Tracer Gas Measurements Research Articles

Air tightness and RH control in museum showcases: Concepts and testing procedures

Abstract This paper analyses the use of museum showcases as a means of improving the control of the indoor environment for the conservation of works of art. It presents and discusses the influence of the air and gas tightness of a showcase on variations of the relative humidity. Attention is first focused on the basic mechanisms that drive the exchange of water vapour and gas between the inside and outside of the showcase. Testing procedures to characterize their performance (e.g. pressurization tests, tracer gas measurements) are then described and critically reviewed. Finally, examples of laboratory and field measurement results are presented and discussed in order to abstract general recommendations about: how to test the air tightness of showcases and how to choose the most suitable air tightness value, in relation to the desired level of control of the RH.

Performance assessment of controlled natural ventilation for air quality control and passive cooling in existing and new office type buildings

Natural ventilation has the potential of achieving high ventilation rates for fresh air supply and summer cooling, although without the possibility of air to air heat recovery in winter. This study aims to compare the overall energetic efficiency and comfort provision of controlled natural ventilation in energy efficient offices and in the non-refurbished building stock with the related mechanically ventilated reference. The goal is to determine the energy savings for modern offices with low heating demand and higher summer cooling loads compared to existing office buildings, where heating loads dominate. To make sure that the simulation assumptions match the reality, the air-flow modelling of a single-sided ventilation strategy is validated by comparing it with results from tracer-gas measurements. Simulation results indicate that properly designed and controlled natural ventilation shows a good functionality in both state-of-the-art buildings and in the stock. In the moderate climate of Stuttgart/Germany no mechanical cooling is necessary. For state-of-the-art buildings ventilation energy losses in the heating season are easily compensated by lower cooling demand in the warm period of the year. In the building stock the conclusions are less clear, especially for densely occupied offices. Energy losses in the heating season can be compensated in the warm period, but primary energy savings are dependent on primary energy factors and hence how heat, cold and electricity are generated.

Impacts of airflow interactions with thermal boundary layer on performance of personalized ventilation

The flow interactions between the personalized air and the thermal boundary layer (TBL) may play an important role to the inhaled air quality and energy efficiency performance of a personalized ventilation (PV) system. This paper aims to investigate these interactions and their impacts on the performance of a PV system. Schlieren imaging technique, Laser Doppler Anemometry (LDA) and tracer gas measurements are employed to identify the airflow patterns in the breathing zone (BZ) and the effect of the interactions on ventilation effectiveness. Although it has always been considered that it is difficult for a PV jet of low flow rate to penetrate the TBL, it is found in this study that the TBL is penetrable even at invading velocities lower than the normally recognized value of 0.3 m/s. The advantage of the reduced blockage effect allows for a more effective delivery of fresh air to the BZ. It is also shown that the airflow interactions alter the airflow distributions in the BZ and affect the inhaled air quality. This interaction depends on the positioning and direction of the non-uniform invading flow from the nozzle, which should be carefully considered for optimal ventilation design to enhance the effectiveness of ventilation at relatively low energy consumptions.

Airtightness of electrical, mechanical and architectural components in South Korean apartment buildings using the fan pressurization and tracer gas method

The purpose of this study is to measure airtightness of building components in newly constructed apartment buildings in South Korea. For the measurements, electrical, architectural and two mechanical components regarding water and air systems were categorized and air leakage rates of these parts were measured by the blower door test. In addition to these building components, air leakage rates on the entrance door and three different building heights were analyzed. Moreover, the results obtained by the blower door test were compared with the tracer gas measurements. As a result, the air leakage rates (ACH50) were between 0.7 and 1.0 h−1, when all parts were sealed. When unsealing all parts, the ACH50 values ranged from 1.6 to 2.7 h−1. In addition, the ACH50 values were highly influenced by the entrance door and window systems. By improving the windows and the entrance door, the air leakages can be significantly reduced in residential buildings. Furthermore, the comparison results obtained by the tracer gas and blower door showed that artificially produced pressure difference condition can cause the overestimated ACH value.

