A study on database of modular façade retrofitting building envelope

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A study on database of modular fac¸ade retrofitting building envelope Yangluxi Li , Lei Chen PII: DOI: Reference:

S0378-7788(20)30060-8 https://doi.org/10.1016/j.enbuild.2020.109826 ENB 109826

To appear in:

Energy & Buildings

Received date: Accepted date:

7 January 2020 28 January 2020

Please cite this article as: Yangluxi Li , Lei Chen , A study on database of modular fac¸ade retrofitting building envelope, Energy & Buildings (2020), doi: https://doi.org/10.1016/j.enbuild.2020.109826

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Highlights 

The insulation capacity of system A could be improved significantly via integrating VIP board into whole construction.



The tube for ventilation significantly deteriorates construction insulation capacity.



Use insulation material to replace the air as levelling layer could improve construction insulation capacity.



Insulation capacity of system A could be improved via integrating VIP board into construction.

A study on database of modular façade retrofitting building envelope YangluxiLi1,*, LeiChen1 1

Welsh School of Architecture, Cardiff University, UK *Corresponding author: [email protected]

Abstract: The purpose of this paper is to investigate the prefabricated retrofit façade construction features of thermal insulation. Research done so far mainly concentrates on specific structures of modular renovation construction for building envelope regardless of common features and thermal insulation characteristics. This study utilizes matrix method to establish an entire structure system basing on a proposed original insulation structure and compare various heat preventing capacity. Different layers in construction are investigated to assess the influence on insulated performance of them. The result shows that the VIP panel, ventilation duct and levelling layer are the most significance factors affecting whole system insulation performance. Diminishing ventilation duct size and adding VIP panels could improve building envelope insulation ability efficiently in the process of building renovation. Keywords: Building retrofit; Building envelope; Construction; Thermal insulation evaluation; 1.

Introduction Currently, building energy consumption is increasing, which brings great pressure and influence

to the ecological environment. After a large amount of data research, the International Energy Agency (IEA) concluded that existing buildings were responsible for more than 40% of the world's total energy consumption and nearly 24% of global carbon dioxide emissions. (IEA, 2006) A high energy efficiency potential lies in the existing buildings leads people to seek solutions of building renovation. Since facade is a key element in ensuring building energy efficiency and interior comfort, prefabricated modular facade retrofit has been the subject of many studies research done in building retrofit projects. One of the aims of this study is to create a database about modular façade renovation constructions and resulting thermal characteristic via python programming language and simulated software. All the relevant data and cases could be divided into two systems generally, and further subdivided into several multiple layers with different functions and construction methods. The establishment of prefabricated modular facade retrofit database can contribute to filter related construction pattern, and provide reference for the modern building energy efficiency design. Modular building is a unique off-site construction form which is composed of modular units. (Ferdous W et al., 2019) All modules could be prefabricated in the factory in advance, and the components are not only structural units but also spatial elements. Due to its characteristics of off-site and prefabricated, modular buildings have a better performance in structural performance, construction period and energy efficiency. (Rogan AL;2000.; Lacey AW et al, 2018) Modular construction technique has been wildly implemented in some developed countries and areas, such as Japan, America and Europe and etc. (Annan C. 2008; Li HX et al, 2013; Steinhardt DA & Manley K, 2016) However, on the other hand, due to the impact of economic factors and construction technology, fewer modular building projects are performed in developing countries. (Mao C et al. 2015) In terms of building envelope, it is a crucial element in prefabricated architecture because it not only operates as an appearance element but the main load-bearing structure. Brown first applied a patent for a modular building related to structural facade in 1974 which invited a construction with sectionalised connecting roof. (Brown L,1974) Since then, a number of related patents have been disclosed. (Pingel NW, 2000; Raynes, 1965; Lindal W, 1985) In 2008, J. Hövels from Delft University of Technology defined a type of openable modular facade and

developed a new alternative facade for the mantal-glass facade establishment. (Hövels J, 2007) Building retrofit is a complicated procedure under any scale, which includes structural transformation of multiple scales and parts, such as outdoor environment, indoor comfort, roof (Aste et al., 2012) façade (Ebbert T, 2010), HVAC and so on. In this case, envelope is one of the significant segments in building renovation process, which has a large impact on the appearance and function of existing building. (Tovarović, J Č et al., 2017) In addition, the construction and physical characteristics of facade determine the external skin temperature (Huttner S, 2012), indoor temperature and air condition affecting the energy level coming from HVAC and mechanical ventilation system correspondingly. (Lassandro P & Turi DS, 2017; Dascalaki E & Santamouris EM, 2002) Therefore, basing on the above analysis, the transformation of the building surface can be broadly divided into 4 types: aesthetics improvement, acoustic renovation, energy efficiency renovation and risk mitigation modification, to meet the requirement of minimizing energy consumption, improving living comfort and maximizing investment value. (Martinez A, 2015; De Geetere, L. & Ingelaere, B. 2016; Lundh H 2017; FEMA, 2014) German architect Thomas Herzog has participated in many building renovation projects, such as the Munich DE warehouse conversion in 1997. In this project, a special irregular double-skin membrane structure was added to the interior of the old building, which forms a heat air buffer between new layer and old facade. (Ingeborg Flagge 2003) After the analysis on the types of building skins, Thomas Herzog listed the facades categories in the basis of material and construction, and mentioned specific cases with regard to facade retrofit. Scholars majoring in architectural facades and products from delft university of technology have performed a lot of researches on energy efficiency renovation of building envelope. Giebeler G published a manual of building refurbishment in 2005, which provided detailed renovation planning, energy saving solution, disaster prevention as well as the cost of project, which has almost covered all the aspects of the transformation. (Giebeler G 2005) Thiemo Ebbert discussed the energy preservation improvement strategies for skins of old office buildings. Multiple new technical methods such as double skin and BIPV solar panels also have been introduced, which definitely prove the diversity and feasibility of building refurbishment. (Ebbert T 2010) Konstantinoua and Ulrich Knaacka proposed a new mean for building renovation, which conducted an assessment on the performance of building components for architecture envelope and roof forming a toolbox. (Konstantinou T and Knaack U, 2011) In view of the number of approximately 250 million high-energy dwellings in current housing stock, the EU (European union) has proposed EPBD (Energy performance of buildings directive) in 2011, which includes the requirements of NZEB (nearly zero-energy buildings). (D’agostino D et al. 2017) Meanwhile, EPBD also needs the promotion to reconstruct existing buildings into NZEB. Under the auspices and command of the European Union, member states have launched a campaign to retrofit built buildings with modular facade solutions. Heikkinen et al. defined basic principles for the energetic modernization of the building envelope using prefabricated large-sized timber frame elements (the Timber-based Element System or TES method). There the basis for the use of prefabricated retrofit building elements is a frictionless digital workflow from survey, planning, o-site production and mounting on site based on a precise initial 3D measurement. (Heikkinen P et al., 2019). An apartment building refurbishment in Finland implemented prefabricated façade elements, which renovated the envelope, roof, floor slabs and heat recovery completely and used the TES system (Timber-based Element System) to renovate the building facade. After that, a series of similar projects, such as ADAPTIWALL, BERTIM BRESAER, Energy Matching Envision, HEART, HERB, MORECONNECT, PLUG-N-HARVEST, ReCO2ST, RenoZEB, RETROKIT and 4RinEU were funded by EU to seek for more flexible solutions for building renovation. These facade modules generally consist of

