Cost Analysis of Simple Phase 

Change Material-Enhanced 

Building Envelopes in 

Southern U.S. Climates

Jan Kosny, Nitin Shukla, and Ali Fallahi

Fraunhofer CSE

January 2013
ii

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iii

Cost Analysis of Simple Phase Change Material-Enhanced Building 

Envelopes in Southern U.S. Climates

Prepared for: 

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program 

Office of Energy Efficiency and Renewable Energy 

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

Prepared by: 

Jan Kośny, Nitin Shukla, and Ali Fallahi

Fraunhofer CSE

25 First Street

Cambridge, MA 02141 

NREL Technical Monitor: Chuck Booten 

Performed Under Subcontract No. KNDJ-0-40345-00

January 2013
iv

Contents

List of Figures ............................................................................................................................................. v

List of Tables ............................................................................................................................................. vii

Definitions................................................................................................................................................. viii

Executive Summary................................................................................................................................... ix

Acknowledgments ...................................................................................................................................... x

1 Introduction........................................................................................................................................... 1

1.1 Phase Change Materials for Building Applications.............................................................1

1.2 Overview of U.S. Performance Data for Concentrated Phase Change Material Building 

Envelope Systems................................................................................................................3

1.3 Research Studies Focused on Concentrated Phase Change Material Applications in Walls 

and Roofs.............................................................................................................................4

2 Phase Change Material Price Challenges .......................................................................................... 8

2.1 Phase Change Material Cost Components...........................................................................8

2.2 Material Cost........................................................................................................................8

2.2.1 Organic Phase Change Materials.............................................................................8

2.2.2 Inorganic Phase Change Materials...........................................................................9

2.2.3 Material Cost of Phase Change Materials................................................................9

2.3 Alternatives to Paraffin......................................................................................................10

2.3.1 Salt Hydrates..........................................................................................................11

2.3.2 Biobased Phase Change Materials.........................................................................13

2.3.3 Shape-Stabilized Phase Change Material ..............................................................14

2.4 Expected Future Cost Reductions......................................................................................14

3 Whole-Building Energy Simulations—Theoretical Performance Limits for Building Envelopes 

Using Conventional Thermal Insulations......................................................................................... 16

3.1 Theoretical Performance Limits for Dynamic Insulations Using Dispersed Phase Change 

Material Applications.........................................................................................................20

3.2 Estimation of the Competitive Price Level for Phase Change Material Attic and Wall 

Applications.......................................................................................................................30

3.3 Payback Period Analysis for Attic Applications of Dispersed Phase Change Materials .31

3.4 Additional Benefits of Thick Applications of the Phase Change Material-Enhanced Attic 

Floor Insulation..................................................................................................................38

3.5 Potential Cost Savings Associated With Phase Change Material Load Reductions in 

Phase Change Material-Enhanced Attic Floor Insulations................................................42

3.6 Payback Period Analysis for Wall Applications of Dispersed Phase Change Materials..44

3.7 Payback Period Analysis for Wall Applications of Phase Change Material-Enhanced 

Gypsum Boards..................................................................................................................49

3.8 Performance Comparisons Between Conventional Insulations and Phase Change 

Material-Enhanced Insulations ..........................................................................................53

4 Discussion of Results ........................................................................................................................ 56

4.1 Selection of Climatic Locations.........................................................................................56

4.2 Phase Change Material Load Levels in Blends With Thermal Insulations.......................56

4.3 Phase Change Material Cost Limits...................................................................................56

4.4 Payback Periods.................................................................................................................57

5 Conclusions ........................................................................................................................................ 59

References................................................................................................................................................. 60
v

List of Figures

Figure 1. Layout of the single-story ranch house used for the energy modeling.............................. 16

Figure 2. Annual energy savings as a function of wall R-value increase in increments of R-4 ....... 17

Figure 3. Annual energy savings as a function of attic R-value increasing in increments of R-4 ... 18

Figure 4. Scanning electron microscope (SEM) images of microencapsulated PCM mixed with (a) 

cellulose fiber insulation, (b) blown fiberglass matrix and fiberglass, and (c) polyurethane

foam ..................................................................................................................................................... 20

Figure 5. Temperature versus effective heat capacity data for PCM used in thermal simulations.. 23

Figure 6. Diurnal external temperature profiles Tes used in numerical analysis with assumption of 

Ti = 68°F (20°C) and Ti = 77°F (25°C) ................................................................................................ 24

Figure 7. Comparison of the daily heat flux profiles at the internal surface of the wall containing 

5.5-in. (0.14-m) thick insulation layer with 0% PCM and 30% PCM for internal temperature 

Ti = 68°F (20°C) and temperature swing schedules with thermal peaks of 113°F (45°C) in 

schedule “a” 149°F (65°C) in schedule “b,” and 185°F (85°C) in schedule “c” ........................... 25

Figure 8. Comparison of the daily heat flux profiles at the internal surface of the wall containing 

5.5-in. (0.14-m) thick insulation layer with 0% PCM and 30% PCM for internal temperature 

Ti = 77°F (25°C) and temperature swing schedules with thermal peaks of 45°C (113°F) in 

schedule “a,” 149°F (65°C) in schedule “b,” and 185°F (85°C) in schedule “c” .......................... 26

Figure 9. Comparison of the daily heat flux profiles at the internal surface of the attic floor 

containing 11.8-in. (0.3-m) thick insulation layer with 0% PCM and 30% PCM for internal 

temperature Ti = 68°F (20°C) and temperature swing schedules with thermal peaks of 113°F 

(45°C) in schedule “a,” 149°F (65°C) in schedule “b,” and 185°F (85°C) in schedule “c”........... 27

Figure 10. Comparison of the daily heat flux profiles at the internal surface of the attic floor 

containing 12-in. (30-cm) thick insulation layer with 0% PCM and 30% PCM for internal 

temperature Ti = 77°F (25°C) and temperature swing schedules with thermal peaks of 113°F 

(45°C) in schedule “a,” 149°F (65°C) in schedule “b,” and 185°F (85°C) in schedule “c”........... 28

Figure 11. Reductions of heat gains calculated for the two thicknesses of the building envelope 

assemblies. For each material configuration and at internal temperatures Ti, heat gains 

represent heat fluxes integrated over the time period. .................................................................. 29

Figure 12. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in 

Atlanta. The external temperature profiles have been defined as “a” and “b.”........................... 33

Figure 13. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in 

Bakersfield. The external temperature profiles have been defined as “a” and “b.” ................... 34

Figure 14. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in Fort 

Worth. The external temperature profiles have been defined as “a” and “b.” ............................ 35

Figure 15. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in 

Miami. Two external temperature profiles have been defined as “a” and “b.”............................ 36

Figure 16. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in 

Phoenix. The external temperature profiles have been defined as “a” and “b.”......................... 37

Figure 17. Percent peak-hour cooling load reductions for 11.8-in. (0.3-m) thick PCM-enhanced 

attic floor insulation ........................................................................................................................... 39

Figure 18. Peak-hour cooling load time-shifting for 11.8 in. (0.3-m) thick PCM-enhanced attic floor 

insulation............................................................................................................................................. 39

Figure 19. Payback periods calculated using cooling cost reductions for 11.8-in. (0.3-m) thick 

PCM-enhanced attic floor insulation computed using the off-peak-hour electricity tariff for 

Phoenix. The external temperature schedules have been defined as “a” and “b.” .................... 40

Figure 20. Reverse heat flow effect generated by significant time shifting of thermal loads in 11.8-

in. (0.3-m) thick PCM-enhanced attic floor insulation in Phoenix. The external temperature 

schedule has been defined as “a”.................................................................................................... 41
vi

Figure 21. Photograph of the test attic with blown PCM-enhanced fiberglass insulation................ 42

Figure 22. Modified levels of payback periods for attic PCM applications in Miami and Phoenix, 

considering a 25% reduction in PCM loading ................................................................................. 43

Figure 23. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Atlanta. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”............................................................................... 45

Figure 24. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Bakersfield. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”............................................................................... 46

Figure 25. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Fort Worth. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”............................................................................... 46

Figure 26. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Miami. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”............................................................................... 47

Figure 27. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Phoenix. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”............................................................................... 47

Figure 28. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Phoenix. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a” and an off-peak tariff is included....................... 48

Figure 29. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Atlanta. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.” ............................... 50

Figure 30. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Bakersfield. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.” ............................... 50

Figure 31. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Fort Worth. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.” ............................... 51

Figure 32. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Miami. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.” ............................... 51

Figure 33: Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Phoenix. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.” ............................... 52

Figure 34. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Phoenix. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a” and an off-peak tariff 

is used. ................................................................................................................................................ 52

Figure 35: Payback period for 3/8-in. thick PCM-enhanced gypsum boards that are used for wall 

application as a function of the PCM price for a single-story ranch house in Phoenix. Wall 

assemblies are assumed to experience the external temperature schedule defined as “a” and 

an off-peak tariff is used.................................................................................................................... 53

Unless otherwise noted, all figures were created by Fraunhofer.
vii

List of Tables

Table 1. Summary of U.S. Test Results for Concentrated PCM Applications ...................................... 7

Table 2. Five Southern U.S. Climates Used in Whole-Building Energy Modeling.............................. 19

Table 3. Energy Load Contributions From Walls and Attic Calculated for a Single-Story Ranch 

House for Five Southern U.S. Climates............................................................................................ 19

Table 4. Cooling Energy Contributions From Walls and Attic Calculated for the Floor Area of the 

1,540-ft2 (143-m2

) Single-Story Ranch House .................................................................................. 19

Table 5. Thermophysical Properties Used in Numerical Modeling...................................................... 23

Table 6. Residential Electric Energy Prices for Five Southern U.S. Climates Used in WholeBuilding Energy Analysis .................................................................................................................. 30

Table 7. Annual Costs of Cooling Electric Energy Generated by the Attic Calculated for a SingleStory Ranch House for Five Southern U.S. Climates ..................................................................... 32

Table 8. Calculated Annual Cooling Electricity Cost Savings Generated by the Attic for a SingleStory Ranch House for Five Southern U.S. Climates ..................................................................... 32

Table 9. Annual Costs of Cooling Electric Energy Generated by 2 × 6 Walls, Calculated for a 

Single-Story Ranch House for Five Southern U.S. climates.......................................................... 44

Table 10. Annual Cooling Electricity Cost Savings Generated by the Attic Calculated for a SingleStory Ranch House for Five Southern U.S. Climates ..................................................................... 45

Table 11. Potential Savings in Annual Costs of Cooling Electric Energy Generated by the Attic 

Calculated for a Single-Story Ranch House and for Five Southern U.S. Climates...................... 54

Table 12. Comparisons of Energy Cost Savings and Material Costs Calculated for a Single-Story 

Ranch House for Five Southern U.S. Climates................................................................................ 55

Unless otherwise noted, all tables were created by Fraunhofer.
viii

Definitions

ACH air changes per hour

ANSI American National Standards Institute

APS Arizona Public Service

ARRA American Recovery and Reinvestment Act

ASHRAE American Society of Heating, Refrigerating and AirConditioning Engineers

ASTM International formerly known as the American Society for Testing and 

Materials

CDD cooling degree-days

CMC carboxymethyl cellulose

CO2 Carbon dioxide

DOE U.S. Department of Energy

DSC Differential scanning calorimetry

GJ Gigajoules

h Hour

HDD Heating degree-days

HDPE High-density polyethylene

IEA International Energy Agency

in. Inch

K Kelvin

L Liter

LA Lauric acid

LBNL Lawrence Berkeley National Laboratory 

m Meter

MF Melamineformaldehyde

OSB Oriented strand board

PCES Phase Change Energy Solutions Inc.

PCM Phase change material

PV Photovoltaic

SAP Super-absorbent polymer

SEM Scanning electron microscope

ss-PCM Shape-stabilized PCM

W Watt
ix

Executive Summary

Traditionally, the thermal design of building envelope assemblies is based on steady-state energy 

flows. In practice, however, building envelopes are subject to varying environmental conditions. 

Design work to support the development of very low-energy homes shows that the conventional 

insulations may not always be the most cost-effective energy solution for improving the thermal 

performance of the building envelope. This report focuses on building envelopes that have been 

enhanced with phase change materials (PCMs), which can simultaneously reduce total cooling 

loads and shift peak-hour loads. 

Researchers at the Fraunhofer Center for Sustainable Energy Systems performed an economic 

analysis to evaluate the cost effectiveness of simple PCM-enhanced building envelopes and 

determined the target cost levels at which PCMs can be cost competitive with conventional 

building thermal insulations. The study team selected two basic PCM applications for analysis: 

dispersed PCM applications and simple building board products using concentrated PCMs. In 

addition to describing Fraunhofer’s work, this report summarizes the results of previous 

experimental and theoretical studies that have been conducted in North America to understand 

the performance of PCM-enhanced building envelopes. The study team used these results as 

performance benchmarks for different PCM configurations that were tested in the United States

for different building applications. This work did not, however, seek to optimize the 

configurations of PCMs. 

The investigators performed numerical parametric analyses exclusively for insulation blends. 

Specifically, the study team used a series of one-dimensional dynamic simulations with 

sinusoidal exterior temperature profiles to generate transient heat flux data for different 

configurations of building insulation containing PCM. The thermal performance characteristics 

obtained for blends of thermal insulations and organic PCMs show significant energy storage 

potential in such mixtures. The study team evaluated two thicknesses of the PCM-enhanced 

insulations in a simulation study: a typical 5.5-in. (0.14-m) thick wall assembly and 11.8-in. (0.3-

m) thick attic floor configuration. From an energy savings perspective, the thinner wall assembly

containing PCM–insulation blends (5.5-in. thick) achieved a lower reduction in cooling loads (by 

three to five times) than the thicker attic floor assembly (11.8 in. [0.3-m]). Comparing the heat 

flux values indicated that PCM-enhanced insulation in the thinner assembly exposed to cyclic 

external temperatures reduces the heat fluxes during peak cooling hours and delays the peak heat 

flux to a later time. The study team noted the same effects in the thicker assembly representing 

attic floor insulation; however, this assembly also resulted in significant reductions of the total 

load. Moreover, the thicker assembly showed a notably larger shift in the time of the peak heat 

flux (reaching 11 hours) and an approximate four-fold reduction in the peak-hour cooling load 

relative to the thinner assembly.

The simulation results also demonstrated that thicker layers of PCM-enhanced insulation, 

exposed to periodic thermal excitations, have the potential to generate a reverse heat flux, a 

phenomenon in which heat starts flowing in the opposite direction, compared to a similar 

assembly without PCM. For an 11.8-in. (0.3-m) assembly with PCM, analysts found that reverse 

heat fluxes can occur up to 70% of the time (~17 hours a day). This effect can result in “passive” 

cooling of internal spaces, reducing air-conditioning energy consumption. For a PCM-enhanced 
x

attic insulation, the simulations suggest that during the summer months, such passive cooling has 

the potential to reduce attic-generated cooling loads by up to 25%.

The study team’s simulations also revealed that the thicker assembly lowers the amplitude of 

exterior thermal excitations. In another interesting observation, investigators found that the 

potential cooling load reductions are greater when the internal set-point temperature is very close 

to the PCM melting point (in this modeling, a 3.6°F - 2°C) difference). Numerical analysis 

demonstrated that these reductions can be at least four times larger than those seen in the case 

with 12.6°F (7°C) difference between internal set-point temperature and the PCM melting point. 

Because PCM-enhanced materials usually perform well only during a part of the cooling season, 

the study team recommends a follow-on study to evaluate the long-term performance using 

annual weather data to assess the dynamic thermal performance of the PCM building 

applications in different climates.

Applications of building systems in which PCM-enhanced materials face the interior of the 

building depend on HVAC systems or overnight pre-cooling to remove heat absorbed by PCM 

during the day. For applications of the PCM-enhanced gypsum boards in walls, cooling energy 

savings ranging between 7% and 20% were previously reported by several research groups in 

different U.S. locations. Following this historical experimental data, in this work, 15% cooling 

energy savings was considered for the PCM-enhanced gypsum board applications. For PCMenhanced gypsum board applications in Phoenix, Arizona, the study team estimated a payback 

period of 7 years for PCMs of enthalpies between 82 and 95 Btu/lb (190 and 220 kJ/kg) with a 

price limit of $3.00/lb, taking into account the reduced off-peak electricity rates. Similarly, a 10-

year payback period was determined for a PCM price level not exceeding $3.50/lb. Another 

finding of the work was that application of a thinner 3/8-in. (1-cm) thick board that contains

PCM in conjunction with carbon or graphite fillers (to enhance thermal conductivity) may be 

considered as an alternative for improving performance and reducing costs.

Finally, the study team analyzed several potential methods for future cost reductions for PCMenhanced building applications. In particular, from a materials perspective, development of the 

following technologies could play a key role in reducing PCM prices in the future: (1) cheaper 

microencapsulation or micropackaging methods for organic PCMs, (2) microencapsulation of 

inorganic PCMs, and (3) less costly inorganic and biobased PCMs with higher enthalpies.

