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Use condensate water from AHU for cooling tower

Saving and recycle water for cooling tower are very important concern today. Learn ways to save and reuse water for cooling tower

In buildings, percent water consumption for cooling tower ranks second after domestic water. High level projects that related to water consumption classified with modern standards such as LEED, Green Mark, Lotus… with many water criteria for each different item. In particular, saving water for cooling tower and energy has been mentioned very specifically.

In factories, depending on productivity and industry, water consumption for the cooling tower also varies significantl

In general, saving water with 4 ways:

  • Reduce current consumption.
  • Recycle of wastewater.
  • Use rainwater.
  • Collect and treat the condensated water from AHU, FCU for cooling tower.

1. Reduce current water consumption – The simplest saving method for cooling water

– According to very specific requirements, each item as mentioned in LEED, Green Mark standards.

– Reduce amount of blowdown to save water by a reasonable treatment program with a high water cycle. For example, the treatment program with NC-PolyA100, NC-NX100 combined with sand filter for cooling water can reduce the amount of blowdown about 50%. Conversely, if the amount of blowdown is reduced without a good water treatment program, it is easy to cause scale, corrosion and create conditions for algae and biofilm to grow.


Using NC-PolyA100 and NC-NX100 will save blowdown significantly

– Installing automatic blowdown valve, water meter with totalizer for blow down and make up to monitor avoiding over discharge and consumed quantity as well as to ensure stable cooling water quality.

– Ensuring the filling of cooling tower and heat exchanger are clean to reduce high load operation in power and water consumption by installing sand filter and cleaning the tower periodically

– Choose a high quality cooling tower with a low drift rate (<0.002% counter-flow, air from bottom; <0.005% cross-flow, air from side). However, the current cooling tower suppliers have designed with a very low water lost by wind drift.

2. Recycle from Wastewater

Technically, it is possible to recycle wastewater to make up to cooling towers (also other purposes or drinking water). However, the investment and operating costs are high and require a very large area – specical inside cities (Please refer to the article Recycle wastewater for cooling tower for more information).
Recycle waste water for cooling tower, watering golf course and other purposes

3. Make use of rainwater from roof and terrace

– Rainwater at beginning of season contains a lot of dust, E.Coli bacteria in the air and roof, and rain gutter, so need to discharge, not use it until its clean then taking advantage of rain water to save for cooling tower

– May contain some gases such as NO2, CO2, SO2 due to emissions from factories and from available in the air. However, although the concentration is not high, it still leads to a slightly low pH, ranging from 5.0 to 6.0. During thunderstorms or in industrial areas, the pH may be lower.

– Therefore, storage tanks need to be the corrosion-resist materials or raise pH. If stored for a long time, it is necessary to disinfect before supplying to the cooling tower. If used for other purposes, generally these rainwater should be absorbed with activated carbon filter before use.


Please reuse rainwater for domestic use in saline areas at

– Rain water is free water, so taking advantage of rain water is an effective solution to save water making up to cooling tower. However, it is necessary to have a collecting system from the roof (should not use rainwater that has flowed on the ground or concrete because it contains much dirt). Therefore, the design of rainwater collection should be calculated from the beginning of project. To save the most rain water, the large tank the better because the amount of rain cannot be regulated and controlled

– The treatment of rainwater depends on the purpose, for example:

+ For cooling tower: Filter garbage -> Tank -> Adjust pH -> Disinfect -> Filter sand, coal -> cooling tower.

+ Watering plants, cleaning the ground: Filter garbage -> Tank -> Disinfection (if long time strorage) -> Watering plants, cleaning


4. Collecting the condensate water from AHU, FCU to make up to cooling tower

4.1 The characteristics of condensate water from air around AHU, FCU

– Significant amount of water is obtained, depending on humidity, air temperature.

– No mineral.

Contains dust and bacteria from the air.

– Water collected at drain pan of AHU, FCU, air-con is:

+ High Microorganism, virus and algae even biofilm.

+ May contain some metal ions due to corrosion from the heat – cool exchanger (Coil).

Air-cooled heat exchanger and condensate water collecting at AHU

Air-cooled heat exchanger and condensate water collecting at AHU

Quantity of water condensate from the air collected at AHU


Q’ty of condensate collected at AHU according to different capacities
(Calculation conditions: Air entering AHU at 27oC has a dry bulb temperature of 27oC, average humidity RH = 55%)

Thus, if cooling tower used in the air conditioning system, the amount of water collected at AHUs can be used to offset 10-15% of feed quantity to cooling tower, significant saving. Example: 1,000RT cooling tower, condensate water collected will be enough to for 100 – 150 RT tower (If concern, please contact us as this article mainly focuses on condensate treatment).

4.2 Treating the condensate water from AHU to supply cooling tower

– At drain pan, condensate water need to be controlled avoiding bacteria, algae, dust that cause clogging with biocide chemical tablet AHU-FCU-7014

Without and with the use biocide tablets AHU-FCU-7014

– At the storage water tank, it is necessary to disinfect again with NC-NX100, Ozone or UV to ensure no microorganisms.
– Continue to filter with sand filter to remove impurities before supply to cooling tower.

Condensate water treatment process at AHU for cooling tower

Condensate water treatment process at AHU for cooling tower

Above is basic information about 4 methods to save water for cooling towers most effectively, hopefully it will be less or more usefull for your project. Currently, if any questions that need to be answered, please contact us directly – UCE Co., Ltd for quick support.