Passive day cooling is a promising technology for reducing energy consumption over time. It prevents solar radiation from heating up buildings and dissipates accumulated heat without the use of external energy.
The use of Phase Change Materials (PCMs) in buildings as a potential method of improving indoor thermal comfort can be accomplished in three ways: passive, active, and free cooling. A large number of studies on the thermal performance enhancement of these methods have been published, revealing that all three methods significantly improve energy efficiency or indoor thermal comfort.
Researchers at the University of Bayreuth have now developed a test system that can reliably characterize and compare passive cooling materials regardless of weather or environmental conditions. The measurement setup described in Cell Reports Physical Science is the first step toward developing a standardized, globally applicable test system for comparing high-performance cooling materials.
Our measurement setup is the first step toward standardized performance comparisons between cooling materials developed around the world in a variety of climatic and weather conditions. Such a test system is a necessary condition for passive cooling to become a widely used technology for significantly reducing energy consumption.
Dr. Qimeng Song
“Increasing fossil energy consumption worldwide is still contributing to global warming and is a major cause of the heating up of our cities. Cooling buildings during the day using passive cooling materials has great potential to establish itself as an effective tool for energy conservation. Many technologically interesting materials and classes of material have consequently been developed for the dissipation of heat, but it is still a challenge to precisely determine and compare their performance. The laboratory set-up we have designed helps to overcome this difficulty. It is a test system that makes important contributions to the characterization of previously existing cooling materials and the design of new ones, regardless of the weather,” says Prof. Dr. Markus Retsch, project leader of the study and Chair of Physical Chemistry I at the University of Bayreuth.
The laboratory-based test system mimics the most important factors that influence passive cooling performance. Essential components are therefore a simulator of sunlight, an aluminium dome cooled with liquid nitrogen that absorbs thermal radiation, a changeable filter that only allows light rays of certain wavelengths to pass through, and a heatable gas flow that can be used to set a specific ambient temperature. This allows the intensity of solar radiation, the temperatures acting on the cooling materials, and other environmental influences to be simulated on a miniature scale.
Outdoors, these factors change quickly and cannot be controlled, but with Bayreuth’s new measurement setup, they can be set with great precision. As a result, regardless of time, place, or weather, the test results are reproducible at any time. This is the only way to precisely characterize and compare the properties and behavior of cooling materials under identical conditions. The measurement setup is robust, cost-effective, and easily replicable without significant technical effort.
The Bayreuth scientists demonstrated the test system’s high performance and reliability on three different materials: a silver mirror (Ag), a polydimethylsiloxane (PDMS) film applied to silver, and a graphite-coated silicon wafer. They not only tested the heating and cooling properties of the materials, but also their cooling performance.
“Our measurement setup is the first step toward standardised performance comparisons between cooling materials developed around the world in a variety of climatic and weather conditions. Such a test system is a necessary condition for passive cooling to become a widely used technology for significantly reducing energy consumption” Dr. Qimeng Song, first author of the study and postdoc at Prof. Dr. Markus Retsch’s research group, says.
