Heat Recovery Research Articles

Technical evaluation and life-cycle assessment of solid oxide co-electrolysis integration in biomass-to-liquid processes for sustainable aviation fuel production

Building upon prior research, this paper integrates solid oxide electrolysis (SOEL) into a Biomass-to-Liquid (BtL) process, facilitating the production of sustainable aviation fuel (SAF) through gasification, co-electrolysis, and Fischer-Tropsch synthesis. Two different integration concepts are developed: An inline integration resulting in a directly electrified-Biomass-to-Liquid (eBtL) process and a parallel integration for a Power-and-Biomass-to-Liquid (PBtL) process. To maximize process efficiency, the SOEL is operated under endothermic conditions with heat supply from syngas cooling after gasification. The developed processes allow for an increase in carbon efficiency up to about 61% to 94%. The electrolysis power required corresponds to electrification ratios of 0.32 to 0.83MWel/MWth. Compared to the conventional H2 addition in PBtL processes, electricity demand can be reduced by 13% to 29% when using co-electrolysis instead of water electrolysis. The resulting increase in energy yield and energy efficiency is because up to 17% of the SOEL’s energy demand can be substituted with heat in the electrified BtL processes. A life cycle analysis shows the absolute requirement to operate the process with renewable electricity to reduce indirect greenhouse gas emissions. A critical evaluation of the technological feasibility indicates further development requirements for the SOEL and the gasification heat recovery technology to enable the integration approach.

A novel hybrid battery thermal management system using TPMS structure and delayed cooling scheme

Phase change material (PCM) cooling plays an important role in battery thermal management systems (BTMS). However, PCM has been suffering from low thermal conductivity and inefficient latent heat recovery. Based on this, this study designs a hybrid BTMS combining triply periodic minimal surface (TPMS), PCM, and liquid cooling, and proposes a cooling scheme that determines the operating time of the coolant based on the battery temperature. The system aims to improve the utilization of PCM in two different ways: structural design and cooling scheme. Numerical analysis was used to compare the effects of different structures on the melting rate of PCM and to study the thermal performance of the battery module under various cooling schemes. The results show that the effective thermal conductivity of PCM/TPMS composites reaches 21 W/(m·K), which can effectively enhance the heat absorption rate of PCM. In particular, the I-graph-and-wrapped-package (IWP) structure combined with PCM is the most effective. Under the continuous cooling scheme, when the coolant flow rate is 0.04 m/s, the temperature of the battery at a 3C discharge rate can be controlled at 308.28 K, but the PCM utilization rate is only 0.25. After adopting the delayed cooling scheme, the performance of the BTMS cooling remains excellent, with the battery temperature at only 309.88 K and the liquid phase rate of PCM reaching 0.97. For the first time, the heat absorbed by passive cooling is comparable to that of active cooling in the BTMS heat absorption energy distribution, with a 73 % reduction in pumping energy consumption. Furthermore, under cycling conditions, the delayed cooling scheme still performs well, recovering all the latent heat from PCM and keeping the battery temperature below 313.15 K. In addition, it should be noted that the flow rate of the coolant should be determined by the charging rate. Additionally, the BTMS is capable of addressing the heat dissipation challenges in different ambient temperatures. This study can guide for the design of PCM in hybrid BTMS.

Impact of the type of heat exchanger on the characteristics of low-temperature thermoacoustic heat engines

