Experimental Study of Thermal Buoyancy in the Cavity of Ventilated Roofs

Bunkholt, Nora Schjøth; Säwén, Toivo; Stockhaus, Martina; Kvande, Tore; Gullbrekken, Lars; Wahlgren, Paula; Lohne, Jardar

doi:10.3390/buildings10010008

Cited by 12 publications

(5 citation statements)

References 31 publications

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“…The solar chimney consists of a solar collector that heats the air inside; this increase in temperature decreases its density so that it tends to rise, thus sucking air from inside the building to the outside, which in turn draws in outside air through the windows, as shown in the scheme of Figure 1. A great variety of works demonstrate the performance of natural ventilation and provide theoretical or experimental solar chimney system performance results; however, there are few works on the integration of these systems into the total or partial volume of a housing model [26][27][28][29][30][31].…”

Section: Solar Chimneymentioning

confidence: 99%

CFD Evaluation of Thermal Conditioning in a House of Social Interest with a Solar Chimney Arrangement in Guanajuato, Mexico

Miranda¹,

Gamboa

Zamora-Antuñano

et al. 2023

Processes

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The aim of using electromechanical air conditioning in buildings is to maintain thermal comfort for its occupants; however, this type of air conditioning represents 40% of the total energy consumption of a building, generating economic and environmental impacts, because fossil fuels are the main source of energy. To reduce the use of electromechanical conditioning, it is possible to take advantage of the climatic conditions of the region to improve its performance. Due to the small number of works that quantitatively support measures aimed at improving the thermal behavior of houses in an integral way and the growth of mass construction in Mexico, in the present work, a solar chimney is incorporated in a typical type of social interest housing in Guanajuato. The incorporation of the solar chimney was simulated by using computational fluid dynamics (CFD) using ANSYS and evaluated by ASHRAE Standard 55-2017. The selected arrangement induces air flow inside without the need for external flow and obtains speeds of 0.2 m/s; thus, it could be considered for rooms within comfort zones up to an operating temperature of 29 °C according to the ASHRAE Standard 55-2017, PMV method.

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Section: Solar Chimneymentioning

confidence: 99%

CFD Evaluation of Thermal Conditioning in a House of Social Interest with a Solar Chimney Arrangement in Guanajuato, Mexico

Miranda¹,

Gamboa

Zamora-Antuñano

et al. 2023

Processes

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“…Bunkholt et al [48] investigated, through a laboratory study, how the air flow through a ventilated roof cavity is affected by temperature and air cavity design. Measurements indicated that the air cavity temperature and flow conditions were affected by the cavity width as well as the roof angle.…”

Section: Roofsmentioning

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 experimental study was performed at one of the laboratories of SINTEF and NTNU in Trondheim, Norway (Bunkholt, 2019;Bunkholt et al, 2020;Svantesson and Sa¨we´n, 2019). Experiments were conducted on a full-scale model of a section of a cavity-ventilated roof construction, represented schematically in Figure 6.…”

Section: Experimental Studymentioning

confidence: 99%

Model of thermal buoyancy in cavity-ventilated roof constructions

Säwén

Stockhaus

Hagentoft

et al. 2021

Journal of Building Physics

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Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

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Experimental Study of Thermal Buoyancy in the Cavity of Ventilated Roofs

Cited by 12 publications

References 31 publications

CFD Evaluation of Thermal Conditioning in a House of Social Interest with a Solar Chimney Arrangement in Guanajuato, Mexico

CFD Evaluation of Thermal Conditioning in a House of Social Interest with a Solar Chimney Arrangement in Guanajuato, Mexico

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

Model of thermal buoyancy in cavity-ventilated roof constructions

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