Air Exchange Effectiveness Research Articles

An Analysis of the Ventilation Efficiency of Various Configurations of Inlet and Outlet Vents in a Residential Building by CFD Simulation

Residential buildings in South Korea have equipped an energy recovery ventilation (ERV) system to improve energy efficiency as well as dilute indoor air pollution. While most studies have focused on the efficiency of energy exchange or the ventilation performance of the ERV itself, the ventilation performance can be improved by the proper location of inlet and outlet vents. For the present study, the ventilation performance of the inlet and outlet vents of the ERV was investigated by using CFD simulation. By varying the locations of inlet and outlet vents, the airflow distributions and the age of air were assessed. In addition, the air exchange effectiveness was analyzed by using the mean age of air quantitatively. As a result, a higher age of air was observed when inlet vents were moved to the center of the plan along the wall and an additional inlet or outlet vent was installed in the kitchen. In addition, the highest air exchange effectiveness was obtained when the inlet vents were located in the center of the plan along the wall. Considering the economic perspective, it is recommended to locate the inlet vents in the center to at least improve the ventilation performance.

Strategic ventilation design for reducing airborne infection transmission in a two-story building: A numerical approach

This study employs Computational Fluid Dynamics (CFD) to assess the impact of various ventilation configurations on respiratory droplet dispersion in a two-story restaurant building, aiming to reduce airborne infection transmission. A total of 24 scenarios, involving three ventilation configurations and eight individuals as potential droplet sources, are studied. The configurations—Case A, Case B, and Case C—are analyzed for their effectiveness in controlling droplet dispersion and improving air exchange effectiveness (AEE). Case B, with an outlet near occupants and an inlet above the zone separation, proved most effective in minimizing the droplet transmission between floors, reducing suspended airborne droplets on each floor, and preventing surface contamination, thereby enhancing indoor air quality. Despite the positioning inlet and outlet vents near crowded areas, Case A falls short in effectively removing droplets due to the intricate airflow patterns caused by air diffusers. Case C showed larger AEE but was less effective in droplet dispersion control, indicating a crucial balance between optimizing air circulation and limiting pathogen dispersion is needed. The findings underscore the importance of strategic ventilation design in mitigating airborne infection transmission in multi-level buildings. An optimal configuration, as demonstrated by Case B, combines efficient air distribution with strategic placement of ventilation components to create barriers against interzonal droplet transmission. This study highlights the potential of targeted ventilation strategies to significantly reduce the risk of airborne infection in enclosed, populated spaces.

Numerical-experimental investigation of a wind tower-room sustainable system: A parametric analysis of the mixed convection with humidification

The wind tower is a sustainable architectural solution designed to improve natural ventilation and thermal comfort in buildings while reducing energy consumption. This study examines thermal comfort, natural ventilation, and heat transfer in a wind tower-room system with air humidification, such that the interaction of mixed convection with these parameters can be linked. The performance of the system is evaluated considering both natural and forced convection, influenced by differential heating and air inlet through the tower, respectively. A parametric analysis explores various parameters like outside air temperature, humidity, and velocity, along with room wall temperatures. Reynolds and Grashof numbers range from 8.57 × 103-1.99 × 105 and 2.20 × 109-1.31 × 1010, respectively. Simulations are validated against experimental data, with deviations under 5.0 %, 10.0 %, and 19.6 % for dry-bulb temperature, wet-bulb temperature, and air velocity. The system shows improved heat extraction efficiency under dominant forced convection conditions. Humidification yields PPD values between 10.0 % and 46.0 % and PMV values below 0 at air temperatures range 25.0–30.0 °C. At air temperatures of 35.0 °C with air humidity below 40.0 %, PPD values remain below 20.0 %. However, above 40 % humidity, humidification is less effective. The air exchange effectiveness reduction due to humidification is minimal at 0.61 %. These results illustrate the combination of parameters necessary for the optimal performance of the tower-room system, this study provides a valuable guide for integrating wind towers with humidification systems in building design and contributing to reduced electricity use and CO2 emissions.

