# Page 231 - WaterSense at Work

October 2012
7-13
7.3
Vacuum Pumps
Current Water Use
To estimate the current water use of an existing vacuum pump, identify the following
and use Equation 7-1:
••
Flow rate of the discharged water from the existing vacuum pump.
••
Average daily use time.
••
Days of operation per year.
Equation 7-1. Water Use of Vacuum Pump (gallons per year)
= Vacuum Pump Discharge Flow Rate x Daily Use Time x Days of
Operation
Where:
••
Vacuum Pump Discharge Flow Rate (gallons per minute)
••
Daily Use Time (minutes per day)
••
Days of Operation (days per year)
Water Savings
Full water recovery and recirculation systems can reduce water use by approximately
80
percent,
21
while partial systems can reduce water use by approximately 50 per-
cent.
22
To calculate the water savings that can be achieved from retrofitting an exist-
ing vacuum pump, identify the current water use of the vacuum pump as calculated
­
using Equation 7-1 and use Equation 7-2, using 80 percent savings for a full system
and 50 percent for a partial system.
Equation 7-2. Water Savings FromVacuum Pump Recovery and Recirculation
System Retrofit (gallons per year)
= Current Water Use of Vacuum Pump x Savings (0.80 or 0.50)
Where:
••
Current Water Use of Vacuum Pump (gallons per year)
••
Savings (percent)
Payback
To calculate the simple payback from the water savings associated with retrofitting
an existing vacuum pump, consider the equipment and installation cost of the retro-
fit recovery and recirculation system, the water savings as calculated using Equation
7-2,
and the facility-specific cost of water and wastewater.
21
Ibid
.
Page 5.
22
Estimate based on manufacturer literature.