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To address the United Nation's sustainable development goal of clean energy, new concepts are required to utilize renewable energy efficiently in buildings. One of the barriers against building-integrated solar thermal systems is the diluted outlet temperatures in winter, corresponding to large demand magnitudes. This study proposes a new design of an integrated and double-insulated active heating wall system, comprising an unglazed solar collector and a low-temperature radiant heating terminal. A hybrid resolution quasi-dynamic finite element model is developed, validated, and then used to test the system performance in a typical cold climate zone. The results suggest achievable daylight average heating capacities up to 60.82 W m−2 and demonstrate a passive heating effect during nighttime hours when the water circulation is disabled. At low flow rates of ~ 0.03 kg s−1, the pumping power is discardable, and the energy performance index reaches 3.1 × 105. The performance of the system is especially enhanced during days with mildly cold temperatures and partially cloudy skies, as well as when the indoor setpoint temperature is reduced. Besides, the integrated wall remarkably reverses the heat transfer direction and offsets thermal losses (up to ~ 21.2 W m−2) during nighttime hours, compared to a plain wall. The cost savings of the system are approximately 16.97 EUR m−2, with a payback period of 5.53 years. [ABSTRACT FROM AUTHOR]

The city of Amsterdam has ambitious goals to achieve a 95% reduction in carbon emissions by 2050 and to phase out natural gas by 2040. Disconnecting the building stock from natural gas requires well-ventilated and well-insulated buildings and a switch to renewable energy sources, making optimal use of heat pumps and sustainable heating solutions available locally. Most buildings in the historical city centre are protected and often insufficiently insulated, leading to increased energy use and a poor thermal environment. Standard retrofitting interventions may be restricted, requiring new approaches to balancing the need for energy efficiency and the preservation of heritage significance. With the case of the Amsterdam City Centre, the goal of this research is to present a parametric modelling approach for energy retrofitting heritage buildings and to identify minimum requirements for preparing the residential stock to lower temperature heat (LTH). Using parametric design and bottom-up energy modelling, the research estimates that a 69.1% of natural gas reduction could be achieved when upgrading the buildings to lower temperature (LT). Results of this paper also demonstrate how the applied approach can be used to guide decisions on the improvement in energy performance of the historic built environment. [ABSTRACT FROM AUTHOR]

Forced convection is the most effective way to improve the thermal efficiency of a radiator under low-temperature conditions. This technical method differs significantly from the heating effects of general radiation and natural convection. Few studies have applied the objective evaluation method based on quantitative calculation to evaluate the effectiveness of indoor heating or optimize the technical parameters (air flow rate, air supply method, etc.) of heating systems. This article couples human metabolic factors with heating environmental factors and uses a 57-node human thermal physiological model to evaluate the effectiveness of forced convection radiator heating from the perspective of the local thermal comfort of the human body and demonstrates the feasibility of this scheme by comparing it with floor radiation heating. The research shows that the air supply speed of a radiator affects human thermal comfort. Continuing to increase the wind speed, at a speed of 3 m/s, the surface temperature of the human body reaches a high value and will then decrease, leading to a decrease in thermal comfort. Research on indoor air distribution shows that the use of bottom-side air supply provides better thermal comfort compared to top air supply. The local skin temperature distribution of the human body indicates that when the indoor average temperature is higher than 20 °C, the overall thermal comfort of convective radiator heating and floor radiant heating is comparable. The article provides a way of objectively calculating and directly quantifying the effect of heating equipment on human thermal physiological parameters. [ABSTRACT FROM AUTHOR]

Gem-quality rubies and sapphires are often commercially heat treated at about 800 °C or higher to enhance their color and clarity, and hence quality. For this study, selected corundum samples containing diaspore and goethite inclusions were heated step-by-step to a maximum of 1000 °C with the aim of monitoring the dehydration and phase transformation of these oxyhydroxides to corundum and hematite during heating. Based on our experiments and in agreement with the literature, the dehydration of diaspore in corundum occurs between 525 and 550 °C, whereas goethite transforms to hematite between 300 and 325 °C. As both diaspore and goethite may be present as inclusions in rubies, sapphires, and other corundum varieties (e.g., pink sapphires, padparadscha), these dehydration reactions and phase transformations can be considered important criteria to separate unheated from heated stones, specifically in cases in which other methods (e.g., microscopy, FTIR) are unsuccessful. [ABSTRACT FROM AUTHOR]

