International Journal of Low-Carbon Technologies, 2024, 19, 2108–2118

https://doi.org/10.1093/ijlct/ctae161
Original Article

Comparative analysis on heat and moisture transfer of

composite insulation walls
Yang Wang1 , Qun Wang2 ,* , Ruifeng Chen1 , Cheng Zhang1 , Jihong Song1
1 School of Urban Construction and Transportation, Hefei University, 99 Jinxiu Road, Jinxiu District, Hefei 230601, China
2 School of Accounting, Tongling University, Cuihuxi Road, Tongguan District, Tongling 244061, China

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*Corresponding author. School of Accounting, Tongling University, Cuihuxi Road, Tongguan District, Tongling 244061, China. E-mail: 154829@tlu.edu.cn

Abstract
Firstly, the influence of heat and moisture transfer on composite insulation walls was initially considered. Relying on the established theory of
heat and moisture coupled transfer in walls and taking into account the specific climate conditions of regions with hot summers and cold winters,
a non-steady-state heat and moisture coupled model was developed to simulate the processes of heat and moisture transfer. Subsequently,
based on the one-dimensional stable heat transfer theory, the heat transfer situation for winter insulation was calculated. Then, practical methods
for on-site temperature and humidity measurements were explored and implemented. Through analysis, comparison, and mutual verification
of the calculated values and the measured values, it was observed that both sets of data showed consistent trends, thereby verifying their
accuracy and correlation. The findings of this study provide valuable reference data for understanding the heat and moisture migration within
building walls and offer solutions for optimizing thermal insulation strategies.
Keywords: external insulation wall; heat and moisture coupling; calculated value; measured value

1 Introduction There are significant variations in parameter selection

The heat and moisture transfer of walls has a substantial among the existing models. Due to the diverse driving poten-
impact on the energy consumption of buildings. Moisture tials employed for heat and moisture transfer, the accuracy and
transfer may result in the buildup of moisture inside the wall, applicability of certain models are constrained, necessitating
leading to bulging, freezing, cracking, or detachment of the corresponding experiments for validation. The experimental
insulation material, which not only damages the structure verification method involves monitoring the temperature and
but also interferes with the heat transfer process. Conducting humidity distribution in specific environments and analyzing
a comprehensive study on the coupled heat and moisture the migration patterns of heat and moisture.
transfer of walls is crucial for accurately designing insulation In recent years, experimental techniques have also been
and moisture-proof walls, enhancing wall performance, and developing rapidly. The key challenge lies in accurately mea-
reducing energy consumption. suring partial moisture content inside the wall. To address
In recent decades, numerous scholars have dedicated them- this issue, researchers have developed a range of measurement
selves to theoretical and experimental research on heat and methods, including nuclear magnetic resonance, gamma ray,
moisture transfer, leading to the establishment and develop- X-ray, capacitance resistance, slice drying and weighing [11–
ment of various theoretical models. Among these models, the 18], and more. However, these methods all have their own
Luikov [1] model and Philip and Devries [2] model have inherent limitations.
emerged as the most widely utilized and renowned ones, Firstly, this study investigates the influence of moisture
utilizing temperature and moisture content as driving poten- transfer on heat transfer in porous media walls, validates the
tials. Building upon this foundation, subsequent researchers use of relative humidity and temperature as driving potentials,
have explored alternative driving potentials, resulting in the and establishes a comprehensive heat and moisture coupling
creation of diverse coupled heat and moisture transfer models. transfer model. The coefficients in this model are straight-
For instance, Budaiwi et al. [3] introduced a model driven forward and solvable. This model can effectively simulate
by temperature and air moisture content. Zhong et al. [4] the heat and moisture coupling processes in multi-layer walls
created a model driven by temperature and water vapor during the summer months.
pressure. Kong et al. [5] focused on new buildings in severely Subsequently, a unique field measurement protocol is intro-
cold regions, establishing a coupling equation with three duced. By leveraging historical thermal and humidity testing
parameters: liquid moisture content, temperature, and solid data from local buildings over several years, continuous on-
ice moisture content, and validating the model’s effectiveness site monitoring of temperature and humidity conditions is
through experiments. Guo et al. [6] used the transfer function carried out. By comparing the collected data with calculated
method to establish a simplified model of heat and humidity values, the accuracy is verified through cross-validation.
process on the interior surface of buildings. Various other Lastly, employing the well-established principle of one-
models have also been proposed [7–10]. dimensional steady-state heat transfer, the temperature and