Acknowledgments

The authors acknowledge the U.S. Department of Energy, particularly Marc LaFrance, for 

funding the U.S. PCM research program. This project was made possible by direct cofunding 

from the Fraunhofer Center for Sustainable Energy Systems.
1

1 Introduction 

Phase change process involves transforming a material from one phase (solid, liquid, or gas) into 

another. For example, melting of ice into liquid water or boiling of liquid water into water vapor 

is classified as a phase change process. During a phase change, molecules rearrange themselves, 

causing an entropy change of the material system. Thermodynamics necessitates that the material 

absorb or release thermal energy or heat because of this entropy change, and this heat associated 

with the unit mass of the material is defined as the latent heat of the material. The latent heat is 

released by a material during melting and evaporation; it is absorbed during freezing and 

condensation phase change processes. The amount of latent heat is significantly larger than the 

sensible heat gain/loss for temperature changes of ~10 K. The difference could be one to two 

orders of magnitude. For example, the latent heat of melting ice to water at 32°F (0°C) is 142 

Btu/lb (330 kJ/kg). Compare this with 18 Btu/lb (42 kJ/kg) of sensible heat, which is required to 

change the water temperature by 10 K. During a phase change, the temperature of the material 

remains constant. In short, a phase change process involves a large amount of heat transfer at a 

constant temperature, and both are attractive features for heating, cooling, and temperature 

stabilization applications. A material that uses its phase-changing ability for the purpose of 

heating, cooling, or temperature stabilization is defined as a phase change material (PCM). 

PCMs have found applications in a wide array of areas such as in thermal energy storage, 

building energy efficiency, food product cooling, spacecraft thermal systems, solar power plants, 

microelectronics thermal protection, and waste heat recovery.

1.1 Phase Change Materials for Building Applications

Continuing improvements in building envelope technologies suggest that residences will soon be 

routinely constructed with low heating and cooling loads. The use of novel building materials 

containing active thermal components (e.g., PCMs, subventing, radiant barriers, and integrated 

hydronic systems) would be an ultimate step in achieving significant heating and cooling energy 

savings from technological building envelope improvements. PCMs have been tested as a 

thermal mass component in buildings for the past 40 years, and most studies have found that 

PCMs enhance building energy performance. Some problems, though, such as high initial cost, 

loss of phase change capability, corrosiveness (in cases of some inorganic PCMs), and PCM 

leaking have hampered widespread adoption. Paraffinic hydrocarbon PCMs generally perform 

well, but they increase the flammability of the building envelope (Kissock et al. 1998; Tomlinson

et al. 1992; Salyer and Sircar 1989). For these reasons, more attention is now paid to PCMs 

based on fatty acids or inorganic salt hydrates. Traditionally, PCMs were used to stabilize 

interior building temperature. In older applications, then, preferable locations for PCM were 

interior building surfaces such as walls, ceilings, and floors. In the more recent research projects 

performed in the United States, PCMs are often used as an integral part of the building thermal 

envelope. 

Microencapsulated PCMs are positioned in the wall cavity or installed as a part of the attic 

insulation system. The development of PCM integrated with thermal insulations was a critical 

step (Kośny et al. 2006). PCM-enhanced cellulose was one of the first successful developments 

of this kind of product in the building arena (Kośny et al. 2007). Subsequently, researchers 

developed PCMs blended with blown fiberglass (Kośny et al. 2010) and plastic foams (Kośny et 

al. 2008; Mehling and Cabeza 2008). The major advantage of PCM-enhanced insulations is their 
2

capability of significantly lessening and shifting peak-hour thermal loads generated by building 

envelopes.

As described in this report, Fraunhofer Center for Sustainable Energy Systems (Fraunhofer) 

performed an economic analysis to evaluate whether simple PCM-enhanced building envelope 

products can be cost effective. Another goal of the work was determining the cost levels at which 

PCMs can be cost competitive with conventional building thermal insulations. The study team 

considered two basic PCM applications in this analysis: (1) dispersed PCMs, and (2) simple 

building systems using concentrated PCMs. A third group of advanced PCM applications uses 

different forms of PCM containers or PCM-enhanced boards in conjunction with thermal breaks, 

reflective insulations, or ventilation channels. Most current experiments show that the thermal 

performance of advanced integrated PCM technologies can be significantly higher than the 

simpler dispersed PCM applications. Because these systems are complex, though, they are 

difficult to analyze using existing whole-building energy simulation tools. As a result, field test 

results are particularly valuable for energy performance and cost analyses before sufficient 

computer tools are developed and validated for these technologies.

Dispersed PCM systems are less complex, easier to analyze, and more forgiving from the 

perspective of potential errors in numerical analysis. Usually, a wide selection of PCMs with 

slightly different PCM functional temperatures can be used for the same climatic conditions and 

for the same location within the building envelope. At the same time, concentrated PCM 

applications require more precise selection of the PCM’s functional temperature range, location, 

and heat storage density. 

In addition to the limited theoretical analysis, this report summarizes the results of experimental 

and theoretical analyses previously performed in North America. These results are subsequently 

used as performance benchmarks for different PCM configurations that were tested in the United 

States for building applications. This work was not intended to optimize the configurations of 

PCMs. Theoretical parametric analysis was used only for the dispersed PCM applications. 

Thermal and building energy simulations are used here for PCM performance comparisons as a 

function of different insulation configurations and thermal conditions. 

To reiterate, a wide variety of PCMs with different temperature profiles, hysteresis, and heat 

storage capacities are available today for building envelope applications. Earlier research 

demonstrated that to accurately analyze the thermal performance of specific PCMs, computer 

models need to use detailed enthalpy/temperature profiles developed during either very slow 

(heating rate about 0.2°F or 0.1°C/minute) differential scanning calorimetry (DSC) (Günther et 

al. 2009; Mehling and Cabeza 2008), or other dynamic testing methods using step function 

procedures (Kośny et al. 2009). Because dynamic testing was not an objective of this project and 

to simplify analysis and minimize the number of necessary simulations, “ideal” PCM thermal 

characteristics with very small hysteresis were used for the parametric thermal simulations. A 

series of these simulations helped to estimate the performance limits for two of the most

common thicknesses representing the wall and attic PCM-enhanced insulation applications and 

for different intensities of exterior thermal excitations. Earlier experiments demonstrated that 

selecting a PCM with a proper functional temperature range is critical for the thermal 

performance of PCM-enhanced building envelope systems (Dincer and Rosen 2011; Kośny

2008). Therefore, in this work, the study team also analyzed the effect of selecting a proper PCM 
3

melting point against the internal space temperature. Thermal performance limits developed 

during this parametric analysis were later used in the whole-building energy consumption 

analysis, which facilitated an estimation of the potential cooling energy savings for each of the 

selected climates.

In this work, only one concentrated PCM system was used for energy and cost performance 

analyses. This system— PCM-enhanced gypsum board—is one of the earliest and the most 

popular PCM applications. In the United States, this application has been tested for at least 40 

years. In cases with this PCM system, theoretical thermal analysis was not conducted because of

a very strong performance dependence on individual properties of PCMs (microencapsulation, 

shape stabilization, impregnation, and heat storage density); PCM loads; internal space 

temperature profiles; and locations, among others. A large number of similar concentrated PCMbuilding products are currently available as well. The study team believes that only the computer 

models developed for these specific systems and validated with the experimental data should be 

used to analyze the performance of each of these individual systems. Fortunately, a substantial 

amount of theoretical and experimental research has been carried out on these technologies 

during the past several decades. In this report, then, the basic performance levels of PCMenhanced gypsum board applications are assessed using either the available experimental data or 

the predictions generated by the validated computer models.

As mentioned before, the economic analysis presented in this report is almost exclusively for 

dispersed PCM systems with fiber insulations and PCM-enhanced gypsum boards. For each of 

the PCM applications analyzed and for five southern U.S. climates, the study team estimated the 

potential cooling energy savings. The cost of the saved energy was estimated based on the unit 

electricity costs in each of the selected locations. Four typical PCM enthalpies used by the 

industry—52 Btu/lb (120 kJ/kg), 65 Btu/lb (150 kJ/kg), 82 Btu/lb (190 kJ/kg), and 95 Btu/lb 

(220 kJ/kg)—were assumed in the cost analysis. The amount of PCM was normalized against the 

heat storage capacity of the basic wall and roof systems using 52 Btu/lb (120 kJ/kg) as a 

baseline. Next, the cost of the PCM was analyzed for the PCM price range between $1.50/lb and 

$7.50/lb. Subsequently, a payback period was computed for each PCM-enhanced envelope

configuration that the study team considered.

The final part of this report is the cost performance analysis of conventional insulation 

applications. Similar energy savings as in cases with PCM applications were used as targets for 

the comparisons. Whole-building energy analyses were performed for different levels of wall 

and attic insulation. Economic effectiveness of conventional attic insulation was estimated based 

on 2011 RSMeans national cost data ( http://www.rsmeans.com/chgnotice/index.asp). Next, 

payback periods were computed for all considered climates and compared with similar 

applications containing PCM.

1.2 Overview of U.S. Performance Data for Concentrated Phase Change Material

Building Envelope Systems

Different technologies utilizing phase transition were investigated for energy performance 

improvement of building envelopes. They included concentrated PCM applications in building 

board products in which PCMs were integrated with thermal insulations or stored in arrays of 

containers. Experimental results were reported for both laboratory-scale and field-scale full-size 

building elements. Some PCM-enhanced building materials, like PCM-enhanced gypsum boards, 
4

PCM-impregnated concretes, or PCM-enhanced fiber insulations have already found limited 

applications in countries outside the United States. To be fully effective, however, concentrated 

PCM systems need to be well engineered, taking into account the amount of PCM, its optimum 

functional temperature, and its location.

Many potential PCMs have been tested for building applications, including inorganic salt 

hydrates, organic fatty acids, eutectic mixtures, fatty alcohols, neopentyl glycol, and paraffinic 

hydrocarbons. There were several moderately successful attempts in the 1970s and 1980s to use 

different types of organic and inorganic PCMs to reduce peak loads and heating and cooling 

energy consumption (Kissock et al. 1998; Tomlinson et al. 1992; Salyer and Sircar 1989; 

Balcomb et al. 1982). Historically, performance investigations focused on impregnating 

concrete, gypsum, or ceramic masonry with salt hydrates or paraffinic hydrocarbons. Most of 

these studies found that PCMs improved the building energy performance by shifting the peak 

demands, thus reducing the peak hour cooling loads. 

During early testing, paraffinic hydrocarbon PCMs generally performed well, but they 

compromised the flammability resistance of the building envelope. Salyer and Sircar (1989) 

reported that during the testing of 4 ft × 8 ft (1.22 m × 2.44 m) wallboard with PCM, no 

statistically significant loss of PCM or “pooling” occurred, even after 3 months of exposure to 

continuously cycled 100°F (37°C) air. In addition, Kissock and coworkers (1998) reported that 

wallboard containing a paraffin mixture made up mostly of n-octadecane, which had a mean 

melting temperature of 75°F (24°C) and a latent heat of fusion of 65 Btu/lb (143 kJ/kg), “was 

easy to handle and did not possess a waxy or slick surface. It scored and fractured in a manner 

similar to regular wallboard. Its unpainted color changed from white to gray. The drywall with 

PCM required no special surface preparation for painting.” 

1.3 Research Studies Focused on Concentrated Phase Change Material

Applications in Walls and Roofs

Initial concentrated PCM testing in whole-building conditions took place about 60 years ago. 

One of the first documented applications of a PCM used for passive solar heating of a home was 

in 1948 in a house designed by Maria Telkes (Dincer and Rosen 2011). This house in Dover, 

Massachusetts, contained a Glauber’s salt PCM, placed in drums housed in spaces between the 

main rooms that were ventilated with fans to move the warm air into the living space in winter. 

In summer the same system delivered cool air to the rooms. This system alone could keep the 

house warm for approximately 11 sunless days.

At the University of Kansas, Zhang and colleagues (2005) developed a thermally enhanced R-11 

frame wall that integrated a paraffinic PCM via macroencapsulating. Results from the field 

testing showed that the PCM wall reduced wall peak heat fluxes by as much as 38%. For walls 

that faced in different directions, over a period of several days, the average wall peak heat flux 

reduction was approximately 15% for a 10% concentration of PCM. When a 20% PCM 

concentration was used, the flux reduction was approximately 9%. The average space-cooling 

load was reduced by approximately 8.6% when 10% PCM was applied and by 10.8% when 20% 

PCM was used.

In 2006, Kissock and Limas of the University of Dayton investigated paraffinic PCM that can be 

added to the building envelope components, such as the walls or roofs, to reduce the peak diurnal 
5

cooling and heating loads transmitted through the envelope (Kissock and Limas 2006). This 

work was a combined numerical-experimental study to quantify the effectiveness of PCM in 

reducing thermal loads through the building envelope components and to develop a design 

strategy for the placement of PCM within the massive walls. The PCM studied was paraffin 

octadecane with an average melting temperature of 78.1°F (25.6°C). For the climate of Dayton, 

Ohio, thermal loads through the PCM-enhanced wood frame wall were simulated using an 

explicit finite-difference procedure with the indoor air temperature held constant. Compared to 

the conventional wall, cooling load savings were close to 16%. The simulation technique has 

been validated against the experimental work.

During the Greenbuild 2009 conference, National Gypsum introduced its ThermalCORE gypsum 

panels, which contain microencapsulated PCM and can store approximately 22 Btu of thermal 

energy per square foot (250 kJ/m2

).

1 Dynamic testing was performed on 1⁄2-in. thick samples of 

the PCM-enhanced gypsum board using an ASTM C-518 heat flow meter apparatus (ASTM 

International 2006a). PCM with a melting point close to 79°F (26°C) was used in these 

experiments. Preliminary thermal performance evaluation that incorporated 300-minute 

temperature ramps showed about a 13.5% reduction in cooling load.

Murugananthama and coworkers (2010) performed a series of field test measurements on two 

test huts in Arizona. One of the test attics contained conventional R-30 fiberglass insulation. The 

other one had arrays of plastic containers with a biobased PCM installed within all building 

envelope components. The structures had enclosed attic spaces with R-30 fiberglass batt between 

61-cm (24-in.) on. center. ceiling framing. Half-inch oriented strand board (OSB) roof sheathing 

was covered with 15 lb roofing felt and standard three tab fiberglass desert tan shingles. Walls 

were constructed with 2 × 4 studs 16-in. o.c. with R-13 fiberglass insulation, T-111 siding, and 

1⁄2-in. finished gypsum board. Arrays of plastic containers holding a PCM with a density of 0.56 

lb/ft3 (9 kg/m3) inside were installed in all walls between the fiberglass insulation and sheetrock 

of one of the test huts. In addition, PCM with a density of 1 lb/ft3 (16 kg/m3

) was installed in 

both the ceiling and the floor. Experimental work was carried out by Arizona Public Service 

(APS) in collaboration with Phase Change Energy Solutions Inc. (PCES) with a new class of 

organic-based PCM. The experimental setup showed maximum energy savings of about 30%, a 

maximum peak load shift of ~60 minutes, and a maximum cost savings of about 30%. During the 

entire cooling season (March through October) average energy savings for the PCM test hut 

reached about 16%, ranging between 12% and 14% during the June–July time period and 

reaching 25% during the shoulder months.

In 2006, Kissock and Limas investigated paraffinic PCMs that can be added to steel roofs to 

reduce the peak diurnal cooling and heating loads (Kissock and Limas 2006). This work was a 

combined numerical-experimental study where the simulation technique was validated against 

the experimental data. The PCM studied was the paraffin octadecane, which has an average 

melting temperature of 78.1°F (25.6°C). Analyzed metal roof had two 1-in. thick layers of the 

polyisocyanurate foam. The bottom layer of the foam was enhanced with the paraffinic PCM. 

For the climate of Dayton, Ohio, thermal loads through the PCM-enhanced polyisocyanurate 

board were simulated using an explicit finite-difference procedure with the indoor air 

 1 See http://www.thermalcore.info/product-info.htm for more information.
6

temperature held constant. When compared to the conventional roof (no PCM), cooling load 

savings were close to 14%. 

A prototype residential roof with a cool-roof surface, natural subventing, and PCM heat sink was 

designed and field tested (Miller and Kośny 2008; Kośny et al. 2007). A multilayer configuration 

of PCM-enhanced polyurethane foams, PCM-impregnated fabrics, and highly reflective 

aluminum foil were used. Loading of PCM was about 0.08 lb/ft2 (0.39 kg/m2) of the surface area. 

