How Phase Change Materials Can Improve Building Comfort: Lessons from Simulation Study

When I started my master's research, I was fascinated by the idea that walls could store and release heat, almost like invisible batteries. This is possible with phase change materials, which absorb and release heat during melting and solidification.

My recent project focused on sandwich walls enhanced with PCMs. The big question I explored:

Does the thickness of the PCM layer and its encapsulation method significantly affect a wall's ability to maintain a cool interior?

What I Did

I created 18 wall models in Rhino and ran transient thermal simulations in ANSYS. These models included:

• A control group consisting of air gaps

• A baseline group composed of traditional rockwool material

• Experimental setups with varying capsule geometries and PCM thicknesses

Each model was "tested" under a simulated hot summer day in Ankara, with solar heat flux applied on the outside surface.

Wall model configurations and IDs (W1–W18)

Wall-assembly models W1–W18

What I Found

• Thicker PCM layers help. Increasing the thickness from 2.5 to 7.5 cm reduced peak interior surface temperature by about 3 °C and delayed heat transfer by over an hour.

• Flat PCMs perform better than honeycombs. Continuous layers consistently kept interior surfaces cooler than encapsulated honeycomb versions.

• Honeycomb trade-off. Larger honeycomb cells (15 mm) worsened performance, raising peak temperatures by up to 5%.

In short, continuity beats geometry for PCM walls under the conditions I tested.

Honeycomb encapsulation patterns in a 10 × 10 cm model, showing cell radius of (a) 5 mm, (b) 10 mm, and (c) 15 mm.

Why It Matters

This research matters for energy-efficient building design. By fine-tuning how PCMs are used, we can passively regulate indoor comfort and reduce reliance on active cooling systems. Flat PCM sheets, while less "innovative" than biomimetic geometries, offer the most effective thermal buffering.

Of course, real buildings are more complex than my simulations; experimental validation and testing under different climates would be the next step. However, these findings help narrow down which PCM configurations are worth pursuing.

Reflections from the Process

This project wasn't just about numbers and simulations but also about navigating the tools and methods behind the scenes. Working in ANSYS came with challenges, mainly since licensing limits restricted how fine I could make my mesh. That meant I had to be creative in balancing accuracy with feasibility. Designing wall geometries in Rhino and moving them across platforms also stretched my workflow skills.

One thing worth mentioning is that my simulations did not use Fluent's complete phase change model. Because of license restrictions, I had to approximate PCM behavior through temperature-dependent specific heat values rather than activating the complete phase change module.

While the results give a clear comparative picture between flat layers and honeycomb structures, the absolute performance values will vary in real-world conditions. In practice, PCMs would behave more dynamically during melting and solidification. Experimental studies and higher-fidelity simulations would likely reveal even more nuanced insights.

Still, even with these constraints, the patterns I observed — especially the advantage of continuous PCM layers over honeycomb capsules — provide valuable guidance for the next steps in PCM-integrated wall design.

This study adds one more piece to the conversation around PCM walls, building comfort, thermal simulations, and the role of sustainable architecture in shaping future buildings.