Cooling Water for Hybrid System

Case Study

Water Treatment for New Generation Hybrid Coolers

Location:  Various Locations
Capacity:  24-3200 m³/day

  • The Need

    Many new installations where a high degree of cooling is required are now fitted with a system that allows the use of water for adiabatic cooling.

    Heat rejection is achieved by two principle modes of operation namely:

    • Dry cooling mode
    • Hybrid mode 

    In hybrid mode cooling water is used to achieve both convective and latent heat rejection. Hybrid condensers have been selected to reduce water consumption, limited the use of water treatment chemicals, remove aerosol/vapour plumes, provide high efficiency operation and give low noise levels in operation.

    Although such units may run on air cooling for the majority of the year it is essential that when water is used as part of the cooling cycle that proper precautions are implemented.

  • The Solution

    If any standing water is present when they are brought into service then they must treated in line with the main recommendations of the HSC Approved Code of Practice and Guidance L8.

    Theoretically there should be no standing water in such designs apart from that in the stored water system for start-up as all water sprayed into the system will be evaporated to dryness.

    Also, theoretically there should be no aerosols produced that can enter the air stream but in practice this cannot be proven.

    In practice some standing water is unavoidable and as such the water needs to be of the correct quality all of the time.

    This includes recognising the following:

    • Using a feed water that does not attack the materials of construction (in this case epoxy coated aluminium and galvanised zinc) and operates within a pH band of 6.5 to 8.0.
    • Ensuring that when evaporated to dryness no residual deposit is left on any contact surfaces. 
    • That the water has to be free of any bacteria that may be harmful to health.

    In order to achieve this, the following needs to be implemented as part of any scheme and Risk Assessment:

    • Use RO water as the main feed water source. This will normally have to have some form of stored water tank and make up pump. Softened water will attack both exposed aluminium and zinc contact surfaces. Hard water that is allowed to evaporate to dryness will lead to a hard deposit on all contact surfaces.
    • Carry out Legionella test four times per year on any standing or recirculation water.
    • Carry out two disinfections per year, preferably with Hydrogen Peroxide as Sodium Hypochlorite at 5-7ppm will attack contact surfaces.
    • Install a recirculation pump with automatic UV disinfection and periodic Hydrogen Peroxide dosing. In some instances include for an inline fine filter, but be conscious of the fact that this may require regular swap outs.
    • Have an automatic system water dump valve that allows water to be periodically dumped from the system to avoid the build-up of any debris/contaminants.
  • The Benefits

    Kirton Engineering can provide such water treatment systems that are complaint with both L8 and the upcoming HSG 274 as well as any relevant Health Building notes etc.

    Such systems currently in use normally have the following elements: Softener/antiscalant, RO, Stored recirculated UV disinfected RO water, In -line dosing and a suitable bleed system.


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