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The award-winning Phase Change Matters blog tracks the latest news and research on phase change materials and thermal energy storage. E-mail tips and comments to Ben Welter, communications director at Entropy Solutions. Follow the blog on Twitter at @PureTemp. Subscribe to the weekly PCM newsletter. Or join the discussion on LinkedIn.

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Hybrid sensible-latent heat storage concept achieves high energy densities

Ben Welter - Tuesday, October 31, 2017

Christoph Zauner of AITChistoph Zauner, a research scientist at the Austrian Institute of Technology, has been investigating the use of phase change material for a variety of applications since 2010. His most recent papers include “Experimental characterization and simulation of a hybrid sensible-latent heat storage,” published earlier this year in Applied Energy. He discussed his work in an email interview. 

Q: How did you first become interested in phase change material?

A: I worked for quite some time in the field of solar thermal energy and was especially focusing on industrial application with non-standard solar collector, so-called medium temperature collectors. This more efficient class of collectors (concentrating and non-concentrating) can produce temperature up to 250° C heating pressurized water, oil and generate steam. In order to achieve high solar fractions (i.e. cover much more than 10% of the total required process energy by solar energy), one needs to store energy. Standard storages (steam, oil, water) have limitations and latent storage certain advantages. Thus, we started developing such storages. In the meantime, we want to use it for a much broader range of applications (not only solar thermal).

Q: Describe the hybrid sensible-latent heat storage concept you have been working on.

Inverted shell and tube heat exchanger

A: In our new concept, we place the PCM inside the tubes of a modified shell-and-tube heat exchanger [shown above]. This is in contrast to the well-known approach of placing it outside. On the shell side we use a heat transfer fluid (in our first prototype we used oil) which at the same time serves as a sensible storage medium. Thus, we achieve a hybrid sensible-latent heat storage, which offers several opportunities:

• Heat transfer fluid (in our case oil) and PCM fractions can be varied over a wide range, i.e. a hybrid sensible-latent heat storage is realized. Advantages of both domains can be exploited, such as high energy density of the PCM and high power density of sensible storages

• Fewer weld seams as for the standard concept (PCM outside many small tubes) leads to storage cost reduction

• Larger heat transfer area between tubes and PCM enables higher storage power

• Our tubes serve as a macroencapsulation of the PCM, which serves as protection and increases storage lifetime.

Q: Is HDPE in use as a PCM in any commercialized application?

A: HDPE is a so-called commodity plastics. It is the kind of polymer used most out of all polymers. As such it is produced in a multi-million-ton scale each year. Also a versatile recycling industry is in place, which allows for further cost reduction potential (we know which types are suitable and which ones are not). Usually HDPE is used to contain PCMs only. There are no commercial applications yet, where HDPE is used as PCM. Currently we are investigating various possible applications.

Q: How do you anticipate the viscosity of the PCM affecting the thermal modeling? At what point does this significantly contribute to the internal convection in the tube?

A: Convection plays a minor role for our HDPE grade. This may be somewhat different for other grades and was analyzed in our lab. Our models can be adapted to incorporate convection, too. If necessary, we also have 3d-CFD models available.

AIT test tank
A 40 kWh, 100 kW peak power hybrid latent-sensible storage system was successfully tested at AIT labs at temperatures up to 200 °C.
Q: Beyond manufacturing costs, what are the benefits of the inverted shell-and-tube in comparison to other geometries such as a packed bed?

A: Apart from the advantages mentioned above, there is one particular key advantage over packed beds: packing density. Our storage can achieve up to 90% PCM volume density, whereas the theoretical limit for ideally packed spheres is 74%. In a packed bed, however, one does not have “ideal packing,” but the situation of “random packing,” where PCM volume fractions of 64% are achieved.

We found a certain way, which we do not disclose, how to actually fill up the whole tubes even for the crystallized (shrinked) PCM. Usually, PCM macroencapsulations are filled up to 100% only in the molten state, which further reduces the final volume PCM fraction of the whole storage (i.e. kWh/m3).

So summing up: We achieve much higher energy densities. 

Q: How was the DSC data implemented into the thermal modeling?

A: Actual measurement data can be easily implemented in our Dymola model. We use different approaches for the two models described in the paper (Stefan-model, cp(T)-model).