Two types of PCMs were used. Their melting temperatures were around 78° and 90°F (26° and 

32°C). The total storage capacity of the PCM heat sink was about 4.8 Btu/ ft2 (54 kJ/m2

) of the 

roof area. The results show that for the metal roof assembly using cool-roof pigments, reflective 

insulation, and subventing air channels, the summertime peak heat flow crossing the roof deck 

was reduced by about 70% compared with the heat flow penetrating the conventional shingle 

roof. Installation of the PCM heat sink generated an additional 20% reduction in the peak-hour 

heat flow, bringing the total reduction to 90%. A similar configuration of a roof containing metal 

roof panels with photovoltaic (PV) laminates and PCM heat sink was field tested during 2009

and 2010 (Kośny et al. 2012) in eastern Tennessee. Under those climatic conditions, PCMassociated cooling energy savings were found to be about 25% compared to the conventional 

shingle roof. 

The capability of PCMs to reduce the peak loads is relatively well documented. For example, 

Zhang and coworkers (2005) found peak cooling load reductions of 35% to 40% in side-by-side 

testing of conditioned small houses with and without paraffinic PCM inside the walls. Similarly, 

Kissock and colleagues (1998) measured peak temperature reductions of up to 18°F (10°C) in 

side-by-side testing of unconditioned experimental houses with and without paraffinic PCM wall 

board. Kośny and coinvestigators (2006) reported that PCM-enhanced foam insulation can 

reduce wall-generated peak-hour cooling loads by about 40%. Miller and Kośny (2008) reported 

over 90% of cooling peak-hour load reductions for a prototype metal roof using a cool-roof 

surface, natural subventing, and PCM heat sink installed over the roof deck.

RADCOOL, a thermal building simulation program based on the finite difference approach, was 

used by Lawrence Berkeley National Laboratory (LBNL; Feustel and Steti 1997; Feustel 1995)

to numerically evaluate the latent storage performance of treated wallboard. Simulation results 

for a living room with high internal loads and weather data in Sunnyvale, California, showed 

significant reduction of room air temperature when heat was stored in PCM-treated wallboards. 

In the case of the prototype International Energy Agency (IEA) building located in California 

climate zone 4, it was estimated that PCM wallboard would reduce the peak cooling load by 

28%.

Table 1 summarizes experimental thermal performance results from different studies presented 

above.
7

Table 1. Summary of U.S. Test Results for Concentrated PCM Applications

Reference PCM Location

PCM 

Enthalpy,

Btu/lb (kJ/kg )

PCM Loading,

Btu/ft2

(lb/ft2; 

percentage

PCM load, if 

available)

Approximate

Cooling Load 

Savings

(%) and 

city/application

Zhang et al. (2005) Wall core,

containers

52

(123.7)

~10

(0.2; 10%)

9

Lawrence, 

Kansas

Zhang et al. (2005) Wall core, pipes 52

(123.7)

~21

(0.4; 20%)

11

Lawrence, 

Kansas

Kissock and Limas

(2006)

Wall, gypsum 

board

65

(143)

~32

(0.5; 30%

16

Dayton, Ohio

Willson (2009) Wall, gypsum 

board

50

(110) 22 ~0.4

13.5

Dynamic Heat 

Flow Meter 

Aapparatus

testing

Murugananthama 

et al. (2010)

Wall, ceiling, 

floor, PCM 

containers

81

(178)

Walls; 45

~0.56

16

Whole building, 

Tempe, Arizona

Kissock (2006)

Metal roof, 

polyisocyanurate 

board

65

(143)

30

0.5

14

Dayton, Ohio

Kośny et al. (2012) Roof deck, PCM 

containers

81

(178)

27

~0.3

25

PCM 

participation,

Oak Ridge, 

Tennessee
8

2 Phase Change Material Price Challenges

2.1 Phase Change Material Cost Components

PCM prices are driven by market demand and supply relationships. Today’s U.S. market for 

PCMs is not yet fully developed, resulting in limited demand that is largely responsible for their 

relatively higher prices. The market potential for PCMs in wide-ranging applications including 

building energy improvements, however, is significant. Because manufacturers base their prices 

on future market expectations, prices are likely to drop in the future. The current energy 

performance studies that the U.S. research community is conducting on PCMs are expected to

play a crucial role in shaping their prospects for building applications. Encouraging field energy 

performance data developed during the last decade by different laboratories and universities will 

help fuel market demand for PCMs, most likely enabling reductions in the cost of these products.

PCM product cost is primarily governed by the cost of the raw PCM material and the cost of 

encapsulation. Encapsulation, or enclosing the material with an inert coating, is required to 

prevent the external environment from contaminating the PCM. At the same time, encapsulation 

allows for easy handling of the PCM for most building-related applications. Two main 

approaches are used to encapsulate PCMs: (1) macroencapsulation or packaging, where PCMs 

are encapsulated in large pouches, tubes, rectangular panels, or spherical capsules; and (2) 

microencapsulation, where microscopic amounts of PCMs are coated with a protective shell 

material. Microencapsulation provides improved heat transfer between the PCM and its

surroundings because of increased surface area but usually adds cost because it involves several 

chemical synthesis steps. The final PCM product cost varies greatly depending on the approach 

adopted to encapsulate the PCM.

2.2 Material Cost

PCMs considered for building applications rely on a solid-liquid transition and can be classified 

into the two categories: organic PCMs and inorganic PCMs. 

2.2.1 Organic Phase Change Materials

Organic PCMs are most often composed of organic materials such as paraffins, fatty acids, and 

sugar alcohols. For building applications, paraffinic PCMs are the most commonly used for

several reasons. First, paraffinic PCMs are straight chain n-alkane hydrocarbon compounds such 

as n-Heptadecane and n-Eicosane. Their melting temperature and phase change enthalpy increase 

with the length of the carbon chain. When the number of carbon atoms in the paraffin molecule 

is between 13 and 28, the melting temperature falls within a range of approximately 23° to 140°F

(–5° to 60°C) (Mehling and Cabeza 2008), a temperature range that covers building applications 

in most climates around the world. In addition, paraffinic PCMs are chemically inert, nontoxic, 

reliable, and biocompatible. They also show a negligible subcooling effect (Boh and Sumiga

2008). Fatty acids are represented by the chemical formula CH3(CH2)2nCOOH (e.g., capric acid, 

lauric acid, and palmitic acid). Fatty acids have storage densities very similar to paraffins, and 

like paraffins their melting temperatures increase with the length of the molecule. Although 

chemically stable upon cycling, they tend to react with the environment because they are acidic 

by nature.
9

Sugar alcohols are a hydrogenated form of a carbohydrate such as D-sorbitol or xylitol, among 

others. They generally have higher latent heat and density than paraffins and fatty acids. Because

they melt at temperatures between 194° to 392°F (90° and 200°C), though, they are unsuitable 

for building applications.

2.2.2 Inorganic Phase Change Materials 

Inorganic PCMs cover a wide range of temperatures. Although inorganic PCMs have similar 

latent heat per unit mass as organic PCMs, their latent heat per unit volume is generally higher 

because of their higher density. Salt hydrates are one type of inorganic salts containing one or 

multiple water molecules such that the resulting crystalline solid has a chemical formula of 

AB.nH2O. Some of the examples are CaCl2.6H2O, LiNO3.3H2O, and KF.3H2O. Salt hydrates 

are nontoxic, nonflammable and less corrosive, with higher thermal conductivity than organic 

PCMs. Salt hydrates have melting temperatures in the range of 41° to 266°F (5° to 130°C), a 

suitable range for building applications.

2.2.3 Material Cost of Phase Change Materials 

The material cost depends significantly on the classification of the PCM (i.e., organic, inorganic, 

or biomaterial). Commercial paraffinic PCMs are byproducts from the oil refineries; therefore, 

they are available in abundant supply at a relatively cheaper price. The price of paraffins 

increases with the purity. Pure paraffin wax (>99%) is more expensive than technical grade pwax (90%−95%) (Mulligan and Gould 2002). The current cost of paraffin wax is $0.85−$0.91/lb 

($1.88−$2.00/kg).

2 As a reference, pure laboratory-grade eicosane is $24.50/lb ($53.90/kg); the 

technical grade is $3.20/lb ($7.04/kg). The estimated cost of microencapsulation for a similar 

paraffin octacosane is ~45%−65% of the total cost of the paraffin PCM.

3 Another low-cost 

paraffin alternative available is Baker Petrolite’s POLYWAX, which costs $2.00/gal ($0.53/L). 

The cost of fatty acid PCMs such as stearic acid, palmitic acid, and oleic acid are $0.65−$0.71/lb

($1.43−$1.56/kg); $0.73−$0.78/lb ($1.61−$1.72/kg); and $0.76−$0.80/lb ($1.67−$1.76/kg), 

respectively. Biodiesel crude glycerine (biocrude) is $0.10−$0.13/lb ($0.22−$0.29/kg) CIF China 

Mainland.4

Entropy Solutions Inc. quotes $0.75−$2.50/lb ($1.65−$5.50/kg) for its commercial volume 

organic PCM products. Chemical components for Entropy’s products are derived from 

agricultural sources and their melting temperature ranges between -40° to 302°F (–40°C and 

150°C). PCES sells biobased PCMs with melting temperatures of 77°, 81°, and 84°F (25°, 27°,

and 29°C). The cost of the PCES products varies with M-values. For example, M-27, M-51, M91, and M-182 products have wholesale prices of $1.94/ft2

, $2.83/ft2, $4.59/ft2, and $8.79/ft2

($20.88/m

2

, $30.46/m

2

, $49.40/m

2

, and $94.61/m

2

), respectively. The prices for M-27, M-51, M91, and M-182 products are $6.47/lb, $5.05/lb, $4.59/lb, and $4.40/lb ($14.26/kg, $11.13/kg, 

$10.12/kg, and $9.70/kg), respectively.

5

 2 See www.icispricing.com/ for more information. 3 Private communication with Tim Riazzi, Microtek Labs 4CIF = cost + domestic fee + overseas freight + overseas insurance + net profit

5 Private communication with Peter Horwath - PCES
10

In 2010, Syntroleum Corporation received a U.S. Department of Energy (DOE) American 

Recovery and Reinvestment Act (ARRA) award (DE-EE0003924) for development of low-cost, 

biobased PCMs for building envelope applications.

6 Syntroleum’s plant was built to compete 

with a commodity product—diesel fuel—it can manufacture the octadecane-rich paraffin 

intermediate at the price of biodiesel (which sells in the $4.50−$5.50/gal ($1.19−$1.45/L) or 

$0.69−$0.85/lb ($1.52−$1.87/kg) range. The cost of converting the paraffin into form-stable 

composites is not yet well defined. But because Syntroleum’s plant uses a low priced commodity 

plastic (high-density polyethylene; HDPE) in a continuous process using “workhorse” polymers 

industry equipment (extruders/pelletizers), the costs are expected to be significantly lower than 

those for microencapsulation. Prices for these new PCM pellets that have 60% to 70% paraffin in 

HDPE are expected to range between $3.00/lb and $4.00/lb ($6.60/kg and $8.80/kg) with a target 

enthalpy of approximately 43 Btu/lb (100 kJ/kg). 

The average cost of inorganic PCM calcium chloride is $0.059−$0.091/lb ($0.13−$0.20/kg); the 

cost of a small quantity of 1 lb (1 kg) is $0.35 ($0.77).

7 Calcium chloride is a salt of calcium and 

chloride, and is a colorless, odorless, and nontoxic solution. PCMEnergy India produces salt 

hydrate PCMs with a melting temperature range of 64° to 118°F (18°−48°C). The PCM is 

prepared in house and contains no impurities. The cost of the raw material used is 

$0.90−$1.80/lb ($1.98−$3.96/kg). The PCM products are in the packaged form instead of

microencapsulated. The price of the final product is $1.40−$2.25/lb ($3.08−$4.95/kg) with the 

packaging step contributing ~20%−35% of the total cost. 

Alderman Research produces inorganic PCMs composed of CaCl2.6H2O as the main compound. 

Viscosity modifiers, nucleating agents, and other stabilizers make up less than 20% of the total 

weight. The PCMs are prepared in house and the melting temperature is kept around 174° to 

176°F (79°−80°F). The product cost breakdown includes $0.21/lb ($0.46/kg) for formula and 

$0.18/ft2 ($1.94/m2

) for packaging the film (raw materials only; no labor, overhead, or profit). 

An ordinary food-packaging machine, similar to the ones that package condiments for national 

fast food chains, is used to package the PCM. The packaging procedure involves cutting the 

individual packets at a desired length rather than slitting them. The final cost of the product is 

$1.00−$2.00/ft2 ($10.76−$21.52/m2

) with the packaging process accounting for 9%−18% of the 

total cost. This product is available in one-pallet size quantities.

2.3 Alternatives to Paraffin

Cost and volumetric latent heat are two key parameters that will decide the market adoption of 

PCMs as a building energy efficiency material. Today, paraffins are the most widely used PCMs 

in building applications because they are nontoxic, abundant in supply, and easy to 

microencapsulate. Other attractive features include small subcooling, chemical inertness, and 

good recyclability. Although the technology is ready for the incorporation of paraffinic PCMs in 

the building materials, the high cost of paraffin chemicals along with low phase change 

enthalpies (4,027−5,369 Btu/ft3

;150−200 MJ/m3) and high fire loads are proving to be major 

 6 See 

http://www.recovery.gov/Transparency/RecipientReportedData/pages/RecipientProjectSummary508.aspx?AwardId

Sur=117469 for more information. 7 See http://www.kaycircle.com/What-Is-the-Average-Cost-of-Calcium-Chloride-per-ton-lb-Average-CalciumChloride-Price for more information.
11

barriers to their widespread acceptance. Because paraffins are derived from crude oil, their prices 

are sensitive to the season and to geopolitical scenarios. In fact, crude oil prices have been on the 

rise in recent years. All these factors underline the need to shift the focus away from paraffinic 

PCM to another class of PCM. Salt hydrates and biobased PCMs are two alternative materials 

with great potential to substitute for paraffin in the future, as well as to compete with the existing 

energy efficient building materials and technologies.

2.3.1 Salt Hydrates

Inorganic salt hydrates with low chemical cost, higher enthalpies (6,711−9,397 Btu/ft3; 250−350

MJ/m3), better thermal conductivity (0.29 Btu/h/ft/°F; 0.5 W/m/K), and suitable melting 

temperatures of 41°–248°F (5°−120°C) show great promise to become a primary PCM for 

building applications. In fact, inorganic salts such as Glauber’s salt were the first PCM ever to be 

applied in building applications (Telkes 1952). So far inorganic PCMs have found very limited 

application in buildings because of their undesirable properties. They have poor nucleating 

properties, meaning that their subcooling effect, corrosive nature, incongruent melting, and phase 

segregation during transition are problematic. With the advances made over the last few decades 

in the field of salt hydrates, however, it is now possible to control these adverse properties to a 

large extent. 

2.3.1.1 Approaches to Improve Phase Change Properties

Garg and colleagues (1985) showed that adding a nucleating agent with a crystal structure 

similar to the energy storage material reduces the amount of subcooling. And because most salt 

hydrates suffer from a low rate of crystallization, uniformly distributing the nucleating seed 

agent throughout the phase change media helps increase the rate of crystallization. 

Inorganic salts experience incongruent melting. This happens when the solubility of the salt is 

not high enough to dissolve all the anhydrous salt in the water of crystallization that is released. 

This effect reduces the PCM product’s efficiency because undissolved salt settles down at the 

bottom of the container and does not contribute to the heat storage process. The extra water 

principle is used to avoid incongruent melting. The method involves using extra water to 

dissolve the entire anhydrous salt during melting. This thickens the material to gel form as 

suggested by Telkes (1952).

Thickening materials are used to minimize the phase separation in solid and liquid phases and 

also to prevent nucleating agents from settling down because of their density. Super-absorbent 

polymer (SAP) synthesized from an acrylic acid copolymer has been used as an effective 

thickener to prevent phase separation of the high-hydrate inorganic salts (Na2SO4.10H2O

Na2HPO4.12H2O, and Na2CO3.10H2O) (Ryu et al.1992). SAP included in the amount of 3–5 wt 

% was found to be an effective thickener for most of these salt hydrates. For the low hydrate 

inorganic salts (CH3COONa.3H2O and Na2S2Oa.5H2O), adding small amounts of 2−4 wt % of 

carboxymethyl cellulose (CMC) stabilized the salt hydrate. Three different powders of carbon 

(1.5−6.7 μm), copper (1.5−2.5 μm) and titanium oxide (2−200 μm) are found to reduce the 

subcooling of thickened Na2HPO4.12H2O. Also, the subcooling of thickened CHaCOONa.3H2O

is reduced from 36°F (20°C) to 3°–5°F (2°−3°C) by adding 2 wt % potassium sulfate.

Thixotropic thickening agents are another low-cost option.
12

To improve thermal/mechanical properties, foreign materials such as graphite fiber or metal can

be embedded into the PCM to form a composite. Alternatively, PCM can be incorporated into 

the matrix of other materials such as graphite, metallic, or polymer matrix. Matrix network holds 

the PCM inside the pores even when it has melted. Li and coworkers (2009) developed novel 

microencapsulation method where organic PCMs were coated with HDPE/wood floor 

compound. They introduced micromist graphite during the microencapsulation of organic PCMs

to increase thermal conductivity. The shell and matrix prevented the leakage when PCM was 

melted, forming a shape-stabilized PCM. Thermal conductivity was enhanced by 17.7% by 

adding 8% weight of graphite. The inclusion of graphite was shown to have no adverse effect on 

the mechanical and thermal stability of the composite PCM.

