Search Results (66)

Buildings account for a substantial share of global energy consumption and greenhouse gas emissions, while a large proportion of the existing building stock remains energy inefficient. Thermal transmittance is a fundamental indicator for assessing the thermal performance of historic building envelopes. This study investigates the application of UAV-based quantitative infrared thermography (UAV-QIRT) for in situ U-value measurement as an alternative to conventional methods. This study proposes a structured workflow for UAV-QIRT-based U-value measurement, developed in accordance with BS EN ISO 6781-1:2023. The study evaluates four U-value calculation formulas using thermographic data acquired during an in situ case study and compares the resulting estimates with a reference U-value obtained using the heat flow meter (HFM) method. The results demonstrate that the reliability of UAV-QIRT-based U-value estimation strongly depends on outdoor thermal boundary conditions and the physical assumptions embedded within the heat balance model. In this case, the measured exterior wall surface temperature was lower than the outdoor air temperature, causing simplified formulas to produce physically unrealistic negative U-values. In contrast, the complete heat balance model, which accounts for radiative exchanges with the sky, surroundings, and ground, as well as convective heat transfer, generated more plausible estimates. Nevertheless, significant discrepancies were observed between the UAV-QIRT and HFM estimates. Sensitivity analysis revealed a high dependence of UAV-QIRT-derived U-values on environmental boundary conditions, including wind speed, outdoor air temperature, and exterior surface temperature. Full article

Accurate knowledge of the thermal transmittance (U-value) of existing building envelopes is essential for reliable energy performance assessment and the planning of energy-efficient refurbishment measures. However, in practice, the material composition of existing walls is often unknown, and installing measurement devices may be restricted due to limited accessibility, the risk of structural damage, or varying on-site boundary conditions. Although several in situ methods for determining the U-value have been proposed in the literature, systematic comparisons of their performance under real environmental conditions remain limited. This lack of comparative evaluation makes it difficult to select the most appropriate method under specific practical constraints. To address this gap, this study presents a comprehensive experimental comparison of four in situ U-value measurement methods applied simultaneously to the same building element under identical real boundary conditions, providing new insights into their accuracy, uncertainty, and practical applicability. In this study, four in situ techniques commonly used to determine the thermal transmittance (U-value) were tested on a double-leaf brick wall at the University of Stuttgart: heat flow meter (HFM), infrared thermography (IRT), infrared thermometer (IRTM), and thermometric method (THM). The measurements were carried out over several days under real boundary conditions, during which air temperature, surface temperature, and heat flux were recorded at regular intervals. The results show that all four techniques can be reliably used under real boundary conditions, with the measured U-values lying within a comparable range. Differences among the methods were observed, largely due to their varying sensitivity to environmental influences and sensor placement. A comparison between the upper and lower parts of the wall indicated that its thermal response is non-uniform, and the observed deviations can be attributed to its inhomogeneous structure. By outlining the strengths and limitations of each technique and comparing their measurement outcomes, this study provides practical guidance for selecting suitable approaches for in situ U-value determination. Furthermore, the findings support future efforts to refine thermal evaluation methods and improve energy performance in existing buildings. Full article

Accurate thermal characterization of building insulation materials is essential for reliable energy performance assessment, regulatory compliance, and the development of high-performance envelopes. On one hand, the growing adoption of innovative insulating products, such as nanoporous materials, aerogel-based composites, bio-based panels, and thin insulating coatings, helps to enhance buildings’ energy efficiency by means of sustainable raw materials. On the other hand, conventional measurement techniques encounter significant challenges, due to their heterogeneity, reduced thickness, and unconventional geometries. In this study, an intra-laboratory comparison of three widely used methods for thermal conductivity determination is presented: the Transient Plane Source (TPS, Hot Disk) method, the Guarded Hot Plate (GHP) method, and the Heat Flow Meter (HFM) method. A total of twelve insulating materials, spanning super-insulating cores, insulating renders, bio-based panels, and nanocomposite coatings, were experimentally characterized under controlled laboratory conditions. A view on the analyzed insulating materials’ cradle-to-grave environmental impact is also given, to enhance the users’ awareness for the highly informed choice. The results highlight systematic differences between transient and steady-state approaches, with TPS measurements generally exhibiting larger deviations for materials characterized by surface roughness, limited thickness, or strong internal heterogeneity. In contrast, GHP and HFM methods show closer agreement when specimen geometry and stabilization requirements are satisfied. The influence of contact resistance, probing depth, specimen preparation, and uncertainty propagation is critically analyzed for each technique. The study provides practical insights into the applicability limits of commonly used thermal characterization methods and emphasizes the importance of selecting measurement techniques in relation to material morphology and testing constraints. These findings support more reliable thermal property assessment of emerging insulation materials and contribute to improved consistency between laboratory measurements and energy performance evaluations for buildings. Full article