However, it is important to emphasize that one has to perform the DSC measurement “in the correct way.” This means one has to use the correct DSC parameter sets. By comparing the data obtained from different DSC settings to experimental storage data, we found out that very often DSC measurements are done in the wrong way. Wrong DSC settings lead to incorrect material values (especially melting temperature, sub-cooling and phase change enthalpy). However, we know now how to do it correctly and implemented the corresponding curves in the models.
 
Q: Would a sharper phase change peak be advantageous to the proposed application? How would this also affect the Stefan model?
 
A: We already designed storages for different applications (various combinations of low/high power, low/high capacity, different temperature levels). Sometimes it is very important to actually have a PCM with a sharp peak and sometimes even large subcooling doesn’t matter. It depends on the application.

Of course, one has to be careful by applying the various models (not only the Stefan model) and not to spoil the underlying assumptions. We learned a lot in that direction by comparing experimental storage data to simulations and know now very well where the limits are.
 
Q: What are the next steps in your investigation of this storage concept for district heating networks and industrial processes? How close is it to possible commercialization?

A: It is important to emphasize that AIT is not a university, but more like a real company which has to do “real business” and earn “real money.” We do business in various ways and offer different business models.

This ranges from material characterization or simulations directly done (and paid) by customers. We also offer storage engineering using our models and experimental know-how to storage manufacturers. We also demonstrate storages at real demo sites (currently we have projects in polymer extrusion and aluminum die casting) and evaluate their potential in various companies (e.g. we are currently investing a specific process in steel industry using a PCM-steam-storage concept).

We can provide various services or even serve as a “one-stop-shop” for energy optimization of industrial processes using storages. This starts from analyzing the process in detail (incl. monitoring), designing the storage (including integration), organization of storage manufacturing, integration at the plant and commissioning. Also this includes financing aspects (contracting, subsidies, R&D projects etc.).

The storages are permanently optimized but can be bought right away as we are only using industrially available PCMs (we also tested [PureTemp PCMs] and might use them, of course) and heat exchanger/storage manufacturing techniques.

Q: What other projects are you working on that might be of interest to the PCM community?

A: We also work on “overheating solutions” using PCM. Some articles have been published in that direction already, including “High temperature phase change materials for the overheating protection of facade integrated solar thermal collectors.” Also, we employ PCMs in car batteries and developed concepts there. We simulated and tested various prototypes of real batteries.

A related topic is development of new insulations, especially aerogel-based. This is very much needed for storages and also for energy efficiency in industries (“stop wasting energy first, then re-use it!”). 

[For more examples, see www.ait.ac.at/en/research-fields/sustainable-thermal-energy-systems/projects/storeitup-if.]

We are very much looking for partners for new PCMs. We do not produce them on our own. However, we do some development with partners on organic PCMs.

PCM briefing: Three molten salt projects projects move forward in U.S., Germany

Ben Welter - Tuesday, September 19, 2017

Terrafore salt encapsulation• The U.S. Department of Energy has released funding to the Argonne National Laboratory for a scaled-up round of independent testing of Terrafore Technologiesencapsulated thermal energy storage in phase change salts. The materials, shown at right, are designed to operate in temperatures to greater than 800° C in a single tank that acts as both storage and heat exchanger.

• The Department of Energy has invited Terrestrial Energy USA to submit the second part of its application for a federal loan guarantee to support the licensing and construction of its Integrated Molten Salt Reactor

DLR has fired up the TESIS thermal storage facility in Cologne, Germany. One hundred tons of molten salt is alternately heated and cooled from 250 to 560 degrees Celsius in the test facility, which is designed to allow industrial-scale testing of temporary storage methods for renewable energy and waste heat. 

• Va-Q-tec AG is reporting a strong increase in its service business in the first half of 2017, up 54 percent to 8.8 million euros. The company, based in Würzburg, Germany, develops, manufactures and sells vacuum insulation panels and phase change materials. 

• New from Zion Market Research: "Global thermal storage market is expected to reach USD 5.7 billion in 2022, growing at a CAGR of 10.7% between 2017 and 2022"

Advanced combat clothing featuring "four-way stretch phase-change material" was on display last week at the annual Defense and Security Equipment International show in London. Royal College of Art researchers and designers collaborated with the Ministry of Defense on the prototypes, which are designed to be easy to run in and comfortable to wear.  

