experimental and numerical energy performance analysis of...
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Experimental and Numerical Energy Performance Analysis of PCM -Enhanced Building Envelope Products and SystemsJan Kosny, Nitin Shukla, and Ali Fallahi, Fraunhofer CSE
Elisabeth Kossecka, Polish Academy of Sciences
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
Agenda
� Introduction: A need for proper
performance data for PCMs used in
building applications – Major
Motivation
� PCM Application Tactics
� Laboratory Testing of PCM Thermal
First successful application of PCMs in buildings
© Fraunhofer USA
� Laboratory Testing of PCM Thermal
Characteristics
� Challenges with Computer Simulations
� Whole building Energy Analysis of PCM
Attic Insulation
� Conclusions
Major Motivation:
Performance Problems of
Conventional Insulation
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Conventional Insulation
Insulation Effectiveness Drops Quickly with Initial Assembly R-Value
Energy Savings: GJ/year
10
12
14
16
18
20
X
R-4
© Fraunhofer USA
0
2
4
6
8Atlanta
Bakersfield
Chicago
Denver
Houston
Knoxville
Miami
Minneapolis
Phoenix
Seattle
Washington DC
X � starting attic R-Value
20x difference !
PCM Application Tactics:
Different PCM Configurations
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European Approach – PCM Impregnated Gypsum Board
� PCM Charged by:
� Interior temperature swings
� Solar gains through glazing
� PCM Discharged by:
Distribution of Heating and Cooling Loads in Old PCM Applications
Exterior Finish
Exterior
Peak Loads Energy Transferred
Back to the
Environment
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� PCM Discharged by:
� Building HVAC system
Energy Discharged Later
by HVAC System
Cavity
Insulation
PCMPCM--Gypsum BoardGypsum Board
Interior
Energy Transferred into the Building Solar Gains
Energy stored
by PCM
30
45[J/g]
Freezing
Problem with PCM Gypsum Board in Air Conditioned Buildings
Thermostat temperature control ± 2°F
[J/g-K] Enthalpy of Common Organic PCM
© Fraunhofer USA
-45
-30
-15
0
15
16 17 18 19 20 21 22 23 24 25 26 [°C]
Melting
New Approach for PCM Installations in the U.S.
� PCM Charged and Discharged by:
� Fluctuations in exterior
temperature
� Solar radiation
Peak Hour Energy Transferred
Back to the Environment
Exterior Finish
Exterior
Peak Loads
Distribution of Heating and Cooling Loads in PCM-Enhanced Envelopes
© Fraunhofer USA
� PCM materials must be able to
fully charge and discharge during
24-hour dynamic cycle. Thermally Active Core
LOW HEAT TRANSFER
ZONE
Gypsum Board
Low Delta T
Min. Heat Transfer
Interior
Thermal insulation
Energy stored
by PCM
Laboratory Testing of PCM:
Thermal Characteristics
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Numerous Dynamic Test Methods are Used Today in Analysis of
Complex PCMs and PCM-enhanced Products
� DSC – only for uniform PCMs
� T-history method
� Dynamic Heat Flow Apparatus
� Symmetrical Process
� Non-symmetrical Process
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� Non-symmetrical Process
� Dynamic Guarded Hot Plate Method (speculation so far)
� Dynamic Hot Box Method
DSC Method is Most Commonly Used but Has Limitations
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Large Selection of Non-Uniform PCMs Cannot be Tested by
Differential Scanning Calorimeter (DSC)
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PCM BlendPCM Blend
Major Thermal Analysis Problem for PCM Systems:
DSC data generated for pure (uniform) PCMs is often
used in analysis of complex PCM products or PCM
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used in analysis of complex PCM products or PCM
blends.
