Mirian Velay-Lizancos in her laboratory at Purdue University. Photo: Purdue University photo/John Underwood.Heating and cooling homes carries a hefty economic and environmental price tag. The US Energy Information Administration reported that more than half of all home energy in the US is used for heating and cooling, representing more than 14% of the nation’s overall energy use. According to the World Green Building Council, the buildings and construction sector is responsible for 39% of global energy-related carbon emissions.
Mirian Velay-Lizancos, an assistant professor of civil engineering from the Lyles School of Civil Engineering at Purdue University, is addressing these issues. She and researchers in her laboratory have developed a patent-pending, scalable, automatable process that improves upon the traditional method for incorporating phase-change materials (PCMs) into construction materials. They report their work in a paper in Construction and Building Materials.
PCMs like paraffin, esters and salt hydrates can be incorporated into building envelope elements such as doors, exterior walls, foundations, roofs, windows and other components that create a barrier between inside and outside to moderate the effect of external temperature changes on the indoor environment. These materials convert changes in thermal energy into phase changes by transitioning from a solid to a liquid, or the opposite. They provide useful cooling or heating by absorbing or releasing energy during those transitions.
“Incorporating PCMs reduces energy consumption in buildings, which reduces carbon dioxide emissions and operational costs,” Velay-Lizancos explained. “It also decreases water permeability of construction materials.
“Increasing the heat-storage capabilities of building envelopes would reduce the effect of temperature fluctuations in a building. This would increase the thermal comfort of the building and decrease energy consumption, carbon dioxide emissions and related economic costs of heating and cooling. It also would make buildings more resilient and energy independent and less susceptible to power outages and other energy supply issues.”
Velay-Lizancos said that traditional methods for adding PCMs into construction materials have drawbacks. “Currently, PCMs are incorporated into other materials via microencapsulation or macroencapsulation. However, these methods limit the use of PCMs. Microencapsulation has a negative effect on the strength and durability of construction materials. Macroencapsulation limits the shape and production method of construction materials.”
Velay-Lizancos’ new method uses liquid immersion and a vacuum to incorporate PCMs into construction materials like bricks, drywall and concrete after they’ve been formed.
“This increases the strength, enhances the durability and increases the thermal inertia of the construction materials,” Velay-Lizancos said. “This new method also distributes PCMs so they are concentrated in the surface layer of the construction materials. More of the PCMs are in contact with external surfaces of the building envelope, which makes the PCMs more effective.”
Velay-Lizancos’ method requires only a vacuum system, which she said is very accessible and easy for manufacturers to work with. “Users will need to be familiarized with the process, but they will not need special training. The process could be easily automatized and incorporated into the production chain of precast elements like bricks, concrete panels, drywall and pavers, among others.”
Velay-Lizancos and her research group tested their innovation at the Pankow Laboratory in the Lyles School of Civil Engineering. The initial tests were conducted with commercial bricks and 15 minutes of vacuum time.
They then conducted a large experimental campaign on cement mortars with three different water-to-cement ratios and, therefore, different initial porosity levels. PCMs were incorporated into the mortars for three different vacuum periods: 15 minutes, one hour and four hours. With just 7% of the volume of the element filled with PCM, Velay-Lizancos and her team observed an increase in thermal inertia of 24% and a more than 22% increase in compressive strength.
According to Velay-Lizancos, the uneven distribution of the PCM, which is concentrated in the surface layer, makes it more effective in enhancing thermal properties.
“The method used in this study introduces the PCM into the layer of the material that is closer to the material's surface, meaning that more will be in contact with the external surfaces of the building envelope, resulting in more effective usage of the PCM,” she said. “Furthermore, this method pushes the PCM material into the capillary pores through the vacuum. Due to the capillary forces, leakage of PCM was not observed, even when the final composite was exposed to high temperatures well above the melting point of the PCM used.”
The next milestone in developing this PCM-incorporation method is to build a full-scale prototype. “This will allow us to visualize with cameras and sensors the thermal performance of the building envelope,” Velay-Lizancos said. “Clients will have the hard data and also be able to visualize the advantages of this technology.”
This story is adapted from material from Purdue University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.