Accurate assessment of exposure using tracer gas measurements

Room airflow interaction, particularly in the breathing zone, is important to assess exposure to indoor air pollution. A breathing thermal manikin was used to simulate a room occupant with the convective boundary layer (CBL) generated around the body and the respiratory flow. Local airflow against the face of the manikin was applied to increase the complexity of the airflow interaction. CO2 was released at the armpits and N2O at the groin to simulate the respective bio-effluents generated at these two body sites. The tracer gas concentration at the mouth/nose of the manikin was measured with gas analyzers with short and long response times, respectively. The tracer gas concentration was characterized by the mean, standard deviation and 95th percentile values. The results revealed that the measurement time needed to determine, with sufficient accuracy, these parameters decreased substantially with a decrease in the response time of the gas analyzer. When only CBL was present, shorter measurement time was needed for the accurate concentration measurement of the tracer gas released close to the breathing zone. For more complex flow, as a result of CBL interaction with the exhalation flow, the needed measurement time was longer. It has been concluded that the accurate exposure assessment requires that the concentration measurements are performed only during the inhalation period. Therefore, gas analysers with low response time and sampling time that is considerably shorter than the inhalation period have to be used.

Assessing the variability of the air change rate through tracer gas measurements

The increasing energy concerns across the European Union enhanced the importance of buildings ventilation and pointed out the reduction of energy for ventilation as one of the targets. The measurement of ventilation and leakage rates are therefore necessary to understand buildings performance, especially in mild climate countries where often dwellings ventilation is adventitious and highly influenced by user behaviour.In mild climate countries, natural ventilation is the most common strategy. The air movement is therefore a combined result of pressure differences produced by wind and buoyancy forces, which are both time-dependent. Under these circumstances, one-time measurements of the air change rate, made over short periods, may not be an accurate indicator.An experimental campaign for the evaluation of the air change rate in a Portuguese dwelling was conducted over a period of two months. During this period, tracer gas measurements were performed in two compartments: (R1) living room; and (R2) bedroom. In each, two different boundary conditions were tested: (i) door closed; and (ii) door opened. A total of 132 tests were carried out. The decay technique was used for the quantification of the air change rate. Simultaneously, indoor and outdoor conditions were continuously monitored.The results highlighted the importance of performing several measurements as some variability was found, especially for the open door scenarios. Moreover, the importance of wind speed was also confirmed as the main trigger mechanism in naturally ventilated buildings, especially in the mid-season period where the indoor/outdoor temperature difference is not significant.

Investigation of the pressure coefficient impact on the air infiltration in buildings with respect to microclimate

Wind pressure coefficients (Cp) are important for calculating the air infiltration rate of a building. Cp depend on a wide range of parameters, such as wind direction and speed, position on the building surface and façade exposure. Most Building Energy Simulation (BES) programs generally calculate air infiltration using simplified pressure coefficients. The Norwegian technical software (SIMIEN) do not consider them. The effect of the pressure coefficients on the air infiltration of the building, taking into consideration the microclimate of the building area, is studied. The wind pressure coefficients are defined through computational fluid dynamics (CFD) simulations. The air infiltration in the building is determined based on the calculated pressure coefficients. Tracer gas measurements were used for validation of the results. Two cases of fully exposed and partially sheltered building were examined. The results indicate that wind pressure coefficients derived from CFD simulations calculate more realistic values for the air infiltration of the building.