Improving the energy efficiency of the building envelope is critical for global decarbonization, yet a gap remains in the comprehensive thermophysical characterization of carbon-enhanced Expanded Polystyrene (EPS). This study evaluates the impact of expansion ratios and moisture content on the thermal behavior of two commercial EPS grades, EPS-A (12.7 ± 0.5 kg/m³) and EPS-B (16.0 ± 1.1 kg/m³), investigating the counterintuitive role of graphite (1.4–1.8 wt.%) in enhancing the thermal insulation properties. Thermal conductivity and diffusivity were independently determined via Transient Plane Source (TPS) and Heat Flow Meter (HFM) methods across a 10–50 °C range, while specific heat capacity (c_p) was analyzed using HFM and Differential Scanning Calorimetry (DSC) through the sapphire comparison method and Temperature-Modulated DSC (TOPEM^®). Methodologically, it was found that standard HFM protocols are unsuitable for c_p determination in low-density foams, yielding an average relative error of ±29%; conversely, the sapphire comparison method provided the most reliable results in agreement with theoretical expectations. Results indicate that the efficacy of graphite as a radiative shield is closely coupled with cellular morphology, proving significantly more effective in the higher expansion grade (EPS-A, 70 wt.% open porosity) than in the denser EPS-B. Furthermore, 30-day water immersion tests revealed that the higher open porosity of EPS-A facilitates increased water uptake of 144 ± 17 wt.% (compared to 97 ± 7 wt.% for EPS-B), causing the geometric densities of the two grades to converge and fundamentally altering thermal transport mechanisms. The study concludes that accurate thermal modeling of carbon-enhanced insulation requires careful selection of testing parameters, particularly when accounting for moisture-induced degradation in high-porosity systems. Full article

This paper presents a pressure-driven liquid transfer system for laboratory automation, along with a physics-based model and calibration method. The device maintains near-isothermal transport by storing reagents at a prescribed temperature and routing the flow through a single PTFE tube enclosed within a heated jacket. The pressure-drop model accounts for temperature-dependent viscosity and the thermal expansion of PTFE. Residual deviations from the no-slip prediction in submillimeter tubing are represented by an effective slip length, which is identified through linear regression. This parameter is subsequently used to calculate the pressure required to achieve a target flow rate. Experimental results compare unheated and heated operating conditions and characterize the dependence of slip length on temperature and flow rate. Under heated operation with slip-compensated pressure commands, the system achieved dispensing accuracy within $\pm 4\%$ over the tested range, whereas unheated operation exhibited larger errors due to axial temperature gradients. These results demonstrate that effective thermal management and slip compensation are critical for accurate pressure-based metering under temperature-sensitive conditions, as validated using water-based tests. Full article

This study aims to improve the operational efficiency of district heating (DH) systems by introducing a novel control method based on variable flow rate control, without compromising indoor comfort. The novelty of this work lies in its integrated analysis of flow control and substation configurations in DH networks, linking real-world operational strategies with mathematical modeling to improve energy efficiency and infrastructure costs. Using a case study from Omsk, Russia, where supply temperatures and energy demand profiles are traditionally rigid, the proposed approach utilizes operational data, including outdoor temperature, supply/return temperature, and hourly consumption patterns, to optimize heat delivery. A combination of flow rate adjustments, bypass line implementation, and selective control strategies for transitional seasons (fall and spring) was modeled and analyzed. The methodology integrates heat meter data, indoor temperature tracking, and Supervisory Control and Data Acquisition (SCADA)-like system inputs to dynamically adapt supply temperatures while avoiding overheating and reducing distribution losses. The results show a significant reduction in excess heat supply during warm days, with improvements in heat demand prediction accuracy (17.3% average error) compared to standard models. Notably, the optimized configuration led to a 21% reduction in total greenhouse gas (GHG) emissions (including 6537 tons of CO₂ annually), a 55.3% decrease in annualized operational costs, and a positive net present value (NPV) by year nine, with an internal rate of return (IRR) of 25.4%. Compared to conventional scenarios, the proposed solution offers better economic performance without requiring extensive infrastructure upgrades. These findings demonstrate that flexible, data-driven DH control is a feasible and sustainable alternative for aging networks in cold-climate regions. Full article

