Air-conditioning Duct Research Articles

Multiphysical design for optimised ventilation and noise attenuation in ducts: an approach using metamaterials

Noise generation and propagation through mechanical ventilation and air conditioning (MVAC) ducts have been increasingly investigated since commercial solutions allow sensible noise attenuation while reducing the duct section. So, a commercial silencer forces the MVAC power to rise to overcome the flow resistance, increasing the noise source. For this reason, this study focuses on soundproofing ventilation ducts through acoustic metamaterials with no inner duct section decreasing. A crucial part of this study falls into the multiphysical interaction between acoustics and fluid dynamics, which is a phenomenon that may result in a challenging analytical model. In conditions of flowing motion, the wave vector has been modelled according to the Lighthill model: the component of the velocity rotor potential becomes significant, influencing the soundproofing performance due to the metamaterial placed at the edge of the inner surface of the duct. FEM analysis helped design a series of samples which then have been tested experimentally in static conditions. Once the numerical method is calibrated, further multiphysical numerical analysis are used to implement the sound insulation properties of the metamaterial-based filter through dynamic flow conditions. Guidelines for multiphysical setup for wave-based simulation are drawn, and preliminary experimental results are presented.

해양 시추선용 경량 수밀 공조 덕트의 구조해석 및 강도 평가

해양 시추선용 경량 수밀 공조 덕트의 구조해석 및 강도 평가

Is line-source modeling suitable for ultraviolet light application in an air cleaner duct?

Ultraviolet-C (UV-C) germicidal light can effectively inactivate airborne pathogens and mitigate the transmission of infectious diseases. As the application of UV-C for disinfection gains popularity, practical estimation of UV irradiance is essential in determining the UV fluence (dose) and designing tubular UV lamp configurations for indoor air treatment. It is generally understood that the inverse square (∼1/d2) law (i.e., irradiance is proportional to the inverse square of the distance) applies well to point light sources. However, there has been a recognition that the ∼1/d2 law does not work well for tubular light sources in the commonly defined near-field applications where the UV source is relatively close to the treated air. Therefore, practical near-field irradiation estimation is needed for designing portable air cleaners and heating, ventilation, and air conditioning (HVAC) ducts with built-in UV light bulbs. This research investigated UV-C light irradiance from tubular (L = 0.9 m) light bulbs at near distances inside an air cleaner prototype duct under three power output (1-, 4-, and 8-bulb) scenarios and conducted theoretical estimation based on a line-source irradiation model. Similarly sized visible fluorescent bulbs were used as a reference. The data were fitted on both ∼1/d2 and ∼1/d correlation of irradiance with distance. Both measured and line source estimated data fit better (i.e., evaluated by R-square, standard errors, root mean squared errors) with the ∼1/d than the ∼1/d2 relationship in the near distance. Although the differences between the measured and the modeled were observed, the pattern of light distribution generally follows an inverse relationship (∼1/d) with distances (d) shorter than two tubular bulb lengths (d < 2L). The pattern applies to both UV and visible light tested in this study. It is recommended that the inverse (∼1/d) correlation be used for near-distance estimation of light distribution, especially for disinfection purposes in air ducting for indoor air quality improvement and airborne disease mitigation.

Autonomous Control of a Hybrid Rolling and Flying Caged Drone for Leak Detection in HVAC Ducts

In this article, a hybrid, rolling, and flying multirotor caged drone is developed for inspection and leak detection of heating, ventilation, and air conditioning (HVAC) ducts. The developed passive-cage drone is designed, manufactured, and controlled autonomously using direct model reference adaptive control (DMRAC). The platform is equipped with a 2-D LIDAR sensor that provides a scan of the surroundings in a plane. Possible leaks are detected using a thermal camera. DMRAC is used for higher level roll, pitch, and yaw control, while lower level motor speed control is achieved through Proportional-Integral-Derivative (PID) controllers. This article compares, for the first time, PID-based controllers for roll, pitch, and yaw control, with standard DMRAC and DMRAC with gain modifications, in a cascaded setting on a hybrid passive-caged drone. Several hardware tests are used to highlight the differences in the control performance when PID controllers/DMRAC with certain gain modifications are used to control the developed hybrid passive-caged drone.