Received 18 April 2024; revised 17 July 2024; accepted 7 August 2024

© The Author(s) 2024. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/),
which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Comparative analysis on heat and moisture transfer 2109

humidity profiles for winter insulation are computed for three vaporization of water vapor, J/kg; J is the diffusion flux of
distinct composite wall structures made of various insulation water vapor, kg/(m2 ·s).
materials. By comparing the measured data from these three According to the energy conservation of unit, the heat
wall configurations, the precision and interrelation of differ- transfer control equation can be obtained asj
ent on-site measurement techniques are further corroborated.     
∂θ ∂ ∂Pvs ∂θ ∂ ∂ϕ
ρc = λ + Lμv ϕ + Lμv Pvs (3)
∂t ∂x ∂T ∂x ∂x ∂x
2 Deduction of heat and moisture transfer
model Where μv is the water vapor permeability coefficient,
kg/(Pa·m·s).
The heat and moisture coupling transfer process within build-
ing exterior walls is highly intricate. To streamline the analysis, Pv = φPvs (4)
this study employs an unsteady state, one-dimensional wall where Pv is the partial pressure of water vapor, Pa; Pvs the

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model. Considering the influence of moisture transfer on heat partial pressure of saturated water vapor, Pa; Φ is relative
transfer within porous media walls, continuous temperature humidity.
and relative humidity are utilized as driving potentials to
develop a model that simulates the heat and moisture transfer 2.2 Moisture transfer equations
process. The validity of the proposed model is confirmed According to Fick’s law, the diffusion rate of water vapor Jv ,
through comparisons with experimental data. kg/(m2 ·s), can be expressed asj
Before initiating the modeling process, it is crucial to
simplify the fundamental physical parameters. Taking into ∂Pv ∂ (φPvs )
Jv = −μv = −μv (5)
account the local climate characterized by hot summers and ∂x ∂x
cold winters, the following approximate assumptions are
established: According to Darcy’s law, the transfer rate of liquid water
Jl can be expressed as
(1) The solid, liquid, and gas phases can be regarded as
continuous media. ∂Pl
(2) Both water vapor and air are assumed to behave like Jl = −μl (6)
∂x
ideal gases.
(3) The heat and moisture transfer process is simplified as where μl is the permeability coefficient of liquid water,
a one-dimensional process along the wall’s thickness kg/(Pa·m·s); Pl is the capillary water pressure. According to
direction. Kelvin relations,
(4) There is intimate contact between the layers of a mul-
Pl = −ρl R0 θ ln φ (7)
tilayer wall, with no thermal resistance or moisture
transfer resistance at the interfaces. where ρ l is liquid water density, kg/m3 ; R0 water vapor gas
(5) The moisture within the material is considered to exist constant, J/(kg·K).
only in vapor and liquid phases. Divides the moisture transfer of multilayer wall into two
components: the diffusion of water vapor and the transfer of
liquid water. According to the law of conservation of mass,
2.1 Heat transfer equations the moisture content of a wall can be expressed as [20]
According to Fourier’s law, the heat flux density of wall q,
measured in W/m2 , can be calculated from the following ∂w  
= −∇ Jv + Jl (8)
equation.j ∂t
∂θ where w is volume moisture content, kg/m3 . It can be charac-
q = −λ (1)
∂x terized as a function of temperature and relative humidity:
where λ is thermal conductivity of a single material, W/(m·K);
∂θ/∂x is the temperature gradient. w = f (θ , φ) (9)
In accordance with the law of energy conservation, the
change in enthalpy within a unit is equivalent to the net Taking the derivative of time on both sides of the formula,
energy inflow. At a specified temperature, the enthalpy of
water vapor can be represented as the sum of the enthalpy ∂w ∂w ∂φ ∂w ∂θ ∂w ∂φ ∂φ
of liquid water and the latent heat of vaporization. In con- = + = =ξ (10)
∂t ∂φ ∂t ∂θ ∂t ∂φ ∂t ∂t
trast, the sensible heat of water vapor and liquid water is
often neglected [19]. From these premises, the following heat
where ξ is the slope of the isothermal moisture curve, kg/m3 .
transfer relationship can be derived.
Substituting Equation (10) into Equation (8) yields the
    moisture transfer equation:
∂θ ∂ ∂θ ∂J
ρc = λ + −L (2)   
∂t ∂x ∂x ∂x ∂φ ∂ θ ∂φ
ξ = Dv Pvs + KL ρl R0
∂t ∂x φ ∂x
where ρ is the density of the material, kg/m3 ; c the specific   
heat capacity of the material, J/(kg·K); t is the time, s; θ ∂ ∂Pvs ∂θ
+ Dv φ + Kl ρl R0 ln φ (11)
the temperature of the material, K; L the latent heat of ∂x ∂θ ∂x
2110 Wang et al.

