Indoor air quality evaluation in naturally cross-ventilated buildings for education using age of air

Natural ventilation (NV) is a strategy of bioclimatic design to promote hygrothermal comfort and indoor air quality (IAQ). Nowadays, COVID-19 pandemic highlights the review of ventilation standards. In Mexico, the IAQ standard states a minimum of 6 ACH for educational buildings. ACH considers NV as an ideal piston flow and does not provide information of indoor airflow distribution. In this work, new age of air associated parameters are proposed, considering the indoor airflow distribution: the air renovation per hour (ARH) and the renovation parameter R. An isolated educational building located in a rural region is studied. Four window configurations of cross-ventilation are considered. All configurations have one windward window located at bottom. The configurations axial and upward have one leeward window at bottom and top, respectively. While, configurations corner and upward corner have one lateral side window at bottom and top, respectively. A CFD model of the educational building is validated with experiments. The axial configuration has the best performance according to ACH, nevertheless has the worst performance according to ARH and R. The results show that NV evaluation using ACH can lead to wrong decisions. An improvement of NV standard with the age of air associated parameters is recommended.

Neural network for indoor airflow prediction with CFD database

Energy efficiency and indoor thermal comfort are both important in built environment, making it necessary to simultaneously take into consideration of the two aspects, building energy performance and indoor environmental quality, at the design stage. Coupled simulation between building energy simulation (BES) and computational fluid dynamics (CFD) enables providing each other complementary information with regard to building energy performance and detailed indoor environment conditions; however, the main drawback of CFD in computational cost limits its application. Neural networks (NNs) are considered as promising alternatives for CFD due to their advanced modelling abilities and high-speed computational powers. This research aims to confirm the feasibility of NN for indoor airflow prediction, which extends previous studies from two-dimensional to three-dimensional indoor space for more realistic conditions. The NN receives boundary conditions as input and outputs corresponding velocity and temperature distributions. Comparisons were made between NN predictions and CFD simulations regarding accuracy and time consumption on testing cases. The results show that the NN reproduces indoor airflow and thermal distributions with relative errors less than 12%. Time consumption for predicting the testing cases is reduced by 80% with the NN. The feasibility of NN for fast and accurate indoor airflow prediction is confirmed.

Heat, Moisture and Airflow coupled Model for Historical Building

The current building simulation of heat air and moisture (HAM) only regards the indoor air as homogeneous, which cannot accurately predict and evaluate the thermal and humid environment of complex historical buildings. In this study, the heat, moisture, and airflow coupled model (HAM-CFD model) was developed by FORTRAN programming, and then the simulation results of the HAM model and the HAM-CFD model were compared to study the characteristics of indoor environment under the action of airflow. The results show that there is a coupling effect between the indoor airflow and heat and moisture transfer of walls. The HAM-CFD model can reflect the temperature stability of the building center, and has a better correlation with rainfall. The HAM-CFD model can more truly reflect the changes of building temperature and moisture content in complex thermal and humid environment.

Airflow Analysis of the Haida Plank House, a Breathing Envelope

The Haida plank house is one of the most important models built by the native American Indians. Built on the southwest coast of Canada, it adapts the tradition of the ancient pit houses to the requirements of the humid and cold climate characteristic of the Haida Gwaii Islands. This construction is composed by two main pieces: the central pit covered by a wooden envelope. Both protect its dwellers and their hearths. The ventilation system is based on two solutions: the gaps between the wall planks and a smoke hole that can be opened or closed in the roof at will. The aim of the present research is to analyze the way these two elements arrange the indoor airflow in order to ensure the comfortability of the house. Four cases have been proposed, according to four different dimensions for the gaps: 1, 2, 3 and 4 cm. Each case has been doubled in order to determine how the state of the smoke hole affected the corresponding results. This way, it has been concluded that if the gaps’ width becomes higher than 4 cm, the airflow velocity comfort level would be exceeded. It is been possible to observe how the state of the smoke hole influences the way the air moves around the dwelling.

The Role of HVAC Design and Windows on the Indoor Airflow Pattern and ACH

The purpose of heating, ventilation, and air conditioning (HVAC) systems are to create optimum thermal comfort and appropriate indoor air quality (IAQ) for occupants. Air ventilation systems can significantly affect the health risk in indoor environments, especially those by contaminated aerosols. Therefore, the main goal of the study is to analyze the indoor airflow patterns in the heating, ventilation, and air conditioning (HVAC) systems and the impact of outlets/windows. The other goal of this study is to simulate the trajectory of the aerosols from a human sneeze, investigate the impact of opening windows on the number of air changes per hour (ACH) and exhibit the role of dead zones with poor ventilation. The final goal is to show the application of computational fluid dynamics (CFD) simulation in improving the HVAC design, such as outlet locations or airflow rate, in addition to the placement of occupants. In this regard, an extensive literature review has been combined with the CFD method to analyze the indoor airflow patterns, ACH, and the role of windows. The airflow pattern analysis shows the critical impact of inflow/outflow and windows. The results show that the CFD model simulation could exhibit optimal placement and safer locations for the occupants to decrease the health risk. The results of the discrete phase simulation determined that the actual ACH could be different from the theoretical ACH as the short circuit and dead zones affect the ACH.