Phase Change Materials (PCMs) can decrease facility envelope heating/cooling loads when utilized in thermally massive components. Facades, insulations, and interior walls can all be formulated with PCMs, which makes them more insulative to their environments. This reduces the cooling and heating loads for the building, which has an immediate reduction in both Scope 1 carbon emissions from lowered boiler loads, and Scope 2 carbon emissions from reduction in electrical demand for chillers. Generally, reducing building envelope loads through different construction materials is one of the simplest paths to decarbonization for both new construction and retrofitted buildings.

Figure 1. Relative Storage Capacities

PCMs allow a wide range of service temperatures, from freezing to beyond boiling. Thermo-chemical materials, also known as TCMs, allow energy transfer during some chemical reaction. PCMs are chemically simpler and safer to use. In Figure 1, notice that the storage capacity of TCMs is far above water as well, which is typically used as an energy storage media.

Technical Description

Phase Change Materials (PCMs) leverage high latent energy required for a material to change phase from a solid into a liquid or vice versa. Just as when ice melts when exposed to an environment warmer than freezing, the temperature for the material remains relatively constant. This makes them an excellent thermal storage media, as they can provide large amounts of thermal energy at consistent temperatures. In the AEC industry, PCMs are being integrated into numerous building envelope materials including gypsum boards, concrete mixes, plaster blends, and window attachments.

Design considerations

PCMs can be carefully selected based on the desired heat transfer temperature. Organic and non-organic materials are available, including ice. In order for adequate heat transfer to occur, the ambient temperature must be consistently above the melting temperature.

Control strategies

PCMs for load shifting should be treated like other thermal energy storage systems. PCMs for load shifting are especially suited for daily temperature cycles, and when daily loads are consistent. If used for conditioning of air or water, the fluid must be at a different temperature than the melting temperature for the PCM.

Best practices

Load shifting thermal storage within the building envelope is the most beneficial application. This is similar to the sensible thermal storage which takes place in concrete buildings. The inside stays relatively cool due to the large thermal mass, and wall temperatures remain warmer at night as it discharges.

Figure 2. Examples of Materials

Some inorganic materials used can be flammable, and this should be taken into consideration for selection of the material and siting for the storage.

How does this decarbonize?

PCMs decarbonize by reducing peak cooling and heating energy demand. They act primarily as a load shifting media. During off-peak times, which typically occur at night when ambient conditions are cooler, the thermal energy can then discharge into the atmosphere. This load is therefore never seen by the cooling system which can trim the chiller peak load by 10-15%. Heat load savings are largely dependent on the PCM melting temperature, and ideal space temperature. With the PCM active, heating energy can be decreased by 5-10%.

Implementation

Barriers: Culture

PCM-infused building materials are still relatively new, and as such they don’t have a proven successful track record yet. Most demonstrations exist at the research level. This technology will be much more economically viable in the years to come.

Strategy

In regards to the physics involved, the goal of PCM is to add thermal mass to a space. PCM can be used in any building materials, regardless of its relative location in the space. Interior walls, paneling, and flooring can all utilize some PCM in their formulation. This offers distributed temperature modulation, rather than from a single source.

The Department of Energy (DOE) and California Energy Commission (CEC) can provide additional funding for pilot projects for PCMs in building materials.

Financial analysis and business case

Once PCM infused building materials are widely available, building owners can compare the cost and energy savings versus traditional materials.

Utilizing BioPCM in ceiling plenums above 42% of existing occupiable space in a medical office building (for 10,770 sf of product), resulted in reduced HVAC energy loads. Overall, the energy savings allowed for an ROI of only 2.25 years.

Figure 3. BioPCM Blanket Above Ceiling Tiles

Full energy model of an existing house found that for a case study in Canada, 5% heating energy savings in the winter and 50% cooling energy savings in the summer was calculated. The difference in heating and cooling savings is due to the relation of wall temperature, and the melting-point of the PCM. For a lower melting-point PCM, the phase change would happen more readily, and heating energy savings would improve. It was shown to decrease zone temperature oscillations which improves thermal comfort. The house was 1,130 sf of living area, built to typical 1970’s Canadian construction standards. The energy model was first validated against real-world energy data, then the envelope was modeled using building materials with “PCM 23”, the composition of which is proprietary information. The research team was provided physical properties by the vendor.