximate factor-ization and full solution procedures. Using the approximate factorization method. a system of block tridiagonal algebraic equation setsis generated. The solution of the linear system of the moisture flow equationsand the energy equations with the block-tridiagonal structure is accomplished using a direct solver. First, the appropriate decomposition of the matrix of coefficients is performed. then back-substitutions are carried outto solve for

x.

The decomposition is a structured

block-LU decomposition.

lip

=

pv

=

where

Po

=

u

=

t

=

thm

=

Moisture transport in a porous building material is a multidimensional problem with multicomponent air-vapor-liquid water flow. The material property characterizing the amount of moisture retained in a structure is the moisture content. Moisture content (u) is defined as the amount of moisture perdryweight of the material under consideration. Each material has its own characteristic relationship between the moisture content and maximum vapor pressure at a cer-tain temperature. represented as the sorption isotherm. The sorption and suction curves relate the moisture content to the relative humidity in both the hygroscopic and capillary re-gions. Moisture content, being a discontinuous potential across interfaces of materials. adds additional complexities in the analysis (Kohonen 1984).

A detailed description of the LATENITE model is given in Karagiozis and Kumaran (1993) and Salonvaara and Karagiozis (1994). and only a brief overview is presented here. Moisture transport potentials used

are

moisture content and vapor pressure. For energy transport. temperature is used as the potential. The equations are developed on a Cartesian rectangular coordinate system. contain explicit and implicit time discretizations. and are spatially discretized using the control volume formulation. Approximate factorization and

full solution procedures

are

incorporated into the model to solve the differential equations in delta form.In the model. a transient two-dimensional control volume formulation is im-plemented to solve each equation. The porous media trans-port of moisture (vapor-liquid) through each material layer is considered strongly coupled to the material properties. i.e.• the sorption curves. The corresponding moisture fluxes

are

decomposed for each phase and are treated separately. The set of governing partial differential equations is thus highly nonlinear. The Newton-Raphson method for linearizing the coefficient/equations is used to provide a more direct stron-ger coupling. The strong coupling between the moisture and energy transport primarily exists due to the presence of phase changes. This,mechanism is very material property de-pendent. A

time-splitting

or

approximate factorization

(AF)

is an option in the model. The procedure consists of dis-cretizing the equations wIth respect to time by placing the equation into implicit form. then adding a perturbation to the implicit terms. linearizing the set of differential equations. and finally rewriting the equations as a product of tensors. Each factor contains operators typically associated with one direction only. Approximate factorization can be introduced before or after the spatial discretization. In the model, AF is vapor permeability, and liquid diffusivity. Since this effort is aimedatinvestigating the influence of experimental inaccu-racies. a one-dimensional formulation was chosen.

LATEN-ITE.

a state-of-the-art hygrothermal model. was chosen for the yearly simulations.

MOISTURE TRANSPORT

This type of moisture flux equation has been extensively used in the literature and has the advantage of using a contin-uous potential field.

Capillary moisture flux

Moisture Transport

(6)

(3) Energy Transport

where

D_w

=

liquid moisture diffusivity(m2/s).

The first term on the right-hand side of Equation 3 is due to moisture gradients present in the porous material, while the second term is the vapor flux generated by vapor pressure gradients.

Heat Balance

(7)

where it is evident that both the temperature and the moisture content variable are strongly interdependent.

WALL STRUCTURE

The heat transfer is as complex as the moisture transport

and includes components such as conduction, convection, evaporation/condensation sources, freezing/thawing pro-cesses (due to moisture), and radiation heat transfer. The equation governing this scalar quantity is given as

aT

(p.c_{p )}ettat = -Vq,+S (4)

The high-rise wall structure selected for the numerical analysis is shown in Figure I. The wall is composed of the following layers starting from the exterior to the interior: a 102-mm (4.25-in.) red brick (or sandlime stone), a 25-mm (0.98-in.) air layer, a 25-mm (0.98-in.) semirigid glass fiber board, an 89-mm (3.50-in.) glass fiber batt, a 6-mil polyeth-ylene film, and a 12.5-mm (0.49-in.) gypsum board.

where BOUNDARY AND INITIAL CONDITIONS

where

£.

=

latent heat of evaporation (Jlkg),

Lice

=

latent heat due to freezing (Jlkg),

Po

=

drydensity of the material (kg/m\ and

it

=

liquid fraction having a value between 0 andI.

