The Energy Apron is a key component of an certain type of smaller Arcology design that would be designed for harshed and colder climates. It was also particularly suited for the mesa that Soleri settled upon as the location for Arcosanti. The Energy Apron collects the surplus solar gain energy collected in the south facing greenhouses. The greenhouse are located below the buildings, which are located at a higher elevation to enable the heat to rise to warm the foundation of the buildings helping to heat them in the wintertime.
Louvers at the bottom of the greenhouse would open when the temperature reached a certain point beyond the optimum growing range of plants as the sun warmed the air. This would let cooler air into the greenhouse. The air would move up the greenhouse as it was heated by sun. At the top of the greenhouse a manifold system would duct the hot air into the Heat Duct Tunnel (HDT).
The air would continue to travel upwards until it reached the buildings to be heated. The heating process is not direct, with a series of tunnels and ducts underneath the Soleri Office and Drafting and East Crescent would allow the thermal mass of the concrete to be warmed or charged during the day. During the cold of the evening the warmth from the concrete thermal mass would then wick out to the buildings up above.
Heat Duct Tunnel (HDT) Operating as Manifold Control Air Flow through Energy Apron
The air in the HDT - which is a multi-use structure built along the spine of the East Crescent Complex at the basement level - continues to travel through the buildings until reaching an exit point at the westernmost point of the East Crescent that allows the air to go back outside. In additional to its main design rationale, which is as a manifold for air flow in the Energy Apron, it is also a chase and a accessway for the EC utilities. It is also art venue for the underground art scene at Arcosanti. Finally its used as a way to transport water (as part of Arcosanti's Water Management System) from the surface above during heavy rains, including an overflow pipe for the two cisterns located in the EC Complex to the Invisible Structures RainStor Cistern built at the end of HDT by the pool and finally out and down the cliff by the pool. The HDT would be shut during the cold nights of Heating Season to keep the cold air out. Its believed that this would be a way to throttle to system just as a butterfly in a car engine manifold controls engine speed (or at least the air / fuel mixture) by regulating air flow.
Core components of Energy Apron include:
Inlet/intake louvers to allow cool to enter the greenhouse
Solar collector in the form of a greenhouse, a connecting pipe to bring the air to the buildings up above,
Heat Duct Tunnel for connecting the Solar Collector with the Plenum
Choke/Cut-off Valve for either restricting of cutting off flow of warm air from the greenhouse into the SOD and East Crescent
Plenum/Heating Plate for enabling the spreading of the heat through the foundation of the buildings from the Heat Duct Tunnel
Chimney/Cut-off Valve for controlling outflow of heat from the Heat Duct Tunnel.
The Arcosanti Energy Apron system is designed to make use of the sun by allowing the cool air to go into the greenhouse in the cooler months.
Summer Utilization
It is less clear about how the system would operate in the summer. People often ask about what happens in the Summer in this system. Of course the hot air of the greenhouse would not be of much use in the summer. However research could be done to cool the incoming air going into the greenhouse through a water wall. The question is could the air be cooled enough to lower