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(a) (b)

(c) (d)
Figure 1. Heat and moisture coupling causes deterioration of exterior wall.

2.3 Boundary conditions α t radiation heat transfer coefficient, and I Solar radiation
Using local meteorological parameters as outdoor boundary intensity, W/m2 .
conditions, which include temperature, relative humidity, and Similarly, the flow rate of moisture and heat on the inner
solar radiation intensity. Using the constant temperature and surface of the wall can be expressed as
humidity created by air conditioning as indoor boundary
conditions. During the process of heat and humidity coupling wi = βi (φi Pis − φis Piss ) (14)
transfer through the wall, the indoor and outdoor environ-
ment can be regarded as sources of heat and moisture. qi = αi (Ti − θi ) + Lwi (15)
The moisture and heat flow rate on the outer surface of the
wall can be expressed as
In Equation (14), β i is the convective mass transfer coef-
we = βe (φe Pes − φes Pess ) (12) ficient on the inner surface of the wall, ϕ i indoor relative
humidity, Pis indoor partial pressure of saturated water vapor,
ϕ is the relative humidity on the inner surface of the wall, and
qe = αe (Te − θe ) + ατ I + Lwe (13)
Piss the partial pressure of saturated water vapor on the inner
surface of the wall.
In Equation (12), β e is convective mass transfer coefficient In Equation (15), β i is the convective heat transfer coef-
on the outer surface of the wall, kg/(Pa·m2 ·s); ϕ e outdoor ficient on the inner surface of the wall, Ti Indoor ambient
relative humidity, Pes outdoor partial pressure of saturated temperature, and θi the inner surface temperature of the wall.
water vapor, ϕ es relative humidity on the outer surface of the
wall, and Pess partial pressure of saturated water vapor on the
outer surface of the wall.
3 Design of on-site measurement methods
In Equation (13), the heat flow through the outer sur- 3.1 Preliminary analysis of heat and moisture
face of the wall includes three components: convective heat transfer in the walls
transfer, latent heat of water vapor, and solar radiation heat. In this study, we examine three types of target walls that
Among them, α e is convective heat transfer coefficient on utilize different external insulation materials: glazed hollow
the outer surface of the wall, W/(m2 ·K); T e outdoor ambient bead insulation mortar (referred to as GBM), rubber powder
temperature, θe external surface temperature of outdoor walls, polystyrene particle insulation slurry (abbreviated as RPS),
Comparative analysis on heat and moisture transfer 2111

Table 1. Comparison of temperature values in different areas of the wall in Fig. 1b.

Date 2023/6/14 Location Gable wall surface

Image time 08:36:45 Object distance 3.0 m
Emissivity 0.90 Ambient humidity 54.3%
Reflected temperature 20.0 ◦ C Wind speed 0.373 m/s
Atmospheric temperature 18.0 ◦ C Weather conditions Sunny
Sp1 temperature 14.7◦ C Sp8 temperature 11.1◦ C
Sp2 temperature 15.2 ◦ C Sp9 temperature 11.5 ◦ C
Sp3 temperature 14.8 ◦ C Sp10 temperature 12.1 ◦ C
Sp4 temperature 14.7◦ C Sp11 temperature 7.4 ◦ C
Sp5 temperature 14.9 ◦ C Sp12 temperature 7.1 ◦ C
Sp6 temperature 9.9 ◦ C Sp13 temperature 7.8 ◦ C
Sp7 temperature 10.2 ◦ C Sp14 temperature 7.1 ◦ C

