New PCM-Enhanced Cellulose Insulation Developed by the ORNL Research Team

Jan Kosny Ph.D 1., Dave Yarbrough Ph.D 1., Ken Wilkes Ph.D., Doug Leuthold

Azam Syad Tennessee Tech

Abstract

This paper is presenting most current developments in research of a new generation of cellulose insulation, which is expected to perform as a building massive component. A thermal mass effect is provided by specially tailored Phase Change Material (PCM). During 2004/05 ORNL team has developed and patented a new generation of cellulose insulation, which was thermally enhanced by addition of microencapsulated PCM. During 2005, first samples of the cellulose/PCM material were produced at the AFT pilot plant. A series of flammability tests were performed to ensure that a new material will not cause fire problems. In aim to measure thermal conductivity, this new material was tested in the heat-flow apparatus. Dynamic full-scale tests in the ORNL hot-box were performed as well. Most current results are discussed in this paper.

Keywords: R-value, Framing Factor, Cavity Insulation, Framing Effect Coefficient, Steel Frame walls, Wood-frame walls

Introduction

During 2004 ORNL established a research team for development of a new type of cellulose fiber insulation, which can thermally perform as a massive component of a building envelope. Since very beginning, this project has been jointly realized by Advanced Fiber Technology (AFT – producer of the cellulose insulation), BASF (global producer of PCM), and ORNL Buildings Envelopes Program (BEP).

Employing cellulose as insulation was first patented in England in 1893. It was used in the US from as early as 1904. More serious application of cellulose insulation dates from the 1920's and came into general use during the post World War II building boom. Cellulose insulation was used extensively in electrically-heated homes during the 1950's, as it was the only insulation that made them affordable to heat. It is an established, time-proven building material. Since it is based on recycled paper, it is well-recognized as an energy-efficient, green insulating product. Fiber glass, rock wool, and plastic insulation may have from 50 to over 200 times more embodied energy than cellulose. In North America cellulose insulation has about 10 to 15% of the residential market. However, in some US regions an application of cellulose insulation is a dominant insulation technique for residential attics.

We expect that a new generation of PCM-enhanced cellulose insulation may have a high potential for successful adoption by the US building market due to:

• Reduction of space conditioning energy consumption.

• Reduction of peak loads, resulting in smaller and less costly energy conversion and distribution equipment

• Improvement of the occupant comfort

• Compatibility to traditional wood and steel framing technologies used in residential and small commercial buildings

• Potential for application in retrofit projects

PHASE CHANGE MATERIALS APPLICATIONS IN BUILDING ENELOPES:

.The main goal of this project was experimental validation of a new type of PCM-enhanced cellulose fiber insulation which combines transient characteristics of PCM with excellent energy performance of conventional loose-fill cellulose. PCMs have been used in buildings for at least thirty years. There were several moderately successful attempts in the 1970s and 1980s to utilize different types of organic and unorganic PCMs to reduce peak loads and heating and cooling energy consumption. Many possible PCMs, including inorganic salt hydrates, organic fatty acids and eutectic mixtures, fatty alcohols, neopentyl glycol, and paraffinic hydrocarbons, were tested for building applications. Historic performance investigations were focused on impregnating concrete, gypsum or ceramic masonry with salt hydrates or paraffinic hydrocarbons. Most of these studies found that PCMs enhanced building energy performance. However, problems such as high initial cost, loss of phase-change capabilities, corrosion, and sweating hampered widespread adoption.

Paraffinic hydrocarbons PCMs generally performed well, except they increased the flammability of the system. For example, Kissock et al. (1998) reported that wallboard including a paraffin mixture made up mostly of octadecane, which has a mean melting temperature of 24 C (75 F) and a latent heat of fusion of 143 kJ/kg (65 Btu/lbm), “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.” In addition, Salyer and Sircar (1989) reported that during tests of 1.22 m (4 ft.) x 2.44 m (8 ft.) wallboard with PCM there was no statistically significant loss of PCM or "pooling" even after three months of exposure to continuously cycled 37 C (100 F) air.

The ability of PCMs to reduce peak loads is well documented. For example, Zhang and Medina (2005) found peak cooling load reductions of 35% to 40% in side-by-side testing of conditioned houses with and without paraffin PCM inside the walls. Similarly, Kissock et. al, (1998) measured peak temperature reductions up to 10 C (18 F) in side-by-side testing of unconditioned experimental houses with and without paraffin PCM wallboard.

In traditional applications, PCMs were utilized to stabilize the temperature of the interior of the building. Thus, the best location for the PCM was the interior surface of the wall, ceiling, or floor. In our project, the PCM-enhanced cellulose insulation is positioned in the wall cavity or it is installed as attic insulation. This placement should significantly reduce flammability issues which were common in earlier technology developments.

