Cooling the Future: The Paint that Beats the Heat

My house embodies the quintessential Canadian design, sharing the common challenges many Canadians face: hot rooms during summers and chilly rooms in winter. In a recent conversation with my friend, Allison A. Bailes III, PhD , I jokingly discussed my search for a high Solar Reflective Index (SRI) film to apply on my kids' bedroom windows to combat the heat coming through.

I let Allison and others know that while the most budget-friendly option would be to use one of those dollar store emergency shelters taped to the windows, aesthetically, it doesn't provide the best view from the windows.

I even considered a chair like this one that Allison took a photo of at Moncrief Heating & Air Conditioning, Inc. What do you think, should I hook this up to my air to water heat pump for a chilled/heated seat?

Back to the actual purpose of todays ramblings. A new study published recently has a novel approach that could revolutionize how we cool our buildings and homes. The research, published in the journal Cell Reports Physical Science, introduces a new type of paint that uses radiative cooling technology to reduce the need for air conditioning. The paint was developed by Xiulin Ruan at 美国普渡大学

This paint, made using calcium carbonate (CaCO3) fillers, has a high solar reflectance and a high sky window emissivity. But what does this mean, and how can it help reduce energy consumption?

Understanding Sky Window Emissivity

If like me you do not actually know what 'sky window emissivity' I did a bit of research. ( We cant all have Angela Bustamante level knowledge of building envelope, but we can strive!! ). Emissivity is a measure of an object's ability to emit infrared energy. It is measured on a scale from 0 (no infrared energy emission) to 1 (maximum possible infrared energy emission).

When we talk about sky window emissivity, we're referring to the ability of a material to emit radiation within the "sky window" - a specific range of wavelengths (8 to 13 micrometers) in the infrared spectrum where the Earth's atmosphere allows radiation to pass into space.

Materials with high sky window emissivity can effectively radiate heat away, cooling the surface of the material. In the case of the CaCO3 paint, it has a sky window emissivity of 0.94, which is remarkably high. This means that the paint can effectively radiate heat away, cooling the surface of the building it's applied to.

The paint has a high solar reflectance of 95.5%. Field tests showed that the paint has a cooling power exceeding 37 W/m2 and can maintain a surface temperature of more than 1.7°C below the ambient temperature at noon.

The Significance of Sub-Ambient Temperature at Noon

This is significant because noon is typically the hottest part of the day when the sun is at its peak. Traditional building materials absorb a lot of this heat, which then needs to be offset with air conditioning in order to maintain a comfortable indoor temperature.

However, the CaCO3 paint's ability to stay below the ambient temperature at noon means that it absorbs less heat than traditional materials, reducing the need for air conditioning. This could lead to significant energy savings, particularly in the summer months when air conditioning use is high.

Implications for Energy Savings in Canada

As we move towards heating our homes with heat pumps having new and innovative ways to not just improve the building envelope but to also improve materials this could be a huge step in the right direction. This technology could have significant implications for energy savings in Canada by reducing the amount of heat absorbed by buildings. The need for air conditioning could be greatly reduced, leading to lower energy consumption and costs.

Most impressively the paint is low-cost and compatible with commercial paint fabrication processes, making it a practical solution for widespread use. I'm genuinely intrigued to gather insights from builders like James Savoie and Doug Tarry regarding their perspective on incorporating this technology into their homes. Could a whiter-than-white paint surface on the exterior of a home serve a practical purpose? I'd love to hear thoughts on the matter.

We do have to as always use a bit of caution however. The effectiveness of this technology in Canada would depend on various factors, including the local climate and the design and insulation of the buildings where it's used. Further research and field testing in different climates and building types would be beneficial to fully understand the potential of this innovative technology.

The development of this CaCO3 paint represents an exciting step forward in the field of energy efficiency. By harnessing the power of sky window emissivity, we can reduce our reliance on energy-intensive air conditioning, contributing to a more sustainable and energy-efficient future.