With 246 sunny days, an average UV index of 6.9, and 74 days of  over 90 °F temperatures a year, Tampa, Florida, experiences high cooling costs for commercial and institutional buildings. Finding a way to reduce those costs was the goal of a recent dormitory refresh project at the University of South Florida (USF), where an infrared, heat-reflective, water-based coating system called TEX-COTE^® COOLWALL^® with KYNAR^® PVDF is helping to lower building surface temperatures and related cooling costs.

“Ph.D. candidates at USF initially approached us about our heat-reflective coating system as part of a research project,” said Simon Reynolds, director of commercial sales, TEX-COTE LLC. “That research dovetailed nicely with work being undertaken by the university’s housing group to renovate one of its dormitories and reduce its energy use.”

How Cool Walls Save Energy

Just as wearing light-colored clothing can help keep a person cool on a sunny day, exterior coatings with solar-reflective surfaces can help maintain lower temperatures on a building’s surface. Lower building façade temperatures translate into reduced solar heat gain — the amount of heat from the sun that enters the building — which helps maintain cooler indoor temperatures compared to less reflective exterior coatings. In turn, cooler indoor temperatures reduce the building’s cooling demand and decrease the amount of waste heat released by air conditioning units.

FIGURE 1| The solar reflective index, or how cool a surface is, measures a surface’s ability to reflect solar heat and return solar energy to the atmosphere. 

Considering that cooling systems consume an estimated 15% of the electricity used by commercial and institutional buildings, property owners can recognize significant savings by reducing the energy required to run them.

“Concrete buildings like the dorm at USF are thermally massive,” Reynolds said. “They soak up energy during the day and hold onto it throughout the night, making it difficult to get any cooling effects from the night air. By reflecting that heat energy and stopping temperature buildup, you can reduce a building’s contribution to the urban heat island effect.”

Military-Grade Heat-Reflective Technology

TEX-COTE was the first paint and coatings manufacturer to be granted a patent for heat-reflective wall coatings. For its heat-reflective coating system with a PVDF-based resin, the company turned to the same heat-reflective technology the military uses in the STEALTH program to reduce the amount of solar heat absorbed, and radar signals detected, on planes and vehicles. This highly reflective pigment technology reflects the invisible portion of the light spectrum, helping to deflect heat without altering the coating’s color.

The system has been tested by the U.S. Department of Energy’s Oak Ridge National Laboratory and has been shown to reduce surface temperatures by as much as 40 °F and provide cooling cost energy savings of up to 21.9%. These benefits have allowed some property owners to apply for energy savings credits under the Leadership in Energy and Environmental Design (LEED) green building certification program.

FIGURE 2 |Testing of COOLWALL with KYNAR PVDF on wood and concrete/masonry construction homes around the country proved the coatings’ energy-savings performance.

At USF, surface temperature readings on the tilt-up concrete dorm coated with the technology were up to 40 °F cooler than before application. Ongoing energy monitoring continues to display a reduction in cooling energy use compared to pre-application levels.

Dark Colors Can Be Cool

Traditionally, white paint has been used to keep a building’s exterior cool because it reflects much of the sun’s radiation back into the atmosphere. Dark colors, while aesthetically pleasing, have historically led to heat buildup.

With heat-reflective coating technology, buildings don’t need to be white to achieve solar reflectance benefits. For the USF dormitory, the coating was supplied in shades of amber, gold, tan and red to match the color scheme used throughout campus.

FIGURE 3 |The USF dormitory features bold and saturated colors.

Durability and Fade Resistance

The heat-reflective technology used in the coating system provides long-term benefits beyond energy savings, including increased durability and fade resistance, which allow the system to last longer with less maintenance.

“Heat accelerates the degradation and fading of exterior coatings, especially in hot, humid locations like Florida,” Reynolds said. “COOLWALL coatings are much more durable and undergo significantly less thermal cycling-related expansion and contraction stress than typical acrylic or elastomeric coatings. Their color, adhesion and other physical properties also are greatly extended, thanks to our use of water-based Kynar Aquatec^® PVDF resin.”

The resin features strong carbon-fluorine bonds that prevent film erosion when exposed to the elements, keeping the film thickness consistent — and the coating’s infrared-reflecting pigments protected — over time. These bonds help maintain solar reflectance, dirt-shedding ability, algae and mold/mildew resistance, color and gloss retention and resistance to chalking and fading. Dirt-shedding and algae/mold resistance properties are particularly important, as dirty surfaces reduce solar reflectance.

Most common architectural coatings degrade in the harsh Florida sun. They chalk and erode quickly, requiring repainting every five to seven years. The resistance to film erosion provided by the PVDF resin allows the reflective pigment technology to remain in place, maintaining lower surface temperatures over time. This combination of materials reduces the cost of frequent repainting and lowers energy consumption in the long run.

“Unlike conventional paints that rely on mildewcides, which leach out over time, this coating system combines mildewcides with the mildew-resistant properties inherent in the PVDF resin, ensuring they last the life of the coating,” Reynolds added.

“For decades, architects have trusted the long-term, fade-resistant performance of PVDF-based finishes, which are baked onto metal surfaces of exterior building products like aluminum doors and window frames in the factory,” said Ron Partridge, senior account manager, Kynar PVDF Coatings, Arkema Inc. “This technology does not need to be baked, allowing it to provide the same long-term weathering performance in an air-dry, field-applied coating.”

“Like many architects and project specifiers we talk with, the decision-makers at USF agreed that the cost-benefit analysis of the reflective coating system came out solidly in its favor for cooling benefits and increased longevity,” Reynolds concluded. “Even five years post-application, we’re seeing great film integrity, excellent color and gloss retention and no mold or dirt buildup. The dorm looks like it was freshly coated yesterday.”

FIGURE 4 | Five years after the COOLWALL with Kynar coatings installation, the deep, bold hues remain true and fade-free, as seen when compared against color swatches from the original application.

Learn more at https://www.texcote.com/coolwall. 

*All images courtesy of TEX-COTE.