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A CRITICAL REVIEW OF LONG-TERM THERMAL
PERFORMANCE OF VACUUM INSULATION PANEL
IN BUILDING ENVELOPE CONSTRUCTION
M. Morlidge
ABSTRACT
The higher level of insulation in building envelopes mandated by recent energy codes in Europe and North
America has provided a fresh impetus to the search for high performance thermal insulation. Among
various nonconventional insulations being introduced in the construction industry, vacuum insulation panel
(VIP) appears to be one of the most promising insulation materials with the highest thermal insulating
capacity (thermal resistance of VIP is up to 10 times or more than those of conventional thermal insulation
materials). This paper provides a thorough review on parameters that influence the long-term thermal
performance of VIP. The material properties that contribute primarily to VIP performance include: pore
structure and thermal properties of core materials, out-gassing of core materials, gaseous diffusion and
water vapour permeability of foil barrier materials and seam joints, moisture sorption and desorption
characteristics of core materials, seals and panel joints, thermal bridging and edge losses, and climatic
conditions (relative humidity, pressure, temperature and time). Built upon existing models that correlate the
long-term thermal resistance to basic material properties, an analytical model is developed to predict the
long-term thermal resistance of VIPs. The model is applied to predict the aging of five VIPs that were
tested under accelerated aging cycles in laboratory and the predicted aging yields close agreement with the
measured data.
INTRODUCTION
Recent upgrades of energy codes in Europe and North America have recommended higher levels of
insulation in building envelopes. Among various non-conventional insulations being introduced in the
construction industry, vacuum insulation panel (VIP) appears to be one of the most promising insulation
materials with the highest thermal insulating capacity (thermal resistance of VIP is up to 10 times or more
than those of conventional thermal insulation materials). Quite naturally, the application of VIP in building
envelope construction offers many advantages such as increased energy efficiency of exterior building
envelope, thinner wall thickness, optimum space use, reduced material consumption etc. Nevertheless real-
life applications of VIP in building envelope constructions are rare and sporadic. There are a number of
issues that are being raised by construction industry professionals and stakeholders and undoubtedly long-
term thermal performance of VIP is one of those issues. At present VIPs are available from different Asian,
European and North American manufacturing sources and come with wide range of choices in terms of
thickness, R-value/inch and size and users know very little or nothing about their long-term performance.
There have been numerous studies, theoretically and experimentally, to determine the thermal performance
of VIPs over time. Several numerical models have also been developed to predict the long-term
performance of VIPs. However, many of these models were implemented based on specific material
properties measured and few models holistically considered all the relevant properties of the material and
the change of properties over time under transient climatic conditions. This paper provides a thorough
review on parameters that influence the long-term thermal performance of VIP. Built upon existing models
that correlate the long-term thermal resistance to basic material properties, an analytical model was
developed to predict the long-term thermal resistance of VIPs. The model is applied to predict the aging of
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five VIPs that were tested under accelerated aging cycles in laboratory and the predicted aging yields close
agreement with the measured data.
LITERATURE REVIEW
The Vacuum Insulation (VIP) systems consist of open-porous core insulation materials that are wrapped
within an exterior metallic layer. The air inside this membrane is mechanically removed and then sealed to
create the interior vacuum. By removing air from the insulation material, the thermal energy losses via air-
convection and air-conduction are reduced to zero. Ideally radiation and solid-conduction would be the
only two heat transfer mechanisms and are significantly less in comparison to its two counterparts. The
typically used core materials include foam, powder and fiber insulations which are open porous, making it
possible to evacuate air from the panels. This core must also be able to withstand atmospheric pressure in
order to maintain the vacuum, without compression failure occurring within the panel (Kwon, 2009). The
most commonly used system is a fumed silica core wrapped in a polymer based film and coated with
metallic foils. Metallic foils differ from aluminum foils in that they use multiple layers of thin aluminum
between polymers. Increasing the number of metal layers is to enhance the performance of the panel by
providing increased durability. Typically VIPs range in thickness from 8-36mm with dimensions ranging
from 10x10cm to 150x150cm.
In comparison to other non-conventional insulation materials including nanostructured materials and
aerogels, VIPs have been found to far outperform these materials in thermal resistance per unit material
thickness. However, their long-term performance is a concern given that the VIPs are evacuated and
gradual or instantaneous loss of vacuum cannot be totally ruled out. Research efforts have been made to
quantify the thermal performance of vacuum insulations. The parameters contributing primarily to VIP’s
performance include: core material properties, outgassing of core materials, gaseous/moisture diffusion
and permeability of the barrier envelope/foil, moisture sorption of core material, integrity of polymer
seal/joints, thermal bridging and edge losses, and climatic conditions. This section summarizes existing
studies on the thermal performance of VIPs and the prediction of their service life.