Thermoacoustic technologies are considered an effective solution for harnessing low-temperature heat, whether from waste or renewable sources. However, in practice, developing and implementing high-performance thermoacoustic systems is a complex challenge. In real waste heat recovery systems, heat exchange between thermoacoustic engines (TAEs) and external heat sources is facilitated by auxiliary systems, such as circulation loops that include recuperative heat exchangers. It is evident that the upper power limit of a TAE is constrained by the thermal performance of its internal heat exchangers. This article investigates the energy transfer processes between the internal recuperative heat exchangers of a TAE and its matrix, and presents a mathematical model describing the interactions between the matrix and the heat exchangers. The model accounts for the effects of temperature inhomogeneities on the surface of the recuperative heat exchangers, which influence the temperature distribution within the TAE matrix. The use of liquid-gas recuperative heat exchangers in TAEs introduces temperature heterogeneity within the components of the thermoacoustic core. This study shows that such temperature variations can reduce the matrix gain factor for additional acoustic energy by a factor of 1.1 to 1.3. Therefore, when designing low-temperature thermoacoustic systems, it is essential to consider the type and characteristics of the heat exchangers used. The analysis indicates that recuperative heat exchangers can reduce the efficiency of thermoacoustic machines, whether they function as engines or refrigerators.

Monitoring the heating energy performance of a heat wheel in a direct expansion air handling unit

This study presents an on-site examination of the heating energy performance of a real ventilation system, running on the flat roof of a shopping complex building in Hungary. The main focus of this study is to delve into the heating energy efficiency of specific air handling elements, such as the air-to-air rotary heat wheel and the direct expansion heating coil supplied by a variable refrigerant volume outdoor unit under real operation conditions. Additionally, an investigation was carried out during the heating season to scrutinize the potential occurrence of CO2 transfer from the exhaust airflow to the supply airflow within the heat wheel, which issue highlights a notable limitation of the heat recovery system. Based on the monitored and measured data, the energy saving impact of the heat wheel was 20.5 % on the electric power consumption of the variable refrigerant volume outdoor unit throughout the entire heating period, compared to operation without heat wheel. Furthermore, the relative average of CO2 cross-contamination is recorded as 3.8 % in the investigated heating season.

Study on optimization of thermal injection parameters in fractured reservoirs of HDR

ABSTRACT To improve the heat recovery of hot dry rock (HDR) and realize the efficient and sustainable development of geothermal energy, it is necessary to analyse the factors affecting the heat recovery performance of HDR fractured reservoir. In this paper, a numerical model of heat recovery in fractured reservoirs with HDR is established. The effects of injection parameters on the heat recovery performance of the Enhanced Geothermal System (EGS) are compared and analysed by means of the average temperature, heat extraction rate, production temperature and heat recovery power of matrix rocks at different locations. The influence degree of injection flow rate and injection temperature on production temperature was analysed by grey correlation analysis method. The results showed that reducing the injection temperature is beneficial to fully extract the heat energy in the rock mass. The injection flow rate is positively correlated with the heat extraction rate and negatively correlated with the extraction temperature. In this simulation scheme, the optimal results are as follows: injection temperature is 298.15K, injection flow is 12 kg/s, and the influence of injection flow on production temperature is greater than that of injection temperature. This study provides a theoretical basis for the development and utilization of geothermal energy in HDR and provides a reference for the design of engineering operation parameters.

Phase change material performance in chamfered dual enclosures: Exploring the roles of geometry, inclination angles and heat flux

This study presents a comprehensive thermal performance analysis of phase change materials (PCMs) within a chamfered dual enclosures subjected to constant heat flux. Utilizing numerical simulations, we investigate the impact of various PCM types, inclination angles (α = 0°, 15°, 30°, 45°, 60°, 75°, 90°), and heat flux levels (Q = 500, 1000, 1500, 2000 W/m²) on melting rates, temperature distribution, and energy storage efficiency. The study examines commercially available PCMs, including RT-25, RT-27, RT-31, RT-35, RT-38, RT-42, RT-47, and RT-50. Our findings reveal that the inclination angle significantly influences thermal performance, with optimal performance observed at angles between 45° and 90° The PCM at 45° exhibited the fastest melting rate and demonstrating the highest energy storage efficiency. Among the PCMs, RT-27 showed the slowest temperature increase, while RT-50 exhibited the highest heat absorption efficiency and rapid temperature rise, making it suitable for applications requiring quick thermal management. Additionally, higher heat flux levels accelerated the phase transition process, with melting rates increases higher at 2000 W/m² compared to 500 W/m². The energy storage capacity varied, with RT-47 and RT-50 demonstrating the highest storage rates, while RT-27 was effective for sustained thermal energy release despite its slower phase change rate. This research bridges gaps in the existing literature by integrating various parameters and providing a holistic understanding of PCM behaviour in thermal energy storage systems. The insights gained from this study can inform the design and optimization of PCM-based thermal management solutions across various applications, including solar heating systems, electronic device cooling, and industrial waste heat recovery.

