Air Change Effectiveness Research Articles

What is the effect of reducing the air change rate on the ventilation effectiveness in ultra-clean operating rooms?

The operating room (OR) department is one of the most energy-intensive departments of a hospital. The majority of ORs in the Netherlands have an air-handling installation with an ultra-clean ventilation system. However, not all surgeries require an ultra-clean OR. To determine the effect of reducing the air change rate on the ventilation effectivenessin ultra-clean ORs. Lower air volume ventilation effectiveness (VELv) of conventional ventilation (CV), controlled dilution ventilation (cDV), temperature-controlled airflow (TcAF) and unidirectional airflow (UDAF) systems were evaluated within a 4× 4m measuring grid of 1× 1m. The VELv was defined as the recovery degree (RD), cleanliness recovery rate (CRR) and air change effectiveness (ACE). The CV, cDVLv and TcAFLv ventilation systems showed a comparable mixing characterin all areas (A, B and AB) when reducing the air change rate to 20/h. Ventilation effectiveness decreased when the air change rate was reduced, with the exception of the ACE. At all points for the UDAF-2Lv and at the centre point (C3) of the TcAFLv, higher RD10Lv and CRRLv were measured when compared with the other examined ventilation systems. The ventilation effectiveness decreased when an ultra-clean OR with an ultra-clean ventilation air-supply system was switched to an air change rate of 20/h. Reducing the air change rate in the OR from an ultra-clean OR to a generic OR will reduce the recovery degree (RD10) by a factor of 10-100 and the local air change rate (CRR) by between 42% and 81%.

COVID-19 STANDARD OPERATING PROCEDURE ADVANCEMENT FOR OFFICE BUILDING USING INDOOR ENVIRONMENTAL QUALITY ELEMENTS

COVID-19 guideline is expected to be part of the 'new norms' for workplace. However, regarding COVID-19 Standard Operating Procedure (SOP) issued by Ministry of Health Malaysia, there is inadequate concentration on Indoor Environmental Quality (IEQ) parameters even it has been proven in various research that COVID-19 transmission spread actively in indoor environment and green elements could mitigate the virus transmission. Therefore, this study aims to enhance existing COVID-19 SOP by discovering sustainable COVID-19 framework for office building. Sets of questionnaires is distributed among employees at Menara Majlis Bandaraya Johor Bahru, Malaysia and analysed using Frequency Analysis and Cross Tabulation Analysis. Overall, result shows that EQ7 Air Change Effectiveness is the most important IEQ parameters that can be selected to improve the current COVID-19 SOP. This study is significant for building manager in workplace to enhance their current SOP by adding green elements which is IEQ parameters to reduce COVID-19 spread in workplace.

Experimental and numerical study of wind tower integrated with solar heating unit to meet thermal comfort in buildings during cold and sunny climate conditions

Natural ventilation techniques are increasingly being adopted in recent times due to the need to cut down on greenhouse gases emission and energy cost. A classic natural ventilation technique, the wind tower, may be utilised to minimize the load on typical HVAC systems. One of the major disadvantage limiting the deployment of wind tower is the additional heating load it demands on the HVAC system during the winter months. The work focusses on improving the year-round capability of a wind tower by attaching a solar heating unit (SHU) that would heat the incoming ambient air through a conjugate heat transfer system before being circulated into the space to be ventilated. For performance validation, the numerical technique was utilised initially, then an experimental setup was created based on the numerical results to validate for practical situations. Using the CFD simulation, ventilation performance of this tower system was evaluated in terms of mean age of air (MAA) and air change effectiveness (ACE). The commercial ANSYS Fluent was used to solve the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) turbulence model. The results showed that SHU has been able to heat up the incoming air of 18 °C by 5 °C–23 °C which is generally considered as a comfortable temperature range. According to the analyses of airflow rate at different incident angles through the four quadrants of tower, the maximum flow rate (0.45 m3/s) of air steam was observed at 45° incident angle. The ACE values in the inhabited space were typically near to 1.0, indicating that the ventilation air mixed up well in the ventilated zone. The wind tower performance was experimentaly investigated in terms of solar radiation variations, wind velocity variations, temperature variation in SHU and inside wind tower, and air change rate (ACR) on the experimental setup. Experimental study shows a variation of 2–4 °C in the indoor temperature and thereby ensuring optimal thermal comfort. The recommended wind speed for an effective mass flow rate is in the range of 3 m/s, and an average ACR of 25 per hour indicates that the air is being ventilated properly.

