The future of energy and sustainable construction is a growing area of interest and concern. According to the IEA’s “World Energy Outlook 2022” report [1], enhancing the energy efficiency of buildings is crucial for achieving greenhouse gas emission reduction targets and combating climate change. The Global State of Buildings and Construction Report 2022 [2] indicates that the building sector contributes almost 40% of global energy consumption and about one-third of greenhouse gas emissions.

Various studies have focused on evaluating and improving the energy consumption of buildings by reducing heating and cooling needs. Hoseinzadeh et al. [3] underlined the importance of implementing specific strategies based on geographical and climatic conditions to achieve energy-saving improvements in buildings located in a mountainous, humid zone.

Researchers have evaluated insulation materials used in buildings to address energy losses through building envelopes. They highlight the importance of selecting appropriate insulation materials to enhance energy performance, taking into account their environmental aspects [4], and examining thermal inertia and insulation effectiveness in building structures [5].

The use of phase-change material (PCM) in exterior walls has been explored for their energy efficiency and CO₂ emissions reduction benefits [6], as well as their potential in enhancing thermal regulation in specific climatic conditions [7]. Research on PCMs demonstrates their ability to store and release substantial thermal energy, thereby attenuating temperature variations in buildings and reducing energy consumption [8]. El-Ganaoui et al. [9] have provided innovative analytical solutions to heat transfer problems involving phase changes and interfaces, forming the basis for numerous advances. Recent advancements in PCM technology highlight their potential for storing thermal energy in buildings [10,11]. Hekimoğlu et al. [12] noted the integration of PCMs into building cooling systems, which reduces the thermal load on air-conditioning systems and minimizes energy consumption, while Zhan et al. [13] focused on the integration of PCMs in buildings in hot climates.

Anter et al. [14] demonstrated the efficiency of integrating PCMs into building walls for thermal energy savings, highlighting the importance of optimizing the design, choice, and quantity of PCMs to maximize thermal benefits. M’hamdi et al. [15] analyzed the energy, environmental, and economic impacts of different building envelopes incorporating PCMs in different climates, showing that PCMs can reduce energy consumption and carbon emissions while offering economic benefits [16,17].

The potential of bio-based materials to enhance the sustainability and energy efficiency of buildings has also been studied [18–20]. These materials have demonstrated promising thermal and hygrothermal performances [21,22] and a low carbon footprint [23,24]. Using bio-based materials with PCMs improves energy performance in buildings [25], but careful assessment of their hygrothermal behavior is essential to prevent building deterioration [26,27].

Researchers have explored the combined use of PCMs with other insulating materials to enhance energy efficiency, such as dynamic insulation boards [28] and recycled waste paper in building enclosures, demonstrating potential for improved thermal performance and sustainability [29].

Recent studies have tackled the importance of fluid dynamics in these systems. Numerical simulations by Wang et al. [30] explored the coupling between solid-liquid phase change and thermal flow, providing valuable insights into fluid behavior in these materials. These studies also underline the crucial role of convection in the behavior of PCMs, as demonstrated by Lappa [31], with significant impacts on boundary conditions, material properties, and the integration of nanoparticles. A multi-physics modeling approach that considers the interactions between heat, mass, and fluid movement is necessary to study natural convection phenomena and heat transfer in phase change materials.

Optimizing material configurations is vital for maximizing building energy efficiency [32]. The application of new technologies, numerical modeling, and advanced simulation methods like Computational Fluid Dynamics (CFD) have been used to analyze and optimize thermal performance and design in buildings [33].

Zhou et al. [34] used CFD modeling to validate the thermal performance of dynamic Trombe walls incorporating PCMs, providing a better understanding of heat flows and more efficient solutions.

Integration PCMs and bio-based materials with advanced modeling techniques has shown promise in improving building efficiency [35]. Khoukhi et al. [36] focused on the effect of varying the dynamic thermal conductivity of insulation materials on temperature variation across wall assemblies.

While PCMs may have varying thermal performance depending on environmental conditions, they may be less effective in extreme climates or environments with minimal temperature variations [37]. To achieve thermal performance equivalent to conventional insulating materials, bio-based materials may require a greater thickness of insulating panels [38].

The importance of thermal performance in building envelopes is well-recognized for its impact on energy efficiency and occupant comfort. Traditional insulation materials often fail to provide adequate thermal regulation, especially in warmer climates.

While numerous studies have explored the use of PCMs and bio-based materials individually for thermal regulation, there is a significant research gap exploring the synergistic effects of combining these materials to maximize their benefits.

This article addresses this gap by investigating the potential benefits of combining PCMs with biobased insulation materials, specifically Wood Wool (WW) and Hemp Wool (HW), in building envelopes to enhance thermal performance. By exploring the latent heat storage capabilities of PCMs and the natural insulating properties of bio-based materials, this research aims to develop sustainable and efficient insulation solutions.

This study’s novelty lies in the experimental and numerical analysis of these composite materials, providing valuable insights into their thermal behavior and practical applications. The research subjects the wall to a sinusoidal outside temperature, simulating typical summer day weather in Morocco, through experimental analysis using the heat flow method and numerical simulations using ANSYS Fluent software. The study provides insights into the dynamic thermal distribution within the insulation wall, with thorough assessment of the thermal performance and fluid mechanical aspects associated with the transition phase change of the different scenarios to determine indoor temperature reduction and heat transfer decrease.