The heat source, S, has two phase-ehange components, one due to evaporation-condensation and another due to the freeze-thaw process:

at,

S = -L.V';'.ap-L/"pouat (5)

The wall was exposed to outsideairtemperature and rel-ative humidity that varied according to the weather data for the selected location. The weather data of Ottawa were se-lected for the numerical analysis. The simulations were car-ried out for a one-year exposure and started from JulyI. The solar radiation and long-wave radiation on the outer surfaces of the wall were included in the analysis. The wall was fac-ing the south. The additional moisture source due to wind-driven rain was also modeled using a three-dimensional commercial particle-tracking code.In this study, noair infil-tration or exfilinfil-tration is considered, so that the primary mode of water transmission is due to diffusion processes. The inte-rior surfaces of the walls were exposed to 40% relative hu-midity (RH) at 20°C (68°F). The simulations started from July I to produce results independent of the starting date (this is true for the location of Ottawa). The initial conditions of the wall were20°C(68°F) at an equilibrium of 30% RH.

MATERIAL PROPERTIES

effective volumetric heat capacity (including both the dry and wet contributions in the mate-rial matrix)(J/m30c),

conductive heat flux CW/m2),and

heat source

CW

1m

3) due to the phase-change phenomena occurring due to moisture trans-port.

=

=

This liquid fraction behavior is very dependent on the mate-rial type.

ONE·DIMENSIONAL FORMULATION

When the governing equations are cast in the Cartesian one-dimensional coordinate system, a system of strongly coupled partial differential equations is obtained:

Table I summarizes the variations of the different types of material properties used in the sensitivity analysis. Mate-rial properties were obtained from the mateMate-rial property data base of the model (Karagiozis eta1. 1994). For each case, the liquid diffusivity and vapor permeability were varied by the same percentage for all materials in the construction. Each simulation is labeled first by the letter F, followed by either 75, 100, or 125 and then by another set of numbers (75,100.

IlIlICIt _

POL...

VAPOUR P·PPIIC'R GYPSUII BOARD

Figure 1 High-rise wall configuration.

TABLE 1

Parametric Study of Moisture Transport Properties

SORPTION· VAPOR UQUID MOISTURE

ISOTHERM PERMEABILITY DIFFUSMTY

75 % ISOTHERM 75 % (6, ) 75 % (D.)

100% ISOTHERM 100% (6, ) 100%(D.)

125% ISOTHERM 125% (6,) 125%(D.)

or 125). The first number set of 75 signifies a reduction in both the vapor permeability and the liquid diffusivity by 25%; 100 signifies no reduction; and 125 signifies a 25% in-crease in these properties. The next set of numbers desig-nates the choice of the value of the sorption isotherm properties in a similar fashion. As an example, the designa-tion F751 00 means that the vapor and liquid diffusivity were reduced to 75% of their true value while the sorption iso-therm was maintained at 100% of its true value. Th deter-mine the sensitivity to the moisture transport properties on the heat and moisture transport of a high-rise wall structure,

19 simulations were performed.

The functional relationship used to prescribe the sorp-tion variasorp-tion was pinned so that the maximum moisture content was not exceeded; the expressions used are as fol-lows. Defining the 100% moisture content asu'(=sorption RH), where RH is the relative humidity (0

<

RH

<

I),an ex-pression for the implemented moisture content is given by

Artificially High Water Permeance of Brick Veneer

(lip[RH

=

30%]

=31.2.10-

10kglm sPa)

(9)

(11)

(10)

Figures 2 through 4 show results for the artificiallyhigh water vapor permeance brick facade. In Figure 2, the results illustrate the strong effect of the variation of the sorption curve. As stated earlier, the starting date for the simulations (time equal to 0) is July I. Here the wetting and drying sea-sons are clearly distinguished. The results show that in Sep-tember the wall starts accumulating moisture, peaks in RESULTS

while the 125% case is given by

f

= (I+RH_RH2).

f

= 1.0 and for the 100% case

(8)

•

u=f·u .

The functional expression for a 75% case is given by

1.0

:r---...,

.

