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Within the central air conditioning systems in public buildings, the energy consumption of fans induced by duct resistance accounts for 30%–50% of the total energy consumption of the buildings. Reducing the resistance within ventilation and air conditioning system is thus an important technical problem. In this research, a novel low-resistance damper, the shape of which based on the energy dissipation characteristics, was introduced for use in a ventilation and air conditioning system. The resistance characteristics were analyzed, the resistance field (the distribution of the resistance at various locations inside the component) was described through the energy dissipation, and a full-scale experiment was carried out to verify the performance of the novel damper. The novel air damper exhibited less fluid deformation, lower intensity, smaller airflow vortex range, and less conversion of mechanical energy into internal energy, which significantly reduced the energy dissipation. Under different air velocities (3–12 m/s), the novel air damper was far more efficient at reducing the resistance than the single-leaf damper with a local resistance reduction rate of 81.4%∼87.16%.

A dynamic thermal environment meeting human health requirements can be created with natural wind simulated by artificial means. Simulating natural wind can provide an innovative air-conditioning mode that reduces the energy consumption of air-conditioning systems and avoids the body-resistance decrease and body-temperature regulation mechanism failure that limit the traditional steady air-conditioning mode. In this paper, new methods for simulating natural wind are presented in which the controllable fluctuation of mechanical wind is improved to make its characteristics more similar to those of natural wind. Experiments carried out to verify the effectiveness of these mechanical-wind methods are reported. A self-operated air supply device improving the fluctuation of the air supply is proposed, which can increase the value of the characteristic parameter β (the negative slope of the double-logarithmic power spectrum curve) to 1.2 when the wind speed is greater than 1 m/s. With a second proposed device based on the gas-washing process, this value can reach 1.4 when the wind speed is greater than 0.5 m/s. In summary, this paper provides simple solutions for simulating natural wind.

Duct fittings are integral parts of a duct system and play important roles in fluid transportation. Resistance within the component directly affects the energy consumed by fans and pumps. This paper proposes a novel low-resistance duct tee by emulating a natural river configuration and theoretically explains the mechanism of resistance reduction in ducts based on variations in dissipation and displacement terms in the N S equation. The novel tee can reduce resistance in straight ducts with any flow ratios and aspect ratios, with a resistance reduction rate from 20.45% to 248.21%. The novel tee can also reduce resistance in branch ducts only when the flows in straight ducts are larger than in branch ducts, and the resistance reduction rate is between 0 and 817.88% (The resistance reduction rate is the degree of resistance reduction achieved by the novel duct tee). The resistance reduction rate can be improved to above 100% when the increased amplitude of momentum dissipation is below the increased amplitude of momentum convection. The turbulence model was selected based on the full-scale experiment. The resistance reduction effect of the novel tee is validated via a full-scale experiment at the end of this paper.

Thermal comfort and energy saving has drawn widespread attention in recent years, and personalized ventilation (PV) is a theoretical air supply method designed for both comfort and energy savings. This study introduces a targeted personalized ventilation (TPV) system formed by a multi-tuyere apparatus and based on the concept of targeted ventilation. Corresponding targeted ventilation indices are introduced to evaluate regional thermal comfort, and the effectiveness of the ventilation systems is presented. Turbulence model selection is conducted by comparing computational fluid dynamics (CFD) and experimental data to determine the practical effect of the TPV. The TPV provides air supply to the controlled area and thus improves the utilization ratio of the flow field. The air supply through the coupled tuyeres results in a uniform flow field with air speeds very close to 0.3 m/s. Compared with other PV systems, the velocity target value of the TPV system proposed in this paper is 40.5% lower, and the energy-saving rate reaches 52.9%. The effects of the TPVs were verified in a full-scale experiment.

Because of the significant resistance effect and the energy consumption effect, increasing attention has been paid to the local resistance represented by tees in ventilation and air-conditioning duct systems in recent years. The resistance reduction method involving installation of a guide vane in dividing flow tees in a ventilation and air-conditioning duct is studied. A reasonable position for installing the guide vane is proposed. The form of the guide vane is optimized. The resistance characteristics of the tee are analyzed under different flow velocities and different aspect ratios of the duct. The implementation effect of optimizing a tee is verified through a full-scale experiment. The results show that the resistance reduction rate of the proposed guide vane is 4.3%–263.8% under different flow ratios (5:1–1:3) and different aspect ratios (4:1–1:4) compared with that of a tee without the guide vane. In some cases, the resistance reduction rate exceeds 100%; the mechanism responsible for this phenomenon is also analyzed. The tee with the proposed guide vane reduces deformation of the fluid, the mechanical energy converted to internal energy and turbulent energy dissipation. The study results are verified through a full-scale experiment; the experimental data are in good agreement with the simulated values and the results reported in previous studies.

