Efficient Envelope Research Articles

The Blue Lurker WOCS 14020: A Long-period Post-common-envelope Binary in M67 Originating from a Merger in a Triple System

Abstract We present Hubble Space Telescope far-ultraviolet (FUV) spectra of a blue lurker–white dwarf (BL–WD) binary system in the 4 Gyr open cluster M67. We fit the FUV spectrum of the WD, determining it is a C/O WD with a mass of 0.7 2 − 0.04 + 0.05 M ⊙ and a cooling age of ~400 Myr. This requires a WD progenitor of ~3 M ⊙, significantly larger than the current cluster turnoff mass of 1.3 M ⊙. We suggest the WD progenitor star formed several hundred megayears ago via the merger of two stars near the turnoff of the cluster. In this scenario, the original progenitor system was a hierarchical triple consisting of a close, near-equal-mass inner binary, with a tertiary companion with an orbit of a few thousand days. The WD is descended from the merged inner binary, and the original tertiary is now the observed BL. The likely formation scenario involves a common envelope while the WD progenitor is on the AGB, and thus the observed orbital period of 359 days requires an efficient common envelope ejection. The rapid rotation of the BL indicates it accreted some material during its evolution, perhaps via a wind prior to the common envelope. This system will likely undergo a second common envelope in the future and thus could result in a short-period double WD binary or merger of a 0.72 M ⊙ C/O WD and a 0.38 M ⊙ helium WD, making this a potential progenitor of an interesting transient such as a sub-Chandrasekhar Type Ia supernova.

Periplasmic Chaperones: Outer Membrane Biogenesis and Envelope Stress.

Envelope biogenesis and homeostasis in gram-negative bacteria are exceptionally intricate processes that require a multitude of periplasmic chaperones to ensure cellular survival. Remarkably, these chaperones perform diverse yet specialized functions entirely in the absence of external energy such as ATP, and as such have evolved sophisticated mechanisms by which their activities are regulated. In this article, we provide an overview of the predominant periplasmic chaperones that enable efficient outer membrane biogenesis and envelope homeostasis in Escherichia coli. We also discuss stress responses that act to combat unfolded protein stress within the cell envelope, highlighting the periplasmic chaperones involved and the mechanisms by which envelope homeostasis is restored.

Validation of 3D thermal simulations of the Double C Block, a novel composite masonry unit, using in-situ U-value measurements

Energy efficient building envelopes, particularly innovative prefabricated building components, can significantly contribute to lower the building industry energy-related emissions. In this research the composite masonry unit Double C Block (DCB) is quantitatively tested by means of three-dimensional thermal simulation validated by in-situ U-value measurements carried out in both summer and winter conditions.The simulations were enhanced by the experimental measurement of the dry thermo-physical material properties (specific heat capacity, thermal conductivity, and density) in laboratory conditions for both concrete and polyurethane. The samples were extracted from real-scale DCB prototypes. Furthermore, site-specific boundary conditions of Malta — representative a case study of a Mediterranean climate − were utilised in the simulations. Both laboratory and in-situ assessments of thermal transmittance, or U-value, had their uncertainty specified as part of the calculations.The validation exercise was performed by means of hourly recorded surface temperature and the selected indices were the root mean square error and mean absolute error. Results showed that these indices were within the recommended accuracy thresholds during both winter and summer assessments. For the hourly-based heat flux measurements, the mean bias error and coefficient of variation of the root mean square error were found lower than values reported in literature, thus supporting the robustness of the overall simulation outputs. Hence the 3D CVM simulation was experimentally validated by in-situ assessments.The convergence value of the experimental U-value provided respectively 1.51 ± 0.20 W/(m2K) (winter) and 1.44 ± 0.19 W/(m2K) (summer). Then, the validated 3D CVM model was adapted to calculate the theoretical U-value of DCB, using monthly values of recorded surface temperatures obtained by the test cells (in both seasons). The predicted thermal transmittance was of 1.47 W/(m2K), in both conditions, and this almost matches the above-mentioned experimental assessments and thresholds established in previous works.

