Design Of Air Distribution System Research Articles

Optimal design of air distribution systems in large indoor spaces during the construction of walls: A case study on liquefied natural gas terminal storage tanks

Efficiently organizing indoor airflow is crucial for optimizing the working environment in large-scale wall construction projects, particularly when constructing liquefied natural gas membrane tanks. This helps prevent membrane corrosion, optimize construction time, and mitigate future safety risks. However, due to their size, these tanks often experience air stratification, posing challenges in meeting simultaneous temperature, humidity, and uniformity requirements during construction. To effectively address this issue, this study developed Computational Fluid Dynamics models that numerically simulated three commonly used ventilation systems: displacement ventilation system, stratified ventilation system, and fabric duct air supply system. Laboratory experiments were conducted to validate the accuracy of numerical simulation. Additionally, response surface methodology (RSM) was used to determine optimal combinations of air supply parameters for superior environmental uniformity control. The findings indicate that the fabric air supply system is more suitable than displacement and stratified ventilation systems for achieving environmental uniformity control in large spaces. It can limit wall temperature nonuniformity coefficient up to 9 % during summer and provide better uniformity in air velocity during winter conditions. Moreover, under summer conditions, the optimal range for air supply speed is between 9.62 m/s - 11.22 m/s with temperatures ranging from 16 °C to 19 °C, while under winter conditions, the optimal range is between 18.3 m/s −19.3 m/s with temperatures ranging from 33.0 °C to 35.0 °C.The optimal design of the ventilation system is advantageous for various building construction scenarios with stringent temperature and humidity requirements, particularly for large-scale buildings.

Widening the applicability of most-open-valve (MOV) strategy for aeration control at full scale WWTPs by combining fuzzy-logic control and knowledge-based rules

An adaptation of a pressure-based most-open-valve control strategy to be applied in aeration control systems of any full scale Wastewater Treatment Plant (WWTP) is described in this paper. This control strategy minimises aeration energy consumption by leading the aeration system to work under the minimum pressure level that is possible given the air distribution system design characteristics and the effluent criteria. Several fuzzy-logic-based control loops are used in the different levels of a supervisory control architecture where knowledge-based rules are also applied. Results obtained in the implementation of this control strategy in three WWTPs with different configurations showed the capability of fuzzy algorithms to maintain dissolved oxygen concentration and pressure always close to setpoint values. Average electrical energy savings of 25 %, 22 % and 16 %, where achieved, respectively, in each WWTP, quantified as kWh per kg of removed COD.

Comparative studies on isothermal attachment ventilation based on vertical walls, square and circular columns

Ventilation and air distribution methods play an important role in indoor air quality and thermal environments. Effective airflow distribution within indoor environments has always been a great cause of concern. Attachment ventilation has drawn considerable interest since it is more energy efficient and space saving than traditional mixing or displacement ventilation methods. As a newly developed and applied attachment ventilation method, vertical wall-based attachment ventilation (WAV) was first proposed in the 1990’s by the authors. Later, the concepts of square column-based attachment ventilation (SAV) and circular column-based attachment ventilation (CAV) were also presented to meet the needs of more industrial applications. In this paper, three attachment ventilation methods— i.e., WAV, SAV and CAV are compared based on experimental studies and numerical simulations. For the vertical attachment region, semi-theoretical equations characterizing the dimensionless centerline velocity of WAV, SAV and CAV are proposed. The velocity profiles of all three types of attachment ventilation methods are similar. Of the three attachment ventilation methods, for the same distance y* along the attached wall measured from the slot inlet, the dimensionless centerline velocity of WAV is the largest, while those of SAV and CAV remain almost identical. In the horizontal air reservoir region (air lake zone), the semi-theoretical equations to predict dimensionless centerline velocity also are presented. The results show that for the same distance x normal to the wall/column, the dimensionless centerline velocity of WAV is the largest, followed by SAV and CAV. Additionally, unified semi-theoretical equations are presented for predicting the jet centerline velocity decay of attachment ventilation, which is helpful for the design of air distribution systems in heating, ventilation and air conditioning (HVAC) engineering applications.