Effects of the height of supply outlet of façade-mounted hybrid downdraft evaporative cooler on the indoor air quality of an office building

The hybrid downdraft evaporative cooler (HDEC) conditions a building by cooling with humidification and hence, inappropriate location of its supply outlet on a building facade has a great impact on the indoor air quality (IAQ) which affect the health, concentration, and productivity of the occupants. This paper investigates the effect of the height of the HDEC supply outlet on the IAQ of an office building equipped with the HDEC system in Bayero University Kano. The building model was created using DesignBuilder software while DesignBuilder CFD was employed for the parametric simulation using air change effectiveness (ACE) as the performance criterion. The height of the HDEC supply outlet was varyfrom 0.1m to 2.4m step 0.1m above the floor level. The results show that higher values of ACE in the occupants’ breathing zone were obtained at lower heights of the HDEC supply outlets with the best ACE of 1.1588 obtained at 0.3m. This information could help engineers to optimally position the HDEC supply outlet on the façade of an office building or any other building with similar characteristics.

Ventilation indices for evaluation of airborne infection risk control performance of air distribution

Air distribution is an effective engineering measure to fight against respiratory infectious diseases like COVID-19. Ventilation indices are widely used to indicate the airborne infection risk of respiratory infectious diseases due to the practical convenience. This study investigates the relationships between the ventilation indices and airborne infection risk to suggest the proper ventilation indices for the evaluation of airborne infection risk control performance of air distribution. Besides the commonly used ventilation indices of the age of air (AoA), air change effectiveness (ACE), and contaminant removal effectiveness (CRE), this study introduces two ventilation indices, i.e., the air utilization effectiveness (AUE) and contaminant dispersion index (CDI). CFD simulations of a hospital ward and a classroom served by different air distributions, including mixing ventilation, displacement ventilation, stratum ventilation and downward ventilation, are validated to calculate the ventilation indices and airborne infection risk. A three-step correlation analysis based on Spearman's rank correlation coefficient, Pearson correlation coefficient, and goodness of fit and a min-max normalization-based error analysis are developed to qualitatively and quantitatively test the validity of ventilation indices respectively. The results recommend the integrated index of AUE and CDI to indicate the overall airborne infection risk, and CDI to indicate the local airborne infection risk respectively regardless of the effects of air distribution, supply airflow rate, infectivity intensity, room configuration and occupant distribution. This study contributes to airborne transmission control of infectious respiratory diseases with air distribution.

Minimizing the COVID-19 spread in hospitals through optimization of ventilation systems.

The rapid spread of SARS-CoV-2 virus has overwhelmed hospitals with patients in need of intensive care, which is often limited in capacity and is generally reserved for patients with critical conditions. This has led to higher chances of infection being spread to non-COVID-19 patients and healthcare workers and an overall increased probability of cross contamination. The effects of design parameters on the performance of ventilation systems to control the spread of airborne particles in intensive care units are studied numerically. Four different cases are considered, and the spread of particles is studied. Two new criteria for the ventilation system—viz., dimensionless timescale and extraction timescale—are introduced and their performances are compared. Furthermore, an optimization process is performed to understand the effects of design variables (inlet width, velocity, and temperature) on the thermal comfort conditions (predicted mean vote, percentage of people dissatisfied, and air change effectiveness) according to suggested standard values and the relations for calculating these parameters based on the design variables are proposed. Desirability functions that are comprised of all three thermal condition parameters are used to determine the range of variables that result in thermally comfortable conditions and a maximum desirability of 0.865 is obtained. The results show that a poorly designed ventilation system acts like a perfectly stirred reactor—which enormously increases the possibilities of contamination—and that when air is injected from the ceiling and extracted from behind the patient beds, the infection spread is least probable since the particles exit the room orders of magnitude faster.