structural framework, thermal insulation, waterproof layer, ventilation pipes and exterior cladding. Beyond to enhance the buildings’ energy efficiency, most of the prefabricated facade modules in these projects also were embedded in other positive or passive energy-saving strategies such as buildingintegrated photovoltaic (BIPV), ventilation pipe, etc. (Table 1) Most of these projects integrate solar and wind energy as sustainable resources into building façade.

Project ADAPTIWALL (CORDIS 2018)

Table 1 projects of building renovation funded by EU government Load bearing Insulation layer External cladding lightweight concrete buffer adaptive insulation Brick cladding steel reinforcement

Integrated energy-saving technologies THEX (Total heat exchanger) Solar thermal PV Solar thermal Ventilation duct

BERTIM (CORDIS. RETROKIT 2018) BRESAER (CORDIS. BRESAER 2018)

batten

rock wool

Ceramic brick

Fibre Reinforced Concrete metallic profiles

Multifunctional insulated panel(IP)

Solar thermal PV Lightweight ventilated façade module (VF)

Energy Matching (CORDIS. EnergyMatching2 018)

Unclear

Wool

Photovoltaic Panels (PV) Photocatalytic functional coating (COAT) Painting panel Variant

Envision (CORDIS. Envision 2018). HEART (CORDIS. HEART 2018) HERB (CORDIS. HERB, 2018 ) MEEFS RETROFITTING (CORDIS 2018)

Metal Timber

Wool

Variant

Unclear

Wool

Variant

Solar heat collectors Solar thermal PV Solar thermal BIPV

Aluminium

Wool

Variant

Photovoltaic-solar thermal (PVT)

Fibre Reinforced Polymer(FRP)

Wool

MORECONNECT (CORDIS. MEEFS

Timber Steel

Mineral.wool

glazing solar protection green facade Photovoltaic panel wood planks

Advanced Passive Solar Protector Energy Absorption Unit,Advanced Passive Solar Collector and Ventilation Unit BIPV Solar thermal PV

BIPV

RETROFITTING 2018) PLUG-NHARVEST (CORDIS. PLUG-NHARVEST 2018 ) ReCO2ST (CORDIS. ReCO2ST 2018) RenoZEB (CORDIS. RenoZEB 2018) RETROKIT (CORDIS. RETROKIT, 2018) 4RinEU (CORDIS. 4RinEU 2018)

aluminium frame

Wool

conventional cladding material building integrated photovoltaics (BIPV) solar thermal collectors

Solar thermal BIPV Ventilation duct

Unclear

Vacuum insulation panels (VIP)

Variant

PV

Metal

Wool

Variant

BIPV or BIPVT

Aluminium Timber

Wool

Variant

Solar thermal PV

Timber

Wool

Variant

Solar thermal

Python is a cross-platform computer programming language, which is one of the most popular FLOSS (Free/Libre and Open Source Software). In this research, python is the main programming language writing code to construct database. 2.

Methodology 2.1 Database building In this study, almost 2000 retrofitted buildings and 173 innovation projects related building energy

efficiency supported by the Horizon 2020 are investigated in terms of the façade structure, place of architecture, application, etc. These cases distribute all over the world and contain various type of building such as office, living etc. Basing on the relevant modular renovation projects reviewed, a excel statistics of retrofitting module façade constructions for different projects are made to form a database. As this paper mainly focuses on the modular renovation methods for built building, all cases are filtered into approximately precise 300 projects according to the construction characteristics. This database mainly includes these 300 projects and indicates all layers of different renovation construction patterns, places, function, substrate and so on. In this database, every item under categories is signed with diverse keywords in order to be identified by program in convenience. In addition, it should be noted that all items are limited to the same specific rules rather than named only depending on researchers’ opinions. The number of all terms are counted to determine the construction model shaping. In addition, the relationship between various items are also analysed to investigate the internal potential connectivity. 2.2 Model construction In this research, in order to enable paradigm database of construction focusing on modular retrofit pattern for built building in the end, it is imperative to analyse wall structure condition in detail. An original building envelope construction is chosen in line with a structure proposed by book named Retrofit Module Design Guide (René L. Kobler, et al. 2011). This book is a manual of project of IEA ECBCS Annex 50 and all studied constructions studied in this paper are established basing on it. Figure 1 shows the ideal paradigm building envelope structure in which each layer could be replaced with different material and thickness. In this case, the paradigm can cover all modularization solutions for building renovation to serve for architects in future.

Figure 1 ideal paradigm building envelope structure Figure 2 presents the workflow of construction model built. I: Cases database. The construction database shaping needs fully to take all structures into account so that explore the internal potential common characteristics among all investigated cases. Depending on the database built, relevant construction terms are selected to form the construction database in order to investigate the commonality of these structures. II: Construction layers. Every construction could be classified into various layers in terms of function. In the following section, these functional tiers form the common model for structure of building envelope. III: Frequency statistics. Basing on above dataset which contains many aspects for projects such as location, function etc., it is indispensable to count the frequency of different types of layers in the construction of the envelope structure. This frequency for various layers indicates whether some layers are imperative or not. In the basis of statistics of frequency for different layers and the original construction described in retrofit module design guide (René L. Kobler, et al. 2011), a model is constructed according to various functions of constructed layers. Note that this model is constructed only related to the functions regardless of sizes such as thickness and material types. As the material and thickness of several tiers concern with thermal conductivity of envelope, hence in the next section, relevant computational equations will be induced to calculate thermal coefficients of entire construction which is impacted by material and thickness. In addition, machine language could achieve automatically this purpose via programming. VI: Array. After finishing above steps, it can be obtained that all constructions consist of two types of layers of fixed and variable. In order to enable final database of structures, it is imperative to combine above two constructed patterns via matrix method. Finally, all layers constitute the paradigm of architecture external structures.