Dynamic simulation of contaminant inleakage produced by human walking into control room

Human walking-induced transport can be a significant mechanism during entry from a contaminated region into a protective enclosure, such as a control room. The passage through the door gives the outside air the opportunity to leak into the control room, endangering the staff inside. The objective of this study is to simulate contaminant transport induced by human walking motion in simplified situations – the person moving from the corridor into the anteroom, with various entrance times (from 2 to 8s). The CFD simulations were made by using the RANS solver with dynamic meshes techniques. The inleakage airflow through the doorway and the inleakage air volume can be both quantified with tracer gas measurements. The simulation results illustrated that the whole inleakage process can be divided into four stages: door draws in air; person entrains the air; door closing cuts short the wake; and door pushes the air in the final movement. It was found that the total inleakage volume is affected by the entrance time, and can be as much as 1.192m3 for an 8.0s entrance time. The data measured in our previous experimental study were employed to validate with the simulation result. The comparison result indicated an agreement when the entrance time was 3–8s, but as the entrance time increased, the simulation values were significantly higher than those measured experimentally. The simulation results can therefore be considered as a conservative estimate, which can guide the prevention of inleakage in future engineering applications.

Application of a miniaturized solid state electrolyte sensor for tracer gas measurements in a two-stage low pressure turbine

A new technique for tracer gas experiments in turbomachinery environments is presented. Instead of ethylene or carbon dioxide - as in previous publications - carbon monoxide is used as tracer gas. The measuring device is a miniaturized solid state electrolyte sensor built into the head of a traverse probe. Due to the lack of extensive tubing the design of the probe allows a short response time of the measuring system. The sensor characteristics, the calibration of the probe and the data analysis are described, and an estimation of measurement uncertainties as well as results from measurements within a two-stage low pressure turbine featuring hot streak injection are provided. Despite different sensor characteristics the results show good agreement between measurements with different probes. The overall quality of the results indicates that the developed technique is a valuable tool for the investigation of migration and mixing.

Natural ventilation and indoor air quality in educational buildings: experimental assessment and improvement strategies

Indoor environmental conditions in classrooms, in particular temperature and indoor air quality, influence students’ health, attitude and performance. In recent years, several studies regarding indoor environmental quality of classrooms were published and natural ventilation proved to have great potential, particularly in southern European climate. This research aimed to evaluate indoor environmental conditions in eight schools and to assess their improvement potential by simple natural ventilation strategies. Temperature, relative humidity and carbon dioxide concentration were measured in 32 classrooms. Ventilation performance of the classrooms was characterized using two techniques, first by fan pressurization measurements of the envelope airtightness and later by tracer gas measurements of the air change rate assuming different envelope conditions. A total of 110 tracer gas measurements were made and the results validated ventilation protocols that were tested afterward. The results of the ventilation protocol implementation were encouraging and, overall, a decrease on the CO2 concentration was observed without modifying the comfort conditions. Nevertheless, additional measurements must be performed for winter conditions.

A Case Study of the Weather Research and Forecasting Model Applied to the Joint Urban 2003 Tracer Field Experiment. Part 2: Gas Tracer Dispersion

The Quick Urban & Industrial Complex (QUIC) atmospheric transport, and dispersion modelling, system was evaluated against the Joint Urban 2003 tracer-gas measurements. This was done using the wind and turbulence fields computed by the Weather Research and Forecasting (WRF) model. We compare the simulated and observed plume transport when using WRF-model-simulated wind fields, and local on-site wind measurements. Degradation of the WRF-model-based plume simulations was cased by errors in the simulated wind direction, and limitations in reproducing the small-scale wind-field variability. We explore two methods for importing turbulence from the WRF model simulations into the QUIC system. The first method uses parametrized turbulence profiles computed from WRF-model-computed boundary-layer similarity parameters; and the second method directly imports turbulent kinetic energy from the WRF model. Using the WRF model’s Mellor-Yamada-Janjic boundary-layer scheme, the parametrized turbulence profiles and the direct import of turbulent kinetic energy were found to overpredict and underpredict the observed turbulence quantities, respectively. Near-source building effects were found to propagate several km downwind. These building effects and the temporal/spatial variations in the observed wind field were often found to have a stronger influence over the lateral and vertical plume spread than the intensity of turbulence. Correcting the WRF model wind directions using a single observational location improved the performance of the WRF-model-based simulations, but using the spatially-varying flow fields generated from multiple observation profiles generally provided the best performance.

