Tropical Forest Conservatory
A total rethinking of greenhouse technology, from earth tubes to computer-driven ventilation and shading.
The success of the LEED® Silver Welcome Center inspired Phipps to rethink its next project - a 12,000 foot Tropical Forest Conservatory. Could green building technologies supersede conventional design assumptions that have defined conservatory construction since the 1840s?
A Revolutionary Approach to Heating & Cooling
Eliminating many of the high costs associated with supplemental heating and cooling was top priority. Phipps started with a question: "What would happen if the design didn't follow conventional roof venting with a single high and low vent and instead had every other row of glass on the roof open?"
Conventional conservatory design is based on the chimney effect to maximize passive cooling, or massive energy-intensive fans to force air exchange in the building. By completing a computational fluid dynamic study, Phipps confirmed that mechanical ventilation and cooling of the building could be eliminated and that 100% passive cooling would be sufficient for visitor comfort and plant performance with the new vent design.
The next concern had to do with conserving heat to minimize energy consumption in the winter. Historic Review Commission concerns led the architects to design a Tropical Forest building with a high south wall and a roof that sloped downwards from south to north so that the building does not impact the view of the Victorian glasshouse.
Originally, Phipps specified single pane glass for the whole building. While double pane insulated glass reduces heat loss, it blocks too much light for plant performance. Phipps requested a winter sun tracking study, which determined that almost all of the direct winter sun enters through the south-facing wall, not the roof. What if Phipps left the south wall as single pane glass, but changed the roof glass (where most heat is lost) to insulated double pane? Engineers estimated that the double pane insulated roof glass would save 1,526 million BTUs annually.
Tropical Forests Innovations at a Glance
- Use of energy-saving insulated roof glass while still maintaining proper light levels for growing plants.
- Radical roof venting system, coupled with earth tubes, fogging and computer controlled shades, make the structure 100% passively cooled.
- A solid oxide fuel cell was manufactured as a prototype by Siemens Power Generation to convert natural gas into electricity. While it is not currently in use, it was the world's first use of a fuel cell in a public garden.
- Root-zone heating and thermal massing in the surrounding walls amplify energy savings.
- Special Events Hall adjacent to the Conservatory features Solarban 70 XL solar control low-emissivity glass, the most energy-efficient glass available at the time, designed and manufactured by PPG Industries, Inc. Phipps represents the first commercial installation of this glass.
The final result? The Tropical Forest Conservatory opened in 2006 as the most energy efficient conservatory in a public garden in the world. Cooling costs are zero; heating costs are estimated to be less than half of those incurred by a typical conservatory.
Advanced Computer Control
- Anticipatory computer controlled weather and temperature reacting system
- Maximum energy efficiency
- Smoother, more uniform growing conditions
- Better plant quality and uniformity
- Precise equipment control and advanced data recording system
- Passive cooling replaces need for HVAC
- Six 24" diameter, 300' long concrete tubes are installed at 15 feet below grade, where the temperature is a steady 55° F (13°C) year round
- Hot outside air cools as it travels through the underground tubes and into the conservatory
- Vacuum created by hot air exiting the roof vents pulls the cooled air into conservatory using no electricity
- Fogging system for evaporative cooling
- Prevent convective and radiant heat loss
- Provide shade in summer and thermal insulation in winter
- Guided electronically by weather station link
- Argus computer controlled
Radical Roof Design
- Tall south-facing wall allows for insulated double-pane roof glass
- Half of the 12,000 sf roof opens to eliminate the "greenhouse effect"
- Vents are Argus computer controlled
Symbiotic Heating Systems
- Radiant floor heat for visitors
- Thermal massing interior concrete walls collect solar energy and release the heat at night
- Green roof over support facilities