Research on Relative Humidity and Energy Savings for Air-Conditioned Spaces without Humidity Control When Adopting Air-to-Air Total Heat Exchangers in Winter

In view of the problem that the exchange effectiveness is calculated according to a fixed value or only considering the influence of outdoor air parameters when analyzing the suitability of total heat recovery for plate heat recovery equipment in air-conditioned spaces without humidity control, the indoor humidity calculation model and moisture balance equation were established in this research to predict relative indoor humidity. Moreover, the relationship between total heat recovery, effective heat recovery, and the reduction in outdoor air heating load was analyzed using a psychrometric chart of the outdoor air treatment process. Referring to the standard for weather data of building energy efficiency in the Ningbo region, 6 typical days were taken as the calculation conditions. The moisture balance differential equation was solved using MATLAB software to obtain numerical solutions for the hourly indoor air humidity ratio, relative humidity, exchange effectiveness, and effective heat recovery when adopting an air-to-air total heat exchanger in an air-conditioned room of an office, classroom, or commercial building in the winter. The results indicate that, under the calculation conditions, the relative indoor humidity of commercial buildings is relatively high, making it unsuitable for a total heat exchanger. The relative humidity of indoor air in offices and classrooms can be maintained above 30%, and the total exchange effectiveness of a total heat exchanger is between 45% and 100%. The effective total heat recovery was calculated as sensible heat recovery under most calculation conditions.

Numerical-experimental study of mixed convection in a wind tower-room system

Passive strategies are employed in buildings to minimize their total energy consumption and emissions of CO2. The wind tower (windcatcher) is a traditional natural ventilation device capable of reducing building energy consumption and improving the indoor environment. In this work, the performance of the mixed convection in a wind tower-room system is studied, considering natural convection by differential heating in the room and forced convection by the wind entering the tower. A parametric analysis has been carried out considering different values of velocities, temperatures, and relative humidity of the air. Different room wall temperatures were also considered. Ri number studied in this work was in the range of 6.6 × 10−2 and 1.5 × 102. An experimental study was also carried out to validate the numerical results. Comparison numerical-experimental results indicate a mean bias error of 0.49 °C for temperature and a percentage deviation of 24.4% for air velocity. The results showed that the wind tower achieves sensation-neutral comfort inside the room when outside temperatures are between 25 and 30 °C. Regarding Ri numbers lower than 1, the air exchange effectiveness is partially constant, while it can vary by 31% for Ri values greater than 1. The results also indicated that for Ri numbers lower than 1, the heat transfer is 71% greater than for Ri values greater than 1. The findings provided in this paper could contribute to a better understanding of the performance of mixed convection in rooms of buildings with a wind tower.

Impact of impinging jet ventilation on thermal comfort and indoor air quality in office buildings

This paper is dedicated to research of impinging jet (IJV) air distribution method. This system provides the desired indoor climate in office buildings. This paper describes the experimental requirements and boundary conditions for the CFD simulation and experiment in the climate chamber. The necessary modelling scenarios were developed to review the operation of the ventilation system according to different climatic conditions (winter, summer), human positions in the room and the shape of the supply duct. It is concluded that the shape of the air opening has little effect on the contaminant and heat removal effectiveness, 114%–122% and 1.12–1.16 respectively. At the same time, there is a large impact on the air exchange effectiveness (0.74–0.91). It was experimentally noted that in terms of contaminant removal and air exchange effectiveness, the circular opening provides better results. The human position depends on the supply temperature and flow velocity. By analyzing different scenarios, it was determined that the minimum acceptable distance to maintain thermal comfort within the standard requirements from the supply outlet is 1.7 m. As the distance from the air opening increases, the vertical air temperature difference at the height of 0.1–1.1 m decreases more than 2 times – from 1.9 K/m to 0.7 K/m. It is concluded that impinging jet ventilation has a great potential for use in office spaces both in winter and summer scenarios. This system significantly improves thermal comfort and indoor air quality. Applying impinging jet ventilation (IJV), limitations and peculiarities of the system such as supply air velocity, temperature and shape of the air duct must be carefully evaluated.