The German government's ambitious goal of achieving CO2 neutrality by 2045 has prompted a focus on improving building insulation as a vital step toward energy efficiency. However, in this process, existing radiators and boilers are often left unchanged. Moreover, during the construction of buildings, heating systems are often designed with excess capacity to ensure there is no risk of insufficient heat supply during operation. This research presents various approaches to reduce the required radiator supply temperature, utilizing data from a study conducted in 100 multifamily buildings. The approaches encompass reducing the heat reserve, shifting the heat output, optimizing radiator utilization, and conducting heat demand analysis. The findings reveal that in pre-existing buildings equipped with radiators, it is possible to significantly lower supply temperatures without affecting the indoor temperature. Applied on the seed, reducing the heat reserve could reduce the median temperature by 18.5 K, thus curtailed by the most utilized radiator in the median to 7 K. Furthermore, the heat demand analysis showed that the consumption could decrease in the median by 13%, the peaks in median even by 29%. While each approach is analyzed individually, their combined implementation has the potential to considerably enhance the efficiency of water-to-water heat pumps, thanks to the reduced requirement for high supply temperatures. [ABSTRACT FROM AUTHOR]

The city of Amsterdam has ambitious goals to achieve a 95% reduction in carbon emissions by 2050 and to phase out natural gas by 2040. Disconnecting the building stock from natural gas requires well-ventilated and well-insulated buildings and a switch to renewable energy sources, making optimal use of heat pumps and sustainable heating solutions available locally. Most buildings in the historical city centre are protected and often insufficiently insulated, leading to increased energy use and a poor thermal environment. Standard retrofitting interventions may be restricted, requiring new approaches to balancing the need for energy efficiency and the preservation of heritage significance. With the case of the Amsterdam City Centre, the goal of this research is to present a parametric modelling approach for energy retrofitting heritage buildings and to identify minimum requirements for preparing the residential stock to lower temperature heat (LTH). Using parametric design and bottom-up energy modelling, the research estimates that a 69.1% of natural gas reduction could be achieved when upgrading the buildings to lower temperature (LT). Results of this paper also demonstrate how the applied approach can be used to guide decisions on the improvement in energy performance of the historic built environment.

Conventional panel radiators are widely used to satisfy indoor heating demands thanks to the heat transfer from the radiator by natural convection and radiation. To increase the heat output from an existing radiator without increasing the supply temperature or replacing the radiator with bigger ones, fans can be mounted below the radiator and this installation carries out heat transfer from the radiator by forced convection. The heat output increases and the changes in the rates of heat transfer mechanisms of these radiators, which are called add-on fan radiators, were experimentally investigated under different supply temperature and fan speed conditions. In addition, the effects of add-on fan radiators on the air temperature values in the test room were also examined. The results show that the addition of the fan unit increased the heat output from the radiator considerably. Also, more enhancement was observed at lower supply temperature conditions. It was also concluded that although the rate of heat output by natural convection and radiation decreased in add-on fan radiators, the total heat output from the radiator was higher than the conventional radiators due to the heat output arising from forced convection prevent this decrease.

Lowering the temperatures in heating systems is the key to decarbonizing the heat supply in the building sector, because it is a door opener to greater integration of renewable heat, the use of excess heat and to improve compatibility for heat pumps. This often fails because heating systems, especially in unrenovated building stock, usually require high supply temperatures. Previous studies on temperature reduction in existing buildings are performed mainly numerically, whereas in this research the numeric calculations are validated by measurements. For this purpose, a demonstrator with two different ceiling heating systems is integrated in the listed architecture building of the Technical University of Darmstadt and the achievable temperature reduction is investigated. Based on this, parameter variations are conducted through a simulation model in order to test the feasibility of the concept for the entire building. The results show that even with an unrenovated building envelope, a significant temperature reduction to below 45 °C is possible without exceeding the normative limits of thermal comfort. With moderate building envelope renovation, the reduction is possible even to below 36 °C. The measures investigated can make the building compatible with renewable heat potentials without negative impacts on the cultural heritage. [ABSTRACT FROM AUTHOR]

The recycling of spent lithium-ion batteries (LIBs) is considered one of the prominent areas of interest in the global community owing to its economic interests and environmental protection. The existence of binder in batteries makes it difficult in the dissociation of electrode material from the fluid collector. This has prompted the need to develop an innovative means of dissociation. In this study, low-temperature heating with low-energy consumption is proposed to enhance the efficiency of dissociation. To determine the ideal heating temperature, the pyrolysis properties of electrode materials and binders were examined by the TG. The dissociation characteristics were analyzed by the grade of the collector (copper, aluminum) and the size composition of crushed electrode material. The surface morphology and element distribution of electrode material and the fluid collection were examined using SEM-EDS. The heating results shows that 500 ºC is the efficient low-temperature which is only slightly higher than the decomposition temperature of the PVDF. The SEM examination reveals that the electrode material's looser structure following heating makes it simpler for the electrode material to fall off of fluid-collecting surfaces, which intensifies dissociation. After heating, the crushing products of the anode and the cathode with size of − 0.074 mm increased by 5.94 % and 38.88 % respectively, the grade of the copper anode and the aluminum cathode in + 2 mm increased by 5.55 % and 38.92 % respectively. [ABSTRACT FROM AUTHOR]

