by J Kosny · 2013 · Cited by 91 — fpl/rates/pdf/Residential.pdf. Fraunhofer ISC – “Annual Report” – Fraunhofer-Institut für Silicatforschung ISC,- Würzburg,. Germany, 2007.
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ii NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, subcontractors, or affiliated partners makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 -0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:reports@adonis.osti.gov Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
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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: Cambridge, MA 02141 NREL Technical Monitor: Chuck Booten Performed Under Subcontract No. KNDJ -0-40345-00 January 2013
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iv Contents List of Figures v List of Tables vii Definitions . viii Executive Summ ary .. 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 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 ..14 3 Whole- Building Energy Simulations ŠTheoretical 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 38 3.5 Potential Cost Savings Associated With Phase Change Material Load Reductions in Phase Change Material – 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
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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 T i = 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 fiafl 149°F (65 °C) in schedule fib,fl and 185°F (85°C) in schedule ficfl 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 fia,fl 149 °F (65 °C) in schedule fib,fl and 185 °F (85 °C) in schedule ficfl .. 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 fia,fl 149 °F (65 °C) in schedule fib,fl and 185 °F (85 °C) in schedule ficfl .. 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 fia,fl 149 °F (65 °C) in schedule fib,fl and 185 °F (85 °C) in schedule ficfl .. 28 Figure 11. Reductions of heat gains calculated for the two thicknesses of the building envelope assemblies. For each material configuration and at internal te mperatures Ti, heat gains represent heat fluxes integrated over the time period. 29 Figure 12. Payback periods for the PCM -enhance d 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 fiafl and fib.fl 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 fiafl and fib.fl . 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 fiafl and fib.fl . 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 fiafl and fib.fl . 36 Figure 16. Payback p eriods 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 fiafl and fib.fl . 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 fiafl and fib.fl .. 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 fiafl . 41
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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 fia.fl . 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 fia.fl . 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 fia.fl . 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 fia.fl . 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 fia.fl . 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 fiafl 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 fia.fl . 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 Bakersfie ld. Wall assemblies are assumed to experience the external temperature schedule defined as fia.fl . 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 fia.fl . 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 hous e in Miami. Wall assemblies are assumed to experience the external temperature schedule defined as fia.fl . 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 fia.fl . 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 ra nch house in Phoenix. Wall assemblies are assumed to experience the external temperature schedule defined as fiafl 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 tem perature schedule defined as fiafl and an off -peak tariff is used. . 53 Unless otherwise noted, all figures were created by Fraunhofer.
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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, Refrigerati ng and Air -Conditioning 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 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
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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. T his 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 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 competiti ve 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 ™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 envelope s. The study team used these results as performance benchmarks for diffe rent 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 insulatio n 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 p erformance 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 assembl y and 11.8- in. (0.3- m) savings perspective, the thinner wall assembl y containing PCMŒinsulation blends (5.5 -in. thick) achieved a lower reduction in cooling loads (by three to five times) than the thicker attic floor assembl y (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 coo ling 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 assembl y also resulted in significant reductions of the total load. Moreover, the thi cker 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. n 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 fipassivefl cooling of internal spaces, reducing air- -enhanced
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x attic i nsulation, 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 thick er assembly lower s the amplitude of ext erior 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 – 2°C) diffe rence). Numerical analysis demonstrated that these reductions can be at least four times larger than those seen in the case with 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 recommend s 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 fac e the interior of the building depend on HVAC systems or overnight pre-cooling to remove heat absorbed by PCM during the day. 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. n this work , 15% cooling energy savings was considered for the PCM-enhanced gypsum board applications. -enhanced 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 cost s. the study team analyzed s everal potential methods for future cost reduction s for PCM -enhanced building applications. In particular, from a material s perspective , development of the following technologies could play a key role in reducing PCM price s 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 funding the U.S. PCM research program. This project was made possible by direct cofunding
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1 1 Introduction Phase change process involves transforming a material from one phase (solid, liquid, or gas) into 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 temperat ure changes of ~10 K. The difference could be one to two orders of magnitude example, the latent heat of melting ice to water at (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, radia nt 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 pa st 40 years, and most studies have found that PCMs enhance building energy performance. Some p roblems, though, such as high initial cost, loss of phase change capability, corrosiveness (in case s of some inorganic PCMs), and PCM leaking have hampered widespread adoption. Paraffinic hydrocarbon PCMs generally perform well, but they increase the flammab ility of the building envelope ( Kissock et al. 1998; Tomlinson et al. 1992; Salyer and Sircar 1989). 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 develop ment of PCM integrated with thermal insulations was a critical step ( et al. 2006) . PCM -enhanced cellulose was one of the first successful developments of this kind of product in the building arena ( et al. 2007). Subsequently, researchers developed PCM s blend ed with blown fiberglass ( et al. 2010) and plastic foams et al. 2008; Mehling and Cabeza 2008). The m ajor advantage of PCM- enhanced insulations is their
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