Airflow Leakage Research Articles

Numerical and experimental investigations on non-axisymmetric D-type inlet nozzle for a squirrel-cage fan

ABSTRACT In this study, the unique reverse-flow around the inlet nozzle of a squirrel-cage fan was numerically studied by computational fluid dynamics (CFD), and a non-axisymmetric D-type inlet nozzle was proposed to inhibit it. It is shown that serious back flow develops at the volute tongue when the fan operates at a low flow coefficient that is lower than the best efficiency point. The airflow passing the blade passages in reverse further crosses the impeller, mixing the clearance leakage airflow, and finally blows into the intake chamber near the circumferential position of . By installing the inlet nozzle along this direction, D-type inlet nozzle schemes with different blockage extent were calculated by CFD. The scheme with a cut distance of 70% of its exit-section radius was chosen as the best design by comprehensively comparing the back flow ratio and fan performance of different working conditions. CFD results illustrated that reverse blowing at the fan entrance was significantly constrained by this D-type inlet nozzle, and the vortex in the inlet chamber correspondingly disappeared. Experimental data illustrated that the new nozzle increased the fan pressure rise under low-flow conditions by about 6% and barely reduced performance at other working points.

Integral Thermo-Anemometers for Average Temperature and Airflow Measurement in Ducts, at Anemostat Outlets and in Ventilation Grilles

When creating ventilation systems, it is important to correctly calculate the volumes of air inflow and outflow. If an error is made in the calculation or a redistribution of air flows is required, measurements are indispensable. The existing methods for determining the air flow rate by using point measurements in the cross-section are laborious and time-consuming, and taking readings at different time points introduces a significant error into the result. A. M. Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine has developed a new hot-wire anemometer whose use greatly simplifies the measuring process. This device allows one to measure the average values of temperature and air velocity (flow rate) in the cross-section of air ducts or at the inlets and outlets of grilles and anemostats, and can be used in real time to monitor and control air flow rate and temperature in ventilation systems. The probe of the hot-wire anemometer is a metal shell with guides on which a sensitive element is laid. Its principle of operation is to change the heat transfer coefficient at different air leakage velocities. The anemometer is preliminarily calibrated in laboratory conditions at various velocities. There has been obtained a calibration dependence that can be used to measure the air flow rate at the inlets and outlets of air distribution devices and directly in the air ducts. To improve the measurement accuracy, it is necessary to provide the 90° angle of airflow leakage on the hot-wire anemometer probe. For this, special air collectors and air flow rectifiers are used.

Study on air leakage and gas distribution in goaf of Y-type ventilation system

ABSTRACT In order to reveal the law of air leakage and gas distribution in goaf of fully mechanized mining face under Y-type ventilation, the numerical simulation of gas distribution in goaf was carried out with Comsol Multiphysics multi-physical field numerical simulation software under the field background of 31009 working face of Yangquan Xinyuan Coal Mine. Through the simulation results, we can see that the Y ventilation mode affects the gas depth 2–3 m more than the U ventilation mode, and the Y ventilation mode uses the airflow of the auxiliary air inlet to disperse the gas accumulation in the goaf and the upper corner. The results show that the air leakage from the 31009 working face to the goaf is 481.92 m3/min; the high air leakage area of the 31009 working face is 46.5 m in front of the working face, and the depth of gas distribution affected by airflow is 59 m; the low air leakage area is 46.5–232.5 m. The results show that compared with U-type ventilation, Y-type ventilation can reduce gas concentration in the working face and upper corner. The three-dimensional spatial distribution law of gas in goaf is similar to the “O” circle theory of mining fissures. Along the strike direction, the gas concentration in the deep goaf increases gradually; in the incline direction, the gas concentration in the middle of the goaf is higher than that on both sides of the goaf; in the vertical direction, the gas concentration increases gradually. The air leakage flow field affects the gas concentration distribution in the goaf. In the position with larger air leakage, the gas concentration is lower and the influence range is larger. The results of field measurement and numerical simulation are consistent, which provides a scientific basis for the problem of gas exceeding the limit in Y-type ventilation control face and upper corner.