The energy consumption of air transportation and distribution systems in ventilation and air-conditioning ducts has drawn worldwide attention. In this study, a method for reducing the local resistance in a duct tee using a protrusion structure is proposed based on biomimicry of the branched structure of plants. The resistance of a duct featuring protrusions is compared with that of the five traditional types of tees. The resistance mechanism of the protrusion structure is analyzed, and the effectiveness of the proposed method is verified through experiments. The resistance of a duct tee with protrusions is much smaller than that of all traditional tees. Relative to the traditional duct tee, the resistance reduction rates of the duct tee with protrusion structure in two flow directions are 36% and 21%. In cases of high flow and low aspect ratios, the resistance becomes negative; that is, the resistance reduction rates are greater than 100%. The protrusions significantly reduce the energy dissipation rate of the duct tee. The effect region of the energy dissipation for duct tees is smaller than that of traditional tees.

In public buildings such as libraries, people are more prone to airborne microbial cross-infection. Therefore, the present study uses cultivation and high-throughput sequencing techniques to explore the seasonal structural characteristics of indoor airborne fungi within four library rooms, and determines the fungal composition on the surface of commonly used books. The results showed that the highest mean fungal propagule concentrations were 634 ± 210 CFU m−3, 534 ± 177 CFU m−3, 780 ± 294 CFU m−3, and 681 ± 227 CFU m−3, and these values were found in the autumn in each room. In all four rooms, the fungal propagule with the highest concentrations had sizes ranging from 1.1 to 3.3 μm in each season which can penetrate to the lower respiratory tract. The dg values (2.62–3.17 μm) of the airborne fungi for all four seasons in each room can reach the secondary bronchi. There was little overlap among the dominant fungal genera across the four seasons in each room, and most of the dominant genera were opportunistic pathogenic or allergenic fungi (Torula, Cladosporium, Candida, Malassezia, Aureobasidium, Gibberella, and Aspergillus). Students and staff members were exposed to the higher levels of airborne fungal propagules in autumn. Five abiotic parameters have seasonal effects on the airborne fungal propagule concentrations. Moreover, four fungal genera from the sampled books were determined to be potential biodegradation. Overall, the information provided by this study will help to strengthen our understanding of indoor airborne fungal pollution and spread in public buildings.

In high-rise residential buildings, channeling in the flue between stories can spread pollutants and airborne diseases. To avoid this issue, it is necessary to use an airflow balance device, which will greatly increase the flow resistance. Based on a centralized exhaust shaft, this paper proposed a novel cycloidal guide confluence flue tee. The resistance characteristics of the flue tee were analyzed at different flow ratios and duct aspect ratios. The quantitative effects of the forward flow resistance decreased and those of the backward flow resistance increased after the guide vane was installed. The performances of the traditional tee and novel tee were tested and verified by performing full-scale experiments under the same duct aspect ratio and different flow ratios. The ranges of the decrease in forward resistance and increase in backward resistance were 44.07–196.97% and 4.30–171.20%, respectively. Under the same flow ratio and different duct aspect ratios, the ranges of the decrease in forward resistance and increase in backward resistance were 17.30–99.90% and 2.23–27.40%, respectively. The results of this work will provide a new perspective on resistance reduction and anti-channeling flue tee shape design in ventilation and air conditioning systems.

Ventilation and air conditioning duct systems have been widely studied for their extensive application, sophisticated duct system and significant resistance effect. The energy consumption of the fan in ventilation and air conditioning systems accounts for approximately 20%–40% of the total building energy consumption, which is equivalent to that of the cooling source. This paper proposes a novel low-resistance bend with a guide vane based on a jugular profile, and through the field synergy principle and the entropy increase principle, the bend internal flow state and the mechanism of resistance reduction are analyzed. The position and shape of the guide vane in the traditional bend are optimized by full-scale experiments and numerical simulations. The effects of resistance reduction for traditional bends and novel bends are compared with different aspect ratios and curvature radii. The results show that the local resistance coefficient of a bend with a tongue-shaped guide vane is significantly smaller than that of the traditional vane, and in the case of the curvature radii of the bend being equal, the resistance reduction effect is better when the aspect ratio of the bend is closer to 1.0. The resistance reduction of a bend with a tongue-shaped guide vane is as high as 31%. This paper provides guidance for the study of resistance reduction in local components of ventilation and air conditioning ducts with guide vanes.

Floor-standing air conditioners (FSACs) have been widely used in civil and office buildings due to their high cooling capacity and easy installation in recent years. Increasing attention has been given to reducing the draft sensation of FSACs. This study introduces a new form of smart terminal for air conditioners that can be automatically adjusted by identifying the positions of humans in the room. The smart terminal has certain practical value given its simple structure and relatively low cost. A target air supply evaluation index for regional thermal comfort evaluation named the air velocity target value is proposed. A computational fluid dynamics model is established, and an orthogonal experiment of 4 factors and 4 levels is designed. The optimal parameters of the terminal are further determined through a series of optimization steps. The effect of the smart terminal is validated with numerical simulation and experimental measures, and the local velocities of the occupied zone are mostly below 0.3 m/s, showing that the draft level in the room is acceptable. Compared with the case of an air conditioner only, the air velocity target value of the room with a smart terminal decreases by 21.3%–63.3%. Compared with other existing manually controlled terminals purchased online, the smart terminal satisfies the minimum air velocity target value in the occupied zone. This study can also be used to guide the positioning and setting of air supplies for different positions of humans in a room under other air distributions.

