One of the more intriguing installations at the 14th International Architectural Biennale is an exhibition by MIT’s Senseable City Lab. Dubbed “Local Warming,” the overhead system features an array of sensors and infrared heat lamps that warm building occupants in a targeted fashion. Rather than dumping conditioned air into a space indiscriminately, as conventional HVAC systems do, Local Warming uses a WiFi-based motion tracking system in conjunction with mirrors and rotating motors to detect building occupants and direct heat toward them. Similar to occupancy sensors for lighting, Local Warming is designed to reduce energy demand, particularly in spaces such as building lobbies that are infrequently occupied.
Local Warming presents a compelling strategy for reducing buildings' heating load, but it is not an original approach. Occupant-sensing HVAC technology has been commercially available in Japan for two decades. In 1994, Mitsubishi Electric developed a sensor for its wall-mounted HVAC unit that "detects room occupant movement in order to redirect airflow.” Although the Mitsubishi approach relies on convection rather than radiation, the philosophy is the same. Like older Japanese technologies, such as kotatsu, or (more generally) portable kerosene heaters and warm indoor clothing, this strategy keeps building inhabitants warm while reducing winter heating bills. This likely contributes to the fact that, in 2005, the average Japanese household consumed about half the energy of the typical U.S. domicile per capita, according to data compiled by NationMaster.
Beyond its use in Japan, occupant-based conditioning has interesting implications for construction. If such systems are sufficiently effective, as they have proven to be in that country, will the focus shift entirely from the building to the occupant? Taken to an extreme: Could we reduce the amount of material resources in building envelopes and increase the circulation of fresh air while cutting overall energy demand? What drawbacks might this strategy bring to our current approach to designing conditioned spaces? And how might it transform the way we consider the interior environment?
Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.
