Long term examination of thermal management of roof structures with air flow systems or/and polyurethane foams

Abstract

We have examined the annual, summer, and winter effect of air flow systems to reduce thermal conduction through roof structures and the temperature rise of roof surfaces due to solar absorption. These systems are proposed as replacement for polyurethane foams (PUFs), which are conventionally used for thermal insulation in roof structures and are concerned about the amount of the usage. We prepared six types of roof structures and installed them on experimental cells. The structures consisted of air flow layers and/or PUF layers. We then measured temperatures, evacuated heat, thermal conduction, solar absorption, and thermal radiation every 10 minutes throughout one year. By installing the air flow system in place of or along with PUF, the temperature rise due to solar irradiance of the top roof sheet is suppressed. This suppression is approximately independent of seasons, although it is slightly more effective in winter than summer. Air flow system/PUF combined roof structures control thermal conduction between roof sheets and concrete slabs, though the total thickness is the same or less than those of a single PUF layer. According to heat flow analyses, the air flow systems can evacuate at maximum about 10% of heat that flows into roof structures through the year. In summer, the heat evacuation reduces thermal conduction to concrete slabs, whereas in winter it increases convective heat from concrete slabs. The air flow system is a promising option to allow reduction of the thickness of roof structures and the amount of PUF employed in construction. It is expected to promote improved architectural design, durability, and energy conservation of roofs.