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and rock wool board (RWB) as their respective external
insulation layers. The first two types of walls exhibit obvious
moisture and heat transfer processes, which are attributed to
structural deficiencies in their waterproofing and insulation
layers. These defects lead to significant degradation, necessi-
tating removal and repair (refer to Fig. 1). Infrared thermal
images obtained using the Flir B360 infrared thermal camera,
in conjunction with the temperature analysis software (as
detailed in Table 1), reveal that these walls contain substantial
moisture and suffer from hollowing issues.
It can be known from Table 1 that the highlighted position
corresponding to Fig. 1b has a higher temperature. This is
because there is a hollow in the wall here, resulting in a
faster temperature increase because of its lower specific heat
capacity. The walls in these areas have structural defects,
affecting the insulation and heat preservation effects, and may (a)
also cause the detachment of the exterior facing tiles, creating
a serious safety hazard.
These images vividly demonstrate that moisture, particu-
larly within the wall’s insulation layer, can severely impact its
functionality. Figure 1a depicts the process of removing the
GBM insulation layer. Figure 1b presents the corresponding
infrared thermal image of the wall before removal. Figure 1c
illustrates the damage to the RPS insulation layer, which has
led to significant dampness inside the wall. Figure 1d exhibits
a classic thermal bridge resulting from defects in the insulation
layer of the gable wall.
Due to high construction quality, suitable insulation struc-
ture, and good waterproof effect, the third type of wall (RWB)
can be the main testing object of this study (Fig. 2a). From the
corresponding infrared thermal image (Fig. 2b), it can be seen
that the wall is undamaged, and there is no obvious partial
moisture or hollowing, making it more suitable for long-term (b)
heat and moisture coupling research.
Figure 2. Visual and infrared thermal images of the rock wool insulation
layer wall.
3.2 Design of on-site measurement plan
The temperature of the inner and outer surfaces of the wall
is measured using a Leitai infrared thermometer, which is
accurate and convenient. Connect the FHA646 sensor with During the construction period of the insulation layer, the
the ALBORN-2908 handheld data collector to measure the front end of the sensor can be implanted in advance (Fig. 5a),
indoor and outdoor environmental temperature and humidity. it can also be embedded through drilling after the construction
The key issue to be addressed below is the measurement is completed. The implanted sensor is a nickel-chromium
of temperature and humidity within the wall. Three repre- thermocouple wire (NiCr -Ni) (Fig. 5b), which is only a metal
sentative measurement points have been established (Fig. 3), wire with a diameter of 0.5 mm. Due to its contact induction,
situated at the interface between aerated concrete and mixed the front of the sensor must be wrapped in rubber putty, and
mortar (point P1), as well as on either side of the insulation then sealed with glass glue to bury the pores, so as to prevent
layer (points P2 and P3). moisture from entering.
2112 Wang et al.

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Figure 3. Location of measure points.

Figure 4. Measuring solar radiation intensity.

