The ventilation efficiency of an artificially controlled experimental piglet house was evaluated using the tracer gas decay (TGD) method, which can predict the airflow pattern by tracking the tracer ...gas. The ventilation rate of the exhausted fan was classified as 120, 80, and 40 m3 min−1. Three inlet types were used as follows: (1) side windows, (2) ceiling slot with opening angle of 90°, and (3) ceiling slot with opening angle of 45°. Then, the local mean age (LMA) and air supply effectiveness (ASE) were calculated from the measured data at 18 points (3 × 3 sensors placed top and bottom). The LMA means the time for the inflow air to reach a point and ASE is the ratio of the LMA at a point to the total average LMA in the facility. When side windows and ceiling slots were used with the ventilation rate of 120 m3 min−1, each ASE was approximately 0.8 and 0.9, respectively, suggesting that ceiling slots could be more efficient than side windows with high ventilation rate. When the ventilation rate was low, the ASE of side windows was higher than the ceiling slots. However, when the angle of ceiling slots was changed to 45° with the ventilation rate of 40 m3 min−1, the ASE was almost 1.0, indicating that the ventilation efficiency was improved. Thus, ventilation efficiency can be sufficiently improved for all ventilation rates by using ceiling slots whilst controlling the angle of the slots.
•The local mean age and air supply effectiveness were evaluated in piglet house.•The ventilation efficiency was evaluated using the LMA and ASE based on TGD method.•The experimental piglet room in ASEC-A3EL has various typical ventilation systems.
•A good IAQ is measured in all the studied cases with DCV even at reduced air flow.•The effect of the reduced air flow on the ventilation efficiency is negligible.•Fan energy reductions ranges from ...25 to 55% compared to constant air volume system.•Ventilation heat losses 25–32% reduced compared to a constant air volume system.
Demand controlled ventilation (DCV) refers to a ventilation system with air flow rates that are controlled based on a measurement of an indoor air quality (IAQ) and/or on a thermal comfort parameter. DCV operates at reduced air flow rates during a large amount of the operation time and thus consumes less energy for fan operation and heating/cooling the supply air. The aim of the present research is to assess the IAQ, ventilation efficiency, and the operation and energy efficiency of real operating DCV systems in moderate climates.
Measurements are carried out for at least two weeks in autumn and winter 2015-2016. The following parameters were monitored: CO2 concentrations and air temperatures at different positions in the room and at the extract air grill, position of the variable air volume (VAV) boxes, supply and extract air flow rates and the occupancy of the room. Four case studies with large and varying occupancy rate and with different use and ventilation systems are selected. Two classrooms and three landscaped offices were evaluated.
The results show that a DCV is interesting in rooms with a large and varying occupancy rate such as lecture rooms and landscaped offices. A good IAQ is measured in all cases studied even at reduced air flow rates. The effect of the reduced air flow on the ventilation efficiency is negligible. The VAV boxes react well to predefined set points for CO2 concentration. During the measurement period, the reduction for fan energy ranges from 25 to 55% and ventilation heat losses 25–32% compared to a constant air volume system (CAV) with a design airflow rate of 29 m3/(h.pers), i.e., IDA3 in EN 13779. However, commissioning of the DCV is necessary to obtain and maintain these performances.
•A CFD model was proposed for simultaneous analysis of IAQ and thermal comfort.•The numerical model was validated against experimental data.•Interactions between MVHR and fan coil system were ...investigated.•Impact of the discharged air from fan coil on ventilation efficiency was addressed.•Results indicate importance of aligning the recirculated air with fresh air supply.
Mechanical Ventilation with Heat Recovery (MVHR) systems are gaining increasing interest in buildings with low energy demand, for improvement of the Indoor Air Quality (IAQ) and reduction of the ventilation energy loss. In retrofitted buildings, MVHRs are often integrated with an additional air heater to cover space heating demand. Hence, evaluation of the interactions between MVHR and heat emitter, and their effects on indoor airflow characteristics is of significant importance. The present study aims to investigate effects of a combined MVHR-fan-coil system in heating mode on IAQ and thermal comfort parameters inside a retrofitted room, by means of a computational fluid dynamic (CFD) code. The proposed CFD model is validated by comparing the numerical results with experimental data. The results yielded by numerical simulations allow evaluating the indoor environmental quality characteristics as well as addressing the MVHR and fan coil interactions. The results indicate that the airflow discharged from the fan coil could have a significant impact on the age of the air; while it provides a desirable thermal comfort condition within the room, it may hinder to some extent delivery of the fresh air to the occupied zone due to creation of counterflow fields. Furthermore, it is shown that although increasing the fan speed (ON mode) would slightly enhance the air change efficiency, the OFF mode yields not only a better distribution of the fresh air but also a higher ventilation efficiency than when fan coil operates.
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•Introduced vortex structure to deconstruct the airflow in the cabin.•Investigated the “lock” phenomenon for contaminants released in the vorticity.•Analyzed effects of thermal buoyancy on the ...contaminant longitudinal transmission.
