This project involves the development of a smart HVAC technology that offers improved comfort, and provides early fault detection. The technology will warn homeowners of HVAC problems, so that the system can be corrected before a major failure occurs, thereby decreasing energy use and cost Current residential heating, ventilation and air conditioning (HVAC) systems consume an unnecessary amount of energy due to equipment oversizing, incorrect refrigerant charge, and incorrect air flow. In addition, these systems do not have humidity control, which leads to discomfort or results in more energy use. This project will develop a device (HSTAT) that combines temperature and humidity control with HVAC fault diagnostics. In Phase I, both theoretical and experimental feasibility studies were conducted. Cost effective HVAC fault detection strategies and innovative humidity control concepts were identified. Extensive field testing will be undertaken in Phase II to develop a simple, rule-based fault diagnosis system that is applicable for all residential and light commercial air conditioners. A prototype system will be designed and built, and laboratory and field testing will be performed. Commercial Applications and Other Benefits as described by awardee: Combining humidity control with HVAC diagnostics should provide significant energy savings and improved comfort. The technology could be applied not only for residential buildings but also for light commercial buildings