Mechanical Study of a Solar Central Air Conditioning Duct Cleaning Robot

Mechanical Study of a Solar Central Air Conditioning Duct Cleaning Robot

Realization of rule-based automated design for HVAC duct layout

In the traditional process of pipeline design, a designer typically creates a general layout of pipeline based on their experience, and then calculates whether the hydraulic calculation of pipeline meets the requirements. This method of design is both time-consuming and labor-intensive. Furthermore, the results are often suboptimal and prone to errors, which creates a lot of waste of human and material resources. The objective of this paper is to propose a computer-aided method for completely automating the heating, ventilation and air conditioning (HVAC) duct system design process. This method incorporates all the necessary design processes, such as duct selection and hydraulic calculation, and introduces a rule-based divide-and-conquer method to the pipe routing design (PRD). The research assesses the practical effect of this piping design algorithm in a BIM environment using varied building scenarios. The findings show that the proposed method is capable of meeting the design requirements of actual projects. The automatic piping design technique presented in this paper can significantly reduce labor costs associated with HVAC design while eliminating calculation errors and compressing the design timeline for most of the complex projects to within 5 min.

Two-dimensional manganese di-telluride based triboelectric nanogenerator

Low-dimensional transition metal chalcogenides (TMDCs) have gained interest as potential energy harvesters. The structural change during dimensional reduction paves the way for better charge repositories compared to their bulk counterparts. Thin flakes of manganese di-telluride (MnTe2) were used to devise a triboelectric nanogenerator (TENG), and the device was capable of producing a maximum power density of 123 mW cm-2, with a sensitivity of ∼ 408 mV kPa-1. The device also has a high surface potential of 1.02 V and surface charge density (SCD) of 2.204 mC m-2, respectively. The effect of uniaxial and biaxial strains on the two-dimensional (2D) TENG was studied using in-situ Raman spectroscopy. The enhanced outputs in the 2D device were attributed to the Te - di vacancies created during exfoliation in the flakes (DFT calculations). The potential application of the fabricated device is to be used as an energy harvester from air-conditioning (AC) ducts.

A multi-port scattering matrix formalism for the acoustic prediction in duct networks

Duct acoustic network modeling is commonly carried out using the transfer matrix formalism which is limited to the low frequency range. The aim of this work is to extend it to higher frequencies by taking into account the multi-mode acoustic propagation. The first step is to compute, via Finite Element Method (FEM), the multi-port multi-modal scattering matrix of each element. The second step is to transform it into a scattering matrix for the acoustic power, relying on assumptions which are often used for the study of medium-to-high frequency broadband noise. The method is applied to typical elements such as expansion chamber mufflers and air conditioning veins. In all cases, the power-flow model is compared to the FEM solution in terms of Transmission Losses. It is concluded that this simplified model is a reliable tool for the analysis of complex networks encountered in Heat and Ventilation Air Conditioning (HVAC) duct networks.

Design and Optimization of Automotive Air Conditioning Duct Based on CFD Algorithm

Nowadays, the air conditioner (AC), as an important guarantee for driving comfort and endurance, has attracted more and more attention. The pipe connecting the air conditioner refrigerator and the air outlet of the cockpit instrument panel is known as the air duct. Its structural characteristics and fluid flow characteristics are related to the refrigeration efficiency of the whole air conditioning system. The air supply performance of the air duct directly affects the uniformity of the temperature field and speed field in the car, thus affecting the comfort performance of the car [2]. Limited by the layout space, the design of air conditioning duct is the most difficult part of the design of automobile air conditioning system [1]. Therefore, how to optimize the air duct of automotive air-conditioning to meet the size design of the car while being more energy-efficient is an important research direction. This paper focuses on the simulation design and further optimization of the model of the air duct of automotive air conditioning through CFD algorithm. The author uses the Soildworks software for preliminary modeling, meshes the established model with Meshing, and applies the Fluent software to simulate the fluid flow characteristics in the pipe. By inputting a given flow to the inlets, the air volume of each outlet can be simulated. Based on the initial air-conditioning duct model of a vehicle model, the pipe turbulence problem and the uneven distribution of air volume at each outlet in the simulation process are improved under the condition of ensuring the existing size, and finally the rationality of the improvement is verified.

