A welding process fresh-air vent system in a non-heated/non-air-conditioned plant consists of ten vent drops (one at each of ten welding stations). The vent system consists of a large metal duct system with one large fan. The fan system requires one 200 HP 3-phase induction motor at the fan drive shaft. The system was originally designed for a single speed, with on/off switching only.
On the first 8-hour shift from 7 AM until 3 PM all of the welding stations are working. On the second shift 50% of the stations are working. And on the third shift only three stations are working. This is a five-days-per-week, 52 weeks-per-year plant, where the welding vent system is shut down on the weekends. The vent system, at the present time, is either on or off. The vent system is currently operational for all three shifts.
A possible energy savings project involves installing a VFD to drop the cfm of the system by 50% on the second shift and by 75% on the third shift. The proposed cfm reductions assume that unused drops will be automatically blocked off so that the vents will pull out the welding fumes in an effective manner.
The cost of electricity is $0.06 per kWh at all times. Demand cost is $9 per kW from May 1 through September 30, between 12 noon and 7 PM; and $3 per kW otherwise. Determine the theoretical annual utility-related savings possible from this project.
Problem #2 -- Compressed Air (25 points). An aerospace components plant currently has one air compressor serving the titanium line. It is a 150 HP 3-phase Atlas Copco unit that does not have a VFD. The unit is operated for two 8-hour shifts from Monday through Friday, for 52 weeks per year. The outlet pressure from the compressor is currently 110 psi. The plant engineer tells you that the maintenance department quickly repairs air leaks and in fact has an ultrasonic leak detector. He admits that the outlet pressure could be reduced to 100 psi, all year without causing problems. He asks you to calculate the annual energy and cost savings from a reduction to 100 psi. You have data-logged the compressor for five days and have determined that the unit operates 60% of all work hours but is manually shut down on weekends and at the close of the second shift. The plant is on a flat rate of $0.07 per kWh and $12 per kW demand, all year.
Problem #3 -- Insulation (25 points). The end cap of a boiler in a hydronic space heating system is 6 feet in diameter, made of 1.5 inch thick mild steel plate. There currently is no insulation at all. This fire-tube boiler provides 200 degree F hot water to a fan coil system. The boiler room temperature averages 80°F during the heating season. The boiler is operated 2,880 hours per year. Natural gas for the boiler costs $5 per MMBtu. The boiler is running at 80% overall efficiency.
If we insulate the end cap with two inches of mineral wool fiber, how much could we afford to pay for the insulation material, supplies, and labor (the entire installation) to yield a simple payback of 0.25 years?