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Floating Condensing Pressure without Expensive PLC

 

During summer operation, to maximize energy efficiency of your refrigeration plant, condensing pressure should be floated based on the fluctuation of wet bulb temperature of ambient air. Usually, to achieve this floating a refrigeration plant should be controlled by PLC with a wet bulb approach feature. These PLCs are typically very expensive. Is it possible to float condensing pressure without expensive PLC? Yes, it can be done.

Sophisticated PLC controls wet bulb approach between condensing temperature and wet bulb temperature of ambient air. If the approach is correct, total energy use (compressors + condensers) will be minimal. This means that capacities of compressors and condensers are balanced. These capacities can be balanced without expensive PLC. Someone should determine the balance and your existing PLC can be reprogrammed to keep this balance.

For example, a refrigeration plant has 2 condensers of equal capacity and 4 compressors of equal capacity. Assume that someone determined that the refrigeration plant is balanced when it operates at 100% capacity (2 condensers and 4 compressors). If required refrigeration capacity is 50%, 1 condenser and 2 compressors should be operated and condensing pressure will float at optimum level. If required refrigeration capacity is 75%, 3 compressors should be operated as well as 1.5 condensers. This means that one condenser should be operated at 100% capacity and the second condenser at a capacity of 50%. If the balance is kept, the condensing pressure will float at optimum level and total energy use of the refrigeration plant will be minimal.

Many refrigeration plants with simple PLCs can benefit from floating condensing pressure. However, to implement this floating the correct balance between compressors and condensers capacities should be determined.

 

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