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Thermal Mass Effect of Solid Block
Aerated Autoclaved Concrete
Bryan Urban, Diana Elliott, Nitin Shukla, Jan Kosny, Fraunhofer CSE
Michael McDonough, Architect P.C., New York, NY
Author Contacts:
Bryan Urban (Presenter) Dr. Jan Kosny (PI)
[email protected] [email protected]
© Fraunhofer USA
[email protected] [email protected]
CESBP 2013
Tuesday, Sept. 10, 2013
Vienna, Austria
Background
© Fraunhofer USA
Three Walls
© Fraunhofer USA
pre-cast panels
$$$
cast in place
$$$
concrete block
$
1 billion per yr
80 million m2
© Fraunhofer USA
80 million m2
1 of these…
© Fraunhofer USA
Aerated Autoclaved Concrete
� Invented in mid 1920s by Swedish
Architect
Advantages
� Lighter weight
© Fraunhofer USA
� Lighter weight
� 20% the weight of concrete
� Up to 80% air by volume
� Lower transport cost
� Easier to shape with tools onsite
� Insulating and energy savings?
© Fraunhofer USA
© Fraunhofer USA
© Fraunhofer USA
© Fraunhofer USA
© Fraunhofer USA
Concrete Density vs Thermal Resistivity
(m·K/W)
insulation
20
30
© Fraunhofer USA
light concrete heavy concrete
mortar
AAC
0
10
0 500 1000 1500 2000 2500
Concrete Density (kg/m3)
Building Energy Codes
Provide thermal mass credit for
certain weight classes of concrete.
© Fraunhofer USA
certain weight classes of concrete.
These may fail to represent the
insulating benefits of lightweight
concrete.
Thermal Mass Credit in ASHRAE 90.1 and 90.2 & IECC
Climate Zone Mass Wall R-Value1
1 3/4
2 4/6
3 8/13
IECC Insulation Requirement for a Mass
Wall (From Table R402.1) (ICC 2012)
© Fraunhofer USA
3 8/13
4 except Marine 8/13
5 & Marine 4 13/17
6 15/20
7 & 8 19/21
1 Second R-value applies when more than half of the
insulation is on the interior of the mass wall.
Data Gaps Exist
Thermal properties of some types
of lightweight concrete were not
© Fraunhofer USA
of lightweight concrete were not
well represented in the literature.
Concrete Class
Strength (MPa)
Nominal Dry Bulk
Density, kg/m3
Density
Limits,
kg/m3
Average Drying Shrinkage,
%
AAC-2 400 350-450
500 450-550
AAC-4 500 450-550
AAC Concrete Strength Classes
© Fraunhofer USA
≤ 0.02600 550-650
700 650-750
AAC-6 600 550-650
700 650-750
800 750-850
Thermal conductivity measurements
missing from the literature
Experiment
© Fraunhofer USA
Experimental Approach
� Receive batch of 14 samples from
manufacturer
� Weigh samples (to measure density)
� Dry samples in thermal chamber
until weight reaches equilibrium
© Fraunhofer USA
� ASTM D4442 says 103±2°C
� We used 52.5 °C and 5% RH to
prevent condensation on the
isothermal plates during testing
� Measure thermal conductivity in
Heat Flow Meter Apparatus
� Weigh samples to confirm moisture
content has not changed
Thermal Conductivity of Concrete vs. Density
0.16
0.18
Th
erm
al
Co
nd
uct
ivit
y (
W∙m
-1K
-1) Experiment
Experiment Fit
ASHRAE Empirical
k=0.0425e(0.0023ρ)
R2=0.9788
© Fraunhofer USA
0.10
0.12
0.14
400 450 500 550 600
Th
erm
al
Co
nd
uct
ivit
y (
W∙m
Density (kg∙m-3)
k=0.026e(0.0738ρ0.5)
(ASHRAE)
Simulation
© Fraunhofer USA
Simulation Challenges
3D heat transfer not easily
modeled in whole building
© Fraunhofer USA
modeled in whole building
simulation tools. Material
descriptions must be 1D layers.
