## 2 Methodology  
This work focuses on the building construction envelope solutions incorporating PCM (walls and ceiling) optimisation, to minimise the overheating risk and total heating demand. Thus, a whole building dynamic simulation of a cold-formed steel-framed (low thermal inertia) detached building was performed, with EnergyPlus(r) 8.7.0 software. EnergyPlus(r) is highly accredited as a software with the capability to simulate PCMs. Nevertheless, several different approaches to simulate the melting and solidification process have been widespread and can be consulted in [42].  
The overheating rate was studied for constant passive parameters applied continuously (considering day or night time) regardless of specific occupation schedules.  
The implemented methodology to assess the impact of the PCM incorporation into the building fabric (see Figure 2) is divided into four main steps:  
Step 1--Dynamic Thermal Simulation: Reference model  
This step starts with the characterization of the building thermal performance considering the constructive solutions applied in the construction (without solutions containing PCM or additional features).  
Step 2--Optimisation of PCM (melting temperature value)  
This step targets the simulation and optimisation of different peak temperature melting values of the PCM. Combining PCM with different melting temperature values as a discrete parameter was simulated to attain the best scenarios that lead to the lowest annual energy demand and lowest overheating risk rate. For this step, the mechanical ventilation system and night ventilation (free cooling through opening windows) were optimised as well.  
Solutions containing PCM were applied and combined in the surfaces with south orientation on the first floor and ceiling to avoid the indoor air temperature stratification effect along the south- and north-orientated surfaces. Results are compared with the reference model (Step 1).  
Step 3--Optimisation of the PCM position into constructive solutions (3 approaches)  
The procedure defined in Step 3 defines the optimisation premise, including the features of the PCM and the layer position into the building envelope solutions.  
The uncertainty of the PCM position into a building construction solution to promote the charging-discharging cycles is an issue. In this step, three situations of the construction solutions incorporating PCM are modelled varying the position of the PCM layer as follows (see Section 5.3):  
- (1) Positioned as the most inner surface layer of the construction solution;  
- (2) Positioned behind the double gypsum board (interior to the exterior);  
- (3) Positioned in the middle of the solution, behind the acoustic layer.  
Step 4--Using a multiscale modelling approach interfacing the combination of different temperature melting values of PCM and PCM position into the constructive solution  
The influence of incorporation two PCMs solutions into the walls and ceiling, with different melting temperature values, was evaluated.  
The best combination of PCM with different melting temperature values was evaluated and optimised for the south-orientated thermal zones. The three possibilities of the PCM position into the construction solutions (defined in Step 3) were simulated in the present step.  
Finally, a list of recommendations is provided to aid designers when choosing PCM and placing this unique layer into building solutions, as well as to demystify several issues in the research community.  
Figure 2 presents the framework/outline of the proposed simulation.