-ｾｯＮｧ

-

0.8 Q) I-< ｾ 0.7

....,

.r!3

0.6

o

S

0.5

-.5

0.4

o

E-<0.3 ... D F10075 - - F100100 -_._. F100125 10000 8000 6000

(hr)

0.2 ＫｾｮＭｔＮＮＬＮＮＮＮＬＮＮＮＬＮＮＬＮＮＮＬＮＬＮＬＮｔＢｲＧＮＮＮＮＮＮＬＮＬＮＬＮＮＮＮＮＮＮＮＮＬＮＮＬＮＮＬＮＬＮＬＮＬＮＬＮＬＮＮＮＮＮＮＮＮＮＬＮｾｮ｟ｔＮＮＮＮＬＮｔＧＢｍＧＢｔＢｔＢｔＧＢｍＭｲｬ

o

2000 4000

Time

Figure2 Effect ofsorption isotherm variation on moisture accumulation in the wall.

0.85

: r - - - ' l

-

ｾＰＮＸＰ

-

0.55 Q) I-< ｾ 0.50

....,

Ｎｾ 0.45

o

S

0.40

-

:ll0.35

....,

o

E-<0.30 G & Eil 9 0 F75100 F100100 - - - F125100 o 2000 4000

Time

(hr)

6000

Figure3 _{Effect ofvariations in vapor permeabiiity and liquid dijfusivity on moisture accumulation in the wall.}

In8 lde 8urf'lllIce Q . . . F10075 F100100 - - F100125 ｾ 2.5

o

C 0.0

-

a=

5.0

:r---.

-....,

CIl -2.5 Q)

..c::

-5.0

§

-7.5

.-....,

0-10.0 Q)

>

I:: -12.5

o

U - 15.0 ＧｊＭＬＭＮＮＬＮＮＮＮＬＮＮｔＧＢｍＮＬＮＬＮＬＮＬＮＮＮｾＧＢｔＢｔＢｔＧＢｍ｟ｲｲｾＮＬＮＬＮｾｲｔｔｾｾＮＮＬＮＮＮＮＬＮＮｲｔＢｬＮＬＮＬＮｔＢｲＧＮＮＮＮＮＮＬＮＮＮＬＮＬＮｊ

o

2000 4000 6000 6000 10000

Time (hr)

November, and dries, out during the spring and summer sea-sons.Iffurther simulations were carried out, this cyclic pat-tern is resumed again for the following year. For thistypeof exterior brick veneer, the total moisture in the structure shows little influence of the 25% increase or decrease in the vapor and liquid moisture transport permeabilities and diffu-sivities, as shown in Figure 3. Figure 4 depicis the thermal performance of the wall. Here it is evident that for this par-ticular wall system, the convective heat flow from inside and outside surfaces, as well the latent heat flows, show negligi-ble influence even for variation of the sorption isotherm. The wall structure displays no particular moisture problems, and the moisture contents in the layers of the wall are low. The increased vapor permeabilities and liquid diffusivities cause larger and more rapid changes in the moisture contents, but because of the low moisture capacity of the wall, the heat flows are only minimally affected by the moisture move-ments. The thermal resistance offered by the brick layer is

only asmallpart of the total thermal resistance of the wall.

Moisture accumulation occurs mainly in the brick layer, and there are no major moisture flows through the insulation layer that would reduce the effective thermal resistance of the wall.

Normal Water Permeance of Brick Veneer

(lip[RH

=

30"04]

=

0.126·1(,10kg/m sPa)

In Figure 5, the effect of the variation of the sorption isotherm on the total moisture accumulation for a brick ve-neer with typical permeance values is shown. Figure 6 shows the effect of the variations in vapor permeability and liquid diffusivity on the total moisture accumulation in the wall as a function of time. The effect of the moisture transport proper-ties shows behavior similar to that in the high vapor per-meance brick veneer study. In Figure 7, the convective heat flows are plotted out for the interior surface of thewallas a function of the sorption isotherm. Here again, behavior simi-lar to that in the case of the high water permeance of the brick facade can be seen.Ingeneral, the effect of moisture storage on the heat flows is also negligible.

Moisture Time Constant

The effect of moisture capacity on the hygrothermal per-formance of the wall section was studied by replacing the brick layer with sandlime stone. A comparison of the mois-ture capacity for three different materials is shown in Figure 8. Samples with a thickness of 10 cm were initially set at +20°C (68°F) and 90% RH. One side of the layer is main-tained at +20°C (68°F) and 50% RH and the other side at O°C (32°F) and 0% RH. The changes in the moisture con-tents were calculated. The differences in the time constants for moisture transfer can be seen in the slopes of the curves in Figure 8. Red brick responds quickly to external changes, whereas pine and especially sandlime stone respond much

652

slower. The red brick with high permeances would respond even faster than the brick in

FIgure

8.

