Phase Change Materials (PCMs) PCM materials offer a high energy density by utilizing a solid-liquid phase transition to store energy at a constant temperature. PCMs store thermal energy in the form of latent heat and provide maximum energy performance with minimal impact on the environment.
Latent heat is typically 100 times higher than sensible heat capacity. Latent heat energy storage (LHES) system PCMs are well known for its excellent thermal energy storage and release during melting and solidifications respectively, and are a key solution for the implementation of renewable energies. Less material is required to store the same amount of heat, which reduces the need for high contact area or a high thermal conductivity.
Markets
A wide range of PCMs have been developed including organic (paraffins and fatty acids), inorganics (salt hydrates and metallic) and eutectic combination of organic and/or inorganic materials. PCMs can be efficiently deployed in applications where significant temperature difference exists in the system for intermittent thermal energy storage.
PCM products are used to improve whole-building energy efficiency in retail, commercial, hospitality, and industrial applications; enable safe transport of sensitive food and pharmaceutical products; and provide enhanced thermal storage capabilities for industrial and commercial processes, among other applications.
Markets where PCMs are applied include:
- buildings for thermal management.
- cement and pavements.
- heat pumps.
- electronic devices.
- solar power plants.
- cooling vests and clothing in medical and textiles.
- thermal management in electric vehicle batteries.
- thermal batteries.
- refrigerated packaging and transport.
Organic, biobased phase change materials
Paraffin and non-paraffin organics are ideal phase change materials because they melt and freeze congruently (i.e. have the same composition before and after freezing) and can therefore be used for applications requiring material stability through several cycles. Paraffins, which are alkanes or saturated hydrocarbons, are inert phase change materials. Non-paraffin organics, other than fatty acids, are mildly corrosive and are more expensive than paraffin materials.
Organic wax PCMs offer the advantages of high latent heat capacity (usually between 170 – 220 kJ/kg), sharp thermal transitions, minimal supercooling, reliable thermal properties and long-term stability. Another advantage is the range of phase change temperatures available, which can meet most applications excluding very high temperatures.
Organic PCMs such as saturated fatty and carboxylic acids and other non-paraffin organics (esters, alcohol, glycols, etc.) are promising PCMs in the low-temperature range. Fatty acid esters, fatty alcohols and even paraffins can be derived from plant lipids or animal fats. These types can be considered to be renewable and may be referred to as “bio-based PCMs”. Fatty acids are easily producible from common vegetable and animal oils and thus provide an assurance of continuous supply.
Salt hydrates
Salt hydrates are inorganic substances (oxides, carbonates, sulfates, and nitrates) composed of ionic salts with crystal phase structures incorporating water molecules (“water of crystallisation”). Pure substances can have high heat capacity, relatively high density and therefore high volumetric heat storage capacity. Many commercial salt hydrate products, however, are carefully formulated to achieve a suitable operating temperature and to overcome shortcomings, notably a tendency to supercool and physical instability.
The latter arises if the formulation melts incongruently i.e. where the crystalline solid phase melts to a mixture of solid and water (rather than a “clean” solid to liquid transition). The dense solid phase may be prone to sedimentation over time and additives such as inorganic or polymeric gelling or thickening agents can be used for stabilisation. This is essential as separation would lead to a gradual reduction in the concentration of the “active” PCM component and deterioration in the thermal transition properties.
Metal and metal alloy PCMs
Low melting metals and metal alloys PCMs are under-utilized due to the low latent heat and weight penalties. Metals used in low temperature applications are cesium, gallium, indium, tin and bismuth, while the metals for high temperature applications include zinc, magnesium, aluminium and their alloys.
Automotive
Although at an early stage of development, PCMs are attractive for the automotive industry for resolving energy and regulatory challenges for HVAC, and cooling systems for high-energy storage density vehicle (EV) battery stacks. PCMs can also minimize temperature variations in electronic devices and accumulators and can keep such components in an optimum temperature range.
Buildings
There is an ongoing need to improve the energy efficiency of buildings and reduce energy usage. Energy consumption reduction under varying climate conditions is a major challenge in buildings design, where excessive energy consumption creates an economic and environmental burden. Building heating and cooling account for over 30 percent of the total residential electricity demand globally .
Improving thermal performance of the buildings through the application of PCMs can improve the energy efficiency of heat and cold supply in the building sector. Using PCMs, excess heat above a certain set temperature can be stored, maintaining the ambient temperature at a constant value during the day. At night, this heat stored in these materials can be used for keeping homes warm and for other purposes. Several uses of PCMs already exist in building materials, such as in drop ceilings, metal roofs and stud walls.
