A residential radiant heating and cooling system has been operating and monitored in the Phoenix, Arizona, area for four years (2000–2004). It has demonstrated that controlling surface temperatures of both high and low mass envelope components can provide stable comfort conditions at a lower cost with less noise and higher air quality than a conventional air-handling system.

The environmental system includes high mass walls, insulated on the exterior, and radiant panels in both the ceiling and the floor mass supplied by a hydronic source (ground-source heat pump). Low mass ceiling panels are used primarily for summer cooling, and the high mass floor panel system is used for both summer cooling and winter heating. The control strategy uses envelope thermal mass to keep the operative temperature of the space within the comfort envelope, using mostly off-peak electrical energy, with less than one hour of on-peak compressor time per day.

Units: Dual