Extremely high-temperature TES prototype under development in Europe

Ben Welter - Thursday, August 03, 2017

https://www.youtube.com/watch?v=D7huVnCnK8s

At seven locations around Europe, a consortium of universities, R&D centers and an Italian company is investigating materials and devices for thermal energy storage at temperatures of up to 2000º C, well beyond the maximum operating temperatures of systems in use today.

The AMADEUS project, funded by the European Union’s Horizon 2020 program, aims to build a prototype of a system that stores electricity in the form of extremely dense heat, using a solid state device known as a hybrid thermionic-photovoltaic converter. The project’s success hinges on the development of novel silicon and boron alloys with melting temperatures well above 1000º C and energy densities of more than 1 kilowatt hour per liter.

Alejandro DatasAlejandro Datas, a research scientist at the Technical University of Madrid’s Institute of Solar Energy, is the project’s scientific coordinator. He responded to questions about the project by email.

Q: What is your role as scientific coordinator?

A: My role is to coordinate the project activities and make them converge at the end in a single prototype, which will demonstrate the feasibility of this new concept. I’m also involved in the development of the infrared-sensitive PV cell (or thermophotovoltaic cell) that will be used to convert radiant heat into electricity in these systems.

Q: Work on the project began about seven months ago and is scheduled to continue through 2019. What important milestones have you reached so far, and what are the next important milestones?

A: During the first six months of the project, we have characterized some Si-B alloys with different compositions to determine their most important thermophysical parameters, such as latent heat and thermal conductivity. By means of solubility and wettability experiments, we have also studied the interaction of these alloys with some nitride- and carbide- refractories that are intended to be used for the container walls. Also, we have fabricated an experimental setup that will enable the characterization of the energy converters at very high temperatures. The next expected milestones will be the fabrication of the first generation of hybrid thermionic-photovoltaic converters, as well as the determination of the optimal Si-B alloy composition based on an exhaustive analysis of their thermophysical properties and their reactivity with the container walls.

Q: Can you describe, briefly, the PCM you are developing, and what is meant by "the silicon-boron system"?

A: The Si-B system refers to an alloy containing silicon and boron elements in some specific proportions. Silicon and boron have two of the highest latent heats among all the elements in the periodic table. But they show some important drawbacks: in the case of silicon, it expands upon solidification (like water) which leads to very severe constraints for the vessel design; in the case of boron, it has a high cost. The Si-B system is expected to exploit the best of both elements. For instance, the eutectic composition of this alloy (having only 5% of boron) is expected to notably improve the properties of pure silicon PCM at a reasonable cost increment. In brief, Si-B alloys have potential to meet the main requirements for being considered an ideal PCM: low cost, high latent heat and high thermal conductivity. Surprisingly, very little attention has been paid to this system so far, and to our knowledge, AMADEUS is the very first project to investigate these materials in detail for energy storage applications.

Q: What are some of the PCM containment materials and structures under consideration?

A: One advantage of Si-B PCMs is their high thermal conductivity. Thus, they could be stored in relatively large containers without needing very advanced encapsulation arrangements. This minimizes the impact of the container in the final cost of the system. In order to achieve the minimum interaction between the container and the Si-B PCM, we are investigating several kinds of vessel liners based on nitrides (e.g. BN or Si3N4), carbides (e.g. SiC) and oxides (e.g. SiO2).

Q: How does AMADEUS differ from the molten silicon storage technology under development by 1414 Degrees in Australia?

A: Apparently, 1414 Degrees uses pure silicon PCM and “conventional” dynamic engines to transform latent heat into electricity. 1414 Degrees probably needs to reach the market soon, so that they must use reliable and mature technologies. In AMADEUS we are exploring new technologies with greater potential that still require further development. This is the case of Si-B alloys, which may enable higher energy densities and more efficient vessel designs. This is also the case of the thermionic and thermophotovoltaic converters, which will eventually enable more efficient, compact and simpler systems, not requiring working fluids or moving parts. We certainly hope that companies such as 1414 Degrees, and others that could start activities in the near future, could benefit from the results of AMADEUS project.

PCM briefing: Tessol featured in Forbes India; Terrafore Technologies selected for Argonne program

Ben Welter - Monday, June 05, 2017

Thermal Energy Service Solutions, maker of a PCM-based "plug-and-chill" refrigeration system for delivery trucks, is profiled in this month's issue of Forbes India. The system's heat exchanger is designed to keep the refrigerator on the truck within the optimal temperature range for a full day’s operation without drawing power from the engine. The heat exchanger can be fully charged in about six hours at any power outlet.

