Thermal Mass Effect of Solid Block Aerated Autoclaved...

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…


� 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?

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

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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


� 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


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


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

[email protected]

Ph: +1-865-607-6962

Presenter: Bryan Urban

[email protected]

Ph: +1-617-588-0618

Thermal Mass Effect of Solid Block Aerated Autoclaved...

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