Originally Posted by Billy356
What is the benefit of air flow downward as opposed to upwards?
Upwards is traditional, it will result in less pressure drop through the hops which means a fan that is just barely big enough will have a better chance of getting the job done. The downside occurs when the hops are almost dry. If you have to much airflow, they will start shaking and may shake the lupulin out. Worse case, you wake up one morning to see your hops blown all over the barn.
Downwards will cause slight compaction, which increases pressure drop. This means you darn well better have enough fan. But it also means you won't have to worry about shaking or blow out.
For the record, nearly all of my designs blow down...but as a disclaimer, I'm the only commercial grower that does it that way.