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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.

Two Entropy advisors, Dr. Mohammed Farid and Lucas B. Hyman, are pleased to take your questions about PCMs and thermal energy storage. Send your questions to bwelter@puretemp.com. We'll select the best and post the answers here each week.

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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.

PCM briefing: Underground heat storage proposed for Hamburg; Solar Decathlon entry will have PCM in ceilings

Ben Welter - Wednesday, February 15, 2017

• The water utility in Hamburg, Germany, wants to build an underground thermal heat storage system that could supply about 25 percent of the city's heating needs with waste heat from industrial and power plants. A huge saltwater aquifer below the city is seen as an ideal "thermal battery" in which to store heat for use in winter.

• The University of Nevada-Las Vegas entry in the 2017 Solar Decathlon will feature phase change material in the ceilings of the 900-square-foot home.

Sonoco has announced a 10 percent price increase on all expanded polystyrene components used in its temperature-assurance packaging products. The company said the increase reflects the rising cost of polystyrene, the key raw material in EPS products.

University of Colorado engineers have developed a metamaterial that can cool objects even under direct sunlight with zero energy and water consumption. The glass-polymer hybrid material measures just 50 micrometers thick and can be manufactured economically on rolls, making it potentially viable for large-scale residential and commercial applications.

StoCalce Functio, a wall covering material developed by the Swiss research institute Empa together with the building specialist Sto, manages interior humidity by absorbing, storing and releasing moisture. Perhaps PCMs could be added to the material to manage temperatures as well. [German]

Alexium International, maker of Alexicool phase change material, is one of nine companies planning to attend Gabelli & Company's 8th annual Specialty Chemicals Conference in New York City on March 22.

Axiom Exergy co-founders Anthony Diamond and Amrit Robbins, who made Forbes' "30 Under 30" in the energy sector this year, shared advice for other young entrepreneurs on energy.gov. Said Robbins: “If you want to build a business, go out and get third party validation for your technology, team and product-market fit."

Sunamp is thinking big with commercial-scale heat battery

Ben Welter - Monday, February 06, 2017

Sunamp Ltd. continues to seek financing to fund development of its commercial-scale heat battery, the SunampCube. The device is designed to store energy generated by wind, solar and other renewable sources, as well as harvest excess heat generated by waste-treatment facilities.

Sunamp CEO Andrew BissellThe Scottish company is in negotiations to use the technology to transport waste heat by barge from the Avonmouth waste processing facility to Bristol for use in the district heating system under construction there. The batteries would be stored in 16 shipping container units, each holding 2 MWh of heat.

"We have built and tested a number of cells that will be used to build the full-scale device," says CEO Andrew Bissell. "Each one is a single cell storing 45-50 kWh."

What type of phase change material is being used?

"It's a salt hydrate ... our own tweak on sodium acetate trihydrate with both a nucleator and a stability enhancer," Bissell says. "58C melt and freeze points - almost no subcooling or hysteresis. And very cycle stable. We have cycled a test heat battery over 26,000 times with no loss of capacity or degradation in any metric."

Bissell says the company is working on financing for the project's next phase.

http://www.sunamp.com/products/sunampcube/

PCM briefing: Stanford energy hub wins AIA award; is that PCM atop a Japanese greenhouse?

Ben Welter - Friday, January 20, 2017

Stanford University's new Central Energy Facility, the heart of a campus-wide energy system, has won a 2017 Institute Honor Award, the American Institute of Architects' highest recognition for design excellence. A 2.5-million-gallon hot water tank in the courtyard showcases the energy plant’s mission.

Greenhouse in Yamaguchi Prefecture• A strawberry-cultivation system that stores excess solar heat in a tank filled with cobblestones reduced heating costs by 80 percent at a greenhouse in Japan's Yamaguchi Prefecture. "A mat-like heat-insulating material" – phase change material, perhaps? – atop the greenhouse, right, is rolled up during the day to let in sunlight.

A power plant under construction in Kiel, Germany, will be able to store more than 1,500 megawatt hours of heat in a 60-meter-high water tank, ensuring the supply of more than 70,000 district heating customers for up to eight hours. The gas-fired Stadtwerke Kiel will simultaneously generate electricity and heat through cogeneration.

