Average daily idle period of the steam sterilizer. Note that some older models
have tempering water that flows constantly, even if the unit is turned off and
not in idle mode. In this case, the average daily use of 24 hours should be used
instead of the daily idle period to calculate daily water use.
Days of sterilizer operation per year. If the tempering water is flowing constantly,
even when the sterilizer is not in use and the facility is closed, 365 days per year
should be used.
Equation 7-4. Steam Sterilizer TemperingWater Use (gallons per year)
= TemperingWater Flow Rate x Daily Idle Period x Days of Operation
Tempering Water Flow Rate (gallons per minute)
Daily Idle Period (minutes per day)
Days of Operation (days of sterilizer operation per year)
A study conducted at the University of Washington showed that a tempering water
retrofit or installing new equipment that addresses tempering water can reduce
tempering water use by up to 90 percent, depending upon how long the sterilizer is
in idle mode.
To calculate the tempering water savings that can be achieved from
retrofitting or replacing an existing steam sterilizer, identify the current water use of
the equipment, as calculated using Equation 7-4, and use Equation 7-5.
Equation 7-5. Water Savings From Steam Sterilizer TemperingWater Retrofit or
Replacement (gallons per year)
= Current Steam Sterilizer TemperingWater Use x Savings (0.9)
Current Steam Sterilizer Tempering Water Use (gallons per year)
To calculate the simple payback from the water savings associated with the temper-
ing water retrofit or replacement, consider the equipment and installation cost of the
retrofit or replacement, the water savings as calculated using Equation 7-5, and the
van Gelder, Roger E. and Leaden, John. University of Washington. 2003.
Field Evaluation of Three Models of Water Conservation Kits for Sterilizer Trap Cooling at
University of Washington