moisture buffer value of materials in buildings apr 2006... · byg dtu department of civil...
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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
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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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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
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Mas
s, g
Mass
quasi-steady cycles
moisture uptake
Normalization:
per m²
per change in %RH
MBV
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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 Dynamic Weight Change8 + 16 hours
-10
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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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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