Mixing Ventilation Research Articles

Experimental study of air distribution and heating performances of deflection ventilation

Deflection ventilation uses a purposely-designed deflector to divert supply air jet into the occupied zone directly. A few numerical studies have shown good indoor air quality with deflection ventilation. However, there was a lack of research on thermal comfort, which is also important to ensure human wellbeing. This study conducted experimental measurements when deflection ventilation was operated for winter heating. Eleven cases with different supply air velocities, supply air temperatures and deflection angles were carried out in an office-layout experimental chamber. As a comparison, another case with mixing ventilation was also measured. The predicted mean vote (PMV), draft rate (DR), air diffusion performance index (ADPI) and energy utilization coefficient (EUC) were adopted to evaluate the heating performances. The results showed that the deflection angle played a decisive role on air distribution. An inclined deflector (deflection angle: 35° downward) could elevate air temperature in the lower occupied zone as compared with a horizontal deflector (deflection angle: 0°), which provided efficient air distribution for winter heating. The average PMV values were in the range of −0.7 – 0.5, and the values of DR and ADPI in the occupied zone were typically less than 20% and higher than 80%, respectively. According to ISO 7730 and ASHRAE 113, deflection ventilation achieved satisfactory indoor environment with regard to thermal comfort. The EUC was typically greater than unity, indicating high energy efficiency of deflection ventilation, especially for the cases with deflection angle of 35°. In comparison with mixing ventilation, deflection ventilation can provide better thermal comfort as well as energy efficiency.

An Aisle Displacement Ventilation System for Twin-Aisle Commercial Airliner Cabin

The environmental control system in most commercial airliner cabins supplies air from shoulder and ceiling level and exhausts air at floor level on both sides of the cabin walls. The ventilation system mixes air in the cabins to create a relative uniform air temperature distribution which is great for passengers’ thermal comfort. However, the mixing ventilation also enhances airborne contaminant transfer. Many displacement ventilation methods have been proposed to use in aircraft cabins, but the disadvantages of the ventilation approach are usually creating draft on the passengers’ ankles and high air temperature stratification between passengers’ heads and feet. This investigation developed an aisle displacement ventilation (ADV) system which can reduce air temperature stratification effectively without occupying the legroom space under the seats, so it is good for passengers and crew members’ comfort and friendly for luggage storage, in addition, it can also be easily installed in aircraft cabins. By installing the system in a five-row, twin-aisle cabin mockup, our study found that the ADV system can create a low air velocity distribution in the cabin and can maintain an acceptable air temperature stratification without draft. The system created an uprising airflow which can effectively remove airborne contaminant which was generated from index passengers’ respiratory activities. The experimental data were used to validate a computational-fluid-dynamics (CFD) program. The validated CFD program was used to compare the ADV with under-seat displacement ventilation (USDV) and underfloor air distribution (UFAD) system along the aisles. The comparison results show that the ADV had obvious better thermal comfort than the other two systems, and the cabin air quality of the three ventilation systems was similar, all far better than the “perfectly-mixed” ventilated condition.

Effects of Indoor Air Curtain and Fan on Cross-Infection Risk for a Space with Displacement Ventilation

Air curtain is an effective control for separating air spaces and reducing the cross-transfer of air, heat, and contaminant between different zones. Studies show that displacement ventilation is better for indoor air quality than mixed ventilation. However, displacement ventilation may be susceptible to a phenomenon called lock-up, whereby contaminants are held in a lower stratified portion of the space and increase infection potential. This study investigates whether indoor air curtain and circulation fan can reduce the lock-up phenomenon for spaces with displacement ventilation and thus reduce infection risk across the breathing zone. Specially, numerical test is conducted to explore if a side-wall diffuser-integrated vertical slot air curtain would be sufficient for reducing infection risk. Additionally, circulation fans above the occupants are applied to explore if they would reduce the lock-up phenomenon. The conclusions are that neither a side air curtain slot nor circulation fans is/are adequate to reduce infection risk. In fact, all methods tested increased infection risk. This increase in infection risk is contrary to previous research and is due to changing air flow patterns throughout the space that disrupted thermal plumes and created contaminant leakage from one side of the room to the other. Circulation fans provided the promising results while further optimization should be conducted in terms of the ideal quantity, location, flow rate, orientation, and size of fans throughout a given space.

