Effect on CO2 Emissions of Building-Urban Area by Introducing Solar Reflective Paint

In recent years, CO₂ emissions from commercial and residential sectors have greatly been increasing in Japan. Although governmental regulations about energy use are very effective for reducing industrial CO₂ emissions, they are found to be ineffective for commercial and residential ones. Low-cost measures for CO₂ reduction are therefore highly desirable for those sectors.

In the present paper, we focus upon solar reflective paint (SRP). SRP is one of low-cost measures, and increases the albedo on the ground surface level and may mitigate heat island phenomenon. To evaluate the efficiency of this technology, we must simulate urban thermal environment as well as building heat load. Here we evaluate the extents of reduction in CO₂ emissions from buildings by SRP, according to the following methods.

We first evaluated the extents of decrease in the solar reflectance of SRP by outdoor exposure experiment, and found that its solar reflectance averaged to be 0.75 for five years, a period warranted for its effectiveness.

We next developed an environment-evaluating model, which combined both buildings' heat load simulation model and urban thermal environment simulation one, through calculating artificial exhaust heat from building and estimating outside temperature throughout year. Based on this model, SRP was found to be effective as a heat island mitigating measure, but not as a CO₂ reducing measure. Installed to all buildings in the commercial sector in the Tokyo area, CO₂ emissions increase by 0.9%, and in the residential sector by 0.5%. The former value is more than a 0.6% increase which is estimated for individual building, and the difference is due to decreased outside temperature by using SRP. When SRP is introduced April through October, we expect an 11.8% decrease, the extent of which is more than 10.7% which is estimated for individual building.

Thus, SRP is helpful for the buildings equipped with new-type air-conditioning and/or the current intelligent buildings. These buildings that are concentrated in a particular area should be installed with SRP.