Ventilation Airflow Rate Research Articles

Mesh Refinement for Dynamics Airflow in Health Care

This studyexplores using computational fluid dynamics(CFD) tooptimize ventilation in healthcare, with a focus on mesh refinement for accurate airflow analysis. The goal is to reduce airborne contaminant spread, which is crucial during COVID-19. Ventilation in healthcare ensures air quality and minimizes pathogen transmission. The research analyzer analyzes mesh element size's impact on airflow accuracy in simulated hospital wards with two coughing patients. The optimal mesh size is determined for reliable predictions. Mesh refinement enhances accuracy in critical zones. The k-epsilon turbulence model is chosen for low error. Experimental validation shows temperature discrepancies, likely due to simulated manikins lacking clothing insulation. Air velocity measurements show minor variations within an acceptable range. Further research on various ventilation configurations and airflow rates in real hospital conditions is crucial. Addressing these limitations optimizer optimizeshealthcare ventilation, enhancing safety and infection control.

Passive ventilation for building not subjected to solar radiation

Some small-height buildings are not exposed to direct solar radiation due to shading from neighboring buildings. Therefore, for these buildings to be ventilated naturally, it was necessary to develop a method using a thermal chimney. This is done by using hot water resulting from the solar heater at the top of the building to heat the base of the chimney instead of direct solar radiation. In this paper, the solar chimney system used to generate power, using some modifications, to be used in ventilation operations is investigated. The effect of different variables on the airflow rate inside the chimney ventilation air drawn was studied. From the experimental result, the ventilation air flow rate increase with the chimney height and diameter. Also, the increase of heated plate area and the heater capacity increases the ventilation air flow rate. Increasing the inlet air gap thickness decreases the ventilation air. For the divergent chimney, the ventilation air increases with the increase of the conical angle.

Експериментальні дослідження ефективності функціонування систем забезпечення мікроклімату від’ємного тиску в тваринницьких приміщеннях

The microclimate of livestock premises is determined by a set of physical, chemical and biological parameters inside the premises for keeping animals and is characterized by the following parameters: air temperature, internal surfaces of walls, ceilings, floors, windows, doors, and other internal structures; humidity of air, internal surfaces of walls, ceiling, floor, windows, doors, and other internal structures; the speed and direction of air flows in the locations of animals, manure, inflow and exhaust channels, windows and doors; the gas composition of the air - the concentration of carbon dioxide, ammonia, hydrogen sulfide, carbon monoxide; the presence of dust and microorganisms in the air; the intensity of natural and artificial lighting; optical radiation; the level of industrial noise, the degree of air ionization. The substantiation of the rational scheme of the negative pressure microclimate system in livestock premises on the basis of production surveys is the main goal of the conducted research. According to the results of the research, it was found that for the livestock room with the ventilation system of the ground channel, more fresh air is provided in the area where the animals are staying, in comparison with the ceiling ventilation system and the ventilation system through the wall channels. For the ground duct ventilation system and the wall duct ventilation system, the efficiency of contaminant removal was influenced by the ventilation rate, which is significantly dependent on the animal's age, weight, and outdoor temperature. For the ventilation system of the above-ground channel in production conditions, the efficiency of pollution removal decreased with an increase in the speed of the air flow in the ventilation. For the wall duct ventilation system, the efficiency of pollutant removal increased as the ventilation air flow rate increased, as the sampling point was located at the back of the room. In a room with a ceiling ventilation system, the efficiency of contaminant removal was significantly influenced by the lying behavior of animals, and a slight decrease in the efficiency of contaminant removal was observed with increasing ventilation.

Organization of natural ventilation of loose-housing barn

The article presents a method for determining the size of supply and exhaust openings to ensure effective aeration of the barn in calm weather. The results of multivariate calculations of ventilation air flow rates in two modes are given: with the organization of slot ventilation and full opening of the supply openings.