1. CORE MATERIAL PROPERTIES
In this review, the focus is on fumed silica as it is the most commonly utilized and researched core material
in building application (Baetens, 2010). The effective U value of VIPs is dependent on the ability to
eliminate air from the core, while also minimizing solid conduction. The way typical cores are fabricated
is by injecting blowing agents into the fumed silica substance to create air pockets and then air is evacuated
from the cells to reduce air conduction and convection (Kwon, 2009). Open cell insulation materials are
typically made by ensuring bubble growth from the injected blowing agents, followed by the cell wall
thinning and breaking. Several analyses have been conducted to determine how the core structure
contributes to the performance of the vacuum, and how core materials could be optimized during the
fabrication process to ensure the maximum thermal resistance.
Tseng and Chu (2008) investigated the variables which influence the radiative and conductive heat
resistance properties of vacuum insulation based on the cell formation of the foam; focusing specifically
on foam density, mean cell diameter, mean bead diameter and inter-bead porosity. The thermal conductivity
of 14 VIP samples with different broken and open cell structures were measured to evaluate the effect of
cell geometry on heat transfer. The study found that as the cell size increases, the heat conduction through
solid decreases while radiative heat transfer increases, resulting in an decrease in the overall thermal
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conductivity since solid conduction accounts for approximately 80% of the total core conductivity (Tseng
and Chu, 2009). An optimum overall thermal conductivity for the core can be achieved with cell sizes
between 100-300 µm. In a further study, Tseng and Chu (2009) investigated the influence of broken cell
ratio, average cell size and solid volume fraction by adding polyethylene to modify the cell structure and
improve the overall thermal conductivity. The broken cell ratio of a material accounts for how many cells
have physically broken within the material during the evacuation of air. The ratio primarily affects the
amount of heat transfer via radiation, as a broken cell ratio which is too high is often accompanied by
internal compression (causing cell walls to collapse on one another), while a broken cell ratio which is too
low does not allow for sufficient evacuation of air. The cell size and broken ratio therefore control an
optimum value to reduce radiative heat transfer, while the solid volume fraction is kept low to minimize
the conductive heat transfer. They concluded that the lowest conductivity achieved was 4.4 mW/mK;
which occurred with a broken cell ratio of 0.95 and a cell size of 170 µm. The addition of 2% polyethylene
to the product was the most effective combination to alter cell structure and reduce heat transfer and the
5% was the percentage where the material no longer improved, and should thus be considered the
maximum additive necessary.
Wong and Tsai (2006) and Wong and Hung (2008) also studied the effect of adding polyethylene to core
materials on the foam density, cell structure, and overall core thermal conductivity of VIPs. They
concluded that the addition of polyethylene within a composite can increase the foam intensity, which
allowed it to achieve a porous open-cell foam core at higher foaming temperature resulting in a lower initial
core thermal conductivity, however, potentially greater deficiency risks due to failure over time. The
modeling of heat transfer through VIPs at a cell-to-cell scale by Kwon, et al. (2009) found that the ranking
of factors affecting the thermal conductivity of the core from the highest to lowest are: density, mean cell
diameter, and inter-bead porosity.
2. OUTGASSING OF CORE MATERIALS
While the core material does not affect the thermal conductivity over time, its properties do contribute to
the amount of outgassing from the core material. The outgassing will produce a rise of internal pressure
that compromises the performance of the VIP as it provides a heat transfer medium in an otherwise
evacuated product. The outgassing rate is influenced by the properties of core materials, blowing agent, its
microscopic surface characteristics, and the exact fabrication process of each individual VIP panel and
temperatures, etc.. Kwon et al., (2011) analyzed the outgassing rate of a polycarbonate core by modeling
and measurements. Measurements on polyurethane foam by Yang and Xu (2007) showed that the
outgassing rate was significantly reduced within the first 84 days after manufacturing and begins to level
out within the first year. Although outgassing of core materials was identified as a significant contributor
to the initial performance deterioration in VIPs (Kwon et al., (2011), the impact on the long-term
performance is considered insignificant given that outgassing occurred within the first year.
