Reference no: EM13748087

Economic analysis of small-scale cogeneration. You are considering an investment in three 60-kW micro turbines that generate both electricity and DHW, for a large apartment complex. The micro turbines will displace output from the existing natural gas-fired boiler for DHW such that 100% of the demand is met by the micro turbines. The micro turbines start running at 5 a.m. in order to generate DHW for the morning peak; they then run continuously at full power until they have made enough DHW for the total day’s demand. Thus the cogen system supplies 100% of the DHW need. It can be assumed that when the system turns off for the night, there is enough DHW in storage to last until it comes back on the next morning. The prices of gas and of electricity are $10.75/GJ and $0.105/kWh, respectively. The turbines cost $85,000 each, with an additional $0.02/kWh produced maintenance contract cost; the project life is 20 years with an MARR or 3%. The turbines convert 26% of the incoming energy to electricity, and 55% of the incoming energy to DHW. The existing boiler system transfers 83% of the incoming energy to DHW. Questions: (a) To the nearest whole hour, what time does the system turn off? (b) Determine the net present value and state whether or not the investment is economically viable. (c) If the complex uses 8000 kWh of electricity per day, what percentage of this total demand do the turbines deliver? (d) Suppose that for 5 months of the year (assume 30 days/month), the system can provide heat for space heating with no additional upfront capital cost, and is therefore able to run 24 h/day. How does the answer in part (b) change?