Estimate the annual cost savings incurred by replacing an existing clothes washer (having 2.65 ft^3 tub volume) with a water/energy-efficient appliance that has an energy factor of 2.50 ft^3/kWh and uses 42 gallons per load.

Question

Estimate the annual cost savings incurred by replacing an existing clothes washer (having 2.65 [latex]ft^{3}[/latex] tub volume) with a water/energy-efficient appliance that has an energy factor of 2.50 [latex]ft^{3}[/latex]/kWh and uses 42 gallons per load. The washer is operated based on 400 cycles (loads) per year. The water is heated using an electric heater. Assume that the electricity cost is $0.07/kWh and that water/sewer cost is $5/1000 gallons.

Accepted Answer

Using the information provided in Table 15.3, the water savings due to using efficient clothes washer is 13.0 gallons per load. Based on 400 loads per year, the annual water savings are 5,200 gallons which amounts to cost savings of $26.
The annual electrical energy savings per load can be calculated using the energy factors as indicated in Table 15.3:

[latex]ΔE = 2.65 f^{3}t/load*[(1/1.18-1/2.50)k Wh/ft^{3}]*400.loads/yr=474.3k Wh/yr[/latex]

Thus the annual electrical energy cost savings are $33.
Therefore, the total annual cost savings achieved by using an energy/water-efficient clothes washer are $59. The cost-effectiveness of the efficient clothes washer depends on the cost differential in purchasing price (between the efficient and the conventional clothes washer models). For nstance, if the cost differential is $200, the payback period for using an efficient clothes washer can be estimated to be:

[latex]Payback=\frac {\$200}{\$59}=3.4 years[/latex]

In this case, the use of water/energy-saving clothes washer is cost-effective.

TABLE 15.3 Water and Energy Efficiencies of Residential Dishwashers and Clothes Washers

Clothes Washers	Dishwashers	Performance
Older models:
55.0	14.0	Water use (gal/cycle)
1.18	0.46	Energy factor a
Energy Star models:
7.5	6.5	Water use (gal/cycle)
1.8	0.46	Energy factor a

a The energy factor is a measure of the energy efficiency of the appliance. For dishwashers, the energy factor is the number of full wash cycles per kWh. For clothes washers it is the volume of clothes washed (in [latex]ft^{3}[/latex] ) per kWh per cycle. The water use for Energy Star clothes washers is expressed in gallons used per [latex]ft^{3}[/latex] of volume of clothes washed per cycle.

Question 15.2: Estimate the annual cost savings incurred by replacing an ex...

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