Forced convection is the most effective way to improve the thermal efficiency of a radiator under low-temperature conditions. This technical method differs significantly from the heating effects of general radiation and natural convection. Few studies have applied the objective evaluation method based on quantitative calculation to evaluate the effectiveness of indoor heating or optimize the technical parameters (air flow rate, air supply method, etc.) of heating systems. This article couples human metabolic factors with heating environmental factors and uses a 57-node human thermal physiological model to evaluate the effectiveness of forced convection radiator heating from the perspective of the local thermal comfort of the human body and demonstrates the feasibility of this scheme by comparing it with floor radiation heating. The research shows that the air supply speed of a radiator affects human thermal comfort. Continuing to increase the wind speed, at a speed of 3 m/s, the surface temperature of the human body reaches a high value and will then decrease, leading to a decrease in thermal comfort. Research on indoor air distribution shows that the use of bottom-side air supply provides better thermal comfort compared to top air supply. The local skin temperature distribution of the human body indicates that when the indoor average temperature is higher than 20 °C, the overall thermal comfort of convective radiator heating and floor radiant heating is comparable. The article provides a way of objectively calculating and directly quantifying the effect of heating equipment on human thermal physiological parameters.

Gem-quality rubies and sapphires are often commercially heat treated at about 800 °C or higher to enhance their color and clarity, and hence quality. For this study, selected corundum samples containing diaspore and goethite inclusions were heated step-by-step to a maximum of 1000 °C with the aim of monitoring the dehydration and phase transformation of these oxyhydroxides to corundum and hematite during heating. Based on our experiments and in agreement with the literature, the dehydration of diaspore in corundum occurs between 525 and 550 °C, whereas goethite transforms to hematite between 300 and 325 °C. As both diaspore and goethite may be present as inclusions in rubies, sapphires, and other corundum varieties (e.g., pink sapphires, padparadscha), these dehydration reactions and phase transformations can be considered important criteria to separate unheated from heated stones, specifically in cases in which other methods (e.g., microscopy, FTIR) are unsuccessful.

This study assesses the readiness of selected building types for low-temperature heating. This is accomplished by comprehensively analyzing buildings from two perspectives: first, by determining the level of insulation required for buildings to connect to 4th Generation District Heating, and second, by identifying techno-economically viable solutions to achieve these insulation levels. The authors used OpenStudio to thoroughly examine buildings' thermal response when the heating supply temperature is reduced from 80 to 45 °C without changing radiators. Under these conditions, the aim was to determine whether the living areas inside the buildings could be maintained at 20 °C throughout the year. Starting from a baseline with no additional insulation and old windows, the study increases the intensity of the renovation packages to assess the minimum requirements needed to maintain the desired 20 °C in the heated areas. An economic feasibility study of the solutions proposed was also conducted. A sensitivity analysis was also performed, adding insight into the impact of energy prices on renovation measures. Eight buildings, encompassing a mix of actual structures and representative archetypes derived from the TABULA project, were examined across two different European climate zones. This study found that unrenovated buildings are particularly unready for low-temperature heating and will struggle to maintain 20 °C, especially during winter. Hence, this study delivers recommendations regarding insulation and heat demand reduction measures necessary to maintain appropriate comfort. The conclusions emphasize the necessity of renovating the building stock based on geographical location to guarantee appropriate indoor comfort when reducing the supply temperature for high-temperature radiators. [ABSTRACT FROM AUTHOR]

The German government’s ambitious goal of achieving CO2 neutrality by 2045 has prompted a focus on improving building insulation as a vital step toward energy efficiency. However, in this process, existing radiators and boilers are often left unchanged. Moreover, during the construction of buildings, heating systems are often designed with excess capacity to ensure there is no risk of insufficient heat supply during operation. This research presents various approaches to reduce the required radiator supply temperature, utilizing data from a study conducted in 100 multifamily buildings. The approaches encompass reducing the heat reserve, shifting the heat output, optimizing radiator utilization, and conducting heat demand analysis. The findings reveal that in pre-existing buildings equipped with radiators, it is possible to significantly lower supply temperatures without affecting the indoor temperature. Applied on the seed, reducing the heat reserve could reduce the median temperature by 18.5 K, thus curtailed by the most utilized radiator in the median to 7 K. Furthermore, the heat demand analysis showed that the consumption could decrease in the median by 13%, the peaks in median even by 29%. While each approach is analyzed individually, their combined implementation has the potential to considerably enhance the efficiency of water-to-water heat pumps, thanks to the reduced requirement for high supply temperatures.

