1. Closed Circuit Wind Tunnels are much more expensive to build due to the construction of the additional air return system.
2. The air in a closed Circuit Wind Tunnel is constantly heated due to friction with the fan. Most designs draw fresh air in to help, some even use air-conditioning, yet enclosed designs are
always uncomfortably hot in the summer.
3. The air in a Closed Circuit Vertical Wind Tunnel is full of dust and debris from clothing, cushions, etc. This is constantly recirculated, and is very difficult to remove.
4. Due to the close proximity of the fan, the flight area of Closed Circuit designs is always very noisy.