Part Two: Variable frequency drives in refrigeration systems
(Part One of this series can be found here)
The thermodynamic efficiency of a refrigeration system is significantly dependent on its operating temperatures. Other important practical issues such as the system design, control, size, initial and operating cost, safety, reliability and serviceability depend very much on the type of refrigerant selected for a given application.
Because of the environmental issues such as ozone layer depletion and global warming, different operating temperatures of the thermodynamic processes depending on the type of application, and because of the significantly higher levels of safety needs in the commercial refrigeration sector, a variety of refrigerants is used in the refrigeration industry. It is therefore important that the frequency drive used for the application allows you to choose between different refrigerants, like for instance natural refrigerant R744.
Improving control in cold storage applications by applying a variable frequency drive increases not only the refrigeration capacity of the installation but at the same time also reduces the energy consumption.
Major cost savings can be achieved by changing from timer-based defrost control schemes to a system where the head pressure in the cooling system is based on the measured outdoor air temperature, also known as floating head pressure control. Further system optimization can be achieved by applying sub-cooling in two stages, reconfiguring the condensers and – if -possible – by increasing the suction pressure.
Optimizing refrigeration system control typically results in high energy efficiency and cost savings. The generally moderate implementation cost result in an average pay back period of less than a year.
Installing a variable frequency drive in an existing refrigeration installation will reduce the energy consumption and at the same time improve the reliability of the system. It will also increase the productivity as a result of a reduction of product waste due to high air speed.
Article by: Deepinder Singh Chani