Sandllme-Stone Wall

The walls with high moisture capacity (Figure 9) show greater differences inthetola! moisture contents than walls with 'lower moisture capacity (Figure 6) when vapor perme-abilities and liquid diffusivities are varied. The moisture con-tents in the walls with sandlime stone are higher than those in the red brick walls. Thehigher moisture contents, how-ever, do not have much effect on the heat flows at the inside surface of the walls, which can be seen in Figure 10.

As for the red brick, the thermal resistance of the sand-lime-stone layeris very small in comparison to the thermal resistance of the insulation layer. The heat flows are mainly controlled by the insulation layer. The heat flows at the in-side surfaces of the walls overlap each other and display no significant differences.

CONCLUSIONS

The hygrothermal behavior of this particular high-rise wall construction showed that the ±25% variation in the moisture transport properties may have an effect dependent on the type of exterior facade used. This effect comparativelyisgreater for variations of the sorption curve of the facade. The results showed insensitivity to the sea-sons, i.e., summer-winter, exhibited in Ottawa. This insensi-tivity exists when monthly or even weekly averaged moisture or heat flow conditions are examined. Again, the one-dimensional results found in this paper are only valid for this type of construction without air infiltration or exfiltra-tion. This limits the scope/conclusions of the work to a cer-tain type of high-rise wall construction.

ACKNOWLEDGMENT

This work was partially supported by Canada Mortgage and Housing Corporation (CMHC) under a joint research project. CMHC's support is greatly appreciated.

, NOMENCLATURE

Cp

=

heat capacity of material (Jlkg·K)

D_wx

=

moisture diffusivity inxdirection(m2/s)

Dwy

=

moisture diffusivity inydirection(m2/s)

It

=

fractionofliquid

k_j

=

thermal conductivity inj direction(W/m·K)

L."

Lice

=

latent heat(J/kg)

mm

₌

total moisture flux (kglm2·s) th_vap

=

vapor moisture flux (kglm2·s)

P_v

=

vapor pressure (pa)

q.

=

conduction heat flux(W1m2)

G&Geo F10075 - - F100100 • F100125 1.2 ＭＺｲＭＭＭＭＭＭＭＭＭＭｾＭＭＭＭＭＭＭＭＭＮＮＮＬ

--

lUl1.1 ｾ _ 1 . 0

e

0.9

.E

0.8 Ｎｾ 0.7

o

SO.6

_0.5 cd

15

0.4 .. ｊｾ Eo-<0.3 0.2 ＢＧｦＭＬＭｾｾｲｔＢｔＮＮＬＮＬＮＮｾｲｔＢｔ｟ｲｲｔＢｔＢＱｲＧＢｔＢｔｾＬＮＮＬＮＮＬＢＢｔｔｔｔＢＬＮＮＬＮＮＬＢＢｔｔｔｔＢＬＮＮＬＮＮＬＢＢｔｔＮＬＮＬＮＮＮＬＮＮＬＮＮＬＮＮＮ｟ｉ

o

2000 4000 8000

TiIne (hr)

6000 10000

FigureS Effect ofsorption isotherm variation on moisture accumuiation in the wall.

0.65 T - - - ...- - - ,

--

lUl ｾＰＮＸＰ

-

.. ee .. " F75100F100100 ---F125100 (I) 0.55

'"'

::;l ..., 0.50 en

...

o

S

0.45

'a;

0.40

...,

o

Eo-<0.35 4000 6000

TiIIle (hr)

8000 10000

Figure 6 FJfect ofvapor permeability and liquid diffusivity variation on moisture accumuiation in the high·rise wall.

10000 8000

In. lde .ur1'ace

4000 6000

TiIIle (hr)

!9 eBB 0 F 1121075 - - F100100 ... F100125

....,.

cd -2.5 (I)

..=

ｾＵＮＰ

=

o

-7.5

...

