A 50,000-cfm CV air-handling unit is to be converted to a VAV system. The motor for the existing supply fan is rated at 35 hp with 90 percent efficiency. The fan is operated for 3,500 hours/year according to the following load profile:
100 percent l • oad, 10 percent of the time
• 80 percent load, 40 percent of the time
• 60 perent load, 40 percent of the time
• 40 percent load, 10 percent of the time
Three options for variable air volume controls have been considered:
(a) Outlet dampers at a cost of $,3,500
(b) Variable inlet vanes at a cost of $8,000
(c) Variable speed drive at a cost of 9,000
Determine the best option for the fan control using simple payback period analysis. Assume that electricity costs $0.05/kWh.