After the construction is completed, the end of the sen-
sor is connected to the desktop data acquisition collector
(device type is Ahlborn MU-56901), and then connected to set to 3.0. The testing depth of this type of instrument is
the computer to achieve output data continuously, timed and 20 mm, so it can meet the requirements of wall surface testing.
automatically (Fig. 6a). This acquisition collector, combined It must be considered that this sensor has a moisture content
with a multichannel expansion card, can collect 64 sets of data measurement range of 0–20%, and excessive humidity cannot
simultaneously (Fig. 6b). be accurately tested.
The following describes how to measure humidity and From these, we can precisely measure the relative humidity
moisture content. In this context, the portable data collector, and moisture content on the surface, at a shallow depth,
model ALBORN 2908, is utilized to connect three distinct and within the interior of the wall. Taking the isothermal
types of humidity sensors (Fig. 7a). The data collected from moisture absorption and desorption curve of the material as a
the three sensors, employing various testing methods, are reference [21], it can be concluded that the partial pressure of
cross-validated and adjusted to ensure the acquisition of more water vapor is a function of the material’s moisture content
precise and reliable values. and temperature, and the moisture content is a function of
The first method involves directly embedding a nickel temperature and relative humidity. This can also validate the
chromium thermocouple sensor (FHA6X6 NiCr-Ni) to correlation among temperature, humidity, and vapor pressure
measure relative humidity (Fig. 7b). The front of the sensor parameters.
must be carefully wrapped with a cotton ball and covered The conversion relationship between moisture content and
with a hard plastic porous protective jacket. This sensor has relative humidity is as follows [22]:
high testing accuracy, does not generate data drift, and need
not require calibration. If the sensor’s end is connected to the  
φ = w Aφ 2 + Bφ + C (16)
56 901 desktop data acquisition device mentioned above, it
can also collect and store data automatically.
The second approach is to use the electrode sensor The empirical coefficients A, B, and C are shown in Table 2.
(ALMEMO FHA936WD) to test the moisture content inside The data conversion among the three humidity measurement
the wall (Fig. 7a). The testing principle requires inserting the methods mentioned above is verified based on this empirical
probe into the material, and the electrical conductivity of formula.
materials varies with different moisture contents, resulting in Indoor temperature and humidity control are jointly reg-
differences in output resistance. A comparative experiment ulated by air conditioning, humidifier and dehumidifier. The
was carried out using the wood moisture content collector intensity of solar radiation on the outer surface of the wall
(MD288) with a similar testing principle. The results indicate is measured using a solar radiometer (Fig. 4). The sources
that the testing depth should not surpass 50 mm to ensure of other parameters of the materials are derived from design
accuracy. When the moisture content exceeds 20%, there is a drawings, on-site measurements, and pertinent references [23,
significant discrepancy between the actual measurement value 24]. The time step for testing and calculations is set at 1 h, with
and the expected reading. The offset compensation amount is the testing and calculation cycle spanning 24 h, encompassing
set to 5.0 through calibration processes. both day and night.
Thirdly, the moisture content of the wall surface can be
measured using the ALMEMO FHA696MF sensor (Fig. 7a).
The principle is to use the built-in probe to contact the
4 Comparison of calculation and
insulation material. The probe emits high-frequency electro-
measurement result
magnetic waves, and the dielectric constant produced varies in 4.1 Environmental temperature, humidity, and
accordance with its moisture content, causing changes in the solar radiation
probe’s capacitance and thus measuring the moisture content. This area is situated in the hot summer and cold winter zone.
In the preliminary calibration experiment, based on the type In accordance with local thermal specifications, the convective
of insulation material, the offset compensation amount was heat transfer coefficient of the wall is 8.7W/(m2 ·K) for the
Comparative analysis on heat and moisture transfer 2113

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(a)
(a)

(b)
Figure 5. Sensor and its embedded layout.
(b)
Figure 6. Sensors connect data collector and computer.
outer surface, 23.0 W/(m2 ·K) for the inner surface in winter,
and 19.0 W/(m2 ·K) for the inner surface in summer.
The test results of temperature, humidity, and solar radi- Similarly, as illustrated in Fig. 9b, the humidity trend is also
ation intensity are presented in Fig. 8. It can be seen that the roughly consistent. This indicates that the moisture measuring
indoor temperature and humidity control are stable. The peak instruments FHA936WD and FHA696MF are also reliable.
solar radiation intensity occurs between 12 and 5p.m. (12:00 The humidity gradient of the crack-resistant mortar layer is a
and 17:00), with a corresponding temperature increase that bit small, while the mixed mortar layer has a larger humid-
lags slightly between 2 and 5 p.m. (14:00 and 17:00), while the ity gradient. This could be attributed to the fact the crack
relative humidity of the outdoor air concurrently decreases. resistant mortar layer is thinner, while the steam permeability
coefficient of the rock wool layer and concrete layer is lower.
4.2 Measurement of temperature and humidity of The steam permeability coefficient of the mixed mortar is also
surfaces and internal layers quite low, and the mixed mortar layer is thicker.
As depicted in Fig. 9a, in the mixed mortar layer, the temper-
ature curves on the inner and outer surfaces nearly overlap; 4.3 Comparison of simulated calculation and
likewise, in the crack resistant mortar layer, the temperature on-site measured values
curves on the inner and outer surfaces coincide. Since the Solve the mathematical model established in sections 2.1,
temperature of the inner and outer surfaces are all measured 2.2 and 2.3. In this study, the finite element method is used
by infrared thermometer, the test results are highly reliable. to discretize the control equations and boundary conditions
The internal points P1 and P3 are consistent with the temper- mentioned above. The partial differential equation system is
ature of the inner and outer surfaces. These findings at least transformed and iterated into an algebraic equation system.
disclose two facts: (1) Using embedded temperature sensors, Based on Matlab programming, the finite difference software
the temperature measurement of points P1 and P3 inside FLAC3D5.0 is used for simulation calculation to obtain the
the wall is also reliable. (2) The temperature gradient of the temperature and humidity values of the discrete points.
inner and outer mortar layers is extremely small, while due to Figure 10a shows the measured and simulated temperature
their good insulation effect of rock wool board and aerated values on the inner side (point P2) of the rock wool insula-
concrete block, the temperature gradient is concentrated in tion layer, while Fig. 10b shows the measured and simulated
these two layers. temperature values on the outer side (point P3).
2114 Wang et al.