• New from QYResearch: "Europe Bio-Based Phase Change Materials Market Report 2017" and "Global Bio-Based Phase Change Materials Market Professional Survey Report 2017."

• The Industrial Fabrics Association International has issued a call for presenters for the IFAI Advanced Textiles Conference, to be held Sept. 26-29 in New Orleans. The deadline for submitting a proposal is Feb. 5.

• In partnership with Technical University Hamburg Harburg and Hamburg Energie, Siemens AG is developing a thermal storage system that will convert excess wind energy to heat and store it in rock fill. A steam turbine will convert the heat energy back to electricity on demand. The full-size system will be able to store about 36 MWh of energy in a container filled with 2,000 cubic meters of rock.

• The global market for thermal energy storage is projected to reach a value of $1.8 billion by 2020, Transparency Market Research reports. Latent heat and thermochemical storage technologies are expected to grab market share from sensible heat technology, which is now the dominant technology in the market.

Pluss Advanced Technologies has an opening for a quality assurance manager at its facility in Bawal, India. The quality manager is responsible for overall development, implementation and maintenance of the quality management system for the company's polymer and PCM business units.

PCM briefing: University of Nebraska installing 2nd TES system; Credo-packing cyclists reach India

Ben Welter - Monday, November 21, 2016

• The University of Nebraska has begun construction on its second thermal energy storage facility in Lincoln. The system will chill water at night and on weekends, when electricity costs are low. The water will be used to cool buildings during the day.

Italian couple cycling across India• Do you remember the Italian couple who began an 18,000-kilometer bike ride in June to raise awareness about diabetes? Chiara Ricciardi and Riccardo Rocchi reached India last week. Ricciardi has type 1 diabetes and requires a daily dose of insulin. She is using Pelican BioThermal's Credo ProMed pack to keep insulin at the right temperature. The pair have pedaled 7,130 kilometers so far, across 13 countries, averaging 49 km per day. Their final destination: Singapore.

• The Naval Post Graduate School’s Integrated Multi-Physics Renewable Energy Laboratory in Monterey, Calif., has integrated the CALMAC's ice-based energy storage technology into an on-site microgrid. The lab is testing and evaluating the integration of a variety of energy storage technologies with solar and wind power.

Boca International Ltd. has signed a $3.4 million contract with Differ Commercial Management Ltd. to supply and install BocaPCM-TES systems in Differ properties in Xiamen City, China. Boca says its salt-based aqueous system is similar to ice- and water-based TES systems but covers a wider range of temperatures, allowing for "even and controllable energy usage, drawing energy from the storage directly during peak hour, which ultimately reduces the operating costs."

Sunamp Ltd. has completed installation of its SunampPV heat batteries in more than a thousand homes at Castle Rock Edinvar, one of Scotland's largest housing associations. The company says the hybrid system will save households up to $370 a year each on their hot water and heating bills.

Research roundup: Composite of wood-plastic and microencapsulated PCM; heat transfer characteristics of alloys; more

Ben Welter - Thursday, October 13, 2016

Composite of Wood-Plastic and Micro-Encapsulated Phase Change Material (MEPCM) Used for Thermal Energy Storage [Applied Thermal Engineering]

Experimental study on phase change heat transfer characteristics of alloys [International Journal of Heat and Mass Transfer]

Renewable Night Cooled Chill Water Source for Energy Efficient Indoor Radiant Cooling [International Journal of Engineering Research in Africa ]

Applied Machine Learning: Forecasting Heat Load in District Heating System [Energy and Buildings]

Melting inside a horizontal cylindrical capsule [Case Studies in Thermal Engineering]

Synthesis and thermal properties of novel sodium nitrate microcapsules for high-temperature thermal energy storage [Solar Energy Materials and Solar Cells]

Natural convection in high temperature flat plate latent heat thermal energy storage systems [Applied Energy]

Experimental investigation of paraffin wax with graphene enhancement as thermal management materials for batteries [International Conference on Electronic Packaging Technology]

Conception and experimental investigation of a hybrid temperature control method using phase change material for permanent magnet synchronous motors [Experimental Thermal and Fluid Science]

Formulation of Nano and Micro-Encapsulated Phase Change Materials with a Solar-Absorbing Metamaterial Shell [Journal of Nanoelectronics and Optoelectronics]

