Changing climate patterns have made millions of people vulnerable to weather extremes. Since temperature fluctuations are becoming more and more frequent worldwide, conventional electricity-guzzling cooling and heating systems need a more innovative, energy-efficient alternative and thus relieve already ailing power grids.
In a new study, researchers at Texas A&M University have developed novel 3D printable phase change material (PCM) composites that can regulate the ambient temperature in buildings with a simpler and cheaper manufacturing process. In addition, these composites can be added to building materials such as paint or 3D printed as decorative living accents to blend seamlessly with various indoor environments.
“The ability to integrate phase change materials into building materials with a scalable method opens up opportunities for more passive temperature control in both new buildings and existing structures,” said Dr. Emily Pentzer, Associate Professor in the Department of Materials Science and Engineering and the Faculty of Chemistry.
This study was published in the June issue of the journal matter.
Heating, ventilation, and air conditioning (HVAC) systems are the most common methods of temperature control in residential and commercial spaces. However, these systems consume a lot of energy. In addition, they use greenhouse materials called refrigerants to create cool, dry air. These persistent problems with HVAC systems have sparked research into alternative materials and technologies that require less energy to function and that can regulate temperature according to HVAC systems.
One of the materials that has attracted a lot of interest for temperature regulation are phase change materials. As the name suggests, these compounds change their physical state depending on the temperature in the environment. So when phase change materials store heat, they convert from solid to liquid when they absorb heat and vice versa when they release heat. In contrast to HVAC systems, which rely solely on external energy for heating and cooling, these materials are passive components that do not require external electricity for temperature control.
The traditional approach to making PCM building materials involves forming a separate shell around each PCM particle, like a cup to hold water, and then adding these newly coated PCMs to the building materials. However, it has been a challenge to find building materials that are compatible with both the PCM and its shell. In addition, this conventional process also reduces the number of PCM particles that can be incorporated into building materials.
“Imagine filling a pot with eggs and water,” said Ciera Cipriani, NASA Space Technology Graduate Research Fellow in the Department of Materials Science and Engineering. “If each egg has to be put in its own container for hard boiling, fewer eggs fit in the pot. By removing the plastic containers, the real shell in our research, more eggs or PCMs can take up a larger volume by fitting closer together in the water / resin. “
To address these challenges, previous studies have shown that when phase change paraffin wax is used mixed with liquid resin, the resin acts as both a shell and a building material. This method traps the PCM particles in their individual pockets so they can safely 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 that improves the production process for PCM-containing building materials and eliminates multiple steps, including encapsulation.
The resin / PCM mixture is soft, pasty and malleable, which makes it ideal for 3D printing, but not for building structures. So they cured a photosensitive resin with ultraviolet light to solidify the 3D printable paste, making it suitable for real-world applications.
They also found that the phase change wax embedded in the resin was not affected by ultraviolet light and made up 70% of the printed structure. This is a higher percentage compared to most currently available materials used in the industry.
Next, they tested the thermoregulation of their phase-change composites by 3D printing a small house-shaped model and measuring the temperature inside the house when it was placed in an oven. Their analysis showed that compared to models made of conventional materials, the temperature of the model differs by 40% from the outside temperatures for both the heating and cooling circuits.
In the future, researchers will experiment with various phase change materials other than paraffin wax to allow these composites to operate in wider temperature ranges and handle more thermal energy during a given cycle.
“We are delighted with the potential of our material to keep buildings comfortable and at the same time reduce energy consumption,” said Dr. Peiran Wei, research scientist at the Department of Materials Science and Engineering and the Soft Matter Facility. “We can combine multiple PCMs with different melting temperatures and precisely distribute them to different areas of a single printed object to work all four seasons and around the world.”
This study was funded by the National Science Foundation’s Division of Materials Research Career Award.