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In the last few decades, rain-screen wall systems have become common in building enclosure designs and construction for the purpose of mitigating moisture damage risk. Existing literature shows an air cavity in rain-screen wall facilitates moisture control performance. However, it is not clear whether it is just the presence of a capillary break created by the air gap or the cavity ventilation. It is a common practice to use a predefined constant cavity ventilation rate while modelling the thermal and hygrothermal performance assessments of rain-screen wall systems. However, cavity ventilation rates in ventilated wall systems vary with driving forces such as, wind and solar radiation. In this paper, three wall types, namely vented, ventilated, and wall system with no air gap, are manufactured and installed in two opposite orientations of a field-experimental test building. The air velocity, relative humidity and temperature in the cavity, and the moisture content and temperature in plywood and wood frame studs are monitored for 15 months. Based on the monitored data and analysis, a cavity ventilation regression model for the combined wind and solar induced flows is developed. The empirical model is presented as a function of hourly wind pressure and the temperature difference between the outdoor and cavity space. The empirical model is tested with the whole measured data and a good fit (R2 value of 0.912) is achieved between the model and measurement. The long-term hygrothermal performance analysis shows that the wall with no air gap accumulates relatively high moisture content and also has high moisture content changes in a year cycle when compared to the vented and ventilated wall systems. The moisture control performance of vented and ventilated wall systems is comparable thus emphasizing the important parameter for enhanced hygrothermal performance is having a cavity vent not the type of ventilation design (vented or ventilated). The temperature readings of the sheathing boards in the vented and ventilated wall systems are somewhat warmer than that of the wall with no air gap for 85.5% and 73% of the experimental measurement time, respectively. • Long-term field-experimental measurements of air flow in rain-screen wall systems is presented. • Cavity pressure and ventilation rates in rain screen wall system are characterized for different seasons. • An empirical cavity ventilation model is developed for hourly hygrothermal and energy performance analysis. • Hygrothermal performance of wall systems with cavity ventilation scenarios: vented, ventilated and no air gap are presented. [ABSTRACT FROM AUTHOR]

Air leakage in buildings can cause health and comfort concerns for occupants and can contribute to mold growth on building materials, or in extreme conditions, rot of building materials. Unwanted air leakage through the building envelope also contributes to approximately 4 quadrillion Btu (1172 TWh) of energy consumption per year in the building sector in the United States. Locating and sealing leakage sites can improve the energy efficiency, comfort, air quality, and moisture durability of the building stock. Typical methods of finding leakage sites, such as infrared imaging and smoke tracing, rely on concurrent blower door operation, which can also measure the total leakage rate of the building. Smoke tracing can be disruptive to occupants, and infrared imaging and smoke tracing cannot measure the contribution of individual leaks to prioritize sealing efforts. In this work, an optical fluid flow imaging technique, reference-free natural background–oriented schlieren imaging, was adapted to visualize air exfiltration. This is the first step in developing a method to noninvasively locate and measure exfiltration or infiltration sites so that sealing efforts can be prioritized. Experimental results of this technique are presented, demonstrating the method's applicability to visualizing exfiltration through three common building claddings in an outdoor environment. Key variables impacting the performance of this technique when applied to building leakage are also discussed. • Sealing building leakage can reduce energy consumption and carbon emission. • Background oriented schlieren photography can visualize transparent fluids. • An indoor-to-outdoor temperature difference is needed to visualize exfiltration. • A wall cladding of sufficient contrast is required for synthetic schlieren. • Successful exfiltration visualization is shown through brick and concrete walls. [ABSTRACT FROM AUTHOR]

This paper aims to study the effects of wind-driven rain load and vapor diffusion on the hygrothermal performance of wall systems in a wet and mild climate through a field experimental study. In the study, four test panels with a combination of vapor barrier and capillary break are manufactured, instrumented and installed in a field experimental facility. The wetting and drying potentials of the test panels in response to a predominately vapor diffusion and a wind-driven rain load are discussed based on the analysis of 15 months of measurement data. The experimental result shows that, in a yearly basis, the wetting and drying rates of a wall without a capillary break are about two times higher than that of the wall with a capillary break. While the wetting and drying rates are comparable in a wall system with a vapor barrier, the drying rate is 38% higher than the wetting rate in a wall with no vapor barrier. In general, a wall with no vapor barrier wets and also dries faster than a wall with a vapor barrier. For the wall types and climate considered in this paper, the wetting rates of walls with a predominately wetting mechanism of vapor diffusion and wind-drive rain load are comparable. In general, the experimental data suggest that even in a mild climate, vapor diffusion is a critical moisture load with comparable effect that wind-driven load induces. [ABSTRACT FROM AUTHOR]

The international residential code (IRC) and most building codes in North America provide attic ventilation codes which allow a certain minimum venting area with an unblocked space by the ceiling insulation. Most of these codes have similar minimum venting ratio, minimum space gap between the roof sheathing and ceiling insulation and vent area location for similar climatic conditions. In this paper, the effects of varying the gap between roof sheathing and ceiling insulation (baffle size) and the locations of vent area under both summer and winter conditions are investigated. Three different baffle sizes and three different locations of the attic vent are used to study their effect on the air distribution and temperature profile inside the attic space. A CFD model is developed and validated using existing experimental measurements. Results show that increasing baffle size hugely affects the air distribution when the air flow is majorly driven by wind. The upper side roof vents have been located at three different locations and our findings show when the upper vent is placed the furthest from the ridge the Air Change per Hour (ACH) value in the attic increases but the air circulation is minimal in the top parts of the attic space and structural elements. [ABSTRACT FROM AUTHOR]