Performance enhancement of horizontal underground-to-inseam gas drainage boreholes with double-phase-grouting sealing method for coal mining safety and clean gas resource

Underground to inseam (UIS) borehole gas drainage is of significance for improving mining safety and turning hazardous methane into a clean gas resource. However, in the horizontal UIS borehole sealing by adopting cement-grout-based sealing method, an upper gap frequently occurs in the sealing section after cement-grout solidification, which could potentially be an air-leakage path and consequently decrease drainage efficiency. Despite extensive previous investigations on borehole sealing, very few studies have been reported in addressing the upper gap issue to enhance drainage performance. In this study, the air-leakage flow models in concentric ring and off-center ring seal gap of horizontal borehole were established. Then by adopting new expansive composite sealing (ECS) material, a double-phase-grouting (DPG) sealing method was developed to seal the upper gap. Based on theoretical fundamentals of seal-gap leakage, procedures and explanations of DPG sealing method were discussed. Finally, coalmine field trials were conducted to examine effects of DPG sealing method. Results show that: (1) there are positive correlations between air leakage quantity into borehole and the gap width, borehole diameter, pressure differences and eccentricity ratio. While the air leakage amount is negatively related to fluid viscosity and sealing-section length; and (2) because of adopting ECS material and the second-phase grouting specially designed for upper gap sealing, DPG sealing method is capable of sealing upper gap well to improve sealing quality. It mainly reflects in increasing drained gas concentration and prolonging the period of high-methane-concentration drainage. In comparison with traditional sealing method, the mean gas flow with DPG sealing method averagely rises by 30%. Outcomes of this study are expected to provide an effective way to solve upper gap issue and enhance drainage performance of horizontal UIS boreholes.

Numerical investigation of coal self-heating in longwall goaf considering airflow leakage from mining induced crack

Self-heating of coal is a long-standing hazard and pollution source in longwall goaf and abnormal air leakage into goaf is a key yet complex drive to the hazard. To investigate such a problem with more insights, a numerical model without considering coal moisture is established based on a Shendong longwall. Abnormal air leakage into goaf mainly sources from the edge cracks resulting in presence of high level oxygen (8 %∼13 %) in start-off area of the longwall. Two heating liable regimes were identified: one is behind longwall face and another one locates in the start-off zone. Heating in the start-off zone develops more quickly than that in heating regime one. On day 25 the maximum temperature of regime two can rise to 500K while it can only increase to approximately 340K in regime one. The heating spot behind longwall face tends to be self-suppressed with longwall advancing while the heating in the start-off zone can develop to a spontaneous combustion incident due to constant airflow leakage from the mining induced cracks. A wide range of inertisation plans including different locations, strategies, and flowrates of nitrogen injection were conducted. An optimum inertisation plan is to proactively inject inert gas with a low flowrate (e.g. 122m3/h) from a seal along the start-off line. A high flowrate of nitrogen stream is preferable to suppress an on-going heating and the reactive inertisation should be maintained for a long run otherwise the heating is very likely to re-develop.

Performance Comparison of N95 and P100 Filtering Facepiece Respirators with Presence of Artificial Leakage