Airflow patterns through single hinged and sliding doors in hospital isolation rooms – Effect of ventilation, flow differential and passage

Negative pressure isolation rooms are used to house patients with highly contagious diseases (e.g. with airborne diseases) and to contain emitted pathogens to reduce the risk for cross-infection in hospitals. Airflows induced by door opening motion and healthcare worker passage can, however, transport the potentially pathogen laden air across the doorway. In this study airflow patterns across the isolation room doorway induced by the operation of single hinged and sliding doors with simulated human passage were examined. Smoke visualizations demonstrated that the hinged door opening generated a greater flow across the doorway than the sliding door. Tracer gas measurements showed that the examined ventilation rates (6 and 12 air changes per hour) had only a small effect on the air volume exchange across the doorway with the hinged door. The results were more variable with the sliding door. Supply-exhaust flow rate differential reduced the door motion-induced air transfer significantly with both door types. The experiments showed that the passage induced substantial air volume transport through the doorway with both door types. However, overall, the sliding door performed better in all tested scenarios, because the door-opening motion itself generated relatively smaller air volume exchange across the doorway, and hence should be the preferred choice in the design of isolation rooms.

Diurnal and seasonal variation in air exchange rates and interzonal airflows measured by active and passive tracer gas in homes

Outdoor air delivery to buildings is an important parameter in the assessment of pollutant exposure indoors. Detailed and well controlled measurements of air exchange rates (AER) and interzonal airflows in residential environment are scarce. We measured the outdoor AERs in up to six rooms in five dwellings across four seasons using active tracer gas. Night time AERs were also estimated in the bedrooms based on occupant-generated CO2. Passive tracer gas measurements were performed for comparison. AERs changed frequently during the day. Differences in outdoor AERs were observed between individual rooms. Window opening behavior had a strong influence on AERs, which were highest during occupied daytime periods, lowest in the night; highest in the summer, lowest in the winter. Significant differences were found between AERs measured by the different techniques. The median nighttime AER in all bedrooms across the four seasons was 0.49 h−1 with the active tracer gas technique and 1.20 h−1 with the CO2 method. The average winter AER in the five homes with the passive tracer (0.63 h−1) differed substantially from the corresponding AER measured with the active tracer gas (0.25 h−1). Additionally, we studied the pollutant distribution from one room (source room) and interzonal airflows across the dwellings. The air within a given floor was well mixed, with the average tracer gas concentration in the non-source rooms reaching approximately 70% of the source room concentration. There was less air movement between different floors. The position of the internal doors had a strong influence on the air movement.

Airflow Patterns through Single Hinged and Sliding Doors in Hospital Isolation Rooms

Door operation and the subsequent passage of occupants through the doorway can cause containment failures in hospital isolation rooms. Typically hinged doors are used between the isolation room and anteroom/corridor in healthcare facilities. However, sliding doors can reduce door induced airflows through the doorway and hence effectively reduce the contaminant outflow during the door operation.Airflow patterns through single hinged and sliding doors, in combination with human passage (simulated with a moving mannequin), inside a full-scale hospital isolation room mock-up, were compared. The experiments were carried out in still air (i.e. without ventilation) in order to examine the effect of different factors without the masking effect of ventilation. Smoke visualizations were performed to qualitatively illustrate airflow through the doorway. Tracer gas measurements were carried out to quantify the air exchange between rooms caused by door operation and passage.Smoke visualization indicated that the sliding door induce a smaller air exchange through the doorway compared to a hinged door. The effect of passage was found to be notable, yet more distinguishable with the sliding door. Airflow volumes through the hinged door varied from 1.2 m3 to 2.4 m3 and through the sliding door from 0.3 m3 to 2.3 m3, depending on parameter values. The effect of passage was found to be around 0.4 m3. Although the passage increased the air exchange across the doorway, its effect was relatively much larger for the sliding than for the hinged door.