Actual energy performance and indoor climate in Finnish NZEB daycare and school buildings

The study addressed the improvement of building energy performance along with a good thermal comfort and indoor air quality (IAQ) in newly built Finnish daycare and school buildings. Indoor Environmental Quality (IEQ), calculated and actual energy performance, investment and life cycle cost (LCC) were monitored. Ventilation airflow rates, temperature, and CO2 were measured onsite in five daycare and school buildings during summer and winter, and an occupant questionnaire survey was conducted in parallel with onsite measurements. Energy performance was evaluated based on an energy performance certificate (EPC) and actual metered consumption to figure out possible performance gaps. Simulations were conducted to calibrate models and analyse improvements in ventilation system operation, which showed energy-saving potential while ensuring good thermal comfort and IAQ. The thermal comfort and IEQ of all buildings were excellent and were in line with the results of the questionaries survey except in ‘School 3’, which had specific odour and noise problems. The measured energy use of all buildings except ‘School 3’ was increased by a factor of 2.1–2.6 compared to the EPC value, caused by poor control of a ventilation system and the presence of some non-regulated uses such as hot kitchens, washing machines, and dryers. LCC considerably depended on actual energy use stressing the importance of accurate energy prediction. It was shown that the reduction of energy use by a factor of 1.9–3.1 is possible without compromising indoor climate by adjustment of correct operation hours, improving ventilation system control, and limiting excessive outdoor airflows in some cases.

Thermal—Airflow Coupling in Hourly Energy Simulation of a Building with Natural Stack Ventilation

Natural ventilation dominates in Polish residential buildings. It is a simple and low-cost system but its performance is affected by varying environmental conditions. Hence, setting up constant ventilation airflow results in errors when calculating heating and cooling energy. In this paper, an attempt to integrate the buoyancy effect in natural ventilation of a residential building at hourly resolution with the hourly simulation method of EN ISO 13790 to obtain energy use for space heating and cooling is presented. The ping-pong coupling algorithm was proposed and applied. Hourly variation of ventilation airflow rate was from −26.8 m3/h (flow from outdoor to the interior of the building) to 87.2 m3/h with 55 m3/h on average. The lack of a cooling system resulted in overheating during summer and indicated the necessity of its application or use of other techniques to reduce solar gains. Application of the cooling system resulted in an hourly ventilation rate from −38.0 m3/h to 87.2 m3/h. Detailed simulation in EnergyPlus and statistical analysis proved the applicability of the proposed method in stack-induced ventilation assessment. The coefficient of determination R2 = 0.936, mean squared error MAE = 5.72 m3/h and root mean square error RMSE = 7.86 m3/h.

Effect of ventilation mode and airflow rate on the flow field and particle mass concentration distribution of a high-speed rail carriage in the putty polishing workshop

Objectives. The putty polishing procedure usually produces a large number of micron-sized particles, which can lead to serious respiratory diseases as well as skin conditions. The diagonal ventilation system is widely used to decrease the particle concentration in different environments. However, it becomes less effective for a large empty factory workshop, such as the polishing workshop for high-speed rail carriages, in which the diagonal ventilation mode usually results in turbulence in the airflow. In this article we report that the situation can be improved by optimizing the number and locations of the air inlets and outlets in the carriage-polishing workshop. Three modified ventilation modes are proposed, whose efficiencies are evaluated by numerical simulations and compared to the diagonal mode. Results. The results show that the mode with two inlets close to the ceiling and two outlets close to the floor yields the best performance. Besides, the optimum airflow rate under this mode is further determined by both simulations and in-situ measurements. The results reported can serve as a reference for the design of the ventilation systems in the polishing workshops of similar sizes.