Figure 2 workflow of construction model built 2.3 Heat flux description simulation In case of building retrofit project, wall thermal characteristics play a crucial role for whole architecture energy efficiency. Furthermore, the heat flow distribution in envelope construction has critical influence on the architecture insulation capacity especially in terms of thermal bridge. In this study, to achieve the heat insulation capacity of different constructions, a software called workbench developed by ANSYS company is implemented to simulate the description of thermal flow condition within building wall. All the geometric objects are divided into more than 30,000 structured grids in ICEM, and each of which is around 2mm*2mm and with the quality of more than 0.999. All the output structured meshes are imported into Fluent to simulate the conduction of heat. SIMPLE algorithm and energy equation are used for this simulation and the number of iterations is set to 700. Convergence is assumed to be obtained when all the scaled residuals levelled off and reached a minimum of 10-6 for energy term.

2.4 Governing equation Thermal conductivity coefficient is a crucial impact factor reflecting building envelope insulation ability directly. Hence, this parameter needs to be taken into account to assess heat flux performance for various constructions. It can be obtained via this coefficient investigation that the relationship between heat transfer value, thickness and material thermal resistance. In this case, this relevance could disclose internal potential optimal construction layer combination to improve structure in accordance with different requirements. Following equations indicate entire progress computing the thermal transmitted factor. Steady-state heat conduction: the temperature of each part of an object does not change with time. Hence the heat flux q is the same everywhere along the wall. 𝜕𝑡 𝜕𝜏

=0

(1)

Q=q1=q2=q3=q4=q5…

(2)

Where 𝜕𝑡 is temperature and 𝜕𝜏 represents the time. Q presents the heat flux and q1, q2, q3, q4, q5 (W/m2) displays the heat flux for various components of envelope construction. If the height size is much larger than the thickness of construction, the heat transmit course can be considered as a one-dimensional heat conduction. The equation can be shown as follow (3): 𝑑𝑡 𝑑𝑥

=

|𝑡𝑒 −𝑡𝑖|

(3)

𝑑

Where te and ti indicate the two sides temperature of enclosure construction, respectively. d expresses the thickness of envelope structure. According to the above formulas, the heat flux for the single-layer flat wall can be obtained as follows. Where 𝜆 is the heat conductivity factor. 𝑞=

𝑡𝑒−𝑡𝑖

(4)

𝑑 𝜆

Considering the steady state heat transfer process and eq. (2), homogeneity multi-layer envelope construction can be calculated as a composite with different materials. Heat flux is equal with each other. Equation (5) governs this process. 𝑅=

𝑑

(5)

𝜆

|𝑡𝑒 −𝑡𝑖| |𝑡𝑒 −𝑡𝑖| 𝑑2 𝑑3 𝑑4 𝑑5 ∑𝑛 𝑅 + + + + 𝑗=1 𝑗 𝜆1 𝜆2 𝜆3 𝜆4 𝜆5

Q=q1=q2=q3=q4=q5=𝑑1

=

(6)

In this equation, R is the material thermal resistance (K/W), number of 1,2,3,4,5 represent different layers material. Whole thermal flow transferred process can be shown in fig. 3.

Figure 3 Heat flux transfer process Fig. 3 not only indicates the thermal flow course but presents the interior and exterior surface convection process for the envelope construction thermal exchange procedure. Hence, apart from above the heat flow process inside the envelope, outdoor and indoor surface convection procedure should also be estimated by the governing equation. Eq. (7) and (8) (9) control the whole progress. 𝑞𝑖 = 𝑎𝑖 |(𝑡𝑖1 − 𝑡𝑖2 )|

(7)

𝑞𝑒 = 𝑎𝑒 |(𝑡𝑒1 − 𝑡𝑒2 )| 𝑞 = 𝑞𝑖 = 𝑞𝑒 =

(8)

|𝑡𝑒−𝑡𝑖| 1 𝑑 1 +∑𝑛 𝑖=1𝜆 + 𝑎𝑒 𝑎𝑖

(9)

Where "ai" and "ae" are the heat transfer coefficients of the two sides surface of envelope construction. Moreover the "te" and "ti" are the air temperatures of the inner and outer surfaces. qi and qe represent the heat flux of general heat transferred system. In order to state thermal resistant ability of 𝑑

different material more distinctly, 𝜆 is replaced by the R used in the Eq. (5). From the above formulas, it can be concluded that the heat transfer coefficient of the enclosure composed of homogeneity multi-layer materials is: 𝐾=

1

(10)

1 1 +∑𝑛 𝑖=1 𝑅𝜆,𝑖+𝑎𝑒 𝑎𝑖

From the reciprocal relationship between heat transfer coefficient and thermal resistance, it can be seen that the total thermal resistance of enclosure structure composed of multi-layer materials is: 𝑅=

1 𝑎𝑖

+ ∑𝑛𝑖=1 𝑅𝜆,𝑖 +

1

(11)

𝑎𝑒

The heat transfer coefficient of inner and outer surfaces varies with location, surface and season. However, this research mainly investigated the solid bracket of enclosure construction with no impact of surface thermal transfer function. Therefore, in this study, the value of heat transfer coefficient of inner surface ai is chosen as 8.7W/(m2/K) and ae is 23 W/(m2·K) which are always adopted in some regions in Europe. In addition, it should be noted that the above calculation method only applied to the enclosure construction comprised by homogeneity materials. For inhomogeneity structure, entire thermal transmitted condition is different with homogeneity construction. Hence, entire relevant heat modulus studied should use another equation to calculate enclosure structure heat coefficients. Followed equation governs the averaged thermal transfer resistance for inhomogenous construction. 𝑅̅ = [ 𝐹1

𝐹0 𝐹 𝐹 + 2 ∙∙∙+ 𝑛

𝑅0,1 𝑅0,2

− (𝑅𝑖 + 𝑅𝑒 )] 𝜑

(12)