Ventilation effectiveness of uniform and non-uniform perforated duct diffusers at office room

Half of the energy usages in buildings is due to HVAC systems, and the efficiency of the subsections plays an essential role in the evaluation of the total energy consumption. Previous works on ventilation systems using perforated duct diffusers (PDDs) were mainly concentrated on the calculation of the thermal comfort indices, while their energy consumption and ventilation effectiveness were omitted. In this paper, a mixed experimental-numerical method has been developed to evaluate the real efficiency of PDDs with different perforation patterns. So, an office room facility is used for the full-scale experiments and the validation of the numerical simulations. Incidentally, five RANS models have been benchmarked to highlight the most accurate numerical model for this specific application. As a result, a k-ε Realizable turbulence model with 4.3 million mesh elements has been preferred over the tested two-equation turbulence models to determine the diffuser parameters like age of air, terminal velocities, air-change effectiveness, and air exchange efficiency. Within this model, the required outdoor airflow for four types of PDDs has been calculated following the ASHRAE standard procedure. The discrepancy of the real efficiency and the calculated value for the nearest application in the standards shows that the performance of PDDs is underestimated, and they require lower airflow in reality. Later, it is shown that for the systems using PDDs, the required airflow and energy consumption decrease by up to 18.4%, and a more uniform air distribution is achieved using a non-uniform perforation pattern.

ASSESSMENT OF AIR CHANGE EFFECTIVENESS AND THERMAL COMFORT IN A NATURALLY VENTILATED KITCHEN WITH INSECT-PROOF SCREEN USING CFD

ABSTRACT Many dwellings in warm-humid climates attain a comfortable environment by natural ventilation. The opening of exterior windows for ventilation allows the entry of insects along with the breeze. As a remedy, occupants install insect-proof screens on windows resulting in reduced airflow into the interior. This study attempts to evaluate the air change effectiveness and thermal comfort in a residential kitchen with insect-proof screens. A kitchen with insect-proof screens on the windows is compared with a case without insect-proof screens. Numerical simulation was conducted using ANSYS Fluent 2019 R2. The insect-proof screen is modelled as a porous media. The air velocity and temperature measurements were validated by measurements in a real scenario. The presence of insect-proof screens reduced the air velocity inside the space by 82%. However, the airflow pattern in the case with screens was more uniformly distributed. The mean age of the air was considerably higher in the case with insect-proof screens, which in turn resulted in a reduced ACE. The presence of an insect-proof screen resulted in a Predicted Mean Vote (PMV) of 2.79 indicating a ‘hot’ sensation, whereas in the other case, the comfort vote is only 1.93 indicating a ‘warm’ sensation. The presence of insect-proof screens on windows reduced the air velocity and ventilation efficiency, contributing to increased thermal discomfort in the kitchen.

On the Ventilation Performance of Low Momentum Confluent Jets Supply Device in a Classroom

The performance of three different confluent jets ventilation (CJV) supply devices was evaluated in a classroom environment concerning thermal comfort, indoor air quality (IAQ) and energy efficiency. The CJV supply devices have the acronyms: high-momentum confluent jets (HMCJ), low-momentum confluent jets (LMCJ) and low-momentum confluent jets modified by varying airflow direction (LMCJ-M). A mixing ventilation (MV) slot jet (SJ) supply device was used as a benchmark. Comparisons were made with identical set-up conditions in five cases with different supply temperatures (TS) (16–18 °C), airflow rates (2.2–6.3 ACH) and heat loads (17–47 W/m2). Performances were evaluated based on DR (draft rating), PMV (predicted mean vote), ACE (air change effectiveness) and heat removal effectiveness (HRE). The results show that CJV had higher HRE and IAQ than MV and LMCJ/LMCJ-M had higher ACE than HMCJ. The main effects of lower Ts were higher velocities, DR (HMCJ particularly) and HRE in the occupied zone as well as lower temperatures and PMV-values. HMCJ and LMCJ produce MV conditions at lower airflow rates (<4.2 ACH) and non-uniform conditions at higher airflow rates. LMCJ-M had 7% higher HRE than the other CJV supply devices and produced non-uniform conditions at lower airflow rates (<3.3 ACH). The non-uniform conditions resulted in LMCJ-M having the highest energy efficiency of all devices.