Reduced personal exposure to airborne cross-infection using wearable exhaust ventilation

This study aimed to explore an alternative solution for protection against cross-infection. Exposure reduction to exhaled airborne contaminants by wearing an exhaust nozzle was studied. Experiments were performed in a full-scale test room (64.8 m3) equipped with a small section of a stadium tribune with six seats. Two breathing thermal manikins and four heated dummies were placed on the tribune. The manikins were equipped with artificial lungs simulating a realistic breathing cycle and respiratory flow. One of the breathing manikins was used to mimic a sick person having an infectious respiratory disease. The exhaled air of the “infecting person” was mixed with tracer gas to imitate pathogens. Four types of air exhaust nozzles were studied for their efficiency to reduce exposure to exhaled contaminants. The nozzle was positioned in front of the mouth of the infecting person. The test room was ventilated with mixing background ventilation. The use of the exhaust nozzle resulted in cleaner air in the room and at the breathing zone of the simulated occupants compared to only using dilution by the background ventilation. The novel device has the potential to capture exhaled air and reduce airborne cross-infection in densely occupied sitting areas.

Thermal Environment, Ventilation Effectiveness, and Infection Risk of Restaurant with Impinging Jet Ventilation

The basic strategy of the impinging jet ventilation system (IJV) is to keep high air quality within the occupied zone. In IJV, the air supplied from ducts impinges on the floor and spread through the lower level of the room. When the air reaches the heat sources, it rises upward and is exhausted around the ceiling. Most of the previous works about IJV focus on simple room set-ups, whereas the studies focus on realistic set-ups are limited. To investigate the applicability of IJV to a more practical situation, CFD analysis was conducted in a room that simulated a restaurant. In this numerical study, thirty-two seated occupants were distributed in the restaurant hall as the heat and contaminant sources (contaminant was released from their mouth), while a large amount of heat was generated by the equipment in the kitchen. The indoor environment of IJV was compared to that of the mixing ventilation system (MV) in terms of thermal environment, ventilation effectiveness, and infection risk. The results showed that IJV were superior to MV in terms of air conditioning efficiency, pollutant removal efficiency, and infection risk reduction. In conclusion, the results suggest that IJV can improve the indoor environment.

Syndromes of gas exchange disorders in patients with pulmonary tuberculosis

Introduction. Measurement of diffusion in the lung is important in the diagnosis and management of most pulmonary diseases. The analysis of diffusion lung capac-ity (DLCO) in combination with body plethysmography is useful for the interpretation of the causes of pulmo-nary gas exchange disorders. The aim: to determine the leading syndromes of pulmonary gas exchange disorders in patients with pulmonary tuberculosis (PT). Materials and methods. 608 patients (244/364 M/W) with veri-fied PT with smoking history of less than 10 pack/years were examined. Spirometry, body plethysmography, and DLCO were performed by the single-breath breath-hold-ing method. Results. DLCO decrease was detected in the majority of patients with PT (76%): in 94% of patients with massive fibrous-cavernous PT, 79.4% with disseminated PT and more than 60% of patients with infiltrative foci, local cavities, tuberculomas. In patients without ventilation dis-orders (58.4%), DLCO decrease was caused by damage to the alveolar capillary membrane, less often by air trapping (35.1%), other cases were rare. In the obstructive variant, mixed disorders of gas exchange (38.2%) and air trapping (34.1%) were most typical. In the restrictive variant, gas exchange surface reduction (62.5%) and mixed disorders (30%) prevailed. In mixed ventilation disorders, the mixed pulmonary gas exchange disorders were most often de-tected (63.8%) and the gas exchange surface reduction was quite common (36.2%) also. Conclusion. Alveolar cap-illary membrane damage (35.1%) and air trapping (28.1%) were most common in patients with PT. The mixed variant and gas exchange surface reduction were detected less frequently (24.7 and 12.1%, respectively), but these syn-dromes led to the most significant DLCO decrease.