Airborne contaminants such as pathogens, odors and CO2 released from an individual passenger could spread via air flow in an aircraft cabin and make other passengers unhealthy and uncomfortable. In this study, we introduced the airflow vortex structure to analyze how airflow patterns affected contaminant transport in an aircraft cabin. Experimental data regarding airflow patterns were used to validate a computational fluid dynamics (CFD) model. Using the validated CFD model, we investigated the effects of the airflow vortex structure on contaminant transmission based on quantitative analysis. It was found that the contaminant source located in a vorticity-dominated region was more likely to be “locked” in the vortex, resulting in higher 62% higher average concentration and 14% longer residual time than that when the source was on a deformation dominated location. The contaminant concentrations also differed between the front and rear parts of the cabin because of different airflow structures. Contaminant released close to the heated manikin face was likely to be transported backward according to its distribution mean position. Based on these results, the air flow patterns inside aircraft cabins can potentially be improved to better control the spread of airborne contaminant.
•A scale experimental model with hybrid ventilation was created.•Hybrid ventilation efficiencies with different mechanical exhaust velocities were analyzed.•A critical mechanical exhaust velocity in ...the hybrid ventilation was identified.•Ventilation efficiency and ventilation strategy of different modes of hybrid ventilation were investigated.
Hybrid ventilation is an effective means of minimizing ventilation energy and improving indoor environment. A scale experimental model with a heat source was created for hybrid buoyancy-driven natural ventilation with a mechanical exhaust system. The aim of this study is to examine the performance of hybrid ventilation in an industrial building. The temperature distributions and hybrid ventilation efficiencies with different mechanical exhaust velocities were analyzed. Results showed that the hybrid ventilation efficiency first increased and then decreased with the mechanical exhaust velocity. A critical mechanical exhaust velocity was identified and the hybrid ventilation efficiency reached maximum at the critical mechanical exhaust velocity. The critical mechanical exhaust velocity was 1.4 m/s at the heat flux of the heat source q = 200 W and 1.0 m/s at q = 500 W, and the corresponding ventilation efficiencies were 24.4 and 6.69, respectively. Four modes of hybrid ventilation were investigated, and ventilation strategies of different modes of hybrid ventilation were given. An excessive mechanical ventilation rate will cause consumption of ventilation energy to increase and may lead to short circuiting of airflow and a bad thermal environment. These results should prove helpful in designing of hybrid ventilation systems for industrial buildings.
In Compost-Bedded Pack Barn (CBP) systems, air velocity is linked with the thermal comfort of housed dairy cattle and bedding quality and, therefore, assessing ventilation efficiency is essential. In ...this context, the objective of this study was to evaluate and characterize dependence and spatial distribution of air velocity at the 1.5 m height (vair,M) and at bedding level (vair,B) in an open CBP system with positive pressure ventilation. The study was conducted in 2021, in a facility located in the Zona da Mata region, Minas Gerais, Brazil. The facility area was divided into a mesh composed of 55 equidistant points, where vair,M and vair,B data were collected in the morning (09:00 a.m.) and afternoon (03:00 p.m.) periods, during three weeks in Brazilian winter. Geostatistics techniques were used to assess dependence and spatial distribution. In both periods evaluated, there were a strong occurrence of spatial dependence and non-uniform vair,M and vair,B distributions. The vair,M and vair,B values were lower than recommended (1.8 m∙s-1) in more than 65.0% of the area. Adequate ventilation levels were observed only in the first 20.0 m of the facility, from Southeast to Northwest, because of the fan lines present.
To improve ventilation efficiency and reduce pollution concentration in urban spaces, eco-strategies, including greening, have been suggested. However, there is still very little evidence to assert ...the benefits of such greening options, particularly at urban street intersections. Therefore, in this work, air flow and pollutant dispersion within urban-like three-way, four-way, and roundabouts intersections are investigated with three simple and five combined greening layouts. Three-dimensional computational fluid dynamics (CFD) analysis using the Reynolds-averaged Navier–Stokes model was conducted considering multiple wind directions. The ventilation efficiency was evaluated using the ventilation indices purging flow rate (PFR) and net escape velocity (NEV). The investigation of simple greening layouts shows that shrubs alone may enhance increase ventilation (i.e., increase PFR and NEV), and trees could increase the pollutant concentration at the pedestrian level. A comparison of greening layouts combining trees and shrubs shows that the presence of greening reduces ventilation and worsens the pollution condition at street intersections, except for shrubs located in the central zone within roundabouts. Specifically, NEV decreases by 16%–43% at four-way and three-way intersections owing to the presence of greening. Greening layouts with two rows of trees located 2.2 m away from buildings show overall significant negative effects on ventilation, particularly for wind directions ϕ = 0°, 45°, and 90°. The impact of shrubs and trees on ventilation at the roundabout is less significant, with NEV varying by 4%–11%.