C-Therm Technologies will be among the exhibitors the Techtextil North America trade show in Chicago June 20-22. The company will demonstrate its non-destructive TCi Property Analyzer, which is designed to characterize the thermal performance (the “warm feel” or “cool touch”) of textiles, fabrics and apparels.

Terrafore Technologies of Minneapolis is one of seven small businesses recently selected to collaborate with researchers at Argonne National Laboratory as part of the Department of Energy's Small Business Vouchers program. Terrafore and Argonne will test the reliability of phase change salt capsules for a compact high-temperature thermal energy storage system for concentrated solar power.

SpecialChem is offering an online course titled "How to Search & Map U.S. Patents for Patentability." The 90-minute course, scheduled for June 28, is designed to for R&D people "looking to avoid patent infringement by enhancing their patent searching and mapping skills." The cost for three attendees on one connection is 300 euros.

PCM briefing: Pluss VP honored as 'Innovator under 35'; BASF partners with Hewlett Packard Enterprise on new supercomputer

Ben Welter - Tuesday, March 21, 2017

Ankit Jhanwar, VP for corporate planning and strategy at Pluss Advanced Technologies, was honored as one of 10 "Innovators under 35" at EmTech India 2017.

Sunamp Ltd., maker of PCM-based heat batteries, is one of eight finalists for an Ashden UK Award. Winners will be announced at a ceremony in London on June 15. The competition recognizes excellence in the field of green energy.

Hewlett Packard Enterprise will work with BASF to develop a supercomputer that will sharply reduce the time it takes to run simulations and modeling in chemical research. "The new supercomputer will promote the application and development of complex modeling and simulation approaches, opening up completely new avenues for our research at BASF,” said Dr. Martin Brudermueller, chief technology officer at BASF.

McKinsey & Co. analysts say a slowdown in the chemical industry's financial performance over the past five years reflects important changes in the industry’s fundamentals. One of their recommendations: "Incumbent specialty-chemical players must prepare for further encroachment of commoditization and erosion of their historical advantages when attackers from developing markets gain more experience and become increasingly technologically savvy."

California lawmakers have introduced legislation to encourage more clean energy resources to address peak load. The bills would require utilities to deploy clean energy during peak demand in order to meet the state's aggressive greenhouse gas and renewable energy goals. 

Finland's Team HeatStock is developing a novel PCM designed to lock in solar, waste heat for later use

Ben Welter - Monday, March 06, 2017

Researchers in Finland are developing a novel phase change material that combines sugar alcohols and sodium polyacrylate, the superabsorbent polymer used in disposable diapers. The material is designed to store solar heat collected in summer and release it for use in winter. The material could also be used to store industrial waste heat.

Team HeatStock, whose members include chemists, energy engineers and physicists from three universities, is one of 20 semifinalists in the 2017 Helsinki Challenge. Finalists, to be selected in June, will compete for a share of 375,000 euros in research funds. The winners will be announced in December.

Team HeatStock PCMTeam HeatStock presented its technology at the Helsinki Challenge pitch night last month.

“The charging of our storage happens by melting the active material of our solution,” said Aalto University research scientist Salla Puupponen. “However, when the melt material starts to cool, it doesn’t release the heat on crystallization as conventional phase change materials, but instead we can keep our material as low temperatures as we want, as long time as we want without losing the stored energy.”

In an interview with Phase Change Matters, team leader Ari Seppälä, a senior scientist at Aalto, describes the technology in further detail.

Q: On the Helsinki Challenge website, you mention that the material will be used to store heat from "solar collectors.” That’s solar thermal, not photovoltaic, correct?

A: Yes, that meant solar thermal collectors. But that is just a one possibility. Other options include such as storing waste heat from industrial processes and storing the surplus heat produced by CHPs (combined heat and power plants) during summertime. As CHPs are often linked with district heating systems (at least in Nordic countries) delivering hot water to residents, the surplus heat could also be exploited for charging the storages of residential buildings during summer for wintertime use.

Q: How is the project being funded now?

A: We have Aalto University strategic funding (Aalto Energy Efficiency Program) and also funding from Fortum Foundation. However, our funding ends during this year. Currently we are looking for new funding possibilities. We are also looking for more collaborators and community members for the research and the competition. So, experts, scientists, companies and organizations who are interested in our research are most welcome to join us!