Performance prediction and manipulation strategy of a hybrid system based on tubular solid oxide fuel cell and annular thermoelectric generator

Abstract Tubular solid oxide fuel cells (TSOFCs) generate high-grade waste heat during operation, but the existing waste heat recovery technologies designed for flat solid oxide fuel cells cannot be directly applied to TSOFC due to the geometry mismatch. To efficient harvest the waste heat, a new geometry-matching hybrid system including TSOFC and annular thermoelectric generator (ATEG) is synergistically integrated to evaluate the performance upper limit. A mathematical model is formulated and verified to describe the hybrid system by considering various thermodynamic-electrochemical irreversible effects. Key performance indicators are established to assess the potential performance. Calculations show that the peak power density and corresponding efficiency of the proposed system are enhanced by 20.39 % and 13.89 %, respectively, compared to a standalone TSOFC. Furthermore, the exergy destruction rate is reduced by 7.04 %. Extensive sensitivity analyses indicate that higher operating temperatures enhance the system’s performance, while larger electrode tortuosity negatively affects it. Additionally, various optimization paths of ATEG are explored to improve the system performance, including considerations such as the number of thermocouples, leg radial width, leg thickness, or annular shape parameter. The three-objective optimization yields an efficient design solution for the entire system, offering valuable insights for its design and operation.

An Analysis of the Ventilation Efficiency of Various Configurations of Inlet and Outlet Vents in a Residential Building by CFD Simulation

Residential buildings in South Korea have equipped an energy recovery ventilation (ERV) system to improve energy efficiency as well as dilute indoor air pollution. While most studies have focused on the efficiency of energy exchange or the ventilation performance of the ERV itself, the ventilation performance can be improved by the proper location of inlet and outlet vents. For the present study, the ventilation performance of the inlet and outlet vents of the ERV was investigated by using CFD simulation. By varying the locations of inlet and outlet vents, the airflow distributions and the age of air were assessed. In addition, the air exchange effectiveness was analyzed by using the mean age of air quantitatively. As a result, a higher age of air was observed when inlet vents were moved to the center of the plan along the wall and an additional inlet or outlet vent was installed in the kitchen. In addition, the highest air exchange effectiveness was obtained when the inlet vents were located in the center of the plan along the wall. Considering the economic perspective, it is recommended to locate the inlet vents in the center to at least improve the ventilation performance.

Interface kinetic manipulation enabling efficient and reliable Mg3Sb2 thermoelectrics

Development of efficient and reliable thermoelectric generators is vital for the sustainable utilization of energy, yet interfacial losses and failures between the thermoelectric materials and the electrodes pose a significant obstacle. Existing approaches typically rely on thermodynamic equilibrium to obtain effective interfacial barrier layers, which underestimates the critical factors of interfacial reaction and diffusion kinetics. Here, we develop a desirable barrier layer by leveraging the distinct chemical reaction activities and diffusion behaviors during sintering and operation. Titanium foil is identified as a suitable barrier layer for Mg3Sb2-based thermoelectric materials due to the creation of a highly reactive ternary MgTiSb metastable phase during sintering, which then transforms to stable binary Ti-Sb alloys during operation. Additionally, titanium foil is advantageous due to its dense structure, affordability, and ease of manufacturing. The interfacial contact resistivity reaches below 5 μΩ·cm2, resulting in a Mg3Sb2-based module efficiency of up to 11% at a temperature difference of 440 K, which exceeds that of most state-of-the-art medium-temperature thermoelectric modules. Furthermore, the robust Ti foil/Mg3(Sb,Bi)2 joints endow Mg3Sb2-based single-legs as well as modules with negligible degradation over long-term thermal cycles, thereby paving the way for efficient and sustainable waste heat recovery applications.