PRODUCTION OF PCM-ENHANCED CELLULOSE INSULATION:

The most common starting material for the production of cellulose insulation is recycled paper grade 8. The input paper stream is subjected to mechanical size reduction steps which produce small bits of paper in the size range around 1/8th inch. Coarse shredding of the incoming paper is followed by high-speed fiberization. As a result cellulose fibers of the size between 20 to 30 microns are obtained. Chemical additives provide resistance to combustion, corrosion and fungal growth. The manufacturing process for cellulose insulation generally involves three major steps: size reduction, the addition of chemicals, and packaging - see Figure 1. In the few cases involving the addition of liquid chemicals, a drying step precedes the packaging step.

Figure 1. Production process of cellulose insulation.

There are at least three types of cellulosic products in use at this time. Conventional loose-fill cellulose insulation is used in closed cavities and attic spaces. Stabilized cellulose, which is loose-fill material with adhesive added to provide inter-particle bonding and resistance to settling after installation, is used for attic floor applications. Self-supporting, wet-spray cellulose is applied directly to horizontal and vertical surfaces.

To reduce project costs, for the research purposes, small amounts of different cellulose-PCM blends were produced with the use of the AFT pilot line. Using this small-scale technology ORNL team was able to experiment with different amounts of PCM added to the cellulose fibers. As shown on the Figure 2. this pilot line is a miniature of the full-scale production facility. On the pilot line all components were separately measured and manually added to the cellulose.

Figure 2. Advanced Fiber Technology pilot line for production of cellulose test samples.

In this project microencapsulated PCM –Micronal 5001X produced by BASF was utilized. Micronal is produced with the use of a new microencapsulation technology that holds microscopic wax droplets inside hard acrylic polymer shells. The small, 2 to 20 micrometer sized microcapsules melt at 78.5 oF. Since production of cellulose insulation already includes the addition of dry chemicals, the addition of a dry PCM component doesn’t require significant changes in the manufacturing or packaging processes.

Figure 3. Smoldering Combustion Tests (ASTM C739) of the cellulose-PCM blend.

 Cellulose insulation with added PCMs, like conventional cellulose insulation, must demonstrate resistance to smoldering and pass other flammability tests. During 2005

A series of the Smoldering Combustion Tests (ASTM C739, Section 14) was performed on samples of cellulose insulation containing 5% to 30% of the microencapsulated PCM. As shown of Figure 3, fire was introduced to the test sample by means of standard cigarette. This test method covers the determination of smoldering combustion potential within fiber-based insulations. All cellulose- PCM blend passed the ASTM C739 test – in all samples less than 1% loss of the mass of the cellulose insulation was observed.

AMOUNT OF PCM IN CELLULOSE AND THERMAL CONDUCTIVITY TESTING:

The addition of dry PCM can be accomplished on existing manufacturing lines where other dry chemicals are added. As shown on the Figure 4, amounts of PCM can be monitored with the use of the Scanning Electron Microscope (SEM) technology.

Figure 4. Scanning Electron Microscope images of cellulose insulation.

Figure 5. Thermal conductivity of PCM-enhanced cellulose as a function of the temperature.

Density of the cellulose-PCM mixture is primarily a function of field application parameters. Currently, ORNL team is working on two recipes for PCM-enhanced cellulose insulation:

1. Wall application: density about 3.0-lb/ft 3, wet application technique, 30% of PCM, 70% of cellulose by weight.
2. Attic application: density about 1.6-lb/ft 3, dry application technique, 25% of PCM, 75% of cellulose by weight.

Figure 6. Results of dynamic heat-flow apparatus experiment and computer modeling.

During 2004/2005 a series of steady-state heat-flow apparatus (ASTM C-518) thermal conductivity measurements were conducted on the 2-in. thick samples of PCM-enhanced cellulose insulation. Thermal conductivity of this material was estimated as a function of the temperature – see Figure 5. For 75 oF thermal conductivity of PCM-cellulose blend is 0.269 – exactly as much as it was tested for the plain cellulose. These test results proved that addition up to 30% of the microencapsulated PCM doesn’t compromise thermal conductivity of the cellulose insulation.

Next, 12x12-in. 2-in. thick samples of PCM-enhanced cellulose insulation were used for dynamic heat-flow apparatus experiment. At the beginning of the measurement, temperatures on both surfaces of specimen were stabilized at 75 oF. Next, temperature of the lower plate was increased to 145 oF. Test results are shown on the Figure 6 as solid and dashed lines. Two finite difference computer models were next utilized to simulate PCM-enhanced cellulose insulation – dotted lines. A very good agreement between experimental data and simulation results was achieved. The space between lines representing cellulose-PCM blend and plain cellulose characterizes a potential for energy savings, which can be generated by PCM during dynamic changes of temperature.