Design of a positive energy district: A Nigerian case study

The potential of possible solutions for the design and implementation of a 50-house Positive Energy District (PED) in Southern Nigeria is presented in this study. Using a transient energy systems simulation software (TRNSYS 18), the energy demand of a typical building is estimated. Different passive design options considering building materials, window sizes, building orientation, roof ventilation are studied to determine the most energy efficient building envelope. TRNSYS and PVSyst (another energy simulation software), are also used to simulate the dynamics of a positive energy building and operation of solar energy systems used for electricity generation, domestic hot water heating and space cooling for Lagos weather conditions. In terms of electric energy balance, the total annual electricity demand is 598,000 kWh while the electricity generated by PV is 728,600 kWh in a year. As regards to site energy balance, annually, the district exports more electricity than it imports. The difference is 110,200 kWh. These results show that in such climatic conditions, despite economic poverty, it is possible to implement the modern PED principles. However, first, it is necessary to reduce energy consumption as much as possible, including solar passive solutions to the building architecture.

Controlling Thermal Bridging as a Value-Added Technique to Enhance Energy Efficient Building Envelopes

Controlling Thermal Bridging as a Value-Added Technique to Enhance Energy Efficient Building Envelopes

Wide Post-common Envelope Binaries from Gaia: Orbit Validation and Formation Models

Astrometry from Gaia DR3 has enabled the discovery of a sample of 3000+ binaries containing white dwarfs (WD) and main-sequence (MS) stars in relatively wide orbits, with orbital periods P orb = (100–1000) days. This population was not predicted by binary population synthesis models before Gaia and—if the Gaia orbits are robust—likely requires very efficient envelope ejection during common envelope evolution (CEE). To assess the reliability of the Gaia solutions, we measured multi-epoch radial velocities (RVs) of 31 WD+MS binary candidates with P orb = (40–300) days and AstroSpectroSB1 orbital solutions. We jointly fit the RVs and astrometry, allowing us to validate the Gaia solutions and tighten constraints on component masses. We find a high success rate for the Gaia solutions, with only 2 out of the 31 systems showing significant discrepancies between their Gaia orbital solutions and our RVs. Joint fitting of RVs and astrometry allows us to directly constrain the secondary-to-primary flux ratio S , and we find S≲0.02 for most objects, confirming the companions are indeed WDs. We tighten constraints on the binaries’ eccentricities, finding a median e ≈ 0.1. These eccentricities are much lower than those of normal MS+MS binaries at similar periods, but much higher than predicted for binaries formed via stable mass transfer. We present MESA single and binary evolution models to explore how the binaries may have formed. The orbits of most binaries in the sample can be produced through CEE that begins when the WD progenitor is an AGB star, corresponding to initial separations of 2–5 au. Roughly 50% of all post-common envelope binaries are predicted to have first interacted on the AGB, ending up in wide orbits like these systems.

Chemical composition of indoor and outdoor PM2.5 in the eastern Arabian Peninsula

Water-soluble and trace metal species in fine particulate matter (PM2.5) were determined for indoor and outdoor environments in Doha, Qatar. During the study period, PM2.5 concentrations showed significant variability across several indoor locations ranging from 7.1 to 75.8 μg m−3, while the outdoor mass concentration range was 34.7–154.4 µg m−3. The indoor and outdoor PM2.5 levels did not exhibit statistically significant correlation, suggesting efficient building envelope protection against outdoor PM2.5 pollution. Rather than outdoor sources, human activities such as cooking, cleaning, and smoking were the most significant influence on chemical composition of indoor PM2.5. NH4+ concentration was insufficient to neutralize SO42− indoors and outdoors, indicating the predominant presence of NH4HSO4. The enrichment factors indicated that outdoor Fe, Mn, Co, Cr, and Ni in PM2.5 mostly originated from crustal sources. In contrast, the remaining outdoor trace metals (Cu, Zn, As, Cd, Pb, and V) were mainly derived from anthropogenic sources. The indoor/outdoor concentration ratios revealed significant indoor sources for NH4+ and Cu. The crustal matter, water-soluble ions, and sea salt explained 42%, 21%, and 1% of the indoor PM2.5 mass, respectively. The same groups sequentially constituted 41%, 16%, and 1% of the outdoor PM2.5 mass.

