Summer is here and temperatures are soaring across the country. Many cities are especially feeling the heat this time of year as they experience urban heat island effect. According to the U.S. Environmental Protection Agency (EPA) these urban areas, made up of buildings, roads, and other infrastructures absorbing and remitting the sun’s heat, become “islands” of higher temperatures relative to outlying areas offering more greenery.
Elevated temperatures from heat islands can affect a community and its quality of life in several ways, including increased energy consumption, air pollution levels, heat-related illness, and impaired water quality. According to The National League of Cities (NLC) climate change is only going to increase these effects, as heat projections for the next several decades continue to rise.
To help reduce heat island effect and lower the mean radiant temperature (MRT), the EPA recommends communities utilize these five main strategies:
- Using cool pavements
- Creating green roofs
- Increasing trees and vegetative cover
- Installing cool, mainly reflective roofs
- Implementing smart growth practices
Now, let’s dive deeper into understanding the science behind MRT, and how sealcoating can help lower pavement temperatures and combat urban heat islands.
What is MRT?
According to the UCLA Luskin Center for Innovation, mean radiant temperature, or MRT, is made up of several climate variables, including incoming solar radiation, air temperature, humidity, airflow, and thermal properties of surface materials. MRT is a measure of the combined effect of all the radiant temperatures in an environment. This measurement is useful because it helps us understand thermal comfort, which refers to the way the human body experiences heat.
Unlike air temperature, which only accounts for the temperature of the air, MRT also considers the heat radiating from all nearby surfaces, such as walls, floors, ceilings, and outdoor surfaces. So even if the air temperature is moderate, high MRT can still trigger feelings of discomfort and heat stress.
Factors that Influence MRT
Now that we have a basic understanding of what MRT is, let’s take a closer look at the four main factors influencing MRT:
- Surface Materials – Different materials will absorb and emit radiant heat in various ways. For example, darker surfaces tend to absorb more heat, which raises the MRT.
- Surface Colors – Colors matter, too. While lighter colors reflect more sunlight, darker colors absorb it, which also impacts MRT.
- Sun Exposure – Any areas that are exposed to direct sunlight will have higher MRT due to increased radiant heat.
- Urban Layout – The arrangement of buildings, streets, and open spaces can affect how heat is radiated and absorbed, which influences the MRT in urban areas.
Measuring MRT
Since MRT includes so many different variables, how exactly can it be measured? MRT is typically measured using a specialized instrument known as a globe thermometer, which can mimic the heat exchange properties of the human body. MRT can also be measured through calculations that consider the temperatures of all surrounding surfaces and the angles at which they are viewed by a person.
With a better understanding of MRT, urban planners can design cities that ease heat stress by incorporating cool pavements, green spaces, and reflective surfaces. Architects can also use MRT data to optimize building orientation, materials, and insulation to enhance thermal comfort. Lastly, reducing MRT can help decrease the chance of heat-related illnesses.
MRT and Cool Pavement
One effective strategy for reducing MRT is the sealcoating application of cool pavements, which are materials and treatments designed to reflect more sunlight and absorb less heat when compared to conventional pavements. Using this type of paving materials on sidewalks, parking lots, and streets not only cools the pavement surface and surrounding air, but can also reduce stormwater runoff and improve nighttime visibility.
According to the EPA, conventional pavements can reach peak summertime surface temperatures of 120-150°F (48–67°C). Heat can be stored in the pavement subsurface, and then re-released as heat at night. Cool pavements like CoolSeal by GuardTop, on the other hand, are designed to reflect the sun’s energy to produce cooler surface temperatures through increased reflectivity. Research shows that they’re doing just that. in a study conducted by Arizona State University (ASU) Researchers as part of the Cool Pavement Pilot Program, the CoolSeal cool pavement used in the program had an average surface temperature 10.5-12°F lower than traditional asphalt at noon and during the afternoon hours. ASU Researchers discovered that CoolSeal’s cooler pavement coating reflects a higher portion of the sunlight that hits it, absorbing less heat. Thanks to this higher reflection, the coating can potentially offset rising nighttime temperatures, helping combat urban heat islands in the city of Phoenix.
Additional Benefits of Cool Pavement
According to the EPA, the decreased energy demand associated with cool pavements will result in lower associated air pollution and greenhouse gas emissions. In addition, cooler air temperatures can also reduce evaporative emissions from vehicles and slow the rate of ground-level ozone formation.
Cool pavements can also have an impact on vehicle fuel consumption. Some cool pavements have structural properties and longevity that can minimize the excess fuel consumption of vehicles caused by road quality. Over the lifetime of a pavement, these fuel savings can add up, even offsetting the higher initial investment of paving with more durable materials.
Read more about the additional benefits of cool pavement here.
Sealcoating with reflecting properties is a cool pavement solution that can significantly lower surface temperatures, which reduces the MRT and improves the overall thermal comfort in urban areas.