Thermal energy storage is a key issue in efficient energy system applications, especially in renewable energies. In this respect, phase change materials (PCM) have attracted interest as an active solution for efficient energy management, particularly in the building sector. This paper presents a modelling of a PCM thermal battery in solar system assisted by heat pump. The storage stores the heat produced by unglazed solar panels (Batisol®) and releases it into a heat pump. Then this heat is sent to two other PCM storages. In this way, the low-temperature heating and domestic hot water needs of a commercial building in winter are met. The storage consists of a block of PCM contained between two plates of heat transfer fluid. It acts as a plate heat exchanger that can be charged and discharged simultaneously. The objective of the study is to dynamically simulate the thermal behaviour of this storage for different hot inlet temperature profiles. A rectangular profile is used to validate the model using experimental results. Then, a solar system assisted by heat pump and three PCM storages is dynamically simulated. This 2D model would be useful to validate a simpler model for optimising the operational parameters of the system. • PCM thermal battery acts as plate heat exchanger which can be charge and discharge simultaneously. • PCM storage model is validate using experimental results. • Three different PCM are chosen according to the temperature levels of each application. • A solar system assisted by heat pump has been dynamically simulated to supply DHW and low-temperature heating requirements. • No auxiliaries are required to meet the building's needs. [ABSTRACT FROM AUTHOR]

Lowering the temperatures in heating systems is the key to decarbonizing the heat supply in the building sector, because it is a door opener to greater integration of renewable heat, the use of excess heat and to improve compatibility for heat pumps. This often fails because heating systems, especially in unrenovated building stock, usually require high supply temperatures. Previous studies on temperature reduction in existing buildings are performed mainly numerically, whereas in this research the numeric calculations are validated by measurements. For this purpose, a demonstrator with two different ceiling heating systems is integrated in the listed architecture building of the Technical University of Darmstadt and the achievable temperature reduction is investigated. Based on this, parameter variations are conducted through a simulation model in order to test the feasibility of the concept for the entire building. The results show that even with an unrenovated building envelope, a significant temperature reduction to below 45 °C is possible without exceeding the normative limits of thermal comfort. With moderate building envelope renovation, the reduction is possible even to below 36 °C. The measures investigated can make the building compatible with renewable heat potentials without negative impacts on the cultural heritage.

Molten salt shielded synthesis (MS3) without salt encapsulation is an environment-friendly, sustainable and energy-efficient method to synthesis high purity non-ceramic oxides at a lower temperature in air using low melting eutectic molten salt. Synthesis of high-temperature carbide and nitride MAX phases requires an inert atmosphere to prevent oxidation. Energy and cost expensive conventional synthesis processes are not useful for large scale productions. Molten salt synthesis is simple but generally carried out in argon atmosphere. Molten salt shielded synthesis (MS3) is carried out in the air but needs salt encapsulation to prevent oxidation below melting point of the salt as reported earlier. In the present work, MS3 method without salt encapsulation in open air has been explored by using low melting eutectic salt mixture to provide oxidation shielding of the metal precursors at high temperature as well as to produce the required phase at lower temperature with shorter soaking time. In this paper, V 2 AlC and Ti 2 AlN have been synthesized using MS3 to obtain satisfactory phase purity. Therefore; this method can be extended to large scale industrial production through its eco-friendliness, sustainability and energy-efficient nature. [ABSTRACT FROM AUTHOR]

In this paper, the phase change plate is made of the organic phase change material (PCM) with the phase change temperature of about 30°C. The PCM is installed in the capillary natural convection radiator with the water supply temperature of 30–60°C. A low-temperature natural convection radiator with heat storage function is formed. The mathematic model is established by enthalpy method and solved by line-by-line iteration method. The applicability and economy of the equipment in Shanghai area are calculated. Taking the time ratio and average temperature of the target domain as the limiting parameters, the operation schemes suitable for three representative days are determined, and the optimum thickness of the phase change plate is 0.05 m for use in Shanghai. The regenerative low-temperature heating radiator provides a new idea for the application of PCMs in the field of low-temperature heating. The conclusions obtained provide a basis for further research and application of the equipment. [ABSTRACT FROM AUTHOR]