Table 2. Material property parameters (data source: drawings and references [ 23 , 24])

Heat and humidity parameters Anti-crack mortar Rock wool board Aerated concrete Mixed mortar
Wall thickness-mm 10 50 200 20
Density-kg/m3 1800 110 650 1600
Thermal conductivity-W/(m2 ·K) 0.93 0.045 0.18 0.93
Heat storage coefficient-W/(m2 ·K) 11.37 0.75 3.60 11.37
Vapor permeability coefficient-kg/(Pa·m·s) 5.467 × 10−11 1.1 × 10−11 3.47 × 10−11 1.2 × 10−11
Parameter A −0.022 −0.5277 −0.1196 0.00674
Parameter B 0.025 0.9647 0.1226 −0.0135
Parameter C 0.0001 0.0710 0.0011 0.0077

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(a)

(a)

(b)

(b)
Figure 7. Handheld collector connects to various humidity sensors.

From the comparison results, it is evident that the measured

values and calculated values share a similar trend [25]. This
indicates that the instruments utilized in this experiment are
accurate and also substantiates the practicality of the con-
structed model. The maximum deviation on the inner side
is less than 1◦ C, with the average deviation of 0.41◦ C; the
maximum deviation on the outer side is less than 2◦ C, and
the average deviation is 0.95◦ C. The reason for the deviation
(c)
maybe that [26], from the perspective of measured values, Figure 8. Temperature, humidity, and solar radiation intensity in summer.
poor contact of the sensor and the entry of moisture can
cause measurement errors; Form the perspective of calculated
values, the model sets the initial conditions for all materials to materials. Moreover, there might be deviations in the values
be the same. But in actual, we only selected 1 day throughout of parameters in boundary conditions, such as solar radiation
the summer season as the research period, resulting in differ- intensity, convective heat transfer coefficient, material physi-
ences in the initial physical property parameters of different cal parameters, and so forth.
Comparative analysis on heat and moisture transfer 2115

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(a) (a)

(b)
(b)
Figure 10. Temperature value on the inner and outer side of the insulation
Figure 9. Temperature and humidity of surfaces and internal layers. layer.

