Spherical PCM Modules and Dome Thermal Battery Performance
Spherical PCM Modules (Huluka & Muthulingam, 2025)
Published in Scientific Reports, Vol. 15, Article 39845 (November 2025).
Experiment
Reinforced concrete roof slab (1.325 × 1.325 × 0.15 m) divided into four thermally isolated zones:
- Conventional concrete (control)
- Empty spherical modules
- Modules filled with OM35 (organic PCM, 35°C melting point)
- Modules filled with OM37 (37°C melting point)
Forged aluminum (Al 1200) semi-spherical bowls welded together. 354-358g of liquid PCM, occupying 75% of sphere diameter. Testing in Rupnagar, India (subtropical), April, J-type thermocouples at 1-minute intervals.
Results
| Zone | Cooling Load Reduction | Surface Temp Decrease | Decrement Factor |
|---|---|---|---|
| 1 (control) | — | — | 0.56 |
| 2 (empty spheres) | 59% | — | 0.50 |
| 3 (OM35) | 68% | up to 11.1°C | 0.38 |
| 4 (OM37) | 69% | min 9.2°C, avg 10.2°C | 0.37 |
Critical Geometric Finding
Spherical and cylindrical PCM shapes provide a 70% increase in energy efficiency compared to rectangular designs. This is directly transferable to dome shell geometry — curved encapsulation outperforms flat.
Mechanism
PCM modules undergo daily phase transitions: absorbing heat as latent heat during melting (daytime) and releasing during solidification (nighttime), creating a self-regulating thermal cycle.
Monolithic Dome Thermal Battery
Source: Monolithic Dome Institute (monolithic.org).
Existing Thermal Mass Performance
Domes already function as "very large thermal storage" systems:
- Each pound of concrete stores ~1 BTU for 5°F temperature range
- 50-ft residential dome: ~200,000 lbs concrete → 200,000 BTUs storage
- 200-ft assembly dome: ~2.5 million lbs → 2.5 million BTUs
- Temperature stability so high that rapid changes are physically impossible
Energy Performance
- HVAC equipment reduced 60-75% vs. conventional buildings
- Power bills 50-70% lower
- Real example: Serenity Dome (Virginia, 50-ft, 2,675 sq ft) — total energy costs under $950/year (2012), 1/3 of previous conventional home
- One dome owner heated through winter with only five 100W ceiling light bulbs
- Professional engineering: R-values "in excess of 80 and generally over 100"
- Thermographic imaging at -25°F: "heat loss virtually zero"
Night Cooling = PCM Analog
"In many parts of the country, it is possible to cool the thermal mass of the shell by utilizing fresh air." This night-cooling-of-thermal-mass strategy is essentially the same operational principle as PCM night solidification, suggesting PCMs would integrate naturally.
The Untested Combination
No published study examines PCM integration with dome or curved-shell geometry. The gap exists at the intersection of:
- PCM in building envelopes: 2-11°C temperature reductions, 15-69% cooling load savings (well-studied in flat roofs)
- Dome thermal performance: 50-75% energy savings, massive thermal inertia (industry data)
Predicted synergy:
- Curved PCM encapsulation already proven 70% more efficient than rectangular
- Less total PCM needed due to dome's lower surface-area-to-volume ratio
- Dome's natural convection patterns promote uniform PCM cycling
- Existing thermal mass + PCM latent heat = combined sensible + latent thermal battery