This paper aims to provide an overview of the costs and benefits of preparing existing space heating systems for low-temperature district heating. Necessary heating system improvements were assessed based on previous work carried out on the topic. This included evaluating the necessity of installing larger heating elements and improving heating system control. The costs of the identified heating system improvements were then estimated and compared with the savings achieved if district heating temperatures were lowered, from the perspective of both the total Danish energy system and the individual district heating customers. The investigations resulted in simple payback times of 1.2–4.3 years from an energy system perspective and 0.3–18.7 years for an individual district heating customer. The current study thus indicates that it is economically feasible to invest in an improved heating system control to enable a reduction in the district heating return temperatures. • Low-temperature heating can be implemented at low costs from a long-term perspective. • Investments in heating systems are attractive from an energy system perspective. • Customer investments in heating systems should be motivated economically. [ABSTRACT FROM AUTHOR]

Renewable energy sources for the purpose of heating buildings cooperate perfectly with so-called low-temperature heating systems. Water loop surface heating systems had been thoroughly tested. In contrast, thermal performance of wall panels with heat pipes have not been fully recognized, yet. The determination of the thermal power as well as the control of panels thermal performance cannot be performed with the methods developed for water loop systems. In this paper, the novel heating panels with heat pipes were tested to analyze the possibility of controlling their performance by changing the mass flowrate of heating water and its temperature. Specific heating power of the investigated panels varies from 16.9 W/m2 to 93.8 W/m2 when supplying a water temperature ranging from 35 °C to 65 °C and mass flowrate from 10 g/s to 47.5 g/s. Investigations revealed that the thermal performance of the panels is more sensitive to the changes of temperature than to the changes of mass flowrate of supplying water, and thus, should be controlled by changing the supply water temperature at low mass flowrates to obtain a low energy usage of pumps (diminished pressure losses) and good quality of controlling.

• Flexible and leakage-proof SAT/BN@PAN film with high latent heat is fabricated. • Sandwich-like structure is constructed to enhance in-plane thermal conductivity. • The SBP film heats chip by 10 °C at −40 °C to increase low-temperature resistance. • The SBP film suppresses chip overheating by 50 °C at 150 °C to prevent thermal runaway. Integration and miniaturization of electronic devices means efficient thermal management is urgently required. In this paper, thermally conductive but electrically insulated boron nitride (BN) is strung by polyacrylonitrile (PAN) fibers to form a flexible and porous BN@PAN film. Subsequently, solution impregnation combining cold pressing is used to fabricate sandwich-like structure SAT/BN@PAN (SBP) that alternately layered by hydrate salt sodium acetate trihydrate (SAT) and BN@PAN film. The flexible and electrically insulated SBP film possesses high leakage-proof temperature and latent heat. Meanwhile, the sandwich-like structure increases in-plane thermal conductivity by 20 times thus largely promotes anisotropic heat transfer. Consequently, the SBP film heats electronics by 10 °C at −40 °C via heat release from solidification maintaining its steady working cycles. More importantly, the SBP film can suppress overheating by 50 °C at 150 °C via melting and thermal chemical reaction indicating potential in thermal runaway prevention. The wide-range (-40 ∼ 150 °C) thermal management capability and simple fabrication technique of the sandwich-like SBP film provide application potential in advanced electronics devices. [ABSTRACT FROM AUTHOR]

The aim of this study was to map the parameters that have the greatest impact on the environmental impact of heating systems usually used in Nordic single-family dwellings. The study focused on mapping the technical requirements for efficient operation of heating systems in a broader context. The results suggest that the ability of a heating system to be operated with a low-temperature water supply depends to a large extent on the heating demand of a building. It was shown that an increase in the water flow rate in hydronic circuits would significantly increase the thermal efficiency from analyzed heating systems. This increase would not increase the pumping power need, nor would it create noise problems in distribution network if the distribution pipes and thermostatic valves were properly selected. However, this increase in water flow rate improved the efficiency of considered closed-loop heat pump. It was further shown that the efficiency of the heat pump could be additionally improved by halving the energy needs for the domestic hot-water and circulators. The main conclusion from this study is that exergy usage, CO2 emission and thereby environmental impact are significantly lower for heating systems that are operated with small temperature drops. [ABSTRACT FROM AUTHOR]