Figure 11a shows the measured and calculated humidity Prior to the commencement of formal testing, ensure that
values on the inner side (P2) of the rock wool insulation layer, the indoor air conditioning system operates continuously for
while Fig. 11b shows the measured and calculated humidity over 8 hours, thereby placing the target wall in a near-ideal
values on the outer side (P3). state of heat transfer. Consequently, the thermal calculations
As depicted in Fig. 11, the humidity values also match are conducted based on one-dimensional, stable heat transfer
well. On the inner side of the insulation layer, the maxi- across four flat walls.
mum discrepancy between the two types of values is less The insulation effect is assessed through the interface tem-
than 10%, with an average discrepancy of less than 5%; perature at the boundary between the insulation layer and the
On the outer side of the insulation layer, the maximum structural layer, denoted as P2. Based on the known conditions
discrepancy between the two is less than 8%, and the average of the four-layer flat wall, calculate θi ,θ2 ,θ3 ,θ4 , and θe . The
discrepancy is less than 4%. Overall, the calculated values temperature θ3 is the calculated value of the interface layer.
of temperature and humidity are slightly higher than the test Among these,θ2 ,θ3 , andθ4 correspond to the temperatures at
values. points P1, P2, and P3 respectively.
The reason for the deviation in humidity calculation is
the same as that in temperature calculation above; As far as Ri + R1 + R2
measured values are concerned, when the relative humidity is θ3 = Ti − (Ti − Te ) (17)
too high, data drift and inaccurate calibration compensation R0
values of the humidity sensor are important reasons for mea-
Among them, Ri , R1 , R2 , and R0 represent the correspond-
surement errors.
ing interlayer thermal resistance and total thermal resistance,
respectively.
As previously stated, the insulation layers of the three
5 Comparison of calculated and measured wall structures are glazed hollow bead insulation mortar
values for winter insulation (GBM, with a thermal conductivity coefficient of 0.06 W/
5.1 Analysis of heat transfer effects of three types (m2 ·K)), rubber powder polystyrene particle insulation
of composite wall structures slurry (RPS, 0.08 W/(m2 ·K)), and rock wool board (RWB,
The aforementioned study pertains to summer insulation and 0.045 W/(m2 ·K)). These walls were constructed identically,
is categorized under unstable heat transfer conditions. The with the sole variation being the insulation material employed.
gradients of temperature and humidity flow from the exterior The testing period spans 10 days, chosen during continuous
to the interior. The subsequent study will concentrate on sunny conditions following rainy weather, ensuring minimal
winter insulation. meteorological fluctuations over the subsequent 10 days.
2116 Wang et al.

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(a) Figure 13. Temperature and humidity variation curve of RPS type wall.

(b)
Figure 11. Humidity values on the inner and outer sides of the insulation Figure 14. Temperature and humidity variation curve of RWB type wall.
layer.

leading to a decrease in the heat transfer coefficient of the

insulation layer. Consequently, the insulation performance is
enhanced, which in turn causes an increase in the interface
temperature between the insulation layer and the structural
layer.
The RPS type wall exhibits a higher initial moisture content,
and the discrepancy between the measured and calculated
values is most pronounced, which aligns with the observations
from the infrared thermal image (Fig. 1). The insulation layer
of this type of wall is severely compromised by moisture,
which consequently precludes it from achieving the desired
level of compression insulation performance.
Figure 12. Temperature and humidity variation curve of GBM type wall. Incorporating the RWB type wall, the measured tempera-
tures for all three wall types are found to be lower than the
calculated temperature values. This discrepancy is attributed
Through infrared thermal image observation (Fig. 1), the to the fact that the GBM and RPS type walls retain a signif-
measured points are arranged in areas with obvious moisture icant moisture content even after 10 days. Additional factors
damage to the structure (In fact, RWB wall has no obvious contributing to this effect include the actual thickness of the
defects). Throughout the measurement duration, the indoor insulation layer being less than specified, and the thermal
temperature is maintained at 25◦ C, and the outdoor properties of the insulation material not meeting the required
temperature is about 2◦ C. standards.
At point P2 for three type of walls, the calculated temper- The completion time of the RWB type building is relatively
ature, measured temperature, and measured moisture content short. Through infrared scanning, no insulation and moisture
values are shown in Figs. 12, 13, 14. defects are detected, and there is no external moisture intru-
sion. However, there is still a certain deviation between the
5.2 Analysis of test and calculation results measured temperature and the calculated temperature values
For the GBM and RPS types of walls, there is an inverse cor- (Fig. 14). The possible reason could be that the moisture inside
relation between the measured moisture content and the cor- the wall has not completely evaporated and has not reached
responding measured temperatures, which is clearly depicted a humidity balance with the environment, thus affecting the
in Figs 12 and 13. This phenomenon occurs because as water insulation effect. It might also be associated with the construc-
evaporates from the material, the moisture content diminishes, tion quality or the performance of the materials.
Comparative analysis on heat and moisture transfer 2117

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