Dynamic Hot-Box Experiment

Next, 8x8-ft wood-framed wall specimen was utilized for dynamic hot-box testing. Test wall was constructed with 2x6 studs installed with 16-in. spacing. Three wall cavities were insulated with plain cellulose of density about 2.6 lb/ft 3. Remaining three wall cavities were insulated with cellulose-PCM blend of density about 2.6 lb/ft 3 and containing about 22% by weight of PCM. It is estimated that about 38-lb of PCM-enhanced cellulose insulation (containing 8-lb of PCM) was used for this dynamic experiment.

At the beginning of the measurement, temperatures on both surfaces of specimen were stabilized at about 65 oF on the cold side and 72 oF on the warm side. Next, temperature of the worm side was rapidly increased to 110 oF. Test-generated heat flux results are shown on the Figure 7 for both parts of the wall.

Figure 7. Heat flux measured during the dynamic hot-box experiment.

It took 15 hours to fully charge the PCM material within the wall. Heat fluxes on both sides of the wall were measured and compared. For 5-hour time intervals heat fluxes were integrated for each surface. Comparisons of measured heat flow rates on the wall surface opposite to the thermal excitation enabled approximate estimation of the potential thermal load reduction generated by the PCM. Most of thermal excitations generated by climate are not longer than 5 hours (peak hour time). It was measured that during first 5-hours after the thermal ramp period, PCM-enhanced cellulose material reduced the total heat flow through the wall by over 40%. A similar load reduction for the entire 15 hours of the PCM-charging time was close to 20%.

Conclusions

During 2004-2006, joint ORNL-AFT-BASF research team developed and tested a new type of cellulose fiber insulation containing PCM. The following series of conclusions can be derived from the above research work:

1. ASTM C-518 tests demonstrated that the addition of 30% of PCM to the cellulose fibers did not show negative impact on the R-value of the insulation
2. Smoldering Combustion Tests (ASTM C-739) proved that the cellulose-PCM blend did not compromise the fire resistance of the material.
3. Dynamic heat-flow apparatus tests were performed on 2-in.-thick samples of the cellulose insulation and cellulose-PCM blend containing 30% of PCM. Heat flow analysis confirmed thermal mass effect in the PCM-enhanced material. Results were used for calibration of two computer models. Good agreement was achieved
4. Dynamic hot-box test, with included 40 oF thermal ramp, was performed on 2x6 wood-framed wall insulated with cellulose insulation containing 22% of PCM. Dynamic hot box test demonstrated about 40% reduction of the surface heat flow due to the application of PCM. It took about 15 hours to fully charge PCM-enhanced cellulose insulation.

References

- ASTM, “ASTM C518, Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus.”

-ASTM, “ASTM C739, Standard Specification for Cellulosic Fiber Loose File thermal Insulation.

- Feustel, H. E. (1995). Simplified numerical description of latent storage characteristics for phase change wallboard. Indoor environmental program energy and environment division Lawrence Berkely Laboratory University of California.

- I. Salyer and A. Sircar, "Development of PCM Wallboard for Heating and Cooling of Residential Buildings," pp. 97-123, Thermal Energy Storage Research Activities Review, U.S. Department of Energy, New Orleans, LA, March 15-17, 1989.

- J. Tomlinson, C. Jotshi and D. Goswami - "Solar Thermal Energy Storage in Phase Change Materials,” pp. 174-79, Proceedings of Solar '92: The American Solar Energy Society Annual Conference, June 15-18, 1992, Cocoa Beach, FL.

- J Kelly Kissock, J Michael Hannig, Thomas I. “Testing and simulation of phase change wallboard for thermal storage in buildings”. In proceedings of 1998 International Solar Energy Conference, 14 - 17, June, Albuquerque, Morehouse J M and Hogan R E(Eds. ) ASME, New York

- J. Kosny, D. Gawin, and A. Desjarlais - 2001 “Energy Benefits of Application of Massive Walls in Residential Buildings” .DOE,ASHRAE, ORNL Conference -Thermal Envelopes VIII, Clear Water, Florida - Dec. 2001.

- Zhang, Meng, Medina, M.A., and King, Jennifer, "Development of a Thermally Enhanced Frame Wall With Phase-Change Materials for On-Peak Air Conditioning Demand Reduction and Energy Savings in Residential Buildings." International Journal of Energy Research. Vol. 29, No. 9, (2005) pp. 795-809.

LIST OF FIGURES

FIGURE 1	Production process of cellulose insulation.
FIGURE 2	Advanced Fiber Technology pilot line for production of cellulose test samples.
FIGURE 3	Smoldering Combustion Tests (ASTM C739) of the cellulose-PCM blend.
FIGURE 4	Scanning Electron Microscope images of cellulose insulation.
FIGURE 5	Thermal conductivity of PCM-enhanced cellulose as a function of the temperature.
FIGURE 6	Results of dynamic heat-flow apparatus experiment and computer modeling.
FIGURE 7	Heat flux measured during the dynamic hot-box experiment.

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© 2006 Oak Ridge National Labs
Updated Sept 15, 2006 by Brett Carmichael