Drives and Controls Magazine

Compressor drive squeezes costs

01 September, 2006

Compressor drive squeezes costs

Danfoss has produced a drive specifically for use with refrigeration compressors. The drive, developed in collaboration with the company`s refrigeration and air-conditioning division, will be sold as part of a plug-and-play package with a matched reciprocating compressor, thus cutting installation costs and set-up times.

Refrigeration compressors are usually selected to meet the maximum expected demand, and are over-sized for long periods — up to 85% of the time they are running. Variable speed drives offer a more efficient way of controlling compressors than traditional regulation systems such as on/off controls, pressure-regulating valves or hot gas bypass systems.

In a conventional hermetic piston compressor, the motor and crankshaft rotate at 2,900 rpm (on a 50Hz supply). With Danfoss` VTZ Compressor Drive (shown above with a compressor) , the frequency varies from 30-90Hz, depending on the cooling needs, with the corresponding motor speed ranging from 1,800-5,400 rpm. The compressor thus performs optimally across its operating range.

This allows the variable speed compressor to be smaller than a fixed-speed compressor, saving space and boosting efficiency. And because the compressor is running slower for much of the time, with fewer stops and starts, mechanical and electrical stresses on the components are reduced, as are noise levels.