Mixed ventilation approach combined with single-shaft complementary system for highway tunnels

Highway tunnel ventilation systems are associated with high civil construction and operation costs, as well as large differences in the total required air volume for uphill and downhill tunnels. Thus, in the current study, a complementary ventilation system is applied to the shaft segmented longitudinal ventilation mode to form the mixed ventilation mode of the complementary combined ventilation shaft. The mixed ventilation formula is derived based on the tunnel ventilation theory. Combined with the design process of tunnel ventilation, the design process from the location of the ventilation shaft, design air volume, the air interchange channel location, the air exchange ratio of air interchange channel to pollutant concentration is determined, and the mixed ventilation mode conditions are analyzed. Moreover, an engineering example is employed to analyze the mixed ventilation, and to compare the traffic wind utilization rate, operation energy consumption and the civil construction scale between conventional segmented longitudinal ventilation and mixed ventilation. The results reveal that compared with the conventional segmented longitudinal ventilation mode, the mixed ventilation mode effectively improves the utilization rate of traffic wind, reduces the adverse effect of surplus traffic wind pressure on tunnel ventilation and minimizes mechanical power usage. In terms of operating energy consumption, taking a vehicle speed of 60 km/h as an example, the mixed ventilation method fully utilizes the traffic wind pressure in the tunnel. Although it is necessary to turn on the jet fan in the tunnel to increase the power, the energy consumption of the axial flow fan is reduced by 31.9 %, and the total power is reduced by 9.5 %, greatly lowering the energy consumption of the tunnel operation. Despite the addition of the traverse ventilation channels by the mixed ventilation method, reductions are observed in the construction of a ventilation shaft, the connecting channels, the overall ventilation civil engineering volume, and the initial civil construction investment cost. Moreover, the mixed ventilation method includes a smoke exhaust channel, thus solving the smoke exhaust problem of tunnel fires.

Numerical Simulation of Different Ventilation Systems in an Airplane Cabin

Airplanes are the most popular way of transportation worldwide, especially for long haul. It facilitates the growth of global trade as well, besides promoting tourism and other employment developments. Passenger comfort and hygiene inside an airplane cabin became main concern for aircraft manufacturers. The possibility for a potential spread of infectious virus or bacteria even maximized this concern. Therefore, supplying sterile and particle-free air inside the aircraft cabin became extremely crucial more than ever. In order to ensure comfort and hygiene, regardless of the environment conditions inside the aircraft cabin, paved the way for researchers to focus on this topic, recently. It is obvious that, an important precaution for the spread of micro-organisms can be selecting an adequate air ventilation system inside the airplane cabin. In this study, a part of an airplane passenger cabin is modelled for four different scenarios. The streamlines of air, which is sent to the cabin from air ducts, are obtained and air flow path is observed for the investigated cases. The results of the numerical simulations are presented as the outcomes of this study. It is observed that the air mixing between different seat rows occur slightly only for sidewall supply and bottom return mixing ventilation and displacement ventilation systems, whereas the air mixing for the same seat row is seen for all ventilation systems. In conclusion, sidewall supply and bottom return mixing ventilation system is found the most appropriate one, even though it causes air recirculation at the same row seats.

