Vacuum Insulation Research Articles

Investigation on Effective Thermal Conductivity of Fibrous Porous Materials as Vacuum Insulation Panels’ Core Using Lattice Boltzmann Method

Vacuum Insulation Panels (VIPs) provide significant adiabatic performance for heat/cooling systems to reduce energy consumption. The application of fibrous porous material (FPM) as the ideal core of VIPs has gained global attention in recent decades. The microstructure and physical properties of FPMs, filled as novel VIPs’ core material, and holding superior thermal performance, affected effective thermal conductivity (ETC) greatly. Aiming to deeply understand heat transfer mechanisms, a holistic simulation method that combined with a developed 3D FPM structure generation method and a D3Q15-Lattice Boltzmann method (LBM) is proposed to simulate the heat transfer in FPM and to illuminate the influence factors of ETC on the microstructure of FPM in a vacuum. The improved and modified mesoscopic 3D fibrous random micro-structure generation approach involved five structural parameters: generation probability of nucleus growth, fiber length, diameter, coincidence rate, and orientation angle. The calculation model of ETC is established, and the discrete velocity, distribution, evolution, and boundary conditions of D3Q15-LBM are invested in detail. The model is validated with influences of different microstructure parameters. It indicated that FPM with finer diameter, smaller average pore size, and bigger orientation angle easily gain the lower ETC in a vacuum. The ETC was also affected by the orientation angles of fibers. The more the heat transfer direction is inconsistent with the length direction of the fiber, the better the adiabatic performance is. The reliability of the model is verified by comparison, and this work is a reference to optimize the fibrous core of VIPs.

A study on thermal bridge effect of vacuum insulation panels (VIPs)

Three kinds of thermal bridges of vacuum insulation panels are studied in this paper. Firstly, for the thermal bridge of a single vacuum insulation panel, its linear thermal transmittance with different barrier films, thickness, and central thermal conductivity is calculated. The result shows that when the barrier film changes from metalized polymer films to laminated aluminum foils, the linear thermal transmittance increases by 6.1 times. In addition, its thickness and central thermal conductivity are negatively correlated with the linear thermal transmittance. Secondly, the thermal bridge caused by gas gap is studied by the insulation box experiment. When the surface gap of the insulation box increases, the electricity consumption increases by 42%. And the influence of the barrier film on the thermal bridge is verified. When the barrier film is changed from metalized polymer films to laminated aluminum foils, the power consumption is increased by 115%. Finally, the thermal bridge of insulated decorative panels for the building envelope is tested. It is found that the thermal bridge has different effects on different positions of insulated decorative panels. The temperature difference between the joint of four insulated decorative panels and the center of the insulated decorative panel can reach 1.5 °C. In addition, when the bending height is higher, the thermal bridge effect is greater, and the temperature difference between insulated decorative panels with 10 mm bending height and insulated decorative panels with 20 mm bending height can reach 1 °C.

Evaluating the Effectiveness of Energy-Efficient Design Strategies in Achieving Net Zero Energy Building through Reduced Energy Consumption

Abstract: Net zero energy buildings (NZEBs) have emerged as a sustainable and energy-efficient solution to the challenges of climate change and rising energy costs. These buildings are designed to generate as much energy as they consume, resulting in zero net energy consumption. The paper explores the evolution of NZEBs and the latest emerging technologies that are enabling their development, including smart building automation systems, energy-efficient lighting and HVAC systems, vacuum insulation panels, Building Integrated Photovoltaic (BIPV) systems, and advanced sensors. The effectiveness of these strategies is analyzed using Autodesk insights and Revit software. The paper also discusses the comparison of Energy Use Intensity (EUI) before and after implementing energy-efficient and renewable energy techniques, which is crucial in determining their effectiveness. The proposed building achieved a significant 57.3% reduction in energy consumption after implementing various NZEB design strategies, resulting in a mean EUI value of 99.8 kWh/sq. m/year. The analysis was conducted using Autodesk Insights and Revit software, utilizing the Building Information Modeling (BIM) approach for building design. This paper concludeswitha discussion on the future of NZEBs and how they are an important step towards achieving sustainable and efficient energy use in the building sector,resultingincostsavings andreducedcarbon emissions

