Suppose the lighting system in a building draws 20 A and the lamps are, on the average, 100 ft from the electrical panel. Table 1.3 suggests that 12 ga wire meets code, but you want to consider the financial merits of wiring the circuit with bigger 10 ga wire. Suppose the lights are on 2500 hours per year and electricity costs $0.10 per kWh.

a. Find the energy savings per year (kWhr/yr) that would result from using 10 ga instead of 12 ga wire.

b. Suppose 12 ga wire costs $25 per 100 ft of “Romex” (2 conductors, each 100-ft long, plus a ground wire in a tough insulating sheath) and 10 ga costs $35 per 100 ft. What would be the “simple payback” period (simple payback = extra 1st cost/annual $ savings) when utility electricity costs $0.10/kWh?

c. An effective way to evaluate energy efficiency projects is by calculating the annual cost associated with conservation and dividing it by the annual energy saved. This is the cost of conserved energy (CCE) and is described more carefully in Section 5.4. CCE is defined as follows

where ∆P is the extra cost of the conservation feature (heavier duty wire in this case), and CRF is the capital recovery factor (which means your annual loan payment on $1 borrowed for n years at interest rate i.

What would be the “cost of conserved energy” CCE (cents/kWhr) if the building (and wiring) is being paid for with a 7-%, 20-yr loan with CRF = 0.0944/yr. How does that compare with the cost of electricity that you don’t have to purchase from the utility at 10¢ /kWhr?