It is proposed to retrofit the supply fan of a 60,000-cfm AHU. The fan has a 25-hp motor with a total efficiency of 85.5 percent. If the fan is operating 5,500 hours per year and if the cost of electricity is $0.08/kWh, determine the simple payback period when the constant-volume fan is retrofitted to:

a. A temperature measurement indicated that when the outdoor air is at 50°F, the mixed air is at 70°F and the return air is at 75°F. Determine the heating fuel savings by reducing the outdoor air to the minimum ventilation requirements (i.e., 20 cfm/person). Outdoor air is provided only during the occupied period.

b. Determine the heating energy and cost savings due to a temperate setback to 60°F during the unoccupied period.

c. If the system is converted into a VAV system, determine the energy and cost savings due to the fan. The average load on the fan is 60 percent of the peak load.