단열용기의 잠열재 배치에 따른 내부 온도 균일성에 대한 영향

An optimized design of the transportation insulated box must be considered to control the thermal damage in order to maintain the fresh condition for temperature-sensitive medicine and frozen food safety. The inside temperature of the insulated box is a natural convection enclosure state, thermal stratification naturally occurs as time passes in case of with outside heat load. The latent heat material (LHM) placement inside the box maintains the target temperature of the product for temperature fluctuations during transport, and LHM application is a common and efficient method. In this work, inside temperature stratification in an insulated box depending on the LHM pack position is numerically simulated and experimented. The insulated box is made up of vacuum insulation panel (VIP), and LHM modules are placed over six faces inside the box, with the same weight. The temperature curves for 72 hrs as experiment results clearly show the temperature stratification in the upper, middle, and lower at the LHM melting time region. However, the temperature stratification state is uniformly changed in accordance with the condition of the upper and lower placement weight of the LHM pack. And also, the temperature uniformity by changed placement weight of LHM has an effect on maintaining time for target air temperature inside the box. These results provide information on the optimized design of the insulated box with LHM.

Novel prediction of thermal conductivities for nano-aerogel and its composites as vacuum insulation panel core

For its advanced adiabatic performance and low effective thermal conductivity (ETC), vacuum insulation panel (VIP), as one of newly developed thermal insulation materials, has already been widely employed in many energy saving fields, especially in buildings industry. Nano-porous aerogel is commonly selected as optimal core materials of VIP. Vacuum is a vital parameter affecting on ETC. A novel theoretical model was proposed and the accuracy was verified by experiments to analyze the ETC. A device was designed and verified in this work to accurately collect the VIP internal pressure. The density, temperature, and vacuum effects on ETC were investigated. The result implied that density had a remarkable effect on ETC. A minimum density of 120 kg/m3 at a temperature 300 K gained the lowest ETC. The increase in temperature caused an increase in the radiative thermal conductivity. At ρa = 100 kg/m3and P > 3 kPa, the gas conduction was predominant part influencing ETC. And at ρa = 200 kg/m3and P > 50 kPa, gas conduction became the major infector. As pure aerogels are fragile, the ETC of aerogel composite core with additive fibers was investigated. It was indicated that the optimal fiber content is about 5% when T < 550 K and about 25% when T > 550 K. At T > 400 K, the total ETC increases significantly versus fiber diameter.

Review on Recent Development in Insulation Research Under Short-Pulse Conditions

This article summarizes the recent developments in insulation research under short-pulse conditions in the Northwest Institute of Nuclear Technology in China, which include four aspects: (1) solid insulation under nanosecond pulses, (2) vacuum insulation under microsecond pulses, (3) insulation design methods, and (4) long-lifetime insulation structures.

A modified pump-down model for high vacuum packaging of vacuum insulation sandwiches under readsorption effect

Thermal insulation performance and service life of vacuum insulation sandwiches depend significantly on the internal residual gas pressure. Degradation of the vacuum can lead to a dramatic increase in thermal conductivity, so the initial internal pressure should be kept as low as possible during fabrication. In this paper, the evacuation and outgassing of vacuum insulation sandwiches are studied by modeling and experimental methods. A modified pump-down model for vacuum insulation sandwiches, called the recombination-dissociation-limited model, is proposed based on diffusion, recombination, and dissociation. The results show that the recombination and the dissociation of hydrogen on the inner surface have a hysteresis effect on the evacuation process, which explains well that the pressure inside the device remains above the ultimate pressure of the vacuum system after packaging. The experimentally measured evolution of the pressure and outgassing rate in the vacuum insulation sandwiches agree well with the calculated results. The simulation analyses the effects of temperature, pump-out port size, and ultimate pressure on evacuation efficiency. It provides a theoretical basis for predicting the dynamic pressure evolution during high vacuum packaging and selecting effective parameters in the packaging process.