Predicting gas dispersion in large scale underground ventilation: A particle tracking approach

The present work highlights the gas dispersion evaluation in large underground tunnel ventilation by means of tracer gas measurement and numerical simulation using particle tracking method. Ventilation system is a tool to control pollutants and/or hazardous gas spreading. The use of grid-based numerical method is limited by the spatial dimension of ventilation network. Therefore, the applicability of such technique for large ventilation network is constrained. A Lagrangian based Particle Tracking method is proposed to evaluate the dispersion of tracer gas from a releasing point to the downstream position in a complex ventilation system. This method simulates mass transport by discretizing mass concentration into numbers of particles. Rather to solving the transport equation in grid system to obtain the mass concentration, this technique simulates mass concentration by counting number of particles at any specified position within the ventilation network. In this research, the network splitting scheme was used to simulate particles' transition in junctions. Further, it was found that by setting effective diffusion coefficient to 47 times larger than those for common underground airway and with velocity correction factor of α = 0.59, a good agreement between particle tracking result and tracer gas measurement data can be achieved. This results suggests that the analytical approach in evaluating gas (or pollutant) dispersion and residence time in large ventilation system by the means of conventional ventilation network analysis have to consider both mechanical dispersion and the effect of delay due to trapping mechanism of gas.

Large Eddy Simulation of Air Escape through a Hospital Isolation Room Single Hinged Doorway--Validation by Using Tracer Gases and Simulated Smoke Videos.

The use of hospital isolation rooms has increased considerably in recent years due to the worldwide outbreaks of various emerging infectious diseases. However, the passage of staff through isolation room doors is suspected to be a cause of containment failure, especially in case of hinged doors. It is therefore important to minimize inadvertent contaminant airflow leakage across the doorway during such movements. To this end, it is essential to investigate the behavior of such airflows, especially the overall volume of air that can potentially leak across the doorway during door-opening and human passage. Experimental measurements using full-scale mock-ups are expensive and labour intensive. A useful alternative approach is the application of Computational Fluid Dynamics (CFD) modelling using a time-resolved Large Eddy Simulation (LES) method. In this study simulated air flow patterns are qualitatively compared with experimental ones, and the simulated total volume of air that escapes is compared with the experimentally measured volume. It is shown that the LES method is able to reproduce, at room scale, the complex transient airflows generated during door-opening/closing motions and the passage of a human figure through the doorway between two rooms. This was a basic test case that was performed in an isothermal environment without ventilation. However, the advantage of the CFD approach is that the addition of ventilation airflows and a temperature difference between the rooms is, in principle, a relatively simple task. A standard method to observe flow structures is dosing smoke into the flow. In this paper we introduce graphical methods to simulate smoke experiments by LES, making it very easy to compare the CFD simulation to the experiments. The results demonstrate that the transient CFD simulation is a promising tool to compare different isolation room scenarios without the need to construct full-scale experimental models. The CFD model is able to reproduce the complex airflows and estimate the volume of air escaping as a function of time. In this test, the calculated migrated air volume in the CFD model differed by 20% from the experimental tracer gas measurements. In the case containing only a hinged door operation, without passage, the difference was only 10%.