PCM wallboard placed on the inner side of the building envelope is the most common application of PCM in buildings, as a passive heating or cooling strategy. PCMs can be packaged in micro- or macro-encapsulated cells for application in interior wall construction (adjacent to insulation and wallboard), between attic joists, above ceiling panels in a drop ceiling, or integrated directly within wallboard, ceiling panels, and floor tiles. The addition of the material above the ceiling grid creates a heat barrier that the PCM will maintain until all of the PCM has fully changed phases. This added benefit reduces the heat transfer from the space above the ceiling grid into the conditioned space.
Advanced building skins composed of building integrated photovoltaic (BIPV) systems have also employed paraffin to control PV temperature and reduce heat gain in buildings. The thermal energy stored in paraffin behind the PV can be utilized in various temperature ranges by an appropriate selection of a paraffin melting point.
Electronics
Thermal management is an essential and ongoing issue for electronics device operation. Removing generated heat has been traditionally carried out via conduction and convection techniques. However, as devices get smaller and more powerful, this becomes more difficult. PCMs absorb energy during power-on operation and other pulse or peak usages, keeping the device at a protected and stable temperature. Since PCMs have high energy absorption, a small volume of material is able to store a large amount of energy. PCMs can stabilize overall temperature of the device and protect it from failure during high demand operations. In addition, PCMs absorb and release this energy for thousands of cycles.
Temperature-controlled shipping
PCMs are commonly used in combination with water-based refrigerants (or by themselves) within insulated shipping containers. To increase the duration of thermal control within a given temperature range, PCMs are normally selected such that their phase change temperature is within the required temperature range of the product being shipped (i.e. +5°C PCM is used to meet a +2°C to +8°C temperature requirement). Use of PCMs allows for smaller, lighter (reduced freight) thermal packaging designs that outperform their water-based counterparts.
Commercial refrigeration
Transport and storage of temperature sensitive products are the main focus of research and commercial applications of PCMs in the temperature range between -20°C and 5°C. PCMs can be integrated in refrigerated trucks, food packaging and medical product, for better thermal buffering capacity to enhance the thermal protection of perishable products. PCMs used for Cold Thermal Energy Storage (CTES) can also help to reduce energy consumption of applications therefore providing financial savings and reducing pollutant emissions (CO2, SO2, NOX and Chloro-Fluoro-Carbons (CFC) etc.).
Temperature controlled fabrics
Textile manufacturers are using PCMS to provide thermal comfort in a wide variety of garments. The thermal insulation capabilities of cold protective clothing materials are significantly improved by the incorporation of Microencapsulated PCM.
Textiles containing PCMs react immediately with changes in environmental temperatures, and temperatures in different areas of the body. When a rise in temperature occurs, PCM microcapsules react by absorbing heat and storing this energy in the PCMs. When the temperature falls again, the microcapsules release this stored heat energy and the PCMs solidify again. Microcapsules are embedded in a coating compound such as acrylic, polyurethane and rubber latex, and applied to a fabric or foam. Capsules can also be mixed into a polyurethane foam matrix, from which moisture is removed, and then the foam is laminated on a fabric.
Main PCM companies and start-ups
Croda Europe Limited
www.croda.com
The company offer a range of bio-based phase change materials under the trade name CrodaTherm™, Applications are in refrigeration, frozen cold storage, shipping, medical & pharmaceutical transport, building materials, HVAC, electronics, textiles and temperature controlled packaging.
Hangzhou Ruhr New Material Technology Co., Ltd.
www.ruhrtech.com
RuhrTech offers a wide range of bulk PCMs from -50 oC to +100 oC. The company also provides solid state PCM (heat sink film & heat sink colloid) as well as liquid state PCM (phase-change slurry, PCS). RuhrTech offers a series of PCM gel pack and passive cold packages.
HeatVentors
www.heatventors.com
HeatVentors started out as a university research project. The company has developed a thermal energy storage tank based on a phase change material technology called HeatTANK. The company uses several types of PCMs from various suppliers.
Henkel AG & Co. KGaA.
www.henkel-adhesives.com
The company develops Phase change thermal interface materials (TIMs) as an alternative to thermal greases. HI-FLOW phase change materials are a replacement for grease as a thermal interface between a CPU or power device and a heat sink. HI-FLOW handles like BERGQUIST SIL PAD materials at room temperature, but flows like grease at its designed phase change temperature.
Microtek Laboratories, Inc.
www.microteklabs.com
Microtek currently offers PCMs in two forms: the phase change material itself (“raw” PCM) and the PCM microencapsulated (MPCM). The company also produces PCM pouches, panels and foam. Microtek is a division of CAVU Group. The company acquired the Micronal ® product line from BASF in 2017.
Further information
The Global Market for Phase Change Materials
Published September 2020, available at https://www.futuremarketsinc.com/the-global-market-for-phase-change-materials/