Investigation on the cross-infection control performance of interactive cascade ventilation in multi-scenario of winter

With the wide spread of COVID-19, numerous cases demonstrate that proper ventilation method can reduce the cross-infection risk obviously. Interactive cascade ventilation (ICV) as a recently proposed ventilation method, the advantage of indoor environment construction has been proven. However, few studies are conducted to investigate the virus prevention and control characteristics of ICV, which is particularly important under epidemic normalizing. Hence, this study explored and compared the cross-infection control performance of three ventilation strategies, namely mixing ventilation (MV), stratum ventilation (SV), and interactive cascade ventilation (ICV), with a validated CFD model. A typical office was selected as the background scene, where an infected person coughs, sneezes with standing or sitting at different positions. Exposure doses, health infection risk, and disease burden (DB) were employed as the evaluation indicators under different ventilation methods of multi-scenario. The research results indicated that the average aerosol exposure dose among the human respiratory region under ICV was 0.29 g/day, which was reduced by 67 % and 50 % compared with MV and SV. In addition, only in ICV can the health infection risk meets the EPA standard. The average disease health burden for exposed persons under ICV was 0.93 × 10−6 DALYs pppy, which was 37 % and 70 % lower than SV and MV. The findings obtained from this study confirm that ICV performs excellently in reducing the cross-infection risk, providing the theoretical basis for future epidemic prevention and control.

Numerical Study of Air Distribution and Evolution Characteristics in Airliner Cabin

The distribution and evolution of air in airliner cabins is an important basis for the study of cabin thermal environment and pollutant propagation. Due to the complex heat and mass transfer problems caused by forced and natural convection in a large-scale space, the accurate prediction of air distribution in airliner cabins still faces huge challenges. This study takes the cabin of the Airbus A320 as the research object. The accurate numerical simulation of the flow and heat transfer process in an airliner cabin under mixing ventilation mode was carried out using the Hybrid Thermal Lattice Boltzmann Method (HTLBM) combined with GPU (Graphics Processing Unit) acceleration technology, and the influence of human thermal plumes on air distribution and evolution characteristics in an airliner cabin was analyzed. The research shows that the human thermal plume changes the air distribution in the passenger cabin. The thermal plume slows down the jet attenuation, increases the energy exchange in the area near the passengers, and offsets the jet trajectory. The airflow self-locking effect is easier to form in the passenger breathing area, which increases the time for the flow field to develop into the steady state. The influence of human thermal plumes on the airflow distribution in the passenger cabin cannot be ignored.

An investigation of a nonthermally insulated mixing ventilated office room for partitioning in hot and dry climate by simulation approach

AbstractDue to the recent situation, especially since the beginning of the spread of COVID‐19, work in administrative or service offices under conditions of social divergence and the working environment has become conditional on the ventilation system; thus, enhancing ventilation's function to minimize the spread of infections, and impurities to larger areas or limiting its transition from one employee to another who work in the same place for long hours. A nonisothermal office room, designed with a mixing ventilation system has been simulated by using AIRPAK3.0.16 software, and RNG k– as a turbulence model, where the adoption of partitions in such rooms was studied and its effect on thermal employee's comfort and quality of fresh air, by monitoring the air diffusion performance index, prediction of the mean vote, and percentage of predicted dissatisfied. The main findings were that partitions are seen as a technique of preventing and protecting against the spread of pollutants and illnesses since they prevent contaminants from reaching the breathing zones of the office's inhabitants. It was noted that the change in the height of the partition with an increase of 10% of the room's height as a gap, gives a more acceptance value of the heat removal efficiency and ventilation rate.

Airflow characteristics of attachment ventilation in a nursery pig house under heating mode

