In state-of-the-art high performance housing it is common to combine high-mass passive solar design with thermal-bridge free, airtight building envelopes. However, the mass component is usually limited to an insulated concrete floor slab. In UrbanEden, the mass has moved to the walls in the form of fully-insulated, precast panels. This seemingly innocuous choice is actually a major innovation. By markedly increasing the surface area and related volume of our thermal mass in the passive solar context, we have been able to implement a hybrid passive/active hydronic cooling system that, unlike conventional hydronics, uses only pump energy to accomplish temperature changes.
Hydronic Fluid Mats (Capillary Tube System)
UrbanEden’s high-mass geopolymer cement concrete walls provide a container in which to store large quantities of thermal energy. In the summer, ambient heat soaks into the thick walls throughout the day, primarily by means of radiation. At the end of each day, this stored thermal energy can be removed from the walls by an innovative hybrid system. Hydronic – BEKA® capillary tube – mats embedded within UrbanEden’s concrete walls provide a vessel for the circulation of a water-based working fluid throughout the building’s envelope, which flushes out the heat accrued during daylight hours.
Once captured within the water, the thermal energy extracted from the walls must be dissipated. Dissipation of this heat is made possible by a network of custom fabricated, rooftop-mounted AET Solar® copper-fintube heat exchangers, designed to serve as radiation emitters. After the sun sets each evening, the water in the tubes in the walls is pumped onto the roof of the house and circulated through this heat-exchanger network. Passing through the serpentine heat-exchanger network, the warm water releases its stored thermal energy into the cool night sky; in fact, the exchange of radiant heat to the night sky is so efficient, the temperature of the fluid on the discharge side of the heat-exchanger network could potentially drop below that of ambient air.