National Institute for Occupational Safety and Health-approved P100 filtering facepiece respirators (FFRs) have a higher filter efficiency compared to the N95 filters. However, the former typically produce higher flow resistance (Rf). Consequently, when faceseal leakage is present, the proportion of leakage airflow for P100 FFRs may exceed that of N95s, resulting in a higher total inward leakage (TIL) of the P100. In this manikin-based study, the performance of two pairs of N95 and P100 FFRs (N95-A versus P100-A; N95-B versus P100-B) were compared under five sealing conditions (fully sealed and partially sealed with one, two, or three leaks of 0.8-mm, and one 2-mm leak). Sodium chloride particles (CMD ~45 nm) were used as the challenge aerosol. Respirators were tested under three constant flows (15, 50, and 85 L/min) and three cyclic flows (mean inspiratory flow = 15, 50, and 85 L/min). Both filter penetration (Pfilter) and TIL were determined. The Rf under constant flows was recorded. Based on Pfilter, TIL, and Rf, the quality factor (qf) was calculated to compare the overall performance of N95 and P100 FFRs. For a fully sealed condition, the Pfilter was much lower for the P100 FFRs than for the N95 FFRs. When small leaks were inserted (0.8-mm and 2 × 0.8-mm), the TIL was higher for the P100 FFRs than for the N95 FFRs under the lowest tested flow (15 L/min), while for greater leaks (3 × 0.8-mm and 2-mm), the TIL of the P100 FFRs was always higher regardless of the flow. The Rf of P100 FFRs was measured twice as high as the N95. The qf values were also found higher for the N95 FFRs than for the P100 FFRs regardless of leak size and breathing flow. With the presence of artificial leakage, a P100 FFR with high-flow-resistance may not be as protective as a low-flow-resistance N95 FFR. This finding suggests that future efforts should be directed to reducing the breathing resistance when designing P100 FFRs.

Modelling building airtightness pressurisation tests with periodic wind and sharp-edged openings

This paper presents an approach to model building airtightness pressurisation tests and to quantify uncertainties due to a periodic wind. Our approach assumes the building under test can be represented as a single zone with two sharp-edged openings, one on the windward side and one on the leeward side of the building. We detail the system of equations obtained which deals with stack effect, air compressibility, and inertia of the air subjected to unsteady pressure conditions at the boundaries of the openings. Solving the system of equations gives the dynamic behaviour of the airflow rates and state variables in the enclosure and in the leaks, making it possible to estimate the uncertainty of the air leakage coefficient in one-point pressurisation tests. Our analyses show that: (a) the wind fluctuations can yield much larger uncertainties on the air leakage coefficient than the average wind alone; (b) the wind frequency influences significantly the uncertainty when it is smaller than the sampling frequency; and (c) the contribution of the zero-flow pressure uncertainty to the uncertainty of leakage airflow rate error is of about the same size as that of the flow and pressure uncertainties at the pressure measurement station.

Test of measurement device for the estimation of leakage flow rate in pneumatic pipeline systems

Background: Indirect measurements of flow rate serve to determine air consumption, leakage values and characteristics of compressed air systems (CASs). Method: A new method of indirect flow rate measurement in a pneumatic pipeline system was developed. The method enables to measure the controlled leakage in a branch line and was used to construct automatic measuring systems auditing the compressed air systems piping. Results: First, the leak-testing instrument LT-I 200 was designed, constructed, and tested as portable measurement device for the estimation of air leakage flow rate in pneumatic pipeline system. Next, based on the authors’ patent, the automatic measuring system for the measurement of the leakage flow rate in industrial compressed air piping was developed. Conclusion: The measurement device was used to estimate of the leakage flow rate and cost of the energy losses in the compressed air piping system.

Porosity model and air leakage flow field simulation of goaf based on DEM-CFD

The air leakage in goaf can easily lead to disasters such as spontaneous combustion process of residual coal and gas accumulation, threatening production safety in underground coal mines. In order to study and master air leakage flow field distribution in goaf, the particle flow numerical simulation software PFC3D is used for the simulation of the collapse of overlying rock strata with the actual situation of the 3308 working face of Liangbaosi Coal Mine in China taken as an example. The quantitative porosity data of goaf are extracted and imported into FLUENT to simulate the air leakage flow field in goaf. The results show that (1) the porosity in the central part and near the working face of goaf is relatively large. With the increase of the length of goaf, the porosity decreases, and with the increase of the height of goaf, the porosity in the two cross headings is first larger than that in the central part and then smaller than that in the central part. (2) The data of air flow along the dip direction of working face obtained through the CFD numerical simulation is consistent with the actual measurement results basically, which validate the simulation. (3) The main air leakage occurs in the range of 0–10 m along the dip direction of working face. In the case of relatively large air supply rate, the residual coal spontaneous combustion area in goaf is far from the working face and the spontaneous combustion area becomes relatively large, resulting in increased risk.