In the current energy saving context, it is important to study the airflow that regulates the environment of an animal-occupied zone (AOZ) and reduces the heating load of the barn in a nursery pig house. Forced convection heating regulates the overall thermal environment in a nursery barn using hot air while reducing the pollutant concentration. This improves air quality and has energy-saving attributes. In this study, we investigated a pen-attached ventilation (PAV) airflow system in a nursery pig house based on the hot air heating method during winter. The air distribution, temperature field diffusion characteristics, and ventilation effectiveness of the PAV were investigated using a full-scale test bench and computational fluid dynamics (CFD) during the heating mode. The results show that PAV can effectively deliver fresh air and heat to the lying area of nursery pigs, as well as reduce the vertical temperature stratification inside the pig house. In addition, the average temperature in the lying area increased by 3.77 °C, the energy utilization coefficient increased by 0.2, and the energy saving rate was 12.7% when compared to the mixing ventilation (MV) airflow regulation mode for the same heat input. The PAV airflow approach reduced the energy consumption in the operation stage of the barn and theoretically justified its application to the thermal regulation of the environment of nursery pigs. • We investigated a PAV airflow system for the hot air heating method. • The average pig house temperature increased by 3.77 °C with this method. • This method reduced energy consumption in the operation stage of the barn by 12.7%.

Occupant’s thermal comfort in a radiant ceiling cooling room with hot wall surface

A radiant ceiling cooling (CC) system integrated with a mechanical ventilation system was extensively applied in a modern office in a glass curtain wall building. Thermal comfort in a radiant ceiling cooling room with mixing ventilation (MV) or underfloor air distribution (UFAD) was investigated by objective measurements and subjective questionnaires. The external wall surface temperature and mean radiant temperature were 33.9–34.6°C and 27.2–27.4°C, respectively, with a heat transfer of 41.5 W/m2 from the external wall and 37.8–38.6°C and 27.4–28.2°C with a heat transfer of 69.5 W/m2 from the external wall. The indoor air velocity in the occupied zone was 0.17–0.23 m/s in the room with CC+MV and 0.09–0.16 m/s in the room with CC + UFAD. There was a considerable difference between occupants’ thermal perceptions with different distances away from the external wall. Both the ventilation system type and hot wall surface temperature did not influence occupants’ overall thermal perceptions, but their local thermal sensation and skin temperature. The results suggest that the impacts of ventilation system type and hot wall surface temperature on occupants’ local thermal response should be considered during the design of a radiant ceiling cooling system combined with a mechanical ventilation system.

Performance evaluation of an architecturally-designed vertical high capacity linear slot diffuser in a tropical atrium

This paper proposed a new approach for the efficient air conditioning of large tropical buildings. The current study has two objectives: the design and numerical investigations of the performance of vertically oriented high capacity linear slot diffusers (HCLSD) in an atrium building and the verification and validation of the different turbulence models through laboratory-scale experiments. The HCLSD was investigated with varying angles of inclination of the blades (ϕ = 0o to 25o) for the in-depth performance analyses. The performance was evaluated by monitoring and comparing the velocity and temperature profiles along the vertical lines drawn at different locations in the studied domain. A relatively longer jet throw was noticed through quantitative analysis at ϕ = 0o. Note that more than 33% increment in the face velocity was recorded at this angle. The corresponding terminal velocity of 0.225 m/s was observed at 8 m distance from the diffuser face. The detailed investigations at 0o deflector angle (case-1) were carried out for velocity, temperature field, and thermal comfort indices, i.e. PMV and PPD models. For the occupied zone, the thermal comfort indices were found within the acceptable ranges (i.e. PMV = + 0.1 to +0.9 and PPD = 4% to 20%). Abbreviations: ACMV: Air conditioning and mechanical ventilation; CFD: Computational fluid dynamics; CMH: Cubic meter per hour; DV: Displacement ventilation; HCLSD: High capacity linear slot diffuser; IAQ: Indoor air quality; MV: Mixing ventilation; PMV: Predicted mean vote; PPD: Predicted percentage dissatisfied; RANS: Reynolds-Averaged Navier – Stokes; RNG: Re-Normalization Group; SST: Shear-Stress Transport: SIMPLE: Semi-implicit method for pressure linked equations; VAV: Variable air volume; VSD: Variable speed drives

Analysis on the thermal performance of low-temperature radiant floor coupled with intermittent stratum ventilation (LTR-ISV) for space heating