Application of passive and active scenarios to a residential building in a dry and hot climate to achieve a positive energy building (PEB)

Designing a nearly zero energy building (NZEB) and more exclusively a positive energy building (PEB) hold significant importance these days. Achieving this objective requires an effective blend of renewable systems and the energy efficient envelope. This study focuses on a villa situated in the southeast of Kerman, Iran with hot and dry summers. Commencing with the current energy-efficient design of the structure, the research conducted various analyses to explore the impacts of different strategies or alternative approaches that contribute to achieving a NZEB or PEB. The parameters examined in the analysis that pertain to the building envelope, encompass insulation scenarios, window-to-wall ratio, and glass types as passive strategies, along with the integration of wind turbine energy production as an active energy solution. The findings indicate that, under hot and dry conditions in this region, the optimal passive strategies for the case study involve a 40 % window-to-wall ratio, polyurethane insulation, and triple-layered glass with argon. This combination results in a noteworthy reduction in total annual energy consumption, decreasing from 24,344.56 kWh to 11,909.64 kWh. To offset the remaining energy requirements and transform the building into a positive energy structure, a wind turbine was employed. This integrated approach not only aligns with the specific climatic conditions of the area but also demonstrates the feasibility of achieving a positive energy building which resulted in a surplus energy of 1,414.13 kWh.

Wide post-common envelope binaries containing ultramassive white dwarfs: evidence for efficient envelope ejection in massive asymptotic giant branch stars

ABSTRACT Post-common envelope binaries (PCEBs) containing a white dwarf (WD) and a main-sequence (MS) star can constrain the physics of common envelope evolution and calibrate binary evolution models. Most PCEBs studied to date have short orbital periods (Porb ≲ 1 d), implying relatively inefficient harnessing of binaries’ orbital energy for envelope expulsion. Here, we present follow-up observations of five binaries from 3rd data release of Gaia mission containing solar-type MS stars and probable ultramassive WDs ($M\gtrsim 1.2\ {\rm M}_{\odot}$) with significantly wider orbits than previously known PCEBs, Porb = 18–49 d. The WD masses are much higher than expected for systems formed via stable mass transfer at these periods, and their near-circular orbits suggest partial tidal circularization when the WD progenitors were giants. These properties strongly suggest that the binaries are PCEBs. Forming PCEBs at such wide separations requires highly efficient envelope ejection, and we find that the observed periods can only be explained if a significant fraction of the energy released when the envelope recombines goes into ejecting it. Our one-dimensional stellar models including recombination energy confirm prior predictions that a wide range of PCEB orbital periods, extending up to months or years, can potentially result from Roche lobe overflow of a luminous asymptotic giant branch (AGB) star. This evolutionary scenario may also explain the formation of several wide WD + MS binaries discovered via self-lensing, as well as a significant fraction of post-AGB binaries and barium stars.

A comprehensive review of the thermal performance in energy efficient building envelope incorporated with phase change materials

As the world's largest energy consumer, the building sector is under growing pressure to reduce energy consumption and CO2 emissions. To confront this challenge, the thermal performance of building elements, especially for cooling purposes, must be enhanced. One promising solution involves the incorporation of PCMs to augment a building's thermal mass. Unlike traditional building materials that store thermal energy sensibly, PCMs store it in a latent form by undergoing phase transitions at constant temperatures. This unique characteristic allows PCMs to store and release more heat efficiently than sensible heat thermal energy storage materials. As a result, PCMs have emerged as a prominent solution for passive cooling and heating applications in buildings. This paper proposes a systematic review of existing literature, classifying it based on building components and effective PCM integration methods while considering climatic influences. The primary objective is to comprehensively analyze the application of PCMs within building envelopes to enhance indoor thermal comfort. This study explores various methods for assessing the thermal properties of PCMs and PCM composites. Notably, integrating PCMs into building components like walls and roofs has shown remarkable potential in reducing energy consumption within the building envelope. This approach is precious in lightweight construction, where conventional passive design strategies may fall short. This study aims to bridge the existing research gap and provide valuable insights for designing energy-efficient buildings across diverse climates by systematically evaluating the impact of directly incorporating thermal energy storage systems into building components.

