Active Solar Heating Systems
Evaluate water-based collectors. A water-based system typically uses heat exchangers to move heat from the collection medium to the heat-storage or distribution medium. Heat exchanges can transfer heat to water-storage, water-distribution, and also air-distribution systems. (See also Active Solar Hot Water for additional issues to consider.)
Consider air-based collectors. Air-based systems are the least complex of active systems; therefore, they avoid many of the problems of water collectors. Air collectors are typically simple, flat-plate collectors with plastic covers. They are easily serviced, and have less extreme and costly failures. While safe from freezing or boiling, they do take up considerably more surface area, and their ducts and fans require more space than water pipes and pumps. In addition, sealing an air system against leakage and finding and repairing leaks are more difficult than repairs in water-based systems.
When considering air collectors:
Consider ventilation air preheat systems. This space heating system uses solar energy to preheat ambient air and bring it into a building's ventilation systems. The system utilizes a dark-colored, perforated, unglazed collector, integrated into the building structure, to preheat the air. These systems have efficiencies as high as 75 percent, require low maintenance, and can be installed economically, depending on the building type, climate, and fuel costs.