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Heat dissipation through glass envelopes accounts for a large proportion of building heating loads in winter. Limiting heat transfer through windows is critical, especially considering the rapid development of glass buildings. A pipe-embedded glass envelope that arranges pipes in the shading device of a double window system is combined with a ground-source heat exchanger (GSHE) for heating in this study. The heat transfer process and energy efficiency of the presented system are simulated in consideration of diverse climatic regions. The results show that the water even much cooler than the room temperature is adequate for auxiliary heating by this system. Water at 12 °C can reduce 30% of the heat flux when the outdoor temperature is 0 °C. In addition, the coefficient of the performance of the piping system exceeds a value of 10 because water temperatures are low. The energy saving rates of the system when applied to Beijing, Shanghai, Guangzhou are 16.8%, 20.2%, and 55.9% during the heating season. In the meantime, capacity of the traditional heating system can be reduced as peak heating loads have been decreased, e.g., a reduction of 40.7% in Shanghai. And the payback period is acceptable in these cities. However, in severely cold regions such as Harbin, the energy efficiency is low because the soil temperature is too low. Overall, the studied heating system is very promising as an energy saving method for glass buildings. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop and test the combination of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) method to assess the proton changes of sea cucumber body wall during low-temperature heating process. NMR relaxometry and MRI measurements indicated a significant proton change in the internal structure for sea cucumber body wall when the heating temperature increased from 45 to 55 °C. Differential scanning calorimetry (DSC) analysis revealed that the denaturation temperature of sea cucumber body wall was in the range of 45-55 °C with an endothermic peak at 51 °C, which is in accordance with the result observed in NMR and MRI. Rheological study showed similar trend to the DSC thermogram. The band change in amide I region of Fourier transform infrared (FTIR) spectra indicated the decrease in α-helix content and possible formation of other secondary structures. Scanning electron microscopy (SEM) further confirmed that the low-temperature heating did induce microstructure changes. The analysis of the Ringerʼs soluble fraction (RSF), enzyme-labile fraction (ELF), and total unaltered fraction (TUF) for sea cucumber body wall during low-temperature heating provided more detailed information on the cause of structure change observed in NMR and MRI. The NMR parameters were highly correlated with the rheology storage modulus (G′), relative enzymatic assay parameters, RSF, ELF, and TUF. All these results demonstrated that it could be possible to use NMR and MRI to assess sea cucumber tenderization during low-temperature heating process. [ABSTRACT FROM AUTHOR]

The aim of this study was to map the parameters that have the greatest impact on the environmental impact of heating systems usually used in Nordic single-family dwellings. The study focused on mapping the technical requirements for efficient operation of heating systems in a broader context. The results suggest that the ability of a heating system to be operated with a low-temperature water supply depends to a large extent on the heating demand of a building. It was shown that an increase in the water flow rate in hydronic circuits would significantly increase the thermal efficiency from analyzed heating systems. This increase would not increase the pumping power need, nor would it create noise problems in distribution network if the distribution pipes and thermostatic valves were properly selected. However, this increase in water flow rate improved the efficiency of considered closed-loop heat pump. It was further shown that the efficiency of the heat pump could be additionally improved by halving the energy needs for the domestic hot-water and circulators. The main conclusion from this study is that exergy usage, CO2 emission and thereby environmental impact are significantly lower for heating systems that are operated with small temperature drops.

Renovation of existing buildings is important in the work toward increased energy efficiency and reduced environmental impact. The present paper treats energy renovation measures for a Swedish district heated multi-family house, evaluated through dynamic simulation. Insulation of roof and façade, better insulating windows and flow-reducing water taps, in combination with different HVAC systems for recovery of heat from exhaust air, were assessed in terms of life cycle cost, discounted payback period, primary energy consumption, CO 2 emissions and non-renewable energy consumption. The HVAC systems were based on the existing district heating substation and included mechanical ventilation with heat recovery and different configurations of exhaust air heat pump. Compared to a renovation without energy saving measures, the combination of new windows, insulation, flow-reducing taps and an exhaust air a heat pump gave up to 24% lower life cycle cost. Adding insulation on roof and façade, the primary energy consumption was reduced by up to 58%, CO 2 emissions up to 65% and non-renewable energy consumption up to 56%. Ventilation with heat recovery also reduced the environmental impact but was not economically profitable in the studied cases. With a margin perspective on electricity consumption, the environmental impact of installing heat pumps or air heat recovery in district heated houses is increased. Low-temperature heating improved the seasonal performance factor of the heat pump by up to 11% and reduced the environmental impact. [ABSTRACT FROM AUTHOR]