Q: Your PCM sounds like a composite. What are its components and how are they combined?

A: Our PCM can be classified more likely as a mixture than as a composite. It is composed of a polyol in a cross-linked polyelectrolyte matrix.

Q: What is the PCM's melting point?

A: The melting point is about 100º C.

Q: What is the PCM’s thermal energy capacity in joules per gram?

A: The heat of melting is 180-280 J/g depending on the composition. The heat of crystallization of the material is currently approximately 140-170 J/g. We aim at developing the latent heat of our material further.

Q. You have describe the material as having “phase-change properties that had never been seen before with any material.” What are those properties?

A: Operation of our novel material is based on so-called cold-crystallization, in which the conventional melt-crystallization on cooling is prevented and the material crystallizes only on heating. Supercooled PCM does not seem to crystallize even with a seed crystal below the cold-crystallization temperature. Anomalously, the PCM seems to be stable also above the glass-transition temperature. The novel operation principle enables long-term storing of thermal energy, and discharge of the storage by a small heat pulse.

Cold-crystallization is previously observed also for hydrated polymers, in which water is absorbed by hydrophilic polymers. However, in these cases the amount of cold-crystallizing water is small and the crystallization properties are not conserved in the repeated melting-crystallization cycles. Our material instead can consist up to 90 percent of actual PCM and can be cycled without notable changes in phase change properties.

In addition, the cold-crystallization temperature can be adjusted by the changing the material composition.

Q: What are the key steps in your scale-up plans?

In the beginning, we aim at scaling-up our sample size from tens of milligrams to a kilogram scale. In the scale-up, it is crucial that the material properties, especially the stability of supercooled state, remain unaltered. That is of course an open question, as it is well known that the stability of metastable states decreases with increasing volume of the sample. However, our small, deeply supercooled samples did not crystallize even with seeds and thus the operation of our material differs substantially from conventional materials. After the scale-up process, we will study the triggering of the crystallization by the heat pulse. We also aim at building a practical demo linked with a heat loading and releasing system.

We will later also look for creating similarly behaving materials based on different PCMs.

Q: Have you published research papers on the material?

A: There are no published papers concerning this new material so far. The manuscript on this material, (Puupponen and Seppälä, Cold-crystallization of polyelectrolyte absorbed polyol for long-term storing of thermal energy) has just been submitted for review and a patent application is pending.

Here are links to recent journal papers related to our other PCM studies:

PCM for long-term storage:

Puupponen S, Mikkola V, Ala-Nissilä T, Seppälä A, (2016) Novel microstructured polyol–polystyrene composites for seasonal heat storage, Applied Energy 172 96–106.

Thermodynamics of solidification and melting:

Seppälä A., Irreversibility of solidification and of a cyclic solidification-melting process, (2012), International Journal of Heat and Mass Transfer, 55 1582-1595.

Heat transfer nanofluids with PCM particles:

Puupponen, S., Seppälä, A., Vartia, O., Saari, K., Ala-Nissilä, T., Preparation of paraffin and fatty acidphase changing nanoemulsions for heat transfer (2015), Thermochimica Acta, 601, 33-38

Mikkola V, Puupponen S, Saari K, Ala-Nissila T, Seppälä A., Thermal properties and convective heat transfer of phase changing paraffin nanofluids, (2017), accepted for publication in International Journal of Thermal Sciences.

Dutch-led consortium develops calculation model for industrial heat storage

Ben Welter - Friday, December 16, 2016

LOCOSTO PCM test tankA consortium led by the Energy Research Center of the Netherlands (ECN) has developed a calculation model to predict the performance of a phase change material buffer for industrial heat storage in the 100-250° C temperature range. The model is used to optimize the design of a heat exchanger to achieve the required performance in the most cost-effective way. According to the ECN:

"A test installation with around 100 liters of PCM (see photo) is used to measure the performance of the storage and compare it with the model calculations. There is a high level of consistency between the experimental and model outcomes, providing a basis for the further development and scaling of PCM heat storage technology."

The consortium continues to work on the selection of PCMs with the desired attributes for industrial heat storage. 

"We consider salt hydrates as most feasible option for industrial heat storage," said Robert de Boer, thermal systems project manager at ECN. "I wouldn’t say it is ideal, but the best we can get at this moment."