𝑅0,𝑛

In eq.12, where 𝑅̅ is the averaged thermal resistance of the inhomogeneity stuff layer (m2· K/W). F0 is the total heat transfer area perpendicular to the direction of heat flow (m2). F1, F2…Fn, is per heat transfer area perpendicular to the direction of heat flow (m2). R0,1, R0,2, … R0,n, is per thermal transmitted resistance corresponding to different part of 1,2…n. 𝑅𝑖 is the internal surface conductive transfer thermal resistance. 𝑅𝑒 is the external surface convection transmitted thermal resistance. 𝜑 is the correction factor. Table 2 presents the value rules for 𝜑 coefficient. Table 2 value rules for 𝜑 coefficient 𝝀𝟐 (𝝀 + 𝝀𝟑 ) ⁄𝝀 𝒐𝒓 𝟐 ⁄𝟐𝝀 𝟏 𝟏 0.09-0.10

𝝋 0.86

0.20-0.39

0.93

0.40-0.69

0.96

0.70-0.99

0.98

In the calculation course, 𝜆 refer to thermal conductivity. If the construction consists of two different materials, 𝜆1 is larger than 𝜆2. In this case, both thermal conductivity coefficients determine the 𝜑 value as shown in table 1. Moreover, if the construction is comprised with three various stuff, 𝜑 should be assigned in the basis of

(𝜆2 + 𝜆3 ) ⁄2𝜆 . Therefore, the 𝜆 is the premise to compute whole structure 1

thermal conductivity coefficient. Note that the circle shape should transfer to rectangle shape under same area when the pattern of material 1 is circle. In terms of thermal bridging system, the area-weighted average heat transfer coefficient (W/m2·K) is used to represent the heat transfer performance of the construction. Area-weighted average heat transfer coefficient refers to the average coefficient values of all parts of the external wall, including the main structure and its structural thermal bridge, basing on area size of various bracket parts. The calculation formula is as follows: 𝐾𝑚 =

𝐾𝑝 ×𝐹𝑝 +𝐾𝐵1 ×𝐹𝐵1 +𝐾𝐵2 ×𝐹𝐵2 +𝐾𝐵3 ×𝐹𝐵3 𝐹𝑝 +𝐹𝐵1 +𝐹𝐵2 +𝐹𝐵3

(13)

Where, Km is the area-weighted average heat transfer coefficient of whole enclosure structure. Kp is the main part (except thermal bridging) heat transfer coefficient of system. Fp represents the whole area of main components. KB and FB are the thermal bridging heat transfer value and area respectively. This study compares the resistance capability of different construction via computing K m values. As above methods have shown, this study mainly investigates modular retrofit techniques via analysing and establishing database of related design pattern. Basing on the database can summarize the corresponded model construction as original paradigm for renovation building envelope which is significant for further database construction. After that, using thermal computed equation, some heat flux analysis will be performed to obtained thermal features of various structures to optimize modular retrofitting structures. 2.5 Program development In the end of the investigation, in order to integrate whole studied results into a complete system, a software language of python is implemented to program entire procedure. Four objects followed need to be enabled: Object 1: Count some specific items in built database. Object 2: Automatic output specific corresponded modular construction graph according to various input conditions. Object 3: Compute different thermal transfer coefficients basing on types of material and respective thickness. Object 4: In accordance with limited condition of material parameter, this program could obtain the optimal construction of modular retrofitted pattern in terms of insulation performance.

3.

Results 3.1 Database construction Providing solutions for modular building envelope renovation is the topic of this study that has

received increasing attentions by research community and architects. Constructing a database for this building enclosure structure is significant indispensable for whole investigation in detail. 300 precise projects are investigated to count related information such as place, area, constructions, etc. This database conceals some potential disciplines between various items which could indicate the relationship between different building information. Figure 4 presents the diagram of total database items. In this study, seven items of location, area, function, part, floors, structure and construction are investigated in detail. However, it should be noted that in order to identify in convenience by computer language, these optional variants under each item displays relatively simple instead of specific instructions. (Fig. 4)

Figure 4 Optional variants under each item Through the analysis of the database information, it can be obtained as follows: Most of building envelope reconstruction projects mainly focus on residential building. Furthermore, for other types of architecture, the relevant energy efficient reconstruction methods usually concentrate on the other aspects of windows or load bearing structure instead of integrating various insulation material. It can be explained that the requirements of energy saving for this type construction are not high as people spend less time in non-residential buildings. For example, in case of buildings implemented with insulation materials, the number of residential building occupies almost more than 90% comparing to non-residential architecture. Building renovation pattern always employs additional transparent structure out the envelope in tropical and subtropical areas. Furthermore, for other climatic regions, buildings harness multiple retrofitting methods including adding insulation materials especially for residential architecture. This phenomenon mainly could be attributed to different requirements for construction enclosure insulation in the ambient environment. In tropical area, the living environment mainly requires ventilation and dehumidification which could improve ambient thermal comfort efficiently. Therefore, appending extra transparent structure is often implemented as the good performance in enhancing air change efficiency by taking advantage of the buoyancy driven principle in terms of ventilation. Moreover, in other regions particularly in cold district such as north Europe, adding addition external skin integrated with insulation

material is the primary solution for residential heat preservation. The above database shows that 100% residential renovation projects use reconstruction method embedding with insulation stuff in tropical and subtropical region which is much larger than that in other districts. In terms of building envelope renovation, the most widely used reconstruction position concentrates on windows and external skin. For instance, nearly all retrofitting strategies counted consist of these two methods which are highly much more than that using insulation material. This is mainly because of the easy replacement performance of above two components. In addition, the external skin renovation method is not limited by region and has high prefabrication performance, which can improve the appearance of the building. However, even though these two patterns could be employed in any areas, the disadvantage in thermal preservation also restricts its application which is caused by large convection effect. Therefore, an additional external skin system integrating insulation material which tends to be installed is imperative to provide solutions for improving building energy efficiency and thermal comfort level. 3.2 Paradigm of model for modular building envelope renovation The main object of this study is to construct a modular building envelope construction paradigm to enhance building insulation capacity further to saving building energy and improving thermal comfort. Hence, figure 5 presents the original constructions for building envelope renovation based on the manual book (René L. Kobler, et al. 2011). It can be seen from the statistics that the entire construction could be divided into several layers in the basis of functions as shown in figure 6. Among these levels, windows, insulation, loadbearing, external skin layers are indispensable for entire structure. Furthermore, other tiers are integrated into building enclosure basing on above three layers. Apart from this, it is also found that for some special renovation construction especially for cold regions, more particular layers such as ventilation ducts are embedded into enclosure structure. In addition, in order to improve insulation capacity efficiently, increasing number of layers gradually utilizes to construct whole building envelope. Therefore, basing on the database built and so as to indicate characteristics of construction in maximum, two systems named system A and system B are established in the aspects of layer application. Each system has several specific layer constructions such as levelling layer, insulation layer, etc. Various concrete items under different systems are shown in Figure 6. It can be obtained from fig.5 and fig. 6 that system A locates beside the substrate wall and system B away from the base structure. In view of function, system A primarily uses for ventilation integrated with insulation, while the capability of insulation is enabled by system B. Note that although external skin structure put in the system B, it is indispensable for entire construction with no regard of the presence of which systems. Following table 3 instructs specific functions of each layer and corresponding parameters. System A