Importance of Thermal Bridging
© Fraunhofer USA
Mortar Joint Insulated Joint
Equivalent Wall Theory
� Represent 3D assemblies as a series of
fictitious 1D material layers that
produce the same thermal response
© Fraunhofer USA
=
3D Simulation of Concrete with Mortar Joint
3-D model of 8-in CMU
Detail of mortar joint usedin numerical analysis
© Fraunhofer USA
T00150.084648.371146.657744.944343.230841.517439.803938.090536.377134.663632.950231.236729.523327.809926.0964
Simulation Cases
� DOE Reference Building for Mid-Rise
apartment building
� ASHRAE Climate Zones 4 and 5
� New York and New Jersey
© Fraunhofer USA
� New York and New Jersey
� Cold winters, warm summers
� 5 Wall Configurations
� 3 CMU configurations
� 2 AAC configurations
Exterior Wall Configurations
Concrete Masonry Units
� 200mm CMU + 63mm XPS
� 250mm CMU + 63mm XPS
� 300mm CMU with vermiculite core
© Fraunhofer USA
Aerated Autoclaved Concrete
� 250mm AAC
� 300mm AAC
Wall Configurations with Equivalent Layer Simulation Properties
Wall Assembly
Thickness (mm)
Conductivity k (W/m·K)
Density (kg/m3)
Specific Heat (kJ/kg·K)
Surface-to-surface R-SI (R-value)
200mm CMU +
63mm XPS
25.4 0.15 1600 0.04 2.3725.4 0.43 1600 0.0425.4 10.19 1600 0.6225.4 1.75 1600 3.17
250mm CMU +
63mm XPS
25.4 0.15 1600 0.05 2.3925.4 0.44 1600 0.0525.4 10.03 1600 0.66
© Fraunhofer USA
25.4 10.03 1600 0.6625.4 1.55 1600 4.27
300mm CMU
with vermiculite
core
25.4 2.59 1600 2.38 0.5925.4 1.20 1600 1.3325.4 1.30 1600 0.9925.4 2.25 1600 3.35
250mm AAC 250.8 1.14 450 0.84 2.09300mm AAC 301.6 1.14 450 0.84 2.51
Representative Summer and Winter Week Temperature Data
15
30
Ambient Air Temperature
Summer
Boston
°C
© Fraunhofer USA
-15
0
15
0 24 48 72 96 120 144 168 Time (hours)
Winter
Boston
Interior South Wall Surface Temperatures on a Winter Day
22
24300-mm CMU R-0.6
200-mm CMU R-2.4
250-mm CMU R-2.4
°C
© Fraunhofer USA
16
18
20
0 4 8 12 16 20 24
250-mm AAC R-2.1
300-mm AAC R-2.5
hour
Interior South Wall Surface Temperatures on a Summer Day
26
27 300-mm CMU R-0.6
200-mm CMU R-2.4
250-mm CMU R-2.4
°C
© Fraunhofer USA
24
25
0 4 8 12 16 20 24
250-mm CMU R-2.4
250-mm AAC R-2.1
300-mm AAC R-2.5
hour
Interior South Wall Surface Heat Flux on a Winter Day
-10
0300-mm CMU R-0.6
200-mm CMU R-2.4
250-mm CMU R-2.4
W/m2
© Fraunhofer USA
-40
-30
-20
0 4 8 12 16 20 24
250-mm AAC R-2.1
300-mm AAC R-2.5
hour
Interior South Wall Surface Heat Flux on a Summer Day
10
15300-mm CMU R-0.6
200-mm CMU R-2.4
250-mm CMU R-2.4
W/m2
© Fraunhofer USA
-5
0
5
0 4 8 12 16 20 24
250-mm CMU R-2.4
250-mm AAC R-2.1
300-mm AAC R-2.5
hour
Annual Cooling Loads
Cooling
300-mm AAC R-2.52
250-mm AAC R-2.10
200-mm CMU R-2.36
250-mm CMU R-2.40 - Baseline
300-mm CMU R-0.58
© Fraunhofer USA
0.E+00 2.E+05 4.E+05 6.E+05 8.E+05
Heating
MJ
Monthly Cooling Loads
1
2
3
4
5
6
300-mm AAC R-2.52
250-mm AAC R-2.10
200-mm CMU R-2.36
250-mm CMU R-2.40 - Baseline
300-mm CMU R-0.58
© Fraunhofer USA
0E+0 5E+3 1E+4 2E+4 2E+4 3E+4 3E+4
7
8
9
10
11
12 Cooling (MJ)
Monthly Heating Loads
1
2
3
4
5
6
300-mm AAC R-2.52
250-mm AAC R-2.10
200-mm CMU R-2.36
© Fraunhofer USA
0.0E+0 5.0E+4 1.0E+5 1.5E+5 2.0E+5 2.5E+5
7
8
9
10
11
12
200-mm CMU R-2.36
250-mm CMU R-2.40 - Baseline
300-mm CMU R-0.58
Heating (MJ)
Conclusions
� Data gaps in the thermal conductivity of AAC were identified
� This resulted in lack of acceptance of lightweight AAC in thermal mass credits
� We measured thermal conductivity of concrete samples to fill the data gap. Results
matched theoretical expectation fairly well.
© Fraunhofer USA
matched theoretical expectation fairly well.
� We used the data to simulate thermal performance of AAC and CMU wall cases in
several climates.
� Performance of AAC wall systems performed comparably to insulated CMUs,
suggesting that thermal mass credit may be appropriate for lightweight AAC-4
blocks.
Thank You!
© Fraunhofer USA
Author Contact: Jan Kosny
Ph: +1-865-607-6962
Presenter: Bryan Urban
Ph: +1-617-588-0618