Train-induced unsteady airflow (TIUA) has a considerable effect on the ventilation and thermal environment of a subway system. Because of the complexity of a subway ventilation network and the variability of train activity, analytical and numerical methods are limited in reflecting the actual situation. In this study, a field test on the TIUA and air temperature in a subway station with full-height platform bailout doors (PBDs) was conducted under four operational conditions. The results showed that the train running parameters and operational modes, including the piston vent shafts, bypass ducts and cotton curtains at the entrances, had substantial effects on the TIUA and thermal environment. The air inflow and outflow rates through the entrances increased by 20.99% and 39.66%, respectively, as the train interval decreased by 104 s (case 2). Moreover, there was a greater difference in the air inflow rate through the entrances under different operational modes. Furthermore, uninstalling the cotton curtains increased the air inflow and outflow rates by 2.09- and 1.36-fold, respectively, at a train interval of 510 s (when comparing case 1 and case 2). In addition, removing the cotton curtains, the maximum decreases in air temperature in the entrances, hall, and platform were approximately 5.10 °C, 4.85 °C, and 1.39 °C, respectively, and the thermal environment with the single open system and closed bypass ducts condition might be better than that with the internal circulation system and open bypass ducts condition. This study provides first-hand data for ascertaining the characteristics of the TIUA and optimizing subway operational modes.

The fan energy consumption caused by the resistance of representative local components, including diffusers, accounts for 10% of building energy consumption. This proportion increases with more stringent requirements for building functionality, intelligence and comfort. This study introduces a high-efficiency diffuser based on a normalized evaluation index of jet length and resistance. The resistance reduction mechanism is analyzed based on the principle of entropy increase. A comprehensive performance evaluation index, the air diffuser effective index (ADEI), is put forward to describe the resistance and jet length of the diffuser. The preliminary results show that compared with the round diffuser, the novel diffuser can mitigate the fluid deformation, weaken the strength of the airflow vortex and reduce the conversion of mechanical energy to internal energy. The jet length and flow resistance of the novel diffuser are respectively 7% longer and 47% lower than those of the round diffuser. The proposed ADEI of the novel diffuser is 56% smaller than the round diffuser.

Oxygen supply is necessary for high-altitude hypoxic areas, especially public spaces with high occupant densities. Traditional oxygen supply systems, including individual oxygen supplies (IOS), distributed centralized oxygen supplies (DCOS) and diffusion-type oxygen supplies (DTOS), are limited in completing oxygen delivery tasks by the balance between low cost and high efficiency. This study elaborated a method for air distribution by adopting guardrail slot diffusers (GSDs) for oxygen-rich air delivery directly to the human breathing zone without changing the basic layouts of high and large spaces. The dynamic breathing zone was obtained by monitoring the swing of people waiting beside a guardrail. Two indicators, the target value of oxygen concentration and the oxygen supply efficiency, were introduced to facilitate the evaluation of oxygen supply through GSDs. Compared with oxygen supply through other existing air distribution systems in high and large spaces, the optimized GSDs have a 9%–27% higher effectiveness, as expressed in terms of the target value of oxygen concentration. The oxygen supply efficiency is 271%–658% higher. The implementation of the system was studied at altitudes of 2000 m, 3000 m, 4000 m and 5000 m, which proved that this oxygen supply system has better implementation effects. By increasing the height of the guardrail by 100 mm, the GSDs can meet the oxygen demand for air inhaled by European and North American adults. The results indicate that this method realized efficient oxygen supply in high-altitude hypoxic areas while reducing oxygen consumption and investment costs.

The presence, flow, and distribution of particle in heating, ventilation, and air-conditioning (HVAC) ducts influence the quality of air in buildings and hence the health of building occupants. To shed a better light on the flow of particles in HVAC ducts this a paper has considered the effects of drag, lift force, gravity, Brownian diffusion, and turbulent diffusion on the dimensionless deposition velocity of particles in smooth vertical ventilation ducts using fully developed and developing velocity profiles. Based on the Reynolds stress transport model (RSM) at two different air velocities, 3.0 m/s and 7.0 m/s, the aforementioned effects were predicted using Reynolds-averaged Navier–Stokes (RANS)–Lagrangian simulation on square shaped ducts under vertical flows. Preliminary results suggest that the gravity of particles does not directly change the dimensionless deposition velocity in vertical flows. Nevertheless, the gravity of particles contributes to changing the Saffman lift force. It is thus the Saffman lift force that directly changes the dimensionless deposition velocity of particles in vertical flows. In addition, the difference in the dimensionless deposition velocities between fully developed and developing flows is owing to the turbulent diffusion, turbulent intensity, and needless to say, the Saffman lift force under different dimensionless particle relaxation time.