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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 monthly PCM newsletter. Or join the discussion on LinkedIn.

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PCM battery shows promise in home heating system

Ben Welter - Tuesday, September 15, 2020

A home heating system equipped with a PCM battery put up encouraging numbers in a small trial in northern Italy earlier this year. The monthlong test “shows that is possible [for such a system] to supply the whole heating demand of a house reducing close to zero the costs,” says Domenico Feo, who developed the system. The full report, prepared by ThermaLink, a trademark of Sunservice Srl of Treviso, Italy, is available here.

ThermaCubeThe system is composed of a 6 kW solar array, an air/water heat pump and a thermal battery filled with BioPCM Q42, a biobased phase change material supplied by Phase Change Energy Solutions of Asheboro, N.C. A control unit, PCDCube, monitors temperatures and manages energy flow to optimize system performance. In an interview with Phase Change Matters, Feo answered questions about the heat battery, recently rebranded as ThermaCube.

Q: Thermal conductivity has proven to be a challenge in thermal energy storage across most types of PCM. Was conductivity an issue with the required charge/discharge cycles?

A: "As already known, the thermal conductivity of the PCM, especially of the organic one that we use, is low. This is, at the same time, a disadvantage and an advantage. The disadvantage has been minimized in using a heat exchanger made with a flat aluminum panel with the various layers just over 1 inch of distance; in this way we are able to make the entire volume of material work in a very efficient way. Vice versa this is an advantage for the very low heat losses during the non-work phases; in conditions of installations inside the buildings, the temperatures can be maintained for several days."

Q: If faster heat transfer is required, do you envision a redesign of the heat exchanger or a modification of the PCM to meet the demand of the energy transfer?

A: "As manufacturer, we can customize the heat exchanger dimensions and shape in order to achieve our goals, but as always in the industrial scalability, the quantities are mandatory for a good price. We designed a single heat exchanger dimension and multiply it in order to be able to produce the different storage capacities and realize a complete modular range. The transfer of energy can be however accelerated by increasing the flow rate of the fluid and the delta T between the fluid and the melting point, of course there is always a limit to this possibility. There are still studies around this point that need to be better understood."

Q: Would implementing several PCMs of different melting temperatures aid in the overall performance of the TES?

A: "Let's say that we expect a slight drop in performance at lower temperatures, but we don't have many other tests to give you a more general opinion."

Q: How is the PCM temperature measured throughout the entire storage to provide input to the PCDCube? Since the melting/solidification of PCM is not a homogenous process, are multiple measurements necessary to get a realistic status of the PCM?

A: "In the documents that we have published, we do not specify that we have installed two temperature probes, one in the center and another one near the walls and it is evident that, when the final phase of the  discharge of the PCM approaches, the perimeter probe shows a decrease of more sudden temperature than the central one. We, however, assume that the fact of having installed our thermal battery outside the building in a very cold climate, has exaggerated the heat loss despite the low heat transmission."

Q: Have you considered other PCM suppliers/products, since many are located in Europe and the RAL quality organization is based there?

A: "This is a possibility, at least for the distribution of our products in Europe and Asia. Currently we try to separate the supply of the case with exchangers (that we manufacture) from the PCM with direct purchase of the client from the supplier, especially in the larger units."

Q: What is the customer value proposition for this product? What is the expected return on investment/payback period?

A: "This is a $1 million question; the proposal is certainly into the growing wave of the storage market, even the electrical ones for PV systems. (A Tesla Powerwall is cool but not economically advantageous if you don’t pay attention at the payback that is higher than the life of the battery). The best value proposition is to separate production from the consumption of the energy and take advantage of renewable energies which, unfortunately, are linked to the day / night cycle and the outdoor temperature conditions. We see perfect the combination HP + Thermal Battery because we can concentrate the HP working hours during the best outdoor conditions that, for many reasons, are affecting and reducing the performances.  Furthermore, we also see a large market in the use of these thermal batteries in all these existing systems which are undersized or which, due to specific situations of changing use of the building, are no longer able to provide the necessary heating or cooling to the whole plant. About the ROI, this really varies a lot country by country because the cost of the electricity has different rates and peak hours schedules. The industrial needs are sometimes much more interesting and attractive than the residential ones."

Q: What are your plans for a commercial rollout?

A: "We are completing the Italian sales force and are looking for international distributors. Our goal is to propose the range of products at an international level with distribution agreements for the case only with exchangers; it will obviously be our responsibility to direct the partner to some reliable and high-quality PCM manufacturers. Obviously, those who will quickly give us the opportunity to build pilot plants, demonstrating the technology, will have an advantage in introducing them into the market and in the exclusivity of the contractual relationship."

Research roundup: Radiant floor heating system; mitigation of supercooling; hot water stratification; more

Ben Welter - Friday, March 08, 2019

From Energies:

Analysis of Thermal Performance and Energy Saving Potential by PCM Radiant Floor Heating System based on Wet Construction Method and Hot Water

From Applied Energy:

Supercooling of phase-change materials and the techniques used to mitigate the phenomenon

From Polymer Chemistry:

Encapsulating an organic phase change material within emulsion-templated poly(urethane urea)s

From AIP Advances:

Thermal expansion effects on the one-dimensional liquid-solid phase transition in high temperature phase change materials

From Journal of Materials Chemistry A:

A thermal energy storage composite with sensing function and its thermal conductivity and thermal effusivity enhancement

From Materials Science and Engineering:

Experimental Measurements of Hot Water Stratification in a Heat Storage Tank

From Thermochimica Acta:

Modification of physical and thermal characteristics of stearic acid as a phase change materials using TiO2-nanoparticles

From Energy and Buildings:

Thermal and Structural Performance of Geopolymer Concrete Containing Phase Change Material Encapsulated in Expanded Clay
An experimental study on applying organic PCMs to gypsum-cement board for improving thermal performance of buildings in different climates

From International Journal of Biological Macromolecules:

Sodium alginate/feather keratin-g-allyloxy polyethylene glycol composite phase change fiber

From Construction and Building Materials:

Thermal properties of lightweight concrete incorporating high contents of phase change materials

From Progress in Organic Coatings:

Fabrication and characterization of microencapsulated n-heptadecane with graphene/starch composite shell for thermal energy storage

From Sustainable Energy and Fuels:

A thermal energy storage prototype using sodium magnesium hydride

From Thermal Science and Engineering Progress:

Experimental investigation of the thermal performance of a helical coil latent heat thermal energy storage for solar energy applications

From International Journal of Sports Physiology and Performance:

Exploring the Efficacy of a Safe Cryotherapy Alternative: Physiological Temperature Changes from Cold Water Immersion vs Prolonged Phase Change Material Cooling

From Applied Sciences:

A Form Stable Composite Phase Change Material for Thermal Energy Storage Applications over 700° C