Application of ventilation simulation to spontaneous combustion control in underground coal mine: A case study from Bulianta colliery

Spontaneous combustion of residual coal in longwall goaf is a long standing hazard. Airflow leakage into goaf is a major driver to the hazard and this issue deteriorates where longwalls are operating in multiple seams and shallow covers because mining-induced cracks are very likely to draw fresh airflow into goaf due to presence of pressure differential between longwall face and surface. To study the problem more critically, a ventilation simulation package “Ventsim” is used to conduct a case study from Bulianta colliery. It was found that isolating and pressurizing active longwall panel can mitigate the problem and the pressure differential can be adjusted by varying performance of auxiliary fan and resistance of ventilation regulator. A booster ventilation system can also mitigate the problem by adjusting fan duties. Ventilation simulation is a powerful tool to study spontaneous combustion control in underground coal mine.

Large-eddy simulation of the containment failure in isolation rooms with a sliding door-An experimental and modelling study.

In hospital isolation rooms, door operation can lead to containment failures and airborne pathogen dispersal into the surrounding spaces. Sliding doors can reduce the containment failure arising from the door motion induced airflows, as compared to the hinged doors that are typically used in healthcare facilities. Such airflow leakage can be measured quantitatively using tracer gas techniques, but detailed observation of the turbulent flow features is very difficult. However, a comprehensive understanding of these flows is important when designing doors to further reduce such containment failures. Experiments and Computational Fluid Dynamics (CFD) modelling, by using Large-Eddy Simulation (LES) flow solver, were used to study airflow patterns in a full-scale mock-up, consisting of a sliding door separating two identical rooms (i.e. one isolation room attached to an antechamber). A single sliding door open/ hold-open/ closing cycle was studied. Additional variables included human passage through the doorway and imposing a temperature difference between the two rooms. The general structures of computationally-simulated flow features were validated by comparing the results to smoke visualizations of identical full-scale experimental set-ups. It was found that without passage the air volume leakage across the doorway was first dominated by vortex shedding in the wake of the door, but during a prolonged hold-open period a possible temperature difference soon became the predominant driving force. Passage generates a short and powerful pulse of leakage flow rate even if the walker stops to wait for the door to open.Electronic Supplementary Material (ESM):supplementary material is available in the online version of this article at 10.1007/s12273-017-0422-8.

Automatic device for indirect measurement of leakage flow rate in compressed air pipeline

The new measurement method of compressed air leakage flow rate in compressed air pipeline is proposed. In this method, the automatic measuring device is connected to a branch of the pipeline. The measuring device can be used to measure compressed air leakage in any place of compressed air pipeline: in main line, distribution line and connection line. The proposed measurement methods of compressed air leakage in pipeline are independent of receiver and compressor parameters, which is not the case with traditional method measuring leaks by emptying the receiver.

Fast POD method to evaluate infiltration heat recovery in building walls

Air infiltration of buildings has a considerable impact on the energy performance of buildings. Permeability or airflow leakage can be evaluated by introducing the Infiltration Heat Recovery (IHR) factor in the energy balance equation. Conventionally, this factor is computed using a Computational Fluid Dynamics (CFD) software, that is time consuming and not very useful for a fast evaluation of balance energy of a building. This article proposes a Reduced-Order model (ROM) approach to evaluate the effect of the permeability of the energy balance for a building. The ROM, based on the well-known Proper Orthogonal Decomposition (POD) method, is developed in the Modelica modeling language. It is successfully applied to the case study of the air infiltration in the low energy consumption building.

