Ozone Generator Cooling

Ozone generators must be cooled. This includes both the power supply unit (PSU) as well as the ozone generator vessel. The PSU and controls may be cooled by standard Cabinet fans or have air conditioned air forced into the cabinets. The rated output of an ozone generator is tied to the ambient air temperature for air cooled generators and the inlet water temperature for water cooled generators. A specific drop in ozone generator output is usually given per degree increase in temperature.

Small ozone generators typically use air cooling for the generating vessel. Larger ozone generators almost always use water cooling. Air cooling helps reduce the cost of the ozone generator, but also makes production dependent on the ambient conditions of the ozone generator. In some cases, air cooled ozone generators must be must be operated in air conditioned rooms or air conditioned enclosures. Air cooled systems rarely are used for more than ten pounds per day of production.

Water cooling adds capital expense, but improves control over the temperature of the ozone generator. In large systems, water is the only effective way to move the amount of heat generated. Three types of water cooing systems are used: once through systems, indirect/once through systems and closed loop systems with chillers. The availability of good quality water and the temperature of the water are factors in selecting the cooling water source.

The delta T across the ozone generator is usually specified from 5 – 10 degrees F. The flow of cooling water for the ozone generating vessel can be between 0.6 and 1.2 gpm/kW of applied power. Additional water may be used to cool the PSU in very large systems. These figures are dependent on the cooling water temperature. Spartan specifies a cooling water with an inlet temperature of 50 degrees F and an outlet temperature of 59 degrees F.

The quality of the cooling water in important to prevent scaling of the heat exchange surfaces and/or corrosion of the generator. For the most part, ozone generators are made from stainless steel. Elevated chloride levels in the water above 50 ppm can result in corrosion. As with any heat exchanger, scale can form on the heat exchange surface and reduce the effectiveness of the generator’s cooling. With respect to biological fouling, some of the ozone generated can be used to maintain micro biological control. Thermal scaling can be prevented with chemical additions.

Once through systems can use treated water for cooling. In certain regions of the world, the water can be quite warm. The higher the temperature of the cooling water, the less efficient the production of ozone. At maximum output an increase in the inlet temperature of the cooling water from 59 degrees F to 77 degrees F can reduce generator output by 15%. This can be compensated for by using a larger ozone generator than would be needed with lower temperature cooling water. In some cases, this may be more economical than using a chiller system:

• A once through system is substantially less expensive than a chilled water system
• A chiller system adds to maintenance costs
• A chiller system requires additional energy, off setting energy saved in ozone generation with the once through system

The once through indirect cooling system employs a plate and frame heat exchanger between the ozone generator and the open loop cooling water source. This protects the ozone generator from water quality issues while maintaining an economical cooling system.