Design of Air Distribution System for Operation Theatre Using Flow Visualization Techniques to Improve Flow Characteristics

Operation Theatre (OT) is the most important area where precise controlled on indoor air quality is required because it is directly related to patient health and its recovery period. This work aims to study and visualize the airflow distribution of conventional flat air diffuser ventilation system and newly designed angular air ventilation system in OT. Angular Air Distribution (AAD) system is designed in such way that, conditioned air is throw in OT with some angle so it can cover the maximum area of OT with laminar flow and minimum installation area. The performance of angular air distribution (AAD) system with varying inlet diffuser angle, constant 0.4m/s inlet velocity and air flow pattern are investigated with the help of numerical simulation and experimental setup of prototype OT model. Detail experimental investigation is done on a prototype with the help of a smoke test and camera target method (CTM). Both numerical and experimental results showed a similar pattern of air distribution for the various design configurations.

Design optimization of air distribution systems in non-residential buildings

Centralized air distribution systems in non-residential buildings are characterized by an extensive air distribution network, that has to be built in a building environment with finite degrees of freedom. The ductwork layout, i.e., the network structure of the ducts, as well as the number and location of the fans, has a large impact on the total cost and performance of the air distribution system. Nevertheless, existing air distribution system design methods are limited to the sizing of each duct (and fan) in the network. The layout itself is considered predetermined, and thus not explicitly taken into account for optimization. In this paper, we meet this shortcoming by presenting the air distribution network design optimization method, that is able to calculate the optimal air distribution system configuration, i.e., the optimal layout and duct and fan sizes, while minimizing the total cost of the air distribution system. A multi-start local search algorithm is developed, consisting of a constructive and a local search phase. In the first phase, multiple air distribution system configurations are generated, and evaluated for feasibility. In the local search phase, all feasible solutions are further optimized in terms of material costs by decreasing and increasing the duct diameters following the steepest descent/mildest ascent approach. An application of the algorithm on a realistic test case demonstrates its usefulness in practice.

Assessment of thermal comfort in high-occupancy spaces with relevance to air distribution schemes: A case study of mosques

In high-occupancy intermittently operated buildings such as mosques and auditoriums, maintaining an acceptable thermal environment may present a challenging task. Variations in the operation and the thermal loads can result in variable and non-uniform thermal comfort conditions when the HVAC system is not properly designed. Non-uniformity of the thermal environment is greatly influenced by the design and scheme of the air distribution system. Mosques, with their distinctive five intermittent short occupancies and the non-fixed posture of occupants, present a unique case for investigation. In this study, the effect of air distribution of various schemes of a ceiling-based system on the thermal comfort in mosques is investigated. Air diffusion performance index and Fanger’s PMV method are used to assess thermal comfort. Three air distribution schemes at four diffuser terminal velocities were studied using the EnergyPlus and computational fluid dynamics techniques. Results indicate major variations in air diffusion performance index with each air distribution scheme type and diffuser terminal velocity. The uniformity of the PMV was entirely dependent on the air diffusion performance index value and exhibited large variations when the air diffusion performance index value was low. In most cases, the space was overcooled with an average PMV of −0.66 or below. Practical application: The effect of air distribution system design on human thermal comfort has been very complex to understand, as it involves different schemes and different diffuser discharge velocities. This study will help engineers and designers in designing better thermal environment for the occupants.

Air distribution system design optimization in non-residential buildings: Problem formulation and generation of test networks

In most heating, ventilation and air conditioning systems, the ductwork layout, i.e., the network structure of the ducts, as well as the number and locations of the fans, is an important determinant of the installation's cost and performance. Nevertheless, the layout is not explicitly taken into account in existing duct design methods. Most methods assume the layout of the air distribution system to be predetermined and focus solely on the sizing of each fan and duct in the network. This paper aims to outline the current state-of-the-art in air distribution system design and highlights the main shortcomings. Additionally, previous research is extended by presenting a novel problem formulation that integrates the layout decisions into the optimization problem. In this problem, called the air distribution network design optimization problem, the optimal air distribution system configuration, i.e., the optimal ductwork layout, is determined jointly with the duct and fan sizes, thereby minimizing the total cost of the system. This novel combinatorial optimization problem is characterized by discrete decision variables, and non-linear constraints. This paper also motivates the need for benchmark instances to evaluate the performance of existing or new developed optimization methods and advance future research in the field of air distribution system design optimization. A test network generator is developed in this research to generate such a set of instances.

Experiment evaluation and simulation optimization of air distribution mode for underwater cabin

The design of air distribution system in a submarine submerged for long periods often faces many constraint conditions. In order to optimize its cabin airflow field, a full-scale experimental bedroom cabin with three three-layer beds was built, and a Flow Visualization with Green Laser (FVGL) method was used to evaluate two types of air distribution mode. Experimental results show that Mode 2 with six individual air vents for lower beds could improve the air quality and heat sensation at lower beds. However, its strong sensation of draft at upper beds could not be avoided. In order to solve this problem, a multi-objective optimal method was built to search the optimal positions of top diffusors. Air age and Predicted Mean Vote (PMV) were chosen as the objective functions. The Micro-Genetic Algorithm (Micro-GA) was used in the presented optimization method to obtain the Pareto-Optimal Front (POF). Finally, the preferred positions of top diffusors can be determined from the POF.

Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

In this paper, the infl uence of solar radiation direction and intensity on thermal fl ux on passenger vehicle driver’s body was analysed. The analysis was carried out on a virtual model of a vehicle cabin. The results showed that the highest heat fl ux caused by solar radiation could occur when the sun is shining in the front of the vehicle, as proposed in standard ISO 14505-2: 2008. Under these conditions, driver’s chest is the segment with the highest heat fl ux. The unfavourable situation due to highly asymmetric thermal condition is also when the sun is shining on the left side of the cabin. From that reason, paying attention to solar characteristics of glass and to design of air distribution system in such way that air-conditioner vents can be directed to areas with the highest fl uxes is an effi cient way to reduce the driver’s and passenger’s thermal stress.

A CFD analysis of room aspect ratio on the effect of buoyancy and room air flow

Comfort conditions in air-conditioned rooms require that temperature in the occupied zone should not vary by more than 1?C and velocity, every where in the room, should be less than 0.15 m/s so that occupants do not feel draft. Recent developments in providing effective insulation and making leak tight buildings are considerably reduced the cooling load requirements and the supply airflow rates. Obtaining uniform temperature distribution with reduced air volume flow rates requires careful design of air distribution system. This study aims to find velocity and temperature distribution in the room towards this end.

Novel air distribution systems for commercial aircraft cabins

Air distribution systems in commercial aircraft cabins are important for providing a healthy and comfortable environment for passengers and crew. The mixing air distribution systems used in existing aircraft cabins create a uniform air temperature distribution and dilute contaminants in the cabins. The mixing air distribution systems could spread infectious airborne diseases. To improve the air distribution system design for aircraft cabins, this investigation proposed an under-floor displacement air distribution system and a personalized air distribution system. This study first validated a computational fluid dynamics (CFD) program with the experimental data of airflow, air temperature, and tracer-gas concentration from an environmental chamber. Then the validated CFD program was used to calculate the distributions of the air velocity, air temperature, and CO 2 concentration in a section of Boeing 767 aircraft cabin with the mixing, under-floor displacement, and personalized air distribution systems, respectively. By comparing the air and contaminant distributions in the cabin, this study concluded that the personalized air distribution system provided the best air quality without draft risk.

Experimental Study of an Air Distribution System for Operating Room Applications

An understanding of airflow patterns in operating rooms is required if the design of air distribution systems in such environments is to be improved and the risk of postoperative infection reduced. To assess a detailed description of contaminant distribution, the airflow patterns and the spread of contaminants in an operating room were analyzed using an experimental model. These experiments were carried out in a test cell, MINIBAT, equipped with an operating table, a medical lamp and a manikin representing the surgeon. A diagonal ventilation system was tested for two types of conditions: (i) isothermal, with the manikin and lamp switched off and (ii) non-isothermal, with the manikin and lamp switched on. Indoor air temperatures, air velocities and tracer gas concentrations were measured automatically at more than 700 points. The overall airflow patterns, due to ventilation, were very similar for the two experiments. However, in the zone between the lamp, the table and the manikin (which was the main area of interest), the tracer gas distribution was different. In the non-isothermal case, the thermal plume from the manikin induced better mixing, and had a beneficial effect on the evacuation of contaminants. The thermal energy emitted by the lamp had almost no impact on the airflow patterns.

Influence of the floor-based obstructions on contaminant removal efficiency and effectiveness

Dimensioning of dilution ventilation is often made using the perfect mixing approximation, assuming uniform contaminant concentration throughout the room space. However, the contaminant removal efficiency and effectiveness of air conditioning system should be accounted for during design. The effectiveness is in this context used as a measure of the contaminant distribution uniformity within the occupied zone. Influence of an occupied zone obstruction level, air distribution method, air change rate, cooling load and contaminant source non-uniformity on the contaminant removal efficiency and occupied zone contaminant concentration uniformity were studied in scale model. The room air distribution method results in contaminant concentration non-uniformity inside the occupied zone. A method was developed to take this into account during the design of air distribution system. Contaminant supply non-uniformity was found to have great influence on the concentration non-uniformity with two tested air distribution methods.