Size-resolved simulation of particulate matters and CO2 concentration in passenger vehicle cabins

The main aim of this study is to develop a mathematical size-dependent vehicle cabin model for particulate matter concentration including PM2.5 (particles of aerodynamic diameter less than 2.5 μm) and UFPs (ultrafine particles of aerodynamic diameter less than 100 nm), as well as CO2 concentration. The ventilation airflow rate and cabin volume parameters are defined from a previously developed vehicle model for climate system design. The model simulates different filter statuses, application of pre-ionization, different airflow rates and recirculation degrees. Both particle mass and count concentration within 10–2530 nm are simulated. Parameters in the model are defined from either available component test data (for example filter efficiencies) or assumptions from corresponding studies (for example particle infiltration and deposition rates). To validate the model, road measurements of particle and CO2 concentrations outside two vehicles were used as model inputs. The simulated inside PM2.5, UFP and CO2 concentration were compared with the inside measurements. Generally, the simulation agrees well with measured data (Person’s r 0.89–0.92), and the simulation of aged filter with ionization is showing higher deviation than others. The simulation using medium airflows agrees better than the simulation using other airflows, both lower and higher. The reason for this may be that the filter efficiency data used in the model were obtained at airflows close to the medium airflow. When all size bins are compared, the sizes of 100–300 nm were slightly overestimated. The results indicated that among others, expanded filter efficiency data as a function of filter ageing and airflow rate would possibly enhance the simulation accuracy. An initial application sample study on recirculation degrees presents the model’s possible application in developing advanced climate control strategies.

Numerical simulation of airflow in naturally ventilated attics for different attic geometries

AbstractAttic geometry and ventilation in a different attic geometry play a very important role in residential building energy performance. To evaluate the effect of ventilation ratio and vent balance on attic performance, a two‐dimensional finite volume model is employed to simulate the buoyancy‐driven turbulent ventilation and heat transfer in an attic space of different geometries like gable, gambrel, and saltbox roofs of residential buildings under winter conditions. The impact of ventilation ratio on ventilating airflow rate, heating load rate, and rate of heat gained is investigated for all three types of roof geometries. The model under consideration consists of a passive ventilation system with a ridge and soffit vent. Meshing is done by using ANSYS Workbench and numerical simulations are carried out by using ANSYS FLUENT 19 analysis software. The effect of passive ventilation on ridge‐vent attic performance is evaluated in this study. Ventilation ratios for soffit vents ranging from 1/400 to 1/25 are investigated. Convection boundary conditions are used for the attic walls to account for thermal resistances of ceilings and roofs. In addition, the performance of these vented attics is compared to the heat transfer in a sealed attic. The results show that the symmetrical airflow pattern exists in a vented attic, in contrast to the asymmetrical airflow patterns found in a sealed attic. From the study, it is evident that an increase in ventilation ratio reduces attic heating load irrespective of the increase in ventilation airflow rate. The rate of airflow increases with an increase in ventilation ratio in all three types of roof geometries that is gable, gambrel, and saltbox roofs. In the case of gable roof configuration, increasing the ventilation ratio from 1/200 to 1/100 results in an increase in ventilating mass flow of 75%, while an increase of ventilation ratio from 1/50 to 1/25 only increases the ventilating mass flow by 40%. In the case of gable roofs increasing ventilation ratio from 1/200 to 1/100 results in a 20% decrease in attic heating, whereas an increase in ventilation ratio from 1/50 to 1/25 results in a 10% decrease in attic heating.

Effect of environmental conditions on fire combustion regimes in mechanically-ventilated compartments

This publication deals with under-ventilated combustion regimes in case of pool fire in a confined- and mechanically-ventilated enclosure. The objective is to improve the understanding of combustion regimes in a ventilated compartment focusing on the effect of fire size and the ventilation rate. It is based on dodecane pool fire tests conducted on a reduced scale (1.875 m3) enclosure and considering two varying parameters, the pool diameter and the ventilation air flow rate prior to ignition. Three combustion regimes were identified: two steady burning regimes with extinction by lack of fuel or oxygen (fuel burnout) and a transient burning regime with extinction by lack of oxygen. A representation of these regimes is proposed with two scaling parameters: the reference global equivalence ratio, φo, and the volumetric fire heat release rate. Results demonstrate that increasing φo reduces the burning rate in comparison to its value in an open atmosphere. While for a low volumetric fire heat release rate (HRR), the reduction in burning rate is mainly due to oxygen depletion, gas temperature has an additional effect at higher volumetric HRR (about 16 kW/m3). The effect of gas temperature compensates for the effect of oxygen depletion and increases the burning rate. The conditions leading to the highest gas temperature inside the enclosure were obtained in fire scenarios with high volumetric fire HRR and moderate φo.