Multi-indicator evaluation on ventilation effectiveness of three ventilation methods: An experimental study

Enhancing ventilation effectiveness can improve indoor air quality (IAQ). Both contaminant removal effectiveness (CRE) and air change effectiveness (ACE) are widely used to evaluate ventilation effectiveness. They reflect two different aspects of IAQ, and an analysis based exclusively on ACE or CRE has important limitations. Firstly, this study is to evaluate the overall IAQ integrating ACE and CRE by using multi-indicator methods. Secondly, this study is to find out an indicator to best characterize the overall IAQ. Twenty-four experiments with different combinations of three ventilation methods (i.e. mixing ventilation (MV), displacement ventilation (DV) and stratum ventilation (SV)), four air exchange rates and two point pollutant source locations are conducted in a simulated office. Three multi-indicator methods are applied and compared, including Z-score method, Rank Sum Ratio method, and Technique for order preference by similarity to an ideal solution (TOPSIS). The results show that, for ACE, in the occupied zone, DV performs best with the values of 0.76–0.84; in the breathing zone, SV performs best with the values of 1.21–1.35. For the overall IAQ, in the occupied zone, DV performs best (ranking in the top 4–33%), followed by SV (ranking in the top 38–92%), and then MV (ranking in the top 50–100%); in the breathing zone, SV performs best (ranking in the top 8–54%), followed by DV (ranking in the top 4–79%), and then MV (ranking in the top 58–100%). All the three evaluation methods indicate that CRE is more representative than ACE for measuring overall IAQ.

Experimental study on the performance evaluation of active chilled beams in heating and cooling operation under varied boundary conditions

This study investigates the thermal comfort, airspeed and temperature distribution, air change effectiveness and importance of the boundary conditions on the selection and performance of Active Chilled Beams (ACB). Many past studies in cooling confirm that the thermal comfort is satisfactory because the temperature gradient and airspeeds are acceptable at the occupant level without addressing the local discomfort. Similarly, no known study was found to address thermal comfort in heating. This paper reports the results of an experimental study that addresses such issues. A laboratory experiment, simulating a multi-occupant open office with an ACB subjected to different boundary conditions, was conducted. The heating test results demonstrate that there is a risk of discomfort due to radiant temperature asymmetry. It also shows no airspeed in the occupied zone, which reduces the air change effectiveness. The cooling test results demonstrate that discomfort draft risk at the ankle level is higher in ACB parallel to window configuration. The results suggest that shape and throw of ACB affect air distribution and emphasize the importance of properly selecting, orienting, and designing ACB, not just to offset the room loads, but to match the proportions and boundary conditions of the space.

Experimental Evaluation of the Ventilation Effectiveness of Corner Stratum Ventilation in an Office Environment

An experimental study was conducted in a room resembling an office in a laboratory environment. The study involved investigating the ability of corner-placed stratum ventilation in order to evaluate the ventilation’s effectiveness and local thermal comfort. At fixed positions, the air temperature, air velocity, turbulence intensity, and tracer gas decay measurements were carried out. The results show that corner-placed stratum ventilation behaves very similar to a mixing ventilation system when considering air change effectiveness. The performance of the system was better at lower supply air flow rates for heat removal effectiveness. For the heating cases, the draught rates were all very low, with the maximum measured value of 12%. However, for the cooling cases, the maximum draught rate was 20% and occurred at ankle level in the middle of the room.

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.