Enhancing hygroscopic capacities of metakaolin based porous insulating geopolymers: Comparative effects of calcium silicate and sodium polyacrylate

The extent of dissolution and polymerization/polycondensation of metakaolin added biomass to alkaline solution was exploited to design highly porous insulating geopolymers using sodium polyacrylate and calcium silicate to enhance their hygroscopic properties. 2.5 to 7.5 wt % of sodium polyacrylate and 20–40 wt % of calcium silicate efficiently embedded into the geopolymer gel were able to increase the absorption and desorption capacities between 30 and 50% while maintaining the thermal conductivity at 0.13–0.16 W m−1K−1 at 70% of relative humidity and 0.22–0.28 W m−1K−1 when the relative humidity is above 80%. The extension of the reactivity of metakaolin added biomass results to a homogeneous gel with improved specific surface area which enhances the hygrothermal properties. The pore size (essentially nano and meso) and their interconnectivity make the obtained porous matrices promising candidates for core vacuum insulation and regulation of the thermal comfort for Net zero Energy buildings. A Machine Learning (ML) method, the polynomial regression, was used to ascertain the close correlation between the thermal conductivity, temperature, moisture absorption and time. Also, the increase in the amount of nano and meso pores increases the tortuosity of the porous matrices and explain the improvement of the hygrothermal properties. The changes in the microstructure with the increase of the volume of fine pores was found to be suitable for hygrothermal behavior (absorption-desorption).

The Use of Advanced Environmentally Friendly Systems in the Insulation and Reconstruction of Buildings

This study is devoted to the possibility of using advanced insulation materials, such as Vacuum Insulation Panels (VIP), in the insulation and reconstruction of buildings, in connection with the green elements that are installed on the facade in the case of the use of external thermal insulation composite systems (ETICS). The use of VIP as part of the insulation system will result in a significant reduction in the required thickness of the insulation layer. In turn, the reduced overall thickness of the system will allow for easier direct anchoring of the elements of the green facade through the insulating layer to the base of the structure. The research carried out proves that, by using VIP in the insulation system (with a VIP thickness of 30 mm in combination with 20 mm of extruded polystyrene XPS), the thermal insulation properties can be significantly improved and, thus, the thickness of the insulation system can be reduced to 1/3 of the thickness of conventional insulation (while achieving the same thermal resistance), thereby enabling the anchoring of green elements on the surface of such an insulation system.

Effective thermal conductivity of vacuum insulation panels prepared with recyclable fibrous cotton core

Known as one of the super adiabatic materials today, vacuum insulation panels (VIPs) is wildly applied in building industry. It has the double advantage of saving energy and improving space utilization. However, its expensive cost is the application obstacle. A new type of VIPs with recycled and economical cotton fiber core was prepared and innovated in this study. The micromorphology of the recycled cotton core material, as well as the barrier and thermal conductivity of the prepared VIPs, was experimentally and mathematically investigated. A designed vacuum measurement device was introduced to analyze the variation of thermal conductivity versus gas pressure. Three types of laminated films were prepared to investigate VIPs’ adiabatic properties. Three typical barriers, respectively AF, MF-Ⅰ, MF-Ⅱ, were involved to investigate the impact of sustainability. The final results showed that AF as the barrier layer for VIPs with performed better than other VIPs considering thermal conductivity. The effective thermal conductivity (ETC) of the VIPs is sensitive to inner pressure and the optimum gas pressure is less than 0.1Pa. The drying process for porous cotton fibers is a continuous heating at a temperature of 120 °C for 30–40 min. The ETC of the VIPs prepared using AF barrier envelopes was about 3.17 mWm−1K−1. The VIPs with cotton fiber core material has good thermal properties and also has the dual characteristics of low price and environmental protection. As a potential candidate for the VIPs core material, the recycled wasted cotton fiber core material is a new development direction.