Need for Development of Enthalpy Charts for PCM-Enhanced
Materials and Systems
� Initial DSC testing results for pure PCMs or PCM microcapsules can be misleading
� Additives to PCM-blends make a difference: Fire retardants, Adhesives, Non-functional PCM pellets
10
12 DSC
80%
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0
2
4
6
8
10
18 20 22 24 26 28
Temp [deg C]
J/g-K
67%
Basic Heat Transfer Equations
The one-dimensional heat transport equation for such a case is as follows:
( ) Th
t x x
∂ ∂ρ λ∂ ∂ ∂ = ∂
ρ = densityλ = thermal conductivityT = temperatureh = enthalpy per unit mass
( ) ( ),,
T x tq x t
xλ
∂= −
∂
Heat flux q is given by:
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( )eff
hc T
T
∂=∂
ceff = effective heat capacity Effective heat capacity is given by:
( )1eff ins effPCMc c cα α= − + α = percent of PCM
cins = heat capacity of pure insulation
ceffPCM = effective heat capacity of PCM
For a blend of insulation and PCM, effective heat capacity may be expressed as:
DSC Output for Bio-Based PCM. Melting and Freezing Cycles
Show sub-cooling of 5°C
0.00
2000.00
4000.00
6000.00
8000.00
10000.00
DSC
uW
ou
tpu
t
DSC uW - 0.3C/min
Bio-PCM - 29degC
© Fraunhofer USA
-10000.00
-8000.00
-6000.00
-4000.00
-2000.00
17.0
19.0
21.0
23.0
25.0
27.0
29.0
31.0
33.0
35.0
37.0
DSC
uW
ou
tpu
t
Temperature [oC]
Two different enthalpy change profiles
for melting and freezing processes
Two different temperature peaks
Volumetric Heat Capacity for Cellulose-PCM Insulation Sample
using Bio-Based Micro-encapsulated PCMs
1000
2000
Melting
kJ/m3K-
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0
1000
10 12 14 16 18 20 22 24 26 28 30 32 34
Temperature (°C)
Freezing
DSC Rate of Temperature Change Affects Enthalpy Profiles
Due to lack of clear eng. guidelines or code regulations, incorrect DSC data is very often used in whole building computer simulations
DSC Melting DSC Freezing
Heating rate Heating rate
Lower temperature limit
of PCM freezing range Upper temperature limit
of PCM melting range
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Temp. deg CTemp. deg C
J/KgK
J/KgK
Freezing threshold temp.
is a moving target
A Standard Heat Flow Meter Apparatus (HFMA) Can Be Modified
To Perform Dynamic Testing of PCM-enhanced Products
5.0E+06
6.0E+06
7.0E+06
Vo
lum
etric
H P
rofil
e, J
/(m
3 )
Volumetric H (A)
Volumetric H (B)
Normally the HFMAs are used to measure the apparent thermal conductivity of materials as specified in ASTM C518.
© Fraunhofer USA
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Vo
lum
etric
H P
rofil
e, J
/(m
Temperature, C
Volumetric H (B)
Volumetric H (C)
M-value – New Energy Performance Label for
PCM-Enhanced Products
Expresses only the phase-change related enthalpy
© Fraunhofer USA
Expresses only the phase-change related enthalpy
change
30
45[J/g]
Potential Misuse of Experimental Performance Data of
PCM-enhanced Products (likely for marketing purposes)
For what temperature range should PCM enthalpy be calculated if cp-related
effects are included together with phase transition–related effects?
This one?
[J/g-K] Enthalpy of commonly-used organic PCM
© Fraunhofer USA
-45
-30
-15
0
15
16 17 18 19 20 21 22 23 24 25 26 [°C]
Or, this one ???
