Leakage Distributions Research Articles

Model-Scale Reproduction of Fan Pressurization Measurements in a Wind Tunnel: Design and Characterization of a New Experimental Facility

In many countries, building airtightness is mandated by national regulations or energy efficiency programs, necessitating accurate measurements using the fan pressurization method. Given the significant influence of wind on measurement uncertainty and the need for reliable regulatory tests, experimental studies in a controlled environment are needed. This paper presents a novel experimental facility designed to replicate fan pressurization measurements on a model scale under controlled laboratory conditions. The key features of the facility include the ability to (1) conduct fan pressurization measurements, (2) generate steady wind conditions across varying wind speeds, and (3) accurately measure parameters like the pressure difference, wind speed, and airflow rate. The experimental facility includes a pressurization device, a wind tunnel, and a model representing a two-story house with nine distinct leakage distributions. A total of 96 fan pressurization measurements were executed using this setup, adhering to the similarity conditions specifically defined for assessing airflow errors due to wind. These tests followed the ISO 9972 standard, with the pressure differences ranging from 10 Pa to 100 Pa and steady wind speeds from 1 m·s−1 to 7.5 m·s−1. This experimental facility marks a significant advancement in understanding the effect of wind on building airtightness measurements.

Autoencoder-enabled model portability for reducing hyperparameter tuning efforts in side-channel analysis

Hyperparameter tuning represents one of the main challenges in deep learning-based profiling side-channel analysis. For each different side-channel dataset, the typical procedure to find a profiling model is applying hyperparameter tuning from scratch. The main reason is that side-channel measurements from various targets contain different underlying leakage distributions. Consequently, the same profiling model hyperparameters are usually not equally efficient for other targets. This paper considers autoencoders for dimensionality reduction to verify if encoded datasets from different targets enable the portability of profiling models and architectures. Successful portability reduces the hyperparameter tuning efforts as profiling model tuning is eliminated for the new dataset, and tuning autoencoders is simpler. We first search for the best autoencoder for each dataset and the best profiling model when the encoded dataset becomes the training set. Our results show no significant difference in tuning efforts using original and encoded traces, meaning that encoded data reliably represents the original data. Next, we verify how portable is the best profiling model among different datasets. Our results show that tuning autoencoders enables and improves portability while reducing the effort in hyperparameter search for profiling models. Lastly, we present a transfer learning case where dimensionality reduction might be necessary if the model is tuned for a dataset with fewer features than the new dataset. In this case, tuning of the profiling model is eliminated and training time reduced.

Additive Statistical Leakage Analysis Using Exponential Mixture Model

Variation-aware leakage analysis becomes an essential design process as the technology node continuously shrinks. This article proposes a novel additive statistical leakage analysis method that uses exponential mixture model (EMM) to estimate the leakage distribution. Using a few leakage data for sub-blocks of an input circuit, we estimate any shape of leakage distribution regardless of new process nodes or operating conditions. Leakage distribution of an input circuit can be obtained by adding the leakage distributions of the sub-blocks. The proposed addition step sequentially adds the leakage distributions of sub-blocks that are expressed as EMMs. Before the addition step, we improve the accuracy by handling linear dependence among leakage simulation data of sub-blocks. In addition, we propose a method to reduce the number of components of an EMM to prevent exponential increase in runtime and memory during the addition process. The proposed method achieved 43.6 times improvement in goodness-of-fit of the estimated cumulative density functions compared to the best results of other analytic model-based methods.

Assessment of wind impact on building air leakage measurements using a model scale experiment

Nowadays, many countries include requirements for building airtightness in their current national regulations or energy-efficiency programs, mainly for concern about reducing building energy consumption due to air leakage. Moreover, more and more countries impose a mandatory justification with an air leakage measurement at building commissioning. Therefore, the uncertainty of the measurements results has become a key concern in several countries over the past year. More specifically, the influence of wind speed has been identified as one of the major sources of error on the measurement result. The goal of this paper is to present the experimental facility we design and built to improve the uncertainty estimates and the measurement protocol based on model scale experiments in controlled laboratory conditions. We first present the similarity criteria we identified for our model scale experiment. Secondly, we present the experimental design. Finally, we characterize the wind speed inside the wind tunnel and we present the preliminary results regarding the reproduction of fan pressurization tests on the model for different leakage distributions.