Historic building energy conservation with wooden attic using vacuum insulation panel retrofit technology

The envelopes in historic buildings must be preserved as aging historic buildings continue to be used. Conservation is necessary to improve the energy performance of historic buildings. The target building of this study has an exposed rafter structure. Modern historical buildings in Korea do not have a passive retrofit, which is insulation. The passive retrofit covering the roof structure needs to be applied taking into account the original protection of the exposed rafters. This study aims to examine the energy improvement effect of a historic building with a roof with an exposed rafter structure. Considering the characteristics of the building, a vacuum insulation panel (VIP) retrofit technology is used instead of general insulation. The VIP is thin and has high heat resistance, so there is little damage to the envelope of historic buildings, and the U-value of the existing roof layer is reduced by 88%. By applying retrofitting technology, the annual energy consumption of the top floor was improved by 55%. Cooling on the top floor showed an improvement of 29.87%. The largest energy savings occurred in May at 49%. This is because the VIP retrofit technology is applied in the form of external insulation. External insulation lowers heat storage owing to solar radiation. The developed VIP was suitable for Korea's preservation considerations and building energy conservation considerations.

Why and which opacifier for perlite based vacuum insulation panels (VIPs) in the average temperature range of 10–70 °C

Little is known on the effect of opacifiers in perlite core vacuum insulation panels at lower temperatures in the range of 10–70 °C, which are important for applications like refrigerators, transport boxes, buildings, and domestic hot water storage tanks. This paper shows that the effect of opacifier on perlite core Vacuum Insulation Panels (VIPs) is radically different than that on fumed silica VIPs. Identifying an optimum proportion of opacifiers for perlite core VIPs is not a trivial task because of a concomitant rise in solid conductivity as the radiative conductivity decreases. Further, the effect of opacifiers on temperature dependent thermal conductivity of VIPs has been resolved. Opacifiers in perlite are shown to yield clear benefits by reducing the overall thermal conductivity for insulation exposed to ≥70 °C. This was not the case for ≤20 °C. Several VIPs were manufactured using a low-density expanded perlite and 3 different proportions of 4 opacifiers i.e., carbon black, graphite and two variants of silicon carbide (SiC I, SiC II). These VIPs were tested at various combinations of sealing pressure and four different average temperatures i.e., 10 °C, 20 °C, 40 °C and 70 °C. A novel methodology has been developed to derive the evacuated thermal conductivity of perlite core VIPs by curve fitting technique, in order to eliminate the effect of gaseous conduction. The results were also compared with fumed silica core vacuum insulation panels with different proportions of carbon black as opacifier. Among the opacifiers tested (carbon black, graphite, SiC I and SiC II) in this research, Silicon carbide I with a mean particle size of 20 μm was found out to be the best opacifier, with one of its composite resulting in a 50% lower thermal conductivity at 70 °C in comparison to pristine perlite core VIPs.

Energy Upgrading of Basement Exterior Walls: The Good, the Bad and the Ugly

Most of today’s buildings will still be in use in 2050 and upgrades should therefore contribute to reducing energy consumption and carbon footprint. This paper addresses a challenge for upgrading of basement exterior walls of single-family dwellings, where ordinary retrofit insulation can lead to the basement wall protruding from the existing outer wall. For some, this will be an aesthetic barrier for an energy upgrade (an “ugly” solution). Superinsulation may solve this challenge without compromising the energy performance. This study analyses energy, cost and carbon footprint, to identify under which conditions upgrading with vacuum insulation panels (VIP) can be a preferred solution. Three alternatives are analysed in a parametric model: ordinary upgrade with XPS (the aesthetically “ugly”), upgrade with VIP above ground and XPS below ground (the aesthetically “good”), and iii) no upgrade (the “bad”, as it does not contribute to reducing energy consumption). Results show that using VIP and XPS to perform energy upgrade of a basement exterior wall may lead to an aesthetically more pleasing solution than with only XPS, but that it will lead to higher carbon footprint and higher costs. The least favourable option is to install a drainage system without doing an energy upgrade, which will have negative impact for energy use, carbon footprint and life cycle cost.

