This is a application directly to the soil to prevent moisture soaking into wood. Moisture build can cause multiple problems one of which being Termites.
These are auto vents that open and close according to the temperature in the crawl space. Approximately 70 degrees vents should be completely open to allowing crawlspace to breath properly. Approximately 40 degrees vents should be completely closed allowing the crawlspace to retain heat resulting in a more efficient house.
These Vents have fans attached forcing air out of the crawlspace. These vents work well in areas where a cross ventilation is not possible. When your crawlspace breaths properly your house becomes more efficient as well having less problems such as Mold, Oder Problems, and many more.