2.3.1.2 Glauber’s Salt

It is worthwhile to describe here the significant technological progress that has been made to 

improve the adverse properties of Glauber’s salt, because it is one of the most inexpensive heat 

storage materials that can be used in building applications. It is composed of 44% Na2SO4 and 

56% H2O by weight and has a high latent heat of 254 kJ/kg (377 MJ/m3). Its melting temperature 

is about 90°F (32°C), which is well-suited to building applications. Glauber’s salt shows a very 

large subcooling of ~27°F (15°C). Borax has been successfully used as a nucleating agent to 

reduce subcooling of this salt to 5°–6°F (3− 4°C). Adding borax to the salt improves thermal 

cycling of the mixture as well. The extra water principle has been employed to prevent 

incongruent melting and to improve thermal cycling (Farid et al. 2004). To avoid phase 

segregation, thickening agents, such as bentonite clay, have been used. Bentonite-enhanced salt 

has an additional advantage in that its application reduces the heat transfer to the salt that results 

from the lower thermal conductivity of the mixture, a desirable feature for peak-hour load 

shifting in building applications. 

2.3.1.3 Calcium Chloride Hydrate

Calcium chloride hydrate (CaCl2.6H2O) is another popular salt hydrate that has received a lot of 

attention in the scientific community because of its high latent heat and its ability to melt 

congruently. SrCl2, BaCO3, SrCO3, and BaF2 have been proposed as nucleating agents to reduce 

subcooling and incongruent melting of CaCl2.6H2O. These were chosen for testing based on 

either their similar crystal structure or using intuition. For example, SrCl2 and CaCl2.6H2O both 

have hexagonal structures. SrCl2 acts as a site for crystals to grow, allowing CaCl2.6H2O to 

solidify without as much subcooling. BaCO3 was also found to be an effective nucleating agent, 

although it is currently unclear why. In certain quantities, both of these additives can eliminate 

subcooling (Lane 1992). These nucleating agents also help prevent phase segregation of highhydrate CaCl2.6H2O into low-hydrate CaCl2.4H2O. A

2.3.1.4 Microencapsulation of Salt Hydrates

Heterogeneous polymerization techniques such as emulsion polymerization, dispersion 

polymerization, microemulsion polymerization, and miniemulsion polymerization have typically 

been used to encapsulate inorganic materials (Jing et al. 2011). The resulting encapsulated 

product suffers from low solid content inside the capsule and poor encapsulation yield. 

Microencapsulation of salt hydrates becomes even more challenging because salt hydrates are 

hydrophilic in nature and contain a well-defined water fraction. To be useful in building 

applications, shell material needs to act as a water/vapor barrier and to be hydrophobic. Both 

characteristics prevent the salt hydrate from evaporating. Organic polymers are typically used as 
13

shell material in the encapsulation process; however, they are chemically incompatible with salt 

hydrates. 

Recently, efforts to microencapsulate salt hydrates have been successful.

8,9 Fraunhofer ISC has 

developed a method in which a salt hydrate melt is encapsulated by an inorganic–organic hybrid 

polymer known as ORMOCER. The process involves injecting salt hydrate melt drops into the 

ORMOCER solution that solidifies locally as it comes in contact with the surface of the drop, 

forming a hard encapsulating layer around the salt hydrate drop. The encapsulated drops are 

removed from the coating solution via mechanical means and washed thoroughly, then allowed

to dry in air under ambient condition. Salt hydrate drops subsequently crystallize as they cool 

down. Capsules produced in this way have diameters ranging from a few micrometers to a few 

millimeters. Although the final product has water permeability and stability issues, this is

nonetheless an encouraging step.

Hessbrugge and Vaidya (1997) developed a novel technique for encapsulating of water-soluble 

salts. The method employs a simple process where additives such as emulsifiers and acid 

acceptors that are needed to stabilize the aqueous–organic interface and to remove the excess 

acid formed by hydrolysis are not required. This results in a cheaper microencapsulation process 

because the post-treatment required to remove additives and their byproducts is no longer 

required. In addition, there is less likelihood of contamination of encapsulated product because

trace amounts of the reaction components and their byproducts are absent.

Brandt and colleagues (2006) encapsulated powdered Na2CO3 hydrate particles with an 

inorganic SiOx layer via a sol-gel process in a TMOS solution (Rößner 1999).

2.3.2 Biobased Phase Change Materials

Biobased PCMs, which are obtained from animal fat such as beef tallow and lard and oils from 

plants such as palms, coconuts, and soybeans, are a renewable and green alternative to paraffinic 

PCMs. They are nontoxic and can be recycled through thousands of cycles without experiencing 

any material degradation. Because they are hydrogenated hydrocarbons with a saturated 

electronic configuration, they are chemically stable and can last for decades. In addition, fat- and 

oil-based PCMs offer similar or improved performance, a greater degree of fire resistance, and 

reduced costs.

2.3.2.1 Fatty Acids

Among all PCMs including biobased PCMs, fatty acids have superior advantages, such as 

congruent melting and cooling, high latent heat of fusion, low costs, fire resistance, nontoxicity, 

very small subcooling and volume change, and good chemical and thermal stability after a large 

number of thermal cycles (Sari et al. 2009; Sari 2003).

10,11 Another attractive feature is that the 

melting temperatures can be adjusted to the match the requirement by selecting a right 

combination of eutectic binary mixtures of fatty acids. The eutectic mixtures of fatty acids as 

 8 See www.messib.eu/about_project/messib_innovative_elements/phase_change_materials/ 

microencapsulation_of_salt_hydrates.php for more information. 9 See www.freepatentsonline.com/y2011/0017944.html for more information. 10 See www.renewablealternatives.com/pcm.htm for more information. 11 See www.reeis.usda.gov/web/crisprojectpages/197095.html for more information.
14

PCMs also retain their good thermal stabilities as a single fatty acid after repeated thermal 

cycling (Sari 2005; Sari et al. 2004).

In fact, these biobased PCMs have the potential to replace petroleum-based PCMs and help 

reduce carbon dioxide (CO2) greenhouse gas emissions. Because major properties of fat and oil 

derivatives are similar to those of paraffin, fat and oil derivatives can be used for similar 

applications. For example, wax products such as candles, pencils, and coatings that have been 

largely dominated by paraffins are now being manufactured using biobased and renewable

feedstocks such as hydrogenated soybean oil. 

2.3.2.2 Coconut Oil

Coconut is a diet staple for millions of people living in tropical regions of the world. Coconut oil 

(oil extracted from coconut fats) is a type of saturated fatty acid containing about 44%−51% of 

lauric acid (CH3(CH2)10COOH). For building applications, it is critical that fatty acids are 

encapsulated well. Otherwise, they tend to flow everywhere when experiencing phase changes. 

Microcapsules using lauric acid (LA) as the core and melamineformaldehyde (MF) resin as the 

shell have been successfully prepared as a PCM for latent heat thermal storage by in situ 

polymerization (Bao et al. 2011; Su et al. 2006). Özonur and coworkers (2006) successfully 

prepared microcapsules of natural coco fatty acid mixture as core and gelatin-gum Arabic as 

shell material by a complex coacervation technique. Chai and colleagues (2007)

microencapsulated stearic acid and palmitic acid with SiO2 using a one-step, solid-state chemical 

reaction at low temperature.

2.3.3 Shape-Stabilized Phase Change Material

Recently, a novel PCM known as shape-stabilized (ss) PCM has been developed that can retain 

the shape of the solid structure during phase transition. ss-PCM is a composite of PCM with 

another material, such as an ss-paraffin composite consisting of paraffin incorporated on a 

microscopic level into a porous supporting structure such as HDPE. ss-PCMs offer several 

benefits including high apparent heat capacity, suitable thermal conductivity, and no need for a 

container because ss-PCMs do not tend to flow out of the porous structure during melting. Inaba 

and Hu (1997) observed no leakage of paraffin through an HDPE network for paraffin loading 

levels as high as 75% by weight. Yinping and coinvestigators (2006) prepared ss-paraffin with 

80% by weight loading of paraffin and found that no containment was required (i.e., samples can 

be cut into pieces without any drainage). Keep in mind that even with all the benefits mentioned 

here, HDPE adds to the cost of the final PCM product.

2.4 Expected Future Cost Reductions

The price of the raw material and the encapsulation process determine the cost of PCM products. 

The cost to macroencapsulate a PCM is ~20% of the total cost. The microencapsulation process 

is even more expensive at ~50% of the final product cost. Currently, paraffins are the most 

popular choice for PCMs because they offer several attractive features (i.e., they are chemically 

inert, nontoxic, and easy to encapsulate). 

For building applications, latent enthalpy per unit volume and flammability are the two main 

performance criteria used to decide on the type of PCM. Paraffins do not fare well on either of 

these criteria. Because of their higher latent heat per unit volume and nonflammability, salt 

hydrates have the potential not only to replace paraffins as a PCM of choice for building 
15

applications, but also to outperform other competing technologies such as thermal insulations. 

There are, however, some technological challenges that need to be addressed before salt hydrates 

can become a commonplace PCM in building applications: the subcooling effect and the 

difficulty in microencapsulating the salt hydrates because of their water content (although there 

have been recent encouraging steps in this area as mentioned previously). Recently, prices of salt 

hydrates have fallen, but the real solution lies in developing low-cost, easy-to-manufacture, and 

chemically, physically, and thermally stable salt hydrate PCMs that will work for building 

applications. 

Biobased PCMs are another renewable, cheap, and ecofriendly option to paraffins. With more 

advanced knowledge to control the transition properties and improvements in the process 

technology, it is possible that biobased PCMs will become commonplace in the near future.
16

3 Whole-Building Energy Simulations—Theoretical Performance 

Limits for Building Envelopes Using Conventional Thermal 

Insulations

Conventional thermal insulations (fiber insulations and plastic foams) are the most popular and 

widely accepted technical means to improve the thermal performance of building envelopes. It is 

also well known, however, that the thermal effectiveness of the conventional insulations is not 

always the same. In fact, a law of diminishing return applies to the energy savings with the level 

of thermal insulation for new and retrofitted projects (Kośny et al. 2010; Huang et al. 1999). 

Furthermore, for building retrofits, a diminishing return on energy savings is obtained with 

increased levels of pre-existing thermal insulation

In this part of the project, the team used a whole-building energy performance analysis to 

estimate energy consumption levels for a single-story ranch house in five southern U.S. climates. 

Figure 1 shows the layout of the house. In addition, a detailed thermal load distribution analysis 

was performed to estimate the cooling energy consumption by the attic and the walls. The study

team used DOE-2.1E, EnergyPlus and AtticSim computer software12 to simulate a single-family 

residence and to perform thermal performance modeling of the residential attic and walls used in 

parametric analysis. To find a relation between the wall R-value and the heating and cooling 

energies, a lightweight ranch-type building of about 1,540 ft2 (143 m2) floor area was simulated 

on 12 different wood-frame walls with R-values from 2.3 to 39.0 h-ft2

-°F/Btu (0.4 to 6.9 Km

2 /W). Similarly, to find a relation between the attic floor insulation R-value and the heating 

and cooling energies, five different attic insulation assemblies with R-values from 12 to 50 h-ft2-

°F/Btu (2.12 to 8.80 K-m

2 /W) were simulated. The main goal of this work was to identify 

situations in which PCM-enhanced building envelopes would become more effective in terms of 

cost and performance compared with the conventional thermal insulations.

Figure 1. Layout of the single-story ranch house used for the energy modeling

 12 http://apps1.eere.energy.gov/buildings/tools_directory/

Living Room

&

Open Kitchen Area Bedroom #3

Bedroom 

#2

Main Bedroom

Bathroom

Main Bath

Single story ranch house – floor area 130 m2 (1400 ft2) 9.5-m (26-ft)

16-m (53-ft)

Single story ranch house – floor area 143 m2 (1540 ft2) 

16.7-m (55 -ft)

8.5-m (28-ft)
17

In DOE 2.1E simulations, the Sherman-Grimsrud Infiltration Method (Sherman and Grimsrud 

1980) was used. For the analysis, the study team assumed an average total leakage area of 

0.0005, expressed as a fraction of the floor area. This can be considered an average value for a 

vintage U.S. single-zone wood-framed residential structure (Huang et al. 1999; Christian and

Kośny 1996; Huang et al. 1987). This number cannot be converted directly to average air 

changes per hour (ACH) because it is used in an equation driven by hourly wind speed and 

temperature differences between the inside and ambient,. For the 11 considered climatic 

locations, this represents an ACH range that will not fall below an annual average of 0.35 ACH. 

This annual average is an ASHRAE Standard 62−1999 requirement for outdoor ventilation of 

residential facilities (ASHRAE - 2001).

Using DOE-2.1E and EnergyPlus simulations, the study team analyzed the total space heating 

and cooling energies for 12 lightweight wood-frame walls and five attic configurations.

Regression analysis was performed to analyze the relation between the steady-state R-values (for 

walls and attic floor insulation) and the whole-house annual energies for ten U.S. climates. To 

illustrate the effectiveness of the conventional insulations in reducing the wall- and atticgenerated space conditioning loads, Figure 2 and Figure 3 show the potential annual energy 

consumption savings resulting from adding conventional insulation in R-4 intervals. For both 

cases, the results showed that, with the application of additional R-4 conventional insulation, the 

energy savings is significantly higher than for assemblies with lower R-values. As shown in 

these figures, an addition of R-16 to the low R-value wall or attic assembly is practically 

reducing effectiveness of the next R-4 insulation layer by a factor of about 10. This fact 

highlights the need to evaluate alternative energy saving options other than the conventional 

insulation for higher R-value walls and attics. PCM-enhanced building envelope components can 

be one such alternative in some climates dominated by cooling loads.

Figure 2. Annual energy savings as a function of wall R-value increase in increments of R-4 Wall-generated energy savings - GJ/year

R-4

Wall R-value change
18

Figure 3. Annual energy savings as a function of attic R-value increasing in increments of R-4

In the next step, the study team performed similar DOE-2.1E and EnergyPlus whole-building 

energy simulations on five southern U.S. climates. The same 1,540-ft2 (143-m

2

) single-story 

ranch house shown in Figure 1 was used for modeling. This time, 2 × 6 wood stud walls 

insulated with an R-19 cavity insulation and conventional pitched R-30 attic insulation were 

assumed in computer simulations. Table 2 presents a list of cities and basic climate data. 

In this analysis, the energy output data generated by these whole-building simulations were used 

to estimate the energy contributions from the walls and the attic for total whole-building cooling 

energy consumption. These contributions were computed based on comparisons of the detailed

whole-building cooling loads against the local cooling loads generated by the above-grade 

opaque walls and the attic. Table 3 shows the computed energy contributions from walls and 

attic on the total whole-building cooling energy consumption of the single-story ranch house. 

Huang and coworkers (1999) reported that for U.S. single-family houses, walls and roofs 

generate an average 20% and 12% cooling energy contributions, respectively. Considering that 

the buildings analyzed by Huang and colleagues had significant configuration differences, the 

cooling energy contributions presented in Table 3 are within the above range, being 3%–6% 

lower for the walls and about 3%–4% higher for the attic.

Analyzed climates were then selected to demonstrate a variety of energy impacts in 

representative southern U.S. locations. The number of cooling degree-days (CDD) on which the 

temperature averages 74°F (23.3°C) are four times different between Atlanta, Georgia, and 

Phoenix. Following this relationship, the whole-house cooling energy consumption in simulated 

locations was found to range between 237 and 961 kWh/year. Table 4 shows the cooling energy 

X starting attic R-value

X

R-4

GJ/year Attic-generated energy savings - GJ/year

Attic floor R-value change
19

contributions from the walls and the attic calculated for the floor area of the analyzed house. In 

the simulated single-story ranch house, the combined area of all four walls was about 1,490 ft2

(138 m2). The area of windows and doors was about 328 ft2 (30 m2).

