Empirical model for cavity ventilation and hygrothermal performance assessment of wood frame wall systems: Experimental study

Tariku, Fitsum; Iffa, Emishaw

doi:10.1016/j.buildenv.2019.04.020

Cited by 16 publications

(4 citation statements)

References 9 publications

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“…In other words, the incoming warmer air increases the heat transfer rate across the cavity region, thereby reducing the thermal resistance based on a temperature difference (T H − T L ) of 16.6 • C. However, when the incoming air is cooler than the hot surface temperature, then there could be an increase in the apparent thermal resistance of the cavity. As the use of ventilated cavities has already been made a requirement by some building codes (e.g., National Building Code of Canada [45]) where ventilated cavities exist in brick walls [46] and wood framing systems [47], the results provided in this paper are applicable for these wall systems with and without reflective insulations. For these wall systems with configurations different than that used in this paper, however, the numerical model used in this study would be useful for modeling ventilated wall designs that result in energy savings.…”

Section: R-values Of Reflective Insulation Assemblies With Wind Washingmentioning

confidence: 99%

Assessing the Effect of Air Intrusion on Reflective Insulations Performance with Horizontal Heat Flow

Saber,

Yarbrough

2023

Buildings

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The determination of thermal resistances (R-values) for enclosed airspaces, including those with one or more low-emittance surfaces, has advanced from one-dimensional heat transfer between large parallel planes to multi-dimensional heat flow in a wide variety of physical configurations. The key elements in this advancement, however, are the evaluation of the heat flow due to conduction-convection and the solution for radiation that includes all surfaces bounding the region of interest. The model used in this study has been validated against several sets of laboratory test data, including the data from the U.S. National Bureau of Standards for the thermal resistance of airspaces, which has been the basis for handbook values for reflective airspaces for five decades. In addition, this model has been previously used to determine the reductions in the R-values of reflective insulations assemblies due to imperfect installations and internal defects in multilayer reflective systems with cross-airflow between the layers. In this study, the model is used to examine the impact on R-value of air intrusion of different air changes per hour (ACH) at various exterior air temperatures into reflective insulation assemblies with a range of effective emittance from 0 to 0.82. Two cases are considered in this study. In the first case, called “infiltration”, exterior air enters the assembly through an opening located in the hot side of the assembly and exits through another opening located in the cold side of the assembly. In the second case, called “wind washing”, the exterior air enters the assembly through an opening located in the hot side of the assembly and exits through another opening located in the same side of the assembly. To quantify the reductions in the R-values due to infiltration and wind washing conditions, a reference case is included in this study for the case in which no air intrusion occurs in the reflective insulation assemblies. Finally, consideration is given to investigating the effect of the aspect ratio on the R-values of reflective insulation assemblies without air intrusion and with air intrusion of different ACH at various exterior air temperatures. The results show that the aspect ratio has a significant impact on the R-value of reflective insulation assemblies with and without air intrusion. Additionally, the results show that the impact of infiltration and wind washing on R-values of reflective insulation assemblies increase as the difference between the exterior air temperature and the undisturbed temperature of the cavity increases.

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Section: R-values Of Reflective Insulation Assemblies With Wind Washingmentioning

confidence: 99%

Assessing the Effect of Air Intrusion on Reflective Insulations Performance with Horizontal Heat Flow

Saber,

Yarbrough

2023

Buildings

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“…In Vancouver, Canada, Tariku and Iffa [58] performed an experimental study assessing the hygrothermal performance of wood frame systems built with different concepts of air cavities (ventilated, vented, no cavity). The findings included that ventilated façades have a vastly higher air change rate; that temperatures behind the façade boards are lower in the wall without an air cavity during winter days; and that the ventilated cavity sees a higher moisture content in the upper section during the wet winter season.…”

Section: Notable Studies From Outside Nordic Climatesmentioning

confidence: 99%

Microclimate of Air Cavities in Ventilated Roof and Façade Systems in Nordic Climates

2022

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Accurate values for the climatic conditions in an air cavity, hereby called the microclimate, are crucial when calculating and simulating the performance of a ventilated roof and façade system. The climatic stress of its components and their mould and rot potential influence the long-term durability of the roof or façade. A scoping study is conducted to gain an overview on research and the scientific literature on the microclimate of air cavities in ventilated roofing and claddings in Nordic climates. From the body of the research literature, 21 scientific works were of particular interest, and their findings are summarized. The review shows that only a limited number of studies discuss the microclimate of air cavities. Roofs are discussed to a greater and more varied degree compared to façades and air cavities behind solar panels. However, the results cannot be compared and validated against each other to generally describe the microclimate of air cavities, as the surveyed papers approach the subject differently. This knowledge gap indicates that calculations and simulations can be performed without knowing whether the results represent reality. If the structure of ventilated roof and façade systems are only designed based on experience, it can be difficult to be proactive and adapt to future climate changes. Further studies are needed to determine the relation between the exterior climate and the air cavity microclimate, so that future climate predictions can be used to simulate the long-term performance of ventilated roof and façade systems.

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“…The use of large ventilated cavities has already been required by some building codes (NBCC 2005). Several research projects have analyzed different hygrothermal aspects of the ventilated cavity incorporated in the exterior surface of the wall assemblies (Finch and Straube 2007;Balocco 2009;Manuel et al 2013;Langmans and Roels 2015;Van Belleghem et al 2015;Gagliano, Nocera, and Aneli 2016;Buratti et al 2018, Meyer et al 2019Tariku and Iffa 2019). A very comprehensive literature review on the factors affecting the airflow rate in the ventilated cavity behind different types of traditional external cladding systems is recently performed by Rahiminejad and Khovalyg (2021).…”

Section: Introductionmentioning

confidence: 99%

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

Rahiminejad

Khovalyg

2021

Science and Technology for the Built Environment

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The presence of an airspace within a building envelope is known to have a varying contribution to the overall thermal performance of the wall assembly due to the combined effect of convection and radiation in the air cavity. In particular, the thermal resistance of a ventilated airspace can vary significantly depending on multiple environmental and thermo-physical parameters. Although the thermal resistance of enclosed air-spaces in the building structures has been thoroughly investigated in the literature, it has not been defined for a ventilated cavity. This paper aims to introduce the plausible definitions of the thermal resistance of a vertical ventilated airspace behind external cladding systems. Both theoretical and applied formulations are provided and compared. The energy balance method is used to model the steady-state heat transfer through two types of traditional external wall systems (i.e., brick and vinyl siding) in summer and winter conditions. A range of air exchange rates in the cavity is examined, and the effect of the presence of reflective insulation in the airspace on the thermal resistance of the air gap is analyzed. The results show that the presence of a ventilated cavity in the wall assembly can influence the thermal performance of the building envelope. In particular, the effective thermal resistance of a ventilated airspace behind a brick cladding wall could be between 0.17 and 1.85 times the thermal resistance of the cladding in the range of air change rate in the cavity from 0 to 100 1/h. The effective thermal resistance of the ventilated air gap behind vinyl siding could reach up to 9 times the thermal resistance of the cladding.

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Empirical model for cavity ventilation and hygrothermal performance assessment of wood frame wall systems: Experimental study

Cited by 16 publications

References 9 publications

Assessing the Effect of Air Intrusion on Reflective Insulations Performance with Horizontal Heat Flow

Assessing the Effect of Air Intrusion on Reflective Insulations Performance with Horizontal Heat Flow

Microclimate of Air Cavities in Ventilated Roof and Façade Systems in Nordic Climates

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

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