Energy and exergy analysis of a new solar hybrid system for hydrogen, power and superheated steam production

This study investigates the amalgamation of solar tower technology and thermal energy storage (TES) within the framework of a supercritical carbon dioxide (S-CO2) Brayton cycle, a copper-chlorine (Cu-Cl) hydrogen production cycle, and a heat recovery steam generator (HRSG) to generate superheated steam. The various subsystems have been merged to enhance overall energy efficiency significantly, ensure uninterrupted operation, and minimize exergy loss. Energy and exergy analyses have been carried out to assess the prerequisites and effectiveness of each subsystem, highlighting the thermodynamic benefits of integration. Engineering Equation Solving Software (EES) was employed to solve the integrated system model and assess the thermodynamic properties provided by the EES library. Results showed that in the basic design mode, exergy destruction in the solar tower, S-CO2 Brayton cycle, and Cu-Cl cycle are 9930 kW, 7111 kW, and 9735 kW, respectively. The system produces 4226 kW of power, 2697 kW of heat, and 0.04971 kg/s of hydrogen. The overall energy and exergy efficiency of the power plant are 17.48 % and 18.72 %, respectively. These findings demonstrate that this integrated system can address key gaps in the literature by presenting a novel combination of solar power-driven Cu-Cl hydrogen production and superheated steam generation. The proposed system contributes to advancing renewable, efficient, and uninterrupted energy production.

Deterministic scenarios guided [formula omitted]-Adaptability in multistage robust optimization for energy management and cleaning scheduling of heat transfer process

The heat transfer process is of paramount importance for energy management and heat recovery, but the inevitable uncertain fouling poses significant challenges to sustainable energy-saving efforts. This study aims to solve the energy management and cleaning scheduling problems under fouling uncertainty. To achieve this, a novel multistage Robust Optimization (RO) method based on the Deterministic Scenarios Guided K-Adaptability (DSGKA) strategy is proposed. The process scheduling problem is initially tackled through long-period Mixed Integer Optimal Control Problems (MIOCPs) with deterministic scenarios. Subsequently, considering the slow transition characteristics of energy efficiency degradation caused by fouling, the candidate paths generation algorithm guided by deterministic MIOCPs is developed. Additionally, the K-Adaptability method is employed to segment decision-dependent uncertainty sets into finite partitions, facilitating the resolution of the multistage RO problem through worst-case analysis. In theory, the rationality of the proposed guidance algorithm is established. Simulation results on a heat exchanger network are also provided to demonstrate the effectiveness of the DSGKA scheme. By transforming the original multistage RO problem into a finite-dimensional optimization problem solvable with intelligent heuristic algorithms, the proposed method adeptly manages nonlinearity in constraint equations, thereby improving its applicability for equipment maintenance scheduling across various slow transition industrial processes.

Advanced Wastewater Treatment: Synergistic Integration of Reverse Electrodialysis with Electrochemical Degradation Driven by Low-Grade Heat

The reverse electrodialysis heat engine (REDHE) represents a transformative innovation that converts low-grade thermal energy into salinity gradient energy (SGE). This crucial form of energy powers reverse electrodialysis (RED) reactors, significantly changing wastewater treatment paradigms. This comprehensive review explores the forefront of this emerging field, offering a critical synthesis of key discoveries and theoretical foundations. This review begins with a summary of various oxidation degradation methods, including cathodic and anodic degradation processes, that can be integrated with RED technology. The degradation principles and characteristics of different RED wastewater treatment systems are also discussed. Then, this review examines the impact of several key operational parameters, degradation circulation modes, and multi-stage series systems on wastewater degradation performance and energy conversion efficiency in RED reactors. The analysis highlights the economic feasibility of using SGE derived from low-grade heat to power RED technology for wastewater treatment, offering the dual benefits of waste heat recovery and effective wastewater processing.

