Mitigating envelope-related energy losses has been at the forefront of the Department of Energy (DOE) and the Department of Defense (DoD) High Priority Performance Goals since the Energy Independence and Security of 2007 (EISA 07). This project sought to explore the impacts of using unique thermodynamic properties of Phase Change Materials (PCM). In this demonstration the PCM was integrated into standard insulation products commonly used to control heat transfer through building envelopes. This project incorporated PCM to enhance the effective “R-value” of insulation, thus reducing energy transfer through the ceiling, while maintaining comfortable temperatures for the building occupants.
The specific objective of this demonstration was to show that by using PCM, significantly less energy is required to maintain comfortable temperatures in a specific building space. It was designed to compare using PCM insulation installed under the roof deck, on gables and on knee walls to (1) cellulose insulation under the roof deck, on gables and on knee walls and (2) the currently used fiberglass insulation only on the attic floor.
The data to analyze the performance objectives was tracked for (1) the existing condition baseline, (2) the new insulation configuration baseline and (3) the new insulation configuration using PCM. Success criteria in Table 1 compare the new insulation configuration without PCM and the new insulation configuration with PCM to the existing R-19 fiberglass batt insulation. Cost calculations compare the cost of installing 3,500 sq. ft. of fiberglass batt insulation on the attic ceiling to the cost of the new insulation configuration without PCM and with PCM. Except for the Reliability goal, none of the goals using the PCM were attained.
Table 1: Summary of Performance Objectives Success Criteria
The PCM enhanced insulation demonstrated is made by combining cellulose insulation with hard shell polymer microcapsules (2-20 microns in diameter) that contain organic fatty acids and fatty acid esters as core materials. The core materials change phase from solid to a liquid or semi-liquid to prevent excessive heat flow and maintain comfortable temperatures; they exhibit a “thermal mass effect,” i.e., capacity to store energy, as latent heat. The latent heat is released back into the building when the temperature drops at night. The innovative PCM–insulation technology was expected to enhance energy efficiency in heating and cooling buildings in moderate climates, by reducing excess sensible heat in the summer and reducing heat loss in the winter. For this project, Phase Change Energy Solutions (https://phasechange.com/) was the selected manufacturer of the PCM. The product selected for the demonstration contains the phase change material enclosed between a polymer layer and a foil layer and can be rapidly applied in large sheets.
The building was monitored for approximately two years prior to installing the PCM-enhanced insulation – Phase 1 monitored the building in its baseline condition with standard R-19 fiberglass insulation on the attic floor. Phase 2 monitored the building with cellulose insulation installed under the roof deck, on gables, and on knee walls. The two sets of baseline data were used to help in determining the effectiveness of the PCM insulation and specifically isolate its the impact. Using lessons learned in Phase 2 a change of the PCM was made to an alternative PCM technology, BioPCMats. This change was expected to improve the quality of the demonstration by using materials that have suitable ruggedness and durability and would decrease labor costs and enhance the potential for rapid technology transfer.
ERDC-CERL and ORNL measured the energy benefits of the retrofits with cellulose-only insulation and PCM-enhanced insulation by installing a suite of instruments in the attic. Four instrumentation packages consisting of a heat flux transducer, five thermistors, and two relative humidity sensors were installed under the roof deck. The packages were selectively located under the roof deck while additional measurements of outdoor temp, roof outdoor surface temp, roof under-deck temp, attic space temp (which will be semi-conditioned after install of PCM-insulation), and indoor temp were tracked. The collected data sets were analyzed and modeled using various industry standard packages.
The demonstration cost analysis was performed using the National Institute of Standards and Technology (NIST) Building Life-Cycle Cost (BLCC) Program for MILCON Analysis (ERCIP Project) to determine the LCC. Existing annual consumption of energy for the HVAC system on typical building such as Building 3-2232 (DPW Classroom) is 16,000 kWh. The cost of this new technology is $3,480 more than the alternative of using conventional insulation.
Since energy consumption data actually showed an increase between phases two and three of the project, no cost savings were achieved by the installation of the PCM. The expected cost savings would have been achieved through the reduction in electrical energy to operate a heat pump that maintains comfort level within the demonstration building. This indicated that using this particular PCM product would not save energy or O&M dollars in this situation. It is potentially possible that the PCM technology might be cost effective in a different climate zone with different temperature gradients.
Another ESTCP project demonstrated a related Phase Change Energy Solutions technology designed for large-scale thermal energy storage for electrical demand reduction and peak shaving. These results are more promising and more information can be found on the project page (EW-201514).
The results of this demonstration showed the sensitivity of the PCM material to the climate region temperature ranges. The demonstration site temperature stayed above the melting point for months at a time so the PCM remained liquid and in the winter the attic temperature was below the freezing point, keeping the PCM solid. The unique thermodynamic properties (benefits) of the PCM were not utilized each night since for significant periods of time the attic temperature did not cross the freeze thaw boundaries. The PCM was rendered ineffective. There were very few days in which the PCM completely changed phases to provide benefit to the building. Energy consumption of the building increased during phase 3 of the demonstration, PCM with cellulose phase, when compared to the cellulose only phase.
Additionally, elevated humidity levels were also observed between the roof deck and the PCM layer following the phase 3 retrofit. During a portion of the year the average humidity remained above 80% for greater than 30 days. This duration could potentially cause problems with the roof deck structure. This moisture concern along with lack of any measurable energy benefits led to the removal of the PCM layer at the completion of the demonstration.