27:00 Thank you so much for such a great explanation! I work in controls and could not understand the purpose of the bypass damper when VFD is used. If I understood correctly, we can skip the bypass when variable geometry nozzles are used with VFD
Correct. The bypass damper is used to control static pressure in the ductwork AND maintain outlet velocity. In this scenario the VFD is used only to balance the fan. With a variable geometry nozzle, you can vary the speed of the fan and use the nozzle to maintain outlet velocity.
27:00 Thank you so much for such a great explanation! I work in controls and could not understand the purpose of the bypass damper when VFD is used. If I understood correctly, we can skip the bypass when variable geometry nozzles are used with VFD
Correct. The bypass damper is used to control static pressure in the ductwork AND maintain outlet velocity. In this scenario the VFD is used only to balance the fan. With a variable geometry nozzle, you can vary the speed of the fan and use the nozzle to maintain outlet velocity.