Best Management Practice #10: Cooling Tower Management

Overview

The guide builds the tower water balance from three items: make-up replaces evaporation, blowdown and drift losses. Basin leaks or overflow add losses that must also be addressed. Measuring make-up alone therefore does not show how much of the water does useful work. A rise on the make-up meter therefore cannot be interpreted until it is split into evaporation, blowdown and leakage.

Cycles of concentration compare dissolved solids in blowdown and make-up water, and can be approximated by the make-up-to-blowdown volume ratio when other losses are negligible. If drift is neglected, make-up equals evaporation plus blowdown, so blowdown = evaporation / (cycles - 1); at 4 cycles, for example, blowdown is one third of evaporation. This derivation is a simple consequence of the relations, not the document's own statement.

The permissible concentration depends on source-water quality and treatment, so the guide does not impose one number. A tower balance is not whole-site WUE: water used in power generation and other uses sits outside it. Water savings are therefore sought in two steps: first the loss items (leaks, overflow) are closed, then the concentration cycle is raised up to the limit the treatment programme allows, which reduces blowdown.

Key points

1. Tower make-up replaces evaporation, blowdown and drift losses.
2. Basin leaks or overflow add losses that must also be addressed.
3. Cycles of concentration compare dissolved solids in blowdown and make-up water.
4. With other losses negligible, cycles can be approximated by the make-up-to-blowdown volume ratio.
5. Permissible concentration depends on source-water quality and treatment.

Using it in design

• Keep evaporation, drift, leaks and blowdown as separate items in the model.
• Set the concentration limit with a water-treatment justification; do not hard-code a default.
• Do not present the tower balance as whole-site WUE.

Who should read it

Mechanical designers and plant operators computing cooling-tower water balance and consumption.

Publication details

Authors

U.S. Department of Energy Federal Energy Management Program (FEMP)

Publisher

U.S. Department of Energy / FEMP

Year

Year not stated

Document number

FEMP BMP 10

Document language

English

Source type

Government / public

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation