Alternatives to energy-guzzling HVAC systems

Texas A&M University researchers have created 3D-printable Phase-Change Material (PCM) composites that can control ambient temperature in buildings using a simpler and cost-effective manufacturing process.

They can be added to building materials such as paint or 3D printed as decorative home accents to integrate seamlessly into a variety of indoor environments.

Changing climate patterns have left millions of people vulnerable to weather extremes, and as temperature swings become commonplace around the world, conventional power-guzzling cooling and heating systems need a more innovative, energy-efficient alternative, and in turn, to ease the strain on already struggling power grids.

“The ability to integrate phase change materials into building materials using a scalable method opens up possibilities to produce more passive temperature control in both new construction and pre-existing structures,” said Emily Pentzer, associate professor in the Department of Materials Science and Engineering at Texas A&M.

Heating, ventilation and air conditioning (HVAC) systems are the most commonly used methods of temperature control in homes and commercial establishments. However, these systems consume a lot of energy and use refrigerants to generate cool, dry air. Ongoing problems with HVAC systems have led to research into alternative materials and technologies that require less energy to function and can regulate temperature just as effectively.

Phase transition materials have gained a lot of interest in temperature control due to the ability of these compounds to change their physical state depending on the temperature in the environment. When PCMs store heat, when they absorb heat they convert from solid to liquid and vice versa when they release it. Unlike HVAC systems that rely solely on external power to heat and cool, these materials are passive components that do not require external electricity to regulate the temperature.

The traditional approach to manufacturing PCM building materials requires forming a separate shell around each PCM particle, such as a cup to hold water, and then adding the newly encased PCMs to building materials. However, it has been a challenge to find building materials that are compatible with both the PCMs and their casings. In addition, this conventional method also reduces the number of PCM particles that can be incorporated into building materials.

“Removing the shells allows our PCMs to occupy a larger volume by coming closer together in the resin,” said Ciera Cipriani, NASA space technology researcher in the Department of Materials Science and Engineering.

Previous studies have shown that when using phase-change paraffin wax mixed with liquid resin, the resin acts both as a shell and as a building material. This method locks the PCM particles in their individual pockets, allowing them to safely undergo a phase change and manage thermal energy without leakage.

Similarly, Pentzer and her team first combined photosensitive liquid resins with a phase-change paraffin wax powder to create a new 3D-printable ink composite, improving the manufacturing process for building materials containing PCMs and eliminating several steps, including encapsulation.

The resin/PCM mixture is soft, paste-like and malleable, making it ideal for 3D printing, but not for building construction. Using a photosensitive resin, they cured it with ultraviolet light to solidify the 3D-printable paste, making it suitable for real-world applications.

In addition, they found that the phase-change wax embedded in the resin was unaffected by the ultraviolet light and made up 70% of the printed structure. This is a higher percentage compared to most currently available materials used in industry.

They then tested the thermoregulation of their phase-change composites by 3D printing a small-scale house-shaped model and measuring the temperature inside the house when placed in an oven. Their analysis showed that the temperature of the model deviated by 40% from the outside temperature for both heating and cooling thermal cycles compared to models made from traditional materials.

In the future, the researchers will experiment with different phase transition materials so that these composites can operate at wider temperature ranges and manage more thermal energy during a given cycle.

The study was funded by the National Science Foundation’s Division of Materials Research Career Award and published in the journal Matter.

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