A new report from the Air-Conditioning and Refrigeration Technology Institute says the right windows and roof can make residential air-conditioning systems work best.

"System Optimization of Residential Ventilation, Space Conditioning and Thermal Distribution" was prepared by Proctor Engineering Group of San Rafael, Calif., and funded by ARTI. The report evaluates products and concepts for homes and ranks them by cost, reliability, energy, health and safety, and other criteria.

Of the 30 ranked, topping the list were load solar gain windows, roofing with reduced heat gain characteristics, proper sizing to load, and reduced infiltration with controlled ventilation.

Of the mechanical systems available, ductless minisplit systems, as well as integrated heating, cooling, dehumidification and ventilation systems ranked highest on the list. The remaining mechanical systems listed near the top of the list were energy-recovery ventilators coupled with reduced infiltration, frostless heat pumps, matched components to combined efficiency, evaporatively cooled condensers, improved aerodynamics of the air handler/furnace and the outdoor air-conditioning unit, higher seasonal energy-efficiency ratings, as well as combined space and water heating.

The top-ranked design installation practices included properly sizing the equipment to loads, sealing ductwork and using shorter duct runs with improved register placement.

In addition to identifying favored concepts for residential air-conditioning systems, another goal of the report was to uncover barriers to best designs. Time, performance and costs ranked as the top roadblocks. Homeowners said they were concerned about the amount of time it would take them to determine which equipment would best meet their needs, while architects were concerned about the time required to learn more-effective design practices.