Techno-Economic Analysis of the Energy Resilience Performance of Energy-Efficient Buildings in a Cold Climate and Participation in the Flexibility Market

Unexpected power outages and extreme weather encouraged research on energy-resilient buildings throughout the world. Resilient building research mainly focuses on hot weather rather than cold extremes. This study defines resilience terminologies based on the available literature and discusses the impact of energy efficiency on energy resilience performance in energy-efficient buildings due to abrupt power outages in an extremely cold climate. The assessment involves the case simulation of a multistory apartment located in southern Finland at design outdoor conditions (−26 °C) in IDA-ICE 4.8, a dynamic building simulation software, and its techno-economic assessment to ensure building resilience for up to 7 days of power outages. The assessment shows the efficient building envelope can enhance the time taken by the building to drop the indoor temperature to the threshold by approximately 15%. Additionally, the efficient heating system along with the building envelope can reduce the instantaneous power demand by up to 5.3 times, peak power demand by up to 3.5 times, and on average power consumption by 3.9 times. Similarly, the study finds that the total energy requirement during a blackout can be reduced by 4.1 times. The study concludes that enhanced building resilience is associated with energy-efficient parameters such as an efficient energy system and an efficient building envelope that has low thermal losses and high thermal inertia retention. The batteries contribute the maximum proportion to the overall retrofitting cost, and the proportion can go up to 70% in baseline configurations and 77% in efficient configurations of buildings. The analysis concludes that the required investment varies largely with the technologies involved and the combination of components of these energy systems. The assessment finds that the high investment costs associated with batteries and battery recharging costs are the main bottlenecks to feasible flexibility in market participation.

Optimising Daylight and Ventilation Performance: A Building Envelope Design Methodology

The future of building envelope design lies in smart adaptation. The current literature overlooks the crucial integration of airflow, ventilation and daylighting in adaptive façade design. Moreover, it neglects the occupants’ locations, activities and interior layouts in this context. This study introduces an innovative approach to adaptive building envelope design, aiming to enhance occupants’ comfort through parametric analysis of daylight and airflow. The research combines parametric simulation, computational fluid dynamics (CFD) analysis and multiobjective optimisation. The optimisation goal is to improve visual comfort and indoor air quality while maintaining air temperature and velocity within the human comfort range. The study contributes to providing designers with a method for building envelope design that considers visual comfort and airflow, resulting in more interactive building envelopes that are adaptable to environmental conditions for enhanced utility and comfort. Results indicated that the optimised façade configuration and design methodology can achieve a 69% improvement in daylight performance, improving useful daylight illuminance (UDI) while reducing glare risk. Additionally, air changes per hour (ACH) showed a 38% annual improvement. This research signifies a significant step towards more efficient and occupant-centric building envelope design, aligning with the evolving demands of the construction industry and sustainable building practices.

Passive cooling strategies in summer for office buildings in temperate clear sky climates. Assessment of effectiveness with Zero Energy Building's criteria.

Abstract Passive energy efficient design in dry climates with high heliophany can lead to a significant reduction in energy use while promoting occupant comfort. This paper presents an optimization in the performance of an office building with mixed-mode run, including night ventilative cooling and shading devices strategies to achieve nZEB requirements in summer. The building design integrates an efficient envelope and renewable energy generation from PV panels on-grid. On-site measurements were taken to collect hygrothermal data and energy demand information. Two office configurations were discussed, Open plan (PL2) and Individual office (BOX NW), both options with a high trend to overheat. For all orientations tested, multiple horizontal overhangs have better performance than vertical ones. Results from Net Energy Balance in Base model present a primary energy demand of 116 kWh/m2/year and the Optimization model of 55 kWh/m2/year. To conclude, the positive impact of the implementation of passive design strategies rises the comfort hours in use period in PL2 70% and in BOX NW a 55% and a decrease of 60% of primary energy demand.

