What Is Corona Discharge

The technologies involved in corona discharge (CD) ozone generation are varied, but all operate fundamentally by passing dried, oxygen-containing gas through an electrical field. The electrical current causes the split in the oxygen molecules.

Past this common feature the variations are many, but the generally accepted technologies can be divided into three types - low frequency (50 to 100 Hz), medium frequency (100 to 1,000 Hz) and high frequency (1,000 + Hz). Since 85% to 95% of the electrical energy supplied to a corona discharge ozone generator produces heat, some method for heat removal is required. Also, proper cooling significantly affects the energy efficiency of the ozone generator, so most corona discharge systems utilize one or more of the following cooling methods: Air or water.

At the heart of a corona discharge ozone system is the dielectric. The electrical charge is diffused over this dielectric surface, creating an electrical field, or corona.

Critical to CD ozone systems is proper air preparation. The gas feeding the ozone generator must be very dry (minimum -80 degrees F), because the presence of moisture affects ozone production and leads to the formation of nitric acid. Nitric acid is very corrosive to critical internal parts of a CD ozone generator, which can cause premature failure and will significantly increase the frequency of maintenance.  The chart below shows that relative ozone output decreases as moisture content increases.

Chart shows that relative ozone output decreases as moisture content increases

For this reason, corona discharge machines are not very useful in high humidity environments and cannot be used in food storage and refrigeration environments.

While the corona discharge technology can be low cost, and the ozone it produces is effective on odors, bacteria, mold and some VOCs, there are many disadvantages to this technology, especially for occupied buildings. For instance, it can convert Nitrogen to airborne Nitric Acid and Nitric Oxide, which can act as an lung irritant and results in a pungent "metallic" or "bleach-like" odor and also causes maintenance problems due to corrosion.

See more information about the drawbacks, and how corona discharge compares to other technologies by clicking here.

 

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