Cooling
55,600 BTU/hr of solar heat enters through the glazing. The cooling system can reject 27–40% of that. The rest becomes higher temperatures. This is physics, not a tuning problem.
Electricity spent, kilowatt-hours consumed, and average daily cost for the selected range.
The Heat Source
Solar radiation is the input side of the equation. At peak (886 W/m²), the glazing’s SHGC of 0.66 admits roughly 55,600 BTU/hr across ~300 sq ft of sun-exposed surface. The opal polycarbonate’s SHGC exceeds its light transmission (0.66 vs 0.57) — 9% of that energy is invisible infrared that heats surfaces without growing plants. This is why shade cloth blocks more heat than useful PAR — almost pure upside for summer.
Where Cooling Fails
Zone temperatures through the day. When all four lines climb together past 82°F, the cooling system is saturated. The south zone leads (narrowest wall, most direct sun), the east zone lags (tree shade + patio door). March 25 at 88°F outdoor produced a 96.5°F indoor peak. The all-time record is 100°F+.
Indoor vs Outdoor Delta
Watch the delta narrow on hot days. When outdoor temp is 90°F, indoor peaks at 97°F — only 7°F above ambient. The cooling system is working hard, but it’s fighting thermodynamics. The fans move 4,900 CFM through 2,250 cu ft of space — a full air exchange every 27 seconds — and it’s still not enough.
Equipment Activity
Fan and vent cycling in real time. The lead fan rotates every 6 hours for wear balance. Stage 1 (one fan + vent) kicks at 82°F. Stage 2 (both fans) at 85°F. Stage 3 (everything including evaporative fog) at 87°F. On a sunny March afternoon, the system lives in Stage 2–3 for hours.
Runtime Trends
Fan runtime hours correlate directly with solar radiation. Cloudy days: 2–3 hours of fan time. Clear days: 8–10 hours. The correlation is so tight you can predict tomorrow’s fan runtime from the weather forecast.
Cooling Stages
| State | Trigger | Equipment | Estimated Rejection |
|---|---|---|---|
| COOL_S1 | temp > 82°F | Lead fan + vent | ~6,000 BTU/hr |
| COOL_S2 | temp > 85°F | Both fans + vent | ~12,000 BTU/hr |
| COOL_S3 | temp > 87°F | All cooling + evaporative fog | ~15,000–22,000 BTU/hr |
Why Software Can’t Fix This
The cooling deficit is physics, not tuning:
- Solar input: ~55,600 BTU/hr at peak
- Fan + vent rejection: ~12,000 BTU/hr
- Evaporative cooling (fog + misters): ~3,000–10,000 BTU/hr
- Gap: ~33,000–40,000 BTU/hr with nowhere to go
No amount of PID tuning, fan staging optimization, or clever scheduling changes the math. The only fix is reducing the input side: shade cloth on the south, southwest, and west faces. A 40–50% shade cloth would cut peak heat gain by roughly a third, potentially dropping peak indoor temps from 97°F to 87°F.
Equipment
| Unit | Spec | Power | Location |
|---|---|---|---|
| Fan1 / Fan2 | KEN BROWN 18” Shutter Exhaust, 2,450 CFM each | 52W each | South wall |
| Vent | 24” × 24” mechanical actuator, screened | ~10W | North wall |
The 4 sq ft vent opening is the intake bottleneck — fans pull more air than it supplies. In summer, the patio door (east wall) becomes the larger secondary intake.
→ See Humidity for how the cooling/humidity tradeoff works — opening vents improves temperature but kills humidity. → See Heating for what happens when the sun goes down and the equation reverses.