Applications
The materials in this technology have been engineered primarily for clothing . The material enables thermal radiative heat transfer to increase user comfort. These fabrics provide cooling regardless of the wearer's activity or surrounding environment.
Problem Addressed
State-of-the-art cooling technologies have predominantly focused on clothing (e.g. moisture wicking, phase change materials, active cooling technologies) for individuals who are performing high levels of physical activity. Additionally, materials currently used for clothing fabrics (e.g. cotton and polyester) have a transmittance of 1-2% in the infrared (IR) spectrum, which doesn't allow cooling via radiation. ITVOF are transparent in the infrared spectrum and increase a person’s cooling rate by >23W. Personal cooling rate and ambient temperature affect personal thermal comfort. Therefore, increasing a person's cooling rate allows a higher ambient temperature to achieve the same level of comfort. Specifically, a >23W increase in cooling rate allows an ambient temperature increase ≥ 4oF (to ~79oF), which leads to lower air conditiong set points and significant energy savings in buildings.
Technology
A model of the system, including a person and their clothes, was created to analyze the effects of incorporating IVTOF in clothing. It was determined that a transmittance of 34-43% in the IR spectrum is required to achieve sufficient cooling. Using polyethylene (PE), with a maximum yarn thickness of 100µm, the minimum spectrally integrated transmittance in the IR spectrum was 48.8%, which is greater than the required transmittance. The second requirement of a clothing fabric is opaqueness in the visible spectrum. Polyester and cotton cloths exhibited uniform reflectance of 40-50% in the visible spectrum and the PE sample exhibited 50-60%. Therefore, PE fabrics are one potential material for IVTOF. Fabrication of these materials consists of three steps; extrusion of molten polymer through a spinneret into a bundle of fibers, drawing of fibers, and spooling the fibers into a yarn. The spinneret is designed to include the total number of fibers in a yarn allowing equal production rate for fibers and yarns. Once the yarns are created, they can be woven into fabric with commercially available looms.
Advantages
- Increased thermal comfort in clothing
- Increased energy savings by increased air conditioning set points
