In 2002, Advanced Energy published a research project that proved that closed crawl spaces outperform vented crawl spaces. This should have killed any argument over what type of crawl space should be preferred and the psychrometric chart shows that there should never have been a choice between the two. Essentially, for those unfamiliar with psychrometrics, the chart shows that in a certain space with an outdoor temperature of 90°F with a relative humidity of 53%, it enters the house’s crawl space and cools, raising its relative humidity to about 70%, which is the unfortunate number where mold begins to grow.
Read the full article here: Vented Crawl Spaces and the Psychrometric Chart Are Not Friends