1. A spherical balloon with a diameter of 10 feet is filled with natural gas (1000 Btu/ft3). Determine the total amount of potential energy contained in the balloon.
2. An oil tanker is carrying 20 000 barrels of #2 fuel oil (42 gallons/barrel). Each gallon can generate 550 kWh of electric energy when burned at a power plant. Determine the total kWh generating capacity of the oil in the tanker.
3. A large city has a population which is served by a coal burning utility. There are 500 000 utility customers using an average of 12 000 kWh per year. The utility transfers energy at 10 500 Btu/kWh. The coal lower heating value is 12 400 Btu/lb. Determine the number of tons of coal the utility requires each year to satisfy customer demand.
4. A factory outlying building has a 25 kW company-owned transformer that is continuously in-service. Core losses from typical similar equipment is 3% of rated capacity. Electrical costs are $0.10 per kWh and demand is $10/kW per month. The building is used 10 hours per (720 hr) month. Estimate annual cost reduction due to installing a switch that would energize the transformer only when the building is in use.
5. A company is considering an energy management investment which will save 2500 kWh/yr at $0.08/kWh. Maintenance cost is $50/yr. Determine the cost/benefit ratio.
6. Estimates of coal resources predict a 500 year supply remains. How long would that supply last if usage increase by 7% each year?
7. An old train station has been converted to a community college center. Currently, there are 82 75-Watt incandescent lamps turned on 12 hours per day that illuminate the outside of the station.. Recommend a replacement scheme that provides equivalent lighting. Specify type of light and fixture.
8. Estimate a daily building heating load in an office building housing 22 people for 8 hours/day.
9. Determine the tons of chilling capacity. The chiller has exit water at 44 oF and return water at 53 oF at 6000 gallons per minute.
10. Estimate the yearly cost of steam leaks from a 600-psi boiler system. There are 50 leaks at 25 lb/hr, 10 leaks at 100 lb/hr and 2 leaks at 750 lb/hr. Coal costs $65/ton. Its useful energy capacity is 14500 Btu/lb.
11. How many maintenance people could you hire to equal losses due to people leaving because work areas are uncomfortable and machinery breaks down? Last year 6 people left at $10000 training per person. A 3-week shutdown at $30000 could have been reduce to one week if preventive maintenance had occurred. Each maintenance person costs $25000 (salary) + $15000 (overhead) per year.
12. A mild steel tank is 4-feet in diameter and 6-feet long. It holds water at 180 oF. All surface area is exposed to ambient at 80 oF. Determine the heat lost to the local atmosphere and cost per year. The convective coefficient is 2.17 Btu/ft2-hr-oF. The water is heated with natural gas at $5 per 106 Btu.
13. Which incentive should plant management choose? 1) $6/hp for the size of the motor or 2) $150/kW saved by replacing a motor. The motor under consideration is 100-hp at 91% efficiency. A new motor would operate at 95% efficiency.
14. A furniture plant develops 10 tons of sawdust per day (6000 Btu/ton). The dust is hauled to a landfill for $10/ton. Alternately the sawdust could be burned in a boiler presently using natural gas at $5/106 Btu. However, sawdust handling equipment and storage would cost $3/ton and delivery equipment maintenance would cost $10000/yr. A sawdust boiler would only be 70% as efficient as a natural gas burning boiler. Are there any cost savings available due to implementing the sawdust boiler idea?