Comparing thermal comfort and air quality performance of two active chilled beam systems in an open-plan office

The traditional air distribution and supply devices in ventilated rooms are not always able to effectively remove excess heat from the space. Therefore, chilled beams, especially the active systems, are used to achieve the desired cooling demand. The focus of this paper was the potential benefit of a newly designed active chilled beam (ACB) system, to improve heat removal effectiveness local thermal condition and indoor air quality in the occupants’ breathing zone. The system based on 1-way flow design (1W-ACB) was installed in an open-plan office and its performance was studied by analysing the temperatures, velocities and tracer gas concentrations in predetermined risky zones. The system was compared against a traditional 4-way flow design (4W-ACB).The obtained results showed that heat removal effectiveness was slightly higher for the 1W-ACB system compared to the 4W-ACB system. The local thermal condition was very good close to the workstations when using 1W-ACB. The benefits of the new system were also shown in the occupied zone by analysing the mean age of air and air-change effectiveness (ACE) in the breathing level at the workstation locations. The 1W-ACB system provided air with lower mean age (fresher air), and therefore higher ACE, near the breathing zone at the workstations compared to the 4W-ACB. On the other hand, the 4W-ACB system had the advantage of providing high thermal and mean age of air uniformity throughout the room.

Application of Wind as a Renewable Energy Source for Passive Cooling through Windcatchers Integrated with Wing Walls

Generally, two-third of a building’s energy is consumed by heating, ventilation and air-conditioning systems. One green alternative for conventional air conditioner systems is the implementation of passive cooling. Wing walls and windcatchers are two prominent passive cooling techniques which use wind as a renewable resource for cooling. However, in low wind speed regions and climates, the utilization of natural ventilation systems is accompanied by serious uncertainties. The performance of ventilation systems can be potentially enhanced by integrating windcatchers with wing walls. Since previous studies have not considered this integration, in the first part of this research the effect of this integration on the ventilation performance was assessed and the optimum angle was revealed. However, there is still gap of this combination; thus, in the second part, the impact of wing wall length on the indoor air quality factors was evaluated. This research implemented a Computational Fluid Dynamics (CFD) method to address the gap. The CFD simulation was successfully validated with experimental data from wind tunnel tests related to the previous part. Ten different lengths from 10 cm to 100 cm were analyzed and it was found that the increase in wing wall length leads to a gradual reduction in ventilation performance. Hence, the length does not have a considerable influence on the indoor air quality factors. However, the best performance was seen in 10 cm, that could provide 0.8 m/s for supply air velocity, 790 L/s for air flow rate, 39.5 1/h for air change rate, 107 s for mean age of air and 92% for air change effectiveness.

Automated mobile sensing: Towards high-granularity agile indoor environmental quality monitoring

Indoor environmental quality (IEQ) is a critical aspect of the built environment to ensure occupant health, comfort, well-being and productivity. Existing IEQ monitoring approaches rely on sensor networks deployed at selected locations to collect environmental measurements, and are limited in scale and adaptability due to infrastructure cost and maintenance requirement. To enable high-granularity IEQ monitoring with agile adaption to the dynamic indoor environment, we propose an “automated mobile sensing” system that dispatches a sensor-rich navigation-capable robot to actively survey the indoor space. Data collected in this fashion is sparse in the joint temporal and spatial domain, and cannot be used directly for IEQ evaluation. To deal with this special characteristics, we developed a spatio-temporal interpolation algorithm to capture the global trend and local variation in order to use the data efficiently to reconstruct the IEQ dynamics. We compared the performance of the automated mobile sensing with a dense sensor network in a laboratory where we measured the air-change effectiveness (ASHRAE standard 129) for four different conditions. Results indicate that automated mobile sensing is able to accurately estimate the parameters with a minimal sensor cost and calibration effort. Potential applications of this system include indoor thermal comfort, lighting, indoor air quality and acoustic monitoring, pollutant source identification, and building commissioning. We shared publicly the source codes for robot control, sensor setup, and interpolation algorithm to encourage comparison study and further development.