3. GASEOUS DIFFUSION AND PERMEABILITY
Gaseous diffusion through the metallic and polymer coatings is the main cause for the degradation of the
VIPs. Gaseous conductivity in the VIP is determined by a number of gas molecules available in the
material as transfer medium. The mean free path of molecules is the average distance, which they travel
before encountering a collision with another gas molecule. At a high pressure, the mean free path of
molecules is smaller, thus collisions between gas particles occur more frequently, causing efficient heat
transfer. Removing air through evacuation reduces the gas pressure, and thus decreases the mean free path
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between molecules (Thorsell, 2010). Gaseous diffusion occurs through the metallic coatings and the rate
of diffusion is increased in areas where there are deficiencies in these coatings. Thorsell (2010) measured
the size, location, and density of deficiencies, which were characterized as pin holes that naturally occurred
during the fabrication and handling process of VIPs. The exterior and interior layers had different
deficiency sizes and distribution (i.e. interior mean defect diameter was 1.3 µm with density of 4x108
defects/m2; exterior mean defect diameter was 3.2 µm with density of 8.6 x 107 defects/m2). They
developed a numerical model based on the characterization of deficiency sizes and distribution to predict
the permeation rate of gases. They concluded that the permeability achieved was able to meet the
performance requirements of VIPs for 30-50 years with only 2 layers of metallization layers; this
performance was improved when utilizing additional layers. Thicker metallic coatings provide a greater
retardant for gaseous diffusion, however, they also cause increased conductivity through the panel edges.
The optimum thickness depends on the type of foil used, typically two or three metallic layers, depending
on the manufacturer’s preference although 3 layers are optimal. By analyzing the typical surface
deformation conditions using chemical analyses, optical microscopy and scanning electron microscopy,
Garnier et al, (2011) classified the deficiencies as either nano-defects (out of equilibrium growth
mechanisms) or macro defects (pinholes and micro-cracks). Their measurements concluded that small
holes in a barrier produce a higher permeation value than large holes with the same total area. The amount
of surface defects was observed to decrease as the thickness of aluminum coatings was increased; however
the addition of metallic coating also causes the effective conductivity to increase due to edge thermal
bridging effect. Although the permeation rate is different for different types of gases, their impact on the
conductivity of VIP does not differ significantly, therefore, typically permeation rate for all gases are
coupled as one transmission rate (Garnier et al, 2011).
4. MOISTURE PERMEABILITY AND WATER CONTENT
The presence of moisture can have a significant impact on the thermal conductivity of VIPs. There is the
initial moisture contained in the core materials and the moisture diffused through the panel during its
service life, a similar process to gaseous diffusion through defects and pin holes. Moisture contributes to
the heat transfer of the VIPs in two ways, one as the gaseous medium and the other the latent heat transport
process, i.e. liquid water evaporates at warmer side and condense at the colder side. Schwab, et al., (2005)
studied the effect of moisture content on the thermal conductivity of VIPs using a hot plate apparatus. The
panels were exposed to different levels of temperature and relative humidity to achieve various levels of
moisture content (MC). This study concluded that for the panels tested the increase of thermal conductivity
was proportional to the MC of the panel, approximately 0.5x10-3 W/mK conductivity increase per mass
percentage of water. For the panels tested they found that the rates of increase in MC were between 0.02-
3.8 % per year, which can contribute to a conductivity increase of approximately 1.9x10-3 W/mK annually.
Garnier et al., (2010) studied the influence of aluminum coating on the vapour permeability of VIPs. The
vapour permeance was measured under different temperatures and relative humidity. They found that the
permeance was inversely proportional to the coating thickness and proportional to the surface fraction of
pin-holes. Through a hygrothermal aging process conducted in a climatic chamber at 70°C, 90% RH,
Garnier et al., (2011) noted that layering multiple sheets of polymer films had no further effect on vapour
diffusion and the increase of water content in the VIPs would cause the degradation of the polymers over
time due to a hydrolysis reaction which results in the delamination of various barriers. Similarly
Heinemann (2008) studied the effect of moisture on the overall thermal conductivity of VIPs using hot
plate apparatus. It was observed that most moisture was adsorbed in the core material while only a small
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amount present in a gas state. With the increase of temperature difference between the hot and cold plate,
the moisture content level increases at the colder side, which is an indication of moisture transport under
temperature gradients.