Experimental Investigation of the Air Exchange Effectiveness of Push-Pull Ventilation Devices

The increasing installation numbers of ventilation units in residential buildings are driven by legal objectives to improve their energy efficiency. The dimensioning of a ventilation system for nearly zero energy buildings is usually based on the air flow rate desired by the clients or requested by technical regulations. However, this does not necessarily lead to a system actually able to renew the air volume of the living space effectively. In recent years decentralised systems with an alternating operation mode and fairly good energy efficiencies entered the market and following question was raised: “Does this operation mode allow an efficient air renewal?” This question can be answered experimentally by performing a tracer gas analysis. In the presented study, a total of 15 preliminary tests are carried out in a climatic chamber representing a single room equipped with two push-pull devices. The tests include summer, winter and isothermal supply air conditions since this parameter variation is missing till now for push-pull devices. Further investigations are dedicated to the effect of thermal convection due to human heat dissipation on the room air flow. In dependence on these boundary conditions, the determined air exchange efficiency varies, lagging behind the expected range 0.5 < εa < 1 in almost all cases, indicating insufficient air exchange including short-circuiting. Local air exchange values suggest inhomogeneous air renewal depending on the distance to the indoor apertures as well as the temperature gradients between in- and outdoor. The tested measurement set-up is applicable for field measurements.

Numerical study on the ventilation performance of a livestock house built in porous panels in Cold Regions

This paper presents a numerical prediction on the assessment of natural ventilation on a livestock house built in porous panels, aided by Computational Fluid Dynamics techniques. A typical climatic environment in Cold Regions was taken into consideration. The ventilation performances have been assessed by the distribution of indoor air velocity, turbulence intensity and local mean age of air through the cases: the house without porous panels, with wind erosion porous panels, and with snow erosion porous panels. The study has found that the porous panels improve the indoor environment in term of the reduction of air velocity and turbulence, and the wind erosion panel performs better than the snow erosion panel. However, applying porous panels may have negative effects on air exchange effectiveness. The presented numerical model is easy to be constructed, flexible to investigate different case scenarios, and quick and cheap to get solutions.

Experimental Investigation of the Ventilation Performance of Different Air Distribution Systems in an Office Environment—Cooling Mode

The performance of a newly designed corner impinging jet air distribution method with an equilateral triangle cross section was evaluated experimentally and compared to that of two more traditional methods (mixing and displacement ventilation). At nine evenly chosen positions with four standard vertical points, air velocity, turbulence intensity, temperature, and tracer gas decay measurements were conducted for all systems. The results show that the new method behaves as a displacement ventilation system, with high air change effectiveness and stratified flow pattern and temperature field. Both local air change effectiveness and air exchange effectiveness of the corner impinging jet showed high quality and promising results, which is a good indicator of ventilation effectiveness. The results also indicate that there is a possibility to slightly lower the airflow rates for the new air distribution system, while still meeting the requirements for thermal comfort and indoor air quality, thereby reducing fan energy usage. The draught rate was also lower for corner impinging jet compared to the other tested air distribution methods. The findings of this research show that the corner impinging jet method can be used for office ventilation.

Using CFD simulations to develop an upward airflow displacement ventilation system for manure-belt layer houses to improve the indoor environment

Heat stress and disease outbreak result in significant losses in large-scale egg productions. New ventilation systems are needed for large-scale layer production facilities to provide safe and uniform indoor environment, especially in the changing climate of global warming. This study developed a new ventilation system, upward airflow displacement ventilation (UADV) system, which allows fresh air to enter a layer house through air ducts located at the bottom of the cages, move upward by thermal buoyancy caused by hens and static pressure differences caused by exhaust fans, and ultimately exit the house through the fans installed on the roof. The performance of the UADV system was evaluated in comparison with a typical tunnel ventilation (TV) system in terms of air-exchange effectiveness, thermal environment, and airborne pathogen dispersal in both summer and winter using a validated Computational Fluid Dynamics (CFD) model. The results showed that the UADV system resulted in 46%–129% greater air-exchange effectiveness within the cages and provided a more homogeneous thermal environment with 9.4% less heat stress in summer and 68% less cold stress in winter compared with the TV system. In addition, transport of pathogens was largely inhibited in the UADV system compared with the TV system due to upward airflow and minimum air mixing across the cages. When coupled with sensible cooling of supply air, UADV system can further improve the thermal environment with a much lower ventilation rate under extremely hot and humid weather conditions. However, higher ventilation rates were more effective for reducing potential pathogen dispersal.