Development and experimental validation of an improved mathematical irradiance model for in-duct ultraviolet germicidal irradiation (UVGI) applications

The application of ultraviolet germicidal irradiation (UVGI) technology inside the heating, ventilation, and air-conditioning (HVAC) air ducts to purify circulating air and improve indoor air quality has attracted extensive interest during the COVID-19 pandemic. In this study, a new view-factor-based mathematical model was developed to calculate the irradiation distribution for a typical twin-tube UV lamp placed at the center of a square duct, in which the contributions from direct emissive irradiance, specular reflection irradiance, and diffuse reflection irradiance were quantified. Furthermore, the “projection area” method was introduced to mathematically estimate the shadowing effects between the two lamps by considering multiple-lamp scenarios in real in-duct UVGI system designs. Subsequently, a computational fluid dynamics (CFD) simulation was employed to compute the average received UV dose and disinfection efficiency of the system. The mathematical model combined with the CFD simulation was validated using the experimental data. It is concluded that by increasing the UV lamps, UV lamp power, and using more reflective duct wall materials, the in-duct UVGI disinfection performance can be improved. For the multiple-lamp arrangements, placing lamps perpendicular to the airflow in the same row results in a more uniform irradiance distribution and higher overall irradiation than placing them in different rows along the duct, thus increasing the disinfection efficiency. In addition, the duct wall with highly diffusive reflection provides a more uniform irradiance distribution and overall higher average radiation, thus providing better disinfection performance for an in-duct UVGI reactor.

Noise distribution law of air-conditioning ducts for metro vehicles

The passenger comforts are directly affected by the air supply uniformity and noise of air-conditioning duct inside the metro vehicle. In order to solve the integrated design problem of air supply uniformity and noise control of air-conditioning ducts, a theoretical model is established to analyze the air supply uniformity, noise attenuation, and airflow regeneration noise of the air-conditioning duct. The distribution law of the sound pressure level along the longitudinal air outlet was calculated, and the calculated results were compared with test ones. For a typical air supply duct with a constant cross section: (1) In order to ensure air supply uniformity at the outlet of the static pressure chamber, the area of the side air hole should be gradually increased in an exponential form along the direction of the main flow, and cannot be designed in the equal area form. (2) The airflow speed of each side hole decreased in sequence along the air duct length. In order to ensure the uniformity air supply of each side hole, the area of each side hole must be gradually increased. (3) The noise in the air conditioner duct was mainly concentrated at the front end of the air duct, and the noise at the subsequent air outlet can fully meet the current requirements of subway vehicles for indoor noise. Therefore, the front end of the air duct is the most important area for noise control.

A Model for incorporating information literacy and collaboration in a project-based learning pedagogical exercise with application to a fluid mechanics course

This paper describes the implementation and the results of an online project-based learning (PBL) pedagogy in an advanced fluid mechanics course in a mechanical engineering technology program. This work is a close collaboration between engineering and education faculty and the engineering librarian, and aligns with the new research areas identified by the National Engineering Education Research Colloquies and the ABET Criteria for Accrediting Engineering Technology Programs Criterion 3 (student outcomes, SLO 1 to 5) and Criterion 5 (curriculum, discipline specific content C, D and E). Students were required to work in teams to design and dimension a heating, ventilation, and air-conditioning (HVAC) duct system, a real-world expression of engineering thinking. Students applied information literacy skills to identify relevant engineering codes and standards, such as ASHRAE, and used previously learned content knowledge from various courses to finalize the project. The PBL exercise was chosen as a culminating experience and in support of engineering competencies development. The results showed improvements in the flow of air in ducts content knowledge, professional communication skills, and the ability to collaborate as part of a team, including improving one's ability to work with other students on assignments, listening to the ideas of others, learning from the ideas of others, and evaluating the ideas of others. The students unanimously agreed that the project improved their heating, ventilation, and air-conditioning (HVAC) knowledge beyond the classroom as well as their information seeking skills. Based on the students end of semester course evaluation, this PBL exercise improved their readiness for the workforce.

