Sunset over a city

Heatwaves made bearable with new wall insulation

Image credit: Lucian Dachman | Unsplash

A new way to reduce heat penetration through building walls could make high summer temperatures more bearable.

With the effects of climate change making the summer heat in many global territories increasingly unbearable and prolonged over the last few decades, the consequent cooling load for buildings has also been on the rise.

Insulation is currently the primary solution for blocking heat from entering a building. However, according to researchers from the Korea Institute of Science and Technology (KIST), by applying an additional material that can delay heat penetration, this could suppress the indoor temperature from rising, which in turn could lower the cooling load of the building.

The KIST research team developed a new material for buildings walls that helps reduce the penetration of heat from the outside. The team, directed by Dr. Sarng Woo Karng from the National Research Agenda Division, KIST, revealed that they have successfully lowered heat penetration through building walls by applying a phase change material (PCM).

PCM refers to materials that absorb or release heat from/to the surrounding area, but do not change the temperature during the phase change. One of the most common types of PCM is paraffin oil, which is used to make candles. A solid PCM absorbs heat as it transitions into liquid phase, so by using a case to hold it when it is in liquid phase without causing any leakage, it is possible to apply them to a building wall to block heat from entering inside.

However, the problem is that PCMs do not melt evenly from the outside toward the inside during phase transition from solid to liquid. More specifically, PCMs turn into liquid starting from the outermost layer and the parts that are hot move upward, while the parts that are still relatively cool move downward.

Thus, while the upper part may have completely melted, the lower part will have not and, as a result, heat will penetrate into the building through the area where the PCM is in liquid phase. Ultimately, the PCM becomes ineffective in controlling the indoor temperature and is rendered useless.

(a) the experimental device (b) the laser module for fluid flow visualisation

Image credit: Korea Institue of Science and Technology(KIST)

Dr Karng's team addressed the non-uniform phase change with bubble injections. By injecting bubbles into the bottom part of the PCM during phase transition, this enabled uniform circulation of the PCM in liquid phase. As a result, the PCM melted from the area closest to the envelope in a uniform manner and heat penetration was inhibited across the building wall until the entire PCM melted.

(a) PCM wall cross section (b) temperature measurement position

Image credit: Korea Institue of Science and Technology (KIST)

Dr. Karng said, "We expect that the insulating wall using the PCM bubble generator used in this study will contribute to reducing the amount of energy used to heat or cool a building. Insulation techniques using PCMs helps reduce heat penetration, in combination with the building insulating material and it can also be used as the outer walls of zero-energy buildings."

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