In energy transition scenarios, hydropower remains the largest source of renewable electricity generation. However, with respect to other means of renewable energy exploitation, like wind turbines or photovoltaics, very few technological advancements are to be expected, due to the technological maturity of hydropower turbines. Therefore, an increase in power production of hydropower plants can only be possible thanks to an optimization of the operation and maintenance policies, leading to improved performance, reducing energy losses and downtimes. This work proposes a practical approach to the continuous monitoring of the operational conditions of hydropower plants through the non-invasive measurement of the electrical efficiency of the generator group. To achieve this, a heat-loss based method is introduced, which enables the measurement of both the electrical generator losses and the electrical input power, along with their associated uncertainties. This method is applicable for plants of any size, does not require a production shutdown, and, since it is applied to the electrical generator, can be used with different turbine types, including Kaplan, Francis, and Pelton. It also relies on relatively simple instruments such as thermo-cameras, thermo-resistances, thermo-couples, and flow meters to measure key variables, including cooling water inlet and outlet temperatures, electrical machine external and frame temperatures, undisturbed ambient temperature, electrical power absorbed, and cooling water flow rate. The proposed methodology has been tested and validated through the application to a laboratory test rig. In all test conditions, the heat loss-based method showed a smaller relative error than the standard efficiency measurement methods. Full article

Metered dose inhalers (MDIs) play a crucial role in managing respiratory diseases, but their effectiveness depends on whether the intended dose is delivered to the target, which can be influenced by various factors. Accurate assessment of MDI performance is crucial for optimizing MDI delivery and ensuring drug efficacy. This study numerically examined the role of evaporation dynamics and dosimetry methods in assessing the efficiency of MDI delivery to different regions in a mouth–lung model extending to the eleventh generation (G11) of lung bifurcations. The experimentally determined spray exit speed, applied dose, and droplet size distribution were implemented as the initial/boundary conditions. Large eddy simulations (LES) were used to resolve the transient inhalation flows, and a chemical species model was applied to simulate vapor and temperature variations in the airflow. A multi-component model was used to consider the heat and mass transfer between the droplets and the airflow. The model was validated against literature data and applied to evaluate the impact of evaporation on pulmonary drug delivery using MDI, in comparison to inert particles. Three methods were used to quantify deposition, which were based on the droplet count, the droplet mass, and the drug carried by the droplets. The results demonstrate that evaporation notably alters the spray droplet size distribution and subsequent deposition patterns. Compared to inert particles, evaporation led to significantly more droplets ranging from 1–5 µm entering the pulmonary region. For a given region, large discrepancies were observed in the deposition fraction (DF) using different dosimetry methods. In the lower lung, the count-based DF (33.9%) and mass-based DF (2.4%) differed by more than one order of magnitude, while the drug-based DF fell between them (20.5%). This large difference highlights the need to include evaporation in predictive dosimetry, as well as to use the appropriate method to quantify the delivery efficiency of evaporating droplets. Full article

