Phase change materials
Published: February 12, 2014
- BENEFITS & BARRIERS
Phase change materials (PCM) are thermal energy storage materials that can replace traditional insulation in buildings. PCMs act as an energy storage device, storing heat energy through the phase change from solid to liquid when there is excess incident heat energy, and releasing the energy as the material transitions from a liquid back to a solid as the room cools. As the temperature rises during daytime hours, the PCM material melts, absorbing thermal energy. As the temperature falls in the evening, the material re-solidifies, releasing the thermal energy stored during the day. Most materials exhibit a phase change process, but the types of materials that are appropriate as a building insulation material are limited to those that have a melting temperature around room temperature as liquid-gas.
PCMs can be installed in walls or flooring and provide reductions to cooling and heating energy usage as well as improved thermal comfort in buildings. A building space with PCM installation experiences a smaller range of temperature fluctuations during the daytime hours, improving the comfort level of the building. The space also sees a reduction in the peak cooling load required, and an offset of this load to later times. The peak load offset can have external benefits if time-of-day rates are utilized. This shift in peak load could potentially be beneficial from a utility perspective as it decreases the maximum power generation capacity required.
There are a number of important considerations related to the selection of material in a PCM application. The optimal material selection depends on a number of factors including the specific climate requirements, cost, availability, building design and layout, etc., and is heavily dependent on the specific application. Among the commercially available PCMs, the physical and thermodynamic properties can vary significantly. Significant consideration should be applied to the selection of the optimal phase change material.
We want to acknowledge our appreciation for the efforts of Tim Lindstrom, Nick Funk, and Dan DelVescovo (students at UW-Madison) for their involvement in the research of this technology
Phase change materials have applications in both the residential and commercial sectors. Wall based PCMs are the most attractive from a residential perspective as floor based PCM is reliant upon incident sunlight to increase performance. Residential PCM installations have the ability to integrate with passive solar systems for even greater energy savings potential. PCM is predominantly relegated to new construction to maximize the efficiency of the system as a whole. The building layout and PCM installations can then be optimized for the specific climate conditions and access to incident solar energy to maximize the energy savings and load reduction. PCM is most applicable to new residential and commercial builds as replacing existing insulation is unlikely to be economically attractive without strict building efficiency mandates, subsidy programs, or significant rebates.
Passive temperature control of the space: PCMs offer a potential for reduction of mechanical heating or cooling needs because the materials passively modulate the temperature throughout the day. The amount of reduction is highly dependent on the design of the system and how the space is being used.
Peak load reduction or load shifting: Because of the passive heating or cooling of the space, a building can shift its mechanical load to another time of day or reduce it absolutely. This may offer a benefit to utility companies looking to transfer peak demand to other times of day.
Increased comfort in the space: Due to PCMs ability to reduce fluctuations in temperature, comfort level may increase in spaces that have PCM materials.
Challenges and market barriers
Cost: Because the technology is so new and very few buildings have PCM incorporated, the cost for design and installation is very high. The main costs are derived from design considerations, such as material selection, refinement of target temperatures for the PCM, and orientation of building and interior layout to maximize the PCM.
Lack of knowledge: The design and engineering community are just now gaining some understanding of PCM's possibility, but the knowledge transfer is very slow, especially given the complexity of design for PCMs.
Most applicable to new construction rather than retrofit: PCMs need to be incorporated into the heating and cooling design load, as well as the spatial orientation of the building to optimize for the specific climate conditions and access to incident solar energy, making them less applicable to retrofit applications.
Materials used as PCM in thermal energy storage in buildings: A review
summary Using phase change materials for thermal energy storage has become a topic of interest recently within the research community, and with architects and engineers. This paper reviews the latest publications on the use of phase change materials in buildings. It includes information about the requirements for using this technology, classification of materials, materials available and problems and possible solutions when applying these materials in buildings.
citation Cabeza, et al. (2011) “Materials used as PCM in thermal energy storage in buildings: A review” Renewable and Sustainable Energy Review
Use of Phase Change Material in a Building Wall Assembly: A Case Study of Technical Potential in Two Climates
summary The use of PCM energy storage was modeled for two climates: Phoenix and Baltimore. The purpose was to identify the optimal installation configuration and potential savings, as well as the economic benefit under two different utility rate schedules.
citation Childs, K and T. Stovall (2012) “Use of Phase Change Material in a Building Wall Assembly: A Case Study of Technical Potential in Two Climates” International High Performance Buildings Conference. Purdue University e-Pubs.
Review on thermal energy storage with phase change materials (PCMs) in building applications
summary This paper presents a summary of the research on latent thermal energy storage in building applications, including PCMS, thermal performance analyses and building simulations.
citation Zhou, D. et. al (2011) “Review on thermal energy storage with phase change materials (PCMs) in building applications” Applied Energy vol 92.
The Capabilites and Barriers of Incorporating Phase Change Material into Residential Building Design in Sydney, Australia.
summaryThis article presents the results of an analysis of studies on the characteristics and performance of PCMs and the optimal conditions for integrating them into residential buildings.
citation “The Capabilites and Barriers of Incorporating Phase Change Material into Residential Building Design in Sydney, Australia. ” International Journal of Engineering Practical Research (IJEPR) Volume 2 Issue 4, November 2013.
Cost Analysis of Simple Phase Change Material-Enhanced Building Envelopes in Southern U.S. Climates
summary This report outlines results from an economic analysis evaluating the cost-effectivness of applying PCMs in building envelopes. The researchers determined the target cost levels at which PCMs can financially compete with conventional thermal insulation, using two types of PCMs: dispersed PCM and simple building board products that include PCMs.
citation Kosny, J. et al. “Cost Analysis of Simple Phase Change Material-Enhanced Building Envelopes in Southern U.S. Climates ” Department of Energy, Building Technologies Program. January 2013.
Phase change material case studies from Phase Change Energy Solutions
summary Phase Change Energy Solutions is a manufacturer of PCMs and currently has a number of PCM installations. This project gallery highlights both commercial and residential projects that have incorporated PCM into the design. Each case study has a link which provides more detail on the project, including photos and key aspects of the project design.
citation “Phase change material case studies” Phase Change Energy Solutions
link http://www.phasechange.com/index.php/en/project-gallery, accessed June 20, 2015.