Applying natural cooling to slab floors

A presentation by Dick Bourne of the Davis Energy Group (Davis, California) on naturally cooled slab floors: circulate water cooled by evaporation or by radiation to the clear night sky through tubing in a concrete slab, so the floor itself becomes the cooling delivery system. The point is to use the floor as a thermal mass that participates in daily heat exchange, instead of treating cooling as only an air-conditioning problem.

Bourne is not a bystander in this archive: the Cool Cell Q&A brochure names “Dick Bourne of Integrated Comfort in Davis, California” as a Zomeworks venture partner working on increasing cooling capacity in hot/humid climates — this presentation documents the parallel California practice.

Main idea

Element	Role
Slab floor	”Stores cooling,” delays delivery, and radiates coolth to occupants.
Natural cooling	Evaporation or night-sky radiation provides the cool side of the cycle; radiation to a clear night sky is the most efficient natural water-cooling process.
Daily cycle	Coolest water is generated at night; the slab carries it into the day.

Mechanism

night sky / evaporative cooler -> chilled water -> tubing in slab -> radiant cooling by day

The slab gives the building inertia: instead of letting interior temperature swing sharply, the cooled floor lowers mean radiant temperature, buffers the load, and can be recharged when outside conditions are favorable. Bourne lists further benefits: low-cost cooling storage, synergy with ceiling fans, an excellent pairing with radiant floor heating, and the ability to shift electrical load to pre-peak periods.

Track record reported

A patent was awarded in 1996, with twelve projects completed at the time of the presentation. Three featured projects, two with monitored results:

• Texaco “DualCoolPlus” convenience store (3,600 ft², near Davis, CA, opened early 1998) — pre-cools condenser and ventilation air and pre-cools the floor at night via tubing in a sand layer; allowed downsizing from a 15-ton to a 10-ton rooftop unit. Monitored June–November 1998 with PG&E support: 46% peak-demand savings, 50% annual energy savings, payback under one year with downsizing credits.
• All Weather Manufacturing “NightSky” (Vacaville, CA, completed March 1998) — a 6,500 ft² roof array cools water at night, storing coolth in an 8,000-gallon tank and in the floor: 87% peak-demand savings, 73% annual energy savings, 2.5-year payback.
• 580 Howard Street (5-story historic San Francisco building) — cooling tower runs at night to cool the slabs.

Bourne’s conclusion tempers the purism: in Sacramento Valley non-residential applications, floor cooling required hybrid features (downsized conventional equipment, auxiliary chillers) to hold peak-day demand — a contrast with Zomeworks’ fully passive thermosiphon approach, though both share the night-recharged slab-and-storage logic.

This page is less about a specific device than about a design move. It takes the night-cooling idea and inserts it into the floor plane, where it can work with the rest of the envelope — the same pattern the archive documents overhead in the Cool Cell ceiling systems.

See also

• Building thermal storage
• Night-sky radiative cooling
• Cool Cell architectural climate-control
• Index
• Night sky radiant cooling potentials in New Mexico