Room HVAC Influences on the Removal of Airborne Particulate Matter: Implications for School Reopening during the COVID-19 Pandemic

(1) Background: Many schools and higher education settings have confronted the issue of reopening their facilities after the COVID-19 pandemic. In response, several airflow strategies spanning from adding portable air purifiers to major mechanical overhauls have been suggested to equip classrooms with what is necessary to provide a safe and reliable environment. Yet, there are many unknowns about specific contributions of the building system and its design and performance on indoor air quality (IAQ) improvements. (2) Methods: this study examined the combined effect of ventilation type, airflow rates, and filtration on IAQ in five different classrooms. Experiments were conducted by releasing inert surrogate particles into the classrooms and measuring the concentrations in various locations of the room. (3) Results: we showed that while the distribution of particles in the space is a complex function of space geometry and air distribution configurations, the average decay rate of contaminants is proportional to the number of air changes per hour in the room. (4) Conclusions: rooms with a central HVAC system responded quicker to an internal source of contamination than rooms with only fan coil units. Furthermore, increasing the ventilation rate without improved filtration is an inefficient use of energy.

“Demand Control” an Innovative Way of Reducing the HVAC System’s Energy Consumption

According to EIA, the Heating Ventilation and Air Conditioning (HAVC) systems account for about 25% of the U.S.’s total commercial building’s energy use. Therefore, advanced modeling and optimization methods of the system components and operation offer great ways to reduce energy consumption in all types of buildings and mainly commercial buildings. This research introduced an innovative integrated two-level optimization technique for the HVAC system to reduce the total energy consumption while improving the indoor thermal comfort level. The process uses actual system performance data collected for the building automation systems (BAS) to create accurate component modeling and optimization process as the first level of optimization (MLO). Artificial neural networks were chosen to be the tool used to serve the process of modeling. The second optimization level utilizes the whole system-level optimization technique (SLO) using a genetic algorithm (G.A.). The proposed two-levels optimization technique will optimize the system setpoints, the supply air temperature, duct static pressure, minimum zone air flowrates, and minimum outdoor air ventilation rate. The proposed technique has contributed to the field of modeling and optimization of HVAC systems through several new contributions. (1) Implementing the demand control methodology with the optimization process to modify the electricity consumption power profile when the demand signal is received. (2) Implement the occupancy schedule inputs into the optimization process to adjust the ventilation airflow rates accordingly. (3) Implement the real-time zone occupancy sensor readings and adjust the zone’s ventilation flowrates and minimum flowrates. (4) Lastly, implementing the method of zone minimum air flowrates setpoint rests to reduce reheat requirements. The proposed optimization process was tested and validated, resulting in savings in the total energy consumed by the chilled water VAV system by 13.4%, 22.4 %, followed by 31% for July, February, and October, respectively.

A review of airflow rate estimation techniques for natural ventilation in buildings

As natural ventilation involves local and global interactions, the estimation of these interactions can be performed by many approaches. Such approaches, rather more experimental and numerical than analytical, often require a great deal of instrumentation and equipment, which results in higher demands on project budget and funding. The present work is devoted to comprehending the natural ventilation concept, and to assess the existing experimental techniques already implemented for past researchers in the estimation of the ventilation airflow rate due to the wind and thermal buoyancy effects. A brief review of modeling techniques is also presented. This will provide a strong theoretical grasp of the natural ventilation process as part of the main elements in the thermal behavior of buildings. Ultimately, these bases are intended to help choose the most suitable techniques to estimate the natural ventilation airflow rate. The adequate benefit-to-budget technique appears to be the airtightness tests (blower door tests), since empirical Equations relating the airflow directly to the pressure difference in the building for both cases: infiltrations (openings closed) and openings opened, can be obtained. Also, the location of the leakages can be identified without complications, and this technique has the potential to estimate in situ the airflow capacity and friction characteristics of the openings.

