smart window coating

Smart window coating cools or heats the interior depending on climate

Image credit: ntu

An energy-saving glass that heats or cools the building’s interior depending on environmental conditions has been developed by scientists from Nanyang Technological University (NTU), Singapore.

A coating is applied to the glass that responds to changing external temperatures and can switch between heating and cooling as needed, potentially saving energy.

The glass has no electrical components and works by exploiting the different wavelengths of light responsible for heating and cooling.

During summer, the glass suppresses solar heating (near infrared light), while boosting radiative cooling (long-wave infrared) - a natural phenomenon where heat emits through surfaces towards the cold universe - to cool the room. In the winter, it does the opposite to warm up the room.

In lab tests using an infrared camera to visualise results, the glass allowed a controlled amount of heat to emit in various conditions (room temperature – above 70°C), proving its ability to react dynamically to changing weather conditions.

Windows are typically the least energy-efficient part of a building’s construction. Window-associated energy consumption (heating and cooling) in buildings accounts for approximately four per cent of their total primary energy usage each year, according to an estimation based on data available from the US Department of Energy.

While various technologies have been developed to ease their energy demand for either cooling or heating, the NTU team believes their technology is the first to be able to do both.

Principal investigator of the study, Dr Long Yi, said: “Most energy-saving windows today tackle the part of solar heat gain caused by visible and near infrared sunlight.

“However, researchers often overlook the radiative cooling in the long wavelength infrared. While innovations focusing on radiative cooling have been used on walls and roofs, this function becomes undesirable during winter.

“Our team has demonstrated for the first time a glass that can respond favourably to both wavelengths, meaning that it can continuously self-tune to react to a changing temperature across all seasons.”

As a proof of concept, the scientists tested the energy-saving performance of their invention using simulations of climate data covering all populated parts of the globe.

They found the glass they developed showed energy savings in both warm and cool seasons, with an overall energy saving performance of up to 9.5 per cent.

First author of the study Wang Shancheng said: “The results prove the viability of applying our glass in all types of climates, as it is able to help cut energy use regardless of hot and cold seasonal temperature fluctuations. This sets our invention apart from current energy-saving windows which tend to find limited use in regions with less seasonal variations.”

Moreover, the heating and cooling performance of their glass can be customised to suit the needs of the market and region for which it is intended.

Last year, another team unveiled transparent solar panels with record-breaking efficiency that could one day be placed on top of windows to generate renewable energy from buildings.

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