CFD Methodology Development for Singapore Green Mark Building Application

In the recent decade, investigation on the total building performance has become increasingly important for the environmental modelling community. With the advance of integrated design and modelling tool and Building Information Modelling (BIM) development, it is now possible to simulate and predict the building energy efficiency, air quality & health assessment, risk analysis& mitigation scenario for our urban planning analysis; all seamlessly in a single urban digital platform. In order to achieve the national goal of at least 80% of the buildings in Singapore to be green by 2030, Singapore Government has introduced the new BCA Green Mark 2015 scheme for accelerating the green building agenda. During the recent third Green Building Masterplan announced in 2015, it was decided to engage building tenants and occupants more actively to drive energy consumption behavioural change and to address the well-being of the people. Following up from this Masterplan, it is important for both the stakeholders and agency to jointly develop Performance Driven and Scientific Based Simulation Methodology and Evaluation Parameters as a frame work to evaluate the building design based on Singapore's hot and humid climate and densely-built-up urban areas for the Green Mark 2015 Scheme. In this paper, we will present the methodology and perform a baseline case study for the natural ventilation performance with the typical Non-Residential Building (NRB) industrial building. This can be resulted in the comprehensive CFD Quality Check List for the Environmental Sustainable Design (ESD) consultant in order to maintain modelling result accuracy. Demonstration on Indoor Air Quality (IAQ) using Air Exchange Effectiveness (AEE) as performance indicator will also be illustrated.

The feasibility of performing high-temperature radiant cooling in tropical buildings when coupled with a decentralized ventilation system

In Singapore's hot and humid environment, air conditioning has moved from being perceived as comfort to now being a necessity. Buildings usually employ large energy-consuming air systems to condition interior spaces. The use of water-based high-temperature cooling concepts is hard to find due to fears of condensation. The objective of this research is to enunciate the decentralized approach adopted in performing space cooling and dehumidification. The experiment aims at understanding the practicability of using radiant panels with high-temperature chilled water for accomplishing sensible cooling coupled with an independent ventilation system for achieving latent dehumidification. The dew point temperature of air surrounding the radiant panels is monitored to check for condensation. The decentralized ventilation system tested was effective in reducing absolute humidity in air from 22.3 g/kg in outside air to 12.8 g/kg at the under-floor air distribution system's diffuser outlet. The associated dew point temperature and dry bulb temperature measured at the diffuser outlet was 13.9°C and 19.9°C (57°F and 67.8°F), respectively. The measured dew point temperature of air surrounding the radiant panels was 18.3°C (64.9°F), which demostrates the viability of operating radiant panels using high-temperature chilled water to achieve sensible cooling. The air exchange effectiveness of the system running at low supply air velocity was determined to be 1.12, which demonstrates a displacement ventilation system. The air change rates measured per hour using tracer gas techniques ranged between 0.9–2.2 when the supply fan speed was varied between 4000–8000 rpm. The amount of outdoor air thus supplied to the designed space ranged between 0.9–2.1 L/s-m2 (assuming the system ventilation efficiency as 1). These values are above 0.7 L/s-m2, which is the minimum requirement for ventilating office spaces according to Singapore standards.

The Effect of Ventilation Rate and Filter Performance on Indoor Particle Concentration and Fan Power Consumption in a Residential Housing Unit

This paper reports a study of the effect of ventilation rate and filters performance on indoor particle concentration and fan power consumption in a residential housing unit with a mechanical ventilation system. Through an adapted mass-balance model, indoor particle concentrations were calculated for various ventilation rates, filter performances and room sizes. Additionally, the influence of air-exchange effectiveness and cross-contamination around the exterior air vent on the indoor particle concentration was considered. Recirculation of indoor air was not considered. From the results, filters for which the performance was lower than MERV07 were found to be insufficient for reducing indoor particle concentrations below the levels obtained under no ventilation. A higher ventilation rate was needed for the given amount of indoor particle sources for a smaller size residential housing unit in comparison to the larger units. The minimum ventilation rate was less sensitive to variations in the air-exchange effectiveness inside the residential housing unit and the cross-contamination index around the exterior air vents. To satisfy the ventilation requirement for gaseous pollutants and keep the particle concentrations below those under no ventilation, a filter with a performance that would exceed MERV11 should be used when the size of the residential housing unit is in the range of 150—300 m3.

