scholarly journals Moisture safety in ventilated cathedral roofs

2021 ◽  
Vol 2069 (1) ◽  
pp. 012018
Author(s):  
G Månhardt ◽  
G Odén ◽  
M Stockhaus ◽  
P Wallentén
Keyword(s):  
Material Properties ◽  
Flow Model ◽  
Driving Forces ◽  
Air Flow ◽  
Initial Moisture Content ◽  
High Similarity ◽  
Thermal Buoyancy ◽  
Safety Assessments ◽  
Coupled Heat And Moisture ◽  
Heat And Moisture

Abstract Cathedral roofs are commonly used when constructing small houses in Sweden. In contrast to roof constructions with a cold attic, where frequent moisture damage has been noted, the cathedral roof is difficult to access for inspection. Furthermore, Swedish building regulations sets high demands regarding moisture safety, although there are no clear guidelines for their compliance. Hence, designing a cathedral roof must be done with great care. Previous studies investigating moisture safety in cathedral roofs, applies a constant air exchange in the ventilated air cavity. In this study a cathedral roof, ventilated from eave to eave, was analysed by examining the relevance of considering the variation in cavity air flow when conducting coupled heat and moisture calculations. The varied cavity air flow was calculated in an air flow model, considering wind and thermal buoyancy as driving forces. The accuracy of moisture safety assessments using the MRD model via hygrothermal calculations in WUFI Pro were also studied. Comparing moisture calculations with measurements showed high similarity when using a model with constant cavity air flow, and even higher resemblance when using a model with varied air flow. When actual conditions are sought, the study indicated that pinpointing important parameters, such as initial moisture content and moisture related material properties, would further increase precision in moisture calculations.

scholarly journals Air Flow Model for Mixed-Mode and Indirect-Mode Natural Convection Solar Drying of Maize

2020 ◽  
Vol 10 (2) ◽  
pp. 1
Author(s):  
Isaac N. Simate
Keyword(s):  
Natural Convection ◽  
Flow Rate ◽  
Mixed Mode ◽  
Flow Model ◽  
Air Flow ◽  
Solar Drying ◽  
Air Flow Rate ◽  
Thermal Buoyancy ◽  
Early Stages ◽  
Grain Moisture

An air flow model for mixed-mode and indirect-mode natural convection solar drying of maize to help understand the factors that influence air flow in the dryer is presented. Temperatures at various sections of the dryer obtained from drying experiments were input to the air flow model to predict the respective thermal buoyancies. The air flow rate was determined by balancing the sum of the buoyancy pressures with the sum of the flow resistances in the various sections of the dryer. To validate the model, the predicted air flow was compared with measured air flow from experiments. For both the mixed-mode and indirect-mode, the biggest driver of the air flow is the thermal buoyancy created in the collector, while the grain bed is the dominant pressure drop. Thermal buoyancy on top of the grain bed is largely responsible for the variation in air flow, translating into low mass air flow during the early stages of drying when grain moisture is high, and higher air flow in the later stages when grain moisture is low. The heating of the grain bed by direct radiation in the mixed-mode translates into a slightly higher air flow rate than the indirect-mode. The implications are that a thinner grain bed results in shorter drying time as it has a higher air flow rate than a thicker one. To mitigate the low air flow at the early stages of drying, the collector length should be appropriately designed for a desired air flow.

scholarly journals Model of thermal buoyancy in cavity-ventilated roof constructions

2021 ◽  
pp. 174425912098418
Author(s):  
Toivo Säwén ◽  
Martina Stockhaus ◽  
Carl-Eric Hagentoft ◽  
Nora Schjøth Bunkholt ◽  
Paula Wahlgren
Keyword(s):  
Analytical Model ◽  
Flow Rate ◽  
Numerical Study ◽  
Air Flow ◽  
Wind Pressure ◽  
Air Flow Rate ◽  
Test Set ◽  
Air Cavity ◽  
Thermal Buoyancy ◽  
The Impact

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.

Development of a numerical approach to assess the effect of coupled heat and moisture transfer on energy consumption of residential buildings in Moroccan context

2021 ◽  
pp. 174425912110560
Author(s):  
Yassine Chbani Idrissi ◽  
Rafik Belarbi ◽  
Mohammed Yacine Ferroukhi ◽  
M’barek Feddaoui ◽  
Driss Agliz
Keyword(s):  
Energy Consumption ◽  
Building Materials ◽  
Moisture Transfer ◽  
Residential Buildings ◽  
Building Design ◽  
Energy Performance ◽  
Climatic Conditions ◽  
Heat And Moisture Transfer ◽  
Coupled Heat And Moisture ◽  
Heat And Moisture

Hygrothermal properties of building materials, climatic conditions and energy performance are interrelated and have to be considered simultaneously as part of an optimised building design. In this paper, a new approach to evaluate the energy consumption of residential buildings in Morocco is presented. This approach is based on the effect of coupled heat and moisture transfer in typical residential buildings and on their responses to the varied climatic conditions encountered in the country. This approach allows us to evaluate with better accuracy the response of building energy performance and the indoor comfort of building occupants. Annual energy consumption, cooling and heating energy requirements were estimated considering the six climatic zones of Morocco. Based on the results, terms related to coupled heat and moisture transfer can effectively correct the existing energy consumption calculations of the six zones of Morocco, which currently do not consider energy consumption due to coupled heat and moisture transfer.

scholarly journals Modeling of Forming Limit Bands for Strain-Based Failure-Analysis of Ultra-High-Strength Steels

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 631 ◽  
Author(s):  
Hamid Bayat ◽  
Sayantan Sarkar ◽  
Bharath Anantharamaiah ◽  
Francesco Italiano ◽  
Aleksandar Bach ◽  
...  
Keyword(s):  
Material Properties ◽  
Driving Forces ◽  
Weight Ratio ◽  
High Strength Steels ◽  
High Strength ◽  
Forming Limit ◽  
Boron Steel ◽  
Passenger Safety ◽  
Ultra High Strength Steels ◽  
Increased Strength

Increased passenger safety and emission control are two of the main driving forces in the automotive industry for the development of light weight constructions. For increased strength to weight ratio, ultra-high-strength steels (UHSSs) are used in car body structures. Prediction of failure in such sheet metals is of high significance in the simulation of car crashes to avoid additional costs and fatalities. However, a disadvantage of this class of metals is a pronounced scatter in their material properties due to e.g., the manufacturing processes. In this work, a robust numerical model is developed in order to take the scatter into account in the prediction of the failure in manganese boron steel (22MnB5). To this end, the underlying material properties which determine the shapes of forming limit curves (FLCs) are obtained from experiments. A modified Marciniak–Kuczynski model is applied to determine the failure limits. By using a statistical approach, the material scatter is quantified in terms of two limiting hardening relations. Finally, the numerical solution obtained from simulations is verified experimentally. By generation of the so called forming limit bands (FLBs), the dispersion of limit strains is captured within the bounds of forming limits instead of a single FLC. In this way, the FLBs separate the whole region into safe, necking and failed zones.

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