CALCULATIONS FOR ENERGY SAVINGS FROM REDUCED WATER CONSUMPTION

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					CALCULATIONS FOR ENERGY SAVINGS FROM REDUCED WATER
                                  CONSUMPTION
 (Based on savings from installing low-flow showerheads, faucet aerators, etc.)


    Assumptions and Constants –
        o Calculate the total amount of water saved per year by installing water-saving
          devices on fixtures using hot water (showers, lavatories, dishwashers, etc.)
        o Calculate how much of this saving is actually hot water (assume 50% unless there
          is a reason to assume otherwise)
        o One therm = 100,000 Btu
        o Cost of natural gas = $1.12/therm
        o Water weighs = 8.34 lb/gal
        o Cost of electricity = $0.11/kWh
        o To increase the temperature of 1 lb of water 1° F requires 1 Btu
        o There are 3412 BTU per kWh
        o Assume a temperature rise (Δt) of 80° (temperature of hot water from water heater
          minus temperature of incoming cold water)

    Procedure
        o Determine the number of gallons of hot water saved by converting to low-flow
          showerheads, faucet aerators, or other water-saving device, assuming that 50% of
          water saved is hot water.
        o Convert the amount of hot water saved to pounds
                 Gallons of hot water saved × 8.34 lb/gal = pounds of hot water saved
        o Calculate the energy required to heat this amount of water
                 Pounds of hot water saved × 80º temperature rise = total Btu
        o Convert the total energy (Btu) to therms or kWh
                 Total Btu ÷ 100,000 = number of therms saved
                 Total Btu ÷ 3412 = number of kWh saved
        o Use a Heating Source Efficiency Multiplier
                 Natural gas heating at 80% efficiency. Multiply total energy by 1.25
        o Calculate the dollar savings
                 For gas water heaters – Total number of therms × $1.50 = dollar savings/yr
                 For electric heaters – Total number of kWh × $0.11 = dollar savings/year




        Waste Reduction Partners: Assessor Reference Materials, March 2006
        Rev. 4/2008