Simulation study of R1234ze and its mixed working medium in TEG‐ORC combined cycle

AbstractThermoelectric generation (TEG) and organic Rankine cycle (ORC) technologies both have their respective limitations in recovering waste heat from ships. However, the combination of TEG and ORC is an effective approach to achieve cascaded waste heat recovery and improve heat utilization efficiency. There has been some progress in research on waste heat recovery in maritime applications based on TEG‐ORC combined cycles. The selection of a working medium is a crucial element that directly influences the design and performance of the entire system, but there is limited research on the impact of different working fluids on combined cycle systems. In this study, a simulation model of a TEG‐ORC combined cycle system was established to examine its output potential using two different working fluids R1234ze and a mixture of R245fa/R1234ze. The results demonstrate that compared to employing the R1234ze working medium, the combined cycle system with the mixed working medium achieved a 13% increase in maximum output power, a 102% improvement in optimum thermal efficiency, and a 53% reduction in optimum power production cost. Additionally, the power output distribution in the system utilizing the mixed working fluid was more uniform compared to the system employing a single working medium. This confirms the great potential of using a mixed working fluid in a combined cycle system.

Comprehensive methodology for the integrating of the organic rankine Cycle-ORC with diesel generators in off-grid areas: Application to a Colombian case study

Efficient fuel management in diesel generator sets for power generation in non-grid areas is a persistent concern. In this context, the use of an Organic Rankine Cycle (ORC) to recover heat from exhaust gases from diesel generator sets represents a promising route for additional power generation. To undertake such projects, it is necessary to understand the critical parameters related to diesel engines, including the specific fuel consumption, mass flow, and exhaust gas temperature. These parameters are fundamental to the sizing process of the ORC heat recovery system. This study introduces an innovative methodology for evaluating the operation of diesel-ORC systems based on the load demand of off-grid communities. The proposed system is a viable solution for the generation of additional power with the objective of improving the overall efficiency and meeting higher energy demands in isolated areas. Four organic fluids were selected for the ORC: R245fa, benzene, cyclopentane, and toluene. This selection was made based on many criteria, including global warming potential (GWP), ozone depletion potential (ODP), and safety classification (ASHRAE 34). In addition, the exergy behaviors of these fluids were reviewed. A comparative analysis was subsequently conducted for a non-interconnected region of Colombia to evaluate the performance of a diesel generator operating independently and in conjunction with the diesel ORC system. The key indicators employed were fuel consumption savings (L/year), energy produced (MWh/year), levelized cost of energy (LCOE, USD/kWh), and payback period (years). The results demonstrated that, over the course of a 1-year simulation period, the benzene ORC system exhibited the highest overall energy efficiency, achieving a value of 41.38%. The exergy analysis indicated that toluene had lower irreversibilities, achieving an exergy efficiency of 44.78%, followed by benzene (43.5%. Furthermore, the diesel-ORC system using benzene demonstrated a notable decrease in the specific fuel consumption from 0.282 to 0.247 L/kWh, signifying a 10.52% reduction in the annual CO2eq emissions. The cost of electricity generation decreased by 4.3%, with investment payback periods not exceeding 14 years.

Analysis of airtightness performance of residential areas in Mediterranean climate: Balıkesir houses

Airtightness is one of the crucial physical characteristics of building envelope that affect the building thermal performance and energy consumption. The airtightness of the building is influenced by the quality of workmanship and various design parameters such as window/wall ratio, type of joinery, size of the usage area, wall material, and thermal insulation on the external wall. In this study aiming to determine the airtightness performance of buildings in the Mediterranean climate of Balıkesir houses, airtightness conditions of 43 different houses were determined by blower door test measurement. The air exchange rate (n50) values of 43 houses/residences were obtained between 1.94 and 49.02 h−1 and compared with the current various standards. The effect level of the design parameters on the air tightness of the building envelope was obtained as a result of the analysis performed with analysis of variance and post hoc methods. According to the analysis, joinery type was the most effective design parameter in terms of airtightness, followed by usage area and transparency of facades. The result will help in deciding on the design parameters affecting the airtightness of the building envelope for energy efficiency in the Mediterranean climate.