Assessment age of air and thermal comfort in a classroom by adopting displacement ventilation with chilled ceiling system

This study aims to investigate the effect of the cooling load ratio covered by the chilled ceiling on the age of air and comfort level in a classroom in a hot and dry climate in Iraq-Hilla city. Air age, air exchange efficiency, and concentrations of pollutants in a classroom are investigated numerically by used AIRPAK software under displacement ventilation combined with a chilled ceiling system. Four cases are studied at different values of the cooling load covered by the chilled ceiling (0%, 25%, 50%, 80%) with respect to total classroom cooling load. Cooling load removes by chilled ceiling varied from (0 to 84.5 W/m2) based on the classroom area, and its temperature varied between (17.5-22.5oC). The displacement ventilation airflow rate was kept at 0.3m3/s, and the air temperature supply varied between (19.5-24.5oC) depend on the amount of cooling load covered by displacement ventilation. The results showed that the mean local air age increasing with height. The room mean air age increase and air exchange efficiency reduce with increasing load portion, which treated by the chilled ceiling. Increasing the portion of the load treated by chilled ceiling tends to improve comfort levels.

Evaluating the cooling potential of a geothermal-assisted ventilation system for multi-family dwellings in the Scandinavian climate

In recent years, the increasing occurrence of heatwaves raises the cooling need of residential buildings in Scandinavian countries, which are traditionally not equipped with active cooling systems. Indoor overheating caused by such heatwaves leads to severe consequences for occupants, especially kids and seniors. Efficient and economical cooling solutions are urgently needed to cope with frequent heatwaves. The present study investigated the novel usage of the geothermal-assisted mechanical ventilation with heat recovery (GEO-MVHR) system for cooling purposes in typical Swedish multi-family dwellings. The cooling potential of the system and its contributions to thermal comfort were evaluated. Dynamic simulations were conducted to assess the system's cooling performance under two climate scenarios: the climate of 2018 representing an extreme year with excessively hot summer and the climate of a typical meteorological year. The GEO-MVHR system shows great potential in mitigating indoor overheating with improved thermal comfort. A ventilation airflow rate of 0.50–0.70 l/s/m2 is suggested for multi-family dwellings to maximize the cooling potential of the GEO-MVHR system. The indoor operative temperature could be reduced by up to 3 °C with the GEO-MVHR system operating for cooling. Modulating the supply air temperature of the GEO-MVHR system based on indoor thermal conditions is recommended, as it shows the advantage of avoiding unnecessary overcooling and energy saving.

Applicability of high-temperature cooling systems in different European countries from the view of the condensation risk

Due to the different approaches in determining the ventilation airflow rate per person for workspaces, where high-temperature air conditioning systems are used for air conditioning, problems with the condensation of water vapour on the cold surfaces of the system can occur. The article analyses the risk of condensation in various European cities using the available climatic data. Systems with cooling ceilings and cooling beams with a ventilation device operating in parallel are taken into account. Different ventilation airflow rates per person were analysed. On the example of a room equipped with high-temperature cooling, an energy simulation calculation is performed, which includes a ventilation and air-conditioning system with the possibility of capacity control. It is clear from the results that the condensation of water vapour can be prevented by technical measures at the cost of reducing the cooling capacity, which can affect the achievement of the thermal comfort of those present. In the end, suitable solutions are discussed, which should already be adopted at the time the device is designed so that the risk of condensation is not a major obstacle in the operation of these energy-efficient systems. An irreplaceable role in the operation of high-temperature cooling systems is played by a measurement and control system with a suitable algorithm to prevent condensation.