5. POLYMER SEALS AND PANEL JOINTS
The manufacturing technique is an important component contributing to the long-term performance of
VIPs. This is particularly the case when it comes to sealing and evacuating the polymer seals and
connecting the panels’ joints. The moment the seal is broken, air is allowed easy passage back into the
panel, eliminating the benefits of the system. Malsen et al. (2008) studied the effect of heat seals on metal
films. The composite investigated comprised a base layer of polyethylene sealant, followed by an
aluminum layer for the metallic coating and lastly a layer of polyethylene terephthalate (PET) for
protection. The heat seal where these layers are connected is considered to be the weakest part of the
coating. This study compared the bond of seals at extremely low temperatures as well as at room
temperature. The temperature at which the polymers are sealed and the amount of time they are heated,
largely determines the strength of the bond. When the films are heated, a small amount of pressure is
applied and the layers fuse. There are various types of failures that can occur as a result of sealing methods.
Peeling occurs when two fused laminates are completely de-bonded. Tearing is a rupture that occurs in the
film in a non-sealed area. The third failure is a combination of peeling and tearing, often resulting is tearing
along the seal. It is also possible for delamination to occur at areas other than the seal. Four types of panels
with different metallic layers were tested. At room temperatures, it was found that the most common type
of panel failure was delamination along the seal. Overall, seals tend to perform better at colder
temperatures.
6. THERMAL BRIDGING AND EDGE LOSS
Since the foil has a much greater thermal conductivity value than the core insulation material, the rate of
heat transfer is significantly increased along the edge of the panel as well as the increased potential for
moisture accumulation in micro-regions of the panels. When two panels are joined, the thermal bridging
effect will be increased as two metal barriers in contact increase the potential for heat transfer. Tenpierik
et al., (2007) developed a numerical model to evaluate the thermal bridging and edge effects of VIPs using
four different types of seaming methods with three types of metallic films. The modeling results were
compared to laboratory measurements for validation. They concluded that the significance of the edge
effect of VIPs depends on the thermal conductivity of core materials, thermal conductivity of the laminate,
thickness of aluminum, and the edge seaming methods resulting in different seaming thickness. Wakili et
al, (2004) carried out hot plate tests to measure the thermal conductivity of VIPs with edge effects included.
The test samples had fumed silica cores with three different seaming methods. They found that the heat
transfer via the edge effect is significant and is dependent on the geometric relation between the volume of
panel and surface area of the foil, thus larger, square panels will provide a lower conductivity value than
smaller, rectangular panels. Through numerical modeling Tenpierik and Cauberg (2010) studied the effect
of eliminating the thermal bridging in VIPs by encapsulating VIPs with an additional layer of expanded
polystyrene (EPS). They found that by integrating VIPs the thermal resistance of EPS could be
significantly improved (up to 35% with 30mm panels, 248% with 100mm.) The addition of EPS may also
contribute to the durability of the VIP and potential reduction of deficiencies in the metallic barriers.
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7. PERFORMANCE OF VIP ASSEMBLIES
The majority of studies on VIPs focused on factors influencing the overall thermal conductivity of the
panel itself. However, in building applications the actual performance of VIPs will be influenced by its
construction and interaction with other materials/elements within the wall assemblies. Nussbaumer et al.,
(2006) tested the thermal performance of VIPs assemblies encapsulated with EPS using a hot box
apparatus. Six sample panels were mounted to a concrete wall and monitored with thermocouples.
Damaged VIPs were also included in the test samples. The damaged area was characterized by the length
of tear in foil seam. The study concluded that the U-value of a 60mm EPS containing VIPs outperforms
120mm conventionally used insulation. The U-value of the 60mm EPS-VIP assembly was slightly higher
than the 120mm insulation with all VIPs damaged. Grynning et al, (2010) carried out hot box
measurements on a complete wall assembly. They studied the single layer application of VIPs versus
double layer configurations, while considering different panel thicknesses, edge effects, and the effects of
staggering panels and taping joints. Temperature measurements showed irregularities in certain areas due
to the compression of panels during installation. A 19% higher overall U-value was found in measurements
when compared to calculations based on the nominal thickness of VIP panel. This study concluded that the
size of the panels had an impact on their overall thermal resistance, as did the orientation and
configurations. It was speculated that this was due to possible convection in gaps between the hot and cold
surfaces of the VIP.