Spawn: coupling Modelica Buildings Library and EnergyPlus to enable new energy system and control applications

Spawn is DOE's next-generation tool chain for whole building energy control simulation. Spawn couples traditional imperative load-based envelope modelling with new equation-based modelling of HVAC and controls. Spawn uses EnergyPlus for the former and the Modelica Buildings Library for the latter. Because it leverages the Modelica Buildings Library, Spawn can evaluate advanced energy systems at the building and district scale, including new architectures and controls for heat pump systems with storage, and the coupling of such systems to electrical distribution networks. Spawn's Modelica integration likewise enables it to simulate realistic control sequences and therefore to bridge energy simulation and control implementation workflows. From EnergyPlus, Spawn inherits efficient envelope simulation and the ability to use existing envelope model authoring tools. This paper describes the architecture and implementation of Spawn, which automatically couples Modelica and EnergyPlus for run-time data exchange. This paper closes with examples that illustrate Spawn's modelling and simulation processes.

Organic cross-linking decreases the thermal conductivity of calcium silicate hydrates

We study the conductive heat transport through calcium silicate hydrate (C-S-H) and organically cross-linked C-S-H via experiments, micromechanical homogenization theory, and molecular simulations. We find that C-S-H's intrinsic thermal conductivity falls below its amorphous limit when cross-linked with short-chain organosilanes. The observed reduction correlates with the alkyl chain length of the bis-organosilane molecule. To understand the underlying fundamental molecular processes accountable for such a reduction, we construct realistic molecular structures of cross-linked C-S-H and validate them against the spectroscopic and pycnometery measurements. The atomistic simulations indicate that the reduction in the contribution of propagons (propagating heat carriers) and diffusons (diffusive heat carriers) to heat transport, and the amplification of locons (localized vibrational modes), are the main driving factors allowing to limit the heat conduction in C-S-H. Presented findings offer new potential directions to nanoengineering novel admixtures for cement composites and resilient lightweight cementitious mesostructures for thermally efficient building envelopes.

A trust-region-based phase envelope construction algorithm

Pressure-temperature (PT) and pressure-composition (Px) phase diagrams play an important role in various chemical and petroleum engineering applications. Lots of algorithms based on the Newton-Raphson method have been proposed to numerically construct PT/Px phase envelopes. No attempt is made to improve the computational efficiency of such Newton-Raphson solution method. This work develops a new trust-region-based algorithm to replace the Newton-Raphson method to provide more robust and efficient phase envelope construction calculations. We first convert the phase envelope construction problem into a minimization problem by defining a least-squares objective function. We then apply the trust-region optimization method with an exact subproblem solver to minimize the objective function. We follow the general strategy proposed by Michelsen (1980) to develop the revised phase envelope construction algorithm. We demonstrate the good performance of the trust-region-based algorithm by comparing it with the conventional Newton's method. The computational results indicate that the new trust-region-based algorithm is more robust and cost-effective than the Newton-based algorithm.

Monitoring and simulation-based optimization of two multi-apartment NZEBs with heat pump, solar thermal and PV

For achieving carbon neutrality, new buildings must be built according to very high-performance standards, such that their energy needs can be covered predominantly by onsite renewables. Although the technical solutions for efficient envelopes are well established, heat pumps together with PV have proven to be a reliable HVAC system, the discussion is ongoing regarding the optimal system concept and design for NZEB. Furthermore, the real performance strongly depends on the design, implementation, commissioning and operation. Given the complexity of building and HVAC with the influence of climate and users, a benchmark for optimal operation requires the combination of monitoring analysis and validated component and system models. Different steps and aspects of the calibration and optimization process are presented. The model, representing a step towards a digital twin, was used to improve the operation and derive guidelines for future optimal NZEB HVAC design, commissioning and operation for maximum primary energy savings. HIGHLIGHTS Integrated simulation-based design, commissioning and optimization of Net-zero energy residential buildings Calibrated component as well as building and HVAC system simulation models Simulation assisted commissioning and optimization leads to relevant energy savings NZE Multi-Apartment Buildings possible with optimized system design and control Monthly evaluation of primary energy highlights the need for reduced winter energy demand

Evaluation of energy efficient building envelope alternatives for sustainable cities

