Post on 30-May-2019
transcript
© Fraunhofer USA 2009
Fraunhofer Center for Sustainable Energy Systems
Thermal Performance Analysis of PCM-Enhanced Insulations
Jan Kosny Ph.D.
August 10, 2011 Denver ,CO
Building America Meeting Aug. 08 - 11, 2011
© Fraunhofer USA 2009
Agenda
Introduction – A need for new thermal-design principles for modern buildings Motivation – A need for detailed thermal characteristics of new dynamic
materials to be used in Building America projects Dynamic testing with use of Heat Flow Meter Apparatus New Performance Label for PCMs Potential for development of the material database for PCM products
used in Northern America
Building America Meeting Aug. 08 - 11, 2011 2
© Fraunhofer USA 2009
Need for a New Thermal Design Principles for Modern Low-Energy Buildings
Building America Meeting Aug. 08 - 11, 2011 3
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Today, Building Enclosures Work More as Thermal Shields
4
Interior Environment
Exterior Environment
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North American Houses are Currently Built Using Igloo Principles - Developed for Large and Static Temperature Differences
Steady-state code requirements Steady-state design principles
Steady-state testing
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MOTIVATION (I): Conventional Insulations are not Always Efficient in High-R-value Assemblies
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Energy consumption change GJ/year
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
20.00
6 to 10
10 to
14
14 to18
18 to
22
22 to26
26 to
30
30to
34
34to
38
38 to42
42
to 46
46
to 50
50 to
54
54to
58
Atlanta Bakersfield Chicago Denver Houston Knoxville Miami Minneapolis Phoenix Seattle Washington DC
X starting attic R-value
X
R-4
GJ/
year
Example #1: Conventional insulation works only effectively for low R-value assemblies
Building America Meeting Aug. 08 - 11, 2011
© Fraunhofer USA 2009
Example #2: Performance of Conventional Insulations can be Easily Improved by Usage of Modern Insulation Configurations
0.20
0.10
0.00
-0.10
6
R-100
12 18 24 30
Two summer days
36 42
R-5
R-50 -0.20
-0.30
-0.40
R-50 -0.50
time [h]
R-50 roof shingle R-100 roof shingle
R-5deck R-50 PCM R-5deck R-50
R-50
R-5 PCM 18.5 BTU per ft2
Btu
/ft2-
h
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MOTIVATION (II):Several PCM-Enhanced Systems Successfully Used in Europe are Ineffective While Used in Northern America – Why?
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© Fraunhofer USA 2009
Old Approach – PCM-Impregnated Gypsum Board
PCM charged by interior temperature swings and solar gains through glazing
Building HVAC system used to discharge PCM
Schematic of Distribution of Heating and Cooling Loads in Old PCM Applications
Energy Discharged Later
Cavity Insulation
PCM-Gypsum Board
Exterior Finish
Exterior
Interior
Peak Loads Energy Transferred Back to the Environment
by HVAC System Solar Gains Energy Transferred INTO the Building
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Main Problem with Application of PCM Gypsum Boards in the U.S. Air-Conditioned Buildings
Enthalpy for commonly-used paraffinic PCM Thermostat temperature control +/-2degF
30
15
0
-15
-30
-45
16 17 18 19 20 21 22 23 24 25 26
TEMPERATURE [C]
45
[J/g
]
melting freezing
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MOTIVATION (III): Traditional DSC Testing is NOT USEFUL for Many Non-Uniform and Complex PCM Products
Building America Meeting Aug. 08 - 11, 2011 13
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Large Selection of Non-Uniform PCMs is in common use today which cannot be tested in DSC
PCM blend
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Complex arrays of PCM containers are extremely difficult to test in conventional equipment Example of estimation of the measure area for the arrays of PCM pouches or PCM containers.
Measure area needs to contain representative geometry of the measured array of PCM containers
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Complexity of H Enthalpy Data for PCM-Enhanced Insulations and blends
Initial Differential Scanning Calorimeter (DSC) tests for pure PCMs or PCM microcapsules, only
Additions to PCM-based blends make a difference; Dynamic Heat Flow MeterApparatus tests were introduced in 2006 for PCM-enhanced insulations - fire retardant effect, adhesives, not-working PCM pellets, etc….
0.00
2.00
4.00
6.00
8.00
10.00
12.00
16.00 18.00 20.00 22.00 24.00 26.00 28.00
Temp [deg C]
J/g
DSC 80% 67%
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New Dynamic Test Method for PCM-Enhanced Products Developed by Fraunhofer CSE
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Dynamic Test Methods Considered Currently for Analysis of PCM-Enhanced Products
DSC – only for uniform PCMs T-history method Dynamic Heat Flow Apparatus Method
• Symmetrical process • Non-symmetrical process
Dynamic Guarded Hot-Plate Method – only speculations so far Dynamic Hot-Box Method
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Testing Temperature Profile Used by Fraunhofer CSE -Symmetrical Testing on Both Plates of the HFMA
Temp.