Increased risk of adverse events among patients with vs. without systemic autoimmune rheumatic disease prescribed sodium-glucose cotransporter 2 inhibitors: a retrospective cohort study.

Systemic autoimmune rheumatic disease (SARD) patients have been excluded from sodium-glucose cotransporter 2 inhibitor (SGLT2i) trials given putative risks, but this risk magnitude is unknown. We aimed to quantify SGLT2i adverse event risks among patients with vs. without SARD. METHODS: In a retrospective cohort study, patients with SARD at Mass General Brigham, a multihospital system in Boston, Massachusetts, prescribed SGLT2i were age-, self-reported race-, and sex-matched to patients prescribed the same SGLT2i between 1/1/2016 and 12/10/2021. Cumulative incidence and Cox models, overall and sex-stratified, estimated patient-reported adverse event risks from prescription date, censoring for discontinuation, death, or study end (12/12/2022). Four hundred sixty-eight SARD and 420 matched non-SARD patients were compared: mean age 64years (SD 11.3), 61% female, and 70% White. SARD patients had shorter SGLT2i use duration (8.4 vs. 12.7months; p < 0.0001) and time to adverse event (0.59 vs. 0.85years; p 0.04). Yeast infections (9.8% vs. 6.2%; p 0.047) and muscular symptoms (3.4% vs. 1.0%, p 0.01) were more prevalent among those with SARD. Adjusting for baseline demographics, adverse event risk was higher (MV HR 1.68;95% CI 1.28, 2.21), in patients with vs. without SARD. Risk was higher in women than men overall and in women with SARD vs. without (adjusted HR 1.86; 95% CI 1.36, 2.54). Patients with vs. without SARD had 68% higher adverse event risk with SGLT2i use. Women with vs. without SARD had > 85% higher adverse event risks, although most were not serious. Trials of safety and efficacy of SGLT2i among SARD patients are warranted. Key Points •To our knowledge, this is the first study to compare adverse events associated with SGLT2i utilization in patients with vs. without SARD, despite RCT exclusion and documented SGLT2i use in the population. •In our comparison of 468 patients with SARD and 420 patients without, we identified a greater than 65% increase in risk of adverse event outcomes among patients with SARD. •Furthermore, we found that this risk disproportionately affected female patients, with a 4.4-fold increased risk among women with SARD compared to men without.

Measurement and thermal characterization of graywater discharge events for house-central collection systems in the context of heat recovery

Measurement and thermal characterization of graywater discharge events for house-central collection systems in the context of heat recovery

OPTIMIZING HVAC EFFICIENCY AND RELIABILITY: A REVIEW OF MANAGEMENT STRATEGIES FOR COMMERCIAL AND INDUSTRIAL BUILDINGS

This study presents a comprehensive review of strategies to optimize HVAC systems in commercial and industrial buildings, focusing on enhancing energy efficiency, system reliability, and environmental sustainability. HVAC systems are major energy consumers, contributing significantly to operational costs in large buildings. With increasing energy costs, regulatory pressures, and the push for sustainability, technological advancements and management strategies have emerged to improve HVAC performance. Following PRISMA guidelines, this review analyzed 58 high-quality peer-reviewed studies published between 2010 and 2023. Key findings show that energy management systems (EMS) can reduce energy consumption by up to 30%, while Building Management Systems (BMS) enhance system reliability through centralized control and predictive maintenance. The adoption of eco-friendly refrigerants and energy-efficient designs, such as heat recovery and variable refrigerant flow (VRF) technologies, further lowers energy usage and environmental impact. Additionally, integrating renewable energy sources like solar and geothermal into HVAC systems can reduce energy consumption by as much as 40%. Green building certifications, such as LEED and BREEAM, drive the adoption of optimized HVAC technologies, delivering both environmental and financial benefits. This review underscores the crucial role of HVAC optimization in reducing energy consumption, lowering carbon footprints, and improving the operational performance of buildings, offering valuable insights for building managers, engineers, and policymakers.