Thermal and ventilation performance of combined passive chilled beam and displacement ventilation systems

Chilled beams provide sensible cooling to an occupied space by using chilled water flowing through modular beams mounted to a room ceiling. Previous studies show that active chilled beam systems can achieve larger sensible cooling than all-air systems. However, most studies have focused on active chilled beams and little information is available for performance of passive chilled beam (PCB) under varied ventilation conditions. The objective of the present study is to investigate ventilation and air conditioning performance of combined PCB and displacement ventilation systems. Using a validated and verified computational fluid dynamics (CFD) model, parametric analyses were performed to examine the ventilation and air conditioning performance depending on five major operating parameters: 1) ventilation strategy, 2) PCB cooling output, 3) supply air temperature, 4) supply diffuser type, and 5) internal heat source arrangement. The results show that thermal comfort and ventilation performance of a combined PCB-DV system notably vary with the PCB cooling output and supply air temperature. When the PCB cooling output increases from 33% to 53% of the total cooling load, air change effectiveness decreases from 1.6 to 1.2 and vertical temperature difference decreases from 4.0°C to 1.5°C in the breathing zone. However, spatial heat source distribution has a marginal effect on the air mixing and temperature distribution. The results suggest that a relatively high PCB cooling output (>50% of the total cooling) combined with a low supply air temperature (e.g., 17°C) could disrupt thermal stratification of displacement ventilation and increase draft rate in the occupied zone.

Experimental study on air change effectiveness: Improving air distribution with all-air heating systems

A major challenge of all-air heating applications is poor air distribution, which is often associated with a high temperature stratification. The two metrics that are commonly used for design and assessment of supply air distribution in the space are: air distribution performance index (ADPI) and the Air Change Effectiveness (E), respectively. All-air heating systems often produce stagnant air in the occupied part of the room. In this case, E may be very low while relatively uniform temperature in this occupied zone results in acceptable ADPI. Since ventilation design is based on ADPI, many all-air heating systems often produce very low E. This experiment based study identifies situation with very low E and provides simple strategies to improve it. The study provides additional design criteria to the ADPI diffuser selection guide that helps with optimal diffuser selection and adjustments. The results show that additional design criteria significantly improve E as well as temperature distribution, measured by temperature effectiveness (ƐT), with all-air heating systems. Appropriate adjustment of the diffuser may improve E and ƐT up to 30%, while the lower supply-room air temperature difference may increase E and ƐT in average 75% and 45%, respectively. Also, proper return air inlet location significantly improves E and ƐT for all-air heating. However, there are certain trades off as: the diffuser adjustment also may require seasonal adjustment for cooling and heating operation, lower supply air temperature difference requires more fan power, and floor exhaust placement may need more space for duct work.

B-27 換気効率の測定方法に関する検討 : その3 ASHRAE規格案に則した測定実験の試行

B-27 換気効率の測定方法に関する検討 : その3 ASHRAE規格案に則した測定実験の試行

Experimental study on air change effectiveness in mixing ventilation

Mixing ventilation is the most common air distribution system, and often the same diffusers provide space cooling and heating. Proper diffuser selection affects characteristics of air distribution. Air distribution with all-air-heating is one of the major challenges for mixing ventilation as temperature stratification and corresponding low ventilation effectiveness may appear. The objective of this study is to provide supporting data for air distribution system designs for several of the most common types of ceiling diffusers in the cooling and heating regime. It defines operation range for selecting diffusers with: high ADPI and ventilation and temperature effectiveness. The study is based on experimental measurements in a full-scale test room. Air change effeteness was measured using CO2 tracer gas decay tests with various types of ceiling diffusers and internal loads. Also, the air flow was changed to produce different corresponding throw for the tested diffusers (T0.25), which with characteristic space length for the diffuser jet flow (L) defined T0.25/L ratio. The results show that under heating conditions the air change effectiveness significantly decreases with decrease of T0.25/L. Even for the recommended range of T0.25/L, the value of air change effectiveness and temperature effectiveness are low: 0.56 to 0.87 and 0.58 to 0.75, respectively. Under cooling conditions, air change effectiveness and the temperature effectiveness were close to or higher than 1, regardless of diffuser type. The range of T0.25/L value that can achieve good mixing under heating condition was significantly smaller than the one under cooling mode.