With increasing energy use and outbreaks of respiratory infectious diseases (such as COVID-19) in buildings, there is a growing interest in creating healthy and energy-efficient indoor environments. A novel heating system named low-temperature radiant floor coupled with intermittent stratum ventilation (LTR-ISV) is proposed in this study. Thermal performance, indoor air quality, energy and exergy performance were investigated and compared with conventional radiant floor heating (CRFH) and conventional radiant floor heating with mixing ventilation (CRFH + MV). The results indicated that LTR-ISV had a more uniform operative temperature distribution and overall thermal sensation, and air mixing was enhanced without generating additional draft sensation. Compared with CRFH and CRFH + MV, the indoor CO2 concentration in LTR-ISV can be reduced by 1355 ppm and 400 ppm, respectively. Airborne transmission risk can also be reduced by 5.35 times. The coefficient of performance for CRFH, CRFH + MV, and LTR-ISV during working hours was 4.2, 2.5, and 3.4, respectively. The lower value of LTR-ISV was due to the high energy usage of the primary air handing unit. In the non-working hours, LTR-ISV was 0.6 and 1.3 higher compared to CRFH and CRFH + MV, respectively. The exergy efficiency of LTR-ISV, CRFH, and CRFH + MV was 81.77 %, 76.43 %, and 64.71 %, respectively. Therefore, the LTR-ISV system can meet the requirements of high indoor air quality and thermal comfort and provides a reference for the energy-saving use of low-grade energy in space heating.

Airplane cabin mixing ventilation with time-periodic supply: Contaminant mass fluxes and ventilation efficiency.

Airplane cabin ventilation is essential to ensure passengers' well-being. The conventional ventilation method is mixing ventilation with a statistically steady supply, which, according to former studies, has reached its limits regarding, for example, the ventilation efficiency. However, the effect of a statistically unsteady (time-periodic) supply on the mixing ventilation efficiency has remained largely unexplored. This research uses computational fluid dynamics (CFD) with the large eddy simulation (LES) approach to study isothermal time-periodic mixing ventilation in a section of a single-aisle airplane cabin model, in which the air exhaled by the passengers functions as (passive) contaminants. Two time-periodic supply strategies are evaluated. The induced time-periodic airflow patterns promote an efficient delivery of fresh air to the passenger zone and affect the passengers' expiratory plumes. This results in increased mean contaminant mass fluxes, causing a strong reduction of the mean contaminant concentrations in the passenger zone (up to 23%) and an increased contaminant extraction from the cabin. Mean velocities increase with up to 55% but remain within the comfortable range. It is shown that the ventilation efficiency improves; that is, the contaminant removal effectiveness and air change efficiency (in the full cabin volume) increase with up to 20% and 7%, respectively.

Air Distribution System for Infection Reduction in Commercial Airplane Premium Economy and Business Class Passenger Seats

In previous works made by the authors, a new air distribution system with Personalized Ventilation (PV) combined with Underfloor Air Distribution (UFAD) has been proposed. The proposed system in four different configurations provided thermal comfort, as well as a shield between passengers for infection reduction in economy class seats in an airplane. This work extends the previous works by studying the same system for premium economy and business class seats which have extra spacing between passengers. The proposed system provided enhanced thermal comfort despite the extra spacing of the seats. The Predictive Mean Vote (PMV) has recorded the best value of 0.38 for the business class seats compared to all the other seating configurations. Predicted Percentage Dissatisfied (PPD) has also been improved with values of 12.2% and 10.9% for the premium economy and business classes respectively. In addition to thermal comfort, the proposed system still provides an adequate air shield for passengers in the widely spaced premium economy and business classes. It is recommended as an alternative to the conventional mixed ventilation system in a commercial airplane for all seating plans.

Integrated system of exhaust air heat pump and advanced air distribution for energy-efficient provision of outdoor air.