Table 2. Five Southern U.S. Climates Used in Whole-Building Energy Modeling

Cities HDDa 65°F (18.3°C) CDD 74°F (23.3°C)

Atlanta 1,705 (3,070) 8,475 (15,255)

Bakersfieldb 1,182 (2,127) 16,641 (29,954)

Fort Worth 1,344 (2,420) 20,163 (36,294)

Miami 110 (198) 21,889 (39,401)

Phoenix 802 (1,444) 30,224 (54,404) a HDD, heating degree-days

b Bakersfield, California

Table 3. Energy Load Contributions From Walls and Attic Calculated for a 

Single-Story Ranch House for Five Southern U.S. Climates

Cities

Wall Cooling 

Loads 

Contributiona

Attic Cooling 

Loads 

Contributionb

Total 

Cooling 

Energy 

Consumption

(kWh)

WallGenerated

Cooling 

Energy 

Consumption

(kWh)

AtticGenerated

Cooling 

Energy 

Consumption

(kWh)

Atlanta 0.14 0.16 1,683 236.8 269.3

Bakersfield 0.16 0.16 2,817 437.7 456.4

Fort Worth 0.15 0.15 3,082 455.6 458.0

Miami 0.14 0.15 6,076 856.7 911.4

Phoenix 0.17 0.15 5,805 960.7 870.8 a Fraction of the total building cooling loads generated by opaque walls

b Fraction of the total building cooling loads generated by attic

Table 4. Cooling Energy Contributions From Walls and Attic Calculated for the 

Floor Area of the 1,540-ft2 (143-m2

) Single-Story Ranch House

Cities

Total Cooling Energy 

Consumption per Floor 

Area,

kWh/ft2 (kWh/m2)

Wall-Generated Cooling 

Energy Consumption 

per Floor Area,

kWh/ft2 (kWh/m2)

Attic-Generated Cooling 

Energy Consumption 

per Floor Area,

kWh/ft2 (kWh/m2)

Atlanta 1.093 (11.76) 0.154 (1.66) 0.175 (1.88)

Bakersfield 1.829 (19.69) 0.284 (3.06) 0.296 (3.19)

Fort Worth 2.001 (21.54) 0.296 (3.19) 0.297 (3.20)

Miami 3.945 (42.46) 0.556 (5.98) 0.592 (6.37)

Phoenix 3.769 (40.57) 0.624 (6.72) 0.565 (6.08)
20

3.1 Theoretical Performance Limits for Dynamic Insulations Using Dispersed 

Phase Change Material Applications

Today, manufacturers around the world are developing a wide variety of different material 

configurations containing PCMs. In PCMs, energy is absorbed or released when the material 

changes from solid to liquid. During the past several decades, different technologies involving

phase transition have been investigated to improve the energy performance of building 

envelopes. Some of these included concentrated PCM applications in which PCMs were installed 

using separate carriers. Two of the best-known applications are PCM-enhanced gypsum boards 

and arrays of plastic or aluminum foil containers containing PCMs. Another group of 

applications uses blends of microencapsulated PCMs with fiber insulations, or plastic foam 

boards containing microencapsulated PCMs. Figure 4 shows electron microscope images of the 

three most common insulation carriers for microencapsulated PCMs.

Figure 4. Scanning electron microscope (SEM) images of microencapsulated PCM mixed with (a) 

cellulose fiber insulation, (b) blown fiberglass matrix and fiberglass, and (c) polyurethane foam

This section of the report focuses exclusively on dispersed PCM applications that use a 30% by 

weight blend of the microencapsulated PCM with fiber insulation. In earlier research focused on 

PCM-enhanced cellulose and fiberglass insulations, different PCM concentrations were studied 

starting from 5% and reaching to 35%, which is close to the physical concentration limit for the 

cellulose insulation (Kośny et al. 2007). Therefore, the assumption of 30% PCM content will 

most likely yield the highest possible PCM cost in this kind of building envelope application. In 

light of the PCM study performed by Oak Ridge National Laboratory (ORNL 2012), for selected 

PCM blends, the PCM amount can be reduced by about 1/4 (from the 30% by weight level used 

in this study to 20% or 25%) without significant reductions in thermal performance. This means 

that “real” cost levels for PCM-enhanced insulations can be up to 25% lower than the predictions 

described in this section.

Remember, however, that in most building envelope applications PCMs are not always working 

in thermal conditions that allow full phase change processes. During the cooling season, the most 

common reason for the lack of phase transitions is too-high night air temperature, which keeps

PCMs melted throughout the night. Historical field test data generated during the ORNL PCMenhanced cellulose testing (Kośny et al. 2007) and the Metal Construction Association -ORNL 

metal roof experiment using a PCM heat sink (Kośny et al. 2012) demonstrated that, during the 

cooling season in eastern Tennessee’s climate, PCM cycling was enabled by weather conditions 

during about 60%–70% of the total number of days. This means that below-computed maximum 

(a) PCM mixed with cellulose (b) Fiberglass and PCM mixed (c) PCM mixed with polyurethane 

fiber insulation with blown fiberglass foam
21

thermal performance levels for specific PCM applications will need to be reduced by about 30% 

to include an impact of days not allowing phase change processes, if eastern Tennessee climatic 

conditions are taken into account. For other climates, additional field testing or detailed dynamic 

thermal simulations of a specific PCM application would be necessary.

Another important assumption for this part of the analysis is that the internal space temperature 

in the analyzed building remains constant. This means that the energy performance analysis 

presented in this report does not cover PCM application strategies that make use of variable 

internal space temperature profiles. Overnight pre-cooling of the conditioned space is a widely

known strategy of this type.

The third assumption is about a perfect selection of the PCM for the specific climatic condition 

and for the specific application. Earlier field experiments have demonstrated that with a good 

knowledge of the temperature profile at the PCM location, it is possible to select PCM thermal 

characteristics that allow the number of days during the cooling season where complete phase 

transition takes place to be maximized (Kośny et al. 2012). The best way to investigate the local 

temperature profile within a building envelope assembly containing PCMs is to conduct fullscale laboratory/field testing or transient simulations using numerical algorithms that are 

validated against the test data. 

In the past, several applications of PCM-enhanced fiber insulations have been tested in 

laboratory and field conditions (Kośny 2008; Kośny et al. 2007). In 2006 and 2007, ORNL 

performed two small-scale field tests on 2 × 6 in. (6 × 15.2 cm) wood frame walls with PCMenhanced cellulose insulation (Kośny et al. 2008). Test walls were installed in Oak Ridge, 

Tennessee, and in Charleston, South Carolina. In both cases, the PCM walls were constructed 

next to identical wood stud walls containing cellulose insulation with no PCM. In these 

experiments, wall cavities were insulated with a cellulose–PCM blend of a density about 2.6 

lb/ft3 (42 kg/m3

) containing about 22% PCM by weight. As described by Kośny (2008), the PCM 

phase transition enthalpy was about 52 Btu/lb (115 kJ/kg). 

After taking measurements during an entire summer, the cooling load reductions were found to 

average 42% at the Oak Ridge south-oriented site, with the peak-hour savings occasionally 

spiking to 80%. Results from the Charleston northwest-oriented site showed about a 5% 

reduction in the cooling load and a 30% reduction in the peak-hour cooling loads. Notable 

differences in the thermal performances recorded during these two field experiments were most

likely caused by different geographic orientations and by significantly different internal space 

temperature profiles in the two locations. In the Oak Ridge experiment, the average interior air 

temperature was almost identical to the PCM melting point, which yielded perfect conditions for 

the PCM to work. In the Charleston experiment, the internal air temperature was about 10°F

(~4°C) lower than the PCM melting point, which resulted in significantly lower overall energy 

performance.

To investigate the theoretical performance limits for the building envelope assemblies containing 

PCMs, the study team performed a series of transient simulations on several such building 

envelopes. Two thicknesses representing wall and attic applications were used in modeling: 

5.5 in. (0.14 m), representing walls and vaulted ceiling applications, and 11.8 in. (0.3 m),

representing attic floor insulations. The study team developed a numerical program for this 
22

purpose using the control volume heat balance method, explicit scheme, with temperaturedependent effective heat capacity and experimentally determined thermal conductivity of the 

PCM carrier (Kossecka and Kośny 2010). The distance between nodes within the insulation was 

0.39−0.79 in. (0.01−0.02 m), and the time step was set to 30 seconds. Table 5 lists the 

thermophysical properties of the materials used in these assemblies. For example, a 5.5-in. (0.14-

m) thick assembly will offer a total thermal resistance of Ru = 23.5 h-ft2-°F/Btu (4.14 m

2

-K/W). 

This includes surface film resistances of Rsi = 0.74 h-ft2-°F/Btu (0.13 m2-K/W) and of Rse = 0.22 

h-ft2

-°F/Btu (0.04 m2-K/W). Considering a 30% PCM content in the 5.5-in. (0.14-m) thick 

insulation layer and an insulation density of 2.1 lb/ft3 (33.6 kg/m3), the PCM load is close to 0.29 

lb/ft2 (1.4 kg/m2). Next, simulations were repeated for the assemblies containing 11.8-in. (0.3-m)

thick insulations. 

To illustrate the effect of PCM melting temperature on the energy, the study team ran computer 

simulations for two different internal air temperatures, Ti, equal to either 68°F (20°C) or 77°F 

(25°C). Meanwhile, the melting point of the PCM material was 81°F (27°C). Earlier research on 

the PCM-enhanced envelope systems demonstrated that it is beneficial to have the PCM melting 

temperature as close as possible to the internal air set-point temperature (Kośny et al. 2008; 

Tomlinson et al. 1992). Figure 5 depicts the effective heat capacity data for the PCMs used in the 

modeling. In simulations, one-dimensional heat transfer was assumed and the effect of structural 

members was neglected. A major goal of this modeling exercise was to analyze the dynamic 

responses of a building envelope assembly containing PCM to different levels of external 

thermal excitations. Note that these thermal simulations were performed with the assumption of a 

constant interior space temperature. 

As shown in Figure 6, Tes represents three diurnal surface temperature swing schedules with 

thermal peaks of 113°F (45°C) in schedule “a”; 149°F (65°C) in schedule “b”; and 185°F (85°C) 

in schedule “c.” These peaks result from solar radiation incident on the external surface during 

the day. According to the field experimental data developed by previous investigators (Biswas et 

al. 2011; Kośny et al. 2011; Murugananthama et al. 2010; Kośny 2008; Miller et al. 2007; Petrie 

et al. 2004), temperature schedule “a” with a temperature peak of 113°F (45°C) most likely 

represents a summer wall surface thermal excitation. Similarly, during the summer in southern 

U.S. locations, the attic floor insulation faces attic space temperature fluctuations falling closely

between schedules “a” and “b.” Where vaulted ceilings and sandwiched roof assemblies exist, 

the exterior boundary conditions will most likely be close to the schedule “c” temperature profile 

with temperature peaks exceeding 167°F (75°C).
23

Table 5. Thermophysical Properties Used in Numerical Modeling

Material Thickness 

(m)

Conductivity 

Btu-in/h·ft2F 

(W/m·K)

Density lb/ft3

(kg/m3

)

cp

Btu/lbF 

(kJ/kg·K)

Gypsum Bboard 1⁄2-in. 0.013 1.10 (0.16) 50 (800) 0.26 (1.088)

Insulation 5.5-in. 0.140 0.27 (0.039) 1.6 (25.6) 0.33 (1.381)

Insulation 11.8-in. 0.300 0.27 (0.039) 1.6 925.6) 0.33 (1.381)

Insulation 30% PCM 0.27 (0.039) 2.1 (33.6) Cp(T)

Plywood 1⁄2-in. 0.013 0.83 (0.12) 34 (544) 0.29 (1.244)

Exterior Finish Layer 1⁄2-in. 0.013 0.48 (0.07) 34 (545) 0.29 (1.255)

Figure 5. Temperature versus effective heat capacity data for PCM used in thermal simulations

0 10 20 30 40 50

20

21

22

23

24

25

26

27

28

29

30

Freezing

Melting

Temp. oC

J/gTemp. oC

kJ/kg
24

Figure 6. Diurnal external temperature profiles Tes used in numerical analysis with assumption of 

Ti = 68°F (20°C) and Ti = 77°F (25°C)

A theoretical model of the material with temperature-dependent specific heat can be used to 

predict the phase change processes in the most common PCM-enhanced materials. The onedimensional heat transport equation for such a case is as follows:

∂

∂t (ρh) = ∂∂x �λ ∂T∂x� , (1)

where ρ is the material density, λ is the thermal conductivity, T is temperature, and h is enthalpy 

per unit mass. 

The enthalpy derivative over the temperature derivative (with consideration of constant pressure) 

represents the effective heat capacity, with the phase change energy as one of the components: 

ceff = ∂h

∂T , (2)

For most PCMs, variations of enthalpy associated with temperature depend to some extent on the 

direction of the process considered, and tend to differ for melting and solidification (Gunther et 

al. 2009). Transient characteristics of PCM-enhanced products depend on the PCM content and 

the quality of the PCM carrier. Usually, a smaller portion of the heat storage capacity (depending 

on the temperature difference) consists of sensible heat; a larger capacity portion represents heat 

of the phase transition. Effective heat capacity, ceff, for a material consisting of a blend of the 

material carrier and PCM can be expressed as follows: 

ceff = (1 − α)ccarr + α ceff_PCM, (3)

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16 18 20 22 24

TEMPERATURE [oC]

TIME [h]

Ti Tes a) Tes b) Tes c)

185 oF (85 oC)

149 oF (65 oC) 

113 oF (45 oC) 

68 oF (20 oC)

77 oF (25 oC) 

PCM melting point

81 oF (27 oC)
25

where α denotes the percentage of PCM, ccarr is the specific heat of a carrier material without 

PCM, and ceff_PCM is the effective heat capacity of the PCM. 

To visualize the dynamic effects, the study team calculated the heat fluxes for steady state, which 

represent the “zero mass” wall. During these calculations, investigators took the dependence of 

insulation conductivity on the temperature into account. An accurate elementary solution to the 

nonlinear steady-state heat transfer problem, in case of a linear dependence of the conductivity 

on temperature, can be obtained using the Kirchoff transform method (Kossecka 1999). Figure 7

and Figure 8 represent a comparison of diurnal heat flux profiles at internal surfaces of the two 

walls—one containing a plain fibrous insulation layer, and the other containing 30% PCMenhanced insulation. The steady-state heat flux profiles were added for comparison. In Figures 7

through 10, label “0% PCM” represents a case of plain fibrous insulation, label “30% PCM” 

represents the 30% blend of PCM and fibrous insulation, and label “steady state” represents the 

steady-state solution with no thermal mass effects taken into account.

Figure 7. Comparison of the daily heat flux profiles at the internal surface of the wall containing 

5.5-in. (0.14-m) thick insulation layer with 0% PCM and 30% PCM for internal temperature Ti = 68°F

(20°C) and temperature swing schedules with thermal peaks of 113°F (45°C) in schedule “a” 149°F 

(65°C) in schedule “b,” and 185°F (85°C) in schedule “c”

a

c

b

2x6 wall Ti = 20oC (68 oF)

TPCM = 27oC (81 oF)
26

Figure 8. Comparison of the daily heat flux profiles at the internal surface of the wall containing 

5.5-in. (0.14-m) thick insulation layer with 0% PCM and 30% PCM for internal temperature Ti = 77°F 

(25°C) and temperature swing schedules with thermal peaks of 45°C (113°F) in schedule “a,” 149°F 

(65°C) in schedule “b,” and 185°F (85°C) in schedule “c”

Comparison of the plots and calculated daily heat flow values indicates that for the 5.5-in.

(0.14-m) thick assemblies and for cyclic processes, the effect of PCMs in an insulation layer 

results in notable time shifting of the heat flux maxima. Heat losses corresponding to minimum 

external temperatures at midnight are shifted to morning. At the same time, large heat gains from 

midday are shifted by about 2 hours to the afternoon. Overall, for the 5.5-in. (0.14-m) thick 

assemblies, the highest reductions of the total heat flow can be observed for temperature swing 

schedules “a” and “b” with thermal peaks of 113°F (45°C) and 149°F (65°C), respectively. For 

Ti = 68°F (20°C), the heat gain maxima are reduced by 18%, 8%, and 4% for schemes “a,” ‘b,”

and “c,” respectively, as external sol-air temperature maxima increases from 113°F (45°C) to 

185°F (85°C). For Ti = 77°F (25°C), the corresponding heat gains (heat fluxes integrated over 

the time) are reduced by 25%, 6%, and 3%. In the case of temperature swing schedule “c,” the 

effect of the PCM in an insulation layer is positive, but perhaps not as strong as one would 

expect. A PCM of about 0.29 lb/ft2 (1.4 kg/m2

) in the insulation layer cannot significantly reduce 

high negative heat fluxes, resulting in cooling loads on the room space for very high external solair temperatures.

a

c

b

2x6 wall Ti = 25oC (77 oF)

TPCM = 27oC (81 oF)
27

Figure 9. Comparison of the daily heat flux profiles at the internal surface of the attic floor

containing 11.8-in. (0.3-m) thick insulation layer with 0% PCM and 30% PCM for internal 

temperature Ti = 68°F (20°C) and temperature swing schedules with thermal peaks of 113°F (45°C) 

in schedule “a,” 149°F (65°C) in schedule “b,” and 185°F (85°C) in schedule “c”

a

c

b

Attic Ti = 20oC (68 oF)

TPCM = 27oC (81 oF)
28

Figure 10. Comparison of the daily heat flux profiles at the internal surface of the attic floor

containing 12-in. (30-cm) thick insulation layer with 0% PCM and 30% PCM for internal 

temperature Ti = 77°F (25°C) and temperature swing schedules with thermal peaks of 113°F (45°C) 

in schedule “a,” 149°F (65°C) in schedule “b,” and 185°F (85°C) in schedule “c”

The study team repeated simulations for the assembly containing a PCM content of 30% and 

having a density of 2.1 lb/ft3 (33.6 kg/m3

); that is, about 0.62 lb of PCM per square foot of the 

wall (3 kg/m2). Similar to the 5.5-in. (0.14-m) thick assemblies, the highest reductions of the 

total heat flow were observed for temperature swing schedules “a” and “b.” For Ti = 68°F 

(20°C), the heat gain maxima are reduced by 48%, 50%, and 45% for schedules “a,” “b,” and 

“c,” respectively, as external sol-air temperature maxima increases from 113°F (45°C) to 185°F 

(85°C). For Ti = 77°F (25°C), the corresponding heat gains (heat fluxes integrated over the time) 

are reduced by 82%, 65%, and 40%. 