Experimental investigation of wind-induced internal pressures in nominally sealed building structures

The action of internal pressure cannot be neglected in wind-resistant design of large-span structures, high-rise buildings, and low-rise residential buildings. In this study, the internal pressure characteristics were first measured in still air in a completely closed building structure without any leakage. Then a series of wind tunnel tests were conducted to study the probability density distribution characteristics of the internal pressure responses in a nominally sealed building with background leakage. The mean and peak internal pressure responses associated with different background leakage distributions and wind directions were further investigated, and the experimental results were compared with those suggested by the Chinese wind load code GB50009-2012. The results indicated that the internal pressure in the completely closed building was non-stationary, and varied significantly when collected at different time points. Furthermore, a period of about 24 h was observed from the measured time history of internal pressure over 9 d. The internal pressure in a nominally sealed building structure nearly fitted a normal Gaussian distribution. When background leakage was uniformly arranged on the surface of the building, the mean internal pressure coefficient remained unchanged with increasing background leakage, varying within the range from −0.15 to −0.14, indicating lower magnitudes than the value of −0.2 suggested by the Chinese wind load code. The minimum negative peak internal pressure coefficient was −0.255 when the peak factor was 3.5, indicating a lower magnitude than the value of −0.326 calculated in the Chinese wind load code.

GUV and LUV Leakage: How All-Or-None and Graded Leakage Scale with Vesicle Size

Many antimicrobial compounds, (anti-cancer) drugs, and drug delivery vehicles harm their target cells by permeabilizing the cell membrane. For more than three decades, the efficiency of membrane permeabilization is studied as leakage of model membrane vesicles and is assumed to correlate with the biological activity. In the more elaborate methods, leakage is assigned to the ideal mechanisms: graded (all vesicles leak some content) or all-or-none (some vesicles are fully permeable). The most recently developed leakage assays use giant unilamellar vesicles (GUVs) for microscopy or large unilamellar vesicles (LUVs) in TCSPC fluorescence measurements. They provide the distribution of degrees of leakage over the vesicle population, i.e., a more detailed mechanism. Here, we compare the two assays using the model detergents CHAPS and C12EO8, causing all-or-none and graded type leakage, respectively. The onset concentration of leakage is the same in GUVs and in LUVs. However, at the same detergent concentration, all-or-none type leakage induces much more leakage in GUVS compared to LUVs. Oppositely, the graded type leakage is more harmful in LUVs as compared to GUVs. I.e., either the entrapped volume opened per pore or the surface to volume ratio governs the flux-efficiency of the two leakage mechanisms. While GUV-microscopy is the gold standard for obtaining the leakage distribution explicitly, LUV-TCSPC has a much higher throughput, and is more flexible for testing various conditions. Practically, it shall be ideal to perform systematic LUV-TCSPC experiments and validate or refine leakage distributions of a few prominent samples by GUV microscopy.

Methods to Reduce Stack Effect and Improve Energy Efficiency in a Nordic High Rise Residential Building

The stack effect creates uncontrolled vertical air movement in buildings. This air movement over the building envelope and internal parts of the building creates noise and draft through gaps of doors and increases energy consumption. The wind and mechanical ventilation may also have a pronounced effect on the air pressure conditions and the movement of the air along the shafts of the building. The objective of this study was to find solutions to minimize the stack effect. The effects of air tightness, air leakage distributions, and outdoor environmental conditions on air pressure conditions and energy consumption in a high-rise residential building were simulated in cold climate conditions. The stack effect is possible to prevent with spatial arrangements and improved air tightness. Based on the analysis carried out, internal air tightness is playing the major role in the control of the stack effect.

