concepts · updated 2026-06-30
Overhead thermal shutters
confidence: high volatility: cold verified: 2026-06-30fresh
Bare aluminum shutters below ceiling water storage, tested in the Andy Shack (March 2001). They control radiant heat flow from 8″ PVC pipes on 12″ centers to the room below — open for heat delivery, c
Bare aluminum shutters below ceiling water storage, tested in the Andy Shack (March 2001). They control radiant heat flow from 8″ PVC pipes on 12″ centers to the room below — open for heat delivery, closed for heat banking. The source calls them “very effective” and reports a 4–5× difference in heat transfer rate between open and closed states.
Andy Shack installation
The Andy Shack is a Zomeworks test building in the Albuquerque yard, in use since 1988. The June 2000 configuration used as the baseline for the shutter experiments:
- Storage: 10 × 8″ PVC pipes × 7 ft = 250 gallons
- Roof radiator: 65 sq ft of copper radiator, kept dry, operating overnight
- Temperature monitoring: June 12–15, 2000 (shack water vs shack air vs ambient) and June 27, 2002 (white plate, Andy Pipe, ambient)
Measured performance
Data from the Andy Shack, March 2001:
| Condition | Room temp | Pipe temp | Outside temp |
|---|---|---|---|
| Shutters closed | ~60°F | ~90°F | ~45°F |
| Shutters open | 75–80°F | ~90°F | ~45°F |
Baer derives the conductivity ratio from these temperatures:
- 30·Uc = 15·Ub → Uc = ½·Ub
- 12·Up = 32·Ub → Up = 32/12·Ub
- Therefore Up ≈ 5·Uc — opening the shutters quintuples the heat transfer rate.
The reflective aluminum provides an estimated R-value of 4–5 when closed. Despite “huge long cracks between the shutters,” warm air does not leak down in winter — “it doesn’t want to” (warm air rises).
Summer vs winter asymmetry
The shutters behave differently by season:
- Winter: Shutters block radiant transfer effectively. Heat stays banked in the ceiling pipes until the shutters are opened. This allows storing enough heat for one or two cloudy days.
- Summer: Cool air around the pipes wants to fall through the cracks, so thermal transfer continues even with shutters closed — Baer estimates over 1 BTU/°F·ft²·hr. When open, transfer reaches about 3 BTU/°F·ft²·hr. The 8″ pipes on 12″ centers offer over 2 ft² of surface per square foot of ceiling.
This asymmetry helps: “Coolth does not need to be stored in such large amounts as heat. Night is certain to recharge coolth every 24 hours; the sun is not so reliable.” The system naturally holds heat tightly (winter need) and releases coolth freely (summer need).
Alternative thermal mass
Sample ceilings with 9 one-liter Coke bottles per square foot transferred 3.75 BTU/°F·ft²·hr — even better coupling than the pipe arrangement.
Shutters are silent and passive; radiant heating and cooling is always pleasant.