8. SERVICE LIFE PREDICTION MODELS
Several studies had focused on developing models to predict the service life of VIPs. The definition of
service life has not yet been standardized, however, it is generally agreed upon within the academic
community that the service life of a VIP is defined by the amount of time it takes for the conductivity to
exceed 8.0 x 10-3 W/mK (Schwab et al, 2005). To perform as an acceptable insulation within a building
envelope, the service life must exceed a minimum of 50 years (Mukhopadhyaya et al, 2011). In Simmler
and Brunner’s model (2005) the overall change in the conductivity was expressed as the change in
conductivity due to internal gas pressure change and moisture content change. The rate of pressure change
is primarily determined by the air permeance, which is influenced by temperature, relative humidity,
surface area and panel length, and manufacturing methods. Similarly the accumulation of moisture within
the core materials is determined by the vapour pressure difference between the interior and exterior of the
panel and the water vapour transmission rate. The thermal bridging and edge effect of the panel was
included in the initial conductivity. Their study concluded that VIPs can provide a sufficient service life;
however special care should be taken in envelope design to prevent exposure to excessive humidity and
minimize the potential for condensation, as moisture accumulation proved to be the largest contributor to
the increased thermal conductivity.
Schwab et al., (2005) carried out comprehensive analyses of VIP performance based on measurements and
developed a service prediction model. The initial model was broken down into the conductivity due to solid
and gaseous conduction, radiation, gaseous diffusion and moisture convection. The contribution of each
term to the overall conductivity over time was described and evaluated individually. The two main
parameters were the change in conductivity due to gas permeation and water vapour transmission. A
mathematical expression of the change of internal pressure over time was formulated based on the
measured gas transmission rate and the ambient temperature, pressure, effective pore volume of the core
materials. The final prediction model included the initial conductivity of the VIPs with two terms
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accounting for the change in conductivity due to gas permeation and change in moisture content. While the
gas portion of this model is consistent with others’ work, this model lumps moisture accumulation and
water vapour transmission as one variable. Upon examining Schwab’s work thoroughly, Wegger et al.,
(2010) proposed an alternate model that separated the water accumulation and water vapour transmission.
Theoretical analyses by Wegger et al. showed that for five types of commonly used VIPs with an initial
thermal conductivity of 4.0 x10-3 W/mK, four laminates can maintain a thermal conductivity of less than
8.0 x 10-3 W/mK for a minimum of 50 years.
All the models reviewed require panel specific performance data such as gas transmission rate and water
vapour transmission rate in addition to basic material properties. However, these material properties are not
yet standardized within the industry and makes it difficult to synthesize and apply these models to make
prediction without conducting specific measurements.
AN ANALYTICAL MODEL
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Assumptions and Excluded Variables
• A two-dimensional steady state heat transfer is assumed. While the edge effect is accounted for by a
linear thermal transmittance, the 3D effect at corners was simplified.
• This model does not account for structural and physical deteriorations. For example, exposure to
ultraviolet radiation may cause the foil to weaken thereby causing higher transmission rates of gas and
moisture. The oxidation of the metallic foil also has an impact on the transmission rate of air as
deficiencies within the foil increase. The model does not account for exposure to pollutants and acidity
that could contribute to degradation of materials over time.
• The outgassing and its contribution to the change in conductivity of core materials was also excluded
in this model. Previous studies showed that the majority of outgassing occurs within the first year after
panel fabrication and therefore on a scale of a 50 year service life, this value is negligible.
• This model applies to fumed silica core materials only.
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Categorization of Variables and Determination of Generic Properties
The model is used to predict the thermal conductivity over time under the same accelerated aging
conditions as NRC’s aging tests in order to evaluate the accuracy of the prediction model. The specific
material properties of the panels tested at NRC were unknown, therefore, a generic material database was
assembled from literature and the gas transmission rate and water vapour transmittance rate were taken
from literature. Six types of commonly used VIPs are chosen. Three of the panels were of the aluminum
foil variety (AF) and the others were metalized foils (MF). Typical examples of these foil compositions are
shown in Figure 1. It should be noted that the material properties for these foils were taken from typical
foils that may be used in the industry, and are not representative of any specific VIP products.
Based on the analysis of material properties assembled from numerous sources, these material properties
were categorized as associated with high, average and low quality VIPs. These material qualities were
determined primarily by the foil thickness, the gas transmission rate, the water vapour transmission rate
and core material density; which are the most influential factors on the VIP performance over time. The
high quality materials typically have greater foil thickness, low gas transmission and water vapour
transmission rates and high material density. Low quality materials typically have smaller foil thickness,
high gas transmission and water vapour transmission rates with lower material density. The average
material was determined based on average values. Tables 1 and 2 list the constants and material properties
used in the calculation. Table 3 lists the climatic conditions for accelerated aging tests by NRC. The values
here represent the initial cycle, as the pressure values inside the panel would increase with each cycle.