As existing buildings are renovated and energy-efficiency measures are implemented to meet requirements for reduced energy consumption, it becomes easier to heat our homes with low-temperature heating. This study set out to investigate how much the heating system supply temperature can be reduced in typical Danish single-family houses constructed in the 1900s. The study provides a simplified theoretical overview of typical building constructions and standards for the calculation of design heat loss and design heating power in Denmark in the 1900s. The heating power and heating demand in six typical Danish single-family houses constructed in the 1900s were estimated based on simple steady-state calculations. We found that the radiators in existing single-family houses should not necessarily be expected to be over-dimensioned compared to current design heat loss. However, there is considerable potential for using low-temperature space heating in existing single-family houses in typical operation conditions. Older houses were not always found to require higher heating system temperatures than newer houses. We found that when these houses have gone through reasonable energy renovations, most of them can be heated with a supply temperature below 50 °C for more than 97% of the year. [ABSTRACT FROM AUTHOR]

Low-temperature heating provides an efficient way of heating our buildings. To obtain a high efficiency it is important that the heating systems in the buildings are operated with both low supply and return temperatures. This study set out to investigate how typical assumptions in the modelling of heat emissions from existing hydraulic radiators affects the heating system return temperatures calculated in a building simulation model. An existing single family house with hydraulic radiators was modelled in the simulation program IDA-ICE. Simulations were performed with various levels of detail and the calculated indoor temperatures and radiator return temperatures were compared to temperatures measured in the case house. The results showed that the detail of the simulation model has a large influence on the results obtained. The estimated return temperatures from the radiators varied by up to 16 °C depending on the assumptions made in the simulation model. The results indicated that a detailed building simulation model can provide a good estimate of the actual heating system operation, provided that actual radiators and realistic indoor temperatures are taken into account in the model. [ABSTRACT FROM AUTHOR]

Sweden is actively engaged in accelerating the sustainable transformation of existing building and energy systems. Most traditional investigations of this subject have been based on final energy savings and CO 2 emission analysis, while most existing evaluation methods for energy-retrofitting have not accurately taken into account the influences of flow temperature patterns of different low-temperature heating (LTH) radiators to operational energy. In addition, comprehensive environmental impact analyses by energy systems, as well as the contributions to indoor air quality (IAQ), have not been fully achieved. Moreover, critical mapping of the sustainability of energy-efficient retrofitting have not yet been done. This omission leads to inaccuracies and misleading estimates of the benefits of LTH retrofitting from system and primary energy perspective. In order to fill these knowledge gaps, the present study evaluated two types of LTH systems combined with ventilation retrofitting, namely heat recovery jointed ventilation radiators (VRs) and baseboard radiators (BRs). A typical Swedish multi-family house was selected for retrofitting practice. This study aims at evaluating ventilation heat recovery jointed low temperature heating (VJLTH) retrofitting on energy conservation, environmental impacts and indoor air quality (IAQ) in typical Swedish multifamily houses. The compatibility of building performance and sustainability contributions were critically analyzed by delivered/primary energy usage, life cycle assessment (LCA), and IAQ modeling. IDA ICE (indoor climate and energy simulation program), SimaPro (LCA environmental impact modeling program), analytical model and on-site measurement data provided by both radiator and heat pump manufactures were employed. The results showed that the studied VJLTH retrofitting can save up to 55% of the final energy. And the corresponding primary energy savings are more than 25%. Compared with conventional radiators, low-temperature heating radiators can improve the COP by 12–18% for air-source heat pumps. The studied retrofit can positively contribute 11 of 16 environmental indicators, 7 of which had environmental impacts reduced by more than 50%. However, neglecting the indicators with negative impacts will increase the risk of over-representing the environmental contributions. The sustainability improvements of retrofitting, particularly for future large-scale implementation, should be critically evaluated from a broader perspective than final energy savings. [ABSTRACT FROM AUTHOR]

In this paper, the process of convective heat exchange between the cooling air and the cylindrical solid is experimentally studied in a chamber furnace at double-sided cross-flow around the solid, and the corresponding criterial equation is obtained. [ABSTRACT FROM AUTHOR]