Proposed Energy Performance Label for PCMs
M-value �TU
MT[J/g]
© Fraunhofer USA
M-value MTL
[J/g]
TU – upper temperature limit of the phase transition
TL – lower temperature limit of the phase transition
Practical Determination of M-value
1.4E+06
1.6E+06
1.8E+06
2.0E+06
2.2E+06
2.4E+06
2.6E+06
Vol
umet
ric s
peci
fic h
eat,
J/(m
^3 K
)
Volumetric Heat Capacity A
Volumetric Heat Capacity B
Volumetric Heat Capacity C
Subtract cp
related change
for melted PCM
Subtract cp
related change
for frozen PCM
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0.0E+00
2.0E+05
4.0E+05
6.0E+05
8.0E+05
1.0E+06
1.2E+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
Vol
umet
ric s
peci
fic h
eat,
J/(m
^3 K
)
Temperature, C
cp
related change for frozen PCM
Phase transition range>5% enthalpy change
per temperature step
cp
related change for melted PCM
Computer Simulation Challenges
Most whole building simulation tools
use one simplified enthalpy curve
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use one simplified enthalpy curve
(usually for melting)
PCM Subcooling Effect is Not Properly Represented
Two independent enthalpy curves and upper and lower temperature limits generated by DSC tests for PCM-enhanced materials or composites still cannot be used today in whole building energy simulations (organic PCM data shown).
4,000
6,000
8,000
10,000DSC uW
27.2 oC (81.0 oF) 24.0 oC (75.2 oF)
© Fraunhofer USA
-10,000
-8,000
-6,000
-4,000
-2,000
0
2,000
4,000
10 15 20 25 30 35 40
24.0 oC (75.2 oF)
31.8 oC (89.2 oF)
oC
25.7 oC (78.3 oF)
Computer Simulation Challenges
Most whole building simulation tools
do not properly represent PCM
© Fraunhofer USA
do not properly represent PCM
thermal characteristics
Complex Arrays of PCM Containers Are Difficult To Test in
Conventional Equipment, Even More Difficult Numerical Analysis
Measure area needs to contain representative
geometry of the measured array of PCM containers
Example estimation of the measure area for arrays of PCM pouches
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Measure AreaMeasure Area
Computer Simulation Challenges
Complex 3D geometries for packaged
PCM products are not properly
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PCM products are not properly
represented by 1D algorithms used in
whole building simulation tools.
Whole building Energy Analysis of PCM Attic Insulations
Single Story Residential Building Modeled Using ESP-r
© Fraunhofer USA
Four Simulation Configurations
As a case study to demonstrate a practical
application of the ESP-r PCM model
SPMCMP56, we modeled a residential
single-story house in a hot climate with
PCM-enhanced cellulose ceilings.
Four Attic Assemblies:
PCM PCM
30cm
© Fraunhofer USA
Two zones:
conditioned space and
unconditioned attic PCMPCM
30cm
Underside Surface Temperature of Ceiling for Different PCM
Configurations
© Fraunhofer USA
Annual Cooling Load Simulation Results
Savings Are Relative to the Non-PCM Ceiling Case
© Fraunhofer USA
Conclusions
� During the last several decades, simple PCM applications like PCM-gypsum boards have dominated the
thermal storage market for building envelope applications. Today the focus has slowly begun to shift to
more complex PCM applications (i.e. PCM blends with insulations, PCM containers, etc.).
� A new dynamic testing procedure utilizing symmetrical step changes of temperature, and whole building
energy simulations using ESP-r model were utilized in this paper.
� A conventional heat-flow meter apparatus was used to obtain transient heat flux data for fiber insulation
© Fraunhofer USA
� A conventional heat-flow meter apparatus was used to obtain transient heat flux data for fiber insulation
material containing microencapsulated PCM.
� The routinely used DSC method for dynamic thermal property measurement of a PCM is valid only for small
quantities of pure PCM and is not appropriate for large-scale PCM-enhanced building components
� In this work, we employed a novel method based on HFMA to measure dynamic thermal properties.
� In this PCM study, we used earlier validated ESP-r PCM model SPMCMP56, for the energy modeling and PCM
performance analysis.
� Simulation result showed PCM-enhanced cellulose yields a whole-building cooling load energy saving from
3.6% to 5.7% depending on the PCM configuration for the Phoenix, AZ climate. These savings correspond to
approximately a 38.0% to 47.5% reduction in the attic-generated cooling loads.
Thank You!
© Fraunhofer USA
Author Contact: Jan Kosny
Ph: +1-865-607-6962
Presenter: Bryan Urban
Ph: +1-617-588-0618