Experimental investigations on heat content of supercooled sodium acetate trihydrate by a simple heat loss method [Solar Energy]

Research roundup: Thermocline sensitivity analysis; solar district heating; d-mannitol stability; more

Ben Welter - Sunday, August 07, 2016

Sensitivity analysis for thermocline thermal storage tank design [Renewable Energy]

Solar district heating systems for small districts with medium scale seasonal thermal energy stores [pdf] [Energy Procedia]

Natural convection heat transfer of molten salt in a single energy storage tank [Science China Technological Sciences]

Assessing the Thermal Performance of Phase Change Material in a Photovoltaic/Thermal System [Energy Procedia]

Stability of D-mannitol upon Melting/Freezing Cycles under Controlled Inert Atmosphere [Energy Procedia]

Numerical simulation on heat transfer enhancement of phase change thermal storage devices for low-middle temperature [Advanced Materials]

Experimental Research of a Partition Composed of Two Layers of Different Types of PCM [Energy Procedia]

Research on Solar Heating System with Phase Change Thermal Energy Storage [Energy Procedia]

Process Steam and Chilled Water Production with CPC-collectors, Steam Jet Ejector Chiller and Latent Heat Storages [Energy Procedia]

Research roundup: Prosthetic cooling device; sodium nitrate-expanded vermiculite; PCM-water heat exchanger; more

Ben Welter - Monday, May 16, 2016

Prosthesis cooling deviceAn Automatic and Portable Prosthetic Cooling Device with High Cooling Capacity Based on Phase Change [Applied Thermal Engineering]

Thermal properties of sodium nitrate-expanded vermiculite form-stable composite phase change materials [Materials & Design]

A PCM-Water Heat Exchanger With Polymeric Hollow Bres For Latent Heat Thermal Energy Storage: A Parametric Study Of Discharging Stage [Journal of Theoretical and Applied Mechanics]

Distributed energy storage: Time-dependent tree flow design [Journal of Applied Physics]

Thermal energy storage project underway on NIH campus in Maryland

Ben Welter - Monday, March 14, 2016

The National Institutes of Health has begun construction of a thermal energy storage tank on its campus in Bethesda, Md. The tank will be 100 feet tall, 120 feet in diameter and hold 8 million gallons of chilled water. The tank is among upgrades designed to ensure uninterrupted cooling capability for a 240-bed hospital, three data centers and more than 12 million square feet of biomedical research facilities. The upgrades are scheduled to be completed by October 2017.

https://nihrecord.nih.gov/newsletters/2016/03_11_2016/story4.htm

Stanford's new heating/cooling system wins top honors in engineering competition

Ben Welter - Thursday, March 10, 2016

SESI central plant drawing

Stanford University's new $485 million heating and cooling system has won the Editors' Choice Award in the annual Engineering News-Record Best of the Best competition. The Stanford Energy System Innovations project, completed in April 2015, has cut campus energy use by 50 percent. Three heat-recovery chillers in the new central energy facility (CEF) strip waste heat from 155 campus buildings via a chilled-water loop and use it to preheat a separate hot-water loop that distributes heat to the same buildings.

ENR describes the system in detail:

"The system captures 57% of building waste heat, reusing it to meet 93% of campus heating needs. For most of the year, the system precludes the need for cooling towers to discharge excess heat, which reduces water consumption on campus by 15%.

"Each heat-recovery chiller (HRC) provides a 2,500-ton cooling capacity for chilled water and simultaneously can produce 40 million BTUs of heat per hour. The HRCs send out chilled water to the campus at 42°F, which returns at 56°F to 60°F. The heat removed from the chilled water as it is cooled back down to 42°F reheats spent hot water (which returns to the CEF from campus at 130°F) back up to 160°F to 170°F to supply heating. ...

"The CEF’s thermal storage system contains two 5-million-gallon tanks to store cold water and a 2.3-million-gallon tank for hot water. The tanks double as reservoirs for power, allowing flexibility to operate the heat-recovery chillers and other equipment during times of lower energy pricing or when outside air temperatures are optimal. For example, when it’s hot during the day, excess heat can be converted and stored as hot water, instead of being rejected out of evaporative cooling towers, and then used during the cooler nighttime hours."

http://www.enr.com/articles/39005-editors-choice-best-energyindustrial-stanford-energy-system-innovations