A Study of Heat Recovery and Hydrogen Generation Systems for Methanol Engines

Biofuels are the most essential types of alternative fuels, which currently have significant potential to reduce CO2 emissions compared to fossil fuels. Methanol is a more efficient fuel than petrol due to its physicochemical properties, such as a higher latent heat of vaporization, research octane number, and heat of combustion of the fuel–air mixture. Also, biomethanol is cheaper than traditional petrol and diesel fuel for agricultural countries. The authors have proposed a new approach to improve the characteristics and efficiency of methanol diesel engines by using biomethanol mixed with hydrogen instead of pure biomethanol. Using a hydrogen–biomethanol mixture in modern engines is an effective method because hydrogen is a carbon-free, low-ignition, highest-flame-rate, high-octane fuel. A small quantity of hydrogen added to biomethanol and its combustion in an engine with a heat exchanger increases the combustion temperature and heat release, increases engine power, and reduces fuel consumption. This article presents experimental results of methanol combustion and a hydrogen-in-methanol mixture if hydrogen was retained due to the utilization of the heat of the exhaust gases. The tests were carried on a single-cylinder experimental engine with an injection of liquid methanol and gaseous hydrogen mixtures. The experiments showed that green hydrogen generated onboard the car due to the utilization of heat significantly reduced fuel costs of engines of vehicles and technological installations. It was established a hydrogen gaseous mixture addition of up to 5% by mass to methanol requires a corresponding change in the coefficient of excess air to λ = 1.25. Also, using an additional hydrogen mixture requires adjustment at the ignition moment in the direction of its decrease by 4–5 degrees of the engine crankshaft. Hydrogen gas mixture addition reduced methanol consumption, reaching a maximum reduction of 24%. The maximum increase in power was 30.5% based on experimental data. The reduction in the specified fuel consumption, obtained after experimental tests of the methanol research engine on the stand, can be implemented on the vehicle engines and technological installations equipped with an onboard heat recovery system. Such a system, due to the utilization of heat and the supply of additional hydrogen, can be implemented for engines that work on any alternative or traditional fuels.

Indoor Environment in Kindergartens Located in the North of Portugal: Evaluation of Thermal Comfort and Carbon Dioxide Concentration

Adequate school buildings are essential for the development of children, young people, and adolescents, as they must provide conditions that support their well-being and health. A healthy and comfortable indoor environment is critical for students’ performance in the learning process. This study aims to evaluate the indoor environment in kindergartens located in northern Portugal, with a primary focus on thermal comfort and indoor air quality. To achieve this, five buildings with varying construction characteristics were monitored, with temperature and relative humidity measurements taken in classrooms of different orientations over time. Additionally, the outdoor climate was also monitored. Based on the collected data, thermal comfort was evaluated using the adaptive model defined by the European standard EN 16798. Continuous monitoring of carbon dioxide concentration was also conducted in three of these buildings. The results reveal significant heterogeneity among the buildings, demonstrating the influence of construction characteristics on the interior thermal conditions. The recorded temperatures ranged from 10 °C to 27 °C, highlighting a substantial variability in performance across the different buildings. Particularly, the orientation and size of glazed openings, together with the lack of thermal insulation in the building envelope, especially in the roof, were found to have an important impact on the thermal comfort of the occupants. Furthermore, a relationship was observed between the daily maximum carbon dioxide concentration and the outdoor temperature, as a result of users’ efforts to minimize uncontrolled air infiltration, by limiting the opening of doors and windows, with consequences in the air exchange between the interior and exterior.