Paint coating cools people by up to 1.5ºC

SINGAPORE: A real-world study by researchers at Nanyang Technological University, Singapore, has shown that the use of cool paint coatings in cities can help pedestrians feel up to 1.5ºC cooler. 

Cool paint coatings contain additives that reflect the sun’s heat to reduce surface heat absorption and emission. They have been touted as one way to cool down the urban area and mitigate the urban heat island effect.

Researchers from Nanyang Technological University (NTU) coated the roofs, walls and road pavements of an industrial area in Singapore and found that by comparison with an adjacent uncoated area, the coated environment was up to 2ºC cooler in the afternoon, with pedestrian thermal comfort level improving by up to 1.5ºC. 

Measurements were based on the universal thermal climate index – the common international standard for human outdoor temperature sensation that takes into account temperature, relative humidity, thermal radiation, and wind speed.

Experiments

The NTU researchers selected four rectangular buildings that created two parallel street canyons – narrow streets flanked by buildings – in an industrial estate west of Singapore managed by JTC Corporation, the government agency championing sustainable industrial development.

One canyon was coated with cool paints on the roofs, walls, and road pavement, while the other canyon remained as it was as a control for the experiment.

Using environmental sensors, the NTU team monitored the conditions in the two canyons over two months, which included air movement, surface and air temperature, humidity, and radiation, to see how well the cool paint coatings worked in reducing city heat.

The researchers found that during a 24-hour cycle, the cool canyon saw up to a 30% reduction in heat released from the built-up surfaces, resulting in the airtemperature in the cool canyon being cooler than the conventional canyon by up to 2ºC during the hottest time of the day, at around 4pm. As a result, pedestrians in the cool canyon can feel up to 1.5ºC cooler.

The NTU research team also found that air temperature in the cool canyon was lowered because less heat was absorbed by and stored in the building walls, roofs, and roads, and which would subsequently have been released to either heat up the surrounding air or the building’s interior.

Compared to conventional roofs, the roofs with the cool paint coating reflected 50% more sunlight and absorbed up to 40% less heat as a result, during the hottest time of a sunny day. The coated walls also prevented most of the heat from entering the industrial buildings.

“This is a minimally intrusive solution for urban cooling that has an immediate effect, compared to other options that often require major urban redevelopment to deploy,” said lead author Dr E V S Kiran Kumar Donthu, who completed the work as a research fellow at NTU’s Energy Research Institute. “Moreover, by reducing the amount of heat absorbed in urban structures, we also reduce heat load in buildings, consequently reducing indoor air conditioning energy consumption.”