ENG06
Adiabatic cooling retrofit for
air-cooled chillers
Your chiller plant will be some of your highest energy consuming assets, this ECM can make a significant reduction to the energy they consume.
The benefits of adiabatic cooling have been used every since the first air-cooled chillers were introduced back in the 1920's, when chiller operators found that when their chiller was struggling to cope, by spraying the chiller with a garden hose greater cooling capacity could be achieved. To this day maintenance technicians still use this method at times of duress to support short term chiller overloads. The reason that spraying the chiller with a hose and adiabatic cooling retrofits both work can be traced directly from engineering first principles.
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How does it work?
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The principle is very simple – water is sprayed in the form of a fine mist into the incoming air stream. The water increases the relative humidity of the air, causing heat to transfer from the hot, ambient air by way of evaporation. This reduces the temperature of the air moving across the chillers coils. This cooler air enables more effective heat transfer from the chiller coils into the discharge air stream leaving the chiller.
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Special screens are fitted in front of the condenser coils which are designed to minimize the pressure drop of the incoming air stream. The screens are non-metallic to avoid ill effects of water. Spray jets are positioned in front of the screens which are sprayed with a measured amount of water in the form of a mist. The control for the spray jets is typically digital, with volume of water water being sprayed and at what frequency being controlled by the system.
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When the ambient temperature exceeds set values, the spray system engages and water is sprayed onto the screens. The air stream temperature is monitored on a continuous basis and is used as a feedback for the jet spray flow and timing. Treated soft water is used to avoid clogging of the jet nozzles. Some form of water treatment is typically employed to avoid any biological growth in the water and prevent Legionella related risks.
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Factors defining feasibility
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While every manufacturer of adiabatic cooling retrofits products are slightly different so general factors which define suitability appear constant.
Ambient humidity - in more tropical environments where ambient humidity is greater than say 70% you can expect these adiabatic retrofits to be less effective. The high water loading of the air stream is the factor at play here. Some systems will automatically shutdown at a defined humidity level, meaning that if you have a variable humidity level through the day this may still be an attractive option.
Ambient temperature - low temperatures can be a concern, at the colder end of the spectrum no benefit is derived from the adiabatic cooling when the air temperature is low.
Chiller size - with the engineering that goes into these systems the smallest chiller systems may struggle to achieve a reasonable payback for these systems.
Run hours - for exactly the same reason as for the chiller size, systems which only run for a few hours per day are unlikely to achieve a reasonable return on investment.
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Many of the adiabatic retrofit manufacturers will have a database of cities around the world with temperature and humidity levels which would make the system unappealing, rather than dismissing it yourself you would be encouraged to get in contact with them and discuss feasibility.