A 50-hp constant-volume fan is to be retrofitted to a variable-volume fan. Three options are considered:

The fan is operated 5,500 hours per year. If the cost of electricity is $0.08/kWh and the discount rate is 6 percent, determine for the following load profiles the best option for retrofitting the fan.
Use both a simple payback analysis and life-cycle cost (LCC) analysis (assume a 15-year life cycle). For the performance of various fan control strategies, you can use and interpolate the values given in Table 7.5. Typically, at a 20 percent load, the fan uses 59 percent of power for outlet dampers and 41 percent of power for inlet vanes. Conclude. 7.2 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

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Option A: Install outlet dampers at a cost of $3,100. Option B: Use inlet vanes fan at a cost of $6,950. Option C: Use VSD at a cost of $8,500. Percent Load 100 90 80 70 60 50 40 30 20 Percent of Occurrence Load Profile 1 5 5 10 15 25 20 10 5 5 Percent of Occurrence Load Profile 2 20 30 25 20 5 0 0 0