4-44
October 2012
4.9
Food Disposals
Equation 4-19. Water Savings From Garbage Disposal Retrofit (gallons per year)
= Current Water Use of Garbage Disposal During Idle Periods –Water Use
of Garbage Disposal During Idle Periods After Retrofit
Where:
••
Current Water Use of Garbage Disposal During Idle Periods (gallons
per year)
••
Water Use of Garbage Disposal During Idle Periods After Retrofit (gal-
lons per year)
Payback
To calculate the simple payback from the water savings associated with retrofitting
an existing conventional garbage disposal with a load sensor, consider the equip-
ment and installation cost of the retrofit load sensor, the water savings as calculated
in Equation 4-19, and the facility-specific cost of water and wastewater.
Because garbage disposals may use hot water, a reduction in water use could also
result in energy savings. Reducing the use time of the garbage disposal can also save
energy. The potential energy savings may further reduce the payback period and
increase the cost-effectiveness.
Conventional Garbage Disposal Replacement—Food Pulper
Conventional garbage disposals can be replaced with a food pulper. A food pulper
can recycle and reuse 75 percent of the water used for the food disposal process,
thus reducing the flow rate of fresh water required to run through the garbage dis-
posal unit.
Current Water Use
To estimate the current water use of an existing garbage disposal, identify the follow-
ing information and use Equation 4-20:
••
Flow rate of water through the garbage disposal. This flow rate typically ranges
from 2.0 to 15.0 gpm.
••
Average daily use time of the garbage disposal.
••
Days of facility operation per year.