•Shrubs and trees with different greening layouts at urban street intersections were investigated.•The porous media model was verified using experimental data to be applied in the study.•The purging flow rate (PFR), net escape velocity (NEV), and normalized average concentration of CO were employed.•Greening reduced the ventilation at street intersections, except for shrubs located in the central zone within roundabouts.•Two-row trees away from buildings negatively affected ventilation, particularly in some wind directions.
Ventilation is of primary importance for the creation of healthy and comfortable indoor environments and it has a significant impact on the building energy heating and cooling demand. The aim of this ...study is to assess the application of time-periodic supply velocities to enhance mixing in mixing ventilation cases to reduce heating and cooling energy demands. This paper presents computational fluid dynamics (CFD) simulations of a generic mixing ventilation case, in which the time-averaged velocities and pollutant concentrations from a reference case with constant supply velocities were compared with those obtained from a case with time-periodic supply velocities (sine function). The unsteady Reynolds-averaged Navier-Stokes (URANS) CFD simulations indicate that the use of time-periodic supply velocities can reduce high pollutant concentrations in stagnant regions, reduces the overall time-averaged pollutant concentrations and increases contaminant removal effectiveness with about 20%. The influence of the period of the sine function was assessed and the results showed that for the periods tested, the differences are negligible. Finally, the URANS approach was compared with the large eddy simulations (LES) approach, indicating that URANS leads to very similar results (NMSE < 3.2%) as LES and can thus be regarded as a suitable approach for this study.
The aims of this study were to determine the concentrations of selected gaseous indoor air pollutants (CO2, VOC, NO2, SO2), evaluate the ventilation system efficiency, and identify the factors ...determining air quality in a typical Polish sports center. Measurements were conducted simultaneously inside and outside the building during the non-heating (05/18/2017–06/21/2017) and heating (10/16/2017–11/20/2017) seasons. CO2 concentrations were measured automatically (MultiRAE), while VOCs, NO2, and SO2 samples were collected by the passive method and determined using gas chromatography, spectrophotometry, and ion chromatography, respectively. The average concentrations of the tested pollutants, except for CO2 outside, were higher in the heating season. Average CO2 concentrations in both seasons were higher inside the building (761–815 ppm) than outside (521–525 ppm). The average VOC (129.4–193.3 μg/m3), NO2 (20.2–21.3 μg/m3), and SO2 (0.9–1.4 μg/m3) concentrations in both seasons were comparatively lower inside. CO2 concentrations were mainly related to physical activity and determined by the number of people exercising on a given day, while VOC, NO2, and SO2 concentrations were influenced mainly by outdoor sources (traffic emissions, combustion of fossil fuels). The presence of specific substances (e.g. propanol, ethanol derivatives) only in indoor air were influenced by specific indoor sources, such as cleaning activities, hall maintenance, and cosmetics. The results can be used to develop appropriate control strategies to improve indoor air quality in sports facilities and improve the safety of their users by minimize the adverse health effects due to exercise in conditions of poor air quality.
•One of the few studies in the world regarding air pollution in sports facilities.•Impact of low air exchange rate and human respiration on indoor CO2 concentrations.•Outdoor air as the main determinant of VOC, NO2, SO2 levels inside the sports hall.•The basis for the development of IAQ monitoring methodology in sports facilities.•Recommendations on how to improve IAQ and thus safety of sports facilities users.
Spaces with high occupancy density e.g.; classrooms, auditoriums and restaurants, provide challenges to ventilate at a lower energy use due to elevated temperatures. To meet occupants' thermal ...comfort requirements traditional systems use a lot of energy. Alternative ventilation strategies that optimize high air movements in the occupied zone allow human activities at elevated temperatures while attaining improve occupants' perception and acceptance of the indoor climate at a low energy use. This paper presents an experimental evaluation of a novel ventilation strategy for high occupancy spaces that provides fresh air and thermal comfort in the sitting zone through a controlled intermittent air jet system. The strategy uses ceiling mounted high momentum air jet diffusers (AJD) made from ventilation duct fitted with nozzles that generate confluent jets. The jets coalesce into a single two-dimensional jet which is directed downwards in the sitting zone. This paper presents an experimental evaluation/analysis of the proposed system with regard to ventilation efficiency and thermal comfort measurements in a classroom mockup. Results show that the system qualifies to be used as a primary ventilation system and has local air change index >1 inside the jet, and a ventilation efficiency >50%. The system also provides better thermal climate than mixing and displacement ventilation at elevated temperatures.
•Intermittent air jet strategy simulates some properties of natural wind: unsteady high-low velocity frequencies.•The measured PMV is close to neutral in both warm and neutral to slightly cool environments with a reduced draft risk.•The resulting ventilation has local air change index >1, air change rate of 3.74 h−1, and ventilation efficiency >50%.•The system provides an effective airflow rate of 8 l/s when it is set to operate with an intermittent airflow of 10 l/s.•The strategy has a high energy saving potential and qualifies to be used as a primary ventilation system.
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