Figure 11 summarizes the results of simulations showing percent load reductions for both 

thicknesses for the building envelope assemblies. The highest energy savings were observed for 

the exterior temperature schedule “a” with the peak temperature of 113°F (45°C). For insulation 

thickness of 5.5-in. (0.14 m), percent load reductions were over 20% when compared to the plain 

thermal insulation. This occurred only when the amplitude of the external temperature Tes was

not too high (with daily peak of 113°F [45°C]) and savings were notably smaller for higher 

a

c

b

Attic Ti = 25oC (77 oF)

TPCM = 27oC (81 oF)
29

external temperature peaks. Note that the potential cooling load savings are significantly higher 

for thick layers of the PCM-enhanced insulation of 11.8-in. (0.3 m; representing PCM-enhanced 

attic floor insulations). In this case, the percent reduction in the cooling loads may reach 70%. As 

shown in Figure 11, the potential cooling load savings can be two to three times lower for thinner 

insulation assemblies (i.e., vaulted ceilings and walls). 

Figure 11. Reductions of heat gains calculated for the two thicknesses of the building envelope 

assemblies. For each material configuration and at internal temperatures Ti, heat gains represent 

heat fluxes integrated over the time period.

Proper selection of the PCM phase transition temperature plays a very important role in the 

overall energy performance. The results of the transient modeling demonstrated that the overall 

load reductions are significantly higher in situations when the PCM melting temperature is closer 

to the internal space set-point temperature. In the analysis of the 11.8-in. (0.3-m) thick layer of 

insulation, the temperature schedules “a” and “b” represented the approximate temperature 

excitations that are characteristic of the attic floor insulation in southern U.S. applications. For 

this case, the numerical results presented in Figure 11 indicate that the daily heat gain savings 

can range between 35% and 70% (considering only a 4°F or 2°C difference between PCM 

melting temperature and the internal space set-point temperature). Accordingly, for a higher 

temperature difference of ~13°F (7°C), the attic-generated heat gain savings can vary between 

8% and 10%. Similar relationships between the PCM melting temperature and the internal space 

set-point temperature can be observed for thinner assemblies. This fact confirms the earlier 

experimental results(Kośny 2008), and indicates that it is beneficial to design the PCM transition 

temperature as close as possible to the internal space set-point temperature.

0

10

20

30

40

50

60

70

80

schedule (a) schedule (b) schedule (c)

0.30-m (11.8-in.) Ti=25C 

(77F)

0.30-m (11.8-in.) Ti=20C 

(68F)

0

5

10

15

20

25

schedule (a) schedule (b) schedule (c)

0.14-m (5.5-in.) Ti=25C 

(77F)

0.14-m (5.5-in.) Ti=20C 

(68F)

%

%
30

3.2 Estimation of the Competitive Price Level for Phase Change Material Attic 

and Wall Applications

The study team’s thermal performance analysis for 11.8-in. (0.3-m) and 5.5-in. (0.14-m) thick 

layers of PCM-enhanced thermal insulation yielded maximum theoretical energy savings 

exceeding 72% and 22% , respectively—assuming that PCM enthalpy was 52 Btu/lb (120 kJ/kg). 

As shown in Figures 7 through 11, the thermal efficiency of PCM-enhanced roof/attic systems 

depends strongly on the thermal characteristics of PCMs and PCM carriers (thermal insulation in 

this analysis). The magnitude of the exterior climatic thermal loads is an additional factor that 

affects the overall thermal efficiency. If the exterior thermal excitations are too large, PCMs can 

be melted or frozen at a very fast rate and the overall thermal effectiveness of the PCM-enhanced 

building envelope can be relatively low (as in the case of cathedral-style roof PCM applications; 

see thermal schedule “c” in Figures 7 and 11).

PCM cost effectiveness was estimated for the PCM systems using dispersed blends with fiber 

insulations and PCM-enhanced wall boards. For each of the PCM applications considered and 

for five southern U.S. climates, potential cooling energy savings were estimated using heating 

and cooling load levels generated by whole-building energy simulations and numerically

estimated heat gain reductions for specific building envelope components (see Section 3.1). 

Table 6 gives residential electricity costs for each location. According to the U.S. Bureau of 

Labor Statistics,

13 the average price of electricity in the United States in 2011 was $0.125/kWh.

In the following analysis, the study team based estimates of the energy saved by employing

PCM-enhanced building envelopes based on the unit electricity costs for each selected location.

Table 6. Residential Electric Energy Prices for Five Southern U.S. Climates 

Used in Whole-Building Energy Analysis

Cities CDD 74°F

(23.3°C)

Electricity 

price,

($/kWh)

Reference

Atlanta 8,475 (15,255) 0.113 Bureau of Labor Statistics (2012) 

Bakersfield 16,641 (29,954) 0.340 Bakersfield News (2011) 

Fort Worth 20,163 (36,294) 0.094 Direct Energy (2012) 

Miami 21,889 (39,401) 0.116 Florida Power and Light (FPL; 2012) 

Phoenix On-Peak 30,224 (54,404) 0.216 APS (2012) Phoenix Off-Peak 0.054

In the United States, different microencapsulated PCMs are available for building applications 

with paraffinic products and blends of different fatty oils, of which esters are the most common.

For the cost analysis, the study team assumed four typical PCM enthalpies used by the 

industry—52 Btu/lb (120 kJ/kg), 65 Btu/lb (150 kJ/kg), 82 Btu/lb (190 kJ/kg), and 95 Btu/lb 

(220 kJ/kg). The amount of PCM was normalized against the heat storage capacity of the basic 

wall and roof systems assuming a baseline enthalpy of 52 Btu/lb (120 kJ/kg). Finally, the cost of 

PCM was analyzed for the PCM price range between $1.50/lb and $7.50/lb. For each of the 

PCM-enhanced envelope configurations, a payback period was computed.

 13 See www.bls.gov/ro4/aepatl.htm for more information
31

3.3 Payback Period Analysis for Attic Applications of Dispersed 

Phase Change Materials

Conventional attic designs with soffit and ridge ventilation are good examples of the dynamic 

building envelopes for cooling-dominated climates. The ventilation air redirects some of the heat 

emanating from the roof deck away from the insulation on the attic floor. The attic insulation 

works against an internal attic air temperature instead of the dynamic temperatures observed on 

the roof surface (for comparison, cathedral-style roofs directly conduct heat into the conditioned 

space). In general, benefits of the attic thermal system are as follows:

• Effectively reduces roof solar loads

• Reduces nighttime cooling effects

• Provides a conduction break between the attic floor and the roof deck

• Causes stratification of the attic air

• Causes a shifting of the attic thermal loads.

Earlier research showed that adding PCMs to the attic floor insulation can be a very efficient way 

to reduce the overall cooling loads generated by the attic and to shift the peak-hour cooling loads 

to the afternoon or nighttime (Kośny et al. 2011; Kośny 2008). As mentioned previously, during

the summer in southern U.S. locations, the attic floor insulation is usually facing attic space 

temperature fluctuations between the range of schedules “a” and “b” (i.e., temperature peaks 

reaching between 113°F [45°C] and 149°F [65°C]). 

In the study team’s energy performance simulations for PCM-enhanced insulations, a 11.8-in.

(0.3-m) thick layer of an ideal insulation was assumed. In the following cost analysis, to simplify

the calculations and limit the number of insulation configurations, analysts assumed only 

cellulose insulation. Considering thermal bridging generated by the attic floor structural 

members, this will yield very conservative thermal performance predictions of PCM-enhanced 

R-30 cellulose insulation installed on the attic floor. The amount of PCM required was calculated 

to be approximately 522 lb (237 kg) of PCM necessary for the attic (30% by weight of the 

insulation). The study team also assumed that the roof pitch was 6 to 12 in. (2.4 to 4.7-cm.), the 

attic floor framing was 16 in. (0.40 cm) o.c., and the central attic floor beam structure was 11.8-

in. (0.305-m) thick.

Table 7 shows the annual costs for attic-generated cooling electrical energy consumed in each of 

the geographic locations. For Phoenix, the study team assumed that all roof-generated cooling 

electricity was used during either peak or off-peak hours. The off-peak assumption is based on 

analysis performed in Section 3.1, which demonstrated that significant time shifting is possible 

in cases of thicker building envelope applications containing PCM.
32

Table 7. Annual Costs of Cooling Electric Energy Generated by the Attic Calculated for a 

Single-Story Ranch House for Five Southern U.S. Climates

Cities

Total Cooling 

Energy 

Consumption 

(kWh)

Attic-Generated

Cooling Energy 

Consumption 

(kWh)

Annual Cost of 

Electricity Used for 

Cooling

(Attic-Generated, $)

Atlanta 1,683 269.3 30.43

Bakersfield 2,817 456.4 155.18

Fort Worth 3,082 458.0 43.05

Miami 6,076 911.4 105.72

Phoenix On-Peak 5,805 870.8

188.09

Phoenix Off-Peak 47.02

Anticipated cooling energy cost savings were calculated for the attic for each of the climatic 

locations. For each location, two levels of savings were calculated considering PCM 

performance predictions for schedules “a” and “b” (as described in Figure 6) and an internal 

space temperature of Ti = 77°F (25°C) as shown in Table 8. Next, using the calculated cooling 

energy cost savings and assuming a PCM price range of $1.50/lb to $7.50/lb, payback periods

were computed for four typical PCM enthalpies; 52 Btu/lb (120 kJ/kg), 65 Btu/lb (150 kJ/kg), 82

Btu/lb (190 kJ/kg), and 95 Btu/lb (220 kJ/kg). Amounts of PCM were normalized against the 

heat storage capacity of the attic system using the PCM of 52 Btu/lb (120 kJ/kg) enthalpy. The 

study team assumed that PCMs represented 30% by weight of the 11.8-in. (0.3-m) thick attic 

insulation. Considering that the cellulose density was about 1.6 lb/ft3 (25.6 kg/m3

) and assuming 

that the attic framing, the roof structural components, the attic entry hatch, and the air-handler 

unit reduced nominal volume of the attic insulation by about 27%, the overall PCM load in the 

attic was close to 522 lb (237 kg). Figures 12 through 16 present the results of these calculations.

Table 8. Calculated Annual Cooling Electricity Cost Savings Generated by the Attic for a 

Single-Story Ranch House for Five Southern U.S. Climates 

Cities

Annual Cost of 

Electricity Used for 

Cooling 

(Attic-Generated, $)

Annual Cooling 

Electricity Cost 

Savings – PCM, 

Schedule “a”

(Attic-Generated, 

$/ft2-Floor Area)

Annual Cooling 

Electricity Cost 

Savings – PCM, 

Schedule “b”

(Attic-Generated,

$/ft2-Floor Area)

Atlanta 30.43 21.91 (0.014) 10.65 (0.007)

Bakersfield 155.18 111.73 (0.073) 54.31 (0.035)

Fort Worth 43.05 31.00 (0.020) 15.07 (0.010)

Miami 105.72 76.12 (0.049) 37.00 (0.025)

Phoenix On-Peak 188.09 135.43 (0.088) 65.83 (0.043)

Phoenix Off-Peak 143.96 (0.093)a 85.64 (0.056)a

a Off-peak savings for Phoenix were calculated as a sum of on-peak savings and savings calculated for price 

differences between on-peak and off-peak rates, assuming that attic-generated peak cooling loads are shifted after 

7:00 p.m.—
33

Figure 12. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in Atlanta. 

The external temperature profiles have been defined as “a” and “b.”

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Atlanta, attic schedule "b"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Atlanta, attic schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

Payback period [years] Payback period [years]

PCM enthalpy

(Btu/kg)

[kJ/kg]

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]
34

Figure 13. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in 

Bakersfield. The external temperature profiles have been defined as “a” and “b.”

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Bakersfield, attic schedule "b"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Bakersfield, attic schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years] Payback period [years]
35

Figure 14. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in Fort 

Worth. The external temperature profiles have been defined as “a” and “b.”

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Fort Worth, attic schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

50.0

100.0

150.0

200.0

250.0

300.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Fort Worth, attic schedule "b"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years] Payback period [years]
36

Figure 15. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in Miami.

Two external temperature profiles have been defined as “a” and “b.”

0.0

10.0

20.0

30.0

40.0

50.0

60.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Miami, attic schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

20.0

40.0

60.0

80.0

100.0

120.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Miami, attic schedule "b"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years] Payback period [years]
37

Figure 16. Payback periods for the PCM-enhanced R-30 cellulose insulation configuration 

installed on the attic floor as a function of the PCM price for a single-story ranch house in 

Phoenix. The external temperature profiles have been defined as “a” and “b.”

As shown in Table 8, installing attic floor insulation that contains dispersed PCM may bring 

substantial energy and cost savings in several southern U.S. locations. Overall cost effectiveness 

of the PCM-enhanced attic floor insulation was estimated for two thermal performance levels 

described previously (see Figure 6, , and 10). To reiterate, detailed thermal modeling of the 

specific attic configuration will help to develop a better understanding of the thermal processes 

within the attic space. In addition, this will be useful in obtaining a more precise estimation of 

the potential energy savings accruing from the PCM application. In this report, the study team

assumed that the thermal performance of the PCM-enhanced attic insulation will be between the

PCM performance levels described earlier, depending on the attic configuration and climatic 

conditions. Analysts also expect that the optimized selection of the PCM (better selection of the 

enthalpy profile in relation to the internal attic air temperature) will bring additional performance 

improvements.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix, attic schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix, attic schedule "b"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years] Payback period [years]
38

For the payback period study, the team assumed a PCM price range between $1.50 and 7.50/lb 

(refer to Figures 12 through 16). If a payback period of 10 years is set as a target and exterior 

temperature schedule “a” is assumed the following three locations will qualify:

• Phoenix—a maximum PCM price of $4.50/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg); a maximum price of $2.50/lb for the case of 52 Btu/lb

(120 kJ/kg), which is a commonly used PCM price in Europe

• Bakersfield—a maximum PCM price of $3.50/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg)

• Miami—a maximum PCM price of $2.50/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg).

If a payback period of 7 years is set as a limit and exterior temperature schedule “a” is assumed, 

the following three locations would qualify:

• Phoenix—a maximum PCM price of $3.50/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg)

• Bakersfield—a maximum PCM price of $3.00/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg)

• Miami—a maximum PCM price of $2.00 /lb for the enthalpy cases of 95 Btu/lb

(220 kJ/kg).

3.4 Additional Benefits of Thick Applications of the Phase Change MaterialEnhanced Attic Floor Insulation

Two additional important features of the thick PCM-enhanced thermal insulations are reductions 

of the peak-hour thermal loads and the capability to significantly time-shift thermal loads in 

place where application is located. As shown in Figures 9 and 10, the peak-hour load reductions 

generated by PCM-enhanced attic floor insulations can easily be between 50% and 80%. For

different climatic locations and for specific PCM configurations, it is also important to consider 

the number of days (as a percentage) on which phase change processes are allowed to take place.

Figure 17 summarizes these findings for load schedules “a” and “b.” For geographic locations 

that have two separate electricity cost rates for on-peak and off-peak hours, the capability to 

reduce load during peak hours is critical. In these places, peak-hour load reductions combined 

with significant load time-shifting can be essential sources of energy cost savings. 

As depicted in Figure 9, 10, 17, and 18, the peak-hour load-shifting generated by 11.8-in. (0.3-m)

thick PCM-enhanced attic floor insulations can be between 4 and 11 hours, depending on the 

PCM selection and the intensity of the exterior thermal excitations (refer to Figure 6). Remember 

that in many locations with a double electricity tariff, the off-peak time starts at 7:00 p.m. For 

such locations, the most useful configuration would be an attic insulation system that provides at 

least a 5-hour time delay for attic-generated cooling loads. Figure 18 shows that all the 

configurations considered in this analysis for an 11.8-in. (0.3-m) thick PCM-enhanced attic floor 

insulation will most likely meet this requirement. Phoenix is the only location that has double 

electricity rates. Cooling energy cost savings calculated for Phoenix as given in Table 8 show 

that it is possible to save up to 30% of the attic-generated cooling electricity cost by taking 
39

advantage of the load-shifting capability of the PCM-enhanced attic insulation. Figure 19

presents the results of the payback period calculations for Phoenix with off-peak energy savings 

taken into account.