The Impact of Air Exchange Effectiveness on Thermal Comfort in an Air-Conditioned Office

Problem statement: Impact of air exchange effectiveness on thermal comfort has not been investigated and, therefore, not well understood .Therefore, the influence of air exchange effectiveness on thermal comfort is investigated in this study. Approach: The main objective of this research is to investigate the thermal comfort level of an air-conditioned office room under 14 windows-door opening arrangements as a function of maximum, minimum and mean Air Exchange Effectiveness (AEE), as has not been inquired into already. The tracer gas decay method has been applied during the experimental procedures to estimate air exchange effectiveness, on the basis of room average and local mean age of air. Simultaneously, thermal comfort variables were measured and through these data, the thermal comforts Fanger's indices (PMV and PPD) were calculated. Staff answered a survey on their sensation of the indoor climate. Results: Results of 60 survey responses to thermal comfort questions in office and indoor air quality are presented. This study has shown that there are relationship between AEE and thermal comfort and three linear regression equations of PMV versus AEE can be derived for this air-conditioned office. Conclusion: Studies on the effect of air exchange effectiveness on thermal comfort in an office have shown that Thermal comfort is influenced by AEE, which go beyond the six factors which have been taken into account in PMV modeling.

Effective Ventilation Parameters and Thermal Comfort Study of Air-conditioned Offices

The study presents objective and subjective studies of thermal comfort levels and ventilation characteristics of two air-conditioned postgraduate study offices. The observations were performed at the offices of Department of Electrical and Electronic Engineering, in University Putra Malaysia. Thermal comfort variables were measured while the students answered a survey on their sensation of the indoor climate. Concurrently, tracer gas analysis, based on concentration decay method, is employed to determine air exchange rate, age of air and air exchange effectiveness. During the air conditioner is working, the study offices had not conditions within the comfort zone, of ASHRAE standard 55 causing occupants to report cold thermal sensations and the objective data analysis showed that the offices were uncomfortable. The thermal neutralities were significantly higher that proposed by ASHRAE Standard 55:1992. The monitored air exchange rates are indicated that the provisions of outside air for ventilation based on design occupancy are adequate for these two study offices. In addition, questionnaires were completed by the students in order to provide a subjective assessment of thermal comfort and indoor air quality. Finally, the outcomes of over 30 surveys for each office responses to the thermal comfort questions are presented and discussed.

Effective Ventilation Parameters and Thermal Comfort Study of Air-conditioned Offices

The study presents objective and subjective studies of thermal comfort levels and ventilation characteristics of two air-conditioned postgraduate study offices. The observations were performed at the offices of Department of Electrical and Electronic Engineering, in University Putra Malaysia. Thermal comfort variables were measured while the students answered a survey on their sensation of the indoor climate. Concurrently, tracer gas analysis, based on concentration decay method, is employed to determine air exchange rate, age of air and air exchange effectiveness. During the air conditioner is working, the study offices had not conditions within the comfort zone, of ASHRAE standard 55 causing occupants to report cold thermal sensations and the objective data analysis showed that the offices were uncomfortable. The thermal neutralities were significantly higher that proposed by ASHRAE Standard 55:1992. The monitored air exchange rates are indicated that the provisions of outside air for ventilation based on design occupancy are adequate for these two study offices. In addition, questionnaires were completed by the students in order to provide a subjective assessment of thermal comfort and indoor air quality. Finally, the outcomes of over 30 surveys for each office responses to the thermal comfort questions are presented and discussed.