Fast Statistical Full-Chip Leakage Analysis for Nanometer VLSI Systems

In this article, we present a new full-chip statistical leakage estimation considering the spatial correlation condition (strong or weak). The new algorithm can deliver linear time, O ( N ), time complexity, where N is the number of grids on chip. The proposed algorithm adopts a set of uncorrelated virtual variables over grid cells to represent the original physical random variables and the cell size is determined by the spatial correlation length. In this way, each physical variable is always represented by virtual variables locally. We prove the number of neighbor cells for each grid cell is not related to the condition of spatial correlation (from no correlation to 100% correlated), which leads to linear time complexity in terms of number of gates. We compute the gate leakage by the orthogonal polynomials-based collocation method. The total leakage of a whole chip can be computed by simply summing up the coefficients of corresponding orthogonal polynomials in each grid cell. Furthermore, we develop a look-up table to cache statistical information for each type of gate instead of calculating leakage for every single instance of gate on a chip. As a result, a new statistical leakage characterization in Standard Cell Library (SCL) is put forward. Furthermore, an incremental analysis algorithm is proposed to update the chip-level statistical leakage information efficiently after a few changes are made. The proposed method has no restrictions on static leakage models, or types of leakage distributions. The large circuit examples in 45nm CMOS process demonstrate the proposed algorithm is 1000X faster than a recently proposed grid-based method with similar accuracy and many orders of magnitude times speedup over the Monte Carlo method. Experimental results also show the incremental analysis provides about 10X further speedup. We expect the incremental analysis could achieve more speedup over the full leakage analysis for larger problem sizes.

Measured and simulated air pressure conditions in Finnish residential buildings

Air pressure conditions in typical Finnish residences are analysed using data from field measurements and computer simulations. Field measurements were conducted in three two-storey detached houses and in two five-storey apartment buildings. The effects of air tightness, ventilation performance, air leakage distributions, and outdoor environmental conditions on air pressure conditions in a detached house were simulated with a multi-zone simulation model using the IDA ICE simulation program. Despite of common design assumption, negative air pressure difference indoors, the results show that there is almost always a positive and negative air pressure difference across the building envelope in detached houses and apartment buildings. For detached houses, the design value of the air pressure difference across the building envelope for moisture convection analysis should be at least ±10 Pa. In the most critical cases (airtight building envelope with unbalanced ventilation), the air pressure difference across the building envelope may rise up to ±30 Pa. To control extremely high air pressure differences in airtight houses, balancing ventilation systems are very important. As in new low-energy houses the airtight building envelope and mechanical supply and exhaust ventilation become the standard solution; the interaction between HVAC systems and building envelope should be carefully designed. Practical application: Based on field measurements and computer simulations the design value of air pressure difference across the building envelope is determined for Finnish dwellings. Results underline the importance of balancing of ventilation in airtight house otherwise is not possible to control extremely high air pressure differences. If ventilation system should control the air pressure difference, building envelope should be airtight, because in normal and leaky houses (n50>41/h) the differences in ventilation airflows are too small and they have only a minor influence on the air pressure difference.

Study of a Rotary Vane Expander for the Transcritical CO2 Cycle—Part I: Experimental Investigation

This paper presents the experimental investigation of a double acting rotary vane expander for work recovery in the transcritical CO2 cycle and focuses on the design improvements for leakage and friction within the expander. The bench tests were carried out to investigate the leakage and friction distributions within the expander. The test results showed that the end gaps caused the major leakage within the improved expander prototype, while the friction losses associated with the vanes—especially due to the springs in the slots—were dominant and accounted for about 70% of the total friction losses. By comparing the pressure-rotation angle diagrams of the improved prototype with the original one, the effects of adding springs in the slots and arranging sealing vanes at the sealing arc on the thermodynamic processes were analyzed. It was shown that the tight contact between the vanes and cylinder wall owing to the springs had a significant improvement on the thermodynamic processes in that the cycle duration resumed being normal and the expander demonstrated a reasonable expansion process. By putting springs in the vane slots and arranging the sealing vane in the cylinder at the sealing arc, the volumetric efficiency increased from 17% to 30%, and the isentropic efficiency improved from 9% to 23%, resulting in a maximum coefficient of performance COP improvement of 14.2% compared with the throttling cycle under the same test conditions.