Measurements of methane emissions from natural gas gathering facilities and processing plants: measurement methods

Abstract. Increased natural gas production in recent years has spurred intense interest in methane (CH4) emissions associated with its production, gathering, processing, transmission, and distribution. Gathering and processing facilities (G&P facilities) are unique in that the wide range of gas sources (shale, coal-bed, tight gas, conventional, etc.) results in a wide range of gas compositions, which in turn requires an array of technologies to prepare the gas for pipeline transmission and distribution. We present an overview and detailed description of the measurement method and analysis approach used during a 20-week field campaign studying CH4 emissions from the natural gas G&P facilities between October 2013 and April 2014. Dual-tracer flux measurements and on-site observations were used to address the magnitude and origins of CH4 emissions from these facilities. The use of a second tracer as an internal standard revealed plume-specific uncertainties in the measured emission rates of 20–47%, depending upon plume classification. Combining downwind methane, ethane (C2H6), carbon monoxide (CO), carbon dioxide (CO2), and tracer gas measurements with on-site tracer gas release allows for quantification of facility emissions and in some cases a more detailed picture of source locations.

Purging of working atmospheres inside freight containers.

This article focuses on prevention of possible exposure to chemical agents, when opening, entering, and stripping freight containers. The container purging process is investigated using tracer gas measurements and numerical airflow simulations. Three different container ventilation conditions are studied, namely natural, mixed mode, and forced ventilation. The tests conducted allow purging time variations to be quantified in relation to various factors such as container size, degree of filling, or type of load. Natural ventilation performance characteristics prove to be highly variable, depending on environmental conditions. Use of a mechanically supplied or extracted airflow under mixed mode and forced ventilation conditions enables purging to be significantly accelerated. Under mixed mode ventilation, extracting air from the end of the container furthest from the door ensures quicker purging than supplying fresh air to this area. Under forced ventilation, purging rate is proportional to the applied ventilation flow. Moreover, purging rate depends mainly on the location at which air is introduced: the most favourable position being above the container loading level. Many of the results obtained during this study can be generalized to other cases of purging air in a confined space by general ventilation, e.g. the significance of air inlet positioning or the advantage of generating high air velocities to maximize stirring within the volume.

Basement radon entry and stack driven moisture infiltration reduced by active soil depressurization

This case study presents measurements of radon and moisture infiltration from soil gases into the basement of an unoccupied research house in Madison, Wisconsin, over two full years. The basement floor and exterior walls were constructed with preservative-treated lumber and plywood. In addition to continuous radon monitoring, measurements included building air tightness, indoor–outdoor pressure difference, indoor and outdoor temperature and relative humidity, wood moisture content, and tracer gas decay. A single-zone air infiltration model was calibrated based on tracer gas measurements. Soil moisture infiltration was determined by mass conservation after accounting for all other moisture flows: humidification, air exchange, diffusion through the above-grade building envelope, sorption in hygroscopic materials, and moisture removal by air conditioning. A moisture balance methodology used in previous work was validated and improved here by including two time scales in the sorption modeling. Active soil depressurization was applied and shown to reduce both radon and soil moisture infiltration. The stack effect is shown to correlate well with soil moisture infiltration but does not fully explain radon entry.

Numerical evaluation of ventilation performance in children day care centres

Modelling of ventilation is strongly dependent on the physical characteristics of the building of which precise evaluation is a complex and time consuming task. In the frame of a research project, two children day care centres (CDCC) have been selected in order to measure the envelope air permeability, the flow rate of mechanical ventilation systems and indoor and outdoor temperature. The data obtained was used as input to the computer code CONTAM for ventilation simulations. The results obtained were compared with direct measurements of ventilation flow from short term measurements with CO2 tracer gas and medium term measurements with perfluorocarbon tracer (PFT) gas decay method. After validation, in order to analyse the main parameters that affect ventilation, the model was used to predict the ventilation rates for a wide range of conditions. The purpose of this assessment was to find the best practices to improve natural ventilation. A simple analytical method to predict the ventilation flow rate of rooms is also presented. The method is based on the estimation of wind effect on the room through the evaluation of an average factor \(\sqrt {2(\Delta P/\rho _\infty )^* }\) and on the assessment of relevant cross section of gaps and openings combined in series or in parallel. It is shown that it may be applied with acceptable accuracy for this type of buildings when ventilation is due essentially to wind action.