_...,

ｾ -10.0

=

-12.5

o

U -15. 0 ＫｲＮＬＮＮＬＮＮＬＮＮＬＮＮＬＢＢｔｔＮＮＬＮＬＮＮＬＮＮＬＮＮＬｃｔＢＢｔｾｔＢｔＢＱｲｔＢｔＮＮＬＮＬＮＮｾｲｔＢｔｯｲＮＬＮＮＬＮＮＬＮＮＬＮＮＬＢＢｔｔＮＮＬＮＬＮＮｾｲｔＢｔ｟ｲｲＮＬＮＮＬＮＮｪ o 2000

--

i!=

5.0

: r - - - ' - - - ,

-

_ｾ 2.5

o

C

0.0

3.5

100

3

90

80

2.5

₇₀

_{Red brick}

ｾ

2

60

ｾ

_{Sondllme stone} Cl

₅₀

ｾ

(2ndY) .:.:

_1.5

'i

40

_'i

30

_ . 0 - . Pine (2ndY)

0.5

20

10

0

0

0

100

200

300

400

nme,h

Figure 8 The effect ofmoisture capacity on the time constant ofthe walls. They axis for the red brick is on the left and the secondy axis on the right is for pine and sandlime stone.

3.2

-r---,

-

bJl ｾＳＮＱ

-

Q) ｾ 3.0 ::l

....,

Ｎｾ 2.9

o

S

2.8

-

....,

_'"

02.7 Eo-< """"""'575100 - - 5100100 ｾ 5125100 2.8 ＫＭｾｾｾｾｾｾｾＢＧｾｾｾ｟ｲｮｾｾｾＢＮＬＮＮＮＮＮＬＮｾｾＭＬＭｪ o 2000 4000 6000 8000 10000

TiIlle level (hr)

Figure9 Effect of vapor permeability and liquid diffusivity variation on moisture accumulation in the high-rise wall (sandlime stone). Ins ld" sUI"''fec8 - - 575100 - 5100100 - 8125100 il= 2.5

o

C

0.0

-

a=

5.0 ＭｲＭＭＭＭＭＭＭＭＭＭＭＭＭｾＭＭＭＭＭＮＮＮＮＮＬ

-....,

'" -2.5 Q)

..c::

-5.0 J::

_o

-7.5

.-

....,

() -10.0 Q)

>

J::-12.5

o

U -15.0 ＫＢＮＬＢＧＮＮＬＮＢ］ｾｾＢＧ｟ｲｹＺｾｾＬＬＮＬｲｲｲＺｲＺｲ｟ＢＧｾ］］ｾｾｾ o 2000 4000 6000 6000 10000

TiIlle level (hr)

Figure 10 The effect of convection heat flow at the interior surface as a function of vapor and liquid transport properties (sandlime stone).

..

'

RH

=

relative humidity(%)

S

=

heat source

CN

1m

3)

T

=

temperature (OC[oFj)

t

=

time (s)

u = moisture content of material (kglkg)

U

=

unknown vector

Greek Symbols

Po

=

drydensity of porous material (kg/m3)

5p

=

vapor permeability inxdirection (kg/s'm·Pa)

6/

_,

=

vapor permeability inydirection (kg/s'm,Pa)

REFERENCES

FSEC. 1992. FSEC users manual, FSEC 3.0 Florida soft· ware for environment computation, version 3. Cape Canaveral, FL: Florida Solar Energy Center.

Hens, H. 1991. lEA, Annex 24, HAMTIE, first common ex-ercise, report no. TI-B-91105. New York: International Energy Agency.

Hens, H., and A. Janssens. 1992. Inquiry on existing HAM-CaT models. lEA, Annex 24, HAMTIE, Report

TI-B-92/01,p. 23, New York: International Energy Agency. Karagiozis, A. 1993. Overview of the 2-0 hygrothermal

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Karagiozis,A.,and M.K. Kumaran. 1993. Computer models for hygrothermal analysis of building materials and

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KieBI. 1993. lEA, Annex 24, HAMTIE, third common exer-cise, October.

Kohonen, R. 1984.A method to analyze the transient hygro-thermal behaviour of building materials and compo-nents.Publication 21. Espoo: Technical Research Centre of Finland.

Kumaran, M.K. 1992. Moisture diffusivity of spruce speci-men, lEA, Annex 24, HAMTIE. New York: Interna-tional Energy Agency.

Pedersen, C.R. 1990. Combined heat and moisture transport in building constructions. Ph.D. thesis. Report 214. Thermal Insulation Laboratory, Technical University of Denmark.

Salonvaara, M., and A. Karagiozis. 1994. Moisture transport in building envelopes using an approximate factoriza· tion solution method. CFD94 Conference, Toronto, Canada, June.

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Tl·SF·91/01, 02, 03. lEA, Annex 24, HAMTIE. New