7-14
October 2012
The facility should also consider the energy impact of the vacuum pump retrofit. The
recovery systems might use energy, which can affect the payback period and cost-
effectiveness.
Vacuum Pump Replacement
Existing liquid-ring vacuum pumps can be replaced with dry vacuum pumps that are
air-cooled rather than water-cooled. This replacement entirely eliminates the water
used to create a vacuum, as well as the water used to cool the vacuum pump.
Current Water Use
To estimate the current water use of an existing vacuum pump, use Equation 7-1.
Water Savings
Because air-cooled, dry vacuum pumps consume no water to create a vacuum, water
savings will be equal to the current water use. To calculate the water savings that can
be achieved from replacing an existing vacuum pump, identify the current water use
of the vacuum pump as calculated using Equation 7-1 and use Equation 7-3.
Equation 7-3. Water Savings FromVacuum Pump Replacement (gallons per year)
= Current Water Use of Vacuum Pump
Where:
••
Current Water Use of Vacuum Pump (gallons per year)
Payback
To calculate the simple payback from the water savings associated with replacing an
existing liquid-ring vacuum pump with an air-cooled, dry vacuum pump, consider
the equipment and installation cost, the water savings as calculated using Equation
7-3,
and the facility-specific cost of water and wastewater.
By replacing a water-cooled or liquid-ring vacuum pump with an air-cooled, dry
pump, facilities should also consider the potential increase or decrease in energy use.
Some dry vacuum pumps can save energy over the existing water-cooled or liquid-
ring pump. The energy use will also affect the payback time and replacement cost-
effectiveness.
7.3
Vacuum Pumps