The Heat Flow Method (HFM) [39] experimental study investigates two different external wall insulation configurations using HW as the main material for its numerous advantages and thermal properties. The study also explores the impact of adding PCM on temperature variation to take advantage of its thermal storage capacity for regulating internal temperature.

HW, with its low thermal conductivity, helps limit heat transmission through walls, ultimately reducing the need for heating and cooling and lowering energy costs. PCM materials have the ability to store and release large amounts of heat energy by transitioning between solid and liquid phases. The study will analyze the thermal properties of HW and the effects of PCM integration, aiming to enhance insulation designs and optimize the thermal performance of buildings.

The simulation was conducted using ANSYS Fluent student version 2023 R2 software [44], allowing to analyze the temperature, velocity, liquid fraction and heat flux within PCM + (HW and WW) during phase change processes.

To model the temperature distribution using the heat Eq. (1), numerical methods, and assumptions about the wall material subjected to transient unidirectional heat transfer were taken into account [45,46].

The simulation of fluid flow and heat transfer in PCMs involves solving the Navier-Stokes equations Eq. (5) for fluid motion, coupled with the energy equation for heat transfer. Here, we consider the Boussinesq approximation for natural convection, which assumes that density variations are significant only in the buoyancy term.

The continuity, momentum, and energy equations for an incompressible fluid with phase change are as follows:

Continuity Equation:(4) ∇.u=0

Momentum Equation (Navier-stokes):(5) ∂u∂t+(u.∇)u=−1ρ.∇P+v∇2u+g where P is the pressure, v is the kinematic viscosity and g is the gravity.

To model the phase change, the enthalpy-porosity technique is often used. In this method, the liquid fraction f_s is determined based on the temperature field:

Energy Equation with phase change:(6) ∂T∂t+u.∇T=α∇2T+LCP∂fs∂t (7) fs={0;T≤TsT−TSTl−Ts;Ts≤T≤Tl1;T≥Tl where T_s and T_l are the solidus and liquidus temperatures, respectively.

Heat transfer analysis of the wall envelope was simulated by the user-defined function (UDF) representing outdoor temperature variation on a typical summer day, modeled as a sinusoidal temperature oscillation. Tout(t) Eq. (8), ranging from 20°C to 40°C. Using the same thermal properties as the thermal insulation materials detailed in Table 1.

(8) Tout(t)=303+10∗sin⁡(ωt)

Here t is the time, and ω=2π/τ , where τ is the 24 h period.

The temperature evolution T (x, t) in the model was studied under certain assumptions [47]. These assumptions include considering laminar flow, neglecting radiation effects due to slow temperature changes, assuming adiabatic horizontal walls, and considering walls to be homogeneous and isotropic. In addition, the model assumes that the thermal properties of the material are constant in space and time and that there are no internal heat sources. These assumptions provide a simplified framework for understanding the temperature distribution within the system.

Boundary conditions for this case require a specific value to be specified, with both the external wall and inner wall having a Dirichlet condition as the type of boundary condition imposed.

Boundary conditions

The bottom and top of the insulation wall are adiabatic:(9) −λ∂T∂y=0

The temperature at x = 0 is  T(0, t)=Tout , and the temperature at x = e is set to 295.96 K.

The finite element method (FME) is used to solve these equations with ANSYS Fluent by discretizing the heat equations and solving them numerically on a mesh of the wall to determine the temperature distribution.

Geometric modeling was performed using the Design Modeler tool in ANSYS software. The study considered four different wall scenarios, as shown in Fig. 2. A quadratic mesh was then generated, comprising 40,000 elements for PCM/HW and PCM/WW, and 35,000 elements for HW or WW.

Simulations were solved using a pressure-based and transient solver configured with implicit pressure and coupled operator splitting, along with a second-order upwind scheme.

Running the simulation allowed for calculating the temperature distribution across the walls and plotting the temperature evolution inside the wall over a 24 h period to analyze heat transfer through the wall.

This study asserts the significant potential of the combination PCM and biobased insulation materials to enhance the thermal performance of building envelopes.

The combination of phase change material (PCM) with biobased insulation materials resulted in significant reductions in temperature oscillations within walls. PCM_HW exhibited a temperature decreases of 3.8 K, while PCM_WW showed a reduction of 1.45 K compared to their respective reference wall insulation without PCM.

PCM composites demonstrated superior thermal management capabilities. The addition of PCM to both Hemp Wool and Wood Wool significantly improved their effectiveness as thermal insulation materials, providing more stable indoor temperatures. This enhancement in thermal stability contributes to improved occupant comfort and reduced energy needs for heating and cooling.

Regarding heat flux, the addition of PCMs resulted in a significant reduction in heat transfer rates. An average decrease of 96% for PCM + (HW, WW) compared to HW and WW without PCM.

The homogeneous distribution of the liquid fraction within the PCM layer and moderate velocities indicate efficient thermal energy storage and release process, which is crucial for maintaining consistent thermal performance in sustainable building applications and contribute to the effectiveness of the composite insulation system.

Future research will explore the hygrothermal performances of these materials, examining how PCM integration affects moisture management and thermal behavior over extended periods. Moreover, exploring the wider impact of PCM usage on sustainable construction and environmental management will provide valuable insights into their role in ecofriendly building solutions.