Table 3 specific functions of each layer and corresponding parameters Layer & function Common material Necessary or not Parameters Windows Low-e Y U value Levelling layer Rockwool N U value Thickness Fireproof and Gypsum fibreboard N U value encase insulation Thickness material Loadbearing Timber & steel N Insulation Rockwool Y U value Thickness Ventilation Metal ducts N U value Thickness

B

Fireproof and encase insulation material Loadbearing Vapour barrier

Gypsum fibreboard

N

U value Thickness

Y N

Insulation

Timber & steel Vacuum insulation panel Rockwool

External skin

Multiple

Y

U value Thickness U value Thickness U value Thickness

Y

(In this table, the parameters mean adaptable data of various layers which will be implemented for heat flux research of all constructions. Layers and function express layers’ name and respective effect. The common material indicates some stuff widely used. The column necessary or not illustrates the necessity of different layers which is determined according to the count statistics of database)

Figure 5 prototype of building renovation façade construction (René L. Kobler, et al. 2011)

Figure 6 Various concrete items under different systems Whole modular construction paradigm is established in accordance with the above two systems

and all specific layers. All tiers condition is instructed as follows: System A: Window: This is the indispensable component for building envelope renovation, no matter how many structures are. The U value performance of glass mainly influence construction insulation ability. Levelling layer: The layer uses for supporting insulation material in case other attaching components lie in an unstable condition. Fireproof and encase insulation material: The function of fireproof panel is to realize flame retardant feature focusing on the flammability characteristic of insulation stuff. It also encloses the incompact insulation material into a box simultaneously. Loadbearing: Loadbearing structure supports entire constructions including system A and B. It penetrates entire structures and connects with external skin. Even though it locates via outside to inside, the thermal bridge doesn’t need to be taken into consideration as the small cross section area and insulation treatment. Insulation: This layer is the core part for system. It is responsible for entire combination performance of preserving heat load. Final thickness for whole construction also depends on this layer situation because the insulation material’s thickness is large. Ventilation: Ventilation components is a special layer for this modular retrofitting building envelope paradigm. This layer mainly provides the fresh air via ventilated ducts encased by other stuff in order to integrate airflow function with building energy efficiency renovation. System B: Fireproof and encase insulation material: This fireproof layer is also one of the parts of it in system A which also encases the insulation material in system A and B. Loadbearing: This loadbearing structure is the same as that in system A as it penetrates entire building envelope construction. Vacuum Insulation Panel (VIP): This panel locates beside the fireproof panel and closest to system A. VIP is one of the most advanced insulation materials in the world with a low heat transfer coefficient and small thickness. This system uses it to prevent possible linear thermal bridge effect caused by ventilation duct in system A and also restrains the condensation generation. In addition, it can also support insulation material in system B as levelling layer. Insulation: This layer implements the same stuff with that used in system A. External skin: External skin layer is imperative for any envelope constructions no matter where the building locates. In this system, skin material often adopts veneer stuff such as texture tiles, coating etc which is supported by loadbearing structure. Its thickness and transmitted coefficient value influence entire structure insulation capacity. Apart from this, it should be noted that many renovation projects of building façade only focused on external skin part for example, adding additional double skin curtain wall. Furthermore, in this study, the research principally concentrates on the insulation ability of external skin regardless of retrofitting strategies. Hence, only two relevant variants of thickness and U value of skin dominate entire construction property. According to above analysis and instruction, various layer constructions constitute different systems. In order to investigate all related construction characteristics of thermal performance, a new database needs to be established in the basis of existence situation of each layer. Followed table 4 presents the fresh structure of system A and B comprised by various layers. Table 4 fresh structure of system A and B comprised by various layers. (The name of construction is defined as the layer existence condition. If this layer exists, signs as Y,

otherwise it is N. The final name is the combination of all Y and N.) System A Category Name Diagram

2y+1n 2ynyyy

N: levelling layer

Category Name Diagram

Name Diagram

Category Name Diagram

Category Name Diagram

System B Category Name

2ynnyy

2yynyy

2yyyny

N: fireproofing and N: ventilation layer encase insulation material 2y+2n 2ynyny

2yyyyn

N: load bearing

2ynyyn

N: levelling layer N: fireproofing and encase insulation material 2yynny

N: levelling layer N: ventilation layer

N: levelling layer N: load bearing

2yynyn

2yyynn

N: fireproofing and encase insulation material N: ventilation layer

N: fireproofing and encase insulation material N: load bearing 2y+3n 2ynynn 2ynnyn

N: ventilation layer N: load bearing

2yynnn

2ynnny

N: fireproofing and N: levelling layer encase insulation N: ventilation layer material N: load bearing N: ventilation layer N: load bearing 2y+0n 2yyyyy

N: levelling layer N: levelling layer N: fireproofing and N: fireproofing and encase insulation encase insulation material material N: load bearing N: ventilation layer 2y+4n 2ynnnn

N:

N: levelling layer N: fireproofing and encase insulation material N: ventilation layer N: load bearing

3y+0n 3yyy

3y+1n 3yny

3y+1n 3yyn

3y+2n 3ynn

Diagram

N:

