An evaporative condenser is a heat exchanger for condensing natural refrigerant gas, such as ammonia, or refrigerants of the freon family using the natural principle of evaporative cooling.

By taking advantage of the latent heat of evaporation of water, this principle allows heat to be subtracted from the refrigerant gas inside the heat exchanger and a small portion of the water sprayed onto the coil to evaporate.

Heat removal in the evaporative condenser is then accomplished by spraying water on the coil heat exchanger. The spraying of water takes place against a flow of fresh air, just as in the case of cooling towers at closed-circuit. Unlike the latter, however, it is refrigerant gas and not water that circulates within the heat exchange coils.

One of the benchmarks for selecting equipment remains the ambient wet bulb temperature, which is that temperature determined using the psychrometric diagram from the ambient temperature and relative humidity. Since the wet-bulb temperature is generally lower than the ambient temperature by about 4~6°C (or even higher values), we can say that an evaporative condenser allows the refrigerant gas to condense at a temperature about 7-9°C higher than the wet-bulb (BU).

How an evaporative condenser works

As previously mentioned, evaporative condensers are cooling systems that use the principle of evaporative cooling to cool a refrigerant gas by matching water with air.

Just as in cooling towers at closed-circuit, in the case of evaporative condensers the gas remains inside the coils isolated from the external environment; thus, two separate circuits are generated:

The primary circuit, where refrigerant gas circulates within the heat exchange coil;

The secondary circuit, where water contained in the collection tank located below the heat exchange coil is pumped above the heat exchange coil.

That said, here is how an evaporative condenser works

• The evaporative condenser receives from the utility a mass of high-temperature refrigerant gas-suppose ammonia that needs to be cooled;
• Ammonia begins to circulate within the heat exchange coil; at the same time, circulation of the secondary circuit is maintained in the unit;
• Water extracted from the tower collection tank is distributed through spray nozzles evenly into the exchange section above the coils, while air is blown or drawn in by fans;
• The airflow combined with the spraying of water from the secondary circuit onto the coil maximizes the effect of evaporative cooling, which, by subtracting heat from the heat exchange coil, allows the refrigerant gas to condense.