Low-temperature heating (LTH) has shown promising advantages and shortcuts to improve the thermal performance of radiators. An investigation, on which renovation measures from the demand side, can cope with LTH or should be selected as ‘pre-retrofit’ to provide building performance improvements, were carried out in this study. IDA ICE was selected to perform the simulation of a typical Swedish multi-family archetype. Five common energy-demand retrofit options were analyzed. Thermal performance and operational energy savings before and retrofitting were in focus. The results showed that LTH with each of the energy-demand retrofit options can improve the thermal performance to an acceptable level. LTH-combined ventilation retrofitting showed the highest contribution in air temperature, predicted percentage of dissatisfied, and energy savings for space heating. Combining LTH with external wall retrofitting showed the highest effect in operative temperature and total operational energy savings. Combining LTH with all energy-demand retrofitting as a package can achieve 55.3% and 52.8% total delivered and primary energy savings, respectively. This research showed that the existing building can cope with LTH when any of the five energy-demand retrofit options from a thermal performance perspective. Optimal selection shall be based on their abilities to reduce operational energy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effects of combing air-heater with existing radiator heating systems were analyzed. [•] These combined systems covered a space heat loss at −15°C using 40°C supply water. [•] Combined systems operated at 20–22.5% lower temperatures than conventional systems. [•] The COP in combined systems was 8–18% higher than in conventional heating systems. [•] Lowering of supply water temperature by 1°C will increase the COP by 1–2%. [ABSTRACT FROM AUTHOR]

The crystal structure of lamellar precipitates formed in alloys 1213 (Al-Cu-Ag), V-1461 (Al-Cu-Li) and V-1469 (Al-Cu-Li-Ag) has been studied during age hardening. The experimental studies have been performed using transmission electron microscopy. The precipitates have {111} habits and thicknesses of several atomic planes. In diffraction patterns, these plates give a system of diffuse streaks. These ultrathin plates scatter electrons similar to two-dimensional crystal lattices. It is shown that thin plates of precipitates in alloys 1213, V-1461, and V-1469 give identical systems of diffuse streaks. The two-dimensional crystal lattices that give the system of these streaks have a hexagonal symmetry with the following orientation relationship: {ie481-1} and the lattice parameter a = 0.495 nm (there is no lattice parameter c for two-dimensional lattices). A sequence of the steps of reconstruction of the spatial structure of plane precipitates is proposed in terms of their thickness, structures of two-dimensional lattices, and type of precipitates (extrinsic or intrinsic). The influence of Ag on the structure of lamellar precipitates in the V-1469 alloy is discussed. [ABSTRACT FROM AUTHOR]

The problem of changes in properties, which are caused by long-term low-temperature exposures, is typical of all Al-Li alloys. In this study, electron transmission microscopy and X-ray diffraction were used to investigate the structure of aged sheets of commercial Al-Mg-Li alloys 1424, 1441, and V-1469, which were subjected to additional long-term low-temperature exposures (LLTEs) at 85°C for up to 7500 h, at 85 and 130°C for up to 2000 h, and at 125 and 150°C for up to 2000 h, respectively. For structural studies, a JEM-200CX electron microscope and a D/MAX 2500 X-ray diffractometer were used. The X-ray diffraction studies included the phase analysis and special measurements of reflection intensities in a 2θ angular range from 1° to 25°, which allowed us to investigate an additional decomposition at 85°C (which yields disperse particles) using small-angle X-ray scattering effects. In the 1424 and 1441 alloys, the structural changes during LLTEs are determined by the specific features of the δ′ phase, whereas the structural changes in the V-1469 alloy after artificial aging and subsequent LLTEs are due to the precipitation of the Ω′ phase. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with heat output optimization of a ventilation radiator by varying the distribution of vertical longitudinal convection fins. A ventilation radiator, which combines ventilation air supply and heat emission to the room, has a higher driving force on air in between the radiator panels compared to traditional radiators and can for this reason have more heat transferring surfaces to improve thermal efficiency. Improving the thermal efficiency means a lower water temperature is required for heating and energy can be saved in production and distribution of heat in systems with heat pumps, district heating or similar. The investigation was made using Computational Fluid Dynamics (CFD) simulations while analytical calculations were used for verification of different flow and heat transfer mechanisms. Results showed that heat transfer can be increased in the section where ventilation air is brought into the room by slightly changing the geometry of the fins, decreasing the fin to fin distance and cutting off a middle section of the fin array. This change in internal design could mean considerable increase in thermal efficiency for the ventilation radiator as a whole. [ABSTRACT FROM AUTHOR]

The present paper assesses the operation of a geothermal heat plant cooperating with an absorption heat pump. The heat plant system is presented in detail together with parameters characterizing its work: the most important relations used in calculations, results of calculations, and conclusions resulting from the accomplished analysis. Calculations have been presented for a heat plant localized in the first climatic zone with accounts of different temperatures of extracted geothermal water. Additionally, the analysis considered is variation of parameters characteristic of heat recipients such as supply and return temperature, type and participation of particular heat receivers. Such an approach enabled us to determine how the considered parameters influence the effectiveness of operation of the considered heat plant installation. In the present paper neither costs nor economic analysis was carried out for such types of installations. Thes will be topics for future activities. [ABSTRACT FROM AUTHOR]