N: fireproofing and encase insulation material

N: vapour barrier

N: fireproofing and encase insulation material N: vapour barrier In table 4, ‘y’,’n’ express whether resulting each layer exists or not. Category indicates that the number of presence and absence layer condition. In terms of system A, ‘2y’ shows the two essential tiers of windows and insulation. The position capital ‘n’ displays the lacking layer which is also marked in table 4. The sequence of layers in system A is window, insulation, levelling layer, fireproofing and encase insulation material, ventilation, load bearing. For example, ‘2ynnyy’ means window, insulation, ventilation and load bearing layer exist and levelling, fireproofing and encase insulation material layer are missing. With regard to system B, ‘3y’ presents three indispensable tiers of insulation, loadbearing and external skin. The order of layers in this system name is insulation, loadbearing, external skin, fireproofing and encase insulation material and vapour barrier. For instance, ‘3yny’ indicates that the insulation, loadbearing, external skin and vapour barrier locate in system. Moreover, fireproofing and encase insulation material layer is missing. Basing on above table drawn by various layers situation, there are 14 cases of building envelope construction in system A. Furthermore, system B only have 4 cases which is much less than system A. This is mainly because that a number of functions in system A has met the requirement of system B in some aspects. Each strategy in table 4 could be estimated as one method for building envelope energy efficiency. In addition, in accordance with above each strategy, system A combines system B to establish a composite building envelope energy efficiency construction as followed table 5 shown. In table 5, horizontal title is system A, moreover, vertical heading is system B. Every strategy is named by the combination of system A and system B as shown below graph. All above constructions constitute entire database for building envelope retrofitting selection. In next section, thermal insulation feature of them will be performed to analyse via heat transmitted coefficient value.

System B

Table 5 Composite building envelope constituted by system A and B System A 2y+1n

2ynyyy

2yynyy

2yyyny

2yyyyn

2ynyyy3yyy

2yynyy3yyy

2yyyny3yyy

2yyyyn3yyy

2ynyyy3yny

2yynyy3yny

2yyyny3yny

2yyyyn3yny

3y+0n

3yyy 3y+1n

3yny

3yyn

2ynyyy3yyn

2yynyy3yyn

2ynyyy3ynn

2yynyy3ynn

2yyyny3yyn

2yyyyn3yyn

2yyyny3ynn

2yyyyn3ynn

3y+2n

3ynn System 2

System A 2y+2n

2ynnyy

2ynyny

2ynyyn

2ynnyy3yyy

2ynyny3yyy

2ynyyn3yyy

3y+0n

3yyy

3y+1n

3yny

3yyn

2ynnyy3yny

2ynyny3yny

2ynyyn3yny

2ynnyy3yyn

2ynyny3yyn

2ynyyn3yyn

2ynnyy3ynn

2ynyny3ynn

2ynyyn3ynn

3y+2n

3ynn System 2

System 1 2y+2n

2yynny

2yynyn

2yyynn

3y+0n

3yyy

2yynny3yyy

2yynyn3yyy

2yyynn3yyy

2yynny3yny

2yynyn3yny

2yyynn3yny

2yynny3yyn

2yynyn3yyn

2yyynn3yyn

2yynny3ynn

2yynyn3ynn

2yyynn3ynn

3y+1n

3yny

3yyn 3y+2n

3ynn System 2

System 1 2y+3n

2yynnn

2ynynn

2ynnyn

2ynnny

3yyy 3y+1n

2yynnn3yyy

2ynynn3yyy

2ynnyn3yyy

2ynnny3yyy

3yny

2yynnn3yny

2ynynn3yny

2ynnyn3yny

2ynnny3yny

3y+0n

3yyn

2yynnn3yyn

2ynynn3yyn

2yynnn3ynn

2ynynn3ynn

2ynnyn3yyn

2ynnny3yyn

2ynnyn3ynn

2ynnny3ynn

3y+2n

3ynn System 2

System 1 2y+0n 2yyyyy

2y+4n 2ynnnn

3yyy 3y+1n

2yyyyy3yyy

2ynnnn3yyy

3yny

2yyyyy3yny

2ynnnn3yny

3y+0n

3yyn

2yyyyy3yyn

2ynnnn3yyn

2yyyyy3ynn

2ynnnn3ynn

3y+2n

3ynn

3.3 Results of various constructions in transfer heat coefficient In this section, the purpose is to study the thermal transmitted coefficient value situation in different positions of construction. Some governing equations in calculation have been provided in section 2.4 and several layers thickness are shown in following table 6. In order to take a research on the insulation capacity for different positions of above proposed constructions, each case is performed to compute respective heat transmitted coefficients under same structure thickness. Note that in this case, missed material are substituted by air cavity or insulation stuff to guarantee the total structure thickness. Table 7 presents the heat resistance coefficients condition for different construction cases. Table 6 Various layers calculation parameter for thermal transfer values System A Layer Thickness Thermal conductivity(W/m·K) System B Layer

window -

Insulation 160mm 0.036

Levelling 30mm 0.036

Fireproof 15mm 0.25

Ventilation 100mm Air

Loadbearing 0.13

Fireproof

Vapour

Insulation

Loadbearing

Air

External skin 10mm 3.49

15mm 20mm 100mm 220mm 20mm Thickness 0.25 0.008 0.036 0.13 Thermal conductivity(W/m·K) Table 7 Heat transfer coefficients condition for different construction cases. System A Missing layer Replaced material Heat resistance Case name coefficients(W/m2·K) Levelling layer Air 2.45 2ynyyy Fireproof layer Insulation material 3.85 2yynyy Ventilation layer Insulation material 5.57 2yyyny Load bearing Insulation material 3.12 2yyyyn Levelling layer Air 3.18 2ynnyy Fireproof layer Insulation material Levelling layer Air 4.92 2ynyny Ventilation layer Insulation material Levelling layer Air 2.44 2ynyyn Load bearing Insulation material Fireproof layer Insulation material 6.29 2yynny Ventilation layer Insulation material Fireproof layer Insulation material 3.85 2yynyn Load bearing Insulation material Ventilation layer Insulation material 5.57 2yyynn Load bearing Insulation material Fireproof layer Insulation material 6.29 2yynnn Ventilation layer Insulation material Load bearing Insulation material Levelling layer Air 4.92 2ynynn Ventilation layer Insulation material Load bearing Insulation material Levelling layer Air 3.18 2ynnyn Fireproof layer Insulation material Load bearing Insulation material Levelling layer Air 5.64 2ynnny Fireproof layer Insulation material Ventilation layer Insulation material Levelling layer Air 5.63 2ynnnn Fireproof layer Insulation material Ventilation layer Insulation material

