Skip to content
gigabiome
Try Plant Check

Free calculator

Cycles of concentration savings calculator

Raising cycles of concentration is the biggest lever on a cooling tower's water use. The same evaporation needs less makeup and much less blowdown. This calculator shows by how much, in gallons and, if you add your water and sewer rate, in dollars.

Formula
Makeup = E × C ÷ (C − 1), at C now and C target
Last reviewed
2026-09-29

Inputs

Example values are pre-filled so you can see the result. Replace them with your plant's.

Many towers run 2–4; 6 or more is often possible (FEMP)

Results

Example values
Water saved per year
459,000 gal
Makeup reduction
20.0%
make-up, gal/yr02M4M246810cycles of concentrationnowtarget
now · 3×
2,295,000 gal/yr
target · 6×
1,836,000 gal/yr
saved
459,000 gal/yr
Makeup per year, now
2,295,000 gal
Makeup per year, at target
1,836,000 gal
Blowdown reduction
60.0%
Show the math
  1. Q = tons × gpm per ton= 500 × 3 = 1,500 gpm
  2. E per year = 0.00085 × Q × R × 60 min × hours= 0.00085 × 1,500 × 10 × 60 × 2,000 = 1,530,000 gal
  3. Makeup now = E × C now ÷ (C now − 1)= 1,530,000 × 3 ÷ (3 − 1) = 2,295,000 gal
  4. Makeup at target = E × C target ÷ (C target − 1)= 1,530,000 × 6 ÷ (6 − 1) = 1,836,000 gal
  5. Saved = makeup now − makeup at target= 2,295,000 − 1,836,000 = 459,000 gal
  6. Makeup reduction = saved ÷ makeup now= 459,000 ÷ 2,295,000 = 20%
  7. Blowdown = E ÷ (C − 1), now and at target= 1,530,000 ÷ (3 − 1) = 765,000 gal; 1,530,000 ÷ (6 − 1) = 306,000 gal

Higher cycles concentrate minerals. How high you can go depends on makeup chemistry and scale control, which is a treatment decision, not a calculator's.

How it's calculated

Evaporation is fixed by the heat the tower rejects, so it stays the same when cycles change. Makeup = E × C / (C − 1) and blowdown = E / (C − 1) both fall as C rises. Going from 3 to 6 cycles cuts makeup by 20% and blowdown by 60% by this arithmetic; FEMP describes the same change as roughly 20% and 50%.

The limit is chemistry. Higher cycles concentrate calcium, silica and other minerals, raising the risk of scale on condenser tubes. Scale insulates the tubes, raises condenser approach and costs chiller energy, so the right target balances water saved against energy risked.

Questions

How much water do you save going from 3 to 6 cycles?

Makeup falls by 20% and blowdown by 60% for the same evaporation. FEMP rounds the blowdown figure to about 50%.

What cycles of concentration is typical?

FEMP notes that many systems operate at two to four cycles, while six cycles or more may be possible depending on makeup water quality and treatment.

What limits cycles of concentration?

Makeup water chemistry. As cycles rise, dissolved minerals concentrate until scale or corrosion risk sets the ceiling, which depends on the water and the treatment program.