Figure 17. Percent peak-hour cooling load reductions for 11.8-in. (0.3-m) thick 

PCM-enhanced attic floor insulation

Figure 18. Peak-hour cooling load time-shifting for 11.8 in. (0.3-m) thick 

PCM-enhanced attic floor insulation

0

10

20

30

40

50

60

70

80

90

schedule (a) schedule (b)

0.30-m (11.8-in.) 

Ti=25C (77F)

0.30-m (11.8-in.) 

Ti=20C (68F)

Peak-hour % load reduction

0

2

4

6

8

10

12

schedule (a) schedule (b)

0.30-m (11.8-in.) 

Ti=25C (77F)

0.30-m (11.8-in.) 

Ti=20C (68F)

Peak load time shifting - hours
40

Figure 19. Payback periods calculated using cooling cost reductions for 11.8-in. (0.3-m) thick 

PCM-enhanced attic floor insulation computed using the off-peak-hour electricity tariff for 

Phoenix. The external temperature schedules have been defined as “a” and “b.”

As shown in Figures 17 through 19, a significantly lower off-peak electricity rate in Phoenix

allows PCMs that cost $0.50 more to be applied. For example, for a 10-year payback period

(schedule “a”), microencapsulated PCM with an enthalpy of 52 Btu/lb (120 kJ/kg) may cost a 

maximum of about $3.00/lb as compared to $2.50/lb, estimated previously under a one-tariff 

schedule. 

Simulation results presented in Figure 9, 10, and 18 indicate that including a PCM in an 

insulation layer can result in a significant time-shifting of the peak-hour loads. The thicker 11.8-

in. (0.3-m) assemblies yield larger load-shifting—in most cases at least four times larger than the 

5.5-in. (0.14-m) thick assemblies (see Figures 7 through 10). In the 11.8-in. (0.3-m) thick 

building envelope assembly containing PCM with an internal set-point temperature of Ti = 77°F 

(25°C), the peak-hour load may be shifted by 11 hours. Figure 20 shows that in this building 

envelope assembly, the heat flows in the opposite direction 70% of the time (~17 hours a day),

compared to a similar assembly without any PCMs. During the day, this PCM-enhanced 

assembly generates a passive cooling effect. These simulation results have confirmed earlier 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix off peak attic schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix off peak, attic schedule "b"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years] Payback period [years]
41

field test data, as described by Kośny and coworkers (2010), for walls and attics containing 

PCM-enhanced insulation.. It is expected that in combination with greater than 70% reduction of 

the total loads and “free” cooling during the day (see Figure 11), this configuration can be an 

attractive alternative to conventional building envelope systems in the future.

Figure 20. Reverse heat flow effect generated by significant time shifting of thermal loads in 11.8-

in. (0.3-m) thick PCM-enhanced attic floor insulation in Phoenix. The external temperature 

schedule has been defined as “a”

In July 2008, a full-scale experimental attic was constructed and instrumented to field-test blown 

fiberglass insulation combined with microencapsulated PCMs (Kośny et al. 2010). One purpose 

of this experiment was to use the collected data to inform future modifications in the attic design, 

and to eventually optimize the PCM thermal characteristics. A full-scale residential attic was 

filled with about 10 in. (0.25 m) of blown fiberglass insulation with an approximate density 1.8 

lb/ft3 (29 kg/m3

). Next, on top of this insulation, four 0.5-in. (0.013-m) thick layers of a PCMadhesive blend were installed with 0.5-in. (0.013-m) thick layers of blown fiberglass installed in

between, as shown in Figure 21. The total thickness of the added PCM-fiberglass multilayer 

“sandwich” was approximately 4 in. (0.10 m). The PCM melting temperature was close to 84°F 

(29°C), and the nominal phase change enthalpy was about 73 Btu/lb (170 kJ/kg). This 

experiment demonstrated that it is possible to observe and measure the theoretically predicted 

reverse heat flow in thick layers of PCM-enhanced insulation under full-scale field conditions. 

Reverse heat flow during the night

Reverse heat flow during the day

Attic schedule “a”
42

Figure 21. Photograph of the test attic with blown PCM-enhanced fiberglass insulation

To develop a better understanding of the reverse heat flow effect within the attics containing 

PCM-enhanced insulation, detailed transient modeling of the attic space temperatures and heat 

fluxes generated on the attic floor is necessary.. Optimization of the insulation thickness and 

configuration of the PCM heat sink may significantly improve the overall energy effectiveness of 

residential and small commercial attics beyond the level of savings shown in the parametric 

analysis.

3.5 Potential Cost Savings Associated With Phase Change Material Load 

Reductions in Phase Change Material-Enhanced Attic Floor Insulations

Recall that one of the goals of this project was to define the energy performance and cost limits 

for PCM-enhanced building technologies. For this reason, the study team assumed a nearmaximum amount of PCM that can be supported by the fiberglass insulation. A uniform PCM 

load level of 30% by weight was assumed for all applications of the PCM-enhanced fiberglass

insulation. This fact yielded very conservative PCM cost predictions and relatively long payback 

periods. 

Previous research has demonstrated, however, that in building applications PCM loads do not 

need to be so high. It is worthwhile to mention that initially the PCM-enhanced cellulose 

insulation was developed with about 22% PCM content (Kośny et al. 2006). At the same time, 

the study team performed most of the tests and numerical analysis of the cellulose- and 

fiberglass-based insulations mixed with microencapsulated PCM for load levels between 20% 

and 25% by weight (Kośny et al. 2010; Kośny 2008). In these studies, performance levels were 

very close to the thermal performance of the samples containing 30% of PCM. Note that the 

latest ORNL numerical study confirmed this finding as well (ORNL 2012). In that light, about a 

25% reduction in the PCM amount (from the 30% by weight level used in this study) can easily 25-cm. (10-in.) 36-cm. (14-in.)

PCM
43

be allowed , with insignificant reduction of the thermal performance of PCMs. Figure 22 shows 

the modified levels of payback period for attic PCM applications in Miami and Phoenix. This 

study found that 25% reduction in the PCM load can reduce the payback period by 

approximately 1 to 2 years, depending on the location, PCM type, and cost level. 

Figure 22. Modified levels of payback periods for attic PCM applications in Miami and Phoenix,

considering a 25% reduction in PCM loading

When a payback period of 10 years was assumed as a top cost level for Miami, two PCMenhanced insulation configurations were found to meet this cost target for a PCM price of 

$3.00/lb and below (under thermal schedule “a”). These configurations are (1) 82 Btu/lb (190

kJ/kg) and (2) 95 Btu/lb (220 kJ/kg). Similarly, the same payback period target for Phoenix 

required the PCM price to be $6.00/lb and below. For Phoenix, at an enthalpy of 52 Btu/lb (120 

kJ/kg), the maximum price was calculated at $3.50/lb and the payback period would be 10 years.

If a payback period of 7 years is the limit and considering enthalpies of 82 and 95 Btu/lb (190 

and 220 kJ/kg), the PCM price (for schedule “a”) would need to be below $3.50/lb and $5.00/lb 

in Miami and Phoenix, respectively. Also, in Phoenix, microencapsulated PCM with an enthalpy

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Miami, attic schedule "a" - 25% reduction of PCM load

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

0.0

5.0

10.0

15.0

20.0

25.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix off peak attic schedule "a" - 25% reduction of PCM load

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years] Payback period [years]
44

of 52 Btu/lb (120 kJ/kg) would need to cost less than $3.00/lb to be considered for this 

application.

In addition, remember that dynamic hot-box testing and transient modeling demonstrated that not 

all PCMs in the wall cavity or on the attic floor always undergo phase transition (Kośny et al.

2007). Experimental work showed that often up to 50% of the PCM content may not perform 

phase transition. For precise analysis of this process and optimization of the PCM amount,

detailed transient modeling is necessary. 

3.6 Payback Period Analysis for Wall Applications of Dispersed 

Phase Change Materials

Conventional 2 × 6 wood-framed wall assemblies usually use either fiberglass batt cavity 

insulation or blown cellulose insulation. In this report, the study team considered only PCMenhanced cellulose cavity insulation. As mentioned previously, during the summer in southern 

U.S. locations, the wall cavity insulation is usually facing temperature fluctuations close to

schedule “a” with temperature peaks reaching 113°F (45°C). To reach the same PCM heat 

storage density that was assumed in the theoretical analysis, 202 lb (92 kg) of PCM was used in 

the cost analysis of wall insulation. 

Table 9 shows the annual costs for wall-generated electric cooling demands in each of the 

study’s geographic locations. For Phoenix, all wall-generated cooling electricity was used either 

during the on-peak hours or during the off-peak hours.

Table 9. Annual Costs of Cooling Electric Energy Generated by 2 × 6 Walls, Calculated for a 

Single-Story Ranch House for Five Southern U.S. climates 

Cities

Total Cooling 

Energy 

Consumption

(kWh)

Wall-Generated

Cooling Energy 

Consumption

(kWh)

Annual Cost of 

Electricity Used for 

Cooling 

(Wall-Generated, $)

Atlanta 1,683 236.77 26.75

Bakersfield 2,817 437.70 148.82

Fort Worth 3,082 455.61 42.83

Miami 6,076 856.73 99.38

Phoenix On-Peak

5805 960.68

207.52

Phoenix Off-Peak 51.88a

a Assuming that the cost of all electric cooling used was calculated using the off-peak tariff for the wall-generated 

portion of the cooling energy

The study team calculated anticipated cooling energy cost savings for walls for each selected 

geographic location. As shown in Table 10, for each climate, two levels of savings were 

calculated based on the efficiency predictions given in Figure 11 for schedule “a” with an

internal space temperature Ti = 77°F (25°C). Next, using the calculated cooling energy cost 

savings and assuming a PCM price range of $1.50–$7.50/lb, payback periods were computed for 

the following four typical PCM enthalpies: 52 Btu/lb (120 kJ/kg), 65 Btu/lb (150 kJ/kg), 82

Btu/lb (190 kJ/kg), and 95 Btu/lb (220 kJ/kg). Amounts of PCM were normalized against the 

heat storage capacity of the wall system using a PCM of 52 Btu/lb (120 kJ/kg) enthalpy as a 

baseline. Results of these calculations are presented in Figures 21 through Figure 26.
45

The simulation results presented in Figures 7 through 10 indicate that the effect of PCMs in an 

insulation layer may result in significant time-shifting of the peak-hour loads. The thicker attic 

insulation assemblies yield larger load shifting—in most cases at least four times larger than the 

thinner case of 5.5-in. (0.14-m) thick wall assemblies. In the case of the 5.5-in. (0.14-m) thick 

building envelope assembly containing PCMs, and where the internal set-point temperature is 

77°F (25°C), the peak-hour load may shift by 3 hours. Because the 3-hour time shift will not 

completely move the peak-hour loads to the off-peak time, only 60% of off-peak savings were 

included in the energy cost savings analysis. More detailed thermal modeling is needed to better 

approximate the scale of this effect for PCM-enhanced wall insulations. In this study, the team 

assumed that PCMs represented 30% by weight of insulation installed in the 5.5-in. (0.14-m) 

thick wall cavity and that the wall framing factor was 25%. Considering that the cellulose density 

was about 1.6 lb/ft3 (25.6 kg/m3

), and windows and doors represent 20% of the total wall area, 

the overall PCM load in all four walls was close to 203 lb (129 kg).

Table 10. Annual Cooling Electricity Cost Savings Generated by the Attic Calculated for a 

Single-Story Ranch House for Five Southern U.S. Climates 

Cities

Annual Cost of 

Electricity Used for 

Cooling 

(Wall-Generated, $)

Annual Cooling Electricity Cost 

Savings—Schedule “a”

(Wall-Generated, $/ft2

-floor area)

Atlanta 26.75 5.89 (0.004)

Bakersfield 148.82 32.74 (0.021)

Fort Worth 42.83 9.42 (0.006)

Miami 99.38 21.86 (0.014)

Phoenix On-Peak 207.52 45.65 (0.030)

Phoenix Off-Peak 61.39 (0.040)

a

a In energy cost savings analysis, the study team included only 60% of off-peak savings.

Figure 23. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Atlanta. Wall assemblies are assumed to experience the external 

temperature schedule defined as “a.”

0.0

50.0

100.0

150.0

200.0

250.0

300.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Atlanta, wall schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

Payback period [years]

PCM enthalpy

(Btu/kg)

[kJ/kg]
46

Figure 24. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Bakersfield. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”

Figure 25. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Fort Worth. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a.”

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Bakersfield, wall schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Fort Worth, wall schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)
47

Figure 26. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Miami. Wall assemblies are assumed to experience the external 

temperature schedule defined as “a.”

Figure 27. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Phoenix. Wall assemblies are assumed to experience the

external temperature schedule defined as “a.”

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Miami, wall schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix, wall schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]
48

Figure 28. Payback period for PCM-enhanced cavity wall insulation as a function of the PCM price 

for a single-story ranch house in Phoenix. Wall assemblies are assumed to experience the 

external temperature schedule defined as “a” and an off-peak tariff is included.

If a payback period of 10 years is set as a target and the exterior temperature schedule “a” is 

assumed, three locations will qualify: 

• Phoenix—a maximum PCM price of $4.00/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg) and a maximum price of $2.50/lb for the case of 52 Btu/lb 

(120 kJ/kg)

• Bakersfield—a maximum PCM price of $2.50/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg)

• Miami—a maximum PCM price of $1.50/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg) (see Figures 23 through 27).

If a payback time of 7 years is established as a limit and the exterior temperature schedule “a” is 

assumed, three locations will qualify:

• Phoenix—a maximum PCM price of $3.00/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg)

• Bakersfield—a maximum PCM price of $2.00/lb for the two enthalpy cases of 82 and 

95 Btu/lb (190 and 220 kJ/kg)

• Miami—a maximum PCM price of $1.50 /lb for the enthalpy case of 95 Btu/lb 

(220 kJ/kg) (see Figures 23 through 27).

Remember that the hot-box testing and numerical analysis showed that in a 2 × 6 wall cavity 

insulated with fiber insulation containing dispersed PCM, not all PCMs may undergo a phase

change. Based on this finding, the analysts believe that there is still a potential for at least a 20% 

reduction in the amount of PCM without compromising the overall thermal performance.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix off peak, wall schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]
49

3.7 Payback Period Analysis for Wall Applications of Phase Change MaterialEnhanced Gypsum Boards

Historically, performance investigations focused on impregnating concrete, gypsum, or ceramic 

masonry with salt hydrates or paraffinic hydrocarbons. PCM-enhanced gypsum board and PCMimpregnated stucco are probably the best-known PCM applications in buildings. Most of the 

research studies performed on these materials found that PCMs improved building energy 

performance by reducing the peak-hour cooling loads and shifting the peak-demand time. During 

early testing in the United States, gypsum boards were impregnated with PCMs. Later, 

microencapsulated PCMs were used. In these tests paraffinic hydrocarbon PCMs generally 

performed well, but they compromised the flammability resistance of the building envelope.

In this study, the team assumed that PCM represented 20% by weight of the 1⁄2-in. (~0.012-m) 

thick drywalls that were installed on the internal surfaces of the exterior walls. Considering that 

the drywall density is about 37 lb/ft3 (593 kg/m3) and assuming that windows and doors 

represent 20% of the total wall area, the overall PCM load in all four walls was close to 284 lb 

(129 kg) for all building configurations described in Section 3.

In this part of the analysis, the study team used either the experimental performance data or

limited numerical predictions yielded by computer programs that were validated with the test 

data (as described in Table 1). For applications of PCM-enhanced drywall in walls, different 

research groups reported cooling energy savings ranging between 7% and 20% for different U.S. 

locations.. Following this historical experimental data, in this work, the study team considered 

15% cooling energy savings for the PCM-enhanced gypsum board applications. Figures 29

through 34 present the results of the payback period calculations. About 1 hour of load-shift time 

was reported for PCM-enhanced gypsum board in earlier research reports (see, for example, 

Tomlinson et al. 1992).

Remember that the PCM applications represented in this report are exclusively for a steady 

internal space temperature. In addition, internal walls are finished with PCM-enhanced drywalls 

in many applications. Given that many successful applications of the PCM-enhanced gypsum 

boards use different variable internal temperature schedules and different PCM loads, the study 

team strongly recommends performing additional, more detailed cost analysis for each of 

individual application scenarios. 
50

Figure 29. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Atlanta. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.”

Figure 30. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Bakersfield. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.”

0.0

100.0

200.0

300.0

400.0

500.0

600.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Atlanta, wall PCM-gypsum board, schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]

0.0

20.0

40.0

60.0

80.0

100.0

120.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Bakersfield, wall PCM-gypsum board, schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]
51

Figure 31. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Fort Worth. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.”