Estimation of energy-saving potential and indoor thermal comfort by the central control of the heating curve in old apartment buildings

In this research, an existing building calibrated simulation model from 1981 was built based on measured energy and indoor temperature data. The model was used to study the central control's energy-saving potential. With parametric simulations, DHW circulation internal heat gain and ventilation airflow rate was determined as 85% and 0.29 l/s/m², respectively. DHW circulation heat loss has been found almost as high as DHW use. Dropping the heating curve from 70/40 °C to 65/35 °C resulted in a saving of 0.6 kWh/m²a (0.8% of space heating energy) on the cost of thermal comfort as yearly hours of the mean air temperature below 21 °C rose from 2.7% to 9.0%. It was necessary to reduce the heating curve to 55/25 °C in a hypothetical scenario with fully open thermostats, indicating heat redistribution from warmer to colder rooms, leading to higher heating energy. The findings indicate no energy saving potential due to compromising thermal comfort even by 5 °C heating curve reduction. It was revealed that the building average indoor temperature is not a factor to estimate energy-saving potential because of too low temperature in the coldest apartments.

Modeling the Applicability of a Displacement Ventilation System

Due to its significant role in improving indoor air quality, displacement ventilation system is widely adopted in current literature. This paper proposes a displacement ventilation system for room conditions with ceilings that are relatively low, internal heat load could be high, walls could be sunlit, and occupants doing the low physical activity. These conditions are prevalent in the Philippines, being a tropical country. Input parameters to the design process such as heat load, the height of the ceiling, comfort, and indoor air quality requirements were generated, and the main output parameters are the stratification height and ventilation airflow rate. To demonstrate the proposed displacement ventilation system, four cases were generated. Results show that the ventilation airflow rates obtained from the four cases were greater than the minimum outdoor air requirements for health in conference rooms and large assembly areas which are 17.5 and 3.5 liters/sec*person respectively, for smoking and no smoking rooms.

Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings

A ventilated window system enhanced by phase change material (PCM) has been developed, and its energy-saving potential examined in previous works. In this paper, the ventilation control strategies are further developed, to improve the energy-saving potential of the PCM energy storage. The influence of ventilation airflow rate on the energy-saving potential of the PCM storage is firstly studied based on an EnergyPlus model of a sustainable low energy house located in New York. It shows that in summer, the optimized ventilation airflow rate is 300 m3/h. The energy-saving of utilizing a ventilated window with PCM energy storage is 10.1% compared to using a stand-alone ventilated window, and 12.0% compared to using a standard window. In winter, the optimized ventilation airflow rate is 102 m3/h. The energy-saving of utilizing a ventilated window with PCM energy storage is 26.6% compared to using a stand-alone ventilated window, and 32.8% compared to using a standard window. Based on the optimized ventilation airflow rate, a demand control ventilation strategy, which personalizes the air supply and heat pump setting based on the demand of each room, is proposed and its energy-saving potential examined. The results show that the energy savings of using demand control compared to a constant ventilation airflow rate in the house is 14.7% in summer and 30.4% in winter.

Experimental Study on Energy Efficiency of Multi-Functional BIPV Glazed Façade Structure during Heating Season

Building integrated photovoltaics (BIPV) is technology that can significantly increase the share of renewable energy in final energy supply and are one of essential technologies for the nearly zero-energy buildings (nZEB), new build and refurbished. In the article (a) an experimental semitransparent BIPV glazed façade structure with 60% of PV cell coverage is shown; (b) energy efficiency indicators were developed based on identified impact parameters using experimental data; and (c) multi-parametric models of electricity generation, preheating of air for space ventilation, and dynamic thermal insulation features that enable prediction of solar energy utilization in different climate conditions are shown. The modeled efficiency of electricity production of BIPV was in the range between 8% and 9.5% at daily solar radiation above 1500 Wh/day, while low impact of outdoor air temperature and ventilation air flow rate on PV cell cooling was noticed. Between 35% and 75% of daily solar radiation can be utilized by preheating the air for space ventilation, and 4.5% to 7.5% of daily solar radiation can be utilized in the form of heat gains through opaque envelope walls.