Determine the annual energy, water, and cost savings associated with replacing an existing showerhead (having a water flow rate of 2.5 gpm) with a low-flow showerhead (1.6 gpm). An electric water heater is used for domestic hot water heating with an efficiency of 95 percent. The temperature of the showerhead water is 110°F. The inlet water temperature for the heater is 55°F. The showerhead use is 10 minutes per shower, 2 showers per day, and 300 days per year. Assume that the electricity price is $0.07/kWh and that the combined water and waste water cost is $4/1,000 gallons.
Question 15.1: Determine the annual energy, water, and cost savings associa...
The annual savings in water usage due to replacing a showerhead using 2.5 gpm by another using only 1.6 gpm can be estimated as follows:
Δm= 2*[(2.5−1.6)gpm]*10min/day *300days/yr = 5,400gal/yr
The energy savings incurred from the reduction in the hot water usage can be estimated as indicated below:
ΔE = 5,400gal/yr *8.33Btu/gal. °F[(110−55) °F]/0.95 = 2.604 *10^{6}Btu/yr
Therefore, the annual cost savings in energy use and in water use are, respectively:
ΔCost =[(2.604x106Btu/yr)/(3.413Btu/Wh)]*1000W/kW*$0.07/kWh = $53/yr
and
ΔCost = 5,400gal/yr *$4.0/1000gal = $22/yr
Thus, the total annual savings incurred from the water-efficient showerhead are $75. These savings make the investment in water-saving showerheads virtually certain to be cost-effective.
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