Background

There are three fresh water cooled chillers (900TR in total) and two heat pumps (200TR in total) providing chilled water and hot water to a high technology building.

Ordinary chemicals such as biocide, scale and corrosion inhibitor are used in the condensing water. Ozonation was also used to increase the disinfection power. Mineral scale deposit and biofilm were coated on the tubes which required annual tube cleaning to restore the cooling power.

Ozonator demanded high maintenance cost and shut down occasionally due to unavailable ozone element.

In order to improve the energy efficiency of chillers and heat pumps and maintain the disinfection power when ozonator is down, AquaKLEAR is installed. The condenser tubes were inspected and the condition is shown in picture 1 before switching on the AquaKLEAR.

Moreover the ozonation system including the ozonator, air dryer, air compressor, water pump were shut down on the day when AquaKLEAR was switched on.

Result

After one year of operation without pre-cleaning of the condenser, biofilm is not detected and existing scale in most area was dissolved as indicated in picture 2. Sample of the remaining deposit on the tubes was collected and submitted to MRC of Hong Kong Polytechnic University for SEM/EDX analysis.

Result shows a high concentration of silicon in a form of silica scale which cannot be dissolved unless higher concentration of acid is used.

Even though there is some remaining on the tubes surface, the result achieved is encouraging. There is a 9.6% reduction of energy consumption by chillers and heat pumps. The investment is paid back in 20 months.

An additional benefit of the installation is the improved condensing water quality with total bacteria count and Legionella count controlled well below the limit.