Members of the LOCOSTO consortium are end-users DOW, Perstorp and EMMTEC; system suppliers IEE and Bronswerk Heat Transfer; materials suppliers PCM Technology and Nedmag; and Dutch research institutes TNO and ECN. "LOCOSTO" stands for "LOw COst STOrage" of heat.

https://www.ecn.nl/news/item/ecn-develops-energy-saving-and-cost-effective-technology-for-industrial-heat-storage/

PCM, foam insulation combine to reduce heat transfer through walls

Ben Welter - Monday, December 12, 2016

Researchers at the Fraunhofer Institute for Chemical Technology in Germany say they have successfully integrated phase change material in foam insulation for use in walls.

What's new about the technology?

"Instead of a few micrograms, several grams of the phase change materials have been integrated. Therefore the thickness of the wall is not changing by increasing the thermal mass," says Sandra Pappert, a scientist at Fraunhofer.

Details of the research will be presented at the BAU trade fair in Munich, Jan. 16-21, 2017. Researchers will use two climatic chambers to demonstrate the extent to which the foam sheets can help manage temperature fluctuations in buildings.

https://www.fraunhofer.de/content/dam/zv/en/press-media/2016/Dezember/ForschungKompakt/rn_12_2016_ICT_Combination%20of%20Isolation%20and%20thermal%20mass.pdf

Patent application: HVAC system for electric vehicle with driving range extension

Ben Welter - Thursday, September 01, 2016

U.S. patent application 20160250906 (applicant Mahle International GmbH, Stuttgart, Germany):

"A heat pump cooling and heating system for an electric vehicle includes a range extending PCM heat exchanger, with a single acting phase change material with a melt temperature between the two comfort temperatures associated with cooling and heating, respectively. In a charging mode, as the vehicle batteries are charged, the same exterior current source runs the compressor, charging the PCM exchanger with heat or 'cold.' During an initial range extending mode, the PCM exchanger/reservoir serves as the heat source or heat sink. The PCM material does not directly heat or cool the air, as is conventional, allowing a single reservoir material to be used in both heating and cooling modes."

http://www.freepatentsonline.com/20160250906.pdf

PCM briefing: EU research focuses on energy retrofits; Axiom Exergy raises $2.5 million

Ben Welter - Tuesday, August 02, 2016

• A European Union research project focused on retrofitting old buildings to meet EU efficiency standards is taking a close look at PCMs built into walls. “By using a phase change material which freezes at 18°C and melts at 25°C,” says Dr. Jürgen Frick, project coordinator, “we can regulate the temperature fluctuations of a room. If the temperature falls to 18°C, the PCM freezes and heats the room. When it rises to 25°, the PCM melts, energy is absorbed, and the room is cooled.”

Rally by Diamond Mattress• The latest entry in the bed-in-a-box mattress competition features open-cell foam infused with copper gel and phase change material to regulate temperature. Diamond Mattress of Rancho Dominguez, Calif., says the company's new Rally line will be sold online and in retail stores.

Eric Buchanan of the West Central Research and Outreach Center in Morris, Minn., has posted an update on his net-zero dairy project. The system's key components so far include solar thermal panels, a heat pump, three heat exchangers and a 2,000-gallon water tank. Fifty-four kilowatts of solar PV and two 10-kW wind turbines are now being added to the system.

Axiom Exergy has raised $2.5 million from investors to help bring its refrigeration battery to supermarkets and cold storage facilities across the United States. The system uses a salt-based phase change material to reduce peak power usage by up to 40 percent and provide backup cooling during power outages.

• The University of Birmingham's Birmingham Centre for Energy Storage is setting up a joint lab on energy storage research with Global Energy Interconnection Research Institute Europe, an organization founded by China's state-run utility. The lab will focus on thermal and cryogenic energy storage systems and their application in energy networks.

• New from Accuray Research: "Global Advanced Phase Change Material (PCM) Market Analysis & Trends - Industry Forecast to 2025"

• A research team at Camosun College in Victoria, British Columbia, has selected PureTemp phase change material for use in a study of greenhouse thermal storage systems. "One of the engineering students is focusing on designing racks for the PCM bottles that will be specifically engineered to slow release and speed recharge of the bottles," writes Becky Mason, an instructor at Camosun who helped organize the research project. "This is intended to optimize use of PCM in off-grid greenhouses where electric fans are not used to circulate air around the PCM."