This study is aimed to create an exemplary project to present the contribution of the new buildings to energy savings when the residential buildings are transformed into green buildings. To create a sustainable built environment in residences, this study emphasizes that low-energy building strategies be combined with efficient and high-performance natural-sourced materials. Our findings show that using a natural-sourced material as the building envelope material has an impact on the use of primary energy and energy costs of the alternatives studied. In this study; In the case of replacing the building external wall components of an existing construction designed with internal insulation in the climatic conditions of Ankara, the change in energy performance has been investigated. The analysis was done with the help of BIM-based Revit Program and “Green buildings studio” where energy simulations were created. In the study, 54 different wall combinations were created by modeling combinations of different construction (porous, gas concrete, and pumice bricks), insulation (glass wool, rock wool, sheep wool, PUR, XPS, and EPS) and, roof (tile, asphalt shingle, and green roof) materials. When the outputs obtained from the analyzes were evaluated, the lowest energy consumption values were observed in the combination of pumice brick wall, green roof, and polyurethane insulation materials. In this scenario, the annual fuel consumption per square meter is determined as 30000.6 MJ/m2. On the other hand, the highest energy consumption values were observed in the combination of porous brick wall, tile roof and sheep wool insulation materials. In this scenario, the annual energy consumption per square meter is determined as 30026.6 MJ/m2. Although there are not high numerical differences between the findings, it has been observed that the results give consistent results with the thermal conductivity coefficients of the materials used in the combinations.

Assessment of the thermal energy flexibility of residential buildings with heat pumps under various electric tariff designs

With the electrification of the heating sector in Europe, there is increased pressure to reduce stress to the electric grid from increased demand. Understanding the flexibility potential of the current building stock, including both efficient buildings as well as less efficient buildings, will be vital to assess the efficacy of demand-side strategies such as time-varying pricing in enabling shifts in consumer heat demand.The aim of this study is to assess the thermal flexibility potential of residential buildings with electric heating under different tariffs, and the effect of these tariffs on heating expenditure and electricity consumption. To accomplish this, a resistance–capacitance heat demand model was integrated into a linear optimization model set to find the lowest cost heating schedule for a consumer under four different tariff designs.The results indicate that time-varying tariffs can be effective in enabling shifts in the heat consumption, although the additional cost savings due to the flexibility provided by an efficient building envelope is limited (1% to 4.65% additional reduction in cost savings). The results suggest that potential flexibility is price sensitive and a function of the alignment of price and heating demand. Measures such as capacity tariffs should be considered to avoid preheating surges.

Giants are bullies: How their growth influences systems of inner sub-Neptunes and super-Earths

Observational evidence points to an unexpected correlation between outer giant planets and inner sub-Neptunes, which has remained unexplained by simulations so far. We utilize N-body simulations including pebble and gas accretion as well as planetary migration to investigate how the gas accretion rates, which depend on the envelope opacity and the core mass, influence the formation of systems of inner sub-Neptunes and outer gas giants as well as the eccentricity distribution of the outer giant planets. We find that less efficient envelope contraction rates allow for a more efficient formation of systems with inner sub-Neptunes and outer gas giants. This is caused by the fact that the cores that formed in the inner disk are too small to effectively accrete large envelopes and only cores growing in the outer disk, where the cores are more massive due to the larger pebble isolation mass, can become giants. As a result, instabilities between the outer giant planets do not necessarily destroy the inner systems of sub-Neptunes unlike simulations with more efficient envelope contraction where giant planets can form closer in. Our simulations show that up to 50% of the systems of cold Jupiters could have inner sub-Neptunes, in agreement with observations. At the same time, our simulations show a good agreement with the eccentricity distribution of giant exoplanets, even though we find a slight mismatch to the mass and semi-major axes’ distributions. Synthetic transit observations of the inner systems (r < 0.7 AU) that formed in our simulations reveal an excellent match to the Kepler observations, where our simulations can especially match the period ratios of adjacent planet pairs. As a consequence, the breaking the chains model for super-Earth and sub-Neptune formation remains consistent with observations even when outer giant planets are present. However, simulations with outer giant planets produce more systems with mostly only one inner planet and with larger eccentricities, in contrast to simulations without outer giants. We thus predict that systems with truly single close-in planets are more likely to host outer gas giants. We consequently suggest radial velocity follow-up observations of systems of close-in transiting sub-Neptunes to understand if these inner sub-Neptunes are truly alone in the inner systems or not.