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g Moisture Buffer Value of Materials in Buildings

Carsten Rode, Ruut Peuhkuri, Kurt K. Hansen – DTUBerit Time – Byggforsk; Arild Gustavsen - NTNU

Kaisa Svennberg, Jesper Arfvidsson, Lars-Erik Harderup - LTHTuomo Ojanen - VTT

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Content of Project

Main work items:• Moisture Buffer Value definition

– Relation to standard properties for moisture transport and storage (“moisture effusivity”)

– Practical Moisture Buffer Value– Property conversion tool

• Principles for test methods “Test Protocol”• Round Robin with industry involvement

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NORDTEST Partners

• VTT, Finland• Byggforsk, Norway• Lund Institute of Technology• Technical University of Denmark

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International Reference Group

• Glasgow Caledonian University UK• INSA-Lyon, France • KU Leuven, Belgium• Fraunhofer Institut für Bauphysik, Germany• Pontifical Catholic University of Paraná, Brazil• Faculdade de Engenharia da Universidade do Porto,

Portugal

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Thermal effusivity

• Density• Thermal conductivity• Heat capacity

• Density• Water Vapour

Permeability• Moisture Capacity• Saturation Vapour

Pressure

”Moisture effusivity”

b cρλ= ms

bpρδξ

=

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g Moisture Effusivity bm

(Calculated)

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

Wood T

Plywoo

dCon

crete

Zeolit

e

Clay

Wood |

|Gyp

sum"C

anos

mosmis" Bric

kCell.

Concre

teExp

. poly

styren

eCellu

lose i

nsul

Mineral

Woo

lM

oist

ure

Buf

fer C

apac

ity, 1

0-7 k

g·/(m

2 ·Pa·

s½)

Moi

stur

e Ef

fusi

vity

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Determination of Practical Moisture Buffer Value(Climatic Chambers)

Determination of Practical MBV(Climatic Chambers)

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RH and Temperature in Chamber

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80

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Time

RH

, % o

r Tem

pera

ture

, °C

RHTemp

RH = 75/33% for 8/16 hours

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Determination of MBVfrom the Weight Change

536

537

538

539

540

541

542

543

23-02-2005 00:00 24-02-2005 00:00 25-02-2005 00:00 26-02-2005 00:00 27-02-2005 00:00 28-02-2005 00:00 01-03-2005 00:00Date

Mas

s, g

Mass

quasi-steady cycles

moisture uptake

Normalization:

per m²

per change in %RH

MBV

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VTT

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Lund University

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Byggforsk

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g MBV & bmSpruce

Conditions @ 20°C with tp = 24 h (86400s)

Theoretical (using steady state prop.s):ρ 430 kg/m3

δ 2.50⋅10-12 kg/(m⋅Pa⋅s)ξ 0.17 kg/kgpsat 2340 Pabm 2.5⋅10-7 kg/(m2Pa⋅s½)kg/m2%RH0.0012MBV

%42ΔRHkg0.0044Δmm20.087Area

MBV (dynamic measurement):

Harmonic analysis of the 8/16 hr cycle yields the relationship:

0.00568 sat m pMBV p b t= ⋅ ⋅ ⋅

3908 0.0011kg/(m²·%RH)mMBV b= ⋅ =

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Materials in Round Robin

Material/Product DTU VTT LTH NBI

0 Spruce Plywood x XX x x

1 Finnish Spruce boards x XX x

2 Concrete XX x x

3 Gypsum x XX x

4 Laminated Wood XX x x

5 Light weight aggregate concrete XX x X

6 Cellular concrete XX x x

7 Brick XX x x

8 Norwegian birch x x XX

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g Example: Finnish Spruce Boards

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g Dynamic Weight Change8 + 16 hours

-10

0

10

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40

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60

0 5 10 15 20

Hour of last cycle

Wei

ght c

hang

e pr

. sur

face

are

a, g

/m²

VTT #1VTT #2VTT #3NBI #1NBI #2NBI #3DTU #1DTU #2DTU #3

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Moisture Buffer Value [g/(m2⋅%RH)] for Spruce Boards

Specimen

Institute#1 #2 #3

VTT 1.19 1.23 1.19

Byggforsk 1.09 1.16 1.10

DTU 1.20 1.17 1.18

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Comparison Between Materials

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MBV Classification

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g Relevance of MBV in Application

Value of moisture buffering effects should be compared with effects of:

• Ventilation• Surface treatments• Convective surface conditions• Other buffer materials, e.g.

furniture

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Conclusions

• The NORDTEST project provides a uniform definition of Moisture Buffer Value

• Principle for test methods is specified• Analytical relationships clarified• A Round Robin Test has been carried out

• At present, MBV itself cannot be used to calculate RH variation for a whole room