Dear Fateme

The main advantage of PCM is the hability to store large amounts of energy, nevertheless, their thermal conductivity can be more than one order of magnitude higher than typical insulator materials. Thus, the use of PCM or thermal insulator materials or both should take in to account not only the thermal conductivity but the combination of thermal conductivity, heat capacity and density, i.e. thermal diffusivity (in cases of insulator materials) and the combination of thermal diffusivity and the Stefan number in cases of PCM.

Additional details of this topic can be found in the following publications

Conference Paper Microstructural design of paraffin/graphite composites for t...

And also this

Article Cellular PCM/graphite composites with improved thermal and e...

And this

Article Highly conducting core–shell phase change materials for ther...

In the heat equation, PCM will mainly play role in the dynamic term (the heat storage term or left side term) whereas the insulation will influence the steady state term (conductivity term or right side term). In a simple term, PCM will store heat while insulation will actually reduce the heat transfer when temperature difference is present.

Dear Fateme,

In our work, we found that PCM in the building envelope helped to shield the building against heat transfer under certain weather conditions. We optimized the melting temperature and the position of the PCM in the envelope. If that is of interest to you, you can find more information in the attached paper. Our simulations were performed for Québec City (Canada).

Article Thermal shielding of multilayer walls with phase change mate...

Sorry for this long answer, but I wanted to share my experience on PCM's thermal performance!!.

As part of my PhD work that was recently completed, I found compelling results (link is provided for further look). I have developed standalone modules in SIMULINK for simulating PCM-enhanced walls; multilayer walls, ventilated cavity walls, double cavities and many other design options for advanced façade systems. This tool has been experimentally validated. The TMY3 weather data is used to provide boundary conditions on exterior side of the wall with indoor environment being set at 24C in summer and 22C in winter. Using standalone module, the results were amazing!!! In some high latent heat cases with narrow melting range, we could eliminate the heat transfer through walls during summer where the walls became adiabatic!!!. The heat is stored by PCM during the day and released back to outside during the night. The climate was the driving potential for charging and discharging the PCM. The results were amazing and so we have integrated those modules in TRNSYS, a whole-building simulation tool. Real boundary conditions were applied in this case. The indoor environment has many heat sources such as internal heat gain from people, lights, equipment with solar penetrating through windows, and air infiltration. The maximum savings in peak and annual loads were not so amazing at all for four climates in USA. The maximum saving was below 15%, even for high latent cases that used to make the walls adiabatic in standalone cases. For the same house in TRNSYS, I then applied ideal sinusoidal boundary conditions to see the potential of PCM. The results are amazing again!!!. Therefore, PCM’s performance is so tricky with climate generally being the driving potential!!!

Louis, have you extended your study on PCM beyond the cases you published?

Thesis MODELING AND SIMULATION OF PCM-ENHANCED FAÇADE SYSTEMS

Both have different functionalities hence PCMs and insulation complements each other in almost all the application and it is not a case of one substitutes another. Insulation and insulating materials have a very low conductivity value and hence its role is to limit or reduce the rate of heat loss to the surrounding. Phase Change Materials absorb or release heat thereby its role is to provide continuous heating or cooling. To know more on what is phase change materials check out the link provided below. 

http://pluss.co.in/about-PCM.php

I recommend you to read this paper:

http://ijens.org/Vol_18_I_05/180505-3737-IJMME-IJENS.pdf

Best regards