A large outdoor air supply is required to control the airborne infection risk of respiratory diseases (e.g., COVID 19) but causes a high energy penalty. This study proposes a novel integrated system of the exhaust air heat pump and advanced air distribution to energy-efficiently provide outdoor air. The system energy performances are evaluated by the experimentally validated thermodynamic model of heat pump and heat removal efficiency model of advanced air distribution. Results show the exhaust air heat pump with advanced air distribution can save energy because of three mechanisms. First, the exhaust air heat pump reuses the exhaust air to reduce the condensation temperature, thereby improving the coefficient of performance. Second, advanced air distribution reduces ventilation load. Third, advanced air distribution reduces the condensation temperature and enhances the evaporation temperature, thereby improving the coefficient of performance. The exhaust air heat pump saves energy by 18%, advanced air distribution saves energy by 36%, and the integrated system of the exhaust air heat pump and advanced air distribution can save energy by 45%. As a specific application, compared with the conventional system (i.e., the outdoor air heat pump with mixing ventilation), the exhaust air heat pump with stratum ventilation saves energy by 21% − 35% under various outdoor air ratios and outdoor air temperatures. The proposed integrated system of the exhaust air heat pump and advanced air distribution contributes to the development of low-carbon and healthy buildings.

Zonal modeling of air distribution impact on the long-range airborne transmission risk of SARS-CoV-2

A widely used analytical model to quantitatively assess airborne infection risk is the Wells-Riley model which is limited to complete air mixing in a single zone. However, this assumption tends not to be feasible (or reality) for many situations. This study aimed to extend the Wells-Riley model so that the infection risk can be calculated in spaces where complete mixing is not present. Some more advanced ventilation concepts create either two horizontally divided air zones in spaces as displacement ventilation or the space may be divided into two vertical zones by downward plane jet as in protective-zone ventilation systems. This is done by evaluating the time-dependent distribution of infectious quanta in each zone and by solving the coupled system of differential equations based on the zonal quanta concentrations. This model introduces a novel approach by estimating the interzonal mixing factor based on previous experimental data for three types of ventilation systems: incomplete mixing ventilation, displacement ventilation, and protective zone ventilation. The modeling approach is applied to a room with one infected and one susceptible person present. The results show that using the Wells-Riley model based on the assumption of completely air mixing may considerably overestimate or underestimate the long-range airborne infection risk in rooms where air distribution is different than complete mixing, such as displacement ventilation, protected zone ventilation, warm air supplied from the ceiling, etc. Therefore, in spaces with non-uniform air distribution, a zonal modeling approach should be preferred in analytical models compared to the conventional single-zone Wells-Riley models when assessing long-range airborne transmission risk of infectious respiratory diseases.

Predicting moisture condensation risk on the radiant cooling floor of an office using integration of a genetic algorithm-back-propagation neural network with sensitivity analysis

Pre-dehumidification time (τpre) and pre-dehumidification energy consumption (Epre) play important roles in preventing the condensation of moisture on the floors of rooms that use a radiant floor cooling (RFC) system. However, there are few theoretical or experimental studies that focus on these two important quantities. In this study, an artificial neural network (ANN) was used to predict condensation risk for the integration of RFC systems with mixed ventilation (MV), stratum ventilation (SV), and displacement ventilation (DV) systems. A genetic algorithm-back-propagation (GA-BP) neural network model was established to predict τpre and Epre. Both training data and validation data were obtained from tests in a computational fluid dynamics (CFD) simulation. The results show that the established GA-BP model can predict τpre and Epre well. The coefficient of determination (R2) of τpre and of Epre were, respectively, 0.973 and 0.956. For an RFC system integrated with an MV, SV, or DV system, the lowest values of τpre and Epre were with the DV system, 23.1 s and 0.237 kWh, respectively, for a 67.5 m3 room. Therefore, the best pre-dehumidification effect was with integration of the DV and RFC systems. This study showed that an ANN-based method can be used for predictive control for condensation prevention in RFC systems. It also provides a novel and effective method by which to assess the pre-dehumidification control of radiant floor surfaces.