1/ A retrofit project is estimated to cost $250,000. The energy savings are expected to last 10 years. The retrofit is expected to save 325 MWh per year. Assuming a discount rate of 6%, and an electricity cost of $0.15/kWh:
a/ What is the net-present value of the system (4 marks)?
b/ What is the equivalent cost of the saved energy (4 marks)?
2/ You have a geothermal source of energy where you can access 100 L/s of hot water at 90ºC. If you operate a heat engine that operates at 70% of the maximum theoretical efficiency of a heat engine, how much energy could be produced in 1 year? Assume that the heat engine can use the nearby ocean (8 ºC) as its cold source (4 marks)?
3/ You are operating a fan with the characteristics shown in the figure below. The 5 HP fan currently operates continuously at full speed with the flow reduced to 90% of its rated capacity using downstream dampers. An evaluation reveals that there is inadequate fresh air being introduced into the building during the day, and too much is supplied at night. The flow rate needs to increase to 100% from 7am to 5pm, and can be reduced to 50% at night. What would be the CHANGE in energy cost per year if this change was done using either downstream dampers, or using a 97% efficient VSD (8 marks)?
• ηmot = 0.97 at the nominal speed
• ηmot = 0.95 at 90% of the nominal speed
• ηmot = 0.90 at 50% of the nominal speed
• Electricity costs $0.15/kWh, no impact on demand charges
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