Cryogenics: Energy Saving for Cryogenic Systems

The Cryogenics Group in the Accelerator Engineering Department of the Accelerator Division of Thomas Jefferson's National Accelerator Facilities has discovered a way of cutting the energy consumption of the compressors involved in cryocooling. The compressors are used to compress helium from about 1 to 21 bars. Until now, they were designed to operate at maximum efficiency regardless of the real operating needs or, at best to operate at a few intermediate operating points. Venkatarao Ganni, the Cryogenics Group Deputy Leader reconfigured the refrigeration system control so as to reduce operating pressures when full capacity isn't needed. Ganni and his colleagues refer to this process in which compressor discharge pressure matches the refrigeration load as "floating pressure". A control system senses the required refrigeration by monitoring the amount of helium used for cooling, and pressure is adjusted accordingly. This mode of operation, dubbed the "Ganni Cycle" is far more efficient and is easy to implement in existing systems as it consists mainly in configuring and regulating equipment in a different way. Thanks to the cycle, the electric capacity required for Jefferson Lab cryogenics has dropped from 6 to 4.2 MW, resulting in direct savings of 33 000 USD each month in electricity costs. It also increases system reliability and extends the lifetime of some of the components.