Characterisation of mechanics and flow fields around in-seam methane gas drainage borehole for preventing ventilation air leakage: A case study

Coal mine methane (CMM) drainage via adopting in-seam horizontal boreholes is an effective way to decrease ventilation cost and production delay, ensure mining safety, reduce greenhouse gas emissions and increase the supply of energy resource. Ventilation air leakage into borehole, however, occurs frequently, which decreases the methane-drainage efficiency. Despite extensive anti-leakage method investigations, a very few studies have been focused on spraying air-proof materials on the roadway rib and optimizing borehole sealing along the borehole, along with taking the effects of sequential excavations of roadway and borehole into account. In this paper, based on data of a real coal mine, a fully coupled mathematical model was developed by incorporating coal permeability with coal mechanical properties and gas adsorption/desorption and was then implemented into a Finite Element software. This numerical simulation was used to analyse transient stress and dynamic air-leakage flow fields around the drainage borehole. Simulation results indicate that: (1) four stress areas (І to IV) exist around the roadway based on different relief status of the tri-axial stress, and stress distributions around the borehole in those four areas are different from each other; (2) based on different air-leakage degrees, on the roadway rib, there are four air-leakage levels around borehole. Meanwhile, there are four leakage areas along the borehole: FAA, SAA, HAA and VAA, and the optimal sealing length should be over 17m (exceeding HAA) to prevent air leakage. Air-leakage results in (2) are verified mutually with the mechanics outcomes in (1). Meanwhile, real data obtained from field experiments is introduced to validate the simulation results. All those outcomes can allow for the optimal design of the spraying area and order and borehole sealing, thus provide scientific basis for an integrated anti-air-leakage method including spraying air-proof materials on the roadway wall and sealing borehole effectively, to prevent ventilation air leakage and maximize methane drainage performance.

Gas flow analysis for the impact of gob gas ventholes on coalbed methane drainage from a longwall gob

A large amount of methane releasing from the residual coal and the surrounding pressure-relieved gas-bearing strata may accumulate in the longwall gob of gas-bearing coal seam, which is increasingly exploited as a major source of coalbed methane (CBM) development in coal mining areas. Meanwhile, if the gob methane emits into the working space along with air-leakage flow, they may impair the safety and productivity of underground coal mines. Thus, gob gas drainage is of great significance to both the CBM development and the control of gob gas emission. Currently, there exist two major technologies for gob gas drainage–gob gas ventholes (GGVs) drainage and underground drainage (such as high-level suction tunnels, high-located boreholes and buried pipes in the upper-corner). In practical engineering applications, the GGVs have greater advantage over the traditional underground drainage in the extraction flux of gob gas and the control of gob gas emission, but the theoretical mechanism of GGVs has not yet been revealed in previous studies. Consequently, the characteristics of gob gas flow with GGVs drainage needs further research.In this paper, the numerical simulation of gas flow in gob gas reservoirs and the in-situ assessment of GGVs drainage are carried out to investigate the mechanism of the control of gob gas flow with GGVs drainage. Firstly, based on fluid mechanics in porous media the mathematical model of gob gas transport is developed. Then, the gas pressure distribution, gas flow patterns and methane concentration distribution in the gob under the conditions of no drainage measures, drainage with buried pipe in the upper-corner and GGVs in different locations are discussed by conducting numerical simulation, respectively. In addition, the influence of distance between GGV and return airway on the gob methane flow and the strong control scope of GGVs are analyzed in detail. It is found that: 1) GGVs has the “flow-interception effect” on the gas in the deep zone of the gob and the “flow-reversal effect” on the gas in the gob close to the longwall face, which accounts for that GGVs drainage advantage over underground drainage. 2) GGVs can be applied to drain the gas in the deep zone of the gob massively and to control the gob gas migration effectively, so they are a top choice for the extraction of gob gas and the control of gob gas emission. Finally, both GGVs drainage and underground drainage are adopted to extract gob gas in east-102 working face in Weijiadi coal mine. The comparison of the extracted and emitted volume of gob gas with two different technologies shows that, GGV can drain the gob gas with greater flux and can better control the gob gas emission, which validated the prediction of numerical stimulation.