Study of the shape optimization of a variable diameter in a ventilation and air-conditioning duct based on the Boltzmann function

Ventilation and air-conditioning systems feature high-resistance ducts and long, complex pipelines. Consequently, how to structurally optimize the local components to reduce resistance and energy consumption has become an urgent problem to be solved. In this paper, the sedimentation-induced variable shape of a river channel was used to study the resistance reduction of local components, and the relationship between silty sediment and resistance within the channel was discussed. On this basis of this theory, a reduced-scale test bench was constructed, and a Boltzmann curve form was obtained and applied for a variable diameter. Finally, a method for optimizing the resistance reduction of variable diameters suitable for different aspect ratios and area ratios was obtained. Through our research, we found that the local resistance coefficients of the novel variable diameter using a Boltzmann curve connection are significantly smaller than those of the traditional variable diameter. Compared with a traditional straight-line variable diameter, the novel variable diameter weakens the fluid deformation, thereby reducing energy dissipation and resistance, and the resistance reduction rate can reach 28.92%. The resistance reduction rates of variable diameters adopting optimized forms were 14.3%–16.2%, 3.0%–25.17%, 5.81%–28.92%, and 4.99%–7.11% when the area ratios were 1.25, 1.28, 1.56, and 2, respectively. • The connection between silty sediment and resistance was discussed. • The Boltzmann curve form was obtained and applied for variable-diameter. • The variable-diameter reduction rate reach up to 28.92%.

Effective ventilation and air disinfection system for reducing coronavirus disease 2019 (COVID-19) infection risk in office buildings.

During the COVID-19 pandemic, an increasing amount of evidence has suggested that the virus can be transmitted through the air inside buildings. The ventilation system used to create the indoor environment would facilitate the transmission of the airborne infectious diseases. However, the existing ventilation systems in most buildings cannot supply sufficient clean outdoor air for diluting the virus concentration. To reduce the airborne infection risk and minimize energy consumption, especially in existing buildings with well-mixed ventilation systems, this investigation used an ultraviolet-C (UV-C) air disinfection device (Rheem's third generation products, RM3) with 99.9% disinfection efficiency to clean air carrying the COVID-19 virus (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2) which could help promote environmental sustainability and create healthy cities. This investigation assessed the impact of the RM3 UV-C units on the infection risk, the number of RM3 UV-C units required, and the strategy for decreasing the infection risk, with the use of computational-fluid-dynamics (CFD) numerical simulations. An actual office building with a combination of individual offices and workstations was selected as an example for the research. According to the numerical results, the best strategy would be to use a combination of 100% outside air and UV-C in heating, ventilation and air-conditioning (HVAC) ducts with air disinfected by the RM3 UV-C units. The infection risk in the office building could thus be reduced to a negligible level. These findings could provide theoretical basis and engineering application basis for COVID-19 epidemic prevention and control.

Aerodynamic and acoustical effects caused by placing two prefabricated duct silencers in series

It once was not uncommon to find ductborne noise control designs and recommendations that would attempt to provide high sound attenuation values, especially for problematic lower frequencies, by using a pair of prefabricated duct silencers in series with one another, sometimes immediately adjacent but typically separated by some distance. Similarly, heating, ventilating, and air-conditioning (HVAC) duct silencers are occasionally required to accommodate fire dampers or access sections that effectively break up the silencer along its length, creating an empty gap between the noise-attenuating internal elements. Typical published performance characteristics of prefabricated duct silencers do not include effects from the use of additional silencers nearby and little information is available in common duct design and application literature. This paper will present information from a series of tests of various silencers in different configurations and spacings in an aero-acoustic test facility that will help describe the effects on insertion loss, generated noise, and pressure drop.

Acoustic study of multi-layered microperforated elements for fibreless noise control applications

Recently fibreless solutions have become a trend in the design of sustainable and environmentally friendly duct silencers. Hereby microperforated panels have been proven to provide adequate performance for the substitution of unfavourable fibrous material layers commonly used in mass-produced silencers. This paper presents an acoustic study of microperforated elements aimed for an effective and eco-friendly heating, ventilation, and air conditioning (HVAC) duct silencer. Several microperforated sheet metal panels have been experimentally tested in a variety of layered configurations in order to maximize the sound absorption coefficient in operational frequency range. The optimal solution is implemented in the design concept of a novel fibreless HVAC silencer presented in this research. The results of the study demonstrate the appropriateness of the double-layered microperforates for a duct silencer as well as for a variety of Noise, vibration and harshness (NVH) implementations were potent noise absorption is aimed.