An Analysis of The Use of Insulation Systems on OTTV Values of Residential Building in Hot Humid Climate

In tropical climates, the main problems are high solar radiation and humidity. The aim of this study is to find the right insulation material to provide thermal comfort of BSPS houses in Pamekasan Regency. The method use in this study is experimental with quantitative data analysis. Experiments were conducted on aspects that affect the value of thermal transmittance (U-value) and type of materials (glass wool, VIPs, and aerogel). The result shows that the best insulation material for thermal comfort is Vacuum Insulation Panels (VIPs). It could provide a significant reduction in OTTV value. The final results of the research by applying the insulation system to the BSPS house of Pamekasan Regency, Proppo Subdistrict, Panaguan Village show that the OTTV value of the alternative model in a house type 24 m2 is 29.505-23.462 W/m2 with a decrease of 22.86%-38.66% while in a house type 33.12 m2 it is 30.205-24.217 W/m2 with a decrease of 22.74% -38.06% and in a house type 84.46 m2 it is 27.223-21.084 W/m2 with a decrease of 26.19%-42.84%. Furthermore, the best type and thickness of insulation material used in this study is Vacuum Insulation Panels (VIPs).

Investigation on Longer Service Life of Vacuum Insulation Panels by Applying Double Envelopes

The conversion of existing buildings to ZEB requires high thermal insulation. Vacuum insulation panels (VIPs) have a potential to be used for retrofitting thermal insulation of existing buildings from the viewpoint of low thermal conductivity, small thickness, and light weight. However, in order to realize vacuum insulation panels applicable to building insulation, it is necessary to overcome the challenge of maintaining the low pressure at which the high insulation performance can be achieved for several decades. The authors applied the double envelopes to VIPs and investigated longer service life of VIPs. The double envelope VIP is fabricated by fabricating a normal VIP, then wrapping the VIP with core materials, and then inserting it into the envelope for vacuum sealing. By applying the double envelopes, the pressure difference and the permeation of gas in inner VIP can be drastically reduced, resulting in a longer VIP lifetime. In this paper, the gas permeabilities of the gas barrier envelopes were experimentally estimated. Then, the pressure ageing in the double envelope VIP is calculated. The inner pressure after 25 years was 1.6 Pa for the envelope of aluminium composite film and 59.3 Pa for the envelope of transparent gas barrier film, indicating that long-term insulation performance could be improved. Next, the authors carried out acceleration test, in which the double envelope VIPs were put in a chamber at 80oC and remove once a month to measure the thermal conductivity. Even after 136 weeks, one sample showed only a 9.1% decrease in thermal resistance. From this result, it was confirmed that long-term insulation performance can be greatly improved by fabricating double envelope VIPs with the getter agent inside and the desiccant agent outside.

Building thermal comfort improving by using PCM and super insulators: Thermal and economic studies

The climate of the northern region of Morocco is Mediterranean, while the southern one is arid-type. They are both characterized by significant solar radiation during nearly eight months of the year, and as a result, direct and indirect solar energy contribute mainly to human discomfort in residential buildings. In this study, passive techniques such Phase Change Material (PCM) and super insulators (Aerogel and Vacuum Insulated Panels (VIP)) are used and analyzed to improve thermal comfort in the building. The resulting thermal behavior was studied using dynamic simulations and an experimental investigation of two test cavities located in the city of Casablanca. The potential energy savings to reach human comfort conditions were evaluated for a real scale cubicle. The comparison is performed with the active solution (air conditioning with classical local building wall composition), and the economic performances of these materials are evaluated by the Net Present Value (NPV) and Internal Rate Return (IRR). Special emphasis is given to the bulling roof. The optimum insulation thicknesses and payback periods were determined in the present study over 20 years. The results showed that PCM, VIP, and Aerogel could provide respectively as much as 94 %, 76.51%, and 73.61% economic benefit during the cooling period and 59.3 %, 46.56%, and 44 % during the heating period than the case of the roof without insulation.

