For this plant, the cost of electricity is $0.10 /kWh including
demand and the power plant emits 2.0 lb CO2/kWh. Compressed air to
the plant is supplied by a 75-hp air-cooled rotory-screw compressor
with a 93% efficiency motor that generates 4 scfm/hp. The
compressor runs in load/unload mode and draws 60% of full load
power when unloaded. The plant and compressor run 5,000 hr/yr. The
estimated lifetime of each savings opportunity is 7 years.

1) In addition to the 75-hp compressor, the company also owns a
50-hp reciprocating compressor that meets variable loads by turning
on and off. The efficiency of the 50-hp motor is 93%. Could the
50-hp reciprocating compressor supply the same amount of air to the
plant? If so, calculate the annual cost savings from operating the
50-hp recip instead of the 75-hp rotary-screw. The initial cost of
operating the 50-hp recip instead of the 75-hp rotary-screw is $0.
Calculate the annual cost savings ($/yr), annual CO₂
savings (lbCO₂ per year), simple payback (yrs), and
return on investment (%) from operating the 50-hp recip instead of
the 75-hp rotary-screw.