8 An elevator company has redesigned their product to be 50% more energy efficient than hydraulic designs. Two designs are being considered for implementation in a new building. Given an interest rate of 10% which bid should be accepted? Alternatives Installed cost 45,000 Annual cost Salvage value ufe, in years Solution 1. Two alternatives have different useful lifes, the analysis period should take na 2700 3000 10 54,000 2850 4500 15 2. PW of Cost of 30 years of alternatives A should be replaced by times in n years, PWCA $ B should be replaced by times in n years, PWC- 3. Thus alternative is selected