Search results

Ventilation of indoor spaces is required for the delivery of fresh air rich in oxygen and the removal of carbon dioxide, pollutants and other hazardous substances. The COVID-19 pandemic brought the topic of ventilating crowded indoors to the front line of health concerns. This study developed a new biologically inspired concept of biomimetic active ventilation (BAV) for interior environments that mimics the mechanism of human lung ventilation, where internal air is continuously refreshed with the external environment. The purpose of this study is to provide a detailed proof-of-concept of the new BAV paradigm using computational models.

This study developed computational fluid dynamic models of unoccupied rooms with two window openings on one wall and two BAV modules that periodically translate perpendicular to or rotate about the window openings. This study also developed a time-evolving spatial ventilation efficiency metric for exploring the accumulated refreshment of the interior space. The authors conducted two-dimensional (2D) simulations of various BAV configurations to determine the trends in how the working parameters affect the ventilation and to generate initial estimates for the more comprehensive three-dimensional (3D) model.

Simulations of 2D and 3D models of BAV for modules of different shapes and working parameters demonstrated air movements in most of the room with good air exchange between the indoor and outdoor air. This new BAV concept seems to be very efficient and should be further developed.

The concept of ventilating interior spaces with periodically moving rigid modules with respect to the window openings is a new BAV paradigm that mimics human respiration. The computational results demonstrated that this new paradigm for interior ventilation is efficient while air velocities are within comfortable limits.

To provide the performance comparison between the conventional mixing ventilation (MV) and the displacement ventilation (DV) with and without cooling ceiling, which can be helpful to design.

The commercial CFD software FLUENT with RNG k‐ε turbulent model was used. The CFD method was validated via comparing with the available experimental data.

It was found that if properly designed, the DV system can supply better indoor air quality in the occupied zone, including better distribution in temperature field, higher ventilation efficiency, lower contaminant field and more thermal comfort compared with the MV system, because of the stratification effect of DV. And the locations of return air outlets have a great effect on the performance of the ventilation system. It was also found that the DV systems can be used to remove air contaminations more efficiently, but the temperature difference in the occupied zone in the DV system is higher than that in the MV system, especially if the heat load is higher. This problem may be solved if the cooled ceiling is combined with the DV, because the vertical temperature in the occupied zone will be reduced and more thermal comfort can be achieved.

More detailed computation should be performed on the thermal radiation between different surfaces in the room.

A very useful source of information for thermal designing of air condition.

This paper provides the performance comparison between the conventional MV and the DV with and without cooling ceiling, based on flow and temperature distribution.

A comprehensive investigation on the outlet air position effects on the thermal comfort and air quality has been achieved. In addition, airflow and temperature distributions in ventilated cavities filled with an air-CO₂ mixture with mixed convection are predicted. The airflow enters from the cavity through an opening in the lower side of the left vertical wall and exits through the opening in one wall of the cavity. This paper aims to investigate the outlet location effect, four different placement configurations of output ports are considered. Three of them are placed on the upper side and the fourth on top of the opposite side of the inlet opening. A uniform heat and CO₂ contaminant source are applied on the left vertical wall, while the remaining walls are impermeable and adiabatic to heat and solute. The cooling efficiency inside the enclosure and the average fluid temperature are computed for different Reynolds and Rayleigh numbers to find the most suitable fluid outlet position that ensures indoor comfortable conditions while effectively removing heat and the contaminant. This is demonstrated by three relevant indices, namely, the effectiveness for heat removal, the contaminant removal and the index of indoor air quality.

The simulations were performed via the finite-volume scSTREAM CFD solver V11. Three different values of CO₂ amount are considered, namely, 10³, 2 × 10³ and 3 × 10³ ppm, the Reynolds number being in the range 100 ≤ Re ≤ 800.

Based on the findings obtained, it is the configuration whose air outlet is placed near the heat source and the contaminant, which provides a better air distribution and a ventilation efficiency compared to the others ventilation strategies.

The studies on heat and mass transfers by natural and forced convection in ventilated cavities remain a fruitful research topic. Thereby, such a study deals with different ventilation strategies through cavities containing an air-CO₂ mixture subjected to a mixed regime. In particular, the air inlet velocity and contaminant sources’ effects on thermal comfort and air quality have been investigated.

At the beginning of the Corona Virus Disease 2019 (COVID-19) pandemic, a digitalized construction environments surfaced in the heating, ventilation and air conditioning (HVAC) systems in the form of a modern delivery system called demand controlled ventilation (DCV). Demand controlled ventilation has the potential to solve the building ventilation's biggest problem of managing indoor air quality (IAQ) for controlling COVID-19 transmission in indoor environments. However, the improper evaluation and information management of infection prevention on dense crowd activities such as measurement errors and volatile organic compound (VOC) generation failure rates, is fragmented so the aim of this research is to integrate this and explore potentials with machine learning algorithms (MLAs).

The method used is a thorough systematic literature review (SLR) approach. The results of this research consist of a detailed description of the DCV system and digitalized construction process of its IAQ elements.

The discussion revealed that DCV has a potential for being further integrated by perceiving it as a MLAs and hereby enabling the management of IAQ level from the perspective of health risk function mechanism (i.e. VOC and CO₂) for maintaining a comfortable thermal environment and save energy of public and private buildings (PPBs). The appropriate MLA can also be selected in different occupancy patterns for seasonal variations, ventilation behavior, building type and locations, as well as current indoor air pollution control strategies. Furthermore, the conceptual framework showed that MLA application such as algorithm design/Model Predictive Control (MPC) integration can alleviate the high spread limitation of COVID-19 in the indoor environment.