Time
Melting Temp.
Initial Temp.
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Limit Limit
16 17 18 19 20 21 22 23 24 25 26
Temperature Range of Phase Change Process
Key Temperatures of the PCM Transition Process
Temperature 45
30
15
0
-15
-30
-45
TEMPERATURE [C]
Enthalpy for commonly-used paraffinic PCM Lower Upper
Temperature
[J/g
]
melting freezing
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Enthalpy change profile developed during Dynamic Heat Flow Meter Apparatus Testing
7.0E+06
6.0E+06
5.0E+06
4.0E+06
3.0E+06
2.0E+06
1.0E+06
0.0E+00 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Volu
met
ric H
Pro
file,
J/(m
3 )
Volumetric H (A) Volumetric H (B) Volumetric H (C)
Temperature, C
Building America Meeting Aug. 08 - 11, 2011 21
© Fraunhofer USA 2009
MOTIVATION (IV): Results from Traditional DSC Testing Can be Misused
Building America Meeting Aug. 08 - 11, 2011 22
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Rate of Temperature Change Effects Enthalpy Profiles
Estimation of upper and lower temperature limits for sample of the PCM-enhanced material or composites using original DSC test data for PCM (paraffinic PCM data shown).
Building America Meeting Aug. 08 - 11, 2011 23
© Fraunhofer USA 2009 24ITCC - June 26 - 30, 2011
Enthalpy for commonly-used paraffinic PCM
Potential area for misuse of the experimental data on PCM-enhanced products for most-likely marketing purposes
For what temperature range PCM enthalpy should be calculated if cp-related effects are included together with phase transition–related effects?
45
30
15
0
-15
-30
-45
TEMPERATURE [C]
This one?
16 17 18 19 20 21 22 23 Or, this one ???
24 25 26[J/g
]
melting freezing
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M-value – New Energy Performance Label for PCM-Enhanced Products Expressing only phase transition-related enthalpy change
Building America Meeting Aug. 08 - 11, 2011 25
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Understanding of Enthalpy Profile in estimation of M-value
H
Temp.
It is possible to analytically estimate and later subtract cp-related enthalpy changes for both frozen and melted stages of the testing.
Building America Meeting Aug. 08 - 11, 2011 26
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Basic Heat Transport Equations: The one-dimensional heat transport equation for such a case is as follows:
where; ρ and λ are the material density and thermal conductivity, T and h are temperature and enthalpy per unit mass. Heat flux q is given by:
The enthalpy derivative over the temperature (with consideration of constant pressure) represents the effective heat capacity, with phase change energy being one of the components:
Effective heat capacity, ceff, for a material which is a blend of insulation and PCM may be expressed as
where α denotes the percentage of PCM, cins the specific heat of insulationwithout PCM and ceffPCM is effective heat capacity of PCM.
Th t x x
, ,
T x t q x t
x
eff h c T T
1eff ins effPCM c c c
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© Fraunhofer USA 2009
Practical determination of M-value based on the DHFMA data
Building America Meeting Aug. 08 - 11, 2011
0.0E+00
2.0E+05
4.0E+05
6.0E+05
8.0E+05
1.0E+06
1.2E+06
1.4E+06
1.6E+06
1.8E+06
2.0E+06
2.2E+06
2.4E+06
2.6E+06
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Volu
met
ric s
peci
fic h
eat,
J/(m
^3 K
)
Temperature, C
Volumetric Heat Capacity A
Volumetric Heat Capacity B
Volumetric Heat Capacity C
cp related change for cp related change frozen PCM for melted PCM
Phase transition
range
Subtract cprelated
change for melted PCM
Subtract cprelated
change for frozen PCM
>5% enthalpy
change per temperature
step
28
© Fraunhofer USA 2009
New energy performance label for PCM-enhanced products
Building America Meeting Aug. 08 - 11, 2011 29
© Fraunhofer USA 2009
ITCC - June 26 - 30, 2011
Future Work within Building America Program
Dynamic testing of PCM-enhanced materials used in the U.S. Development of Energy Plus and BEopt modules enabling
modeling of the PCM-enhanced building assemblies Comparisons of DHFMA data against DSC or T-history test data Modeling leading to optimization of the temperature range and
PCM load – as a function of application thermal conductivity, location, and thickness Development of configuration recommendations for PCM
applications in basic U.S. climates
Building America Meeting Aug. 08 - 11, 2011 30