Application of Vacuum Insulation Panel and Semiconductor Freezer in Cold Chain Portable Container

Application of Vacuum Insulation Panel and Semiconductor Freezer in Cold Chain Portable Container

Experimental investigation of methods to reduce outgassing from core materials in the fabrication process of transparent vacuum insulation panels

The notion that modern buildings should strive to be net-zero energy buildings (NZEBs) is widely accepted. In order to improve window’s insulation in existing buildings, structured-core transparent vacuum insulation panels (TVIPs) are proposed. TVIPs mainly consist of the structured core material, the low-emissivity film, and the transparent gas barrier envelope. TVIPs have high insulation performance and are inexpensive to manufacture and can be easily installed. However, it is necessary to overcome the issue of preventing the pressure rise inside TVIP after vacuum sealing. The authors constructed an experimental setup by applying the pressure-rate-of-rise-method to establish the fabrication process for TVIPs that prevents the pressure rise. In this experiment, a gas barrier film with a straw was used as the vacuum chamber. This could reproduce the pressure increase in the TVIP after sealing and the gas flow rate in the TVIP is evaluated. The experimental results showed that the internal pressure of TVIP could be reduced to about 1 Pa after vacuuming while heating for 8 hours, coating the core material, and sealing the getter material.

Experimental study on insulation performance of structured-core transparent vacuum insulation panels for different core materials

The conversion of existing buildings to ZEH and ZEB requires increased thermal insulation, in which the insulation of window surfaces is particularly important. This study focused on measuring and comparing the changes in thermal conductivity of transparent vacuum insulation panels (TVIP), which could be used as simple and easy to install insulation to building windows. These changes were later compared with the results obtained from previous studies conducted by other research group members. The measured thermal conductivity values ranged between 0.017 W/(m*K) of the best performing frame-type with the thickness of 5.1 mm, and 0.011 W/(m*K) of the best performing double-layered peak-type core with the thickness of 7.8 mm. The calculated U-values of the samples ranged between 4.1 W/(m2*K) and 1.4 W/(m2*K). From the experimental results it could be seen that changing the core composition had a larger effect on the overall thermal conductivity of the sample than the added parameters of coating, getter agent, and heating had. These parameters, however, have had a substantial effect on the longevity of the vacuum inside the sample envelopes, and will thus be experimented further.

Experimental analysis of vacuum pressure and gas flow rate in structured-core transparent vacuum insulation panels

The notion that modern buildings should strive to be net-zero energy buildings (NZEBs) is widely accepted. One of the causes leading to high energy usage for space heating, resulting in avoidable carbon emissions, is heat loss via building windows. In order to improve window’s insulation in existing buildings, structured-core transparent vacuum insulation panels (TVIPs) are proposed. TVIPs mainly consist of the structured core material, the low-emissivity film, and the transparent gas barrier envelope. TVIPs have high insulation performance and are inexpensive to manufacture and can be easily installed. Therefore, TVIPs have the potential to improve window’s insulation in existing buildings at a low cost. However, it is necessary to overcome the issue of preventing the pressure rise inside TVIP after vacuum sealing. The authors constructed an experimental setup to quantify the effect of reduction of gas flow rate in TVIP after evacuation by applying the pressure-rate-of-rise-method. In this experiment, a gas barrier film with a straw was used as the vacuum chamber. This could reproduce the pressure increase in the TVIP after sealing and the gas flow rate in the TVIP is evaluated. The experimental result shows that the coated core material and the enclosing getter agent lowered the pressure rise and gas flow rate in TVIP by combining concurrent evacuation and heating. Furthermore, after extending the simultaneous vacuuming and heating period to 8 h and applying the coated core material, and enclosing the getter agent, the internal pressure in TVIP may be lowered to around 1 Pa after 30 min after halting vacuuming. It was confirmed that this pressure satisfied the performance required for TVIPs, and the result was much closer to the realization of TVIPs.