Ventilation Parameters and Thermal Comfort of Naturally and Mechanically Ventilated Offices

This paper discusses thermal comfort for a postgraduate study office room in the Mechanical Engineering Department of University Putra Malaysia (UPM), which maybe either naturally ventilated or air-conditioned. Thermal comfort variables were assessed by survey of sensation of the indoor climate. Tracer gas analysis, based on the concentration decay method, was employed to determine air exchange rate, age of air, and air exchange effectiveness (AEE). When the air conditioner was working the study office had conditions within the comfort zone of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 55; and the occupants reported they were ``slightly cool.'' Objective data analysis showed that the office was thermally comfortable. Under naturally ventilated conditions objective results showed that the office was uncomfortable but a subjective study revealed that students found the conditions to be ``slightly warm.'' The neutral temperature showed a wider thermal comfort range for Malaysian students than that suggested by ASHRAE Standard 55-1992, which indicates that Malaysians are acclimatized to higher environmental temperatures. However, the result is in line with the current version of ASHRAE Standard 55-2004 that includes an adaptive comfort standard that allows warmer indoor temperatures for warmer climate zones. The results of a ventilation study indicated air flow patterns in the occupied zones, which approximated to ``perfect mixing'' under both ventilation conditions. The measured air exchange rate also indicated that the provision of outside air for ventilation was adequate when the room was mechanically ventilated (air-conditioned). Results of over 50 survey responses to thermal comfort questions in the study room at UPM are given.

Influences of Air Exchange Effectiveness and its Rate on Thermal Comfort: Naturally Ventilated Office

This article presents the effects of air exchange rate (ACH) and air exchange effectiveness (AEE) on thermal comfort level of a naturally ventilated office room. The study was conducted in an office at UPM, Malaysia. Influence of ACH and AEE on thermal comfort has not been investigated and is, therefore, not well understood. The main objective of this research is to investigate and assess these influences through the variable windows-door opening arrangements. To determine the windows-door opening performance in terms of ventilation air flow rate, 14 opening configurations have been considered. Thermal comfort variables were measured at the same time when ACH and AEE were evaluated. Through these data, the thermal comfort Fanger's indices (Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD)), ACH and AEE were calculated. These results showed that for a naturally ventilated office room three linear regression equations of PMV versus ACH and three linear regression equations of PMV versus AEE can be derived.

Investigation of air quality, comfort parameters and effectiveness for two floor-level air supply systems in classrooms

The method of distributing the outdoor air in classrooms has a major impact on indoor air quality and thermal comfort of pupils. In a previous study, ( [11] Karimipanah T, Sandberg M, Awbi HB. A comparative study of different air distribution systems in a classroom. In: Proceedings of Roomvent 2000, vol. II, Reading, UK, 2000. p. 1013–18; [13] Karimipanah T, Sandberg M, Awbi HB, Blomqvist C. Effectiveness of confluent jets ventilation system for classrooms. In: Idoor Air 2005, Beijing, China, 2005 (to be presented).) presented results for four and two types of air distribution systems tested in a purpose built classroom with simulated occupancy as well as computational fluid dynamics (CFD) modelling. In this paper, the same experimental setup has been used to investigate the indoor environment in the classroom using confluent jet ventilation, see also ( [12] Cho YJ, Awbi HB, Karimipanah T. The characteristics of wall confluent jets for ventilated enclosures. In: Proceedings of Roomvent 2004, Coimbra, Portugal, 2004.) Measurements of air speed, air temperature and tracer gas concentrations have been carried out for different thermal conditions. In addition, 56 cases of CFD simulations have been carried to provide additional information on the indoor air quality and comfort conditions throughout the classroom, such as ventilation effectiveness, air exchange effectiveness, effect of flow rate, effect of radiation, effect of supply temperature, etc., and these are compared with measured data.

Indoor air quality and energy issues of refrigerant modulating air-conditioning systems in the tropics

The concept of refrigerant modulating air-conditioning systems for medium sized office buildings is increasingly becoming popular owing to their simplicity in installation and maintenance as well as the potential to conserve energy. However, it is important to evaluate the issues of ventilation and indoor air quality (IAQ) associated with such systems. In this paper, the results of an integrated IAQ-energy audit of two buildings in Singapore, employing the refrigerant modulating air-conditioning systems are presented and compared with those from conventional central air-conditioning systems. Two different designs of providing the outside air to the occupied zones are considered and it is observed that the design involving a direct connection of the outside air duct to the fan coil units is better than the design that involves supplying the outside air directly into the occupied zones. Key performance parameters such as the ventilation index, air exchange effectiveness characteristics and the energy index of the refrigerant modulating air-conditioning system are comparable to conventional central air-conditioning systems.