2yyyyy 3ynn 3yny 3yyn 3yyy 2ynyyy3yyy 2yynyy3yyy 2yyyny3yyy 2yyyyn3yyy 2ynyyy3yny 2yynyy3yny 2yyyny3yny 2yyyyn3yny 2ynyyy3yyn 2yynyy3yyn 2yyyny3yyn 2yyyyn3yyn 2ynyyy3ynn

2yynyy3ynn

2yyyny3ynn

2yyyyn3ynn

2ynnyy3yyy 2ynyny3yyy 2ynyyn3yyy 2yynny3yyy 2yynyn3yyy 2yyynn3yyy 2ynnyy3yny

2ynyny3yny

Load bearing -

Insulation material System B Fireproof layer Insulation material VIP Insulation material Fireproof layer Insulation material VIP Insulation material System AB Levelling layer Air Fireproof layer Insulation material Ventilation layer Insulation material Load bearing Insulation material Levelling layer Air Fireproof layer Insulation material Fireproof layer Insulation material Fireproof layer Insulation material Ventilation layer Insulation material Fireproof layer Insulation material Load bearing Insulation material Fireproof layer Insulation material Levelling layer Air VIP Insulation material Fireproof layer Insulation material VIP Insulation material Ventilation layer Insulation material VIP Insulation material Load bearing Insulation material VIP Insulation material Levelling layer Air Fireproof layer Insulation material VIP Insulation material Fireproof layer Insulation material Fireproof layer Insulation material VIP Insulation material Ventilation layer Insulation material Fireproof layer Insulation material VIP Insulation material Load bearing Insulation material Fireproof layer Insulation material VIP Insulation material Levelling layer Air Fireproof layer Insulation material Levelling layer Air Ventilation layer Insulation material Levelling layer Air Load bearing Insulation material Fireproof layer Insulation material Ventilation layer Insulation material Fireproof layer Insulation material Load bearing Insulation material Ventilation layer Insulation material Load bearing Insulation material Levelling layer Air Fireproof layer Insulation material Fireproof layer Insulation material Levelling layer Air Ventilation layer Insulation material Fireproof layer Insulation material

3.12 3.93 5.87 3.57 5.51 7.76 8.77 10.85 8.41 8.10 8.41 10.50 8.07 5.81 6.84 8.91 6.48 6.17

7.20

9.26

6.84

8.10 10.18 7.75 11.21 8.77 10.86 8.45

10.54

2ynyyn3yny

2yynny3yny

2yynyn3yny

2yyynn3yny

2ynnyy3yyn

2ynyny3yyn

2ynyyn3yyn

2yynny3yyn

2yynyn3yyn

2yyynn3yyn

2ynnyy3ynn

2ynyny3ynn

2ynyyn3ynn

2yynny3ynn

2yynyn3ynn

2yyynn3ynn

2yynnn3ynn

Levelling layer Load bearing Fireproof layer Fireproof layer Ventilation layer Fireproof layer Fireproof layer Load bearing Fireproof layer Ventilation layer Load bearing Fireproof layer Levelling layer Fireproof layer VIP Levelling layer Ventilation layer VIP Levelling layer Load bearing VIP Fireproof layer Ventilation layer VIP Fireproof layer Load bearing VIP Ventilation layer Load bearing VIP Levelling layer Fireproof layer Fireproof layer VIP Levelling layer Ventilation layer Fireproof layer VIP Levelling layer Load bearing Fireproof layer VIP Fireproof layer Ventilation layer Fireproof layer VIP Fireproof layer Load bearing Fireproof layer VIP Ventilation layer Load bearing Fireproof layer VIP Fireproof layer Ventilation layer Load bearing Fireproof layer VIP

Air Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Air Insulation material Insulation material Air Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material

8.10

11.56

9.12

11.21

6.17

8.23

5.81

9.27

6.84

8.91

6.52

8.59

6.17

9.62

7.19

6.84

9.62

2ynynn3ynn

2ynnyn3ynn

2ynnny3ynn

2yynnn3yny

2ynynn3yny

2ynnyn3yny

2ynnny3yny

2yynnn3yyn

2ynynn3yyn

2ynnyn3yyn

2ynnny3yyn

2ynnnn3yyy

2ynnnn3yny

2ynnnn3yyn

Levelling layer Ventilation layer Load bearing Fireproof layer VIP Levelling layer Fireproof layer Load bearing Fireproof layer VIP Levelling layer Fireproof layer Ventilation layer Fireproof layer VIP Fireproof layer Ventilation layer Load bearing Fireproof layer Levelling layer Ventilation layer Load bearing Fireproof layer Levelling layer Fireproof layer Load bearing Fireproof layer Levelling layer Fireproof layer Ventilation layer Fireproof layer Fireproof layer Ventilation layer Load bearing VIP Levelling layer Ventilation layer Load bearing VIP Levelling layer Fireproof layer Load bearing VIP Levelling layer Fireproof layer Ventilation layer VIP Levelling layer Fireproof layer Ventilation layer Load bearing Levelling layer Fireproof layer Ventilation layer Load bearing Fireproof layer Levelling layer Fireproof layer Ventilation layer Load bearing

Air Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material Insulation material Air Insulation material Insulation material Insulation material

8.59

6.52

8.95

11.56

10.53

8.45

10.90

9.26

8.23

6.17

8.59

10.53

10.89

8.59

2ynnnn3ynn

2yyyyy3yyy 2yyyyy3yny 2yyyyy3yyn 2yyyyy3ynn

VIP Levelling layer Fireproof layer Ventilation layer Load bearing Fireproof layer VIP Fireproof layer VIP Fireproof layer VIP

Insulation material Air Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material Insulation material

8.95

8.41 8.77 6.48 6.84

Figure 7 The difference between various construction and original of system A in heat resistance coefficient It can be obtained from table 7 and 8 that: 

For system A, the tube for ventilation enclosed by insulation material significantly deteriorate whole construction insulation capacity. This is mainly because that the air cavity in various vent pipes splits entire insulating layer impairing construction heat resistance performance. For example, fig. 7 shows all thermal resistance coefficient of construction which misses ventilation layer in system A are averaged 70% larger than that without any missing layers. This means that the setting of ventilation layer diminishes 70% insulation capacity for building envelope. However, these vent pipes integrate the additional building envelope with other function of interior ventilation which saves the ceiling space for ventilated duct. Hence, it is imperative for engineers to assess the enclosure structure insulation performance after utilizing vent pipes.