FIGURE1: TYPICAL SECTIONS OF ENVELOPE MATERIALS FOR VIPS. (TENPIERIK ET AL, 2007)
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TABLE 1: LIST OF CONSTANTS USED IN THE CALCULATIONS.
TABLE 2: LIST OF MATERIAL DEPENDENT VARIABLES FOR EACH VIP TYPE CALCULATED.
MF=METALIZED FOIL, AF=ALUMINUM FOIL.
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TABLE 3: CLIMATE CONDITIONS USED TO SIMULATE ACCELERATED AGING (7 DAYS PER
CYCLE).
RESULTS AND DISCUSSION
The experimental results published by the National Research Council of Canada (Mukhopadhyaya, 2011)
were used to compare with the model predictions. Five types (3 samples for eack type, total 15 samples)
of VIPs with initial thermal resistances ranging from RSI 4.29 to 4.85 m2K/W were subjected to accelerated
aging in the lab. These panels were identified by 482-171, 487-61, 482-88, 487-115, and 499-106. During
the first half of each cycle, the panels were kept under conditions of 23°C, 95% RH for seven days. For the
next seven days the panels were kept under conditions at 70°C, 5%RH. The panels went through these
fourteen-day cycles nine times. The thermal resistance of each panel was measured at the end of each half
cycle. Since the initial thermal resistances varied, these values were normalized to their initial RSI in order
to compare the change over time in each panel. As shown in Figure 2, three VIP products behaved in a
similar manner (487-61, 482-171 and 487-115) where their thermal resistance was reduced to 95% of the
initial value. Product 499-106 had a much faster rate of reduction in thermal conductivity over the
accelerated testing. Results for the product 482-88 showed an initial thermal resistance increase after the
first elevated temperature (70°C) exposure, due to enhanced getter/desiccant performance, before reducing
at a rate similar to the average cases.
Figure 3 shows the results of the calculations under the same climatic conditions used in the accelerated
aging process. When comparing the results in Figure 3 to those presented by the NRC tests, it can be
observed that the average metalized foil VIP (MF avg.) follows a very similar trend to products 487-61,
482-171, and 487-115. It also appears that MF low follows a similar trend to product 499-106. Although
the predicted results are based on assumed material properties (which are assembled from commonly used
materials and construction methods), the good agreement achieved between prediction and measurements
indicates the validity of the prediction model and the applicability of the model to commonly used VIPs.
The other observation that can be made from the normalized thermal resistances is that the rate of change
in thermal resistance among the metalized foil products varies greatly in comparison to the aluminum foil
films, and they generally decrease in thermal resistance more quickly than the aluminum foils. This is
likely because the aluminum foils tend to have lower gas and water vapour transmission rates.
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FIGURE 2: MEASURED RESULTS PROVIDED BY NRC OF ACCELERATED AGING OF 5 VIP
PRODUCTS. (MUKHOPADHYAYA, 2011)
FIGURE 3: NORMALIZED THERMAL RESISTANCE OF SIX TYPES OF COMMONLY USED VIP
PANELS USING THE PROPOSED MODEL UNDER NRC’S ACCELERATED AGING TEST
CONDITIONS (20CM THICKNESS).
CONCLUSIONS
This paper provides a thorough review on parameters that influence the long-term thermal performance of
VIPs. The critical material properties that contribute primarily to the aging of VIPs are the gas permeation
and water vapour transmission through the foil barrier and seam joints. The literature reviewed covered
most of the known and relevant findings regarding this material. These findings allowed the development
of generic material properties based on previously conducted experiments. A simplified numerical model
built upon existing models was proposed and used to predict the performance of five types of commonly
used VIPs under accelerated aging test conditions. The predictions generally agree well with
measurements, which indicated that the proposed model can be used as a viable tool to predict the
approximate long-term performance of VIPs.
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Tenpierik M., & H. Cauberg. 2007.Analytical Models for Calculating Thermal Bridge Effects Caused by Thin High
Barrier Envelopes around Vacuum Insulation Panels. Journal of Building Physics, 30 (3).
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optimization.Building Research and Information, 35 (6), 660-669.
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Mechanical Engineering, National Chiao Tung University, Springer-Verlag.
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panels. International Journal of Heat and Mass Transfer, 52, 3084-3090.
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Under Vacuum Condition. Journal of Cellular Plastics, 43, 17-30.
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