Modeling carbon monoxide spread in underground mine fires

Carbon monoxide (CO) poisoning is a leading cause of mine fire fatalities in underground mines. To reduce the hazard of CO poisoning in underground mines, it is important to accurately predict the spread of CO in underground mine entries when a fire occurs. This paper presents a study on modeling CO spread in underground mine fires using both the Fire Dynamics Simulator (FDS) and the MFIRE programs. The FDS model simulating part of the mine ventilation network was calibrated using CO concentration data from full-scale mine fire tests. The model was then used to investigate the effect of airflow leakage on CO concentration reduction in the mine entries. The inflow of fresh air at the leakage location was found to cause significant CO reduction. MFIRE simulation was conducted to predict the CO spread in the entire mine ventilation network using both a constant heat release rate and a dynamic fire source created from FDS. The results from both FDS and MFIRE simulations are compared and the implications of the improved MFIRE capability are discussed.

Effect of Tracheal Cuff Shape on Intracuff Pressure Change During Robot-Assisted Laparoscopic Surgery: The Tapered-Shaped Cuff Tube Versus the Cylindrical-Shaped Cuff Tube.

Although the cuff of tracheal tubes can reduce airflow leakage and prevent aspiration, excessive intracuff pressure can cause tracheal mucosal injury. Robot-assisted laparoscopic surgery (RALS) can increase intracuff pressure by the Trendelenburg position and pneumoperitoneum. The aim of our current study was to investigate the effect of tracheal cuff shape on the intracuff pressure increase by comparing two different-shaped cuffs during RALS. Ninety-eight patients undergoing RALS were allocated randomly into two groups (tapered-shaped cuff [TSC] and cylindrical-shaped cuff [CSC] groups). The intracuff pressure was measured at nine specific time points: after intubation, immediately after surgical preparation (Trendelenburg position with CO2 insufflation), at 5, 10, 15, 30, 60, and 90 minutes after surgical preparation, and at the end of surgery. Postintubation airway symptoms were measured by assessing sore throat, hoarseness, and excessive cough 1 hour after postanesthesia care unit admission. Intracuff pressure significantly increased during surgery in both groups. The trend of intracuff pressure change decreased in the TSC group compared with the CSC group, although no statistically significant changes were found (P=.450). Also, there were no statistically significant differences in the postintubation airway symptom between the two groups. The TSC tube has a tendency to decrease intracuff pressure change compared with the CSC tube during RALS. However, neither of them was beneficial in preventing intraoperative intracuff pressure increase during RALS.

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%.

A Characterization of time-dependent air infiltration rates in retail stores using calibrated multi-zone model

The main goal of this article is to quantify the time-dependent air infiltration rates for two retail stores using a calibrated multi-zone model. The calibration focused on the automatic entrance doors as the flow element with significant infiltration rates. This study examined the application of a modified leakage airflow element for automatic entrance doors to predict physical conditions, including differential pressures and airflow rates across the doors. The results show that the simulation of differential pressures across the entrance doors was consistent with the measured data after the model used the corrected flow coefficient (C) based on an hourly rate of people passing through the doors. The airflow rates through the automatic entrance doors represented 75%–80% of the total air infiltration and accounted for 12%–19% of the total ventilation rates. Furthermore, installing a door vestibule decreased the infiltration airflow rates through the automatic entrance doors by approximately 23%. Overall, the present study proposes and validates a method based on the calibrated multi-zone model to quantify the time-dependent infiltration rates in retail buildings.

Air Tightness of Ventilation Ductwork in Recently Built Low-Energy and Conventional Houses

The air tightness of ventilation ductwork was measured in two recently built low-energy houses and in two conventionally built houses in the summer of 2013. The ducts and components were metal in three houses and plastic in one house. The air tightness of the ductwork had been checked by an installation survey after construction. The measured leakage airflows corresponded to air tightness class A or lower, therefore did not satisfy the minimum requirement set for class B regarding the air tightness of ventilation ductwork. Leakage airflow of the ductwork per duct surface area was estimated to be 47 times higher at a typical ventilation duct pressure of 100 Pa than leakage airflow in the house envelope per internal surface area at a typical house air pressure of 5 Pa. The results showed that the installation survey was not a sufficient method for ensuring the air tightness of ductwork in these houses. Therefore, it is recommended that the air tightness of ventilation systems that serve a single room or a single dwelling are measured during commissioning. A larger study of the air tightness of ventilation systems in Finnish buildings would be necessary.