presented by Dick Bourne, Davis Energy Group
- Uses natural heat transfer forces without a refrigeration process
- Direct evaporative cooling can efficiently cool water
- Multiple stage evaporative cooling is less efficient but generates lower temperatures
- Most efficient natural water cooling process uses radiation to clear night sky
- Circulate naturally-cooled water through tubing in concrete slabs
- Water is cooled by evaporation or night sky radiation
- Coolest water can be generated at night
- Slab mass "stores cooling" and delays delivery
- Cool slab delivers radiant cooling and lowers mean radiant temperature
- Low cost cooling storage strategy
- Large mass improves natural cooling efficiency
- Cooled floor improves occupant comfort
- Synergistic with ceiling fans
- Excellent combination with radiant floor heating, an industry with strong growth
- Can shift load to pre-peak periods
- Patent awarded in 1996
- 12 projects completed to date: 3 demonstration residences, 3 privately-funded residences, 2 multi-story San Francisco apartments, 4 commercial projects totaling 62,000 ft²; other projects in design
Texaco "DualCoolPlus" — New 3600 ft² Davis CA convenience store; pre-cooler added to rooftop unit.
580 Howard Street — 5-story, 30,000 ft² historic SF building; cooling tower runs at night to cool slabs.
All Weather Manufacturing — New 6,300 ft² plant office in Vacaville CA; NightSky system cools slabs and tank.
- New 3600 ft² store, opened early 1998, 20 miles west of Sacramento
- 24 hour operation; base case had 15 ton RTU with 5 hp blower motor (5500 cfm total, 870 cfm ventilation air)
- The DualCoolPlus System: pre-cools condenser air, pre-cools ventilation air, operates at night to pre-cool floor using tubing in sand layer under floor
- Downsizing: 15 ton RTU down to 10 tons; 5 hp blower down to 2 hp; ductwork down for 33% less supply air
Results (monitored 6/98–11/98 with PG&E support): Satisfied loads on 112°F peak day; lowered condenser air 20–30°F on-peak. Key results: 46% peak demand savings, 50% annual energy savings, payback < 1 year with downsizing credits.
- New 70,000 ft² mfg. plant completed 3/98; 6300 ft² offices, 23 ton base case with five zones
- NightSky Integrated System: cools water at night with 6500 ft² roof array; stores cooling in 8000 gal tank and in floor; delivers cooling and heating through floor and five zoned fan coils; floor delivers steadily, fan coils respond fast; includes dedicated vent air fan coil. Auxiliary 10 ton chiller cools tank only when needed.
Results (monitored 7/98–present): 87% peak demand savings, 73% annual energy savings, payback 2.5 years.
- Natural floor cooling saves energy, improves comfort, and helps radiant heating economics
- In Sacramento Valley non-residential applications, floor cooling requires hybrid features to reduce peak day demand
- In hybrid systems, floor delivery facilitates down-sized blowers that save energy all year
- Floor cooling projects to date show excellent economics that should further improve
Source: Davis Energy Group presentation. Text from Acrobat OCR of scanned document.
PDF: 1998-01-01-applying-natural-cooling.pdf