Advanced salicides for 0.10 μm CMOS: Co salicide processes with low diode leakage and Ti salicide processes with direct formation of low resistivity C54 TiSi2

The scaling of CMOS technologies to 0.10 μm and beyond imposes increasingly demanding constraints to self-aligned silicide (salicide) processes. For high performance devices, it is essential that salicide processes achieve low gate and source-drain sheet resistance as well as low silicide to source-drain diffusion contact resistance, and maintain low junction leakage. This becomes increasingly difficult as junction depths and linewidths are scaled. In this paper we present an overview of the development of advanced Ti and Co salicide processes, with implementations into a high performance 0.10 μm complementary metal-oxide-semiconductor (CMOS) technology. For Co salicide, the main scaling issue is diode leakage on shallow junctions. We show that the use of pre-amorphization implants or a pre-Co deposition sputter etch improves diode leakage distributions, but fails to eliminate high leakage outliers. Co deposition temperature and rapid thermal processing (RTP) variables were found to have a strong effect on diode leakage, with optimization of either one resulting in tight low leakage distributions on shallow junctions. For conventional Ti salicide processes, the main scaling issue is sheet resistance on narrow lines due to incomplete high resistivity C49 TiSi2 to low resistivity C54 TiSi2 transformation. We present X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) studies that indicate that direct growth of C54 TiSi2 bypassing the C49 phase is achieved at low temperatures on polycrystalline or amorphous Si with the addition of Mo impurities, eliminating the narrow line effect. The mechanism is demonstrated to be nucleation of MoSi2 and an unidentified phase at the Ti/Si interface, followed by epitaxial growth of C54 TiSi2 on these templates. Ti salicide processes with Mo impurities were evaluated, demonstrating an optimized one-step RTP process combining Mo and pre-amorphization implants that maintains low sheet resistance to 0.06 μm gate lengths. Successful implementations into a 0.10 μm flow were achieved both for optimized Co salicide or Ti salicide processes.

Indirect Estimation of Leakage Distribution in Steam Boiler Rotary Regenerators

Leakages are inherently associated with the heat transfer process in a rotary heat exchanger, owing to clearances brought about by construction difficulties and rotor-housing thermal distortions. The method proposed permits one to evaluate leakage distributions within steam boiler rotary regenerators. In principle, the method is based on a gas flow diagram of the regenerator, where gas streams are arranged into a network in which the corresponding mass flow rates are governed by pressure drops in the seals and matrix rotation. Moreover, energy and mass balances are taken into account where appropriate. On this basis, a nonlinear equation system modeling gas flows within the rotary regenerator is derived. Supplementing this system with data determined experimentally, one obtains a closed form of the gas flow problem, the solution of which gives particular gas mass flow rates within the regenerator and the leakage distribution resulting from it. On the basis of experiments carried out on real devices, the approach presented is exemplified with two particular cases accompanied by evaluation of uncertainties in the final results. A comparison of the results presented with those available by another method concludes the article.

Single-Zone Stack-Dominated Infiltration Modeling

Simplified, physical models for calculating infiltration in a single zone, usually calculate the air flows from the natural driving forces separately and then combine them. For most purposes -- especially minimum ventilation or energy considerations -- the stack effect dominates and total ventilation can be calculated by treating other effects (i.e., wind and small fans) as perturbations, using superposition techniques. The stack effect is caused by differences in density between indoor and outdoor air, normally attributable to the indoor-outdoor temperature difference. This report derives an exact, but practical, expression for calculating the stack effect from the air densities and leakage distribution using the power law formulation of envelope leakage. The neutral height -- the height at which there is no stack-related indoor-outdoor pressure difference -- is a key intermediate in stack modeling. This report defines a computable parameter called stack height, which contains all of the leakage distribution information necessary for estimating stack flows, thus freeing the model from specific assumptions (e.g., that the leakage is separable into evenly distributed floor, wall, and ceiling components). Example calculations including comparisons with other models, as well as validations using measured data from dwellings, are also presented. The dimensionless neutral level, which ismore » related to the neutral height, is often used as an indicator of leakage distribution and in superposition. Its definition and role in these regards are discussed in detail. The more exact formulation is then used to analyze the simple box cases normally assumed in infiltration modeling and other approximations. Measured ventilation data will be used to infer leakage distributions and neutral levels as well as for example calculations.« less