Glazing — Gallina PoliCarb 2P, 6mm Twin-Wall, Opal
Manufacturer Specifications
| Property | Value | Notes |
|---|---|---|
| Light Transmission (LT) | 57% | Lab, perpendicular incidence |
| Solar Heat Gain (SHGC) | 0.66 | 66% of solar energy enters |
| Shading Coefficient | 0.76 | vs clear (0.91) |
| R-value | 1.639 | ft²·°F·hr/BTU |
| U-value | 0.61 | BTU/hr·ft²·°F |
| UV protection | One side (99%) | Printed side faces outward |
| Warranty | 10 years | ~2.25 years old as of March 2026 |
Spec vs Measured
| Metric | Spec | Measured at Sensor | Estimated Plant-Available |
|---|---|---|---|
| Light Transmission | 57% | 12–18% | ~25–35% |
The gap between spec (57%) and measured (12–18%) is explained by:
- Sun angles — halve transmission vs perpendicular spec
- East tree shadow — blocks sensor position until 10:18 AM
- Sensor position — LDR not in growing zone
- Panel age/dirt — minor contribution
- Structural framing — reduces effective glazing area
The Critical Insight: SHGC > LT
SHGC (0.66) exceeds visible light transmission (0.57). That 9% gap is “hidden heat” — infrared energy that the panels absorb and re-radiate inward. This means:
- The greenhouse overheats before it over-lights
- Shade cloth blocks more heat than useful PAR
- Shade cloth is almost pure upside for plant welfare
Transmission by Sun Direction
| Sun Facing | Measured Transmission | Notes |
|---|---|---|
| SW (210–240°) | 23.5% | Best angle — afternoon sun |
| West (240–300°) | 20.0% | Late afternoon |
| South (150–210°) | 14.9% | Solar noon — high angle |
| SE (120–150°) | 8.4% | Morning, partially blocked |
| East (60–120°) | 6.9% | Early morning, worst |
The greenhouse transmits 2–3× more light from the southwest than the east, confirming the physical orientation and tree shadow analysis.
Heat Loss Calculation
~640 sq ft of exposed glazing × U-value 0.61 = ~390 BTU/hr per °F of indoor-outdoor delta.
At 20°F outdoor (42°F delta): ~16,400 BTU/hr heat loss. Well within the combined heating capacity of 80,120 BTU/hr.
Live Transmission
The hexagonal shape creates a daily signature — transmission peaks when the southwest face catches afternoon sun, and drops when the east tree blocks morning light.
Left: estimated indoor PPFD (green) derived from outdoor lux (yellow) × glazing model. Right: measured light transmission percentage over time.
Live Transmission
The hexagonal shape creates a daily signature — transmission peaks when the southwest face catches afternoon sun, and drops when the east tree blocks morning light.
Left: estimated indoor PPFD (green) derived from outdoor lux (yellow) × glazing model. Right: measured light transmission percentage over time.