Finally, the research concludes that a large unexploited potential within integration and innovation is recognized in the DCV system and MLAs which can be improved to optimize level of IAQ from the perspective of health throughout the building sector DCV process systems. The requirements of CO₂ based DCV along with VOC concentrations monitoring practice should be taken into consideration through further research and experience with adaption and implementation from the ventilation control initial stage of the DCV process.

The purpose of this paper is to compare two different ventilation strategies, displacement and mixing, in heat, ventilating and air conditioning (HVAC) systems with recourse to computational fluid dynamics (CFD).

The flow and the heat and mass transfer are numerically predicted inside an air‐conditioned room with a desk and an occupant for the cooling and heating periods in moderate climate regions, like Mediterranean countries. Focus is placed on energy efficiency, thermal comfort and internal air quality (IAQ), evaluated from the simulations of the three‐dimensional, turbulent, non‐isothermal and buoyant flow of moist air.

For the cooling period, displacement exhibits higher energy and ventilation efficiencies promoting simultaneously better comfort for the occupant. For the heating period, mixing performs better due to the short‐circuit phenomenon occurring with the displacement flow. Overall, mixing behaves better for air‐conditioning of typical office rooms in Mediterranean‐climate countries, where heating and cooling climatization modes have to be alternated according to the season.

Room, desk and occupant are designed as parallelepipeds. No experimental work is performed but models used are previously validated by other authors against experimental data.

The results indicate a short‐circuit flow phenomenon that must be avoided when designing HVAC systems.

Use of grilles layout typical for the cooling period to study the air‐conditioning of a typical office room during the heating period, incorporating in the model a transport equation for the moisture. IAQ is simulated together with the flow, the heat and the comfort conditions: velocities, temperature, predicted mean vote (PMV), predicted percentage of dissatisfied (PPD), draught rating (DR), PPD due to air quality (PDQ) and air moisture content are calculated simultaneously.

Due to the ongoing Covid-19 pandemic, ventilation in a small cabin where social distancing cannot be guaranteed is extremely important. This study aims to find out the best configuration of open and closed windows in a moving car at varying speeds to improve the ventilation efficiency. The effectiveness of other mitigation measures including face masks, taxi screens and air conditioning (AC) systems are also evaluated.

Each window is given three opening levels: fully open, half open and fully closed. For a car with four windows, this yields 81 different configurations. The location of virus source is also considered, either emitting from the driver or from the rear seat passenger. Then three different travelling speeds, 5 m/s, 10 m/s and 15 m/s, are examined for the window opening/closing configurations that provide the best ventilation effect. A study into the effectiveness of face masks is realised by adjusting virus injection amounts; and the simulation of taxi screens and AC system simply requires a small modification to the car model.

The numerical studies identify the top window opening/closing configurations that provide the most efficient ventilation at different moving speeds, along with a comprehensive ranking list. The results show that fully opening all windows is not always the best choice. Simulations evaluating other mitigation measures confirm good effect of face masks and poor performance of taxi screens and AC systems.

This work is the first large-scale numerical simulation and parametric study about different window opening/closing configurations of a moving car. The results provide useful guides for travellers in shared cars to mitigate Covid-19 transmission risks. The findings are helpful to both individuals' health and society's recovery in the Covid-19 era and they also provide useful information to protect people from other respiratory infectious diseases such as influenza.

Most people spend a great deal of their lives in an artificial environment, seeking refuge from a sometimes harsh and destructive outdoor climate. Clever architecture and engineering can make use of natural energy and forces to create a comfortable indoor climate using minimum non‐renewable resources.

The improvement in the quality of life together with thermal comfort, air quality, health, workplace security and energy conservation measures justify the integral education of environmental (outdoor and/or indoor) phenomena. Environmental education, through the appropriate tool, can play an important and vital role in this domain. Computational fluid dynamics (CFD) is the analysis of systems involving fluid flow, heat transfer and associated phenomena such as distribution of pollutants by means of computer‐based simulation. This technique, allowing the simulation and the visualization of environmental problems, represents a powerful tool to motivate, guide and educate on the environment. The main objective of this paper is to introduce this new advanced active tool in environmental education, directed to indoor‐environment quality, that permits the prediction and visualization of air movement, air temperature and air contaminant (such as tobacco smoke) distribution in rooms. With suitable mathematical models and boundary conditions, a computational code has been developed to predict and visualize these phenomena. In order to demonstrate its applicability, the simulation of air contamination distribution in an office room with a smoker was performed.

This paper aims to develop a multi-criteria decision framework (MCDF) for the selection of appropriate low carbon building (LCB) measures for office buildings in Hong Kong.

The research was carried out through a critical literature review and a case study with a low carbon office building project.

In total, 26 LCB measures were identified, under the five groups of building envelope, heating, ventilating and air conditioning system, lighting and elevators, renewable energy and appliances. Also identified were 16 decision criteria, centred on the implementation-related, economic, environmental and production-related aspects. The identified measures and criteria, coupled with the information and business processes of office building project delivery, formed the conceptual MCDF. The MCDF was also verified using an office building project.

The limitation of this research was the absence of the energy bill which could help to further verify the model in the case study.

The developed framework should add value to knowledge of the use of multi-criteria decision-making methods and support the design decision-making of selecting LCB measures for office building projects in Hong Kong. The findings should also inform LCB design in other hot and humid subtropical urban environments.