Ground Penetrating Radar Survey of the Floor of the Accademia Gallery (Florence, Italy)

This paper reports the results of a ground penetrating radar (GPR) survey of the ground-floor of Academia Gallery (Florence, Italy) where the Michelangelo’s David is exhibited to the public. The equipment used was a step-frequency GPR operating in the 100 MHz-1 GHz band, named ORFEUS. The survey covered an area of 13 m × 7.3 m, and the scans were performed along two orthogonal directions. Acquisitions in the same direction were separated by 0.25 m from each other. The GPR was able to confirm the underground structure, as it can be deducted by planimetry and historical documentation. In particular, the radar clearly detected the air-conditioning ducts under the floor and an approximately circular foundation below the basement of the statue.

Investigating the conjugate heat transfer phenomena on various ducts for aircraft environmental control system

All commercial aircraft employ a system called Environmental control system (ECS) to ensure an environment that accomplishes the physiological and comfort demands by passengers and aircrew. This task requires functionalities like temperature control, humidity regulation apart from the governing of cabin pressure. The energy source for ECS is a pressurized hot air bleed (180 °C-250 °C, 2.75 bar) from the engine or Auxiliary Power Unit (APU) along with the ram air. During the functional operation, the unit of Heating, Ventilation, and Air Conditioning (HVAC) duct experiences repetitive temperature fluctuations in addition to the cyclic pressurization leading to thermal fatigue and cyclic stress over the duct material, promoting crack propagation at weld zones in the duct. Therefore, a comparative investigation on conjugate heat transfer analysis is done at welded joints annexed to the bypass valve and trim air valve using airflow bench set up and validated by computational fluid dynamics. During this investigation, the circular duct with spherical junction (D/d = 3.84 & L/d = 6) was the most efficient and economical design that could fit in for designing air conditioning duct undergoing high thermo-cyclic stress.

Optimization analysis of air-conditioning duct structure of high-velocity train

In order to improve the comfort of the air conditioning system in the driver’s cabin of a high-velocity train and advance the distribution of air supply, a 3D simulation software is used to establish the model of the air supply pipeline of the driver’s cabin. The air flow field and the rationality of the air distribution are analysed accordingly. The results indicate that the structure of the air supply pipe is optimized and the air flow rate in the left and right air chambers is solved and air flow rate in each outlet of the air supply pipe are achieved.

Truncation method for calculating the resistance of ventilation air-conditioning duct systems under nonfully developed flow boundary conditions

Calculating the resistance of ventilation air-conditioning ducts under nonfully developed flow is a crucial problem that must be addressed. Based on the characteristics of the resistance in ventilation air-conditioning ducts, the truncation method—a computational method that is appropriate for nonfully developed flow boundary conditions—was proposed in this study. The resistance distributions in the upstream and downstream ducts from typical local components, including reducers, bends and tee ducts, were investigated. Using the resistance values of the local components under fully developed flow, the resistances that did not belong to nonfully developed flow were truncated and removed. Finally, the calculation steps of the proposed method were discussed, an engineering case study was presented, and the accuracy of the developed model was analyzed. The results showed that for the local components in the system (reducers, bends and tee ducts), their proportions of the total resistance exhibited similar trends under different width-to-height ratios. The resistance of these local components included upstream resistance, downstream resistance and their own resistance. The upstream resistance accounted for 2%–6% of the total resistance, whereas the downstream resistance of the reducers, bends and tee ducts accounted for 40%–60% of the total resistance. A functional relationship was established between the local resistance and cutoff distance of the reducers, bends and tee ducts. Hence, the truncation method can calculate the local resistance from the cutoff distance. Moreover, in the presented engineering case study, the error between the actual measured resistance values and those simulated with the truncation method was only 4.28%, which was far less than that of the results simulated with the traditional calculation methods (53.64%).