Quantitative infrared thermography (QIRT) has emerged as a prominent topic within the field of thermal performance testing of building enclosures. The majority of the previous research has been conducted in Europe and North America, with limited research activity in Asia. Against the backdrop of China’s carbon emission reduction goals, quantitative infrared thermography offers a promising avenue for advancing building energy efficiency testing. This study conducted QIRT testing on three buildings with different insulation capabilities (old buildings, conventional insulated buildings, nearly zero-energy buildings) in Shenyang, China. The objective was to assess the efficacy of the internal QIRT method for walls with varying insulation capabilities and to ascertain the requisite testing environment parameters in the context of China’s climatic conditions and building regulations. The heat flow meter method was employed to verify its accuracy. Furthermore, correlation analysis was conducted on various testing parameters across different building cases and temperature-difference ranges. The results indicate that walls with different insulation capabilities require corresponding indoor–outdoor temperature differentials to establish a stable heat flow environment. For uninsulated buildings, a temperature difference of 10 °C between indoor and outdoor environments is sufficient to meet testing requirements, with a testing error of only 2.28%. For conventionally insulated buildings, a temperature difference greater than 20 °C reduces the relative error to below 10%. For nearly zero-energy buildings, it is recommended to maintain a temperature difference of 25 °C or higher to achieve optimal testing results. Once a stable thermal flow environment has been achieved, the variation in the instantaneous heat transfer coefficient maintains a high correlation with the temperatures recorded at various measurement points. For buildings with high insulation performance, high temperature-difference environments pose higher demands on the testing procedures and data collection using the QIRT method. During the testing process, it is essential to monitor changes in outdoor air temperature, enhance the accuracy of infrared thermography, and avoid interference from indoor radiation sources. Full article

The study aims to address the need for cleaner and more efficient combustion technologies in the context of global energy demand and sustainability goals. It focuses on microflame techniques to enhance the performance of gas turbines and water heating boilers. This research investigated, for the first time, the operation of a micromodular burner for hot water boilers and a microflame burner for gas turbines, based on patented inventions. Methods for assessing efficiency included analyzing heat flows, fuel conversion rates to thermal energy, and emission analysis. Using high-precision measuring equipment, such as TESTO 350-XL, thermocouples, flow meters, and others, optimal operating modes were determined for the gas turbine combustion chamber and hot water boiler. This resulted in achieving high efficiency and reducing harmful emission levels (NO_x < 15 ppm, CO < 140 ppm). Theoretical calculations were compared with experimental data, confirming the reliability of the results obtained. Full article

In the context of remodeling old buildings, enhancing insulation performance in the exterior skin necessitates an accurate assessment of a wall’s thermal performance. The conventional method for determining the thermal transmittance (U-value) of a wall is the heat flow meter (HFM) as outlined in the ISO 9869-1. However, this measurement is susceptible to errors influenced by indoor and outdoor environmental conditions and the wall’s material composition. This study evaluates the U-value of an internally insulated wall, specifically constructed for this purpose, utilizing both the average and dynamic methodologies of an HFM. Furthermore, it introduces a novel estimation method: the extended average method (EXAM). The effectiveness of this proposed method is ascertained by comparing the accuracy and convergence of the U-value estimations with those derived from existing methodologies. Additionally, the study explores the limitations of the HFM by analyzing the heat flow traversing the interior of a wall. The findings revealed that the EXAM method enhanced the precision of U-value estimation in all scenarios. Particularly, in walls with superior insulation, the HFM tended to underestimate the heat flow observed indoors, leading to negative errors. The EXAM method, incorporating considerations of both insulation and structural materials, offers an accurate in situ measurement of the U-value relative to the HFM. Full article

The accurate evaluation of the thermal performance of building envelope components (e.g., facade walls) is crucial for the reliable evaluation of their energy efficiency. There are several methods available to quantify their thermal resistance, such as analytical formulations (e.g., ISO 6946 simplified calculation method), numerical simulations (e.g., using finite element method), experimental measurements under lab-controlled conditions or in situ. Regarding measurements, when using the heat flow meter (HFM) method, very often, the measured value is based on surface conditions (e.g., temperature and heat flux), achieving in this way the so-called surface-to-surface or conductive thermal resistance ($R_{cond}$). When the building components are made of homogeneous layers, their $R_{cond}$ values are constant, regardless of their internal and external surface boundary conditions. However, whenever this element is composed of inhomogeneous layers, such as in lightweight steel-framed (LSF) walls, their $R_{cond}$ values are no longer constant, depending on their thermal surface resistance. In the literature, such systematic research into how these $R_{cond}$ values vary is not available. In this study, the values of four LSF walls were computed, with different levels of thermal conductivity inhomogeneity, making use of four finite elements’ numerical simulation tools. Six external thermal surface resistances ($R_{\mathrm{s}\mathrm{e}}$) were modelled, ranging from 0.00 up to 0.20 m²·K/W. The average temperature of the partition LSF walls is 15 °C, while for the facade LSF walls it is 10 °C. It was found that the accuracy values of all evaluated numerical software are very high and similar, the $R_{cond}$ values being nearly constant for walls with homogeneous layers, as expected. However, the variation in the $R_{cond}$ value depends on the level of inhomogeneity in the LSF wall layers, increasing up to 8%, i.e., +0.123 m²·K/W, for the evaluated $R_{\mathrm{s}\mathrm{e}}$ values. Full article