In case of system A, harnessing insulation material wool instead of air for levelling layer could significantly improve entire heat preservation capacity. This phenomenon attributes to the insulation stuff heat transfer coefficient. The mineral wool resistance performance is better than air under same size. For instance, any cases’ heat resistance coefficient of levelling layer with mineral wool almost presents 20% larger than that with air cavity construction. This result indicates that it is recommended to employ insulation material such as wool to replace the air to establish envelope structure levelling layer. Furthermore, for loadbearing and

fireproof, both layers have little impact for envelope insulation performance. Especially for loadbearing layer, since its cross-section area is so small that the thermal bridge effect led by this part operates under a low level.

Figure 8 The difference between various construction and original of system B in heat resistance coefficient 

In terms of system B, the results of heat resistance value show that vacuum insulation panels (VIP) could significantly enhance insulation property of whole closure structure. This phenomenon is caused by the superior thermal insulation performance of the VIP board. For instance, fig .8 indicates that both the case of ‘3ynn’ and ‘3yyn’ including missed layer of VIP decreases the insulation performance approximately by 30% with regard to heat resistance value. In addition, the fire proof construction has little impact on entire heat preservation capacity.



According to above analysis, it can be obtained that VIP panel had apparently improving performance in terms of blocking heat transmission. Therefore, the insulation capacity of system A could be improved significantly via integrating VIP board into whole construction. The calculated results present that the coefficient of heat resistance for system A increase from 3.12 to 5.65 after adding a VIP layer into it.



For system AB, every layer performs similar functions with sub-system of A and B. In this system, the A construction plays a more sensible role than B because of the ventilation layer existence. The ventilated duct deteriorates this system insulated property to the greatest extent by almost 30% which is significantly larger than fireproof layer of 5%. The reason for this phenomenon is that the discrete air cavity thermal preservation nature is much weaker than surrounding enclosed insulation material which decreases entire system thermal resistance performance. On the other hand, it should also be noted that the ventilation pipes in system AB was the most crucial layer in influencing insulation capacity even exceeds the VIP effect. Hence, decreasing the duct relevant coefficient could significantly improve insulation ability.



The VIP board plays an enhancing performance with regard to building insulation capacity for system AB. This is due to its low heat transfer coefficient which can neutralize apparently the heat preservation negative effect of ventilation pipes. For example, almost every case with missing VIP board’s heat resistance values are lower than the original construction which

displays that the excellent expression of VIP in intensifying heat preventing ability. 

Basing on above analysis, the results indicate that the VIP panel, ventilation duct and levelling layer are the most significance factors affecting whole system insulation performance. For levelling layer, using insulated stuff to replace air cavity is the best method which not only works in levelling but increase thermal resistance performance. For VIP panel, adding it into system A or replacing fireproof panel in part by it are recommended as efficiency method in insulated construction establishment. For ventilation pipes integrated into system A, reducing the impact of air is an effective way to improve insulation performance such as diminishing the size of ducts.

4.

Discussion This paper investigates a proposed building renovation construction insulation performance in

detail. Thermal resistance coefficient is designed as perform indicator to study the final results. However, the distribution of heat flow is also a significant aspect impacting entire system thermal insulated condition in terms of the thermal bridge effect. Therefore, it is imperative to harness simulating software to investigate heat flow situation of various construction systems. Ventilated pipes are integrated into systems in order to promote air flow and save interior spaces. Nevertheless, this construction significantly diminishes the insulation capability and increases the thickness of entire construction. Through improving the heat preventing ability of the air interlayer, the thermal insulation performance can be effectively enhanced. Future investigations need to be performed to study the method of decreasing ventilated duct’s heat transfer ability such as diminishing the radius of pipes. In this study, the sensitivity of different functional layers under various systems has been studied and the layers that have the greatest impact on the thermal insulation performance of the entire system have been found. However, it is insufficient to investigate the optimized size or material for different layers under some certain conditions. As a consequence, future relevant studies should be done to investigate optimal insulation materials or thickness under some definite values of thickness or material types. 5.

Conclusion This paper studies the building envelope insulation feature for architecture prefabricated

renovation construction of IEA ECBCS Annex 50. Three system cases are built basing on the original structure via dividing and combination method. The enclosure insulation thermal resistance coefficient is regarded as the perform indicator to measure the insulation capacity. Following conclusions can be obtained: 

Most of building envelope reconstruction projects in Europe mainly focus on residential building. Furthermore, for other types of architecture, the relevant energy efficient reconstruction methods usually concentrate on the other aspects of windows or load bearing structure instead of integrating various insulation material. Building renovation pattern always employs additional transparent structure out the envelope in tropical and subtropical areas. Furthermore, for other climatic regions, buildings harness multiple retrofitting methods including adding insulation materials especially for residential architecture.



The tube for ventilation enclosed by insulation material significantly deteriorate whole construction insulation capacity regardless which systems.



In case of system A, harnessing insulation material wool instead of air for levelling layer could significantly improve entire heat preservation capacity. It is recommended to employ

insulation material such as wool to replace the air to establish envelope structure levelling layer. 

Vacuum insulation panels (VIP) could significantly enhance insulation property of whole closure structure and the fire proof construction has little impact on entire heat preservation capacity.



The insulation capacity of system A could be improved significantly via integrating VIP board into whole construction.



For system AB, the A construction plays a more sensible role than B because of the ventilation layer existence. The ventilation pipes in system AB was the most crucial layer in influencing insulation capacity even exceeds the VIP effect. Hence, decreasing the duct relevant coefficient could significantly improve insulation ability. The VIP board plays an enhancing performance with regard to building insulation capacity for system AB.



VIP panel, ventilation duct and levelling layer are the most significance factors affecting whole system insulation performance.



Under no circumstance limitation on thickness of envelope reconstruction, the thermal insulation performance of system AB is much better than that of system A and system B. In addition, replacing the fireproof board with a VIP board can further improve the system's thermal insulation capacity.



When there is a thickness limitation, adding a VIP board can effectively enhance the heat insulated situation of system A without increasing greatly thickness size. Acknowledge

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Conflict of interest The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.