Search

This paper evaluates the thermal performance of ducts partially or fully buried in loose-fill attic insulation. The overall thermal resistance between the ducts and the attic is referred to as an effective R-value. This paper shows a strong dependency of assumed attic temperature on the effective R-value. Based on the results, the effective R-value can be about twice as much with an attic temperature of 130 °F [54.4 °C], compared to when the attic temperature is 80 °F [26.7 °C]. Thus, this paper provides a polynomial regression equation based on a large set of simulations to determine the effective R-value of buried ducts depending on attic temperature and whether the HVAC system runs in cooling or heating mode. Further, the work presented in this paper investigated the potential impact of convective airflow within the attic insulation, particularly around the ducts. The analysis was based on computational fluid dynamics (CFD) and indicated that convectional forces are presented around the exterior surface of the ducts, but with negligible impact on the overall heat balance between the duct and the attic space. [ABSTRACT FROM AUTHOR]

Unvented attics are an energy-efficiency measure to reduce the thermal load of the conditioned space and decrease the space conditioning energy consumption by about 10%. This retrofit is usually done by spraying polyurethane foam underneath the roof sheathing, and on the gables and soffits of an attic to provide an air barrier and a thermal control layer. Unvented attics perform well from this perspective, but from a moisture perspective sometimes homes with unvented attics have high interior humidity or moisture damage to the roof. As homes become more air tight and energy efficient, a better understanding of the hygrothermal dynamics of homes with energy-efficient envelopes becomes more important. One proposed reason for high unvented attic humidity has been that moisture can come through the asphalt shingle roof system and increase the moisture content of the roof sheathing and attic air. This has been called "solar-driven moisture." Oak Ridge National Laboratory investigated this proposed phenomenon by examining the physical properties of a roof and the physics required for the phenomenon. Results showed that there are not favorable conditions for solardriven moisture to occur. Oak Ridge National Laboratory also conducted an experimental study in a home with an unvented attic and compared the humidity below the roof sheathing before and after a vapor impermeable underlayment was installed. There was no statistically significant difference in absolute humidity before and after the impermeable underlayment was installed. The outcomes of the theoretical and experimental studies suggest that solar-driven moisture does not occur in any significant amount. [ABSTRACT FROM AUTHOR]

Deep basements, crawl spaces and slab on grade are typical foundations in residential buildings in North America. The foundation of a house is a somewhat invisible and at sometimes ignored component of the building. Appropriate foundation design and construction practice must not only include thermal performance, but also design for a durable and safe hygrothermal performance.A hygrothermal simulation tool can be used to evaluate and predict the hygrothermal behavior of an insulated foundation constructions, in cooperation with the surrounding soil. Though, further development of the tool might first be needed and validated to fulfill the prerequisites. Transient hygrothermal simulation tools have existed in Building Science for more than 20 years, but are mainly used for building envelope simulation above ground. A lot of knowledge already exists in Soil Science concerning the variation of the soil material properties in relation to soil texture, moisture content etc. However, Soil Science uses these properties for other purpose and with different modeling approaches, hence a conversion is needed.This paper studies the existing knowledge of soil properties, converted to apply for simulation in Building Science. Further, the soil properties are implemented in a transient hygrothermal simulation tool, studying the applicability for modeling soil temperature and moisture flow. Finally the results are compared with measurement and followed by a discussion of further investigations and development needed. [ABSTRACT FROM AUTHOR]