This paper presents a design study focusing on the thermal safety of an induction motor integrated with a pump unit, which operates submerged in liquefied natural gas (LNG) in the LNG tanks of LNG carrier ships ranging from 150 K to 200 K cubic meters (CBM). In this study, we carried out the electromagnetic design of the induction motor and verified the thermal safety against a temperature increase due to losses during the motor operation through thermal fluid analysis, taking into account the discharge flow of the emergency pump and the air gap of the motor. In the electromagnetic design, the resistivity of the stator winding copper conductors and the rotor aluminum bars, which act as important design constants for the rated operating and starting characteristics of the induction motor in cryogenic temperature environments, reflects the characteristic of linearly changing with the temperature. In cryogenic environments, the reduction in the resistance of the rotor bars of the induction motor leads to a decrease in the starting torque characteristics. Therefore, the shape optimization design of the rotor bar was performed to improve the starting torque characteristics, and 2D electromagnetic analysis was performed on the magnetic flux density distribution and magnetic saturation using Ansys Electromagnetics 16.0. After the electromagnetic design, a 3D thermal flow analysis was conducted using Ansys Fluent 17.0, considering the stator iron losses, rotor bar losses, stator and rotor iron losses, and stray load losses as heat sources. The flow analysis aimed to analytically verify the thermal safety concerning the vaporization of the LNG flowing through the emergency pump’s discharge flow path and the motor’s internal air gap. The motor was manufactured, and the rated and starting operating characteristics of the motor were measured under LN2 submerged conditions according to the IEEE 112 F1 method, to validate whether the performance characteristics met the specifications’ requirements. Subsequently, the thermal safety of the motor was finally verified through a temperature increase test under LNG submerged conditions after assembling it with the emergency pump. Full article

The heat flow meter method (HFM) is one of the most-used methods for the in situ measurement of wall thermal resistance. However, the standard HFM method has some issues: it is challenging to balance simplicity and accuracy in data analysis and the measurement period needs to be shorter. In this paper, a new dynamic data analysis method for the in situ measurement of wall thermal resistance is introduced, which is based on a truncated form of the infinite response factors for a wall heat conduction process and has a theoretically deducted convergence criteria for the automatic termination of an in situ measurement. The efficacy of the proposed method is validated by a theoretical analysis and by experiments from one simulation dataset and one measurement dataset. Preliminary experimental results show that the proposed method can reduce the measurement time by about one-third on average while maintaining the same accuracy as the standard average method. Due to the advantages of a clear physical meaning, a simple principle, and a short measurement period, the proposed method contributes to the quick and accurate estimation of the wall thermal resistance in buildings. Full article

Accurate and rapid in situ measurements of the thermal resistance (R-value) of building envelopes are necessary for assessing planned performance and identifying appropriate retrofitting strategies. Although there are several approaches for in situ R-value estimation, the average method of ISO 9869-1 based on the heat flow meter method is the most widely used. However, discrepancies between theoretical and in situ R-values are frequently reported in many studies that employ this method. This study aimed to investigate the cause of this discrepancy in estimating in situ R-values of highly insulated building walls using the average method of ISO 9869-1 by conducting long-term experiments. This study was made possible due to a specially constructed test wall wherein more sensors were installed than are required by the ISO 9869-1 standard. The findings showed that discrepancies between heat fluxes on the internal surface and heat passing through the wall is the main cause of the error in in situ R-value estimation. Measurement results from winter showed that deviation from the theoretical R-value was 9.12% for the average method and 0.6% for the extended average method, determined by additionally using the temperature and heat flux inside the wall. Full article