Figure 32. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Miami. Wall assemblies are assumed 

to experience the external temperature schedule defined as “a.”

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Fort Worth, wall PCM-gypsum board, schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Miami, wall PCM-gypsum board,schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]
52

Figure 33: Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Phoenix. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a.”

The figures (Figure 29 through 34) show that if a payback time of 10 years is assumed as a 

maximum cost level, PCMs with a price $2.00/lb and lower with enthalpies between 82 and 95 

Btu/lb (190 and 220 kJ/kg) can meet this target in Phoenix. Figure 34 shows the approximate 

payback times computed for Phoenix, considering energy cost savings resulting from applying

the off-peak electricity rate. Similar to applications with PCM-enhanced fiber insulation, notable 

improvements in the cost effectiveness can be observed.

When cost reductions resulting from off-peak electricity rates are included, a payback period of 7 

years is calculated for two PCMs of enthalpies between 82 and 95 Btu/lb (190 and 220 kJ/kg) 

with a price limit $3.00/lb. In addition, Figure 34 shows that for these two PCMs, a 10-year

payback period is possible for a PCM price not exceeding $3.50/lb.

Figure 34. Payback period for PCM-enhanced gypsum boards that are used for wall application as 

a function of the PCM price for a single-story ranch house in Phoenix. Wall assemblies are 

assumed to experience the external temperature schedule defined as “a” and an off-peak tariff is 

used.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix, wall PCM-gypsum board, schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix, wall PCM-gypsum board, schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(Btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]
53

Remember that when PCM-enhanced gypsum boards are used in a house, they are often installed 

on the exterior and interior walls and the ceilings. This significantly changes the whole-house 

dynamic energy response. In such cases, when overnight pre-cooling is used, the energy 

performance for these systems can improve considerably. This method is mostly used in Europe. 

For applications in the United States, detailed whole-building modeling that uses variable 

internal space temperature schedules will be necessary to assess potential energy savings and 

enable cost analysis. In addition, full-scale field testing can be helpful in predicting additional

energy savings for cases with variable internal space temperature profiles and PCM applications 

on internal walls and ceilings. This is important to remember because, in practice, for these cases

payback periods can be significantly different from the experimental data presented in this report 

for constant internal temperatures.

An application of thinner 3⁄8-in. (1-cm) thick boards that contain PCM in conjunction with carbon 

or graphite fillers (to enhance thermal conductivity) may be considered as an alternative for 

performance improvement and cost reduction. Figure 35 depicts the payback times computed for 

a 3⁄8-in. (1-cm) thick PCM-enhanced drywall in Phoenix. The study team assumed that the board 

thickness reduction brought about 25% savings in the PCM cost. At the same time, an addition of 

highly conductive fillers added an extra 5% to the cost, bringing total cost savings to 20%.

Figure 35: Payback period for 3/8-in. thick PCM-enhanced gypsum boards that are used for wall 

application as a function of the PCM price for a single-story ranch house in Phoenix. Wall 

assemblies are assumed to experience the external temperature schedule defined as “a” and an 

off-peak tariff is used.

3.8 Performance Comparisons Between Conventional Insulations and Phase 

Change Material-Enhanced Insulations

The whole-building energy analysis results presented in Figures 2 and 3 indicated that in 

building envelopes with higher R-values, the thermal effectiveness of conventional insulations 

can be surprisingly low. Analytical data presented in Figures 7 through 10, however, indicate that 

if these insulations are mixed with microencapsulated PCMs, the overall efficiency of the PCMinsulation composite can be significantly higher. 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Payback time [years]

PCM price [$/lb]

Phoenix off peak, wall PCM-gypsum board, 3/8-in. , schedule "a"

120 150

190 220

PCM enthalpy

[kJ/kg]

(btu/lb)

(52) (65)

(82) (95) 

PCM enthalpy

(Btu/kg)

[kJ/kg]

Payback period [years]
54

Based on the study team’s whole-building energy performance analysis, Table 11 shows the 

computed approximate energy savings for the attic used in the analysis. Two applications were 

analyzed, one with conventional insulation only, and the other with PCM-enhanced insulation

added to the conventional insulation. In both analyzed cases, the initial attic floor was insulated 

with R-30 insulation. In the case of the conventional insulation, additional R-19 was installed on 

top of the existing R-30. This scenario yielded about 9% to 10% of the attic-generated cooling 

energy savings in the whole-building energy model. In case of the PCM application, the R-30

conventional insulation was replaced by a 30% by weight blend of PCM and conventional 

insulation of the same thickness. To enable performance comparisons, PCM enthalpy of 82 

Btu/lb (190 kJ/kg) was assumed. As in earlier analysis, an equivalent amount of PCM was 

calculated using a PCM of enthalpy of 52 Btu/lb (120 kJ/kg) as a baseline. 

Next, energy savings were calculated for schedules “a” and “b.” The results showed that by 

using PCM-enhanced insulation and assuming schedule “a,” the cost of saved cooling energy is 

up to eight times higher compared to case in which conventional R-19 insulation was added. 

Correspondingly, under schedule “b,” the cost of saved cooling energy is about four times 

higher.

Table 12 shows comparisons of energy cost savings and material costs calculated for a singlestory ranch house in five southern U.S. climates. The table shows that adding microencapsulated 

PCM would be about 1.3 times more expensive than applying the R-19 blown fiberglass and 

about 1.9 times more expensive than installing the cellulose. Notice that, as described in previous 

sections, the amount of PCM can still be significantly reduced without compromising the overall 

energy efficiency of the PCM-enhanced insulation. In that light, PCM-enhanced insulations in 

cooling-dominated climates can be considered as cost-effective alternatives for future thermal 

improvements of moderately insulated attics, or for new constructions with higher energy 

efficiency targets.

Table 11. Potential Savings in Annual Costs of Cooling Electric Energy Generated by the Attic 

Calculated for a Single-Story Ranch House and for Five Southern U.S. Climates 

Cities

AtticGenerated

Cooling 

Energy 

Consumption

(kWh)

Annual Cost 

of Electricity 

Used for 

Cooling 

(AtticGenerated, $)

Annual Cost Savings of Electricity Used for Cooling

(Attic-Generated, $)

R-19 Insulation 

Over Existing 

R-30 (Level of 

Savings for 

Each Location)

30% by Weight 

Blend of

Microencapsulated 

PCM and R-30

Conventional 

Insulation (Savings 

Level for Schedule 

“a”)

30% by Weight 

Blend Of

Microencapsulated 

PCM and R-30 

Conventional 

Insulation 

(Savings Level for 

Schedule “b”)

Atlanta 269.3 30.43 2.74 (9%) 21.91 10.65

Bakersfield 456.4 155.18 15.52 (10%) 111.73 54.31

Fort Worth 458.0 43.05 3.87 (9%) 31.00 15.07

Miami 911.4 105.72 9.52 (9%) 76.12 37.00

Phoenix 870.8 188.09 16.93 (9%) 135.43 65.83
55

Table 12. Comparisons of Energy Cost Savings and Material Costs Calculated for a Single-Story 

Ranch House for Five Southern U.S. Climates 

Cities

Annual Cost Savings of Electricity Used 

for Cooling

(Attic-Generated, $)

Approximate Cost of Materials

(Assuming Net Attic Floor Area of 1,108 ft2, $)

R-19 Insulation 

Over Existing 

R-30 (Level of 

Savings for Each 

Location)

30% by Weight 

Blend of

Microencapsulated 

PCM and R-30 

Conventional 

Insulation, Savings 

Levels for Schedules 

“a” and “b”

R-19 Insulation—

Based on U.S.

RSMeans

Fiberglass, $0.77/ft2

(Cellulose, $0.55/ft2)

Addition of 

Microencapsulated 

PCM at $3.50/lb

(Assuming Enthalpy 

of 82 Btu/lb [190 

kJ/kg])

Atlanta 2.74 (9%) 21.91 (10.65) 853.16 (609.40) 1151

Bakersfield 15.52 (10%) 111.73 (54.31) 853.16 (609.40) 1151

Fort Worth 3.87 (9%) 31.00 (15.07) 853.16 (609.40) 1151

Miami 9.52 (9%) 76.12 (37.00) 853.16 (609.40) 1151

Phoenix 16.93 (9%) 135.43 (65.83) 853.16 (609.40) 1151
56

4 Discussion of Results

4.1 Selection of Climatic Locations

Energy and cost performance analysis presented in this work indicate that successful applications 

of PCM-enhanced building envelope insulations and PCM-enhanced drywall are most likely

possible in southern U.S. locations that fall in ASHRAE climatic zones 1, 2, and 3 with CDDs

(74°F [23.3°C]) preferably greater than 16,667 (30,000).

The local electrical energy cost is equally important. Preferably, on-peak and off-peak electricity 

tariffs should be available in these locations, or the overall electricity price should be higher than

$0.20/kWh. For other locations, detailed energy modeling would be necessary to establish a 

relationship between energy savings and energy costs. 

4.2 Phase Change Material Load Levels in Blends With Thermal Insulations

Remember that initially, PCM-enhanced cellulose insulation was developed with about 22% 

PCM content. In this study, the study team assumed a uniform PCM load level of 30% by weight 

for all applications of the PCM-enhanced fiber insulation investigated. Most of the this study’s 

tests and numerical analyses of the cellulose and fiberglass-based blends mixed with 

microencapsulated PCM, however, were performed for load levels between 20% and 25% by 

weight. As a result, the analysts believe that this study yielded very conservative PCM cost 

predictions and relatively high payback periods. 

Another important fact is the experimental work performed by ORNL, which demonstrated that 

not all PCM in the wall cavity or on the attic floor may undergo a phase transition. Hot-box tests 

have shown that often up to 50% of the PCM content may not be cycling. For precise analysis of 

this process and optimization of the amount of PCM, detailed transient modeling is necessary. 

These computer simulations would need to take into account specific thermal characteristics of 

the PCMs and boundary conditions on both sides of the building assembly containing PCM. 

In summary, the nominal 30% PCM content evaluated in this report was relatively higher than

the configurations tested and analyzed during the last decade. In both situations, it is possible to 

reduce amount of PCM by 25%–50% without significantly compromising the nominal thermal 

performance. For precise optimization of the amount of PCM for each specific building 

application, , the study team recommends detailed transient modeling.

4.3 Phase Change Material Cost Limits

The cost analysis presented in this report indicates that the effective enthalpy of the PCMenhanced building envelope components plays an important role in determining the overall cost 

effectiveness and payback period. Historically, microencapsulated paraffin PCMs with 

enthalpies between 43 and 52 Btu/lb (100 and 120 kJ/kg) have been the most popular around the 

world. This team’s research data presented show that in most of the applications studied, the 

PCM price needs to be below $2.00/lb to achieve a 10-year payback period. At this point, an

imposing question is whether the PCM industry can achieve this price level.

Higher PCM enthalpies result in improved energy performance and cost effectiveness. For the 

locations where PCM-enhanced building envelopes can be paid back within a maximum of 10 

years, the highest acceptable PCM price with enthalpies between 82 and 95 Btu/lb (190 and 220 
57

kJ/kg) should be between $3.50 and $4.00/lb for the microencapsulated product. The best-known 

PCM candidates for these cost levels are biobased PCMs (mixtures of fatty acids and fatty esters)

and low-cost salt hydrates.

The most promising developments to reduce the cost of PCM products are the reduction of 

microencapsulation cost for organic PCMs, and the development of microencapsulation 

technology for inorganic PCMs. Inorganic PCMs are nonflammable and have significantly 

higher enthalpies. The European Union has already recognized the potential for significant cost 

reductions of PCM heat storage. An international program involving most of the European 

research centers working in the area of PCMs—with a focus on encapsulation of inorganic 

PCMs—has been already initiated (see Fraunhofer ISC 2007).

This study’s thermal performance and cost analysis showed that for most locations with a single 

electric tariff, the most critical factor would be the development of PCM-insulation blends that 

would have the highest potential for dynamic load reductions in a desired temperature range. 

Earlier research found that it is very important to optimize a PCM’s concentration, overall heat 

storage capacity, and enthalpy profile to maximize the performance of PCM-enhanced building 

envelope assemblies.

A second important characteristic affecting energy performance and cost effectiveness is peakhour load shifting. This feature is especially important for locations with time-of-use pricing. 

Cost analysis presented in this report demonstrated that it is possible to reduce the cooling 

energy costs by up to 30% with PCM applications of significant peak-hour load shifting 

capability and by taking advantage of the off-peak electricity tariff. In most locations, off-peak

time starts at 7 p.m. Because of this, developing PCM building envelope products with at least a 

5-hour load shifting potential is critical.

The thermal modeling presented in this work showed that high R-value blends of PCM and 

thermal insulation yield significant time-shifting of thermal loads. It is possible during 70% of 

the time (~17 hours a day) to have heat flowing in the opposite direction as a similar assembly 

without PCMs. As a result, a passive cooling effect is caused by this kind of PCM-enhanced 

assemblies during the day. These simulation results have already been confirmed by the fieldtest-generated attic heat flow profiles recorded for the experimental attic containing PCMfiberglass insulation, as described by Kośny and coworkers (2010). It is expected that this 

passive cooling phenomena may significantly enhance the overall cost effectiveness of the 

dispersed PCM applications—well above the cost saving levels described previously. The study

team strongly recommends more research in this area.

4.4 Payback Periods

One of the goals of this work was to investigate the possibility of finding a dispersed PCM 

configuration in a southern U.S. location that would allow 7- to 10-year payback periods for 

building envelopes containing PCMs. In general, the results were encouraging. For the five 

southern U.S. locations analyzed in this work, two locations showed potential to pay back in 7 

years with a PCM price range between $3.00/lb and $4.50/lb. If a 10-year payback period was 

considered, three locations qualified with a PCM price range between $2.00/lb and $4.50/lb. 
58

Earlier research, though, demonstrated that it is possible to reduce the amount of PCM from the 

nominal 30% content used in this analysis, without significant reduction in the PCM thermal 

performance. On the other hand, because of the passive cooling effect, or other positive effects of 

integration with other building envelope components, the overall performance can be notably

higher than the theoretical predictions in this report. The study team also found that a 25% 

reduction in PCM load can lower the payback period by approximately 1 to 2 years, depending 

on the location, PCM type, and cost level. 

From the other perspective, remember that in most building envelope applications, PCMs are not 

always deployed in thermal conditions that a full phase change process. Too-high nighttime air 

temperatures, which keep the PCM melted all night during the summer, are the most common 

reason for the lack of the phase transition. Historical field test data generated in eastern

Tennessee climatic conditions showed that PCMs were cycling about 60%–70% of the total 

number of days. For different locations, additional field testing or detailed dynamic thermal 

simulations of a specific PCM application would be necessary to assess the potential of climaterelated performance reductions.

For the PCM-enhanced gypsum board application in Phoenix, when cost reductions resulting 

from off-peak electricity rates are included, a payback period of 7 years can be expected for 

PCMs with enthalpies between 82 and 95 Btu/lb (190 and 220 kJ/kg) with a price limit of 

$3.00/lb. A 10-year payback period, then, would be possible for a PCM price level that does not 

exceed $3.50/lb. 
59

5 Conclusions

The main purpose of this report was to evaluate the cost levels for simple PCM systems at which 

they can be cost competitive with conventional building thermal insulations. Two basic PCM 

applications were examined in this analysis: dispersed PCM applications and simple building 

systems using concentrated PCMs. The study team reports the following list of findings:

1. Dispersed PCMs in attic and wall applications are an effective means of cooling load 

reductions:

a. Through overall reductions of the attic or wall heat flow rates

b. Through the significant time-shifting of thermal loads.

2. Dispersed PCMs in attic and wall applications can be cost effective and payback periods

for their building applications can be less than 10 years.

3. Southern U.S. locations with CDDs (74.0°F [23.3°C]) preferably higher than 16,667 

(30,000) and an electricity cost higher than $0.20/kWh, or locations with on-peak and 

off-peak electricity tariffs are the best candidates for these applications.

4. Off-peak electricity tariffs significantly improve the overall cost effectiveness of the 

PCM-enhanced building applications

5. Future PCM cost reductions can be achieved through:

a. Applying PCMs of higher enthalpies (around 86 Btu/lb or 200 kJ/kg); the bestknown PCM candidates are biobased PCMs (mixtures of fatty acids and fatty 

asters) and low-cost salt hydrates

b. Reducing the cost of basic raw PCM; for example, by using inorganic PCMs

c. Reducing microencapsulation costs or finding less costly methods of 

micropackaging

d. Developing low-cost methods for microencapsulation of inorganic PCMs

e. Optimizing PCM loads in building envelope products

f. Considering the PCM price; for the southern U.S. locations with a maximum

expected payback period of 10 years, the highest acceptable PCM price should be 

between $3.50 and $4.00/lb for the microencapsulated products with enthalpies 

between 82 and 95 Btu/lb (190 and 220 kJ/kg).

More theoretical and experimental work is necessary to select a proper PCM type for specific 

applications and climatic conditions. 
60

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