Boiler and Steam Systems
often expressed in terms of cycles of concentration, which is the inverse of the blow-
Equation 6-6. Boiler or Steam System Blowdown Percentage (percent)
= Conductivity of Make-UpWater ÷ Conductivity of Blowdown
Conductivity of Make-UpWater (milligrams per liter of TDS)
Conductivity of Blowdown (milligrams per liter of TDS)
Controlling the blowdown percentage and maximizing the cycles of concentration
will reduce make-up water use; however, this can only be done within the constraints
of the make-up and boiler water chemistry. As the TDS concentration in the blow-
down water increases, scaling and corrosion problems can occur, unless carefully
The amount of make-up water required is a key driver of the overall water use of the
boiler. Make-up water quantity is dictated by the amount of water that is lost from
the system, particularly steam condensate that is discharged and not returned to the
boiler, and the amount of blow down, as illustrated in Equation 6-7.
Equation 6-7. Boiler or Steam SystemMake-UpWater (gallons)
= Condensate Loss + Blowdown
Condensate Loss (gallons)
By recovering steam condensate and carefully controlling the amount and frequency
of blowdown, boiler water and energy use can be significantly reduced.
Operation, Maintenance, and User Education
There are a number of ways to improve water efficiency of boiler and steam systems
by changing operation, maintenance, and user education techniques. Best manage-
ment practices include: maintaining boilers, steam lines, and steam traps; choosing a
water treatment vendor that focuses on water efficiency; reading meters and water
chemistry reports to closely monitor water use; minimizing blowdown; and improv-
ing make-up water quality to increase cycles of concentration.
North Carolina Department of Environment and Natural Resources, et al. May 2009.
Water Efficiency Manual for Commercial, Industrial and Institutional Facilities